Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989a%26a...208..201v&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 208, no. 1-2, Jan. 1989, p. 201-207. Previously announced in STAR as N89-10741
Astronomy and Astrophysics
Astronomy
6
Binary Stars, Iue, Lyman Alpha Radiation, Spaceborne Astronomy, Stellar Activity, Stellar Rotation, Ultraviolet Astronomy, Ultraviolet Spectra, Interstellar Extinction, Light Curve, Stellar Atmospheres, Stellar Orbits
Scientific paper
Observations with IUE that cover the entire 6.4 hr orbital cycle of the late-type contact binary 44i Bootis are presented. Intrinsic stellar hydrogen Lyman alpha emission flux was determined from low-resolution IUE spectra, compensating for geocoronal emission and for interstellar absorption. The variation of the stellar Lyman alpha emission flux correlates well with the variation of the CII and CIV emission fluxes, and shows orbital modulation in phase with the visual light curve. The ratio of Lyman alpha to CII flux (15 to 20) is similar to that observed in solar active regions. Hydrogen Lyman alpha emission is thus one of the most important cooling channels in the outer atmosphere of 44i Boo. A high-resolution spectrum of the Lyman alpha line was obtained between orbital phases 0.0 and 0.6. The integrated flux in the observed high-resolution Lyman alpha profile is consistent with the fluxes determined using low-resolution spectra, and the composite profile indicates that both components of this binary have equally active chromospheres and transition regions. The uncertainty in the interstellar hydrogen column density cannot mimic the observed variation in the integrated Lyman alpha flux, because the stellar line is very much broader than the interstellar absorption.
Neff James E.
Rahunen T.
Vilhu Osmi
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