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We present Spitzer observations of the dark globule CB190 (L771). We observe a roughly circular 24 micron shadow with a 70 arcsec radius. The extinction profile of this shadow matches the profile derived from 2MASS photometry at the outer edges of the globule and reaches a maximum of ~32 visual magnitudes at the center. The corresponding mass of CB190 is ~10 Msun. Our 12CO and 13CO J = 2-1 data over a 10 arcmin X 10 arcmin region centered on the shadow show a temperature ~10 K. The thermal continuum indicates a similar temperature for the dust. The molecular data also show evidence of freezeout onto dust grains. We estimate a distance to CB190 of 400 pc using the spectroscopic parallax of a star associated with the globule. Bonnor-Ebert fits to the density profile, in conjunction with this distance, yield xi_max = 7.2, indicating that CB190 may be unstable. The high temperature (56 K) of the best fit Bonnor-Ebert model is in contradiction with the CO and thermal continuum data, leading to the conclusion that the thermal pressure is not enough to prevent free-fall collapse. We also find that the turbulence in the cloud is inadequate to support it. However, the cloud may be supported by the magnetic field, if this field is at the average level for dark globules. Since the magnetic field will eventually leak out through ambipolar diffusion, it is likely that CB190 is collapsing or in a late pre-collapse stage., 16 pages, 13 figures, accepted for publication in ApJ

The Multiband Imaging Photometer for Spitzer (MIPS) provides long-wavelength capability for the mission in imaging bands at 24, 70, and 160 ?m and measurements of spectral energy distributions between 52 and 100 ?m at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point-spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The 24 ?m array has excellent photometric properties, and measurements with rms relative errors of about 1% can be obtained. The two longer-wavelength arrays use detectors with poor photometric stability, but a system of onboard stimulators used for relative calibration, combined with a unique data pipeline, produce good photometry with rms relative errors of less than 10%.

We present the Early Release Observations of the HH 46/47 system and HH 46 IRS 1 source, taken with the three instruments aboard the Spitzer Space Telescope. The optically invisible southwest lobe, driven by the HH 47C bow shock, is revealed in full detail by the Infrared Array Camera (IRAC) images and displays a 'loop'-like morphology. Both of the mid-infrared outflow lobes are narrower than those of CO flow. We believe that the combination of emission by H2 rotational lines [S(11)-S(4)] and some atomic lines, which fall within the IRAC passbands, are responsible for the bulk of the observed emission, although contributions from the 3.3, 6.2, and 7.7 micron polycyclic aromatic hydrocarbon emission bands cannot be ruled out. Weak spectral features corresponding to these emitters are present in the Infrared Spectrograph spectrum of the HH 47A bow shock. The spectrum of HH 46 IRS 1 shows remarkable similarities to those of high-mass protostars, which include the presence of H2O, CO2, CH4, and possibly NH3, CH3OH, and ices. The high ice abundances and the lack of signs of thermal processing indicate that these ices in the envelope are well shielded from the powerful outflow and its cavity. Emission from the Bok globule at 24 micron is detected and displays a similar structure to that observed at 8 micron.

We have identified vibrationally excited CH3CH2CN (ethyl cyanide) for the first time in the interstellar medium. Using the Caltech Submillimeter Observatory, the Berkeley-Illinois-Maryland Association Array, and the Caltech Millimeter Array, we have detected several transitions from both the vb = 1 in-plane bending state and the vt = 1 torsional state in the Sgr B2(N-LMH) source. Because these excited states lie near 300 K above ground, vibrationally excited CH3CH2CN is potentially a useful probe of the hottest regions of dense, dusty molecular cloud cores where massive star formation is occurring. In addition, this identification will help account for many unidentified and misidentified spectral lines observed in hot molecular cores.

