Stellar Lyα Emission Lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres

We search the Hubble Space Telescope (HST) archive for previously unanalyzedobservations of stellar H I Lyman-alpha emission lines, our primary purposebeing to look for new detections of Lyman-alpha absorption from the outerheliosphere, and to also search for analogous absorption from the astrospheressurrounding the observed stars. The astrospheric absorption is of particularinterest because it can be used to study solar-like stellar winds that areotherwise undetectable. We find and analyze 33 HST Lyman-alpha spectra in thearchive. All the spectra were taken with the E140M grating of the SpaceTelescope Imaging Spectrograph (STIS) instrument on board HST. The HST/STISspectra yield 4 new detections of heliospheric absorption (70 Oph, Xi Boo, 61Vir, and HD 165185) and 7 new detections of astrospheric absorption (EV Lac, 70Oph, Xi Boo, 61 Vir, Delta Eri, HD 128987, and DK UMa), doubling the previousnumber of heliospheric and astrospheric detections. When combined with previousresults, 10 of 17 lines of sight within 10 pc yield detections of astrosphericabsorption. This high detection fraction implies that most of the ISM within 10pc must be at least partially neutral, since the presence of H I within the ISMsurrounding the observed star is necessary for an astrospheric detection. Incontrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond10 pc. Our Lyman-alpha analyses provide measurements of ISM H I and D I columndensities for all 33 lines of sight, and we discuss some implications of theseresults. Finally, we measure chromospheric Lyman-alpha fluxes from the observedstars. We use these fluxes to determine how Lyman-alpha flux correlates withcoronal X-ray and chromospheric Mg II emission, and we also study howLyman-alpha emission depends on stellar rotation.Comment: 56 pages, 15 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by ApJ