CHANDRA HIGH-ENERGY TRANSMISSION GRATING SPECTRUM OF AE AQUARII

Journal Article · Fri Nov 20 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/706/1/130· OSTI ID:21378219

Mauche, Christopher W., E-mail: [e-mail] ^[1]

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1. Lawrence Livermore National Laboratory, L-473, 7000 East Avenue, Livermore, CA 94550 (United States)

The nova-like cataclysmic binary AE Aqr, which is currently understood to be a former supersoft X-ray binary and current magnetic propeller, was observed for over two binary orbits (78 ks) in 2005 August with the High-Energy Transmission Grating (HETG) on board the Chandra X-ray Observatory. The long, uninterrupted Chandra observation provides a wealth of details concerning the X-ray emission of AE Aqr, many of which are new and unique to the HETG. First, the X-ray spectrum is that of an optically thin multi-temperature thermal plasma; the X-ray emission lines are broad, with widths that increase with the line energy from sigma approx 1 eV (510 km s{sup -1}) for O VIII to sigma approx 5.5 eV (820 km s{sup -1}) for Si XIV; the X-ray spectrum is reasonably well fit by a plasma model with a Gaussian emission measure distribution that peaks at log T(K) = 7.16, has a width sigma = 0.48, an Fe abundance equal to 0.44 times solar, and other metal (primarily Ne, Mg, and Si) abundances equal to 0.76 times solar; and for a distance d = 100 pc, the total emission measure EM = 8.0 x 10{sup 53} cm{sup -3} and the 0.5-10 keV luminosity L{sub X} = 1.1 x 10{sup 31} erg s{sup -1}. Second, based on the f/(i + r) flux ratios of the forbidden (f), intercombination (i), and recombination (r) lines of the Healpha triplets of N VI, O VII, and Ne IX measured by Itoh et al. in the XMM-Newton Reflection Grating Spectrometer spectrum and those of O VII, Ne IX, Mg XI, and Si XIII in the Chandra HETG spectrum, either the electron density of the plasma increases with temperature by over three orders of magnitude, from n {sub e} approx 6 x 10{sup 10} cm{sup -3} for N VI [log T(K) approx 6] to n {sub e} approx 1 x 10{sup 14} cm{sup -3} for Si XIII [log T(K) approx 7], and/or the plasma is significantly affected by photoexcitation. Third, the radial velocity of the X-ray emission lines varies on the white dwarf spin phase, with two oscillations per spin cycle and an amplitude K approx 160 km s{sup -1}. These results appear to be inconsistent with the recent models of Itoh et al., Ikhsanov, and Venter and Meintjes of an extended, low-density source of X-rays in AE Aqr, but instead support earlier models in which the dominant source of X-rays is of high density and/or in close proximity to the white dwarf.

• OSTI ID: 21378219
• Journal Information: Astrophysical Journal, Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/130; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
ELECTRON DENSITY
EMISSION
METALS
NOVAE
ORBITS
PLASMA
RADIAL VELOCITY
RECOMBINATION
SPECTROMETERS
TRIPLETS
WHITE DWARF STARS
X-RAY SPECTRA
BINARY STARS
DWARF STARS
ELEMENTS
ERUPTIVE VARIABLE STARS
MEASURING INSTRUMENTS
MULTIPLETS
SPECTRA
STARS
VARIABLE STARS
VELOCITY