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19 April 2024 |
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High-resolution spectroscopy of the intermediate polar EX Hydrae. I. Kinematic study and Roche tomography | | K. Beuermann
; K. Reinsch
; | | Date: |
18 Feb 2008 | | Abstract: | EX Hya is one of the few double-lined eclipsing cataclysmic variables that
allow an accurate measurement of the binary masses. We analyze orbital
phase-resolved UVES/ VLT high resolution spectroscopic observations of EX Hya
with the aims of deriving the binary masses and obtaining a tomographic image
of the illuminated secondary star. We present a novel method for determining
the binary parameters by directly fitting an emission model of the illuminated
secondary star to the phase-resolved line profiles of NaI lambda 8183/ 8195 in
absorption and emission and CaII lambda 8498 in emission. The fit to the NaI
and CaII line profiles, combined with the published K1, yields a white-dwarf
mass M1 = 0.790 +/- 0.026 Msun, a secondary mass M2 = 0.108 +/- 0.008 Msun, and
a velocity amplitude of the secondary star K2 = 432.4 +/- 4.8 km s-1. The
secondary is of spectral type dM5.5 +/- 0.5 and has an absolute K-band
magnitude of MK = 8.8. Its Roche radius places it on or very close to the main
sequence of low-mass stars. It differs from a main sequence star by its
illuminated hemisphere that faces the white dwarf. The secondary star
contributes only 5% to the observed spin-phase averaged flux at 7500 A, 7.5% at
8200 A, and 37% in the K-band. We present images of the secondary star in the
light of the NaI doublet and the CaII emission line derived with a simplified
version of Roche tomography. We have discovered narrow spectral lines from the
secondary star in EX Hya that delineate its orbital motion and allow us to
derive accurate masses of both components. The primary mass significantly
exceeds recently published values. The secondary is a low-mass main sequence
star that displays a rich emission line spectrum on its illuminated side, but
lacks chromospheric emission on its dark side. | | Source: | arXiv, 0802.2339 | | Services: | Forum | Review | PDF | Favorites | |
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