Search

The relative abundances of singly deuterated methanol isotopologues, [CH2DOH]/[CH3OD], in star-forming regions deviate from the statistically expected ratio of 3. In Orion KL, the nearest high-mass star-forming region to Earth, the singly deuterated methanol ratio is about 1, and the cause for this observation has been explored through theory for nearly three decades. We present high-angular resolution observations of Orion KL using the Atacama Large Millimeter/submillimeter Array to map small-scale changes in CH3OD column density across the nebula, which provide a new avenue to examine the deuterium chemistry during star and planet formation. By considering how CH3OD column densities vary with temperature, we find evidence of chemical processes that can significantly alter the observed gas-phase column densities. The astronomical data are compared with existing theoretical work and support D–H exchange between CH3OH and heavy water (i.e., HDO and D2O) at methanol’s hydroxyl site in the icy mantles of dust grains. The enhanced CH3OD column densities are localized to the Hot Core-SW region, a pattern that may be linked to the coupled evolution of ice mantle chemistry and star formation in giant molecular clouds. This work provides new perspectives on deuterated methanol chemistry in Orion KL and informs considerations that may guide future theoretical, experimental, and observational work.

PURPOSE: Controversy exists as to whether patient age, either independently or as a marker of concomitant illness or medication use, is associated with the dose or complication rate of warfarin prophylaxis. The aim of this study was to assess this relationship in patients receiving warfarin prophylaxis after hip fracture repair. PATIENTS AND METHODS: We undertook a retrospective ohort study of 215 patients 55 years of age or greater who underwent surgery for a fractured hip between January 1, 1990, and December 31, 1991, and received warfarin prophylaxis. The mean age was 78.9 (SD 9.5) years. The average daily warfarin dose, the decrease in hemoglobin in the postoperative period, and the rate of bleeding complications were assessed. RESULTS: Elderly patients required a significantly lower average daily warfarin dose than younger patients. This effect persisted even after controlling for the number of medical conditions, number of medications on admission, proportion of time the international normalized ratio (INR) was in therapeutic range, and gender. Postoperative hemoglobin decrease was associated with patient age as well as with the use of antibiotics postoperatively. Factors associated with bleeding complications included a history of alcohol abuse and a smaller proportion of time spent in the targeted anticoagulannit range. CONCLUSIONS: Older age itself are not as a marker for polypharmacy or increased number of medical conditions is associated with lower requirements warfarin and a greater hemoglobin decrease postoperatively even when the proportion of time the INR fell within the therapeutic range is controlled. Advanced patient age, in this study, was not associated with an increased incidence of bleeding complications.

Customized Cu3(PO4)2and CuO nanosheets and commercial CuO nanoparticles were investigated for micronutrient delivery and suppression of soybean sudden death syndrome. An ab initio thermodynamics approach modelled how material morphology and matrix effects control the nutrient release. Infection reduced the biomass and photosynthesis by 70.3 and 60%, respectively; the foliar application of nanoscale Cu reversed this damage. Disease-induced changes in the antioxidant enzyme activity and fatty acid profile were also alleviated by Cu amendment. The transcription of two dozen defence- and health-related genes correlates a nanoscale Cu-enhanced innate disease response to reduced pathogenicity and increased growth. Cu-based nanosheets exhibited a greater disease suppression than that of CuO nanoparticles due to a greater leaf surface affinity and Cu dissolution, as determined computationally and experimentally. The findings highlight the importance and tunability of nanomaterial properties, such as morphology, composition and dissolution. The early seedling foliar application of nanoscale Cu to modulate nutrition and enhance immunity offers a great potential for sustainable agriculture.

We demonstrate that halogenated methane (HM) two-dimensional (2D)-terahertz-terahertz-Raman (2D-TTR) spectra are determined by the complicated structure of the instrument response function (IRF) along ω1and by the molecular coherences along ω2. Experimental improvements have helped increase the resolution and dynamic range of the measurements, including accurate THz pulse shape characterization. Sum-frequency excitations convolved with the IRF are found to quantitatively reproduce the 2D-TTR signal. A new reduced density matrix model that incorporates sum-frequency pathways, with linear and harmonic operators, fully supports this (re)interpretation of the 2D-TTR spectra.

Nonlinear THz-THz-Raman (TTR) liquid spectroscopy offers new possibilities for studying and understanding condensed-phase chemical dynamics. Although TTR spectra carry rich information about the systems under study, the response is encoded in a three-point correlation function comprising of both dipole and polarizability elements. Theoretical methods are necessary for the interpretation of the experimental results. In this work, we study the liquid-phase dynamics of bromoform, a polarizable molecule with a strong TTR response. Previous work based on reduced density matrix (RDM) simulations suggests that unusually large multiquanta dipole matrix elements are needed to understand the measured spectrum of bromoform. Here, we demonstrate that a self-consistent definition of the time coordinates with respect to the reference pulse leads to a simplified experimental spectrum. Furthermore, we analytically derive a parametrization for the RDM model by integrating the dipole and polarizability elements to the 4th order in the normal modes, and we enforce inversion symmetry in the calculations by numerically canceling the components of the response that are even with respect to the field. The resulting analysis eliminates the need to invoke large multiquanta dipole matrix elements to fit the experimental spectrum; instead, the experimental spectrum is recovered using RDM simulations with dipole matrix parameters that are in agreement with independent ab initio calculations. The fundamental interpretation of the TTR signatures in terms of coupled intramolecular vibrational modes remains unchanged from the previous work.

Broadband spectroscopy is an invaluable tool for measuring multiple gas-phase species simultaneously. In this work we review basic techniques, implementations, and current applications for broadband spectroscopy. We discuss components of broadband spectroscopy including light sources, absorption cells, and detection methods and then discuss specific combinations of these components in commonly used techniques. We finish this review by discussing potential future advances in techniques and applications of broadband spectroscopy.

Observational and theoretical evidence suggests that high-energy Galactic cosmic rays are primarily accelerated by supernova remnants. If also true for low-energy cosmic rays, the ionization rate near a supernova remnant should be higher than in the general Galactic interstellar medium (ISM). We have searched for H+ 3 absorption features in six sight lines which pass through molecular material near IC 443--a well-studied case of a supernova remnant interacting with its surrounding molecular material--for the purpose of inferring the cosmic-ray ionization rate in the region. In two of the sight lines (toward ALS 8828 and HD 254577) we find large H+ 3 column densities, N(H+ 3) [?] 3 x 1014 cm-2, and deduce ionization rates of z2 [?] 2 x 10-15 s-1, about five times larger than inferred toward average diffuse molecular cloud sight lines. However, the 3s upper limits found for the other four sight lines are consistent with typical Galactic values. This wide range of ionization rates is likely the result of particle acceleration and propagation effects, which predict that the cosmic-ray spectrum and thus ionization rate should vary in and around the remnant. While we cannot determine if the H+ 3 absorption arises in post-shock (interior) or pre-shock (exterior) gas, the large inferred ionization rates suggest that IC 443 is in fact accelerating a large population of low-energy cosmic rays. Still, it is unclear whether this population can propagate far enough into the ISM to account for the ionization rate inferred in diffuse Galactic sight lines.

