Low-mass Dense Cores Research Articles

Low-mass Population III Star Formation due to the HD Cooling Induced by Weak Lyman–Werner Radiation

Lyman–Werner (LW) radiation photodissociating molecular hydrogen (H2) influences the thermal and dynamical evolution of the Population III (Pop III) star-forming gas cloud. The effect of powerful LW radiation has been well investigated in the context of supermassive black hole formation in the early Universe. However, the average intensity in the early Universe is several orders of magnitude lower. For a comprehensive study, we investigate the effects of LW radiation at 18 different intensities, ranging from J LW/J 21 = 0 (no radiation) to 30 (H-cooling cloud), on the primordial star-forming gas cloud obtained from a three-dimensional cosmological simulation. The overall trend with increasing radiation intensity is a gradual increase in the gas cloud temperature, consistent with previous works. Due to the HD cooling, however, the dependence of gas cloud temperature on J LW deviates from the aforementioned increasing trend for a specific range of intensities (J LW/J 21 = 0.025–0.09). In HD-cooling clouds, the temperature remained below 200 K during 105 yr after the first formation of the high-density region, maintaining a low accretion rate. Finally, the HD-cooling clouds have only a low-mass dense core (above 108 cm−3) with about 1–16 M ⊙, inside of which a low-mass Pop III star with ≤0.8 M ⊙ (a so-called “surviving star”) could form. The upper limit of star formation efficiency Mcore/Mvir,gas significantly decreases from 10−3 to 10−5 as HD cooling becomes effective. This tendency indicates that, whereas the total gas mass in the host halo increases with the LW radiation intensity, the total Pop III stellar mass does not increase similarly.

Massive core/star formation triggered by cloud–cloud collision: Effect of magnetic field

Abstract We study the effect of magnetic field on massive dense core formation in colliding unequal molecular clouds by performing magnetohydrodynamic simulations with sub-parsec resolution (0.015 pc) that can resolve the molecular cores. Initial clouds with the typical gas density of the molecular clouds are immersed in various uniform magnetic fields. The turbulent magnetic fields in the clouds consistent with the observation by Crutcher et al. (2010, ApJ, 725, 466) are generated by the internal turbulent gas motion before the collision, if the uniform magnetic field strength is 4.0 μG. The collision speed of 10 km s−1 is adopted, which is much larger than the sound speeds and the Alfvén speeds of the clouds. We identify gas clumps with gas densities greater than 5 × 10−20 g cm−3 as the dense cores and trace them throughout the simulations to investigate their mass evolution and gravitational boundness. We show that a greater number of massive, gravitationally bound cores are formed in the strong magnetic field (4.0 μG) models than the weak magnetic field (0.1 μG) models. This is partly because the strong magnetic field suppresses the spatial shifts of the shocked layer that should be caused by the nonlinear thin shell instability. The spatial shifts promote the formation of low-mass dense cores in the weak magnetic field models. The strong magnetic fields also support low-mass dense cores against gravitational collapse. We show that the numbers of massive, gravitationally bound cores formed in the strong magnetic field models are much larger than in the isolated, non-colliding cloud models, which are simulated for comparison. We discuss the implications of our numerical results on massive star formation.

