Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...440..241c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 440, no. 1, p. 241-253
Astronomy and Astrophysics
Astronomy
33
Absorption Spectra, Abundance, Atomic Spectra, Galactic Halos, High Resolution, Interstellar Gas, Line Spectra, Ultraviolet Astronomy, Ultraviolet Spectra, Astronomical Spectroscopy, Chromium, Iron, Magnesium, Silicon, Spectrographs, Zinc
Scientific paper
We present high-resolution (3.5 km/s) Goddard High Resolution Spectrograph (GHRS) measurements of the Mg II, Si II, Cr II, Fe II, and Zn II lines toward HD 167756, a low-latitude halo star at a distance of 4 kpc in the direction l = 351.5 deg, b = -12.3 and at a Galactic altitude of z = -0.85 kpc. Supplemental Na I, Ca II, and H I data are also presented for comparison with the UV lines. Our analysis centers on converting the observed absoprtion-line data into measures of the apparent column density per unit velocity. Na(v), over the velocity range -25 less than or = vlsr less than 30 km/s for each species observed. We use these Na(v) profiles to construct logarithmic abundance ratios of Mg II, Si II, Cr II, Fe II, and Ca II relative to Zn II, normalized to solar abundances, as a function of velocity. Compared to Zn, these species show an underabundance relative to their solar values, with the largest underabundances occurring in the vlsr approximately equals 5 km/s component(s), for which we find logarithmic abundances ASi/Zn greater than -0.38, A(Mg/Zn) = -0.82, ACr/Zn = -1.18, and AFe/Zn greater than 1.40 dex. We show that ionization effects, abundance gradients, or intrinsic abundance variability cannot be significant sources for the underabundances observed. The most likely explanation is gas phase depletion of elements onto dust grains. Comparisons with the gas phase abundances along other diffuse, warm gas sight lines, like the halo sight line to HD 93521, support this interpretation as do the derived physical properties of the sight line.
Cardelli Jason A.
Savage Blair. D.
Sembach Kenneth Russell
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