We present a Spitzer InfraRed Spectrometer search for 10-36 mm molecular emission from a large sample of protoplanetary disks, including lines from H2O, OH, C2H2, HCN, and CO2. This paper describes the sample and data processing and derives the detection rate of mid-infrared molecular emission as a function of stellar mass. The sample covers a range of spectral type from early M to A, and is supplemented by archival spectra of disks around A and B stars. It is drawn from a variety of nearby star-forming regions, including Ophiuchus, Lupus, and Chamaeleon. Spectra showing strong emission lines are used to identify which lines are the best tracers of various physical and chemical conditions within the disks. In total, we identify 22 T Tauri stars with strong mid-infrared H2O emission. Integrated water line luminosities, where water vapor is detected, range from 5 x 10-4 to 9 x 10-3 L , likely making water the dominant line coolant of inner disk surfaces in classical T Tauri stars. None of the five transitional disks in the sample show detectable gaseous molecular emission with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios (apart from H2), but the sample is too small to conclude whether this is a general property of transitional disks. We find a strong dependence on detection rate with spectral type; no disks around our sample of 25 A and B stars were found to exhibit water emission, down to 1%-2% line-to-continuum ratios, in the mid-infrared, while more than half of disks around late-type stars (M-G) show sufficiently intense water emission to be detected by Spitzer, with a detection rate approaching 2/3 for disks around K stars. Some Herbig Ae/Be stars show tentative H2O/OH emission features beyond 20 mm at the 1%-2% level, however, and one of them shows CO2 in emission. We argue that the observed differences between T Tauri disks and Herbig Ae/Be disks are due to a difference in excitation and/or chemistry depending on spectral type and suggest that photochemistry may be playing an important role in the observable characteristics of mid-infrared molecular line emission from protoplanetary disks.

Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 um feature strength above the continuum declines for holes with radii larger than [?]7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases.

NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the [?]8-10 um region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 um silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at [?]9 um in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 n2 umbrella mode and derive abundances with respect to water between [?]2% and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the n4 C-O stretch mode of this molecule at [?]9.7 um in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 um data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of nitrogen is locked up in known ices.

The material that formed the present-day solar system originated in feeding zones in the inner solar nebula located at distances within [?]20 AU from the Sun, known as the planet-forming zone. Meteoritic and cometary material contain abundant evidence for the presence of a rich and active chemistry in the planet-forming zone during the gas-rich phase of solar system formation. It is a natural conjecture that analogs can be found among the zoo of protoplanetary disks around nearby young stars. The study of the chemistry and dynamics of planet formation requires: (1) tracers of dense gas at 100-1000 K and (2) imaging capabilities of such tracers with 5-100 mas (0.5-20 AU) resolution, corresponding to the planet-forming zone at the distance of the closest star-forming regions. Recognizing that the rich infrared (2-200 mm) molecular spectrum recently discovered to be common in protoplanetary disks represents such a tracer, we present a new general ray-tracing code, RADLite, that is optimized for producing infrared line spectra and images from axisymmetric structures. RADLite can consistently deal with a wide range of velocity gradients, such as those typical for the inner regions of protoplanetary disks. The code is intended as a back-end for chemical and excitation codes, and can rapidly produce spectra of thousands of lines for grids of models for comparison with observations. Such radiative transfer tools will be crucial for constraining both the structure and chemistry of planet-forming regions, including data from current infrared imaging spectrometers and extending to the Atacama Large Millimeter Array and the next generation of Extremely Large Telescopes, the James Webb Space Telescope and beyond.

We present and categorize Spitzer infrared spectrometer spectra of 294 objects in the Large Magellanic Cloud (LMC) to create the largest and most complete catalog of massive young stellar object (YSO) spectra in the LMC. Target sources were identified from infrared photometry and multiwavelength images indicative of young, massive stars highly enshrouded in their natal gas and dust clouds. Several objects have been spectroscopically identified as non-YSOs and have features similar to more-evolved stars such as red supergiants, asymptotic giant branch (AGB), and post-AGB stars. Our sample primarily consists of 277 objects we identify as having spectral features indicative of embedded YSOs. The remaining sources are comprised of seven C-rich evolved sources, eight sources dominated by broad silicate emission, and one source with multiple broad emission features. Those with YSO-like spectra show a range of spectral features including polycyclic aromatic hydrocarbon emission, deep silicate absorption, fine-structure lines, and ice absorption features. Based upon the relative strengths of these features, we have classified the YSO candidates into several distinct categories using the widely used statistical procedure known as principal component analysis. We propose that these categories represent a spectrum of evolutionary stages during massive YSO formation. Using our catalog we put statistical constraints on the relative evolutionary timescale of processes involved in massive star formation. We conclude that massive pre-main-sequence stars spend a majority (possibly as high as 90%) of their massive, embedded lives emitting in the UV. Half of the sources in our study have features typical of compact H II regions, suggesting that massive YSOs can create a detectable compact H II region half-way through the formation time present in our sample. This study also provides a check on commonly used source-selection procedures including the use of photometry to identify YSOs. We determine that a high success rate (>95%) of identifying objects with YSO-like spectra can be achieved through careful use of infrared color-magnitude diagrams, spectral energy distributions, and image inspections.

We present high-resolution (R = 80,000) spectroscopy of [Ne II] emission from two young stars, GM Aur and AA Tau, which have moderate to high inclinations. The emission from both sources appears centered near the stellar velocity and is broader than the [Ne II] emission measured previously for the face-on disk system TW Hya. These properties are consistent with a disk origin for the [Ne II] emission we detect, with disk rotation (rather than photoevaporation or turbulence in a hot disk atmosphere) playing the dominant role in the origin of the line width. In the non-face-on systems, the [Ne II] emission is narrower than the CO fundamental emission from the same sources. If the widths of both diagnostics are dominated by Keplerian rotation, this suggests that the [Ne II] emission arises from larger disk radii on average than does the CO emission. The equivalent width of the [Ne II] emission we detect is less than that of the spectrally unresolved [Ne II] feature in the Spitzer spectra of the same sources. Variability in the [Ne II] emission or the mid-infrared continuum, a spatially extended [Ne II] component, or a very (spectrally) broad [Ne II] component might account for the difference in the equivalent widths.

