SIMULTANEOUS X-RAY AND ULTRAVIOLET OBSERVATIONS OF THE SW SEXTANTIS STAR DW URSAE MAJORIS
- Spitzer Science Center, California Institute of Technology, MS 220-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States)
- Institute of Astronomy, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
- School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)
- NASA Ames Research Center, Moffett Field, CA 94035 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
We present the first pointed X-ray observation of DW Ursae Majoris, a novalike cataclysmic variable (CV) and one of the archetype members of the SW Sextantis class, obtained with the XMM-Newton satellite. These data provide the first detailed look at an SW Sex star in the X-ray regime (with previous X-ray knowledge of the SW Sex stars limited primarily to weak or non-detections in the ROSAT All Sky Survey). It is also one of only a few XMM-Newton observations (to date) of any high mass transfer rate novalike CV, and the only one in the evolutionarily important 3-4 hr orbital period range. The observed X-ray spectrum of DW UMa is very soft, with {approx}95% of the detected X-ray photons at energies <2 keV. The spectrum can be fit equally well by a one-component cooling flow model, with a temperature range of 0.2-3.5 keV, or a two-component, two-temperature thermal plasma model, containing hard ({approx}5-6 keV) and soft ({approx}0.8 keV) components. The X-ray light curve of DW UMa shows a likely partial eclipse, implying X-ray reprocessing in a vertically extended region, and an orbital modulation, implying a structural asymmetry in the X-ray reprocessing site (e.g., it cannot be a uniform corona). We also obtained a simultaneous near-ultraviolet light curve of DW UMa using the Optical Monitor on XMM-Newton. This light curve is similar in appearance to published optical-UV light curves of DW UMa and shows a prominent deep eclipse. Regardless of the exact nature of the X-ray reprocessing site in DW UMa, the lack of a prominent hard X-ray total eclipse and very low fraction of high energy X-rays point to the presence of an optically and geometrically thick accretion disk that obscures the boundary layer and modifies the X-ray spectrum emitted near the white dwarf.
- OSTI ID:
- 21443201
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 140, Issue 5; Other Information: DOI: 10.1088/0004-6256/140/5/1313; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ACCRETION DISKS
BOUNDARY LAYERS
ECLIPSE
FLOW MODELS
HARD X RADIATION
MASS TRANSFER
NOVAE
PHOTONS
SATELLITES
ULTRAVIOLET RADIATION
WHITE DWARF STARS
X-RAY SPECTRA
BINARY STARS
BOSONS
DWARF STARS
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ERUPTIVE VARIABLE STARS
IONIZING RADIATIONS
LAYERS
MASSLESS PARTICLES
MATHEMATICAL MODELS
RADIATIONS
SPECTRA
STARS
VARIABLE STARS
X RADIATION