Science with the
Atacama Large Millimeter Array

Protoclusters Forming Low Mass Stars

Philippe André
CEA Saclay, Service d'Astrophysique, France

While most stars are believed to form in clusters, our current understanding of the star formation process is largely limited to isolated cloud cores and single protostars. To make progress, detailed observational studies of the genesis and evolution of prestellar condensations in cluster-forming cloud cores are of prime importance. Recent wide-field (sub)millimeter continuum imaging of nearby protoclusters with the IRAM 30 m and JCMT telescopes (e.g. Motte, André & Neri 1998), as well as with the OVRO interferometer (e.g. Testi & Sargent 1998), has made possible the identification of several dozens of cold, gravitationally-bound starless condensations in, e.g., Oph and Serpens. Remarkably, the mass spectrum of these pre-stellar condensations resembles the shape of the stellar initial mass function (IMF), suggesting the IMF is at least partly determined by fragmentation at the pre-collapse stage of star formation. With present (sub)millimeter instrumentation, however, the dynamical properties of these protocluster condensations are difficult to assess, and only the nearest protoclusters are accessible. If ALMA can routinely mosaic fields up to 0.1 deg², its high resolution and sensitivity in both continuum and lines will allow a complete census of prestellar condensations and their properties to be taken in the major protoclusters of the Galaxy. This will greatly help develop a satisfactory theory of cloud fragmentation and star cluster formation.

Héctor G. Arce, Alyssa A. Goodman
Harvard Smithsonian Center for Astrophysics

We show how new millimeter observations with higher spatial and velocity resolution reveal new components of molecular outflows from young stellar objects. Small scale, high-velocity components in the outflow, discovered with the IRAM 30-m telescope, were detected not only due to high velocity resolution spectra which enable one to distinguish the high-velocity components from the parent cloud emission, but also due to the 30-m's high spatial resolution. Telescopes with large beams can dilute the small scale spatial and kinematical components, making them impossible to detect.

We also present new ¹³CO FCRAO maps of dense star-forming cores known to harbor outflow sources. The observations have higher velocity resolution than previous observations of these cores. We find two very distinct populations of spectra in each of the ¹³CO core maps. One group of spectra shows a clear increase of line width with antenna temperature, while the other group is clustered in a ``blob'' with mean line width substantially below the first group's and showing no line width-antenna temperature trend. Remarkably, the component whose line width is anti-correlated with antenna temperature is coincident with the outflow. We show how the outflow spectra's dependence of width on antenna temperature can be explained by assuming a momentum-conserving outflow.

Mary Barsony
Harvey Mudd College

Grace A. Wolf-Chase
Adler Planetarium & Astronomy Museum

JoAnn O'Linger
Jet Propulsion Laboratory

We present sensitive (), large-scale (47' x 7'--corresponding to 4 pc x 6 pc at the source) maps of the CO J = 1 0 emission of the L1448 dark cloud at 55" resolution. The maps were acquired using the On-The-Fly (OTF) capability of the NRAO's 12-meter telescope. Careful comparison of the spatial and velocity distribution of the high-velocity CO with previously published optical and near-infrared images and spectra has led to the identification of four distinct, parsec-scale molecular outflows from our maps. These CO flows are powered by four Class 0 protostars: L1448C, L1448N(A), L1448N(B), and L1448 IRS2 and end at the cloud's boundaries. The famous, well-collimated, high-velocity molecular outflow powered by L1448C can now be traced to distances an order of magnitude greater than previously. We present strong evidence for interactions between all four outflows on scales over a parsec from the driving sources. The magnitude of the combined flow momenta, as well as the combined kinetic energy of the flows, are sufficient to disperse the 50 M ammonia core in which the protostars are currently forming. It remains to be shown whether the combined directions of the outflow momenta, and the efficiency of momentum transfer from outflow to ambient material, are sufficient for dispersal of the L1448 molecular cloud.

John Bieging
Steward Observatory

The dynamic range of aperture synthesis images at short mm wavelengths is often limited mainly by atmospheric fluctuations which perturb the measured source visibility. If the emission is sufficiently bright and the instantaneous (u,v) coverage is sufficiently complete, self-calibration techniques can be used to recover lost dynamic range and approach the limit set by the system thermal noise.

This paper presents maps of the circumstellar envelope of the carbon star IRC+10216 in the J=13-12 emission line of silicon sulfide (SiS) at 1.3 mm made with the OVRO array. The spatial resolution is 2.5 arcsec and the velocity resolution across the ~30 km/s-wide line is 0.6 km/s. Self-calibration of the integrated line emission yielded an image with a dynamic range in excess of 400:1. By applying the time-dependent antenna gain solutions derived from the self-cal image to individual spectral channels, a dynamic range of >100:1 was obtained in most of the channel maps. These maps imply that the SiS emission arises from numerous small---mostly unresolved---clumps which occur at discrete velocities across the line profile. The images suggest that the mass loss process in this AGB star occurs by ejection of many small dense clumps of gas distributed randomly over the stellar photosphere. These gas clumps may be related to the warm dust clumps seen in high resolution IR images of IRC+10216.

Andrew Blain
University of Cambridge

ALMA will observe galaxies containing interstellar dust and molecular gas with unprecedented sensitivity and angular resolution from their formation to the present. Observations of both the intensity of background radiation, from COBE, and discrete galaxies, from SCUBA, at ALMA's millimeter(mm), sub-mm and far-IR wavelengths have provided an excellent first view of dust in distant galaxies, and galaxies discovered using SCUBA have been studied on finer angular scales with existing mm-wave interferometers that are precursors to ALMA. The dramatically enhanced sensitivity and resolving power of ALMA as compared with existing instruments will allow great advances in the study of high-redshift galaxies, perfectly complementing the optical and IR performance of the NGST. This presentation point outs the advantages of ALMA's resolving power and sensitivity in two key areas:

1. Extremely deep unconfused surveys for normal galaxies at redshifts greater than five, galaxies up to several hundred times fainter than those detected using SCUBA.

2. Resolving gravitationally lensed galaxies, allowing their internal dynamics and the dark-matter distribution in the lens to be traced in great detail.

Alberto D. Bolatto, James M. Jackson
(Institute for Astrophysical Research, Boston University)

Frank P. Israel
(Leiden Observatory, The Netherlands)

Xiaolei Zhang, Antony A. Stark
(Harvard-Smithsonian Astrophysical Observatory)

We present new CO (SEST, AST/RO) and [CI] (AST/RO) observations of the N159/N160 molecular cloud complex in the LMC. The complex features three distinct and spatially well separated regions: 1) the northern region (N160), where massive star formation is well evolved and the parent clouds have been strongly photodissociated. 2) The central region, comprising the N159E and N159W GMCs, which is undergoing strong star formation activity but still is wrapped in molecular gas. And, 3) the southern region (N159S), which is mostly quiescent, with little or no star formation activity as evidenced by its far-infrared, H_alpha, and [CII] emission.

The new SEST data shows extended, previously undetected, CO J= 1 emission throughout the complex that appears to be originating in optically thin CO. Part of this extended envelope is also bright in [CI]. Surprisingly, the neutral carbon emission peaks in the quiescent southern cloud, suggesting that an important fraction of the C⁰ may not be related to photodissociation regions. Combining these observations with existing [CII] and CO data produces a picture of the intricate interaction between star formation and the interstellar medium.

Alan P. Boss
Carnegie Institution of Washington

The terrestrial planets are universally believed to have formed through the collisional accumulation of successively larger solid bodies -- micron-sized dust grains, kilometer-sized planetesimals, and Moon-sized planetary embryos, culminating after about 100 Myr in the formation of the Earth and other terrestrial planets. The conventional wisdom is that gas giant planets form by the process of core accretion, where a roughly 10 Earth-mass solid core forms first by collisional accumulation, and then accretes disk gas. Alternatively, gas giant protoplanets might form rapidly through a gravitational instability of the gaseous portion of the disk, outracing the core accretion mechanism. Core accretion and disk instability might both be able to form gas giant planets, depending on the circumstances in different protoplanetary disks -- ALMA will help to decide the issue by searching for gas giant protoplanets and their associated spiral density waves and disk gaps. The ice giant planets are believed to have formed by collisional accumulation of icy solids, but the theory of their formation must still be considered to be in an embryonic stage. ALMA will be able to map the physical and chemical structure of protoplanetary disks with higher spatial resolution than ever before, placing crucial constraints on planet formation theories.

L. Bronfman, J. May
U. de Chile

D. Nürnberger
U. Würzburg

D. Shepherd
NRAO

The most conspicuous massive molecular outflow candidate identified in our CS(2-1) survey of UC HII regions (Bronfman et al 1996) is G34.4 (IRAS 18507+0121) in the I Galactic quadrant. At a distance of 3.8 kpc, it is near (about 11') the very bright HII region G34.3 (Carral & Welch 1992), embedded in the same GMC with a VLSR of 57 km/s. The CS velocity profile obtained with SEST shows very broad wings, about 25 km/s wide at the 0.1 K level, indicating strong outflow activity. Near infrared images of the field, 90'' in size (0.35'' per pixel), obtained with the du Pont 100'' Telescope at Las Campanas, show a remarkably reddenned source visible only in the K' filter, elongated in shape, about 15'' in extent. We have recently observed the G34.4 region, using the OVRO array, in the 3 mm continuum band and in the H¹³CO⁺ line, at a resolution of 5''. Most of the H¹³CO⁺ flux (33.64 Jy) comes from two strong cores; while one of these cores is closely associated with the ! NIR source, the other one is associated with a single, unresolved continuum source that has a total flux of 56.8 mJy. The mass of gas and dust in this second, possibly "star-less" core is estimated from the millimeter continuum to be approximately 355 M, consistent with the presence of a massive, embedded OB protostar.

Bronfman, L., May, J., & Nyman, L. 1996, A&AS 115, 81
Carral & Welch 1992, ApJ 385, 244

Bryan J. Butler
NRAO Socorro

Mark A. Gurwell
Center for Astrophysics

Observations of solar system bodies with the ALMA array will undoubtedly allow significant progress to be made on our understanding of the individual bodies therein, their interactions, and possibly their formation. With its fantastic resolution, sensitivity, and speed, ALMA will be one of the most important ground based observatories for planetary science. While it is nearly impossible to predict what will be learned about the solar system and its bodies, we can predict some general areas where we expect that ALMA will make significant contributions. We will concentrate here on 2 such areas: observations of small bodies, and observations of the solid surfaces of the larger bodies.

Small bodies Observations of comets will help disentangle the story of their formation and history, and shed light on the physical processes occuring in their atmospheres. Observations of NEAs by ALMA will contribute to knowledge of their properties and orbits (ALMA can observe in daytime). Observations of KBOs will help to determine their properties and origin.

Larger bodies We imagine that observations of Mercury, Mars, the larger asteroids, the moons of Jupiter, Saturn, Uranus, and Neptune, and the Pluto/Charon will be undertaken to determine properties and physical processes of their surfaces and subsurfaces.

