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

By B. Wood, S. Redfield, J. Linsky, H. Mueller, Gary Zank. 2005

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We search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lyα emission lines, our primary purpose being to look for new detections of Lyα absorption from the outer heliosphere and to also search for analogous absorption from the astrospheres surrounding the observed stars. The astrospheric absorption is of particular interest because it can be used to study solar-like stellar winds that are otherwise undetectable. We find and analyze 33 HST Lyα spectra in the archive. All the spectra were taken with the E140M grating of the Space Telescope Imaging Spectrograph (STIS) instrument on board HST. The HST STIS spectra yield four new detections of heliospheric absorption (70 Oph, ξ Boo, 61 Vir, and HD 165185) and seven new detections of astrospheric absorption (EV Lac, 70 Oph, ξ Boo, 61 Vir, δ Eri, HD 128987, and DK UMa), doubling the previous number of heliospheric and astrospheric detections. When combined with previous results, 10 of 17 lines of sight within 10 pc yield detections of astrospheric absorption. This high detection fraction implies that most of the ISM within 10 pc must be at least partially neutral, since the presence of H I within the ISM surrounding the observed star is necessary for an astrospheric detection. In contrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond 10 pc. Our Lyα analyses provide measurements of ISM H I and D I column densities for all 33 lines of sight, and we discuss some implications of these results. Finally, we measure chromospheric Lyα fluxes from the observed stars. We use these fluxes to determine how Lyα flux correlates with coronal X-ray and chromospheric Mg II emission, and we also study how Lyα emission depends on stellar rotation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/b9296d7d78033833f44d26db7ecfe913ee18ddbb

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Citations in the corpus

• THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS (2012, background): “However, as shown by Wood et al. (2005), neutral interstellar hydrogen columns rarely exceed log10 N(HI) = 18.5 cm −2 for stars nearer than 50 pc.”
• High stellar FUV/NUV ratio and oxygen contents in the atmospheres of potentially habitable planets (2013, background): “However, no Lyman-α (1216 Å) data were available except for 4 active M dwarfs (Wood et al., 2005).”
• TESTING A PREDICTIVE THEORETICAL MODEL FOR THE MASS LOSS RATES OF COOL STARS (2011, methodology): “If instead these values were used, our modeled mass loss rates would be in better agreement with the astrospheric observations of Wood et al. (2005a).”
• THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, background): “Additionally, it is likely that the stellar mass-loss rates are higher earlier in their evolution (Wood et al. 2005a), increasing the potential planetary mass-loss.”
• A CORRELATION BETWEEN STELLAR ACTIVITY AND HOT JUPITER EMISSION SPECTRA (2010, methodology): “We address this issue by selecting a sample of 26 stars with effective temperatures between 5000 − 6000 K observed in Lyman α by the Hubble Space Telescope STIS instrument and its precursor GHRS as described in Wood et al. (2005).”
• PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR (2008, background): “FUV radiation now stems only from stellar chromospheric activity and scales with the X-ray luminosity (Wood et al. 2005).”
• Evaporation of the planet HD 189733b observed in H I Lyman-α (2010, methodology): “Using the results of Wood et al. (2005) and a distance of 19.3 pc for HD 189733b, we infer an H i column of density, NHI, of about 10 18.3 cm−2.”
• The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present (2016, methodology): “The same base spectrum was used by Wood et al. (2005) to estimate the intrinsic H Lyα stellar line profile and the integration results in a flux of 130 erg s−1 cm−2 at the orbital distance of Proxima b.”