Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...441..806a&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 441, no. 2, p. 806-820
Astronomy and Astrophysics
Astrophysics
10
Absorption Spectra, Accretion Disks, Balmer Series, Eclipsing Binary Stars, Emission Spectra, H Alpha Line, Orbital Elements, Radial Velocity, Spectrum Analysis, Stellar Envelopes
Scientific paper
U Sagittae (U Sge = HD 181182) belongs to the group of short-period Algol-type binaries which have orbital periods P less than 5-6 days. One hundred and forty H-alpha spectra obtained at Kitt Peak National Observatory (KPNO) show evidence of weak emission components in the wings of the line profile which are rarely strong enough to extend above the continuum flux level. However, Balmer line emission with a strength of approximately 2% of the continuum flux was seen above the continuum at one phase near mid-primary eclipse; the first such detection in over 40 years. The observed emission components were enhanced by subtracting the photospheric H-alpha absorption profiles of the stars from the observed line profiles. The resulting H-alpha difference profiles of U Sge revealed the presence of double-peaked emission features at most phases outside of primary eclipse, and excess absorption at phases throughout primary eclipse. The strength of these absorption/emission features was typically within approximately 16% of the quadrature continuum flux. The double-peaked emission features indicate the presence of a transient accretion disk in U Sge. The radius of the trailing side of the disk was determined to be 1.68 +/- 0.1 ORA with electron density Ne greater than or = 8 x 1010/cu cm, and mass M less than or = 8 x 10-12 solar mass. These measurements were made during an epoch of enhanced mass transfer. The gas distribution in the disk was found to be highly variable in just a few orbital cycles.
Albright Geary E.
Richards Mercedes T.
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