Nuria Calvet
Harvard-Smithsonian Center for Astrophysics

Detailed radial/vertical structure modeling of observations of disks in Young Stellar Objects (YSOs) can provide information on the physical conditions and on the characteristics of the gas and dust in their interiors. I describe recent results of self-consistent modeling of spectral energy distributions, optical and infrared images, and millimeter fluxes of YSOs. I discuss observations and interpretations of the different stages of planet formation, from the indications of dust growth and settling in the very young objects to the tens of AU size holes observed in young debris disks. I also discuss how the unprecedented resolution and sensitivity of ALMA may help us access the interior of the innermost disks, a region unaccessible with present day instrumentation, and witness the very first stages of planet formation.

Fabienne Casoli
DEMIRM, Observatoire de Paris

Laurent Loinard
IRAM

We present preliminary results of an ongoing survey of the CO(1-0) line emission in a sample of quasars observedwith the Plateau de Bure interferometer. The sample is extracted from a recent survey with the HST of nearby (z < 0.3) bright quasars (Bahcall et al. 1997). First results indicate that a large fraction of these quasars host considerable amounts of molecular gas (ranging from several 10⁹ M to 5 10¹⁰ M. In one of the sources, PKS2349-014, we have detected the millimeter counterparts of the radio lobes seen at 21 cm.

Bahcall, J. N., Kirhakos, S., Schneider, D. P., 1997, ApJ 479, 642

Richard M. Crutcher
University of Illinois

This talk will review the motivation for the study of magnetic fields in star-forming regions and discuss observational techniques that will be possible with the ALMA. Although observations of densities, temperatures, kinematics, and structures in dense interstellar clouds have yielded a considerable volume of information about star formation, empirical information about magnetic fields is much more sparse. The ALMA has the potential to greatly expand our knowledge of the role of magnetic fields in the evolution of molecular clouds and in the star formation process. Three types of observations will be possible. (1) Imaging of linearly polarized thermal radiation from dust grains aligned by magnetic fields, (2) imaging of linearly polarized molecular spectral-line emission, and (3) imaging of the Zeeman effect in molecular lines. The first two techniques have been used successfully by observers with University-operated millimeter-wave arrays. Both techniques yield maps of the morphology of the magnetic field in the plane of the sky. If magnetic fields are strong, field lines should be regular with an hourglass morphology centered on contracting molecular cores. If turbulence dominates, magnetic fields would be more irregular or random. Moreover, the role of magnetic fields in outflows from young stars may be explored using these techniques.

Jeremy Darling
Department of Astronomy, Cornell University

We report the discovery of 11 OH megamasers and one OH absorber, along with upper limits on the OH luminosity of 54 other luminous infrared galaxies at z > 0.1. The new megamasers show a wide range of spectral properties, but are consistent with the extant set of 55 objects, 8 of which have z > 0.1. The new OH detections are the preliminary results of a OH megamaser survey in progress at the Arecibo Observatory, which is expected to produce several dozen detections.

The ultimate goal of the survey is to calibrate the luminosity function of OH megamasers to the low-redshift galaxy merger rate (0.1 < z < 0.2), and to use this measure to estimate the merger rate at higher redshifts using pointed and blind surveys. The survey will also provide an enhanced sample of OH megamasers for the study of their environments, engines, lifetimes, and structure.

James Di Francesco, Philip C. Myers, David J. Wilner (Harvard-Smithsonian CfA)

Stars form typically in clusters, in short time intervals ( 1 Myr) and in small ( 0.5 pc) regions of turbulent dense gas (e.g., see Lada, Strom, & Myers 1993). Millimeter interferometers can now provide wide-field, high-resolution observations of protoclusters, where objects are typically too proximate and embedded to observe by other means. Following Testi & Sargent (1998), who mosaicked the Serpens NW+SE protocluster at OVRO, we have observed mosaics of other regions with high surface densities of protostellar objects including the NGC 1333 IRAS 4 region in Perseus (at the IRAM PdBI), the Oph A region of Ophiuchus (at BIMA, with P. André), the L1551 IRAS 5 region in Taurus (at BIMA), and the OMC-2 region in Orion (at OVRO). Continuum mosaics at = 3.2 mm were made alongside line mosaics of N₂H⁺ (1-0), a dense gas tracer of quiescent material that avoids confusion from outflow motions. These maps will provide data on relative spacings, masses, and velocities that address key issues in cluster formation, and demonstrate a compelling future scientif c programme for ALMA.

Lada, E. A., Strom, K., & Myers, P. C. 1993, in "Protostars and Planets III", ed. E.H. Levy, J. Lunine, & M. S. Matthews, (University of Arizona Press: Tucson), p. 245 Testi, L., & Sargent, A. I. 1998, ApJ, 508, L91

A.Dutrey
IRAM, France

Understanding how planets and life appeared is one of the older dreams of Mankind. Today, more and more circumstellar disks are found around Young Stellar Objects (YSOs) called TTauri stars. These stars are indeed young suns at the stage where our Sun was still surrounded by a flattened structure of rotating gas and dust: the so-called proto-solar Nebula which provided the material to build the Solar System. Therefore, understanding the physics, the chemistry and the evolution of these disks, is the important clue to find how planetary systems form around Solar-type stars. In protoplanetary disks, except very close to the star, the gas and the dust remain at low temperatures and radiate at long wavelengths, from the Far-Infrared to millimeter waves. Unfortunately, these systems are relatively far away. With a sensitivity 30-40 times larger than that of the best mm array (IRAM interferometer), ALMA will provide images with details as small as a few astronomical units, allowing to image disks at the scale at which planetary formation is believed to occur. In this talk, I will review the kinematics and the physical properties of the gas surrounding YSOs, from the early stages of planet formation to more evolved ones such as the Pic-like disks, showing how our knowledges are definitely limited by the possibilities of current mm arrays. In conclusion, I will show that ALMA will allow the first quantitative studies of gas evolution towards planet formation.

A. S. Evans
SUNY

J. M. Mazzarella and J. A. Surace
Caltech

Galaxy interactions are responsible for the most luminous galaxy phenomena in the universe, be it starbursts or active galactic nuclei (AGN). Here, we present high-resolution, CO(1 0) interferometry and HST imaging of a sample of 5 double nuclei, ultraluminous infrared galaxies (ULIGs) in order to observe the distribution of star-forming molecular gas in the progenitor galaxies prior to nuclear coalescence. The 2 cool (f_25m /f_60m < 0.2) ULIGs in the sample, whose near-infrared colors are consistent with reddened starbursts, have CO emission associated with both of their stellar nuclei, similar to what is observed for the cool ULIG Arp 220 (Sakamoto et al. 1999). In contrast, the 3 warm f_25m /f_60m > 0.2, similar to Seyfert galaxies) ULIGs have CO emission associated with only the redder, AGN nucleus. These CO morphologies differ from those of less luminous infrared galaxies with similar nuclear separations (< 5 kpc), which have a dominant CO component between the stellar nuclei. We conclude that (i) ULIGs have large bulge-to-disk ratios which prevent gas from being stripped as the merger proceeds and (ii) some cool ULIGs may achieve their high luminosities primarily from starbursts occuring in both galaxies, whereas the luminosity from some warm ULIGs primarily emanates from an embedded AGN.

Neal J. Evans II
Univ. of Texas and University College London

The ALMA will revolutionize the study of star formation by providing a combination of angular resolution and sensitivity that far exceeds that of present instruments. I will focus on studies of relatively isolated cores that are forming low-mass stars. There is a general paradigm for the formation of such stars, and there are detailed theoretical predictions for the evolution of the density and velocity fields for different assumptions about the initial conditions. Because the theory is well developed, observational tests are particularly revealing.

The two primary probes of the conditions in dense cores are continuum emission from dust and spectral lines from molecules. These are complementary in many ways. The dust emission traces dust column density very effectively, and it is not affected by molecular depletion to first order. Substantial grain growth may affect the emission, but this can also be studied. In addition, dust and gas distributions may differ because of ambipolar diffusion. In principle, the molecular spectroscopy probes the gas column density, but it is more sensitive to variations in chemical abundances. Molecular lines can probe the local density and velocity fields, but it is important to constrain the analysis with information on column density. Together these two probes can be very powerful.

D. T. Frayer and N. Z. Scoville
Caltech

We present CO and mm continuum observations of the luminous population of high-redshift sub-mm galaxies taken at the OVRO Millimeter Array. Studies of sub-mm galaxies are vital to our understanding of the formation and early evolution of galaxies since this population could account for a significant fraction of the total amount of star formation and AGN activity at high redshift. We discuss the CO detections for SMM ,J02399-0136 at z=2.8 and SMM J14011+0252 at z=2.6. The CO data show the presence of massive molecular gas reservoirs (M(H₂) ~ few x 10¹⁰-10¹¹ M) and provide the only two confirmed redshifts for the sub-mm population of galaxies. These data suggest that the sub-mm galaxies are gas-rich systems which have properties similar to ultraluminous infrared galaxies. Many sub-mm galaxies are thought to be at very high redshift (z 3) since their radio and optical emissions are extremely weak. In these cases, interferometric mm-continuum observations are required to obtain an accurate position for the sub-mm counter-part. We report the detection of mm-continuum emission from one sub-mm galaxy which has yet to be detected at optical/near-infrared wavelengths (I 26, K 21). These results highlight the importance that future mm/sub-mm observations will have on our understanding of the high redshift universe.

Y. Fukui
Nagoya University

I will present new molecular views of southern sky based on the CO survey for star forming regions conducted by Nagoya University with the NANTEN 4-m millimeter wave telescope. The NANTEN telescope is installed at the Las Campanas Observatory in Chile under a mutual agreement between Nagoya University and the Carnegie Institution of Washington. Through the survey, molecular gas distribution and the physical properties of cluster forming regions in the Magellanic Clouds, Galactic star forming GMCs, dark clouds, high latitude clouds, and interacting clouds with HII regions and/or SNRs are studied at a beam size of 2.'7 in the ¹²CO, ¹³CO, and C¹⁸O (J=1-0) molecular emission. I will review the expected contribution of the southern CO survey to the ALMA project, and discuss the scientific targets related with star formation at the time the ALMA becomes available.

Yu Gao
IPAC, Caltech

Jeffrey D. Goldader
Univ. of Pennsylvania

Ernest R. Seaquist
Univ. of Toronto

Cong Xu
IPAC, Caltech

We present BIMA CO(1-0) image of the luminous infrared galaxy II~Zw 96 which shows huge molecular gas concentrations outside the apparently on-going merging spiral disks. Similar to other well studied mergers like Arp 299 and VV 114, II Zw 96 is almost an ultraluminous system, but has not yet reached the late stage of coalescence which is the norm for most ultraluminous galaxies. II Zw 96 shows four distinct star-forming regions, as revealed by optical and near-IR imaging. The dominant extra-disk CO concentrations correspond to two star-forming knots hidden by heavy dust, whereas the other two CO concentrations correspond to the two nuclear gas disks. It is intriguing how such huge molecular gas concentrations could be accumulated far away outside the merging disks. We here explore the exotic nature of the extra-disk gas concentrations in one of the few known examples of a major merger caught in mid-act.