We report the results of a search for pure rotational molecular hydrogen emission from the circumstellar environments of young stellar objects with disks using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for mid-infrared H2 emission in the S(1), S(2), and S(4) transitions. Keck/NIRSPEC observations of the H2 S(9) transition were included for some sources as an additional constraint on the gas temperature. We detected H2 emission from 6 of 29 sources observed: AB Aur, DoAr 21, Elias 29, GSS 30 IRS 1, GV Tau N, and HL Tau. Four of the six targets with detected emission are class I sources that show evidence for surrounding material in an envelope in addition to a circumstellar disk. In these cases, we show that accretion shock heating is a plausible excitation mechanism. The detected emission lines are narrow (~10 km s[?]1), centered at the stellar velocity, and spatially unresolved at scales of 0.4 '', which is consistent with origin from a disk at radii 10-50 AU from the star. In cases where we detect multiple emission lines, we derive temperatures [?]500 K from ~1 M[?] of gas. Our upper limits for the nondetections place upper limits on the amount of H2 gas with 500"/> T > 500 K of less than a few Earth masses. Such warm gas temperatures are significantly higher than the equilibrium dust temperatures at these radii, suggesting that the gas is decoupled from the dust in the regions that we are studying and that processes such as UV, X-ray, and accretion heating may be important.

We present velocity-resolved spectroastrometric imaging of the 4.7 mm rovibrational lines of CO gas in protoplanetary disks using the CRIRES high-resolution infrared spectrometer on the Very Large Telescope (VLT). The method as applied to three disks with known dust gaps or inner holes out to 4-45 AU (SR 21, HD 135344B, and TW Hya) achieves an unprecedented spatial resolution of 0.1-0.5 AU. While one possible gap formation mechanism is dynamical clearing by giant planets, other equally good explanations (stellar companions, grain growth, photoevaporation) exist. One way of distinguishing between different scenarios is the presence and distribution of gas inside the dust gaps. Keplerian disk models are fit to the spectroastrometric position-velocity curves to derive geometrical parameters of the molecular gas. We determine the position angles and inclinations of the inner disks with accuracies as good as 1deg-2deg, as well as the radial extent of the gas emission. Molecular gas is detected well inside the dust gaps in all three disks. The gas emission extends to within a radius of 0.5 AU for HD 135344B and to 0.1 AU for TW Hya, supporting partial clearing by a <1-10 MJup planetary body as the cause of the observed dust gaps, or removal of the dust by extensive grain coagulation and planetesimal formation. The molecular gas emission in SR 21 appears to be truncated within ~7 AU, which may be caused by complete dynamical clearing by a more massive companion. We find a smaller inclination angle of the inner disk of TW Hya than that determined for the outer disk, suggestive of a disk warp. We also detect significant azimuthal asymmetries in the SR 21 and HD 135344B inner disks.

We present Submillimeter Array observations of several deuterated species in the disk around the classical T Tauri star TW Hydrae at arcsecond scales, including detections of the DCN J = 3-2 and DCO+ J = 3-2 lines and upper limits to the HDO 31,2-22,1, ortho- H2D+ 11,0-11,1, and para- D2H+ 11,0-10,1 transitions. We also present observations of the HCN J = 3-2, HCO+ J = 3-2, and H13CO+ J = 4-3 lines for comparison with their deuterated isotopologues. We constrain the radial and vertical distributions of various species in the disk by fitting the data using a model where the molecular emission from an irradiated accretion disk is sampled with a two-dimensional Monte Carlo radiative transfer code. We find that the distribution of DCO+ differs markedly from that of HCO+. The D/H ratios inferred change by at least 1 order of magnitude (0.01-0.1) for radii <30 to [?]70 AU, and there is a rapid falloff of the abundance of DCO+ at radii larger than 90 AU. Using a simple analytical chemical model, we constrain the degree of ionization, x(e [?]) = n(e [?])/n(H2) , to be ~10[?]7 in the disk layer(s) where these molecules are present. Provided the distribution of DCN follows that of HCN, the ratio of DCN to HCN is determined to be (1.7 +- 0.5) x 10[?]2; however, this ratio is very sensitive to the poorly constrained vertical distribution of HCN. The resolved radial distribution of DCO+ indicates that in situ deuterium fractionation remains active within the TW Hydrae disk and must be considered in the molecular evolution of circumstellar accretion disks.

CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH4 abundance toward a large sample of low-mass young stellar objects. A total of 25 out of 52 ice sources in the "Cores to Disks" (c2d) Legacy program have an absorption feature at 7.7 mm, attributed to the bending mode of solid CH4. The solid CH4/H2O abundances are 2%-8%, except for three sources with abundances as high as 11%-13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H2O column densities above 2 x 1018 cm[?]2, the CH4 abundances (20 out of 25) are nearly constant at 4.7% +- 1.6% . Correlation plots with solid H2O, CH3OH, CO2, and CO column densities and abundances relative to H2O reveal a closer relationship of solid CH4 with CO2 and H2O than with solid CO and CH3OH. The inferred solid CH4 abundances are consistent with models where CH4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass young stellar objects compared with high-mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH3OH and formation in gas phase with subsequent freezeout.

This paper presents Spitzer IRS l/D l [?] 600 spectroscopy of the CO2 15.2 mm bending mode toward 50 embedded young low-mass stars, taken mostly from the "Cores to Disks" (c2d) Legacy program. The average abundance of solid CO2 relative to water in low-mass protostellar envelopes is 0.32 +- 0.02, significantly higher than that found in quiescent molecular clouds and in massive star-forming regions. A decomposition of the observed CO2 bending mode profiles requires a minimum of five unique components. Roughly \frac{2}{3} $&frac;{2}{3}$ of the CO2 ice is found in a water-rich environment, while most of the remaining \frac{1}{3} $&frac;{1}{3}$ is found in a CO environment with strongly varying relative concentrations of CO2 to CO along each line of sight. Ground-based observations of solid CO toward a large subset of the c2d sample are used to further constrain the CO2:CO component and suggest a model in which low-density clouds form the CO2:H2O component and higher density clouds form the CO2:CO ice during and after the freezeout of gas-phase CO. The abundance of the CO2:CO component is consistent with cosmic-ray processing of the CO-rich part of the ice mantles, although a more quiescent formation mechanism is not ruled out. It is suggested that the subsequent evolution of the CO2 and CO profiles toward low-mass protostars, in particular the splitting of the CO2 bending mode due to pure, crystalline CO2, is first caused by distillation of the CO2:CO component through evaporation of CO due to thermal processing to ~20-30 K. The formation of pure CO2 via segregation from the H2O rich mantle may contribute to the band splitting at higher levels of thermal processing ([?]50 K) but is harder to reconcile with the physical structure of protostellar envelopes around low-luminosity objects.

