SIMULTANEOUS X-RAY AND ULTRAVIOLET OBSERVATIONS OF THE SW SEXTANTIS STAR DW URSAE MAJORIS

Journal Article · Mon Nov 15 04:00:00 EST 2010 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/140/5/1313· OSTI ID:21443201

Hoard, D W; Wachter, S ^[1]; Lu, Ting-Ni ^[2]; Knigge, Christian ^[3]; Homer, Lee; Szkody, Paula ^[4]; Still, M ^[5]; Long, Knox S ^[6]

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1. Spitzer Science Center, California Institute of Technology, MS 220-6, 1200 E. California Blvd., Pasadena, CA 91125 (United States)
2. Institute of Astronomy, National Tsing Hua University, Hsinchu 30013, Taiwan (China)
3. School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
4. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)
5. NASA Ames Research Center, Moffett Field, CA 94035 (United States)
6. 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), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 5 Vol. 140; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BINARY STARS
BOSONS
BOUNDARY LAYERS
DWARF STARS
ECLIPSE
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
ERUPTIVE VARIABLE STARS
FLOW MODELS
HARD X RADIATION
IONIZING RADIATIONS
LAYERS
MASS TRANSFER
MASSLESS PARTICLES
MATHEMATICAL MODELS
NOVAE
PHOTONS
RADIATIONS
SATELLITES
SPECTRA
STARS
ULTRAVIOLET RADIATION
VARIABLE STARS
WHITE DWARF STARS
X RADIATION
X-RAY SPECTRA