Reinhard Genzel
Max-Planck-Institut für extraterrestrische Physik, Garching, Germany

Starting from recent progress in infrared to millimeter spectroscopy and high resolution imaging of the nuclei of starburst galaxies, AGNs, and ultra-luminous galaxies a discussion will be given what ALMA might contribute to this field.

S.Guilloteau
Institut de Radio Astronomie Millimetrique

In the last 5 years, molecular line emission has been discovered in distant galaxies, at redshift ranging from z = 1.4 to 4.7, by means of long integrations with the existing mm arrays (IRAM, NRO, OVRO). These findings enable to study the dynamics of young galaxies, which are often undetectable in the optical domain because of the large dust extinction. Because of the distance, the emission from these galaxies is very dim, and current millimeter arrays have only been able to detect the ``tip of the iceberg'', that is either exceptionally bright sources (analogous to the nearby ultra-luminous IR galaxies, perhaps the progenitors of giant elliptical galaxies) or gravitationally lensed objects. Moreover, the angular resolution of the current arrays is often insufficient to allow detailed modeling of the observed sources. ALMA will alleviate the limitations of the current instrument in several ways. It will provide an improvement in sensitivity of a factor 40, which will allow detection of more normal systems, as well as detailed studies of the brighter objects. The wide instantaneous frequency coverage of ALMA, combined with appropriate search strategies, will also allow blind redshift searches. High resolution images will allow detailed gravitational lens models to be developed when necessary. Studies of the chemical composition of the molecular medium at high redshift may even be possible through absorption line searches toward the line of sight of quasars.

Mark A. Gurwell
Harvard-Smithsonian Center for Astrophysics

Duane O. Muhleman
Caltech

Bryan J. Butler
NRAO

The Atacama Large Millimeter Array will be the finest earth-based observatory for studying planetary atmospheres ever conceived. ALMA will have very superior sensitivity and imaging capabilities, coupled with a extremely broad spectrometer passband, allowing unprecedented exploration of the atmospheres of all the planets. ALMA will be able to spatially resolve nearly all planetary bodies (and many of their moons) save perhaps Pluto and Triton, allowing us to probe the three-dimensional structure of temperature and species abundances. In addition, the high sensitivity and rapid imaging ability of ALMA will allow direct detection of atmospheric winds through measurement of minute ( 5 m/s) Doppler shifts of line cores.

We will present state-of-the-art interferometer observations of Titan and Mars and use these bodies as test cases of what ALMA will be able to help us learn about their atmospheres. We will also consider the cases for observing all planetary atmospheres, including: tenuous atmospheres (such as Mercury, Io, Pluto, and Triton, where linewidths are thermal), moderate atmospheres (Mars, Titan, Venus, with moderate pressure broadening out to at most a few GHz), and giant planet atmospheres (where observable pressure broadened lineshapes of NH₃ exceed 100 GHz or more).

Jorma Harju
Observatory, University of Helsinki

Jim Higdon
Kapteyn Institute, University of Groningen

Kimmo Lehtinen, Mika Juvela
Observatory, University of Helsinki

The R Coronae Australis core was imaged with the Australia Telescope Compact Array (ATCA) in continuum at 3 and 6 cm. The aim was to investigate if any of the quiescent DCO⁺ clumps detected recently (Anderson et al. 1999) contain compact HII regions. Such a source in a dense clump without associated infrared emission may indicate the presence of a very young protostar. No continuum sources, except those previously detected with the VLA (Brown 1987) were found. In particular, no trace was found of the compact radio continuum source in the southern part of the core reported on by Brown & Zuckerman (1975). The properties of the detected continuum sources, their infrared counterparts and their relation to the surrounding molecular material are discussed.

Anderson I.M., Caselli P., Haikala L.K., Harju J. 1999, A&A 347, 983

Brown A. 1987, ApJ 322, L31

Brown R.L., Zuckerman B. 1975, ApJ 202, L125

Mark Heyer
FCRAO/Univ. of Massachusetts

Wide field imaging of the interstellar medium is an essential tool to investigate the physical processes which operate within a range of size scales or densities. The ability to construct images with high spatial dynamic range at millimeter wavelengths has increased in recent years with focal plane arrays on single dish telescopes and routine mosaicing of interferometers. In this contribution, I will demonstrate the value of wide field imaging from images of the molecular interstellar medium obtained with focal plane arrays on the FCRAO 14 meter telescope. These include data from wide field surveys of the Galaxy, a ¹²CO J=1-0 image of M31, and ¹³CO J=1-0 major axis maps of several galaxies. The images enable investigations of the equilibrium state of the molecular gas, interstellar turbulence, and radial variations of molecular gas properties and emissivities.

P. R. Jewell
NRAO Green Bank

The 100 m Green Bank Telescope will be completed in early 2000. The GBT is the most ambitious, single radio telescope ever constructed. It has a large number of unique design and performance features including an offset feed (clear aperture), an active surface, a closed-loop laser metrology system for surface figure and telescope pointing control, a feed turret for ready selection of numerous receivers, and a multi-input, 256k-channel spectrometer. The GBT will operate over a frequency range of 100 MHz to 115 GHz.

The GBT and ALMA have great potential for complementary observations. The GBT will cover millimeter wavelengths longward of 2.6 mm and thus has a significant overlap with ALMA. The total physical collecting areas of 7854 m² for the GBT and 7238 m² for the 64x12-m ALMA configuration will give the facilities comparable flux sensitivities. The GBT has a wide field of view at its Gregorian focus that extends > 5 arcmin at 90 GHz with minimal aberrations. When equipped with focal plane array receivers, the GBT will be able to image large fields with high sensitivity very quickly. Such images will provide the astrophysical context of regions studied at high angular resolution with ALMA. The clean beam response and accurate absolute calibration of GBT data will make it ideal for combination with ALMA images. These, and other areas in which the GBT and ALMA will work in concert will be described in this poster.

David Jewitt
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822

Some of the most fundamental and topical questions in astronomy concern the origin and evolution of planetary systems. In the solar system, these questions are most directly addressed through observations of chemically and physically primitive bodies in which a record of the initial conditions may be preserved. The most primitive materials in the solar system reside near its outer edge, in a trans-Neptunian ring known as the Kuiper Belt and in a surrounding spherical cloud first postulated by Oort. These regions supply comets to the inner solar system and, in the case of the Kuiper Belt, preserve evidence of dynamical processes operative in the first 100 million years after formation. The Kuiper Belt is also a source of collisionally produced dust and may be analogous to the dusty rings observed encircling a number of nearby main-sequence stars. I will review the currently known properties of these primitive objects, and discuss how ALMA can contribute to our understanding of the early solar system.

Mika Juvela
Helsinki University Observatory

Paolo Padoan
Harvard University Department of Astronomy

The high resolution provided by ALMA will reveal new small scale structures in many sources, e.g. in star forming regions. Such inhomogeneities may not have been considered in the analysis of past observations but they will be essential to the understanding of future data. Radiative transfer methods are needed to decipher the observations and the presence of complicated source structures and small scale inhomogeneities requires 3D models.

We will describe work we have done in modelling molecular line emission from inhomogeneous molecular clouds. Examples include the modelling of multitransitional CS observations of massive star forming cores where the clumpy density and velocity structures have a clear effect on the line emission (Juvela 1998). Some radiative transfer calculations based on the MHD models of interstellar clouds are also discussed (Padoan etal 1998).

Our radiative transfer code is based on Monte Carlo simulation. We will show that radiative transfer calculations with large 3D models have already become practicable and that the Monte Carlo method can be applied also in cases of hight optical depths.

Juvela M. 1998, A&A, 329, 659

Padoan P., Juvela M., Bally J., Nordlund AA 1998, ApJ, 504, 300

William D. Langer, Thangasamy Velusamy
Jet Propulsion Laboratory, Caltech

Paul F. Goldsmith
NAIC, Cornell University

We report the detection of emission from gas phase methanol in a protostellar disk in the young, class 0 infrared source located in L1157. Spatially unresolved emission was detected in the 2_k$-1_k transitions of methanol at 3mm using the Caltech Owens Valley Millimeter Array. The fractional abundance of methanol is about 3 x 10^-7 for a flared disk model. Substantial chemical processing probably takes place in the disk via depletion and desorption from grains. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter--wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a gas and dust temperature probe. We discuss the potential of ALMA to improve on such chemical studies in the innermost disk regions. WL and TV's research was conducted at the Jet Propulsion Laboratory, Caltech with support from NASA. The National Astronomy and Ionospheric Center is operated by Cornell University under a cooperative agreement with the National Science Foundation.

R. Launhardt
Caltech Pasadena

Th. Henning
AIU Jena

P. Hofner
Arecibo

A. I. Sargent
Caltech Pasadena

CB 17 (L 1389) is a small, relatively isolated, simply structured molcular cloud (Bok globule) located at a distance of ~ 300 pc. The total mass of this small globule amounts to only a few solar masses and its size (FWHM) is ~ 2.5' (~0.2 pc). Measurements of different isotopes and transitions of of CO, CS, HCO⁺, and H₂CO toward the core of CB 17 have been obtained using the IRAM 30m and CSO 10.4m telescopes (Launhardt etal 1998, ApJS, 119, 59). High-resolution measurements of the HCO⁺(1-0) transition were performed with the OVRO millimetre wave array. In addition, the submm and mm continuum emission was observed with the JCMT 15m and IRAM 30m telescopes (Launhardt & Henning 1997, A&A, 326, 329; Launhardt etal 1997, MNRAS, 288, L45). These measurements reveal the presence of a central dense core of ~0.5M (Launhardt etal 1999, in prep.). Although the properties of this core resemble mostly those of a pre-stellar core (Ward-Thompson etal 1994, MNRAS, 268, 276), spectral signatures of mass infall suggest that the protostellar collapse has already started. Microturbulent radiative transfer calculations and dust models are used to constrain the kinematic state and physical conditions of this star-forming globule core.

