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Title:
Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359
Authors:
Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin
Affiliation:
AA(Massachusetts Institute of Technology, Cambridge, MA, US), AB(Massachusetts Institute of Technology, Cambridge, MA, US), AC(University of Wisconsin-Madison, Madison, WI, US)
Publication:
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 2, p. 672-681 (ApJ Homepage)
Publication Date:
02/1995
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
Abundance, Data Reduction, Galactic Halos, Interstellar Gas, Milky Way Galaxy, Ion Concentration, Kinematics, Spectrographs, Ultraviolet Spectra, Velocity Distribution
DOI:
10.1086/175206
Bibliographic Code:
1995ApJ...439..672S

Abstract

We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II vLSR approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

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