The Mg II and Lyman-alpha Lines of Nearby K Dwarfs: ISM Components and Flux Measurements

Abstract

We analyze local ISM absorption observed in the Lyman-alpha and Mg II h & k lines of six nearby K dwarf stars, using UV spectra of these stars obtained with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. For four of the six stars, we detect an absorption component with a velocity and column density consistent with the Local Interstellar Cloud (LIC). For HD 197890, there is no observed component at the expected LIC velocity, or at the projected velocity of the G cloud, which is a nearby cloud in the general direction of the Galactic Center. It also seems doubtful that either of the two components seen toward HD 82558 are LIC or G cloud absorption. The total H I column density toward HD 82558 (d=18.3 pc) is extremely high (log N(H)=19.05 +/- 0.15), representing the largest average H I density detected for any line of sight through the nearby LISM (n(H)=0.2 cm^-3). This is particularly remarkable considering that this star is only 39 degrees from the "interstellar tunnel" toward Epsilon CMa, where column densities are an order of magnitude lower than this toward stars which are an order of magnitude farther away.

23 pages, 4 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by ApJ

References in corpus (3)

• The Ionization of the Local Interstellar Medium, as Revealed by FUSE Observations of N, O and Ar toward White Dwarf Stars
• Heliospheric, Astrospheric, and Insterstellar Lyman-alpha Absorption Toward 36 Oph
• The D/H Ratio in Interstellar Gas Towards G191-B2B

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