APEX observations of ortho-H2D+ towards dense cores in the Orion B9 filament

Context. Initial conditions and very early stages of star formation can be probed through spectroscopic observations of deuterated molecular species Aims. We aim to determine the ortho-H2D+ properties (e.g. column density and fractional abundance with respect to H2) in a sample of dense cores in the Orion B9 star-forming filament, and to compare those with the previously determined source characteristics, in particular with the gas kinetic temperature, [N2D+]/[N2H+] deuterium fractionation, and level of CO depletion. Methods. We used the Atacama Pathfinder EXperiment (APEX) telescope to observe the 372 GHz o-H2D+(JKa, Kc = 11, 0−11, 1) line towards three prestellar cores and three protostellar cores in Orion B9. We also employed our previous APEX observations of C17O, C18O, N2H+, and N2D+ line emission, and 870 μm dust continuum emission towards the target sources. Results. The o-H2D+(11, 0−11, 1) line was detected in all three prestellar cores, but in only one of the protostellar cores. The corresponding o-H2D+ abundances were derived to be ~ (12−30) × 10−11 and ~ 6 × 10−11. Two additional spectral lines, DCO+(5−4) and N2H+(4−3), were detected in the observed frequency bands with high detection rates of 100 and 83%, respectively. We did not find any significant correlations among the explored parameters, although our results are mostly consistent with theoretical expectations. Also, the Orion B9 cores were found to be consistent with the relationship between theo-H2D+ abundance and gas temperature obeyed by other low-mass dense cores. The o-H2D+ abundance was found to decrease as the core evolves. Conclusions. The o-H2D+ abundances in the Orion B9 cores are in line with those found in other low-mass dense cores and larger than derived for high-mass star-forming regions. The higher o-H2D+ abundance in prestellar cores compared to that in cores hosting protostars is to be expected from chemical reactions where higher concentrations of gas-phase CO and elevated gas temperature accelerate the destruction of H2D+. The validity of using the [o-H2D+]/[N2D+] abundance ratio as an evolutionary indicator, which has been proposed for massive clumps, remains to be determined when applied to these target cores. Similarly, the behaviour of the [o-H2D+]/[DCO+] ratio as the source evolves was found to be ambiguous. Still larger samples and observations of additional deuterated species are needed to explore these potential evolutionary indicators further. The low radial velocity of the line emission from one of the targeted prestellar cores, SMM 7 (~ 3.6 km s−1 versus the systemic Orion B9 velocity of ~ 9 km s−1), suggests that it is a chance superposition seen towards Orion B9. Overall, as located in a dynamic environment of the Orion B molecular cloud, the Orion B9 filament provides an interesting target system to investigate the deuterium-based chemistry, and further observations of species like para-H2D+ and D2H+ would be of particular interest.

Multicomponent Kinematics in a Massive Filamentary Infrared Dark Cloud

Abstract To probe the initial conditions for high-mass star and cluster formation, we investigate the properties of dense filaments within the infrared dark cloud (IRDC) G035.39–00.33 (G035.39) in a combined Very Large Array and Green Bank Telescope mosaic tracing the NH3 (1, 1) and (2, 2) emission down to 0.08 pc scales. Using agglomerative hierarchical clustering on multiple line-of-sight velocity component fitting results, we identify seven extended velocity-coherent components in our data, likely representing spatially coherent physical structures, some exhibiting complex gas motions. The velocity gradient magnitude distribution peaks at its mode of 0.35 and has a long tail extending into higher values of 1.5–2 , and it is generally consistent with those found toward the same cloud in other molecular tracers and with the values found toward nearby low-mass dense cloud cores at the same scales. Contrary to observational and theoretical expectations, we find the nonthermal ammonia line widths to be systematically narrower (by about 20%) than those of N2H+ (1–0) line transition observed with similar resolution. If the observed ordered velocity gradients represent the core envelope solid-body rotation, we estimate the specific angular momentum to be about 2 × 1021 cm2 s−1, similar to the low-mass star-forming cores. Together with the previous finding of subsonic motions in G035.39, our results demonstrate high levels of similarity between kinematics of a high-mass star-forming IRDC and the low-mass star formation regime.

A CATALOG OF LOW-MASS STAR-FORMING CORES OBSERVED WITH SHARC-II AT 350 μm

ABSTRACT We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350 μm. Our observations have an effective angular resolution of 10″, approximately 2.5 times higher than observations at the same wavelength obtained with the Herschel Space Observatory, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ∼3″, approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350 μm observations.

Synthetic observations of first hydrostatic cores in collapsing low-mass dense cores

First hydrostatic cores are predicted by theories of star formation, but their existence has never been demonstrated convincingly by (sub)millimeter observations. Furthermore, the multiplicity at the early phases of the star formation process is poorly constrained. The purpose of this paper is twofold. First, we seek to provide predictions of ALMA dust continuum emission maps from early Class 0 objects. Second, we show to what extent ALMA will be able to probe the fragmentation scale in these objects. Following our previous paper (Commer\c{c}on et al. 2012, hereafter paper I), we post-process three state-of-the-art radiation-magneto-hydrodynamic 3D adaptive mesh refinement calculations to compute the emanating dust emission maps. We then produce synthetic ALMA observations of the dust thermal continuum from first hydrostatic cores. We present the first synthetic ALMA observations of dust continuum emission from first hydrostatic cores. We analyze the results given by the different bands and configurations and we discuss for which combinations of the two the first hydrostatic cores would most likely be observed. We also show that observing dust continuum emission with ALMA will help in identifying the physical processes occurring within collapsing dense cores. If the magnetic field is playing a role, the emission pattern will show evidence of a pseudo-disk and even of a magnetically driven outflow, which pure hydrodynamical calculations cannot reproduce. The capabilities of ALMA will enable us to make significant progress towards understanding fragmentation at the early Class 0 stage and discovering first hydrostatic cores.

