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Session 17 - The Galactic Interstellar Gas.
Display session, Monday, January 13
We present high S/N GHRS G140M spectra of the nearby stars Altair (\alpha Aql, A7 V, d = 5.0 pc, l = 48, b = --9), \alpha Cep (A7 V, d = 15 pc, l = 101, b = 9), and \alpha Hyi (F0 V, d = 21 pc, l = 289, b = --54), which were obtained as part of a program to study the onset of chromospheric activity in late-type stars. These three stars are valuable probes of the local interstellar medium because they are of sufficiently early spectral type to have a large rotation (v \sin i > 150 km s^-1), and yet are sufficiently cool to show Ly\alpha in emission. The short line of sight toward Altair is particularly interesting because Ca II and UV absorption line studies have indicated the presence of three distinct interstellar components.
The GHRS spectrum of each star shows a broad Ly\alpha emission cut by interstellar hydrogen and deuterium. We will fit the Ly\alpha profiles to derive column densities and broadening parameters along the lines of sight.
Program listing for Monday