We have obtained high-resolution (approximately 35 km/s) spectra toward the molecular cloud Sgr B2 at 63 micrometers, the wavelength of the ground-state fine-structure line of atomic oxygen (O(I)), using the ISO-LWS instrument. Four separate velocity components are seen in the deconvolved spectrum, in absorption against the dust continuum emission of Sgr B2. Three of these components, corresponding to foreground clouds, are used to study the O(I) content of the cool molecular gas along the line of sight. In principle, the atomic oxygen that produces a particular velocity component could exist in any, or all, of three physically distinct regions: inside a dense molecular cloud, in the UV illuminated surface layer (PDR) of a cloud, and in an atomic (H(I)) gas halo. For each of the three foreground clouds, we estimate, and subtract from the observed O(I) column density, the oxygen content of the H(I) halo gas, by scaling from a published high-resolution 21 cm spectrum. We find that the remaining O(I) column density is correlated with the observed (13)CO column density. From the slope of this correlation, an average [O(I)]/[(13)CO] ratio of 270 +/- 120 (3-sigma) is derived, which corresponds to [O(I)]/[(13)CO] = 9 for a CO to (13)CO abundance ratio of 30. Assuming a (13)CO abundance of 1x10(exp -6) with respect to H nuclei, we derive an atomic oxygen abundance of 2.7x10(exp -4) in the dense gas phase, corresponding to a 15% oxygen depletion compared to the diffuse ISM in our Galactic neighborhood. The presence of multiple, spectrally resolved velocity components in the Sgr B2 absorption spectrum allows, for the first time, a direct determination of the PDR contribution to the O(I) column density. The PDR regions should contain O(I) but not (13)CO, and would thus be expected to produce an offset in the O(I)-(13)CO correlation. Our data do not show such an offset, suggesting that within our beam O(I) is spatially coexistent with the molecular gas, as traced by (13)CO. This may be a result of the inhomogeneous nature of the clouds.

We present large-scale observations of the 3P1→3P0 transition of neutral carbon, as well as observations of 12CO, 13CO, and C18O, in four molecular clouds with nearby ultraviolet sources: W3, L1630/NGC 2024, S140, and Cep A. The observations cover approximately 30'×30' regions with a 3' beam. A typical C0 column density is about 1.6×1017 cm-2. The overall extent and morphology of the C I emission is similar to that of the 12CO and 13CO J=2→1 emission. There is a strong correlation of C I and 13CO line intensities. The column densities and line strengths of the C I lines imply that these lines arise in gas at the edge of the molecular cloud that is dissociated by ultraviolet radiation. The correlation of C I and 13CO intensity can arise as a result of a combination of column density variations, volume density variations, and unresolved cloud structure. In the latter case, however, any unresolved structures containing both C I and CO need not be more than a few times smaller than the telescope beam. Taken together with C+ observations, the C I data imply that only about half of the gas-phase carbon in molecular clouds is in CO. The observations indicate that the large 13CO/C18O abundance ratio (~20) seen at the edges of molecular clouds results from isotope-selective photodissociation of C18O.

We have used the Submillimeter High Angular Resolution Camera (SHARC) bolometer camera at the Caltech Submillimeter Observatory to map the distribution of the broadband 350 ?m continuum emission toward the Orion A molecular cloud. A comparison of the 350 ?m flux densities in OMC-1 with previous 1100 ?m measurements indicates a strong spatial variation of the grain emissivity exponent, ?. The lowest value of the exponent (? 1.75) is found toward the Orion Bar photon-dominated region (PDR), while the highest value (? 2.5) is found toward the Orion Ridge north of IRc2. This variation is consistent with the destruction of grain mantles by the UV photons from the Trapezium cluster. The observed spatial variation of ? in OMC-1 suggests that the long-wavelength grain emissivity may also vary significantly in GMC cores on small linear scales (0.5 pc), affecting H2 column density and mass estimates. The 350 ?m continuum emission in the Orion Bar region correlates well with the CO (6-5) peak brightness temperature and is shifted by ~10'' from the molecular component traced by the 13CO (6-5) emission. This indicates that the 350 ?m dust emission in this region originates predominantly in the outer high-temperature PDR layers. Several filamentary structures previously detected in molecular tracers are also seen in our map at flux levels comparable to those seen in the Bar. Over 30 compact dust sources are detected in the OMC-2 and OMC-3 clouds, including a dozen sources not previously known. The average 350/1300 ?m flux ratio based on our data and previous observations of this region (63 ? 19) indicates low dust temperatures (17 ? 4 K, assuming ? = 2) for most of the sources. The brightest 350 ?m source in OMC-3 has a low 350/1300 ?m ratio (~23), indicating a very low dust temperature (~10 K), or a significant opacity at 350 ?m (~2.5). This source appears to be a deeply embedded and cold young protostar. A comparison of the mass estimate for the OMC-2/3 filament based on the 350 ?m continuum emission with previous C18O mass estimates indicates a relatively high grain emissivity, Q(350) = 4 ? 10-4, in this region.