Synthetic observations of first hydrostatic cores in collapsing low-mass dense cores

The low-mass star formation evolutionary sequence is relatively well-defined both from observations and theoretical considerations. The first hydrostatic core is the first protostellar equilibrium object that is formed during the star formation process. Using state-of-the-art radiation-magneto-hydrodynamic 3D adaptive mesh refinement calculations, we aim to provide predictions for the dust continuum emission from first hydrostatic cores. We investigate the collapse and the fragmentation of magnetized one solar mass prestellar dense cores and the formation and evolution of first hydrostatic cores using the RAMSES code. We use three different magnetization levels for the initial conditions, which cover a large variety of early evolutionary morphology, e.g., the formation of a disk or a pseudo-disk, outflow launching, and fragmentation. We post-process the dynamical calculations using the 3D radiative transfer code RADMC-3D. We compute spectral energy distributions and usual evolutionary stage indicators such as bolometric luminosity and temperature. We find that the first hydrostatic core lifetimes depend strongly on the initial magnetization level of the parent dense core. We derive, for the first time, spectral energy distribution evolutionary sequences from high-resolution radiation-magneto-hydrodynamic calculations. We show that under certain conditions, first hydrostatic cores can be identified from dust continuum emission at 24 microns and 70 microns. We also show that single spectral energy distributions cannot help to distinguish between the formation scenarios of the first hydrostatic core, i.e., between the magnetized and non-magnetized models. Spectral energy distributions are a first useful and direct way to target first hydrostatic core candidates but high-resolution interferometry is definitively needed to determine the evolutionary stage of the observed sources.

Intermittency of interstellar turbulence: extreme velocity-shears and CO emission on milliparsec scale

The condensation of diffuse gas into molecular clouds occurs at a rate driven largely by turbulent dissipation. This process still has to be caught in action and characterized. A mosaic of 13 fields was observed in the CO(1-0) line with the IRAM-PdB interferometer in the translucent environment of two low-mass dense cores. The large size of the mosaic compared to the resolution (4 arcsec) is unprecedented in the study of the small-scale structure of diffuse molecular gas. Eight weak and elongated structures of thicknesses as small as 3 mpc (600 AU) and lengths up to 70mpc are found. These are not filaments because once merged with short-spacing data, they appear as the sharp edges of larger-scale structures. Six out of eight form quasi-parallel pairs at different velocities and different position angles. This cannot be the result of chance alignment. The velocity-shears estimated for the three pairs include the highest ever measured far from star forming regions (780 km/s/pc). Because the large scale structures have sharp edges, with little or no overlap, they have to be thin CO-layers. Their edges mark a sharp transition between a CO-rich component and a gas undetected in the CO line because of its low CO abundance, presumably the cold neutral medium. We propose that these sharp edges are the first directly-detected manifestations of the intermittency of interstellar turbulence. The large velocity-shears reveal an intense straining field, responsible for a local dissipation rate several orders of magnitude above average, possibly at the origin of the thin CO-layers.

Intermittency of interstellar turbulence: parsec-scale coherent structure of intense, velocity shear

Guided by the duality of turbulence (random versus coherent we seek coherent structures in the turbulent velocity field of molecular clouds, anticipating their importance in cloud evolution. We analyse a large map (40' by 20') obtained with the HERA multibeam receiver (IRAM-30m telescope) in a high latitude cloud of the Polaris Flare at an unprecedented spatial (11") and spectral (0.05 km/s) resolutions in the 12CO(2-1) line. We find that two parsec-scale components of velocities differing by ~2 km/s, share a narrow interface ($<0.15$ pc) that appears as an elongated structure of intense velocity-shear, ~15 to 30 km/s/pc. The locus of the extrema of line--centroid-velocity increments (E-CVI) in that field follows this intense-shear structure as well as that of the 12CO(2-1) high-velocity line wings. The tiny spatial overlap in projection of the two parsec-scale components implies that they are sheets of CO emission and that discontinuities in the gas properties (CO enrichment and/or increase of gas density) occur at the position of the intense velocity shear. These results disclose spatial and kinematic coherence between scales as small as 0.03 pc and parsec scales. They confirm that the departure from Gaussianity of the probability density functions of E-CVIs is a powerful statistical tracer of the intermittency of turbulence. They disclose a link between large scale turbulence, its intermittent dissipation rate and low-mass dense core formation.