Chin-Fei Lee, Lee Mundy, James Stone, Eve Ostriker
University of Maryland, College Park

We have mapped the CO J=1-0 emission from molecular outflows associated with 10 young stellar systems of class 0 to class II with BIMA interferometry array and FCRAO single dish. Many of our outflows are closely related to jet like and bow shock structures detected in H₂ or H_alpha emission. The CO emission generally forms a hollowed structure around the jet and bow shock structures. Most of the CO outflows show a nested shell structure with velocity increasing with the distance from the star, but the detailed behavior can vary widely. Here, we presents five outflows to illustrate the different kinematics. Two of them are well described by a single parabolic shell with a Hubble law velocity, consistent with a wide-angle wind driven model. Two of them seem better explained with a jet-driven bow shock model, with a broad range of velocity near the bow shock. The last one appears to have elements of both models. To better understand the observations and test specific outflow models, we are performing a number of numerical simulations. This poster presents simulations of a jet propagating into a stratified ambient material. In these simulations, the jet-driven bow shock forms a thin cylindrical shell of swept-up gas around the jet, with the velocity vector of the material perpendicular to the shell surface. The simulations produce a wide range of velocity observed near the bow shock, but fail to produce the other CO kinematics in our observations.

Tarja Liljeström
Metsähovi Radio Observatory, Helsinki Univ. of Technology

Carl Gwinn
University of California, Santa Barbara

We demonstrate using the rich water maser cluster W49N as an example, how simultaneously obtained 22 GHz single-dish and multi-epoch VLBI observations of the masing water line can be used to quantitatively diagnose shocked and turbulent regions around protostars. The principal factors that determine the physical properties of a shocked region are the preshock density, the shock velocity (obtained from proper motion measurements of the masers), and the preshock magnetic field parameter (obtained from non-thermal variations in the Doppler velocity within maser features). When two of these are observationally well constrained, all other physical quantities can be determined with available shock and maser models. We succeeded to observationally fix the free parameters in the shock model of Hollenbach and McKee and the maser model of Elitzur, Hollenbach, and McKee. This enabled us to determine some 20 shock and maser parameters of W49N. The high-resolution imaging capabilities of ALMA should allow detailed studies of a variety of shocked regions of the interstellar medium and also sample transitions at higher frequencies and molecular species other than water.

Robert Lucas
IRAM, Grenoble, France

Harvey S. Liszt
NRAO, Charlottesville, USA

With IRAM instruments in the last few years, we have been using compact extragalactic millimeter wave radio sources as background objects to study the absorption spectrum of diffuse interstellar gas at millimeter wavelengths. The molecular content of interstellar gas has turned out to be unexpectedly rich. Simple polyatomic molecules such as HCO⁺, C₂H are quite ubiquitous near the Galactic plane ( < 15^o), and many species are detected in some directions (CO, HCO⁺, H₂CO, HCN, HNC, CN, C₂H, C₃H₂, H₂S, CS, HCS⁺, SO, SiO). Remarkable proportionality relations are found between related species such as HCO⁺ and OH, or CN, HCN and HNC. The high abundance of some species is still a challenge for current models of diffuse cloud chemistry.

A factor of 10 increase in the sensitivity will make such studies achievable in denser clouds, where the chemistry is still more active and where abundances are nowadays only available by emission measurements, and thus subject to uncertainties due to sometimes poorly understood line formation and excitation conditions.

John C. Mather
NASA Goddard Space Flight Center

William Langer
NASA Jet Propulsion Laboratory

David Leisawitz, S. Harvey Moseley, Jr.
NASA Goddard Space Flight Center

Mark Swain, Harold Yorke
NASA Jet Propulsion Laboratory

Xiaolei Zhang
Raytheon & NASA GSFC

NASA is studying space-based far-IR/submillimeter interferometry, a prospect that has received considerable support from the astronomical community. We describe concepts for the Space Infrared Interferometry Trailblazer (SPIRIT) and the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). Both are imaging and spectral Michelson interferometers operating in the range ~ 40 - 500 m, with cryogenic optical components and arrays of sensitive detectors, and are sky background limited. SPIRIT, which could be launched in a decade, is built on a deployable boom and has a maximum baseline of ~ 30 m, providing arcsecond resolution in the far-IR. SPECS uses formation flying to attain baseline lengths up to ~ 1 km.

SPIRIT and SPECS would give us access to many important cooling and diagnostic spectral lines and to the bulk of the thermal emission from dust, and make observations complementary to those obtained with ALMA and NGST. Together, NGST, SPECS and ALMA would provide virtually continuous spectral coverage at tens of milliarcsecond resolution from visible to millimeter wavelengths.

Hiroshi Matsuo
National Astronomical Observatory, Japan

Astro-F or IRIS (Infrared Imaging Surveyer) is a Japanese infrared satellite with 70cm liquid Helium cooled telescope planned to be launched in 2003. On board are near-infrared and middle-infrared imaging arrays (IRC) and a far-infrared survey instrument (FIS). Both instruments also have spectroscopic capability. During the first half year period, the Astro-F will concentrate on the all sky survey at four wave-bands in the far-infrared and it is expected that more than 10⁶ galaxies will be observed. Among the galaxies more than 1000 will have redshift larger than 1.0.

The galaxies detected by the Astro-F FIS instrument will be the largest database of distant galaxies at the time when ALMA start operation. A strategy for extracting the most distant galaxies is as follows. First the FIS colors are used to pre-select candidate galaxies. Next submillimeter-wave observations determine their photometric redshifts. Then spectroscopic observaions of far-infrared lines are made in submillimeter-wave. After all these, ALMA observations will reveal the formation and evolution of the most distant galaxies.

Kawada, M. 1998, SPIE, 3354, 905

Takeuchi, T. T. et al. 1999, PASP, 111, 288

F. Melchiorri, B. Melchiorri
Dept. of Physics of Rome University

P. Encrenaz, R. Maoli, M. Signore
DEMIRM, Observatoire de Paris

In the range of redshifts 1000 > z > 10 the matter in the Universe is expected to be neutral and cold: high density regions characterize the loci of galaxy formation . These conditions are ideal for molecular formation. The interaction between CBR photons and molecules (resonant scattering) may be the most important signature in the millimetric and submillimetric region of the spectrum. We discuss the role of LiH as a tracer of high density regions in primordial structures and the possibility of detecting it toward primordial galaxies by high spatial resolution observations of the redshifted LiH lines.

Karl M. Menten
Max-Planck-Institut für Radioastronomie, Bonn

Massive stars strongly shape the molecular clouds in which they form. This is most obvious where the embedded stars begin ionizing their environment, producing ultracompact HII regions. However, interactions of the stars with the surrounding medium may even start at earlier phases of (proto)stellar development in the form of energetic outflows, which have been observed in a number of regions. Little is known about the mechanisms driving these outflows. In fact, our knowledge of the earliest stages of massive star formation is very incomplete in general. Moreover, only a few bona fide high mass protostars have been found so far. The large distances of high-mass star-forming regions call for interferometric measurements and over the past 15 years interferometers working at centimeter and millimeter wavelengths have provided a great wealth of information. However, further progress requires brightness sensitivies and spatial resolutions not available with current instruments. ALMA will allow studies of the chemistry, energetics, and kinematics of the dense circumstellar envelopes surrounding deeply embedded protostars with unprecedented angular resolution and sensitivity and revolutionize our understanding of massive star formation.

T. J. Millar
UMIST, Manchester, UK

It has become clear in recent years that regions of massive star-formation contain small clumps of hot, dense gas. These so-called hot molecular cores are known to be strong emitters of rotational line emission and contain very large abundances of certain molecules, particularly hydrogenated species, and are particularly suitable for observation by interferometers such as ALMA. This review will discuss recent observations which suggest that the chemical composition of the gas is determined to a large extent by the evaporation of molecular ices and subsequent gas-phase processing. Despite their high temperatures, hot molecular cores contain species which are significantly fractionated in deuterium. The degree of fractionation may give information on the ice condensation temperature in such regions. The connection between the `ices' in hot molecular cores and comets will also be discussed.

A. Mizuno, T. Hayakawa, T. Onishi, Y. Fukui
Nagoya University

We carried out ¹³CO and C¹⁸O (J=1-0) surveys for dense molecular gas toward the Chamaeleon-Musca dark cloud complex with the NANTEN 4-m millimeter-wave telescope. The ¹³CO survey covered ~ 16 deg x 17 deg area, and 25 small dense clouds are identified in addition to the four previously known large clouds. The C¹⁸O survey were made toward the Chamaeleon (Cha) I, II, and III clouds, and we identified 23 C¹⁸O dense cores. The typical mass, radius, peak column density, line-width of the C¹⁸O cores are 22 M, 0.22 pc, 9.7 x 10²¹ cm^-2, and 0.82 km s^-1, respectively. The surface density of CTTSs abruptly increases for the area whose column density is greater than 10²² cm^-2, suggesting that this value gives a certain thleshold for star formation. Star formation efficiency varies over a wide range among the three clouds, 13%, 1%, and 0% in Cha I, II, and III, respectively. The C¹⁸O cores in Cha I are characterized by (1) high column density, (2) being almost in virial equilibrium, and (3) high M_core/M_cloud ratio. The cores in Cha III show the opposite trend, and those in Cha II are in between. Such trends suggest that Cha I is well-evolved or well gravitationally relaxed cloud-core system, which is probably related to the very high star formation activity in the cloud.

A. Mizuno, T. Onishi, N. Yamaguchi, A. Hara, T. Hayakawa, S. Kato, N. Mizuno, R. Abe, H. Saito, R. Yamaguchi, Y. Mine, Y. Moriguchi, S. Mano, K. Matsunaga
Nagoya University

K. Tachihara
Max-Plank Institute

A. Kawamura
University of Tokyo

Y. Yonekura, H. Ogawa
Osaka Pref. University

Y. Fukui
Nagoya University

Large scale ¹²CO and ¹³CO (J=1-0) surveys have been carried out by using two 4-m radio telescopes at Nagoya University since 1990 in order to obtain a complete sample of the Galactic molecular clouds. The southern survey started in 1996 with one of the telescopes, named "NANTEN", installed at the Las Campanas Observatory in Chile. The observations made at a grid spacing of 2' - 8' with a 2.'7 beam allow us to identify and resolve the individual star forming dense cores within 1-2 kpc of the sun. The present coverage in the ¹²CO and ¹³CO are ~ 7% and ~ 21% of the sky, respectively.

The data are used to derive physical parameters of dense cores and to study the mass spectrum, morphology, and conditions for star formation. For example, the survey revealed that the cloud mass function is fairly universal for various regions (e.g., Yonekura et al. 1998, ApJS, 110, 21), and that star forming clouds tend to be characterized by low M_vir/M_LTE (e.g., Kawamura et al. 1998, ApJS, 117, 387; Mizuno et al. 1999, PASJ, in press). The survey will provide invaluable database of southern star and planet forming regions, one of the important scientific targets of ALMA.

Gerald H. Moriarty-Schieven
National Research Council/Joint Astronomy Centre

Jane S. Greaves
Joint Astronomy Centre

Polarization of dust or synchrotron emission in the sub-millimetre-wave regime directly traces magnetic field directions. The magnetic field energy is similar to that of gravity and turbulence in interstellar gas, and so plays a major role in the dynamics and evolution of the interstellar medium. We present some early results from the aperture polarimeter on the SCUBA sub-mm bolometer array on the JCMT from a wide variety of sources, and briefly discuss the importance of a polarimetric capability for ALMA.

