A Closer Look at Some Gas-Phase Depletions in the ISM: Trends for O, Ge, and Kr vs. $F_{\ast }$, $f({\mathrm{H}}_2)$, and Starlight Intensity

Abstract

In a survey of archived ultraviolet spectra of 100 stars recorded by the echelle spectrograph of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), we measure the strengths of the weak absorption features of O I, Ge II and Kr I in the interstellar medium. Our objective is to undertake an investigation that goes beyond earlier abundance studies to see how these elements are influenced independently by three different environmental properties: (1) values of a generalized atomic depletion factor $F_{\ast }$ due to condensations onto dust grains (revealed here by the abundances of Mg and Mn relative to H), (2) the fraction of H atoms in the form of molecular hydrogen, $f({\mathrm{H}}_2)$, and (3) the ambient intensity $I$ of ultraviolet starlight relative to an average value in our part of the Galaxy $I_0$. As expected, the gas-phase abundances of all three elements exhibit negative partial correlations with $F_{\ast }$. The abundances of free O atoms show significant positive partial correlations with log $f({\mathrm{H}}_2)$ and $\log (I/I_0)$, while Ge and Kr exhibit negative partial correlations with $\log (I/I_0)$ at marginal levels of significance. After correcting for these trends, the abundances of O relative to H show no significant variations with location, except for the already-known radial gradient of light-element abundances in the Milky Way. A comparison of Ge and O abundances revealed no significant regional enhancements or deficiencies of neutron-capture elements relative to alpha-process ones.

77 pages, 10 figures, page 40 onwards contains a long table that most readers may wish to disregard. Accepted for publication in the Astrophysical Journal

References in corpus (15)

• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Distances to Galactic high-velocity clouds. Complex C
• Ubiquitous argonium (ArH${}^{+}$) in the diffuse interstellar medium -- a molecular tracer of almost purely atomic gas
• An Accurate Distance to High-Velocity Cloud Complex C
• The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
• Revisiting the radial abundance gradients of nitrogen and oxygen of the Milky Way
• The Composition of Interstellar Grains Toward Zeta Ophiuchi: Constraining the Elemental Budget Near the Diffuse-Dense Cloud Transition
• The Fractional Ionization of the Warm Neutral Interstellar Medium
• New measurements on water ice photodesorption and product formation under ultraviolet irradiation
• ArH2+ and NeH2+ as Global Minima in the Ar+/Ne+ + H2 Reactions: Energetic, Spectroscopic, and Structural Data
• Interstellar Krypton Abundances: The Detection of Kiloparsec-scale Differences in Galactic Nucleosynthetic History
• Observational Properties of Rotationally Excited Molecular Hydrogen In Translucent Lines of Sight
• Abundances and Depletions of Neutron-Capture Elements in the Interstellar Medium

Cited by in corpus (11)

• Large Metallicity Variations in the Galactic Interstellar Medium
• The Origin of Galactic Cosmic Rays as Revealed by their Composition
• A Far Ultraviolet Spectroscopic Explorer Survey of Interstellar Molecular Hydrogen in the Galactic Disk
• Water and Methanol Ice in L1544
• Interstellar Extinction and Elemental Abundances
• The Distribution of Metallicities in the Local Galactic Interstellar Medium
• A High Precision Survey of the D/H Ratio in the Nearby Interstellar Medium
• Interstellar Extinction and Elemental Abundances: Individual Sight Lines
• A Reexamination of Phosphorus and Chlorine Depletions in the Diffuse Interstellar Medium
• Gas-phase condensation of carbonated silicate grains
• Investigation of the nature of the wind interaction in HD93205 based on multi-epoch X-ray observations