We present new data on the photodissociation regions associated with the reflection nebula NGC7023. 13CO(3-2) emission, delineates a molecular cloud containing a cavity largely devoid of molecular gas around this star. Neutral carbon is closely associated with the 13CO emission while ionized carbon is found inside and at the edges of the cavity. The ionized carbon appears to be, at least in part, associated with HI. We have mapped the northern and southern rims in 12CO(6-5) emission and found a good association with the H2 rovibrational emission, though the warm CO gas permeates a larger fraction of the molecular cloud than the vibrationally excited H2. The results are compared with PDR models. We suggest that a second PDR has been created at the surface of the molecular cloud by the scattered radiation from HD 200775. This second PDR produces a layer of atomic carbon at the surface of the sheet, which increases the predicted [C]/[CO] abundance ratio to 10%, close to the observed value., Comment: 34 pages, 8 figures

The close approach to the Earth of comet C/1996 B2 (Hyakutake) in March 1996 allowed searches for minor volatile species outgassing from the nucleus. We report the detection of deuterated water (HDO) through its 1(sub 01)-0(sub 00) rotational transition at 464.925 GHz using the Caltech Submillimeter Observatory. We also present negative results of a sensitive research for the J(5-4) line of deuterated hydrogen cyanide (DCN) at 362.046 GHz. Simultaneous observations of two rotational lines of methanol together with HDO in the same spectrum allow us to determine the average gas temperature within the telescope beam to be 69 +/- 10 K. We are thus able to constrain the excitation conditions in the inner coma and determine reliably the HDO production rate as (1.20 +/- 0.28) x 10(exp 26)/s on March 23-24, 1996. Available IR, UV and radio measurements lead to a water production rate of (2.1 +/- 0.5) x 10(exp 29)/s at the time of our HDO observations. The resulting D/H ratio in cometary water is thus (29 +/- 10) x 10(exp -5) in good agreement with the values of (30.8(sub - 5.3, sup +3.8) (Balsiger et al. 1995) and (31.6 +/- 3.4) x 10(exp -5) (Eberhardt et al. 1995) determined in comet P/Halley from in situ ion mass spectra. The inferred 3 a upper limit for the D/H ratio in HCN is 1%. Deuterium abundance is a key parameter for studying the origin and the early evolution of the Solar System and of its individual bodies. Our HDO measurement confirms that, in cometary water, deuterium is enriched by a factor of at least 10 relative to the protosolar ratio, namely the D/H ratio in H2 in the primitive Solar Nebula which formed from the collapse of the protosolar cloud. This indicates that cometary water has preserved a major part of the high D/H ratio acquired in this protosolar cloud through ion-molecule isotopic exchanges or grain-surface reactions and was not re-equilibrated with H2 in the Solar Nebula. Scenarios of formation of comets consistent with these results are discussed.

We report the first detection of the submillimeter emission from the 13C isotope of atomic carbon in the interstellar medium. The F=5/2-3/2 component of the 3P2-3P1 transition was observed with the Caltech Submillimeter Observatory in a region ~4' S of Orion IRc2, near the western end of the Orion Bar. The 12C-to-13C isotopic abundance ratio is 58±12 corrected for opacity of the 12C I line and the fractional intensity of the 13C I hyperfine component (60%). This is in agreement with the value for the equivalent ratio in C+. In comparison, our measurement of the C18O-to-13C18O ratio from observations of 2-1 and 3-2 lines toward the same position gives a value of 75±9. Photodissociation region models predict that the 12C-to-13C abundance ratio is particularly sensitive to chemical fractionation effects. If13C+ is preferentially incorporated into 13CO at cloud edges, there will be a dramatic reduction in the abundance of 13C. This is contrary to our observations, implying that the importance of chemical fractionation is small or is compensated for by isotopic-selective photodissociation of 13CO in this region with a large UV illumination.