Lee G. Mundy
Astronomy Dept.
University of Maryland
College Park, MD

Dust continuum emission from circumstellar material in the immediate environments of stars provides a valuable probe of the formation and evolution of stellar and planetary systems. High resolution millimeter and submillimeter wavelength observations are uniquely capable of determining the mass and temperature distributions in material 10 to 1000's of AU from solar type stars. This material is an integral part of the star formation process and is the gas and dust rich birthplace of planets. Current observations are providing insights into the frequency of circumstellar disk in young systems, the evolution of disks, the circumstellar environment of young multiple star systems, and the nature of debris disks. At the highest resolution, we are beginning to resolve disks to get estimates of sizes and rough radial distributions. The ALMA is a major leap forward in sensitivity and resolution which will enable the study of disks and debris material on the scale of AU's in a large number of systems. At its highest resolution, ALMA is capable of detecting disk holes and gaps which are expected to be signpost of well-developed planetary formation. It may also be possible to detect localized over-densities in the disk associated with protoplanetary activity.

Steven T. Myers
NRAO and U. Pennsylvania

John Carlstrom
U. Chicago

The ALMA receiver suite includes provisions for covering the Ka and Q bands from 30 - 45.5 GHz. This contribution summarizes some of the scientific drivers for this capability, in particular observations of the Cosmic Microwave Background Radiation anisotropy, gravitational lensing by massive galaxies, and studies of thermal, non-thermal, molecular line, and maser emission from galaxies at cosmological redshifts. In addition to its unique capabilities at millimeter and submillimeter wavelengths, ALMA will also be a superb instrument at the smallest centimeter wavelengths. ALMA will complement the VLA with its substantial collecting area (0.55 VLA in raw area, comparable when considering aperture efficiency) and a full view of the Southern Sky. We use examples from current CMB, SZE, gravitational lensing, and other extragalactic observations along with theoretical models of large scale structure evolution and galaxy formation to extrapolate the capabilities of ALMA for these programs.

Nagayoshi Ohashi
Academia Sinica Institute of Astronomy & Astrophysics, Taiwan

Molecular envelopes are sites of star formation, and their geometrical and kinematical properties are very important to understand star formation. Particularly, their velocity structures, such as infall or rotation, need to be studied in detail to understand processes essential for star-formation. In order to investigate the physical properties of molecular envelopes in very detail, we need fine angular and velocity resolutions, which resolve both geometrical and velocity structures of molecular envelopes. A millimeter & submillimeter-wave interferometer is a very powerful tool providing high angular and velocity resolutions. Interferometric observations have realized direct imaging of infalling motions in molecular envelopes. In my talk, I will review what we learned about the physical properties of molecular envelopes with and without young stellar objects (YSOs) through interferometric observations. I will also discuss what we may learn about star-formation using a large millimeter & submillimeter array.

Hans Olofsson
Stockholm Observatory

Extensive post-main sequence mass loss occurs for low- and intermediate-mass (up to ~8M) stars on the asymptotic giant branch (AGB), and for the higher-mass stars during their red supergiant evolution. These winds have a profound effect on the evolution of the stars, as well as for the enrichment of the interstellar medium with heavy elements and grain particles. The mass loss on the AGB is the by far most well studied, but a good deal of the basic processes are still not understood or cannot be described in a proper quantitative way, e.g., the mass loss mechanism itself. Furthermore, these objects provide us with fascinating systems, where intricate interplays between various physical and chemical processes take place, and their relative simplicity in terms of geometry, density distribution, and kinematics makes them excellent astrophysical laboratories. In this review we will concentrate on those aspects of AGB mass loss that are particularly well studied using a large millimetre array.

Toshikazu Onishi, Akira Mizuno
Nagoya University

Akiko Kawamura
University of Tokyo

Yasuo Fukui
Nagoya University

We present the results of a survey for dense molecular condensations in Taurus and the succeeding detection of a high-density condensation that is very close to the moment of the formation of a protostellar core within a time scale of ~ 10⁴ yr. We have carried out a survey for dense molecular condensations with a 45-m telescope at Nobeyama in H¹³CO⁺ (J=1-0) on the basis of a complete C¹⁸O survey made with the 4-m telescope at Nagoya. We detected ~55 dense condensations, of which ~45 are starless. These starless condensations are compact (R 0.1 pc) and of high-density (~10⁵ cm^-3) and thus are highly probable candidates for protostellar condensations.

One of the starless condensations, named MC 27 in our catalog, is the densest, ~ 10⁶ cm^-3, based on the observation in H¹³CO⁺ (J=1-0, 3-2). A statistical analysis indicates a very short time scale of ~ 10⁴ yr. These properties strongly suggest that MC 27 is in a very early stage of star formation. The HCO⁺ (J=3-2, 4-3) profiles show the existence of an infalling envelope. The derived infall velocity profile can be explained by a dynamical-collapse model of supercritical condensation prior to formation of the first protostellar core by ~ 10^3-4 yr.

Deborah L. Padgett
SIRTF Science Center, Caltech

Karl R. Stapelfeldt
Jet Propulsion Laboratory

We present a comparison of Owens Valley Radio Observatory millimeter interferometry of the IRAS 04302+2247 circumstellar disk to near-infrared images obtained by the Hubble Space Telescope. IRAS 04302+2247 is a low-luminosity Class I young stellar object in the Taurus star-forming clouds at a distance of 140 pc. The HST/NICMOS image shows a sharp central absorption lane 7" (1000 AU) in length running directly between a bright scattered light background from bipolar reflection nebulae of roughly equivalent brightnesses. This dark lane has been interpreted as an optically thick disk seen precisely edge-on, occulting the star (Padgett et al. 1999 AJ 117, 1490). OVRO maps of the ¹³CO(1-0) emission indicates that dense gas is resolved along the position angle of the dust lane observed by HST. In addition, channel maps show a velocity gradient primarily along the major axis of this molecular bar, indicating rotation around a central source and supporting the disk interpretation of the scattered light structure. The resolution in the 3 mm OVRO image prevents us from making definitive statements about the relationship between the molecular gas and the detailed morphology seen by NICMOS. However, the 0".1 resolution of the ALMA array will rival that of the Hubble Space Telescope, providing complementary long wavelength molecular gas morphology and kinematics.

Padgett, D. L., Brandner, W., Stapelfeldt, K. R.,Strom, S. E., Terebey, S.,Koerner 1999, AJ 1 17, 1490

Nimesh A. Patel, Lincoln Greenhill
CfA

James Herrnstein
NRAO Socorro

Qizhou Zhang, James Moran, Paul T. P. Ho
CfA

Paul F. Goldsmith
NAIC

We present VLBA observations of water maser emission associated with the star forming region IRAS 21391+5802, which is embedded in a bright rimmed cometary globule in IC1396. The angular resolution of the maps is about 1 mas, corresponding to a spatial resolution of ~0.75 AU, at an assumed distance of 750 pc. Proper motions are derived for most of the maser features identified consistently over three epochs that were separated by intervals of about one month. The masers appear in four groups aligned linearly on the sky, roughly along a northeast--southwest direction, with a total separation of ~0."7 (520 AU). The mean magnitude of proper motions is ~35 km s^-1 (7.5 AU yr^-1). The average error on the derived proper motions is ~0.2 mas yr^-1.

The overall pattern of proper motions is indicative of a bipolar outflow. There is no evidence of Keplerian rotation, as has been claimed elsewhere. A nearly circular loop of masers lies near the center of the source. The radius of this loop is 0.8 AU and the line-of-sight velocities lie within 2 km s^-1 of the systemic velocity of the region. The loop of masers presumably depicts the radius at which significant dust condensation occurs in the outflow away from the star.

R.L. Plambeck and M.C.H. Wright
U.C. Berkeley Radio Astronomy Lab

Many studies of molecular clouds require quantitative comparisons of images at widely different wavelengths. For example, one may map dust spectral index variations to search for evidence of grain growth in protostellar cores, or use 3-2/2-1/1-0 C¹⁸O line ratios to derive gas kinetic temperatures, or search for chemical abundance anomalies caused by shocks or MHD waves. ALMA will dramatically improve the accuracy of these measurements because it will provide almost complete sampling of visibilities across the u,v plane, allowing one to synthesize mathematically perfect, matched beams at different wavelengths. The reliability of such comparisons will be limited by the difficulty in measuring the flux from extended structures. For a homogeneous array such as ALMA, visibilities on spacings smaller than the antenna diameter are recovered by mosaicing. Pointing and surface errors lead to errors in these data, limiting the image fidelity (Cornwell, Holdaway, & Uson 1993), particularly at submillimeter wavelengths. One could improve the image fidelity by measuring the short spacing visibilities directly with an auxiliary array of smaller antennas.

Charlie Qi, Geoffrey A. Blake, Anneila I. Sargent
California Institute of Technology

We are conducting an intensitve multi-species imaging study of two T Tauri and two Herbig Ae stars with the Owens Valley Millimeter Array. Interferometric images of several species in each of the important chemical families (C-, N-, O-, and S-bearing), including a number of isotopic variants, have been acquired. Even at moderate resolution (5") there appear to be interesting morphological differences between species expected to follow different (photo)chemical paths. The HCN velocity structure is similar to that seen in CO(2-1) showing that HCN participates in the same disk rotation. The integrated intensity map of HCN, however, shows a double peaked morphology suggestive of depletion of HCN in the inner disk. The H¹³CO⁺ emission provides an important lower bound to the gas fractional ionization of a few 10^-10. The first detection of DCN in this kind of object has made possible a determination of the critical D/H ratio (DCN/HCN) in the circumstellar gas. At present, the data provides an approximate value of the D/H ratio of 0.01 since even H¹³CN(1-0) is optically thick, judging by its three hyperfine components. Still, this very high D/H ratio is comparable to those in comets, and suggests an evolutionary history in which cometary materials remain at very low temperatures throughout their assemblage and for the bulk of their lives.

E. A. Richards, Arizona State University

Using a combination of radio and optical imaging at 0.1" to 0.2" resolution with the VLA/MERLIN and HST has led to a breakthrough in our understanding of radio emission from distant (0.1 < z < 3) starburst galaxies. We have recently isolated a number of high redshift, dusty starburst galaxies that remain invisible in ground based images to I_AB=25 and I_AB=28.5 in the Hubble Deep Field. These galaxies appear as faint radio sources, often accompanied by very red counterparts (I - K > 4 - 6) and submillimeter sources with S > 2 mJy at 850 microns as measured with SCUBA on the JCMT. The far-infrared luminosities of these galaxies exceeds even the most intense starbursts found in the local universe (e.g., Arp 220).

These galaxies, completely absent in optical surveys, constitute 50% - 90% of the star-formation density in the distant Universe.Upcoming developments in radio instrumentation (the Expanded VLA Array and Square Kilometer Array) will increase sensitivity and resolution orders of magnitude, providing a natural complement to parallel developments in sub-mm facilities (e.g., ALMA). With dual radio continuum and sub-mm surveys of the distant Universe, a census of galaxy evolution to the earliest cosmic epochs (z = 5-30) will soon be possible.

