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2003MNRAS.345..506O - Mon. Not. R. Astron. Soc., 345, 506-528 (2003/October-3)
The DA+dMe eclipsing binary EC13471-1258: its cup runneth over ... just.
O'DONOGHUE D., KOEN C., KILKENNY D., STOBIE R.S., KOESTER D., BESSELL M.S., HAMBLY N. and MacGILLIVRAY H.
Abstract (from CDS):
Hubble Space Telescope (HST) STIS spectra show strong Lyman-α absorption with weak metal lines of C I,II and SI II superimposed. Model atmosphere analysis yielded an effective temperature of 14 220±300 K and logg of 8.34±0.20 for the white dwarf with these errors being strongly correlated. Its metal abundance is 1/30th solar with an uncertainty of 0.5 dex, and it is rapidly rotating with V1sin i 400±100 km/s. The white dwarf also shows radial velocity variations with a semi-amplitude of 138±10 km/s. The gravitational redshift of the white dwarf was measured as 62 km/s.
From optical spectroscopy the spectral type of the M dwarf was found to be M3.5-M4, its temperature 3100±75 K, its rotational velocity 140±10 km/s, its radial velocity semi-amplitude 266±5 km/s, its mean V -I colour 2.86 and its absolute V magnitude 11.82. Intriguingly, its metal abundance is normal solar.
The Hα emission line shows at least two distinct components, one of which is uniformly distributed around the centre of mass of the M dwarf and provided the estimate of the rotational velocity of the M dwarf. The other arises from the other side of the binary centre of mass, well within the white dwarf Roche lobe. This behaviour is confirmed by Doppler tomography, which shows the presence of two distinct velocity components within the primary Roche lobe. The interpretation of these features is uncertain. Variations in strength of the components with binary phase can be attributed to optical thickness in the Balmer lines. Similar behaviour is seen in the observations of the other Balmer emission lines, although with a poorer signal-to-noise ratio. Flares in Hα were observed and are consistent with arising from the vicinity of the M dwarf.
Dynamical solutions for the binary are discussed and yield an inclination of 75.5°± 2.0°, a white dwarf mass and radius of 0.78±0.04 M☉ and 0.011±0.01 R☉, and an M dwarf mass and radius of 0.43±0.04 M☉and 0.42±0.02 R☉. These parameters are consistent with the Wood mass-radius relation for white dwarfs and the Clemens et al. mass-radius relation for M dwarfs; we argue that the M dwarf just fills its Roche lobe. The radius of the white dwarf and the model fit imply a distance of 48 ± 5 pc and an absolute V magnitude of 11.74.
The rapid rotation of the white dwarf strongly suggests that the system has undergone mass transfer in the past, and implies that it is a hibernating cataclysmic variable. The M dwarf shows the properties expected of secondaries in cataclysmic variables: chromospheric activity and angular momentum loss.
Abstract Copyright: 2003 RAS
Journal keyword(s): binaries: eclipsing - stars: individual: EC13471 - stars: binaries-1258
Simbad objects: 13
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