The apparition of Comet C/1996 B2 (Hyakutake) offered an unexpected and rare opportunity to probe the inner atmosphere of a comet with high spatial resolution and to investigate with unprecedented sensitivity its chemical composition. We present observations of over 30 submillimeter transitions of HCN, H 13 CN, HNC, HNCO, CO, CH 3 OH, and H 2 CO in Comet Hyakutake carried out between 1996 March 18 and April 9 at the Caltech Submillimeter Observatory. Detections of the H 13 CN (4–3) and HNCO (16 0,16 –15 0,15 ) transitions represent the first observations of these species in a comet. In addition, several other transitions, including HCN (8–7), CO (4–3), and CO (6–5) are detected for the first time in a comet as is the hyperfine structure of the HCN (4–3) line. The observed intensities of the HCN (4–3) hyperfine components indicate a line center optical depth of 0.9 ± 0.2 on March 22.5 UT. The HCN/HNC abundance ratio in Comet Hyakutake at a heliocentric distance of 1 AU is similar to that measured in the Orion extended ridge— a warm, quiescent molecular cloud. The HCN/H 13 CN abundance ratio implied by our observations is 34 ± 12, similar to that measured in giant molecular clouds in the galactic disk but significantly lower than the Solar System 12 C/ 13 C ratio. The low HCN/H 13 CN abundance ratio may be in part due to contamination by an SO 2 line blended with the H 13 CN (4–3) line. In addition, chemical models suggest that the HCN/H 13 CN ratio can be affected by fractionation during the collapse phase of the protosolar nebula; hence a low HCN/H 13 CN ratio observed in a comet is not inconsistent with the solar system 12 C/ 13 C isotopic ratio. The abundance of HNCO relative to water derived from our observations is (7 ± 3) × 10 −4 . The HCN/HNCO abundance ratio is similar to that measured in the core of Sagittarius B2 molecular cloud. Although a photo-dissociative channel of HNCO leads to CO, the CO produced by HNCO is a negligible component of cometary atmospheres. Production rates of HCN, CO, H 2 CO, and CH 3 OH are presented. Inferred molecular abundances relative to water are typical of those measured in comets at 1 AU from the Sun. The exception is CO, for which we derive a large relative abundance of 30%. The evolution of the HCN production rate between March 20 and March 30 suggests that the increased activity of the comet was the cause of the fragmentation of the nucleus. The time evolution of the H 2 CO emission suggests production of this species from dust grains.

Since the construction of the first specialized submillimeter telescopes nearly a decade ago, there has been extensive mapping of astronomical sources in the previously difficult to observe ground-state fine-structure transition of [C I] at 492 GHz. We discuss recent CSO observations of [C I] and 13CO (2 → 1) lines toward bright photon-dominated regions (PDRs). These observations have revealed an interesting effect. In many sources and over a broad range of column densities, the observed intensity of the [C I] line is proportional to that of the 13CO (2 → 1) line with exceptions mainly in dense, active star-forming regions, where C I appears to be under-abundant relative to 13CO. In this paper we quantitatively display this effect.

We present infrared and millimeter observations of Barnard 335, the prototypical isolated Bok globule with an embedded protostar. Using Spitzer data we measure the source luminosity accurately; we also constrain the density profile of the innermost globule material near the protostar using the observation of an 8.0 um shadow. HHT observations of 12CO 2 --> 1 confirm the detection of a flattened molecular core with diameter ~10000 AU and the same orientation as the circumstellar disk (~100 to 200 AU in diameter). This structure is probably the same as that generating the 8.0 um shadow and is expected from theoretical simulations of collapsing embedded protostars. We estimate the mass of the protostar to be only ~5% of the mass of the parent globule., 15 pages, 17 figures, emulateapj format, accepted for publication in ApJ

The Spectral Energy Distribution (SED) mode of the Multiband Imaging Photometer for Spitzer (MIPS) Space Telescope provides low-spectral resolution (R ~ 15-25) spectroscopy in the far infrared using the MIPS 70 um detector. A reflective grating provides a dispersion of 1.7 um per pixel, and an effective wavelength coverage of 52.8--98.7 um over detector rows 1-27. The final 5 detector rows are contaminated by second-order diffracted light and are left uncalibrated. The flux calibration is based on observations of MIPS calibration stars with 70 um flux densities of 0.5--15 Jy. The point-source flux calibration accuracy is estimated to be 10% or better down to about 0.5 Jy at the blue end of the spectrum and to 2 Jy near the red end. With additional uncertainties from the illumination and aperture corrections included, the surface brightness calibration of extended sources is accurate to ~15%. Repeatability of better than 5% is found for the SED mode through multiple measurements of several calibration stars., To Appear in PASP

The 492 GHz ground-state fine-structure transition of neutral carbon has been observed extensively with the Caltech Submillimeter Telescope since 1990. During this time we have mapped several Galactic molecular clouds, including star-forming regions, photodissociation regions, dark clouds, a shocked region, and the Galactic Center. In addition, we have detected some nearby galaxies and some evolved stars.