Masao Saito, Maria T. Beltran, Paul T. P. Ho
Center for Astrophysics

Ryohei Kawabe
Nobeyama Radio Observatory

We carried out 3.6 cm VLA observations of 17 embedded sources with CO wing emission in Taurus. We detected continuum emission toward 12 embedded sources and 7 were newly detected. Most detected sources are not resolved with 3" beam. The X band emission at the embedded phase likely originates from partially thick thermal free-free emission of ionized jets (e.g. Anglada et al. 1998). Our results indicate that the compact thermal jets (< 100 AU) are ubiquitous phenomena even in low-mass protostars. Although X band fluxes of some detected sources in our study are in agreement with those measured previously, we found that the flux of L1551 NE became stronger by a factor of a few as that in 1994 (Rodriguez et al. 1995). This result suggests that the jet activity, probably related to accretion rate, changed in a few years. We also discuss observations of jets around low-mass protostars with the ALMA array.

Anglada, G. et al. 1998, AJ, 116, 2953
Rodriguez, L. F. et al. 1995, ApJ, 454, L149

Göran Sandell
NRAO Green Bank

We present large continuum maps (13' x 18') continuum maps at 850m and 450m of the active star formation region NGC 1333, obtained with the bolometer array camera SCUBA on JCMT, Mauna Kea, Hawaii. These maps are sensitive enough to detect dust surrounding any YSO and protostar to a mass limit of 0.01 M, and also sensitive enough to probe the the dense molecular gas surrounding these YSOs and protostars. We find more than 30 discrete sources, some of which are extended and may contain multiple condensations. We compare the continuum survey with the CO J=3-2 (Knee & Sandell, 1999), which shows ast least eight different outflows in the main NGC 1333 cloud, many of which are spatially overlapping. Most of the outflows are driven by protostellar or deeply embedded young PMS stars, all of which show up as strong continuum sources in our SCUBA survey.

The continuum maps show dust ridges and shells, which are caused by powerful outflows that we see in our CO J=3-2 maps. In two cases we indentify proto--stellar sources, which have been triggered by powerful bowshocks in the outflows. Almost all of the strong sources, IRAS 4 A,B, IRAS 2, and SSV 13 B have been identified as Class 0 sources, but this survey suggests that many of the fainter sources are likely to be even lower mass Class 0 objects. Very few of the submillimeter sources have optical or near-IR counterparts.

Knee, L.B.G. & Sandell, G. 1999, A&A, being revised

F. Peter Schloerb
FCRAO/University of Massachusetts

Focal plane array receivers enable single dish telescopes to obtain sensitive maps of sources efficiently. In this paper, we summarize results of the detailed mapping of the chemistry of molecular cloud cores and comets with the focal plane array on the FCRAO 14m antenna by a number of investigators. Surveys of the emission from approximately 20 different molecular species have been carried out in GMC cores and dark clouds. The GMC core chemistry is remarkably homogeneous and rather similar from source to source. Time dependent chemical modelling finds good agreement with the observations at early evolutionary stages (t ~ 10⁵ yr) suggesting that the GMC cores are dynamically evolving objects. Surveys of dark cloud cores have revealed significant abundance variations within the sources. The pattern of variations is best explained by small differences in the chemical evolutionary age within the source, with a typical value for the entire cloud also in the vicinity of ~10⁵ years. Images of the molecular emission from comets provide important clues about the physical processes and chemistry of the cometary coma. Chemical models reveal that HCO⁺ is created in the coma via ion-molecule chemistry; its detailed distribution reflects its interaction with the solar wind and provides important tests of MHD models of these effects.

F. P. Schloerb
FCRAO/University of Massachusetts

L. Carrasco
Instituto Nacional de Astrofisica Optica y Electronica

J. Baars
LMT Project/University of Massachusetts

The Large Millimeter Telescope (LMT) is a joint project of the University of Massachusetts (USA) and the Instituto Nacional de Astrofisica Optica y Electronica (Mexico). The LMT will be a filled aperture, millimeter-wave telescope with a diameter of 50m. The antenna is being constructed atop Cerro la Negra in the state of Puebla, Mexico. This site is at an elevation of 4600m and at a latitude of 19 degrees. Site development and foundation work for the telescope has begun, and steel assembly will begin early during the year 2000. Telescope commissioning is expected to begin in 2002. The main wavelength bands for operation of the LMT will be the 1.2, 2, and 3mm windows. Site conditions for millimeter-wave operation are excellent, with the median optical depth at 230 GHz below 0.15 throughout September-May. An initial complement of instruments is under development and includes a 32-pixel heterodyne focal plane array for the 3mm band and a 144-pixel bolometer system for continuum work, primarily in the 1.2mm window. We expect that LMT will serve as a pathfinder for many of the exciting, frontier areas that ALMA will eventually explore in detail.

Nick Scoville
Caltech

We review recent high resolution imaging of the molecular gas, dust, and luminosity sources in the nuclei of galaxies based on current mm-interferometry and HST NICMOS data.

Yutaro Sekimoto, Ryohei Kawabe
Nobeyama Radio Observatory, National Astronomical Observatory of Japan

Satoshi Yamamoto, Tetsuo Hasegawa
Faculty of Science, University of Tokyo

We have a plan to operate a new 10 m telescope at Pampa la Bola (4800 m) in Chile as one of Japanese R&D activities for Atacama Large Millimeter/Submillimeter Array. Technical and scientific purposes in this experiment are

1. to develop and evaluate a high precision 10 m antenna under exposed conditions at the site,
2. to develop and test low-noise submillimeter receivers and new SIS photon detectors,
3. to test various techniques for submillimeter observations, and
4. to explore the southern hemisphere in the submillimeter band: Galactic Center, Magellanic Clouds, and so on.

Ronak Y. Shah
University of Virginia/NRAO Charlottesville

Alwyn Wootten
NRAO Charlottesville

We report on a survey of NH₂D towards protostellar cores in low--mass star formation regions in the Galaxy. Twenty--three out of thirty observed sources have significant (> 5) detections. Ion--molecule chemistry, which preferentially enhances deuterium in molecules above its cosmological value of 2 x 10^-5, primarily through exchange reactions with H₂D⁺, sufficiently explains these abundances. These gas--phase reactions produce molecules which deplete onto grains and later (>10⁶ yrs) reappear in the gas as the radiation from protostars evaporates icy mantles. Predictions of ``early-time'' gas-phase chemical networks, though qualitatively correct, underpredict the fractionation in the coldest (10-20 K) sources. This suggests that evolution of sources, branching ratios, alternative reaction pathways, or abundances have not been accurately taken into account by current models.

Kartik Sheth, Stuart Vogel, Andy Harris
University of Maryland

Leo Blitz, Douglas C.-J. Bock, Tony Wong
University of California - Berkeley

Tamara T. Helfer
University of Arizona

Michael W. Regan
CIW-DTM

Michele D. Thornley
NRAO

We present results from the CO (J=1-0) BIMA Survey of Nearby Galaxies (SONG). The BIMA SONG includes 44 spiral (Sa-Sd) galaxies with M_B < 11, V_HEL < 2000 km s^-1 , inclination < 70^o and declination > -20^o. The 30 galaxies for which CO emission is known to be extended were observed with a 7-field mosaic with a 3-4' FOV at 7" angular resolution and 5 km/s spectral resolution; the remaining 14 galaxies were observed with a single central pointing (FOV ~ 2'). In this poster, we also concentrate on the gas distribution in barred spirals and compare the observations to predictions of a secular evolution scenario in which late type bars evolve into early type bars.

J. Staguhn, A.I. Harris, L.G. Mundy
University of Maryland, College Park

D.P. Woody
Caltech, Owens Valley Observatory

R.L. Plambeck
University of California, Berkeley

Monitoring the line emission from tropospheric water vapor can be used for phase correction of mm and sub-mm signals, since phase fluctuations at these wavelengths are predominantly caused by fluctuations in the distribution of water vapor.

We have built a prototype cooled broad band 16-channel radiometer which allows us to measure the shape of the optically thin 22 GHz water vapor line. In the optically thin limit, line intensity and shape information allows the measurement of the total water vapor column and a coarse separation of the altitude distribution of the fluctuating water vapor component. This altitude information can be used to reduce the uncertainties in the conversion between the measured sky fluctuations and the actual phase fluctuations of astronomical signals. The use of a multi channel measurement will allow robust phase corrections over a wide range of weather conditions, including the presence of liquid water clouds. The system that we are building is targeted for implementation on the BIMA array with a goal of path length correction to 35 m rms. The system is the low frequency analogy to the 183 GHz system planned for the ALMA array. It will provide valuable experience in high accuracy phase correction.

Karl R. Stapelfeldt and Deborah L. Padgett
Jet Propulsion Laboratory, California Institute of Technology

We present the first millimeter interferometer observations of HH 30, an edge-on young stellar object accretion disk system located in the Taurus L1551 molecular cloud. Maps were made in the ¹²CO(2-1), ¹³CO(2-1), and ¹³CO(1-0) lines, and in the adjacent continuum. The dust continuum fluxes are weak, and imply a relatively small circumstellar disk mass (__10^-3 M) consistent with estimates from Hubble Space Telescope images. Detailed comparison of the line maps and the HST images shows that the ¹²CO(2-1) traces both the disk and the optical jet; since the outflow lies nearly in the plane of the sky, it is difficult to disentangle the two components. However, the ¹³CO(2-1) emission appears confined to the disk plane and shows a velocity gradient indicative of orbital motion. The gas disk has a diameter comparable to that of the dust absorption lane seen in the optical images. Future ALMA observations with the spatial resolution of HST will provide huge gains in our understand of HH 30, one of the faintest YSO disks mapped to date at millimeter wavelengths.

Linda Tacconi, Reinhard Genzel, Eva Schinnerer, Andreas Eckart, Matthias Tecza
MPE, Garching

We are carrying out a program of 0.6"-0.8" resolution 12CO observations with unprecedented high sensitivity in a sample of nearby AGN and mergers with the IRAM interferometer. These data provide the exciting possibility of studying the circumnuclear regions on scales ranging from tens to a few hundred pc. For the nearby Seyfert galaxies we find that central molecular condensations observed previously at lower resolution are resolved into 100-200 pc diameter clumpy rings or disks with evidence for gas lying closer to the nucleus. We will preset results of detailed kinematic modeling of the Seyfert galaxies N1068 and N3227. For the mergers and ultraluminous galaxies, the molecular gas distributions and kinematics are providing valuable diagnostics to determine the phase of the merger. In NGC6240 the CO emission is concentrated in a rotating, but highly turbulent thick disk structure centered between the two radio nuclei. We show, from kinematic modeling of the molecular gas and from a comparison with stellar dynamics and mass distributions, that this galaxy is in an earlier merging stage than the prototypical ULIRG, Arp220, and that it may well be about to experience a major starburst like that observed in many other ULIRGS.

