Molecular line profiles from contracting dense cores

Stahler, Steven W.; Yen, J. J.

doi:10.1111/j.1365-2966.2010.17073.x

Cited by 16 publications

(21 citation statements)

References 54 publications

(88 reference statements)

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“…Eventually, all gas materials would continue to fall toward the center to form a protostellar core. This scenario is consistent with both theoretical (e.g., Stahler & Yen 2010) and observational (e.g., Lee & Myers 2011) pictures concerning the evolution of internal motions in starless cores.…”

Section: Conclusion and Discussionsupporting

confidence: 75%

“…Both theoretical (e.g., Broderick et al 2007;Stahler & Yen 2010) and observational (e.g., Lee & Myers 2011) works reveal that a static core would show expansive or oscillatory motions once perturbed on large scales. While a molecular cloud is undergoing an expansive or oscillatory mode on large scales, its core may begin to collapse or contract due to nonlinear instabilities under self-gravity.…”

Section: Introductionmentioning

confidence: 99%

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Starless Cloud Core L1517b in Envelope Expansion With Core Collapse

Lou

2011

ApJ

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Various spectral emission lines from the star-forming molecular cloud core L1517B manifest red asymmetric double-peaked profiles with stronger red peaks and weaker blue peaks, in contrast to the oft-observed blue-skewed molecular spectral line profiles with blue peaks stronger than red peaks. Invoking a spherically symmetric general polytropic hydrodynamic shock model for the envelope expansion with a core collapse (EECC) phase, we show the radial flow velocity, mass density, and temperature structures of a self-similar evolution for L1517B in a dynamically consistent manner. By prescribing simple radial profiles of abundance distribution for pertinent molecules, we perform molecular excitation and radiative transfer calculations using the publicly available RATRAN code set for the spherically symmetric case. Emphatically, the spectral profiles of line emissions from the same molecules but for different line transitions as well as spectra of closely pertinent isotopologues strongly constrain the self-similar hydrodynamics of a cloud core with prescribed abundances. Our computational results show that the EECC model reproduces molecular spectral line profiles in sensible agreement with the observational data of the Institut de Radioastronomie Millimétrique (IRAM), Five College Radio Astronomical Observatory, and Effelsberg 100 m telescopes for L1517B. We also report the spatially resolved observations of the optically thick line HCO + (1 − 0) using the Purple Mountain Observatory 13.7 m telescope at Delingha in China and the relevant fitting results. Hyperfine line structures of NH 3 and N 2 H + transitions are also fitted to consistently reveal the dynamics of the central core collapse. As a consistent model check, radial profiles of 1.2 mm and 850 μm dust continua observed by the IRAM 30 m telescope and the Submillimeter Common-User Bolometer Array, respectively, are also fitted numerically using the same EECC model that produces the molecular line profiles. L1517B is likely undergoing an EECC shock phase. For future observational tests, we also predict several molecular line profiles with spatial distributions, the radial profile of the sub-millimeter continuum at wavelength 450 μm, as well as the radial profiles of the column density and visual extinction for L1517B.

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Section: Conclusion and Discussionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Starless Cloud Core L1517b in Envelope Expansion With Core Collapse

Lou

2011

ApJ

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“…We adopt values of n d = 2 × 10 4 cm −3 for the depletion density and A 0 = 4 × 10 −9 for the low-density abundance limit, based on the typical values given in Tafalla et al (2002). Stahler & Yen (2010) recently carried out line modeling of diffuse cores with and without CS depletion, and found that the models with depletion were a better match to observations, and so we adopt it here. Due to depletion, the number density of CS is almost negligible in the densest regions of our cores.…”

Section: Molecular Speciesmentioning

confidence: 99%

“…The study of spherical core line profiles has continued in more recent years. In particular, Rawlings & Yates (2001), Tsamis et al (2008), and Stahler & Yen (2010) have shown the importance of accurately modeling the chemical abundances within cores, particularly since optically thick carbon-bearing species, such as CO and CS, freeze out within the dense core centers (Tafalla et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Line Profiles of Cores Within Clusters. I. The Anatomy of a Filament