We present maps of 14.4 deg2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high-quality maps depict both numerous point sources and extended dust emission within the star-forming and non-star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 mm and 81 sources at 70 mm at the 10 s level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus K [?] [ 24] color-magnitude diagrams, as compared to 24 mm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.

We present maps of 7.78 deg2 of the Lupus molecular cloud complex at 24, 70, and 160 mm. They were made with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the Spitzer Legacy Program "From Molecular Cores to Planet-Forming Disks" (c2d). The maps cover three separate regions in Lupus, denoted I, III, and IV. We discuss the c2d pipeline and how our data processing differs from it. We compare source counts in the three regions with two other data sets and predicted star counts from the Wainscoat model. This comparison shows the contribution from background galaxies in Lupus I. We also create two color-magnitude diagrams using the 2MASS and MIPS data. From these results, we can identify background galaxies and distinguish them from probable young stellar objects. The sources in our catalogs are classified based on their spectral energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample of young stellar object candidates. From 2MASS data, we create extinction maps for each region and note a strong correspondence between the extinction and the 160 mm emission. The masses we derived in each Lupus cloud from our extinction maps are compared to masses estimated from 13CO and C18 O and found to be similar to our extinction masses in some regions, but significantly different in others. Finally, based on our color-magnitude diagrams, we selected 12 of our reddest candidate young stellar objects for individual discussion. Five of the 12 appear to be newly discovered YSOs.

Observations by the Cores to Disk Legacy Team with the Spitzer Space Telescope have identified a low-luminosity, mid-infrared source within the dense core, Lynds 1014, which was previously thought to harbor no internal source. Follow-up near-infrared and submillimeter interferometric observations have confirmed the protostellar nature of this source by detecting scattered light from an outflow cavity and a weak molecular outflow. In this paper, we report the detection of centimeter continuum emission with the VLA. The emission is characterized by a quiescent, unresolved 90 mJy 6 cm source within 0.2'' of the Spitzer source. The spectral index of the quiescent component is a = 0.37 +- 0.34 between 6 and 3.6 cm. A factor of 2 increase in 6 cm emission was detected during one epoch and circular polarization was marginally detected at the 5 s level with Stokes V/I = 48% +- 16%. We have searched for 22 GHz H2O maser emission toward L1014-IRS, but no masers were detected during seven epochs of observations between 2004 June and 2006 December. L1014-IRS appears to be a low-mass, accreting protostar, which exhibits centimeter emission from a thermal jet or a wind, with a variable nonthermal emission component. The quiescent cm radio emission is noticeably above the correlation of 3.6 and 6 cm luminosity versus bolometric luminosity, indicating more radio emission than expected. In this paper, we characterize the centimeter continuum emission in terms of observations of other low-mass protostars, including updated correlations of centimeter continuum emission with bolometric luminosity and outflow force, and discuss the implications of recent larger distance estimates on the physical attributes of the protostar and dense molecular core.

One of the central goals of the Spitzer Legacy Project ``From Cores to Disks'' (c2d) is to determine the frequency of circumstellar disks around weak-line T Tauri stars (WTTSs) and to study the properties and evolutionary status of these disks. Here we present a census of disks for a sample of over 230 WTTSs located in the c2d IRAC and MIPS maps of the Ophiuchus, Lupus, and Perseus Molecular Clouds. We find that ~20% of the WTTSs in a magnitude-limited subsample have IR excesses at IRAC wavelengths. These disks frequencies are ~3-6 times larger than that recently found for a sample of relatively isolated WTTSs located outside the highest extinction regions covered by the c2d maps. The disk fractions we find are more consistent with those obtained in recent Spitzer studies of WTTSs in young clusters such as IC 348 and Tr 37. According to their location in the H-R diagram, the WTTSs with excesses in our sample are among the younger part of the age distribution. Still, up to ~50% of the apparently youngest stars in the sample show no evidence of IR excess, suggesting that the circumstellar disks of a sizable fraction of pre-main-sequence stars dissipate in a timescale of ~1 Myr. We also find that none of the stars in our sample apparently older than ~10 Myr have detectable circumstellar disks at wavelengths <24 mm. The WTTS disks in our sample exhibit a wide range of properties (SED morphology, inner radius, Ldisk/L*, etc.) that bridge the gaps observed between the CTTSs and the debris disk regimes.

We present a survey of mid-infrared gas-phase lines toward a sample of 76 circumstellar disks around low-mass pre-main-sequence stars from the Spitzer "Cores to Disks" legacy program. We report the first detections of [Ne II] and [Fe I] toward classical T Tauri stars in ~20% and ~9% of our sources, respectively. The observed [Ne II] line fluxes and upper limits are consistent with [Ne II] excitation in an X-ray irradiated disk around stars with X-ray luminosities LX = 1029-1031 erg s-1. [Fe I] is detected at ~10-5 to 10-4 L, but no [S I] or [Fe II] is detected down to ~10-6 L. The [Fe I] detections indicate the presence of gas-rich disks with masses of [?]0.1 MJ. No H2 0-0 S(0) and S(1) disk emission is detected, except for S(1) toward one source. These data give upper limits on the warm (T ~ 100-200 K) gas mass of a few Jovian masses, consistent with recent T Tauri disk models that include gas heating by stellar radiation. Compact disk emission of hot (T [?] 500 K) gas is observed through the H2 0-0 S(2) and/or S(3) lines toward ~8% of our sources. The line fluxes are, however, higher by more than an order of magnitude than those predicted by recent disk models, even when X-ray and excess UV radiation are included. The [Ne II]/H2 0-0 S(2) ratios for these sources are similarly lower than predicted, consistent with the presence of an additional hot molecular gas component not included in current disk models. Oblique shocks of stellar winds interacting with the disk can explain many aspects of the hot gas emission but are inconsistent with the nondetection of [S I] and [Fe II] lines.

We present maps of 1.5 deg2 of the Serpens dark cloud at 24, 70, and 160 mm observed with the Spitzer Space Telescope MIPS camera. We describe the observations and briefly discuss the data processing carried out by the c2d team on these data. More than 2400 compact sources have been extracted at 24 mm, nearly 100 at 70 mm, and four at 160 mm. We estimate completeness limits for our 24 mm survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets: a 0.50 deg 2 set on a low-extinction region near the dark cloud, and a 5.3 deg2 subset of the SWIRE ELAIS N1 data that was processed through our pipeline. These results show that there is an easily identifiable population of young stellar object candidates in the Serpens cloud that is not present in either of the reference data sets. We also show a comparison of visual extinction and cool dust emission illustrating a close correlation between the two and find that the most embedded YSO candidates are located in the areas of highest visual extinction.