Survey of ortho-H$\mathsf{_{2}}$D$\mathsf{^{+}}$ (1$\mathsf{_{1,0}}$–1$\mathsf{_{1,1}}$) in dense cloud cores

Aims. We present a survey of the ortho-H2D + (11,0−11,1) line toward a sample of 10 starless cores and 6 protostellar cores, carried out at the Caltech Submillimeter Observatory. The high diagnostic power of this line is revealed for the study of the chemistry, and the evolutionary and dynamical status of low-mass dense cores. Methods. The derived ortho-H2D + column densities (N(ortho-H2D + )) are compared with predictions from simple chemical models of centrally concentrated cloud cores. Results. The line is detected in 7 starless cores and in 4 protostellar cores. N(ortho-H2D + ) ranges between 2 and 40 × 10 12 cm −2 in starless cores and between 2 and 9 × 10 12 cm −2 in protostellar cores. The brightest lines are detected toward the densest and most centrally concentrated starless cores, where the CO depletion factor and the deuterium fractionation are also largest. The large scatter observed in plots of N(ortho-H2D + ) vs. the observed deuterium fractionation and vs. the CO depletion factor is likely to be due to variations in the ortho-to-para (o/p) ratio of H2D + from >0.5 for Tkin < 10 K gas in pre-stellar cores to � 0.03 (consistent with Tkin � 15 K for protostellar cores). The two Ophiuchus cores in our sample also require a relatively low o/p ratio (� 0.3). Other parameters, including the cosmic-ray ionization rate, the CO depletion factor (or, more in general, the depletion factor of neutral species), the volume density, the fraction of dust grains and PAHs also largely affect the ortho-H2D + abundance. In particular, gas temperatures above 15 K, low CO depletion factors and large abundance of negatively charged small dust grains or PAHs drastically reduce the deuterium fractionations to values inconsistent with those observed toward pre-stellar and protostellar cores. The most deuterated and H2D + -rich objects (L 429, L 1544, L 694-2 and L 183) are reproduced by chemical models of centrally concentrated (central densties � 10 6 cm −3 ) cores with chemical ages between 10 4 and 10 6 yr. Upper limits of the para-H3O + (1 − −2 + ) and para-D2H + (11,0−10,1) lines are also given. The upper limit to the para-H3O + fractional abundance is � 10 −8 and we find an upper limit to the para-D2H + /orthoH2D + column density ratio equal to 1, consistent with chemical model predictions of high density (2 × 10 6 cm −3 ) and low temperature (Tkin < 10 K) clouds. Conclusions. Our results point out the need for better determinations of temperature and density profiles in dense cores as well as for observations of para-H2D + .

SHARC-II Mapping ofSpitzerc2d Small Clouds and Cores

We present the results of a submillimeter survey of 53 low-mass dense cores with the Submillimeter High Angular Resolution Camera II (SHARC-II). The survey is a follow-up project to the Spitzer Legacy Program ``From Molecular Cores to Planet-Forming Disks'', with the purpose being to create a complete data set of nearby low-mass dense cores from the infrared to the millimeter. We present maps of 52 cores at 350 microns and three cores at 450 microns, two of which were observed at both wavelengths. Of these 52 cores, 41 were detected by SHARC-II: 32 contained one submillimeter source while 9 contained multiple sources. For each submillimeter source detected, we report various source properties including source position, fluxes in various apertures, size, aspect ratio, and position angle. For the 12 cores that were not detected we present upper limits. The sources detected by SHARC-II have, on average, smaller sizes at the 2sigma contours than those derived from longer-wavelength bolometer observations. We conclude that this is not caused by a failure to integrate long enough to detect the full extent of the core; instead it arises primarily from the fact that the observations presented in this survey are insensitive to smoothly varying extended emission. We find that SHARC-II observations of low-mass cores are much better suited to distinguishing between starless and protostellar cores than observations at longer wavelengths. Very Low Luminosity Objects, a new class of objects being discovered by the Spitzer Space Telescope in cores previously classified as starless, look very similar at 350 microns to other cores with more luminous protostars.