We present measurements obtained with the Spitzer Space Telescope in five bands from 3.6-24 microns of the northern inner radio lobe of Centaurus A, the nearest powerful radio galaxy. We show that this emission is synchrotron in origin. Comparison with ultraviolet observations from GALEX shows that diffuse ultraviolet emission exists in a smaller region than the infrared but also coincides with the radio jet. We discuss the possibility, that synchrotron emission is responsible for the ultraviolet emission and conclude that further data are required to confirm this., 4 pages, accepted by ApJL

Spitzer mid-infrared images of the dusty warped disk in the galaxy Centaurus A show a parallelogram-shaped structure. We successfully model the observed mid-infrared morphology by integrating the light from an emitting, thin, and warped disk, similar to that inferred from previous kinematic studies. The models with the best match to the morphology lack dust emission within the inner 0.1 to 0.8 kpc, suggesting that energetic processes near the nucleus have disturbed the inner molecular disk, creating a gap in the molecular gas distribution., submitted to ApJ

The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

The Spitzer Space Telescope, NASA's Great Observatory for infrared astronomy, was launched 2003 August 25 and is returning excellent scientific data from its Earth-trailing solar orbit. Spitzer combines the intrinsic sensitivity achievable with a cryogenic telescope in space with the great imaging and spectroscopic power of modern detector arrays to provide the user community with huge gains in capability for exploration of the cosmos in the infrared. The observatory systems are largely performing as expected and the projected cryogenic lifetime is in excess of 5 years. This paper summarizes the on-orbit scientific, technical and operational performance of Spitzer. Subsequent papers in this special issue describe the Spitzer instruments in detail and highlight many of the exciting scientific results obtained during the first six months of the Spitzer mission., Accepted for publication in the Astrophyscial Journal Supplement Spitzer Special Issue, 22 pages, 3 figures. Higher resolution versions of the figures are available at http://ssc.spitzer.caltech.edu/pubs/journal2004.html

L1551NE is a very young (class 0 or I) low-mass protostar located close to the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum interferometric observations at ~1'' resolution, for a binary companion to L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The millimeterwave emission from the primary component may have been just barely resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion emission was unresolved (, 8 pages, 1 figure

We present a comparison of histograms (or PDFs) of CO (2−1) line centroid velocity increments in the ρ Ophiuchi and ζ Ophiuchi molecular clouds with those computed for spectra synthesized from a three-dimensional, compressible, but non-star forming and non-gravitating hydrodynamic simulation. Histograms of centroid velocity increments in the two molecular clouds show non-Gaussian wings, similar to those found in histograms of velocity increments and derivatives in experimental studies of laboratory and atmospheric flows, as well as numerical simulations of turbulence. The magnitude of these wings increases monotonically with decreasing separation down to the angular resolution of the data. This behavior is consistent with that found in the phase of the simulation which has most of the properties of incompressible turbulence. This is consistent with the proposition that ISM velocity structure is vorticity dominated like that of the turbulent simulation. The ρ Ophiuchi molecular cloud contains some active star formation, as indicated by the presence of infrared sources and molecular outflows. As a result shocks may have important effects on the velocity field structure and molecular line shapes in this region. However, the ζ Ophiuchi cloud represents a quiescent region without ongoing star formation and should be a good laboratory for studies of interstellar turbulence. Introduction Early spectroscopic observations of interstellar lines of HI, OH, and CO have revealed that observed line widths (or velocity dispersions) in interstellar clouds are larger than thermal line widths expected for these low-temperature regions (see e.g. Myers 1997 and references therein).

International audience; We present a comparison of histograms of CO (2-1) line centroid velocity increments in the rho Ophiuchi molecular cloud with those computed for spectra synthesized from a three-dimensional, compressible, but non-star-forming and nongravitating, hydrodynamic simulation. Histograms of centroid velocity increments in the rho Oph cloud clearly show non-Gaussian wings similar to those found in histograms of velocity increments and derivatives in experimental studies of laboratory and atmospheric flows, as well as numerical simulations of turbulence. The magnitude of these wings increases monotonically with decreasing separation, down to the angular resolution of the data. This behavior is consistent with that found in the phase of the simulation that has most of the properties of incompressible turbulence. The time evolution of the magnitude of the non-Gaussian wings in the histograms of centroid velocity increments in the simulation is consistent with the evolution of the vorticity in the flow. We cannot exclude, however, the possibility that the wings are associated with the shock interaction regions. Moreover, the effects of shocks may be more important in an active star-forming region like the rho Oph cloud than in the simulation; however, being able to identify shock interaction regions in the interstellar medium is also important, since numerical simulations show that vorticity is generated in shock interactions.

IC 443 is a prominent, well-studied supernova remnant. Optical pictures show multiple filaments through the midst of which runs a lane of extinction. Bright H2 emission marks the region of interaction between the SNR and the foreground cloud. Clump G is at the western side of the SNR and is heavily obscured. At its position the velocity of supernova shock is nearly in the plane of the sky and the radial velocity of the shocked material is displaced very little from that of the ambient foreground material.

