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Record 36 of 2659
Gas kinematics and ionization along the extended sight line to HD 116852
External Online Source: doi:10.1086/174478
Author and Affiliation:
Sembach, Kenneth R.(Massachusetts Inst. of Technology, Cambridge, MA, United States)
Savage, Blair D.(Univ. of Wisconsin-Madison, Madison, WI, United States)
Abstract: We present Goddard High-Resolution Spectrograph intermediate observations of the interstellar medium toward HD 116852, a low halo star at a distance of 4.8 kpc (z = -1.3 kpc) in the direction l = 304. deg 9, b = 16.deg 1. The small science aperture observations have signal-to-noise ratios ranging from 30 to 90 and resolutions of 11 to 18 km/s (FWHM). We confirm the optical MK classification of this star through an analysis of its ultraviolet photosperic and stellar wind profiles. We detect interstellar lines of Al III, Si IV, C IV, and N V together with lines of C I, C I*, C I**, Si II, Ge II, P II, and Ni II. We convert the Mg II, P II, S II, Al III, Si IV, C IV, and N V profiles into measure of apparent column density as a function of LSR velocity. Gas scale height, velocity dispersion, and differential Galactic rotation effects govern the profile shapes. A simple computer model of the expected sight line column density profiles for the low and high ion species indicates that the gas velocity dispersions and scale heights increase as the ionization level of the gas increases. We find scale heigts H greater than or = 1 kpc for the high ions, which are comparable to the z-distance of the star, whereas we find H approximatley = 0.6 to 0.7 kpc for A1 III and H approximatley 0.1 kpc for P II and Ge II. An enhancement in the Al II profile near -15 km/s accounts for approximately 25% of the A1 III column along the sight line and probably arises within gas located approximately 500 pc below the Sagittarius-Carina spiral arm link. Portions of the broad underlying A1 III distribution are associated with the higher ionization lines, perhaps in conductive interfaces. The presence of N V and the column density ratios of Si IV, C IV, and N V favor the interpretation that much of the high ion absorption is produced by collisional ionization in gas with T = 1-3 x 10(exp 5) K. An enhancement near -35 km/s in both the Si IV and C IV profiles may be due to an outflow from the Norma spiral arm at a z-distance of about -1 kpc. The smooth decrease of the N(C IV)/N(Si IV) ratio at negative velocities may be due to an ISM ionization structure for hot gas that changes distance from the Galactic plane or to a two phase gas distribution in which the relative contribution from each phase changes with distance from the Galactic plane.
Publication Date: Aug 10, 1994
Document ID:
19950030860
(Acquired Dec 28, 1995)
Accession Number: 95A62459
Subject Category: ASTROPHYSICS
Document Type: Journal Article
Publication Information: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 431; 1; p. 201-222
Publisher Information: United States
Contract/Grant/Task Num: NAS5-26555; NAG5-1852
Financial Sponsor: NASA; United States
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Description: 22p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: ABSORPTION SPECTRA; ABUNDANCE; GALACTIC HALOS; INTERSTELLAR MATTER; IONIZED GASES; PHOTOIONIZATION; DENSITY DISTRIBUTION; GALACTIC ROTATION; SIGNAL TO NOISE RATIOS; SOLAR WIND; STELLAR COMPOSITION
Imprint And Other Notes: The Astrophysical Journal, Part 1 vol. 431, no. 1 p. 201-222 August 10, 1994
Availability Source: Other Sources
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