Interstellar Carbon in Translucent Sight Lines

By U. Sofia, J. Lauroesch, D. Meyer, S. Cartledge. 2004

178 citations recorded by the source corpus.

We report interstellar C II column densities or upper limits determined from weak absorption of the 2325.4029 Å intersystem transition observed in six translucent sight lines (AV ≳ 1) with the Space Telescope Imaging Spectrograph (STIS). The sight lines sample a wide range of interstellar characteristics, including total to selective extinction, RV = 2.6-5.1; average hydrogen density along the sight line, ⟨n(H)⟩ = 3-14 cm-3; and fraction of H in molecular form, 0-~40%. Four of the sight lines, those toward HD 37021, HD 37061, HD 147888, and HD 207198, have interstellar gas-phase abundances that are consistent with the diffuse sight line ratio of 161 ± 17 carbon atoms in the gas per million hydrogen nuclei. We note that while it has a gas-phase carbon abundance that is consistent with the other sight lines, a large fraction of the C II toward HD 37061 is in an excited state. The sight line toward HD 152590 has a measured interstellar gas-phase carbon abundance that is well above the diffuse sight line average; the column density of C in this sight line may be overestimated because of noise structure in the data. Toward HD 27778 we find a 3 σ abundance upper limit of ≤108 C atoms in the gas per million H, a substantially enhanced depletion of C as compared to the diffuse sight line value. The interstellar characteristics toward HD 27778 are otherwise not extreme among the sample, except for an unusually large abundance of CO molecules in the gas.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/946c56fbec96a8e1727fcb03da35a1edb82fe224

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In Astronomy and Astrophysics

1. Mark R. Krumholz
2. Simon Bruderer
3. S. Glover
4. E. Dishoeck
5. Ralf Klessen
6. C. McKee
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In Atmospheric Science

1. Simon Bruderer
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8. E. Peeters

Citations in the corpus

• HERSCHEL SURVEY OF GALACTIC OH+, H2O+, AND H3O+: PROBING THE MOLECULAR HYDROGEN FRACTION AND COSMIC-RAY IONIZATION RATE (2014, background): “In determining fH2 we take xe = 1.5 × 10−4 (assuming xe = x(C+); Cardelli et al. 1996; Sofia et al. 2004) and T = 100 K (typical value of the H i spin temperature) in computing the various reaction rate coefficients.”
• The chemical composition of the Sun (2009, background): “The local abundances of the volatile elements C (Sofia et al. 2004), N (Jensen, Rachford & Snow 2007) and O (Cartledge et al. 2006, Jensen, Rachford & Snow 2005) in the interstellar medium support our recommended solar values in general.”
• Hot and Diffuse Clouds near the Galactic Center Probed by Metastable H3+ (2005, background): “The gas phase carbon to hydrogen ratio after depletion in the solar vicinity, (nC/nH)SV = 1.6 × 10 −4 (Sofia et al. 2004), is multiplied by RX = (nC/nH)GC/(nC/nH)SV which takes into account the higher carbon to hydrogen ratio near the Galactic center than in the solar vicinity.”
• A UNIFIED REPRESENTATION OF GAS-PHASE ELEMENT DEPLETIONS IN THE INTERSTELLAR MEDIUM (2009, background): “The paucity of data for C in our survey toward distant stars can be traced to the need to observe a weak intersystem transition at 2325 Å (Sofia et al. 2004) at a high S/N, since the allowed transi- tions at 1036 and 1335 Å are always strongly saturated.”
• INVESTIGATING THE COSMIC-RAY IONIZATION RATE IN THE GALACTIC DIFFUSE INTERSTELLAR MEDIUM THROUGH OBSERVATIONS OF H+3 (2011, background): “For all other sight lines, the average fractional abundance measured in various diffuse clouds, x(C+) ≈ 1.5 × 10−4 (Cardelli et al. 1996; Sofia et al. 2004), is adopted for xe.”
• [Si II], [Fe II], [C II], and H2 Emission from Massive Star-forming Regions (2006, methodology): “We have calculated the expected ratio based on updated collision strengths and new measurements of the relative abundances of nitrogen and carbon (Sofia et al. 2004; Meyer et al. 1997) and find that k50% of the [C ii] emission arises from neutral gas exposed to FUV radiation (M. G. Wolfire et al.…”
• The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “In the diffuse ISM, Article published by EDP Sciences A91, page 1 of 28 about 40−60% of the carbon is locked into amorphous carbon grains (Savage & Sembach 1996; Sofia et al. 2004, 2011).”
• THE DARK MOLECULAR GAS (2010, methodology): “We adopt the gas phase carbon abundance AC = 1.6×10−4 from Sofia et al. (2004), where AC = nC/n and where nC is the gas phase number density of elemental carbon and n is the number density of H nuclei.”
• Cool outflows in galaxies and their implications (2020, background): “For optically thick emission from a self-gravitating cloud (or an ensemble of clouds), where the velocity dispersion is a reflection of self-gravity, the mass-tolight ratio of the ground rotational transition has been calibrated to be αCO ≈ 4.4 M (K km s−1 pc2) −1 for large (Mmol > 105 M ) Giant Mol”
• The CO-to-H2 Conversion Factor (2013, background): “For a Milky Way gas phase carbon abundance, and assuming all gas-phase carbon is locked in CO molecules, ZCO ≈ 3.2 × 10−4 (Sofia et al. 2004).”
• Variations of the Mid-IR Aromatic Features inside and among Galaxies (2008, methodology): “We adopt the values given in Table 3 and assume that the electrons result from photoionization of carbon and that all the gasphase carbon is ionized in PDRs, so that ne ’ C=Hð ÞnH ’ 1:6 ; 10 4nH; ð4Þ where we have adopted the carbon abundance by Sofia et al. (2004).”