Although the CO J=1−0 transition is the most frequently used tracer of molecular outflows from protostars, CO J=6−5 is a better probe of warm, dense gas in outflows, since the upper state energy of the J=6 level is 110 K above ground in comparison to 5.5 K for J=1. In this short contribution we compare CO J=6−5 to lower J observations of the NGC 2071 outflow, and concentrate the discussion on the outflow structure, overall density and temperature, and the extremely high velocity (EHV) CO features. We present data here for the NGC 2071 outflow, but in an associated journal article we will also present data on several other outflows. The CO J=6-5 data were obtained in December 1994 at the Caltech Submillimeter Observatory (CSO) on Mauna Kea, Hawaii.

The Orion Bar is a limb-brightened edge of the cavity carved out in the Orion molecular cloud by the expanding HII region surrounding the Trapezium cluster. The Bar is one of the best studied Photon-Dominated Regions (PDRs; see Genzel in this volume for a review). Tauber et al. (1995) found a tight correlation between the distributions of the neutral atomic carbon and 13CO (2−1) emission toward the Bar, which is difficult to explain in terms of classical PDR models. A possible explanation for this correlation was given by the geometric model of Hogerheijde et al. (1995) in which the PDR geometry changes from face-on to edge-on and back with increasing distance from the ionizing stars. The observed maximum of the molecular emission toward the Bar thus corresponds to a molecular column density peak and there are no significant variations in the excitation conditions across the Bar. In the present paper we investigate the uniformity of the excitation conditions across the Bar through observations of the 13CO (6−5) and 12CO (6−5) emission. We argue that the 13CO (6−5) emission provides a critical test for models of this region and PDRs in general.

We have detected the 626 GHz J = 1 → 0 transition of hydrogen chloride (H^(35)Cl) in absorption against the dust continuum emission of the molecular cloud Sagittarius B2. The observed line shape is consistent with the blending of the three hyperfine components of this transition by the velocity profile of Sgr B2 observed in other species. The apparent optical depth of the line is t ≈ 1, and the minimum HCl column density is 1.6 x 10^(14) cm^(-2) A detailed radiative transfer model was constructed which includes collisional and radiative excitation, absorption and emission by dust, and the radial variation of temperature and density. Good agreement between the model and the data is obtained for HCl/H_2 ~ 1.1 x 10^(-9). Comparison of this result to chemical models indicates that the depletion factor of gas-phase chlorine is between 50–180 in the molecular envelope surrounding the SgrB2(N) and (M) dust cores.

We have obtained maps of C I (3 P 1→3 P 0) emission at 492 GHz in the Supernova Remnant IC 443, concentrating on clump G. Broad-line shocked CI emission (≈10 kms−1 FWHM) with spatial distribution similar to that of 12CO is observed. Also, very interestingly, we see a narrow-line (≈1 kms−1 FWHM) component of C I emission that corresponds to no observed 12CO emission and its distribution is very different from that of the shocked component, apparently lying upstream from the shock front. Both wide and narrow components are also weakly visible in our 13CO(2→1) map. The inferred ratio of C I to CO in the shocked component is >0.5 and in the narrow-line component is >2, rather than the usual value of about 0.1. We speculate that this predominantly atomic region may mark the radiative precursor of the shock.

Measurements at a wavelength of 1.25 mm have been obtained for 17 IRAS galaxies selected on the basis of high far-infrared luminosity. These measurements are used to estimate the lower and upper limits to the mass of cold dust in infrared galaxies. As a lower limit on dust mass, all of the galaxies can be successfully modeled without invoking any dust colder than the dust responsible for the 60 and 100 micron emission that was detected by IRAS. As an upper limit, it is possible that the dust mass in a number of the galaxies may actually be dominated by cold dust. This large difference between the lower and upper limits is due primarily to uncertainty in the long-wavelength absorption efficiency of the astrophysical dust grains.

The H3O+ ion is a key species in the oxygen chemistry leading to H2O, OH and O2. Chemical models predict O2 and H2O to be the dominant oxygen-bearing molecules in interstellar clouds. However, neither of them can easily be observed in the bulk of the interstellar medium because of blockage from the Earth’s atmosphere. Determination of the abundance and distribution of the precursor H3O+ ion might thus provide an important indirect measure of their abundances.

This review summarizes 1) the observations which provide evidence of disks surrounding young, intermediate mass stars (1.5 3 M⊙). The initial stellar angular momentum reflects a balance between the angular momentum added from accreting disk material, and that carried away by a wind.

