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Pulsations and Accretion Geometry in YY Draconis: A Study Based on Hubble Space Telescope Observations

Haswell, Carole A.; Patterson, Joseph; Thorstensen, John R.; Hellier, Coel and Skillman, David R. (1997). Pulsations and Accretion Geometry in YY Draconis: A Study Based on Hubble Space Telescope Observations. Astrophysical Journal, 476(2) pp. 847–864.

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We present 1 resolution fast ultraviolet spectroscopy of YY Dra, coordinated U, B, V, R, and I photometry, and Hα spectroscopy. The UV continuum is strongly pulsed: we found 16% semiamplitude pulses with period 264.7(1) s; there was no evidence for power at twice this period. The UBV pulses are in phase with the UV continuum pulsation. A color temperature of 105 K was found for the pulse spectrum, with a corresponding area 0.5% of the white dwarf surface. We refine the white dwarf spin period, obtaining Pspin = 529.31 ± 0.02 s. Optical pulses at 273(1) s were also detected; we attribute these to reprocessing in structures fixed in the orbital frame. Variations in the C iv line profile are apparent when the data are folded on Pspin. Faint, broad line wings extending to ±3000 km s−1 appear simultaneously with the continuum pulsation maxima. This implies that accretion was occurring onto both magnetic poles. Consequent constraints on the accretion geometry and white dwarf mass are derived, and a minimum white dwarf mass of 0.62 M is obtained. A color temperature T 30,000 K is derived for the unpulsed emission.

Item Type: Journal Article
ISSN: 1538-4357
Keywords: stars : individual (YY Draconis) È stars : oscillations È ultraviolet : stars È white dwarfs
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 11141
Depositing User: Astrid Peterkin
Date Deposited: 25 Jul 2008 11:25
Last Modified: 14 Jan 2016 17:02
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