Updated Spin Ephemeris for the Cataclysmic Variable EX Hydrae [electronic resource].
- Washington, D.C. : United States. Dept. of Energy, 2009. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
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- PDF-file: 7 pages; size: 0.2 Mbytes
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- Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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- Free-to-read Unrestricted online access
- Recent satellite observations demonstrate that the phase of maximum flux of the 67 min spin modulation of the white dwarf in the cataclysmic variable EX Hya is drifting away from the optical quadratic ephemeris of Hellier & Sproats (1992, hereafter HS92). Relative to that ephemeris, the peak of the spin-phase extreme ultraviolet (EUV) flux modulation measured with the Extreme Ultraviolet Explorer (EUVE) was φ₆₇ = 0.040 ± 0.002 in 1994 May (Mauche 1999) and φ₆₇ = 0.115 ± 0.001 in 2000 May (Belle et al. 2002). Similarly, the peak of the spin-phase X-ray flux modulation measured with the Chandra X-ray Observatory was φ₆₇ ≈ 0.1 in 2000 May (Hoogerwerf, Brickhouse, & Mauche 2004) and φ₆₇ ≈ 0.2 in 2007 May (Luna, Brickhouse, & Mauche 2008). Because the discrepancy between the observed O and calculated C phases of the spin-phase flux modulation of EX Hya is now approaching a significant fraction of a spin cycle, we have undertaken the task of updating the ephemeris. Toward that end, we have combined the optical data of Vogt, Krzeminski, & Sterken (1980, hereafter VKS80), Gilliland (1982), Sterken et al. (1983), Hill & Watson (1984), Jablonski & Busko (1985), Bond & Freeth (1988), HS92, Walker & Allen (2000), and Belle et al. (2005) with the optical, EUV, and X-ray data listed in Table 1. The optical data were obtained by CS at ESO La Silla using the Danish 1.5-m telescope and the DFOSC CCD camera. Differential V-band magnitudes were obtained by aperture photometry extracted from flat-fielded and bias-corrected CCD frames. Other than the EXOSAT and Ginga data, which have been taken from the given references, all other times of spin maximum in the table have been derived by us from the various datasets. In the processes, we have corrected an error in the (spin and orbit) phases of the ASCA data published by Ishida, Mukai, & Osborne (1994) and the RXTE data published by Mukai et al. (1998). We note that our result for the second EUVE observation agrees within the errors with the result derived independently by Belle et al. (2002). Table 1 lists the observed times of spin maximum in Barycentric Julian Date, the corresponding cycle number derived from the HS92 quadratic ephemeris, and the O-C residuals relative to the VKS80 linear ephemeris, the HS92 quadratic ephemeris, and our cubic ephemeris (eqn. 1).
- Published through SciTech Connect., 01/23/2009., "llnl-jrnl-410535", Information Bulletin on Variable Stars, N/A, N/A, February 10, 2009, pp. 5876 FT, and Mukai, K; Mauche, C W; Brickhouse, N S; Hoogerwerf, R; Sterken, C; Luna, G M.
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