We have observed a group of luminous IRAS galaxies in the continuum at 1.25mm with the Caltech Submillimeter Observatory in 1988 May and September. Table I lists the galaxies and their measured flux densities in a 30 beam. The observing conditions for these observations were excellent and stable. Uranus was the fundamental flux density calibrator, it was assumed to have a brightness temperature of 100 K at 1.25 mm (Hildebrand et al. 1985; Ulich 1974). Integration times were typically a half hour per night, repeated for a total of two or three nights. The bolometer NEFD is 0.5 Jy Hz-1/2 giving statistical errors of 8 to 12 mJy. Systematic uncertainties have not been included in the error estimates, but we believe that they are small, at most 20%.

We searched for CS(7–6) emission in a range of young stars, to test for the presence of dense gas. CS emission was detected only towards high-luminosity objects. We suggest that this is because the low-luminosity objects cannot heat a sufficient volume of gas to produce detectable CS emission.

We have obtained 800 and 1100 micron photometric observations of a complete, flux-limited, IRAS-selected sample of cold sources in Taurus, whose infrared and molecular properties indicate them to be low-mass protostars which are younger than T Tauri stars. The goal of this study is to understand the role of the circumstellar envelope and disk during low-mass star formation and to search for signs of evolution. We find a good correlation between the submillimeter flux density (as well as of envelope mass) with both the mechanical luminosity of the molecular outflow and with the far-infrared luminosity, presumably produced by accretion onto the protostar. This suggests that the mass of the disk/envelope may be linked to the rate of accretion onto the protostar and to the generation of outflows. However, in contrast to the results of Cabrit & Andre (1991) we see no evidence for a lower limit to the disk/envelope mass which can produce outflow. We also find a significant difference between the spectral energy distributions at submillimeter wavelengths of embedded protostars compared to optically visible T Tauri stars. The more evolved (T Tuari) objects tend to have shallower spectral indices than embedded sources, suggesting (1) an evolution of dust grains, and/or (2) a more compact envelope and optically thick disk in the older objects.

We report observations of C I(^3P_1 - ^3P_0) emission at 492 GHz toward the starburst galaxy M82. Both the C I/C II intensity ratio and the C/CO column density ratio are a factor of 2-5 higher than observed toward Galactic photodissociation regions (PDRs) or predicted by PDR models. We argue that current PDR models are insufficient to explain the observations, and propose that some of the emission is due to atomic carbon existing within molecular clouds. Employing new chemical models, which use a fast H_3^+ dissociative recombination rate, we find that enhanced cosmic-ray flux supplied by supernova remnants in the M82 starburst lead to an enhanced atomic carbon abundance and elevated temperatures deep within the molecular clouds, resulting in a higher C I emissivity than found in previous PDR models.

We report observations of the 3 P 1 → 3 P 0 transition of atomic carbon at 492 GHz in IRC+10216, made at the Caltech Submillimeter Observatory. The C I emission from the central position of IRC+10216 was found to have a main beam temperature of about 0.4 K and to be doubly peaked at the expansion velocity of the CO envelope. Its spatial distribution can be modeled by two shells of radius ∼15″ and 45″ with column densities to the central star in the 3 P 1 state of 7×10 15 and 4×10 15 cm -2 , respectively

We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 and its associated molecular core. Infrared observations at lambda = 3.5 microns reveal a heavily obscured, central point source which is coincident with a compact lambda = 2.7 mm continuum and C18O emission region. The source radiates about 310 solar luminosities, primarily at FIR wavelengths, suggesting that it is a young stellar object of intermediate mass. The steeply rising spectral energy distribution and the large fraction of the system mass residing in circumstellar material imply that IRAS 21391 + 5802 is in an early stage of evolution. The inferred dust temperature indicates a temperature gradient in the core. A comprehensive model for the surrounding core of dust and gas is devised to match the observed dust continuum emission and multitransition CS emission from this and previous studies. We find a r exp -1.5 +/- 0.2 density gradient consistent with that of a gravitationally evolved core and a total core mass of 380 solar masses. The observed dust emission is most consistent with a lambda exp -1.5 - lambda exp -2 dust emissivity law; for a lambda exp -2 law, the data are best fit by a mass opacity coefficient of 3.6 x 10 exp -3 sq cm/g at lambda = 1.25 mm.

We report on the search for molecular outflows from a complete, flux-limited, IRAS-selected sample of cold, low-mass protostar candidates located in the Taurus cloud complex. We find that 18 of the 24 sources have outflows associated with them, only four of which have been previously reported, implying that these sources are predominantly protostars in an early stage of evolution. We argue that at least a few of the outflows are very small in extent, indicating that their dynamical ages are less than a few thousand years.