Smith

Shetty

Stutz

et al. 2012

ApJ

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Observations are revealing the ubiquity of filamentary structures in molecular clouds. As cores are often embedded in filaments, it is important to understand how line profiles from such systems differ from those of isolated cores. We perform radiative transfer calculations on a hydrodynamic simulation of a molecular cloud in order to model line emission from collapsing cores embedded in filaments. We model two optically thick lines, CS(2-1) and HCN(1-0), and one optically thin line, N 2 H + (1-0), from three embedded cores. In the hydrodynamic simulation, gas self-gravity, turbulence, and bulk flows create filamentary regions within which cores form. Though the filaments have large dispersions, the N 2 H + (1-0) lines indicate subsonic velocities within the cores. We find that the observed optically thick line profiles of CS(2-1) and HCN(1-0) vary drastically with viewing angle. In over 50% of viewing angles, there is no sign of a blue asymmetry, an idealized signature of infall motions in an isolated spherical collapsing core. Profiles that primarily trace the cores, with little contribution from the surrounding filament, are characterized by a systematically higher HCN(1-0) peak intensity. The N 2 H + (1-0) lines do not follow this trend. We demonstrate that red asymmetric profiles are also feasible in the optically thick lines, due to emission from the filament or one-sided accretion flows onto the core. We conclude that embedded cores may frequently undergo collapse without showing a blue asymmetric profile, and that observational surveys including filamentary regions may underestimate the number of collapsing cores if based solely on profile shapes of optically thick lines.

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“…As long as the temperature is low enough, CS and other sulphur-bearing molecules are expected to be strongly depleted towards the centre of dense cores where the density is high (e.g., Tafalla et al 2004;Bergin et al 2001). Depletion occurs due to the freezing-out process onto the dust grains (e.g., Tafalla et al 2002;Stahler & Yen 2010) and observations of starless cores, such as L1544, or Class 0 protostars, such as IRAM 04191, also showed CS depletion towards the centre by a factor of ∼20 Belloche et al 2002).…”

Section: Abundancementioning

confidence: 99%

The dynamical state of the first hydrostatic core candidate Chamaeleon-MMS1

Tsitali¹,

Беллоче²,

Commerçon³

et al. 2013

A&A

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Context. First hydrostatic cores represent a theoretically predicted intermediate evolutionary link between the prestellar and protostellar phases. Studying the observational characteristics of first core candidates is therefore vital for probing and understanding the earliest phases of star formation. Aims. We aim to determine the dynamical state of the first hydrostatic core candidate Chamaeleon-MMS1 (Cha-MMS1). Methods. We observed Cha-MMS1 in various molecular transitions with the APEX and Mopra telescopes. Continuum data retrieved from the Spitzer Heritage Archive were used to estimate the internal luminosity of the source. The molecular emission was modelled with a radiative transfer code to derive constraints on the kinematics of the envelope, which were then compared to the predictions of magneto-hydrodynamic simulations. Results. We derive an internal luminosity of 0.08 L −0.18 L for Cha-MMS1. An average velocity gradient of 3.1 ± 0.1 km s −1 pc −1 over ∼0.08 pc is found perpendicular to the filament in which Cha-MMS1 is embedded. The gradient is flatter in the outer parts and, surprisingly, also at the innermost ∼2000 AU to 4000 AU. The former features are consistent with solid-body rotation beyond 4000 AU and slower, differential rotation beyond 8000 AU, but the origin of the flatter gradient in the innermost parts is unclear. The classical infall signature is detected in HCO + 3−2 and CS 2−1. The radiative transfer modelling indicates a uniform infall velocity in the outer parts of the envelope. In the inner parts (at most 9000 AU), an infall velocity field scaling with r −0.5 is consistent with the data, but the shape of the profile is less well constrained and the velocity could also decrease toward the centre. The infall velocities are subsonic to transonic, 0.1 km s −1 −0.2 km s −1 at r ≥ 3300 AU, and subsonic to supersonic, 0.04 km s −1 −0.6 km s −1 at r ≤ 3300 AU. Both the internal luminosity of Cha-MMS1 and the infall velocity field in its envelope are consistent with predictions of MHD simulations for the first core phase. There is no evidence of any fast, large-scale outflow stemming from Cha-MMS1, but excess emission from the high-density tracers CS 5−4, CO 6−5, and CO 7−6 suggests the presence of higher velocity material at the inner core. Conclusions. Its internal luminosity excludes Cha-MMS1 being a prestellar core. The kinematical properties of its envelope are consistent with Cha-MMS1 being a first hydrostatic core candidate or a very young Class 0 protostar.

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Molecular line profiles from contracting dense cores

Cited by 16 publications

References 54 publications

Starless Cloud Core L1517b in Envelope Expansion With Core Collapse

Starless Cloud Core L1517b in Envelope Expansion With Core Collapse

Line Profiles of Cores Within Clusters. I. The Anatomy of a Filament

The dynamical state of the first hydrostatic core candidate Chamaeleon-MMS1

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