Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...19915805a&link_type=abstract
American Astronomical Society, 199th AAS Meeting, #158.05; Bulletin of the American Astronomical Society, Vol. 34, p.567
Astronomy and Astrophysics
Astronomy
Scientific paper
The broad coverage, high sensitivity, and precise wavelength calibration of the Space Telescope Imaging Spectrograph's E140M medium-resolution echelle mode make it ideal for studies of broadly dispersed spectral features, such as molecular band systems, in the 1150--1700 Å far-UV interval. The present work focuses on the B--X electronic rovibration bands of H 2, which can be radiatively pumped by H I λ 1215 Lyα resonance emission in stellar environments where cold molecular gas (T< 4000 K) is irradiated by hotter, chromospheric (T ~ 104 K) material. We compare three very different stellar objects whose only common feature appears to be extensive fluoresced H 2 bands: The 10 Gyr old red giant Arcturus (α Bootis; K2 III); the 10 Myr young T-Tauri star TW Hya; and the enigmatic accretion/wind source Mira B, which apparently was caught in a low state during the 1999 August STIS observations. We discuss implications of spectral differences among these objects concerning physical properties (temperatures and column densities) in the different environments where the molecular hydrogen is pumped (stellar ``COmosphere,'' PMS accretion disk, and wind-shock interaction zone), as well as intrinsic profiles of the Lyα irradiation field, which can be deduced free from the usual strong interstellar absorption that affects the H I emission core. This work was supported by STScI grant GO-08614.02-02A to the University of Colorado, and NASA grant S-56500-D to NIST and CU. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555.
Ayres Thomas R.
Herczeg Gregory J.
Linsky Jeffrey L.
Wood Brian E.
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