We present an interstellar medium study of the three reasonably accessible low-lying submillimeter lines of the H 3 O + molecular ion at 396, 364, and 307 GHz. Emission at the frequencies of the latter two lines has previously been reported, but only from the spectroscopically confused regions Orion/KL and SgrB2. This work reports the first study of the 396 GHz line and, possibly more significantly, the detection of H 3 O + lines in less confused regions

The proposition that Herbig Ae/Be stars are young intermediate mass stars surrounded by optically thick accretion disks is explored. From a study of 47 such objects, a subset of 30 stars is identified whose spectral energy distributions can be interpreted convincingly in terms of pre-main sequence stars surrounded by massive optically thick circumstellar accretion disks. Constraints on the physical properties of the disks, such as size, mass, accretion rate, lifetime, and radial structure are derived from the photometric data.

We report observations of the 3 P 1 → 3 P 0 transition of atomic carbon at 492 GHz in IC 342, made at the Caltech Submillimeter Observatory, which represent the first extragalactic submillimeter detection of C I. The C I emission from IC 342 was found to have a main beam temperature of about 1 K, which is a factor of 2 greater than that for 13 CO(2→1) in the same size beam. Comparing our data with COBE observations of the Milky Way, we find that the ratio of C I to CO(2→1) is approximately a factor of 2 lower in IC 342 than in our Galaxy

Results are presented of observations of 1.3- and 0.8-mm continuum emission toward the cores of three Galactic center molecular clouds with ongoing massive star formation, Sagittarius B2, C, and D, which were made in order to study possible variations in the high-mass star formation rate per unit mass between the Galactic center and the disk. The luminosity-to-mass ratio, based on the mass estimates derived from the millimeter continuum emission, is used as a tracer of the high-mass star formation rate in GMC cores. The magnitude of errors involved in using millimeter continuum emission for determining the core mass is estimated through radiative transfer modeling. It is inferred from the present millimeter data, along with previously published far-infrared data, that the Sgr C and D cores are very similar in terms of mean dust optical depth and temperature. The luminosity-to-mass ratios derived for the Sgr C and D cores are found to be consistent with those of typical disk GMC cores with comparable far-infrared luminosities.

New observations are made of the extremely high velocity (EHV) outflow recently discovered near HH 7-11. Maps of CO(2-1) and CO(3-2) EHV emission show that the emitting regions are compact and significantly displaced from the position of the infrared source SVS 13, which drives the outflow. The positional offset similar to the blueshifted EHV lobe and the redshifted lobe has been found for other tracers of shocked gas on the red side of the flow. The EHV lobes could be either bullets or gas swept up by jets interacting with the ambient cloud. The present evidence is not sufficient to rule out the bullet model, but the explanation that the EHV CO is swept-up material is preferable. 18 refs.

Interferometric and single-dish observations of the continuum emission from L1551-IRS 5 were made at wavelengths from 1.0 mm to 6.2 cm. These observations show that, at millimeter wavelengths, there are two distinct components to the source, an envelope with a radius about 2000 AU, and a compact core with a radius not greater than 64 AU. In both components, the continuum radiation is due predominantly to thermal dust emission. The compact core has a large optical depth, indicating a high column density (about 1000 g/sq cm). By modeling the temperature in the region of the compact core, it is shown that its size must lie in the range 45 + or - 20 AU. The compact core is most plausibly identified with an accretion, or preplanetary, disk around the star, although the present observations do not have sufficient angular resolution to rule out other structures. 63 refs.

The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely.

A new heterodyne receiver has been developed for the submillimeter wavelength region. The mixing element is liquid helium cooled bulk n-InSb in a quantizing magnetic field. The value of the magnetic induction is such that the detector photoresponse is dominated by cyclotron-resonance absorption. Laboratory tests have yielded double-sideband receiver noise temperatures of 250 K at 492 GHz, 350 K at 625 GHz and 510 K at 812 GHz. The magnetic induction for these tests was ≈2.5 KG and the mixer operating temperature was ≈1.6 K.

The J_K = 1_0 → 0_0 transition of ammonia at 572.5 GHz has been detected in OMC-1 from NASA's Kuiper Airborne Observatory. The central velocity of the line (V_(LSR)≈ 9 km s^(-1)) indicates that it originates in the molecular cloud material, not in the hot core. The derived filling factor of ≳ 0.09 in a 2' beam implies a source diameter of ≳ 35" if it is a single clump. This clump area is much larger than that derived from observations of the 1_1 inversion transition. The larger optical depth in the 1_0 → 0_0 transition (75-350) can account for the increased source area and line width as compared with those seen in the 1_1 inversion transition.