We present mid-infrared Spitzer IRS spectra of the UX Orionis star VV Ser, combined with interferometric and spectroscopic data from the literature covering UV to submillimeter wavelengths. The full set of data are modeled by an axisymmetric Monte Carlo radiative transfer code to test the prediction of Dullemond et al. that disks around UX Orionis stars are self-shadowed and seen nearly edge-on. Our model is consistent with all the available observational constraints, providing strong support for this interpretation. The mid-infrared SED is declining and exhibits weak silicate emission features, consistent with a self-shadowed geometry. MIPS imaging shows that the disk has a small grain dust mass as low as 0.8 x 10-7 M, which may be due to strong grain growth and settling. The grains in the upper layers of the puffed-up inner rim must be small (0.01-0.4 mm) to reproduce the colors (RV ~ 3.6) of the optical light curve, while the silicate emission features indicate that grains in the outer disk (>1-2 AU) are somewhat larger (0.3-3.0 mm). If grains in the inner disk are small, the location of the puffed-up inner rim is estimated to be at 0.7-0.8 AU. This is almost twice the rim radius estimated from near-infrared interferometry. Since larger (more gray) grains are able to penetrate closer to the star for the same dust sublimation temperature, we suggest a model in which large grains in the disk midplane reach to within 0.25 AU of the star, while small grains in the disk surface create a puffed-up rim at ~0.7-0.8 AU.

We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6-70 mm images show bright, localized, and nebulous emission extended over 4' centered on VV Ser. This nebulosity is due to transiently heated grains excited by UV photons emitted by VV Ser. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this as the shadow cast by the inner regions of a near-edge-on disk, allowing the PAHs to be excited only outside of this shadow. We extend an axisymmetric radiative transfer model of the VV Ser disk described in a companion paper to include quantum-heated PAH molecules and very small grains (VSGs) in the thermal cooling approximation. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. The nebulosity at 5.6-8.0 mm and the 2175 A absorption feature seen in an archival spectrum from the IUE can be fit using only PAHs, consistent with the main carrier of the 2175 A feature being due to the graphite-like structure of the PAHs. The PAH component is found to be relatively smoothly distributed in the cloud, while the population of VSGs emitting at 20-70 mm is strongly concentrated ~50'' to the southeast of VV Ser. Depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5% +- 2% of the total dust mass. Although relatively rare, quantum-heated nebulosities surrounding single, well-defined stars are well-suited for gaining unique insights into the physics of very small particles in molecular clouds.

We present IRAC (3.6, 4.5, 5.8, and 8.0 mm) observations of the Chamaeleon II molecular cloud. The observed area covers about 1 deg2 defined by AV > 2. Analysis of the data in the 2005 c2d catalogs reveals a small number of sources (40) with properties similar to those of young stellar or substellar objects (YSOs). The surface density of these YSO candidates is low, and contamination by background galaxies appears to be substantial, especially for sources classified as Class I or flat spectral energy distribution (SED). We discuss this problem in some detail and conclude that very few of the candidate YSOs in early evolutionary stages are actually in the Cha II cloud. Using a refined set of criteria, we define a smaller, but more reliable, set of 24 YSO candidates.

Infrared images of the dark cloud core B59 were obtained with the Spitzer Space Telescope as part of the "Cores to Disks" Legacy Science project. Photometry from 3.6-70 mm indicates at least 20 candidate low-mass young stars near the core, more than doubling the previously known population. Out of this group, 13 are located within ~0.1 pc in projection of the molecular gas peak, where a new embedded source is detected. Spectral energy distributions span the range from small excesses above photospheric levels to rising in the mid-infrared. One other embedded object, probably associated with the millimeter source B59-MMS1, with a bolometric luminosity Lbol ~ 2 L, has extended structure at 3.6 and 4.5 mm, possibly tracing the edges of an outflow cavity. The measured extinction through the central part of the core is AV [?] 45 mag. The B59 core is producing young stars with a high efficiency.

We present observations of 3.86 deg2 of the Perseus molecular cloud complex with the Spitzer Space Telescope Infrared Array Camera (IRAC). The maps show strong extended emission arising from shocked H2 in outflows and from polycyclic aromatic hydrocarbon features. More than 120,000 sources are extracted toward the cloud. Based on their IRAC colors and comparison to off-cloud and extragalactic fields, we identify 400 candidate young stellar objects. About two-thirds of these are associated with the young clusters IC 348 and NGC 1333, while the last third is distributed over the remaining cloud. The young stellar objects are classified according to the slope of their spectral energy distributions. Significant differences are found between the numbers of embedded Class I objects and more evolved Class II objects in IC 348, NGC 1333 and the remaining cloud, with the embedded Class I and "flat-spectrum" YSOs constituting 14%, 36% and 47% of the total number of YSOs identified in each of these regions. The high number of Class I objects in the extended cloud (61% of the Class I objects in the entire cloud) suggests that a significant fraction of the current star formation occurs outside the two main clusters. Finally, we discuss a number of outflows and identify their driving sources, including the deeply embedded Class 0 sources outside the two main clusters. The Class 0 objects are detected by Spitzer and have very red [3.6] - [4.5] colors, but they do not show similarly red [5.8] - [8.0] colors. The Class 0 objects are easily identifiable in color-color diagrams but are problematic to extract automatically due to the extended emission from shocked gas or scattered light in cavities related to the associated outflows.

We present maps of 0.89 deg2 of the Serpens dark cloud at 3.6, 4.5, 5.8, and 8.0 mm observed with the Spitzer Space Telescope Infrared Array Camera (IRAC). We discuss in detail the data processing carried out by the c2d team on IRAC data. More than 100,000 compact sources have been extracted, but we confine most of our discussion to the most reliable subset of these sources. This includes those that are detected above 7 s in all four IRAC bands or those detected in the two shorter IRAC bands together with 2MASS. We estimate completeness limits for our survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets, a 0.10 deg2 set of low-extinction regions near the dark cloud and a 1 deg2 subset of the SWIRE Elais N1 data that was processed through our pipeline. We find that it is possible to identify more than 200 young stellar object (YSO) candidates from color-magnitude and color-color diagrams, most of which were previously unknown. In addition to the dense area of new star formation known before in the "core" region (cluster A), we also find a moderately rich area to the south (cluster B). Our mapped area also includes the Herbig Ae star VV Ser, whose Spitzer images have been carefully modeled in a separate study. The extreme sensitivity of Spitzer IRAC allows us to search to very low luminosity limits for young substellar objects. The comparison of the Serpens region with the reference areas suggests that a population of infrared excess sources exists in Serpens at least down to luminosities of L ~ 10-3 L and possibly lower.

