High-Velocity Gas in GHRS Spectra of Three OB Stars
1996; IOP Publishing; Volume: 468; Linguagem: Inglês
10.1086/177690
ISSN1538-4357
AutoresJ. Trapero, D. E. Welty, L. M. Hobbs, J. T. Lauroesch, D. C. Morton, Lyman Spitzer, D. G. York,
Tópico(s)Astronomy and Astrophysical Research
Resumoview Abstract Citations (26) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Velocity Gas in GHRS Spectra of Three OB Stars Trapero, Joaquin ; Welty, D. E. ; Hobbs, L. M. ; Lauroesch, J. T. ; Morton, D. C. ; Spitzer, L. ; York, D. G. Abstract In Hubble Space Telescope (HST) GHRS spectra of the B1 V star 23 Ori, we observed interstellar absorption lines of C II, C 11*, Mg II, Al II, Al III, Si II, Si III, and S II at a heliocentric radial velocity of about -100 km s-1. Lines of N I, O I, and Fe II that normally are strongly saturated in low-velocity interstellar gas were not detected at all in the high-velocity gas, apparently owing to collisional ionization of these species. Echelle exposures of the Mg II λ2800 doublet resolved those high-velocity features into four blended line components. The widths of the partially resolved components require upper limits Tmax ≤ 12,000 K, while the ionization balance of the gas is crudely characteristic of collisional ionizational equilibrium near Tmax = 25,000 K. With a total column density N(H) ≈6 x 1017 cm-2, these high-velocity clouds appear to consist of warm, ionized gas, which is now cooling after having been previously shocked; the gas is over-ionized with respect to its temperature and has not yet reached a steady-state equilibrium. Comparable spectra of the O9 Ib star τ CMa revealed high-velocity interstellar clouds with properties generally similar to those of the 23 Ori clouds, except for a much smaller total column density of N(H) ≈ 1 x 1017 cm-2. Similar spectra of the B7 III star η Tau showed absorption lines at heliocentric radial velocities of -149 and - 42 km s-1. Each absorbing region produces detectable, narrow absorption lines of C II, C II*, Mg II, Al II, and Si HI, although not of N I, O I, S II, and Fe II. The λ1335 C 11* lines from the excited J = 3/2 level are much stronger than the λ1334 C II lines from the ground level, even when uncertainties in the interpolated stellar continuum are taken into account. The suprathermal C II* excitation seen in both high-velocity regions arises in the spectrum of a relatively nearby star, which also is a close binary. These circumstances suggest that the absorption lines observed at high velocity are formed in matter flowing within or near the binary system, and that optical pumping by η Tau may produce the high-C II excitation found in this circumstellar gas. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177690 Bibcode: 1996ApJ...468..290T Keywords: ISM: ABUNDANCES; ISM: KINEMATICS AND DYNAMICS; STARS: EARLY-TYPE; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (13) MAST (1) ESA (1)
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