Interstellar abundances in dense, moderately reddened lines of sight. I - Observational evidence for density-dependent depletion

Joseph, Charles L.; Snow, Theodore P.; Seab, C. G.; Crutcher, R. M.

doi:10.1086/164647

Cited by 57 publications

(48 citation statements)

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“…We therefore model the evolution of silicate dust independently of carbon dust. Note that, in the present work, we investigate the accretion of refractory elements on the grains thatproceeds prior to the accretion of complex ice mantles and coagulation in dense cores of molecular clouds (e.g., Joseph et al 1986;Weingartner & Draine 1999;Voshchinnikov & Henning 2010).…”

Section: Growth In the Ismmentioning

confidence: 99%

Modeling Dust Evolution in Galaxies With a Multiphase, Inhomogeneous Ism

Zhukovska

Dobbs

Jenkins

et al. 2016

ApJ

151

160

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We develop a model of dust evolution in a multiphase, inhomogeneous interstellar medium (ISM) using hydrodynamical simulations of giant molecular clouds in a Milky Way-like spiral galaxy. We improve the treatment of dust growth by accretion in the ISM to investigate the role of the temperature-dependent sticking coefficient and ion-grain interactions. From detailed observational data on the gas-phase Si abundances Si H ] and the local gas density n H ( )thatwe use as a critical constraint for the models. This relation requires a sticking coefficient that decreases with the gas temperature. The relation predicted by the models reproduces the slope of −0.5 forthe observed relation in cold clouds, which is steeper than that for the warm medium and is explained by dust growth. We find that growth occurs in the cold medium for all adopted values of the minimum grain size a min from 1 to 5nm. ] -n H ( ) relation, and provide a better match to observations. The rates of dust re-formation in the ISM by far exceed the rates of dust production by stellar sources. After the initial 140Myr, the cycle of matter in and out of dust reaches a steady state, in which the dust growth balances the destruction on a similar timescale of 350Myr.

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Section: Growth In the Ismmentioning

confidence: 99%

Modeling Dust Evolution in Galaxies With a Multiphase, Inhomogeneous Ism

Zhukovska

Dobbs

Jenkins

et al. 2016

ApJ

151

160

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“…Therefore, the low value of the correlation coefficient for CH + is not unexpected. Furthermore, note that significant amounts of CH are needed before CN is produced (Federman et al 1984), with the latter tracing also relatively dense material (Joseph et al 1986). Work by Crawford (1989) suggests that the ratio of N(CH + ) and N(CH) is indicative of the turbulent or quiescent nature of the interstellar medium in the line-of-sight.…”

Section: Diatomic Molecules and Dustmentioning

confidence: 99%

Diffuse interstellar bands in Upper Scorpius: probing variations in the DIB spectrum due to changing environmental conditions

Vos

Cox

Kaper

et al. 2011

A&A

177

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Aims. We study the effects of local environmental conditions affecting the diffuse interstellar band (DIB) carriers within the Upper Scorpius subgroup of the Sco OB2 association. The aim is to reveal how the still unidentified DIB carriers respond to different physical conditions prevailing in interstellar clouds, in order to shed light on the origin of the DIB carriers. Methods. We obtained optical spectra with FEROS on the ESO 1.52 m telescope at La Silla, Chile, and measured the equivalent widths of five DIBs (at 5780, 5797, 6196, 6379, and 6613 Å) as well as those of absorption lines of di-atomic molecules (CH, CH + , CN) and atoms (K i, Ca i) towards 89 targets in the direction of Upper Scorpius. We construct a simple radiative transfer and chemical network model of the diffuse interstellar medium (ISM) sheet in front of Upp Sco to infer the effective radiation field. Results. By measuring the DIB and molecular spectrum of diffuse clouds towards 89 sightlines in the Upper Scorpius region, we have obtained a valuable statistical dataset that provides information on the physical conditions that influence the band strengths of the DIBs. Both the interstellar radiation field strength, I UV , and the molecular hydrogen fraction, f H 2 , have been derived for 55 sightlines probing the Upp Sco ISM. We discuss the relations between DIB strengths, CH and CH + line strengths, E (B−V) , I UV , and f H 2 . The ratio between the 5780 and 5797 Å DIBs reveals a (spatial) dependence on the local environment in terms of cloud density and exposure to the interstellar radiation field, reflecting the molecular nature of these DIB carriers.

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“…In diffuse molecular gas, CN is a probe of relatively dense regions (e.g., Joseph et al 1986). A survey of 15 lines of sight with known molecular hydrogen abundances was used to identify the basic reactions which are responsible for the formation of CN in diffuse clouds (Federman et al 1984;Federman & Lambert 1988).…”

Section: Introductionmentioning

confidence: 99%

Interstellar CN toward CH$\mathsf{^+}$-forming regions

Gredel¹,

Forêts²,

Federman³

2002

A&A

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Abstract. Measurements on interstellar CN absorption are presented for stars in three southern OB associations, NGC 2439, Vela OB1, and Cen OB1. CN is detected in 21 out of 31 stars observed. The doublet ratio for the R(1) and P (1) lines of the (0, 0) band of the B 2 Σ + -X 2 Σ + violet system and a comparison of violet system data with measurements of the (1, 0) and (2, 0) bands of the A 2 Π-X 2 Σ + red system are used to derive Doppler parameters and total column densities. Inferred CN column densities vary by more than an order of magnitude for lines of sight with similar CH column densities. Observations of the (0, 0) band of the CH B 2 Σ − -X 2 Π system are used to revise previously published CH column densities toward the lines of sight studied in CN. Together with earlier results on CH, CH + , and C2, the CN data presented here provide a homogeneous set of column densities and radial velocities of diatomic molecules in three individual translucent clouds. We use these data to study CN production via chemical models. Gas densities are inferred from models based on production via CH and C2 in cool gas. Most sightlines in our sample test densities typical for diffuse molecular gas (a few hundred cm −3 ) when the ultraviolet flux permeating the gas is between 1 and 5 times the average interstellar flux. A few lines of sight indicate that CN is produced under dark cloud conditions because relatively large densities are obtained or because this simple chemical scheme is unable to reproduce the observed CN columns. Low densities are indicated for directions with upper limits on CN. We add an ad hoc component of a number of low-velocity (<10 km s −1 ) criss-crossing MHD shocks to explain observed column densities of interstellar CH + . These shocks also produce about 10 to 30% of the total CH column along the line of sight.

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Interstellar abundances in dense, moderately reddened lines of sight. I - Observational evidence for density-dependent depletion

Cited by 57 publications

References 0 publications

Modeling Dust Evolution in Galaxies With a Multiphase, Inhomogeneous Ism

Modeling Dust Evolution in Galaxies With a Multiphase, Inhomogeneous Ism

Diffuse interstellar bands in Upper Scorpius: probing variations in the DIB spectrum due to changing environmental conditions

Interstellar CN toward CH$\mathsf{^+}$-forming regions

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