Dissipative structures of diffuse molecular gas

Aims. This paper belongs to a series of four, dedicated to the analysis of the dynamical, thermal and chemical properties of translucent molecular gas, with the perspective of characterizing the processes driving the dissipation of supersonic turbulence, an anticipated prerequisite of dense core formation. Methods. We analyze the small scale morphology and velocity structure of the parsec-scale environment of a low mass dense core (1 M� ). Our work is based on large maps made with the IRAM-30 m telescope in the two lowest rotational transitions of 12 CO and 13 CO with high angular (20 �� or 0.015 pc at 115 GHz) and spectral (0.055 km s −1 ) resolutions. The field is translucent, hence providing strong constraints on the column density and physical conditions in the gas. Results. More than one third of the field mass (6.5 M� ) lies in an elongated tail of dense and cold gas, possibly extending beyond the edge of the map and connected to the core in space and velocity. This core tail is highly turbulent and sub-structured into narrow filaments of aspect ratio up to 20. These are pure velocity structures with velocity shears in the range 2–10 km s −1 pc −1 . Another third of the mass, according to the weak extinction of the field, lies in more dilute molecular and atomic gas. Its molecular fraction, largely traced by optically thick 12 CO lines, is even more turbulent than the dense core tail. The gas emitting in the broad wings of the 12 CO lines is organized into a conspicuous network of narrow criss-crossed filaments, whose pattern at the parsec scale is seen for the first time. The gas there is optically thin in the 12 CO(1–0) line (τ12 < 0.2), warmer than 25 K and more dilute than 1000 cm −3 . These optically thin 12 CO-filaments, though contributing to about 10% of the mass of the environment, have a CO cooling rate a few times larger than that of the whole field on average. Whether dense or dilute, all the filamentary structures in the field (with transverse sizes 0.015–0.03 pc), are preferentially oriented along the direction of the magnetic fields, as measured a few parsecs away. Using the Chandrasekhar-Fermi method, we estimate the intensity of the magnetic fields intensity in the dilute molecular gas to be Bpos = 15 µG. We infer that the turbulent motions in the dilute gas are in the trans-Alfvenic range. –––

The turbulent environment of low-mass dense cores

AbstractThe signatures of intermittent dissipation of turbulent energy have been sought in the translucent environment of a low-mass dense core. Molecular line observations reveal a network of narrow filamentary structures, found on statistical grounds to be the locus of the largest velocity shears. Three independent properties of these structures make them the plausible sites of intermittent dissipation of turbulence: (1) gas there is warmer and more diluted than average, (2) it bears the signatures of a non-equilibrium chemistry triggered by impulsive heating due to turbulence dissipation, and (3) the power that these structures radiate in the gas cooling lines (mostly H2) is so large that it balances the total energy injection rate of the turbulent cascade, for a volume filling factor of only a few percents, consistent with other observations in the Solar Neighborhood. These filamentary structures may act as tiny seeds of gas condensation in diffuse molecular gas. They do not exhibit the properties of steady-state low-velocity magneto-hydrodynamic (MHD) shocks, as presently modelled.

Dynamical and chemical properties of the “starless” core L1014

Spitzer Space Telescope observations of a point-like source, L1014-IRS, close to the dust peak of the low-mass dense core L1014 have questioned its starless nature. The presence of an object with colors expected for an embedded protostar makes L1014-IRS the lowest luminosity isolated protostar known, and an ideal target with which to test star formation theories at the low mass end. In order to study its molecular content and to search for the presence of a molecular outflow, we mapped L1014 in at least one transition of 12CO, N2H+, HCO+, CS and of their isotopologues 13CO, C18O, C17O, N2D+ and H13CO+, using the FCRAO, the IRAM 30 meter and the CSO. The data show physical and chemical properties in L1014 typical of the less evolved starless cores: i.e. H2 central density of a few 10^5 molecules cm^-3, estimated mass of ~2M_sun, CO integrated depletion factor less than 10, N(N2H+)~6*10^12 cm^-2, N(N2D+)/N(N2H+) equal to 10% and relatively broad N2H+(1--0) lines (0.35 km/s). Infall signatures and significant velocity shifts between optically thick and optically thin tracers are not observed in the line profiles. No classical signatures of molecular outflow are found in the 12CO and 13CO observations. In particular, no high velocity wings are found, and no well-defined blue-red lobes of 12CO emission are seen in the channel maps. If sensitive, higher resolution observations confirm the absence of an outflow on a smaller scale than probed by our observations, L1014-IRS would be the only protostellar object known to be formed without driving an outflow.

