Dense cores in dark clouds. I - CO observations and column densities of high-extinction regions

Myers, P. C.; Linke, R. A.; Benson, P. J.

doi:10.1086/160619

Cited by 227 publications

(165 citation statements)

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“…Rieke & Lebofsky (1985) derive A V = Si % 17 for grains in the interstellar medium. This would indicate A V ¼ 10 30 for the present Class I objects, to compare with the general extinction determined toward Taurus association stars of A V ¼ 1 5 and the total extinction through the densest Taurus molecular-cloud cores of A V ¼ 2 20 ( Myers et al 1983). Only one of our targets ( IRAS 04108+2803B) lies near a cloud core ( L1495) dense enough that its silicate feature could be explained by a location on the far side and absorption by the intervening cloud; even if this were the case, the 15.2 m CO 2 ice feature would still be unusually strong.…”

Section: Analysis and Conclusionmentioning

confidence: 63%

Mid‐infrared Spectra of Class I Protostars in Taurus

Watson

Kemper

Calvet

et al. 2004

ASTROPHYS J SUPPL S

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We present Spitzer Space Telescope Infrared Spectrograph observations in the 5.3-20 m range of five young stellar objects in Taurus that have Class I continuum spectral energy distributions (kF k k n ; n ! 0), often taken to represent the youngest stellar objects in this star formation region. The spectra include a rich collection of broad absorption features that we identify with amorphous silicates and various ices, notably those of carbon dioxide and water. We show that the absorption features are produced mainly in the envelopes of these systems. The apparent depths of silicate and 15.2 m CO 2 ice features vary among the objects in a manner that is consistent with a variation of inclination with respect to the line of sight, contribution to the silicate features from material throughout the envelopes, and an origin for the CO 2 ice feature in the outer parts of the envelope. Thus, these features provide new and useful constraints on models of the physical structure of Class I protostars.

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Section: Analysis and Conclusionmentioning

confidence: 63%

Mid‐infrared Spectra of Class I Protostars in Taurus

Watson

Kemper

Calvet

et al. 2004

ASTROPHYS J SUPPL S

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“…Compared to the broad, supersonic 12 CO and 13 CO line profiles, roughly equal contributions of thermal and non-thermal motions are found in the observed C 18 O linewidths in nearby clouds (Myers et al 1983;Vilas-Boas et al 1994;Onishi et al 1996). Originally thought to be restricted to cores at scales of 0.1 pc (Goodman et al 1998), constant (tran-)sonic-like C 18 O linewidths have been found to be characteristic of filaments and fibers at scales of 0.5 pc (Hacar & Tafalla 2011;Arzoumanian et al 2013;Hacar et al 2013).…”

Section: Introductionmentioning

confidence: 92%

“…Assuming similar and uniform local termodynamic equilibrium (LTE) conditions along the line of sight, the opacities of a given J transition for the different CO lines can be estimated by their relative abundances as τ(A) X(A/B) · τ(B) (e.g., Myers et al 1983). Characteristic values of τ(C 18 O) between 0.2 and 0.6 based on the study of the C 18 O (1−0) transition are found in different studies of dark clouds (Myers et al 1983;Vilas-Boas et al 1994Onishi et al 1996). Assuming typical relative abundances for the main three CO isotopologues in the local ISM (i.e., X(C 18 O):X( 13 CO):X( 12 CO) = 1:7.3:560 Wilson & Rood 1994) these opacities translate into characteristic line opacities ranging between τ( 13 CO) ∼ 1.5-4.4 and τ( 12 CO) ∼ 110-340 for the J = 1−0 transitions of the most abundant CO isotopologue (e.g., Phillips et al 1979;Wong et al 2008).…”