Michele D. Thornley
NRAO Charlottesville

Much attention is being focused on the improvements ALMA will make in our knowledge of high-redshift galaxies. So far, detections of molecular gas at high redshift support the view that metallicity enhancements can occur quickly with the onset of the first starburst events (see review by Combes, Maoli, & Omont 1999). Thus a more complete understanding of star formation activity in the local universe, which can be pursued with high spatial resolution over a range of environments and metallicities, is valuable in studies of galaxies at all redshifts.

In this talk, I will briefly review work on molecular gas in nearby galaxies that has been pursued at existing mm-wave interferometers (BIMA, OVRO, NMA, IRAM), and discuss prospects for new science which can be achieved with ALMA. For instance, ALMA will be able to resolve giant molecular clouds in galaxies outside the Local Group, making it possible to conduct studies of extragalactic star formation on scales more compatible with those of Galactic studies of gas and stars. Furthermore, it will be possible to refine star formation prescriptions which have been developed over more global scales (e.g., Kennicutt 1989). This discussion will show the important contribution ALMA will make to understanding the ISM in nearby galaxies.

Combes, F., Maoli, R., & Omont, A. 1999 A&A, 345, 369
Kennicutt, R.C. Jr., 1989, ApJ, 344, 685

Ewine F. van Dishoeck
Leiden Observatory, The Netherlands

\footnotetext{The formation of stars is accompanied by orders of magnitude changes in the physical conditions, with densities in the envelopes and disks increasing from 10⁴ cm^-3 to > 10¹³ cm^-3 and temperatures from ~ 10 K in the cold quiescent gas to 10,000 K in shocked regions. The abundances and excitation of the various molecules respond to these changes, and are therefore excellent probes of the physical evolution of YSOs. Moreover, a comprehensive inventory of the chemical composition of envelopes and disks at different evolutionary stages is essential to study the chemistry of matter as it is incorporated into new solar systems. Recent observations of the envelopes of YSOs using single-dish telescopes and millimeter interferometers clearly reveal the potential of submillimeter lines to probe these physical and chemical changes. However, the existing data generally lack the spatial resolution to separate the different physical components, such as the warm inner envelope or `hot core', the region of interaction of the outflow with the envelope and any possible circumstellar disk. ALMA will be essential to provide an `unblurred' view of the YSO environment and unravel the chemical evolution during star formation.

In this talk, an overview will be given of recent single-dish and interferometer results of the chemistry in the envelopes and disks around low- and high-mass young stellar objects. Together with ISO data on solid-state material, these observations lead to a chemical scenario in which both gas-phase and gas-grain chemistry (in particular freeze-out and evaporation) play an important role. The evaporated molecules drive a rich chemistry in the warm gas, which can result in complex organic molecules. The potential of ALMA to test chemical theories and determine the composition of gas and dust as it enters forming planetary systems will be illustrated.}

François Viallefond
DEMIRM, Observatoire de Paris

K.R. Anantharamiah
Raman Research Institute

The observation of radio recombination lines (RRL) over a wide range of quantum levels gives valuable information on the physical state of the ionized gas. With the sensitivity of the existing radiotelescopes, at long as well as at short wavelengths, only less than 10 galaxies have been detected. The most distant galaxy detected so far is the starburst galaxy Arp 220. The remarkable feature in observing millimeter RRLs is that they allow to probe high density regions although this represent only a small fraction of the total mass of ionized gas. Starburst nuclei are heavily obscured in the visible but also in the near infrared, RRLs offer probably the unique tool to measure recent star formation rate (SFR). Centimeter lines can be used to determine the average SFR on a time scale of ~ 5 10⁶ years while the millimeter lines offer the access to the very instantaneous SFR rate ( ~10⁵ years). The total infrared luminosity is related to the average SFR on longer time scales, a few 10⁷ years. Hence a multi-wavelength approach gives informations about the star formation history. Some recent results are presented. They illustrate the potentiality of ALMA which will have the sensitivity to detect a large number of galaxies and at much larger distances.

Stuart N. Vogel
University of Maryland

Tamara T. Helfer
University of Arizona

Kartik Sheth, Andrew I. Harris
University of Maryland

Michele D. Thornley
National Radio Astronomy Observatory

Michael W. Regan
Department of Terrestrial Magnetism

Leo Blitz, Tony Wong, Douglas C.-J. Bock
University of California, Berkeley

We present a 62-field mosaic of CO 1-0 emission from the grand design spiral galaxy M51 obtained with the BIMA millimeter array. The mosiac, constructed from four tracks in each of the two low-resolution configurations, covers the entire optical disk of M51 and extends to the interacting companion galaxy, NGC 5195. CO emission is distributed in a striking spiral pattern beginning in the nuclear region and overlapping the companion galaxy. We compare the molecular gas emission traced by CO with the neutral atomic, ionized, and stellar distributions.

Sara Watt, Lee G. Mundy
University of Maryland

Hot cores attract attention because of their bright emission line spectra, but their importance in the massive star formation process makes them key sources to study. It is thought that hot cores may be the next generation of massive stars, so understanding their origins, their effect on the surrounding environment, and their future is vital to understanding massive star formation.

We present high resolution millimeter observations of two well-known hot cores, G34.26+0.15 and G31.41+0.31, illustrating positional offsets of emission from different molecular species. We compare our observation with the models of Millar etal (1997). We suggest that external heating by the nearby UC~HII region is a viable mechanism to produce hot core emission rather than internal heating by forming stars.

Millar, T. J., Macdonald, G. H., & Gibb, A. G. 1997, A&A, 325, 1163

Adrian Webster
University of Edinburgh, Scotland

A class of designs for the ALMA is discussed which is very different from the array of about four identical nested rings considered previously. The new designs are composite, in that they are made up of several configurations of different sizes and very different shapes, hybrid in that they are planned to work well with some of the antennas on the stations of one configuration and the remainder on those of an adjacent configuration, and zoomable in that the antennas may be deployed to provide a synthesized beam whose width lies within about 1 percent of any required value in the entire range. A typical design is presented consisting of a compact configuration, with all of the stations packed closely within a disk, an intermediate configuration, in which the density of stations drops off as the square of the distance from the array centre, and an outer ring in the form of a circle or Reuleaux triangle. As well as the zoom property, the design has other advantages over an array of nested rings, including sidelobe levels that are nearly an order of magnitude lower and a capability to redeploy the antennas in order to provide near-circular beams when observing well away from the zenith. The mode of operation is likely to be very different, with one or two antennas being moved every day or 5 - 10 every week, rather than moving all the antennas at once every few months or so. The advantages and disadvantages are summarized and it is concluded that the former probably outweigh the latter considerably, and that designs of this type are competitive with nested rings for the ALMA.

Martina C. Wiedner
Harvard-Smithsonian Center for Astrophysics

Richard E. Hills
MRAO, Cavendish Laboratory

At millimeter wavelengths, phase fluctuations caused by changing amounts of water vapor in the atmosphere disturb the images formed by ground-based instruments, in a manner similar to the effects of "seeing" familiar to optical astronomers. Unless corrections are applied, these fluctuations will render impossible observations of faint objects with an angular resolution of better than a few tenths of an arc second, even on a good site, such as Chajnantor.

Our poster will explain the cause of these phase corrections and methods of phase correction. We describe the first water vapor monitors (wvm's) designed to allow phase correction by measuring the atmospheric emission from the 183 GHz water vapor line (Wiedner, 1998). The two radiometers were tested on Mauna Kea, Hawaii, and in fair weather (2.2 mm pwv) phase correction reduced the rms phase fluctuations from 60^o (140 m) to 25^o (60 m) over 30 minutes, i.e. 75% of the intensity of the decorrelated signal was retrieved. Though more testing is necessary, this seems a very promising method to reduce phase fluctuations at ALMA.

Wiedner, M. C. 1998, Atmospheric Water Vapour and Astronomical Millimetre Interferometry, PhD Thesis, University of Cambridge (http://www.mma.nrao.edu/workinggroups/cal_imaging/183GHz.html)

Wolfgang Wild
Kapteyn Institute, University of Groningen

Andreas Eckart
MPE Garching

Centaurus A (NGC 5128) is the closest radio galaxy, and its molecular interstellar medium has been studied extensively in recent years. However, these studies used mostly molecular lines tracing low to medium density gas (see e.g. Eckart et al. 1990. Wild et al. 1997). The amount and distribution of the dense component remained largely unknown.

We present spectra of the HCN(1-0) emission - which traces dense (n(H₂) > 10⁴ cm^-3) molecular gas - at the center and along the prominent dust lane at offset positions 60" and 100", as well as single CS(2-1) and CS(3-2) spectra, observed with the SEST on La Silla, Chile. At the central position, the integrated intensity ratio I(HCN)/I(CO) peaks at 0.064, and decreases to 0.02 to 0.04 in the dust lane. Based on the line luminosity ratio L(HCN)/L(CO) we estimate that there is a significant amount of dense gas in Centaurus A. The fraction of dense molecular gas as well as the star formation efficiency L_FIR/L_CO towards the center of Cen A is comparable to ultra-luminous infrared galaxies, and falls in between the values for ULIRGs and normal galaxies for positions in the dust lane. Details will be published in Wild & Eckart (A&A, in prep.).

Eckart et al. 1990, ApJ 363, 451
Rydbeck et al. 1993, Astr.Ap. (Letters) 270, L13.
Wild, W., Eckart, A. & Wiklind, T. 1997, Astr.Ap. 322, 419.

Jonathan Williams
NRAO

One of the primary science goals of the Atacama Large Millimeter Array is to image star forming regions in unprecedented detail and sensitivity. Here, we present BIMA observations of a young embedded stellar group in Serpens that demonstrate some of the issues in this field that ALMA may address in the future. The high resolution of the interferometer enables us to to follow the structure, dynamics, and chemistry of the overall cluster forming cloud down to the scale of individual star forming cores. There is an approximately equal mix of cores with and without continuum sources suggesting that new stars are continually being added to the group. There is evidence for large scale collapse onto the cluster with concentrations toward regions where the velocity dispersion is at a local minimum. There are also significant differences in relative abundances throughout the cluster indicating that molecule formation and depletion timescales are comparable to or less than dynamical timescales for core formation and that chemistry may be used as a signature of their evolution. We discuss a scenario for cluster formation through the condensation and collapse of individual cores via turbulent dissipation and point out a few ways in which ALMA may contribute to future studies.