We present an interferometric search for large molecules, including methanol (CH3OH), methyl cyanide (CH3CN), ethyl cyanide (CH3CH2CN), ethanol (CH3CH2OH), and methyl formate (CH3OCHO), in comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4) with the Berkeley-Illinois-Maryland Association (BIMA) array. We also searched for transitions of the simpler molecules CS, SiO, HNC, HN13C, and 13CO. We detected transitions of CH3OH and CS around comet LINEAR and one transition of CH3OH around comet NEAT within a synthesized beam of ~20''. We calculated the total column density and production rate of each molecular species using the variable temperature and outflow velocity (VTOV) model recently described by Friedel et al. Considering the molecular production rate ratios with respect to water, comet T7 LINEAR is more similar to comet Hale-Bopp, while comet Q4 NEAT is more similar to comet Hyakutake. It is unclear, however, due to such a small sample size, whether there is a clear distinction between a Hale-Bopp and Hyakutake class of comet or whether comets have a continuous range of molecular production rate ratios.

Infrared ~5-35 mm spectra for 40 solar mass T Tauri stars and 7 intermediate-mass Herbig Ae stars with circumstellar disks were obtained using the Spitzer Space Telescope as part of the c2d IRS survey. This work complements prior spectroscopic studies of silicate infrared emission from disks, which were focused on intermediate-mass stars, with observations of solar mass stars limited primarily to the 10 mm region. The observed 10 and 20 mm silicate feature strengths/shapes are consistent with source-to-source variations in grain size. A large fraction of the features are weak and flat, consistent with micron-sized grains indicating fast grain growth (from 0.1 to 1.0 mm in radius). In addition, approximately half of the T Tauri star spectra show crystalline silicate features near 28 and 33 mm, indicating significant processing when compared to interstellar grains. A few sources show large 10-to-20 mm ratios and require even larger grains emitting at 20 mm than at 10 mm. This size difference may arise from the difference in the depth into the disk probed by the two silicate emission bands in disks where dust settling has occurred. The 10 mm feature strength versus shape trend is not correlated with age or Ha equivalent width, suggesting that some amount of turbulent mixing and regeneration of small grains is occurring. The strength versus shape trend is related to spectral type, however, with M stars showing significantly flatter 10 mm features (larger grain sizes) than A/B stars. The connection between spectral type and grain size is interpreted in terms of the variation in the silicate emission radius as a function of stellar luminosity, but could also be indicative of other spectral-type-dependent factors (e.g., X-rays, UV radiation, and stellar/disk winds).

We present interferometric detections of HCN in comets LINEAR (C/2002 T7) and NEAT (C/2001 Q4) with the Berkeley-Illinois-Maryland Association (BIMA) array. With a 25.''4 x 20.''3 synthesized beam around comet LINEAR and using a variable temperature and outflow velocity (VTOV) model, we found an HCN column density of [?]NT[?] = (6.4 +- 2.1) x 1012 cm-2 and a production rate of Q(HCN) = (6.5 +- 2.2) x 1026 s-1, giving a production rate ratio of HCN relative to H2O of ~(3.3 +- 1.1) x 10-3 and relative to CN of ~4.6 +- 1.5. With a 21.''3 x 17.''5 synthesized beam around comet NEAT and using a VTOV model, we found an HCN column density of img1.gif = (8.5 +- 4.5) x 1011 cm-2 and a production rate of Q(HCN) = (8.9 +- 4.7) x 1025 s-1, giving a production rate ratio of HCN relative to H2O of ~(7.4 +- 3.9) x 10-4 and relative to CN of ~0.3 +- 0.2. For both comets, the production rates relative to H2O are similar to those found in previous comet observations. For comet LINEAR, the production rate relative to CN is consistent with HCN being the primary parent species of CN, while for comet NEAT it is too low for this to be the case.

We present maps of over 1.5 deg2 in Chamaeleon (Cha) II at 24, 70, and 160 mm observed with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) and a 1.2 deg2 millimeter map from SIMBA on the Swedish-ESO Submillimetre Telescope (SEST). The c2d Spitzer Legacy Team's data reduction pipeline is described in detail. Over 1500 24 mm sources and 41 70 mm sources were detected by MIPS with fluxes greater than 10 s. More than 40 potential YSOs are identified with a MIPS and 2MASS color-color diagram and by their spectral indices, including two previously unknown sources with 24 mm excesses. Our new SIMBA millimeter map of Cha II shows that only a small fraction of the gas is in compact structures with high column densities. The extended emission seen by MIPS is compared with previous CO observations. Some selected interesting sources, including two detected at 1 mm, associated with Cha II are discussed in detail, and their SEDs are presented. The classification of these sources using MIPS data is found to be consistent with that of previous studies.

Diffuse interstellar bands (DIBs) have been detected for the first time along the peculiar translucent line of sight toward HD 62542, which passes through a diffuse cloud core. Although only a small fraction (18 out of more than 300) of generally weak DIB features have been shown to correlate with C2 and C3 (the "C2 DIBs"), it is predominantly these DIBs that are observed toward HD 62542. The typically strong DIBs ll5780 and 5797 are detected but are significantly weaker than toward other lines of sight with similar reddening. Other commonly observed DIBs (such as ll4430, 6270, and 6284) remain noticeably absent. These observations further support the suggestion that the line of sight toward HD 62542 crosses only the core of a diffuse cloud and show that the correlation between the C2 DIBs and small carbon chains is maintained in environments with very large fractions of molecular hydrogen, fimg1.gif > 0.8. A comparison of CH, CN, C2, and C3 column densities and C2 DIB strengths toward HD 62542, HD 204827, and HD 172028 suggests that the line of sight toward HD 204827 passes through a diffuse cloud core similar to that seen toward HD 62542, as well as what might be referred to as a diffuse cloud envelope. This indicates that the bare core toward HD 62542 may not have significantly different relative chemical abundances from other diffuse cloud cores and that the C2 DIBs may serve as a diagnostic of such cores.