Section: Co Linewidths: Differential Opacity Broadeningmentioning

confidence: 99%

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

Hacar

Alves

Burkert

et al. 2016

A&A

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Context. Since their first detection in the interestellar medium, (sub-)millimeter line observations of different CO isotopic variants have routinely been employed to characterize the kinematic properties of the gas in molecular clouds. Many of these lines exhibit broad linewidths that greatly exceed the thermal broadening expected for the low temperatures found within these objects. These observed suprathermal CO linewidths are assumed to originate from unresolved supersonic motions inside clouds. Aims. The lowest rotational J transitions of some of the most abundant CO isotopologues, 12 CO and 13 CO, are found to present large optical depths. In addition to well-known line saturation effects, these large opacities present a non-negligible contribution to their observed linewidths. Typically overlooked in the literature, in this paper we aim to quantify the impact of these opacity broadening effects on the current interpretation of the CO suprathermal line profiles. Methods. Combining large-scale observations and LTE modeling of the ground J = 1−0 transitions of the main 12 CO, 13 CO, C 18 O isotopologues, we have investigated the correlation of the observed linewidths as a function of the line opacity in different regions of the Taurus molecular cloud. Results. Without any additional contributions to the gas velocity field, a large fraction of the apparently supersonic (M ∼ 2-3) linewidths measured in both 12 CO and 13 CO (J = 1−0) lines can be explained by the saturation of their corresponding sonic-like, optically thin C 18 O counterparts assuming standard isotopic fractionation. Combined with the presence of multiple components detected in some of our C 18 O spectra, these opacity effects also seem to be responsible for most of the highly supersonic linewidths (M > 8-10) detected in some of the broadest 12 CO and 13 CO spectra in Taurus.Conclusions. Our results demonstrate that most of the suprathermal 12 CO and 13 CO linewidths reported in nearby clouds like Taurus could be primarily created by a combination of opacity broadening effects and multiple gas velocity components blended in these saturated emission lines. Once corrected by their corresponding optical depth, each of these gas components present transonic intrinsic linewidths consistently traced by the three isotopologues, 12 CO, 13 CO, and C 18 O, with differences within a factor of 2. Highly correlated and velocity-coherent at large scales, the largest and highly supersonic velocity differences inside clouds are generated by the relative motions between individual gas components. In contrast to the classical interpretation within the framework of microscopic turbulence, this highly discretized structure of the molecular gas traced in CO suggest that the gas dynamics inside molecular clouds could be better described by the properties of a fully resolved macroscopic turbulence.

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“…However, for several molecules with large abundances, we observe the corresponding transitions of their main and rare isotopologues, e.g., OCS (J = 19 → 18) − O 13 CS (19 → 18), 13 CO (2 → 1) − CO (2 → 1) − C 18 O (2 → 1) and CH 13 3 CN (12 2 → 11 2 )−CH 3 CN (12 2 → 11 2 ). By measuring the ratio between main beam brightness temperature of the main line T B, α,0 and its rare isotopologue T B, β,0 , we can estimate the optical depth at line centre of a given transition τ α,0 (Myers et al 1983 where α is the intrinsic abundance of the main isotope (e.g., 12 C) compared to its rare isotope (e.g., 13 C) in the ISM (Table 4, e.g., Wilson & Rood 1994;Chin et al 1996). …”

Section: Molecular Column Densitiesmentioning

confidence: 99%

Resolving the chemical substructure of Orion-KL

Feng

Beuther

Henning

et al. 2015

A&A

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Context. The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a high-mass star-forming environment. Studying the resolved chemical substructures of this complex region provides important insight into the chemistry of high-mass star-forming regions (HMSFRs), as it relates to their evolutionary states. Aims. The goal of this work is to resolve the molecular line emission from individual substructures of Orion-KL at high spectral and spatial resolution and to infer the chemical properties of the associated gas.Methods. We present a line survey of Orion-KL obtained from combined Submillimeter Array (SMA) interferometric and IRAM 30 m single-dish observations. Covering a 4 GHz bandwidth in total, this survey contains over 160 emission lines from 20 species (25 isotopologues), including 11 complex organic molecules (COMs). Spectra are extracted from individual substructures and the intensity-integrated distribution map for each species is provided. We then estimate the rotation temperature for each substructure, along with their molecular column densities and abundances. Results. For the first time, we complement 1.3 mm interferometric data with single-dish observations of the Orion-KL region and study small-scale chemical variations in this region. (1) We resolve continuum substructures on ∼3 angular scale. (2) We identify lines from the low-abundance COMs CH 3 COCH 3 and CH 3 CH 2 OH, as well as tentatively detect CH 3 CHO and long carbon-chain molecules C 6 H and HC 7 N. (3) We find that while most COMs are segregated by type, peaking either towards the hotcore (e.g., nitrogenbearing species) or the compact ridge (e.g., oxygen-bearing species like HCOOCH 3 and CH 3 OCH 3 ), the distributions of others do not follow this segregated structure (e.g., CH 3 CH 2 OH, CH 3 OH, CH 3 COCH 3 ). (4) We find a second velocity component of HNCO, SO 2 , 34 SO 2 , and SO lines, which may be associated with a strong shock event in the low-velocity outflow. (5) Temperatures and molecular abundances show large gradients between central condensations and the outflow regions, illustrating a transition between hot molecular core and shock-chemistry dominated regimes. Conclusions. Our observations of spatially resolved abundance variations in Orion-KL provide the nearest reference source for hot molecular core and outflow chemistry, which will be an important example for interpreting the chemistry of more distant HMSFRs.

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Dense cores in dark clouds. I - CO observations and column densities of high-extinction regions

Cited by 227 publications

References 0 publications

Mid‐infrared Spectra of Class I Protostars in Taurus

Mid‐infrared Spectra of Class I Protostars in Taurus

Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

Resolving the chemical substructure of Orion-KL

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