David J. Wilner
Harvard-Smithsonian Center for Astrophysics

Chris G. Depree
Agnes Scott

W. Miller Goss
NRAO

W. Jack Welch
Berkeley

Elizabeth McGrath
Vassar

We have made multi-frequency observations of the high mass star forming region W49N using the VLA and BIMA. The images, with resolution from 0.045 arcseconds (VLA at 7 mm) to 0.35 arcseconds (BIMA at 3.3 mm), obtain high dynamic range in an environment of complex emission, a hint of the capabilities to come with ALMA. Located on the far side of the Galaxy at a distance of 11.4 kpc, the W49N core contains more than a dozen ultracompact HII regions arranged in a 2 pc diameter ring (Dreher et al. 1984). This large scale organization has led to numerous speculations about mechanisms for triggering coherent events of high mass star formation. The large population of young sources appears at odds with the dynamical timescales for free expansion, a manifestation of the ``lifetime problem'' for ultracompact HII regions. The new millimeter images resolve individual ultracompact HII regions at the 500 AU size scale and reveal morphologies for many of them. Most show shell or ring structures. In all cases, the 3.3~mm emission is dominated by free-free emission; there is no evidence for any spectral breaks corresponding to the emergence of a dust component. Interestingly, the sources with rising radio spectral indices (, ) also have the broadest H66 radio recombination lines, phenomena likely explained by powerful ionized winds.

C. D. Wilson
McMaster

N. Scoville
Caltech

S. Madden
Saclay

V. Charmandaris
Paris

As the closest example of a merger of two massive spiral galaxies, the Antennae system (NGC 4038/39) offers a unique opportunity to study the physical and dynamical properties of the interstellar medium in an active merger system. The Antennae have one of the largest populations of luminous star clusters known (Whitmore & Schweizer 1995), while ISO observations have revealed luminous regions of massive star formation that are completely invisible at optical wavelengths (Vigroux et al. 1996; Mirabel et al. 1998). Studying the properties of the molecular gas out of which these star clusters formed is important for understanding the triggering of intense star formation in galaxy mergers. We have observed the CO emission in the Antennae using the Caltech Millimeter Array. These data reveal extremely massive concentrations of molecular gas (> 10⁸ M ), a chaotic velocity field, and evidence for cloud collisions near the strongest mid-infrared peak. It seems likely that the formation of the luminous star clusters takes place in these massive gas concentrations, while cloud-cloud collisions may provide an explanation for the unusually strong 15 m peak seen with ISO.

Mirabel, I. F. et al. 1998, A&A, 333, L1
Vigroux, L. et al. 1996, A\&A, 315, L93
Whitmore, B. C. & Schweizer, F. 1995, AJ, 109, 960

T.L. Wilson, Dirk Muders, William L. Peters, Harold M. Butner, Paul D. Gensheimer
SMTO, Tucson

Keven I. Uchida
Cornell University

Carsten Kramer, Achim R. Tieftrunk
I. Phys. Institut, Universität zu Köln

Radio astronomers have studied only small regions of the sky in the necessary detail, with accurate pointing, calibration and high signal-to-noise ratio needed for the accurate modelling of molecular clouds. For ALMA, such studies with single telescopes are needed before high resolution imaging can be undertaken. In addition, cloud imaging in the sub-mm wavelength range allows us to select warm regions with high H₂ densities. Such regions are more likely to collapse to form stars or contain newly-formed stars.

We have used the Heinrich Hertz 10-m telescope (HHT) to take these data. The HHT is located on Mt. Graham at an elevation of 3.2 km. The RMS pointing error is 2.5'', the beam size at 806 GHz is 13", and the telescope beam efficiency at 806 GHz is ~38%. We expect to improve these telescope parameters in the coming year. The receivers at the HHT are located in two naysmth foci to the left and right of the telescope axis. The left focus contains the facility SIS heterodyne receivers, while the right side is reserved for bolometers and P.I. instruments. Changing foci is accomplished in less than a minute by flipping a flat mirror under remote control. This flexibility makes the HHT an ideal 'test bed' for new, experimental receiver systems.

All of the results in this report were taken with heterodyne receivers. The spectra were analyzed using either filter banks or Acoustic Optical Spectrometers. The results were taken with either position switching or beam switching with a beam throw of 4'. The efficiency of data taking and reliability of the results were improved using the spectral line On-The-Fly (OTF) mapping technique. After its implementation in December 1998, OTF mapping was used for several projects at frequencies up to 806 GHz (CO 7-6) using the CfA Hot Electron Bolometer Receiver. We show maps of the ongoing scientific programs dealing with star formation, outflow dynamics, the interaction of HII regions with molecular clouds and the chemistry, ionization and structure of the interstellar medium. Our images of galactic sources include CO J=7-6 data for Orion KL, Cepheus B and Sharpless 106. Maps of extragalacitc sources such as M82, IC 342 and Maffei 2 were taken by other groups and will be presented in another forum.

Jennifer J. Wiseman
Johns Hopkins University

Large millimeter arrays such as ALMA provide a means to map the warm dust and molecular gas in regions encircling protostellar accretion zones. Line observations, in particular, provide the means not only for excitation studies but for kinematical studies of the protostellar environment. Radio and millimeter interferometers are already being used to trace infall, rotation, and outflow of dense gas. Recently, flattened large (~10,000 AU) molecular gas disks around protostars were detected and show strong evidence for rotation (Zhang et al. 1998, Wiseman et al. 1998). We present here our most recent VLA ammonia maps showing flattened gas disks with velocity gradients indicative of rotation around the sources of the jets HH111, HH211 and HH212. We discuss interaction with the jets and outflows. We also discuss how line maps from ALMA and radio interferometers complement each other.

Wiseman, J., Wootten, A., Zinnecker, H., & McCaughrean, M. 1998, in The Physics and Chemistry of the Interstellar Medium, abstract book of the 3rd Cologne-Zermatt Symposium, ed. V. Ossenkopf

Wiseman, J., Fuller, G., & Wootten, A. 1999, in preparation

Zhang, Q., Hunter, T., & Sridharan, T. 1998, ApJ, 505, L151

Friedrich Wyrowski
University of Maryland, College Park

T.K. Sridharan
CfA, Cambridge

Karl M. Menten, Peter Schilke
MPIfR Bonn, Germany

To systematically search for high mass protostars without any free-free emission, meaning that no UC HII has formed yet, we studied 70 candidate sources, selected according to their FIR radiation characteristics and their non-detection in Galaxy wide cm continuum surveys (Ramesh & Sridharan 1997), in the water vapor and ammonia lines with the 100 m and, in case of detections, with the 30 m telescope (Menten et al. 1999; Sridharan et al. 1999). This lead to the detection of several new water masers, ubiquitous outflow activity, and several new hot core sources as evident from bright CH₃CN emission. As a follow up we started interferometric observations of selected sources using the BIMA array. Here we present observations of IRAS 18089-1732, a source at a distance of 3.6 kpc with about 4 x 10⁴ solar luminosities derived from the IRAS fluxes. The massive core is seen in 3 mm dust continuum emission and is associated with compact (~ 0.03 pc) and hot (T ~ 100 K) strong line emission of CH₃CN suggesting an enhancement and heating of this molecule through very recent evaporation of dust grains by a newly born high mass (proto) star.

Harold W. Yorke
JPL, California Institute of Technology, Pasadena, CA 91109 USA

Sabine Richling
Institut fér Theoretische Astrophysik, University of Heidelberg, Germany

The evolution and appearance of circumstellar disks in star forming regions are influenced strongly by the radiation from either the central star itself or close companions and nearby hot stars. UV radiation can heat the outer layers of the disk and induce expansion up to escape velocities. Hollenbach et al. (1999, PPIV, in press) consider this ``photoevaporation'' of disks as a principal, if not the most important, disk destruction mechanism. Assuming axial symmetry, we have previously performed radiation hydrodynamic calculations of the evolution of internally (Richling & Yorke, 1997, A&A, 327, 317) and externally (Richling & Yorke, 1998, A&A, 340, 508) UV-irradiated disks. These simulations provide us with the distributions of gas density, temperature and velocity as well as the dust temperature distribution of protostellar disks undergoing photoevaporation, useful for diagnostic radiation transfer modeling. We find sharp transitions between a) the neutral, molecular material in the disk, in Keplerian rotation, b) the neutral, mostly atomic outflowing (several km s^-1) PDR material, and, if sufficient EUV is present, c) the ionized, outflowing (several 10 km s^-1) HII material. High resolution line and continuum studies combined with detailed modeling will provide important constraints regarding the structure of protostellar disks and their UV environment.

Hollenbach D., Yorke H.W., Johnstone D., 1999, Protostars and Planets IV, eds. V.Mannings, A. Boss, S. Russell, (Tucson: Univ. of Arizona Press), in press
Richling S., Yorke H.W., 1997, A&A, 327, 317
Richling S., Yorke H.W., 1998, A&A, 340, 508

M. S. Yun and C. L. Carilli
NRAO/AOC

Sensitive observations at submm wavelengths are revealing what may be a population of active star forming galaxies at high redshift which are unseen in deep optical surveys due to dust obscuration (e.g. Smail et al. 1997, ApJ, 490, L5; Barger et al. 1998, Nature, 394, 248; Hughes et al. 1998, Nature, 394, 341). Most of these sources are associated with optically faint counterparts (R > 25, K > 21; Smail et al. 1999, MNRAS, submitted), and obtaining reliable optical redshifts remain problematic. In a recent paper, we have proposed the technique of using the radio-to-submm spectral index as a redshift indicator, taking advantage of radio-FIR correlation obeyed by all star forming galaxies (Carilli & Yun 1999, ApJ, 513, L13). Here, we present the analysis of the scatter in the relationship using the observed spectral energy distribution of low redshift star forming galaxies. The scatter is found to be roughly constant with redshift, and the flattening of the relationship with increasing redshift leads to increasing uncertainty at high-z. Thus only a gross redshift estimation is possible for any individual source. On the other hand, the statistical inference on the redshift distribution should still be valid, and we derive a conservative lower limit to the median redshift of 2.0 for the published sample of faint submm sources. More than 75% of these source are likely located at z 1.5.

Qizhou Zhang, Todd R. Hunter, T.K. Sridharan
Harvard-Smithsonian Center for Astrophysics

J. H. Kawamura
California Institute of Technology

We present images of a disk/outflow system around a high-mass protostar IRAS 20126+4104. In the NH₃ (1,1) and (2,2) lines, we have resolved a flattened disk-like structure (6'' x 3'' or 10000 x 5000 AU). The disk rotates faster toward the center, consistent with the Keplerian motion. In the direction roughly perpendicular to the disk, there exists a warm bipolar CO (7-6) outflow and the shock excited NH₃ (3,3). The CO (7-6) outflow is much more compact and appears in a different orientation from the arcminute-scale north-south flow seen in the CO (2-1). Since most of the high-mass stars are formed in cluster environment and are located at kiloparsec distances, sensitive and high resolution observations of high density and highly excited molecular transitions are crucial to pinpoint the massive objects. Designed to have those capabilities, ALMA will make a significant contribution to the understanding of the protostellar environment of high-mass stars.