We present 5.2-37.2 mm spectroscopy of the edge-on circumstellar disk CRBR 2422.8-3423 obtained using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. The IRS spectrum is combined with ground-based 3-5 mm spectroscopy to obtain a complete inventory of solid-state material present along the line of sight toward the source. Archival JHKs imaging, as well as 350 mm Caltech Submillimeter Observatory mapping, 850 mm SCUBA mapping, and 3 mm Owens Valley Radio Observatory interferometry, is used to obtain a set of spectrophotometric data covering 1.2-3000 mm. The ices observed toward CRBR 2422.8-3423 are compared with archival ISOCAM-CVF 5-16 mm ice spectra of other nearby sources within 2'. We model the object with a two-dimensional axisymmetric (effectively three-dimensional) Monte Carlo radiative transfer code using all the available observations to constrain the source geometry and dust composition. In particular, the location of the observed ices in the disk and envelope material is included in the model. It is found that the model disk, assuming a standard flaring structure, is too warm to contain the very large observed column density of pure CO ice but is possibly responsible for up to 50% of the water, CO2, and minor ice species. In particular, the 6.85 mm band, tentatively ascribed to NHimg1.gif, exhibits a prominent red wing, indicating a significant contribution from warm ice in the disk. The shape of the CO2 bending mode suggests an interaction with up to 20% of the CO ice. It is argued that the pure CO ice is located in the dense core Oph-F in front of the source seen in the submillimeter imaging, with the CO gas in the core highly depleted. Up to 50% of the CO ice embedded in water or CO2 ice (no more than 20% of the total amount of CO) may still be located in the disk, assuming constant abundances of these types of CO ice throughout the system. Discrepancies among the strength of different water ice bands are discussed. Specifically, the observed water ice libration band located at 11-13 mm is significantly weaker than that of the model. The model is used to predict which circumstances are most favorable for direct observations of ices in edge-on circumstellar disks. Ice bands will in general be deepest for inclinations similar to the disk opening angle, i.e., ~70deg, except for very tenuous disks. Because of the high optical depths of typical disk midplanes, ice absorption bands will often probe warmer ice located in the upper layers of nearly edge-on disks. The ratios between different ice bands are found to vary by up to an order of magnitude depending on disk inclination because of radiative transfer effects caused by the two-dimensional structure of the disk. Ratios between ice bands of the same species can therefore be used to constrain the location of the ices in a circumstellar disk.

Silicate features arising from material around pre-main-sequence stars are useful probes of the star and planet formation process. In order to investigate possible connections between dust processing and disk properties, 8-13 mm spectra of 34 young stars, exhibiting a range of circumstellar environments and including spectral types A-M, were obtained using the Long Wavelength Spectrometer at the W. M. Keck Observatory. The broad 9.7 mm amorphous silicate (Si-O stretching) feature that dominates this wavelength regime evolves from absorption in young, embedded sources, to emission in optically revealed stars, and to complete absence in older "debris" disk systems for both low- and intermediate-mass stars. This is similar to the evolutionary pattern seen in Infrared Space Observatory (ISO) observations of high/intermediate-mass young stellar objects (YSOs). The peak wavelength and FWHM are centered about 9.7 and ~2.3 mm, respectively, corresponding to amorphous olivine, with a larger spread in FWHM for embedded sources and in peak wavelength for disks. In a few of our objects that have been previously identified as class I low-mass YSOs, the observed silicate feature is more complex, with absorption near 9.5 mm and emission peaking around 10 mm. Although most of the emission spectra show broad classical features attributed to amorphous silicates, small variations in the shape/strength may be linked to dust processing, including grain growth and/or silicate crystallization. For some of the Herbig Ae stars in the sample, the broad emission feature has an additional bump near 11.3 mm, similar to the emission from crystalline forsterite seen in comets and the debris disk b Pictoris. Only one of the low-mass stars, Hen 3-600A, and one Herbig Ae star, HD 179218, clearly show strong, narrow emission near 11.3 mm. We study quantitatively the evidence for evolutionary trends in the 8-13 mm spectra through a variety of spectral shape diagnostics. Based on the lack of correlation between these diagnostics and broadband infrared luminosity characteristics for silicate emission sources, we conclude that although spectral signatures of dust processing are present, they cannot be connected clearly to disk evolutionary stage (for optically thick disks) or optical depth (for optically thin disks). The diagnostics of silicate absorption features (other than the central wavelength of the feature), however, are tightly correlated with optical depth and thus do not probe silicate grain properties.

We present Owens Valley Radio Observatory Millimeter Array l = 3.4-1.2 mm dust continuum and spectral line observations of the accretion disk encircling the T Tauri star LkCa 15. The 1.2 mm dust continuum emission is resolved and gives a minimum diameter of 190 AU and an inclination angle of 57deg +- 5deg. There is a noticeable but, at present, poorly constrained decrease in the continuum spectral slope with frequency that may result from the coupled processes of grain growth and dust settling. Imaging of the fairly intense emission from the lowest rotational transitions of CO, 13CO, and HCO+ reveals a rotating disk substantially larger than that observed in the dust continuum. Emission extends to ~750 AU and the characteristic radius of the disk is determined to be ~425 AU (HWHM), based on model fits to the CO velocity field. The measured line ratios demonstrate that the emission from these species is optically thick, while that from C18O and H13CO+ is optically thin, or nearly so. The disk mass derived from the CO isotopologues with typical dense cloud abundances is still nearly 2 orders of magnitude less than that inferred from the dust emission, the most probable explanation being extensive molecular depletion in the cold, dense disk midplane. Thus, while CO, HCO+, and their isotopologues are excellent tracers of the disk velocity field, they are not reliable tracers of the disk mass. N2H+ 1 - 0 emission has also been detected which, along with HCO+, sets a lower limit to the fractional ionization of 10-8 in the near-surface regions of protoplanetary disks. This first detection of N2H+ in circumstellar disks has also made possible a determination of the N2/CO ratio (~2) that is at least an order of magnitude larger than those in the envelopes of young stellar objects and dense clouds. The large N2/CO ratio indicates that our observations probe disk layers in which CO is depleted but some N2 remains in the gas phase. Such differential depletion can lead to large variations in the fractional ionization with height in the outer reaches of circumstellar disks and may help to explain the relative nitrogen deficiency observed in comets.

The rotationally resolved spectrum of the A1Pu - X1Simg1.gif 000-000 transition of C3, centered at 4051.6 A, has been observed along 10 translucent lines of sight. To interpret these spectra, a new method for the determination of column densities and analysis of excitation profiles involving the simulation and fitting of observed spectra has been developed. The populations of lower rotational levels (J [?] 14) in C3 are best fitted by thermal distributions that are consistent with the kinetic temperatures determined from the excitation profile of C2. Just as in the case of C2, higher rotational levels (J > 14) of C3 show increased nonthermal population distributions in clouds that have been determined to have total gas densities below ~500 cm-3.

