Dust and gas emission in Barnard 5

Langer, W. D.; Wilson, R. W.; Goldsmith, Paul F.; Beichman, Charles

doi:10.1086/167108

Cited by 62 publications

(66 citation statements)

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“…The escape probability model gives typical gas kinetic temperatures of T kin = 12−13 K for the position in the core and IRS 4 region, in agreement with the LTE discussion above and the results by Young et al (1982) and Langer et al (1989). Note, that the higher gas temperatures of T > 25 K derived by Young et al (1982) for the cloud edge correspond to larger offsets from the cloud center (∆δ > ∼ 20 relative to the "(0,0) position" used in the present paper).…”

Section: Molecular Cloudsupporting

confidence: 87%

“…Young et al (1982) derive a kinetic temperature between 10-15 K and an average density of n ∼ 1.7 × 10 3 cm −3 for the shielded molecular gas using multi-line CO observations. Similar temperatures of T = 12−14 K are noted by Langer et al (1989). The C 18 O observations by Goldsmith, Langer & Wilson (1986) probe the CO gas deeper in the cloud and reveal a clumpy density structure with gas densities between (3−7) × 10 3 cm −3 for the clumps.…”

Section: Molecular Cloud B5supporting

confidence: 72%

“…However, the total luminosity of the embedded IRAS sources is low, and these objects do not significantly heat the gas in the cloud. In fact, the IRAS dust emission maps presented by Langer et al (1989) show that B5 is externally heated by the diffuse ISRF. This is indicated by the higher dust temperature at the cloud surface, derived from the IRAS 60 µm and 100 µm bands and the limb-brightened 12 µm emission.…”

Section: Molecular Cloud B5mentioning

confidence: 99%

“…Several authors (Langer et al 1989;Yu et al 1999;Goodman 2004;Sun et al 2005) have reported extensive mapping observations of the rotational-line emission of CO and its isotopologues 13 CO, C 18 O. These maps have an angular resolution between 0.…”

Section: Molecular Cloud B5mentioning

confidence: 99%

“…The angular extent of the cloud 1 is ∼1 • × 0.5 • , corresponding to a linear size of ∼4.4 × 2.3 pc at a distance of 260 pc. Langer et al (1989) estimate a total cloud mass of 930 M and a virial mass of 1390 M using 13 CO J = 1 → 0 observations and assuming d = 350 pc. This corresponds to M cloud ≈ 510 M and M vir ≈ 1000 M for the distance of d = 260 pc adopted in the present paper.…”

Section: Molecular Cloud B5mentioning

confidence: 99%

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Neutral carbon and CO emission in the core and the halo of dark cloud Barnard 5

Bensch

2006

A&A

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Aims. The physical conditions and chemical structure in the dark cloud of Barnard 5 and its surrounding atomic halo is studied. The impact of the halo on the line emission emerging from the molecular cloud is investigated. Methods. We present observations of the [CI] 3 P 1 → 3 P 0 transition of neutral carbon and the low-J transitions of 12 CO and 13 CO. The CO maps extend from the core (A v > ∼ 7) to the northern cloud edge and into the halo (A v < ∼ 1). They are complemented by deeply integrated [CI] spectra made along a 1D cut of similar extent. Escape probability and photon-dominated region (PDR) models are employed to interpret the observations. Results. 12 CO and 13 CO are detected in the cloud and the halo, while [CI] is detected only toward the molecular cloud. This occurs even though the neutral carbon column density is > ∼ 5 times larger than the CO column density in the halo, but it can be understood in terms of excitation. The [CI] excitation is governed by collisions even at the low halo densities, while the CO excitation is dominated by the absorption of line photons emitted by the nearby molecular cloud. The upper limit on the neutral carbon column density in the halo is 6 × 10 15 cm −2 . The PDR studies show that even small column densities of H 2 and CO, such as those in the B5 halo, can significantly change the [CI] and CO line emission (pre-shielding). Since this effect decreases the [CI] intensity and increases the CO intensity, the largest impact is noted for the [CI]/CO line ratios. For the B5 cloud, a PDR model with a molecular hydrogen column density of ∼6 × 10 19 cm −2 in the halo matches the observed [CI]/CO line ratios best. Models with no pre-shielding, in contrast, suggest high gas densities that are in conflict with independently derived densities. The PDR models with a χ < 1 demonstrate that the [CI]/CO ratios cannot be attributed solely to a reduced FUV field.Key words. ISM: abundances -astrochemistry -ISM: clouds -ISM: individual: B5 -radio lines: ISM IntroductionDark clouds are noted at optical wavelengths by their absorption of the stellar background, showing that they have a column density of at least several magnitudes in visible extinction (A v ). Many of the dark clouds are relatively quiescent with either no active star formation or low-mass star formation proceeding in a few isolated cores. Gas heating is provided by the diffuse interstellar radiation field (ISRF) via photo-electric heating and by cosmic rays for the FUV-shielded parts of the cloud. Protostars embedded in dense cores can heat the gas locally, and the interaction of a linear jet emerging from the protostar with the parental cloud can give rise to shock-heated molecular gas and drive a molecular outflow. However, these processes have generally not had a significant impact on the global thermal balance of the gas, while the cloud is recognized as a dark cloud.Far ultraviolet photons of the ISRF dominate the chemistry at the dark cloud surface, dissociating and ionizing the molecular gas. This resu...

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Section: Molecular Cloudsupporting

confidence: 87%