A Molecular Filament Threaded by Helical Magnetic Fields?

We present a multitransition study in the 13CO(1-0), 12CO(2-1), 12CO(3-2) and 12CO(4-3) lines of a parsec scale elongated structure connected to a low-mass dense core. Densities larger than n H 2 = 104 cm−3 are inferred in the central regions of this structure, supporting the proposition that it is a genuine filament denser than its environment. The sharp observed drop of the 12CO and 13CO emissions requires a power law density fall-off steeper than r −1 although a single density law cannot reproduce the spatial shift of 0.1 pc between the 13CO and 12CO drops. Our results support the previous proposition that this elongated structure is a filament threaded by helical magnetic fields, channeling the gas inflow onto the dense core.

Non-Gaussian velocity shears in the environment of low mass dense cores

We report on a novel kind of small scale structure in molecular clouds found in IRAM-30m and CSO maps of 12CO and 13CO lines around low mass starless dense cores. These structures come to light as the locus of the extrema of velocity shears in the maps, computed as the increments at small scale (~0.02 pc) of the line velocity centroids. These extrema populate the non-Gaussian wings of the shear probability distribution function (shear-PDF) built for each map. They form elongated structures of variable thickness, ranging from less than 0.02 pc for those unresolved, up to 0.08 pc. They are essentially pure velocity structures. We propose that these small scale structures of velocity shear extrema trace the locations of enhanced dissipation in interstellar turbulence. In this picture, we find that a significant fraction of the turbulent energy present in the field would be dissipating in structures filling less than a few % of the cloud volume.

L183, a Quiescent Core?

Some observed results of NH3 (1, 1) and (2,2) line emission in the starless dark cloud L183 are reported. Our observation suggests that the dense core of L183 has a size of similar to 0.16pc x0.1pc with a mass of similar to 12M(circle dot). A velocity gradient of 4km s(-1)pc(-1) from the north to the south was detected. The velocity shift corresponds to a central mass of similar to 5M(circle dot). If it is caused by rotation, the mass would be much less than the value above. This suggests that there may be more mass in the envelope of L183 than in the central region. The analysis of our data and the evidence in the literature about L183 indicate that it may be undergoing a process of collapsing to form a low-mass binary dense core.

In search of evidence for protostellar collapse - A systematic study of line formation in low-mass dense cores

view Abstract Citations (129) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS In Search of Evidence for Protostellar Collapse: A Systematic Study of Line Formation in Low-Mass Dense Cores Zhou, Shudong Abstract Radiative transfer models of low-mass dense cores are presented as depicted in two theoretical models of protostellar collapse: the Larson-Penston flow and the theory of Shu and coworkers based on the 'inside-out collapse' model. In particular, line profiles of the first three rotational transitions of the CS molecule are calculated for hypothetical dense cores evolving according to these theories. The results are compared with CS observations of nearby dense cores. It is shown that the Larson-Penston flow overestimates the velocity width of the CS lines by a large margin and cannot be reconciled with the observations. In contrast, the theory of Shu and coworkers predicts the right velocity width for the CS lines during the formation stage of dense cores. The models indicate that 'inside-out' collapse should significantly enhance the CS line widths and the enhancement should be easily observable, particularly at high resolution. A list of line properties are presented for hypothetical dense cores undergoing 'inside-out' collapse. These properties are found to be unique to collapse motions; hence, they can be used as a guide in searching for protostellar collapse. Publication: The Astrophysical Journal Pub Date: July 1992 DOI: 10.1086/171572 Bibcode: 1992ApJ...394..204Z Keywords: Gravitational Collapse; Line Spectra; Protostars; Radiative Transfer; Star Formation; Astronomical Spectroscopy; Computational Astrophysics; Interstellar Matter; Molecular Clouds; Stellar Cores; Stellar Models; Astrophysics; ISM: CLOUDS; RADIATIVE TRANSFER; STARS: FORMATION full text sources ADS | data products SIMBAD (1)