Crucial steps in the formation of stars and planets can be studied only at mid- to far-infrared wavelengths, where the Space Infrared Telescope(SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTFinstruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF[MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star-forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6-70 ?m) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg2of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground-based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow-up studies with ground-based telescopes, as well as with SIRTFitself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin.

Emission from the $2_{12} \hbox{-} 1_{11}$line of $\mathrm{H}_2\mathrm{CO}$has been detected and marginally resolved toward LkCa 15 by the Nobeyama Millimeter Array. The column density of $\mathrm{H}_2\mathrm{CO}$is higher than that observed in DM Tau and than predicted by theoretical models of disk chemistry; also, the line-intensity profile is less centrally peaked than that for CO. A similar behavior is observed in other organic gaseous molecules in the LkCa 15 disk.

The physical structure of the envelopes around a sample of 14 massive young stars is investigated using maps and spectra in submillimeter continuum and lines of C17O, CS, C34S, and H2CO. Nine of the sources are highly embedded luminous (103-105L?) young stellar objects that are bright near-infrared sources but weak in radio continuum; the other objects are similar but not bright in the near-infrared and contain "hot-core"-type objects and/or ultracompact H IIregions. The data are used to constrain the temperature and density structure of the circumstellar envelopes on 102-105AU scales, to investigate the relation between the different objects, and to search for evolutionary effects. The total column densities and the temperature profiles are obtained by fitting self-consistent dust models to submillimeter photometry. The calculated temperatures range from 300 to 1000 K at ~102AU and from 10 to 30 K at ~105AU from the star. Visual extinctions are a few hundred to a few thousand magnitudes, assuming a grain opacity at 1300 ?m of ?1 cm-2g-1of dust, as derived earlier for one of our sources. The mid-infrared data are consistent with a 30% decrease of the opacity at higher temperatures, caused by the evaporation of the ice mantles. The CS, C34S, and H2CO data as well as the submillimeter dust emission maps indicate density gradients nr-?. Assuming a constant CS abundance throughout the envelope, values of ? = 1.0-1.5 are found, which is significantly flatter than the ? = 2.0 ± 0.3 generally found for low-mass objects. This flattening may indicate that in massive young stellar objects, nonthermal pressure is more important for the support against gravitational collapse, while thermal pressure dominates for low-mass sources. We find ? = 2 for two hot-core-type sources but regard this as an upper limit since, in these objects, the CS abundance may be enhanced in the warm gas close to the star. The assumption of spherical symmetry is tested by modeling infrared absorption line data of 13CO, CS emission-line profiles and near-infrared continuum. There is a distinct, but small deviation from spherical symmetry: the data are consistent with a decrease of the optical depth by a factor of ?3 in the central 10''. The homogeneity of the envelopes is verified by the good agreement of the total masses in the power-law models with the virial masses. Modeling of C17O emission shows that ?40%-90% of the CO is frozen out onto the dust. The CO abundances show a clear correlation with temperature, as expected if the abundance is controlled by freeze-out and thermal desorption. The CS abundance is 3 × 10-9on average, ranging from (4-8) × 10-10in the cold source GL 7009S to (1-2) × 10-8in the two hot-core-type sources. Dense outflowing gas is seen in the CS and H2CO line wings; the predominance of blueshifted emission suggests the presence of dense, optically thick material within 10'' of the center. Interferometric continuum observations at 1300-3500 ?m show compact emission, probably from a 03 diameter, optically thick dust component, such as a dense shell or a disk. The emission is a factor of 10-100 stronger than expected for the envelopes seen in the single-dish data, so that this component may be opaque enough to explain the asymmetric CS and H2CO line profiles. The evolution of the sources is traced by the overall temperature (measured by the far-infrared color), which increases systematically with the decreasing ratio of envelope mass to stellar mass. The observed anticorrelation of near-infrared and radio continuum emission suggests that the erosion of the envelope proceeds from the inside out. Conventional tracers of the evolution of low-mass objects do not change much over this narrow age range.

A ? = 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10' to 10'' is presented, concentrating on the northwest condensation and the embedded sources, S68 FIRS1 and S68 N. We adopt temperatures of 25 K for the extended structure (several arcminute scale) and 35 K for the embedded sources. With these values, we use molecular line ratios and LVG statistical equilibrium calculations to derive physical properties in the region. We obtain densities between 0.4-1.2 × 106cm-3and an overall mass of 250-300 M?. The majority of the mass is found in extended cloud material with two peaks of 30-45 M?each. Values of the molecular column densities are derived on scales of 60''-75'' (condensation) and 25''-30'' (embedded sources). The column densities in the condensation are typically as high as in the embedded sources, despite a factor of 4-5 in beam area, though there is some suggestion of mild depletions on smaller scales based on interferometric observations. Derived abundances for the region show similarities to both warmer cores and colder, dark cloud regions, with some values and ratios falling cleanly between this range of properties. Measurements of several deuterated species indicate enhanced abundances, suggesting the recent evaporation of grain mantles.

Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2''=800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at l=3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0+-0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 M for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within ~100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 M assuming Td=24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 22-11 transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5''-10'' (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular transitions have been observed with the James Clerk Maxwell and Caltech Submillimeter telescopes in the 230, 345, 490, and 690 GHz atmospheric windows toward all four sources, containing, among others, lines of CO, HCO+, HCN, H2CO, SiO, SO, and their isotopomers. These lines show 20-30 km s-1 wide line wings, deep and narrow (1-2 km s-1) self-absorption, and 2-3 km s-1 FWHM line cores. The presence of highly excited lines like 12CO 4-3 and 6-5, 13CO 6-5, and several H2CO transitions indicates the presence of material with temperatures [?]100 K. Monte Carlo calculations of the molecular excitation and line transfer show that the envelope model derived from the dust emission can successfully reproduce the observed line intensities. The depletion of CO in the cold gas is modest compared to values inferred in objects like NGC 1333 IRAS 4, suggesting that the phase of large depletions through the entire envelope is short lived and may be influenced by the local star formation density. Emission in high-excitation lines of CO and H2CO requires the presence of a small amount of ~100 K material, comprising less than 1% of the total envelope mass and probably associated with the outflow or the innermost region of the envelope. The derived molecular abundances in the warm (Tkin>20 K) envelope are similar to those found toward other class 0 YSOs like IRAS 16293-2422, though some species appear enhanced toward SMM 1. Taken together, the presented observations and analysis provide the first comprehensive view of the physical and chemical structure of the envelopes of deeply embedded young stellar objects in a clustered environment on scales between 1000 and 10,000 AU.