Back to the Abstracts Index PageJ.R. Thorstensen (1), S. Vennes (2), and S. Bowyer (3)
1) Department of Physics and Astronomy, Dartmouth College,
Hanover, NH 03755
2) Center for EUV Astrophysics, 2150
Kittredge St., University of California, Berkeley, CA 94720 USA
3)
Astronomy Department, University of California, Berkeley, CA 94720 USA
The optical counterpart of the new extreme ultraviolet source EUVE J1016-053 (RE 1016-053) is known to show intermittent sharp Balmer and He I emission and traces of an M-dwarf associated with a white dwarf optical spectrum. We present extensive optical spectroscopy showing the emission lines vary in velocity and intensity on a period of 0.78929 +/- 0.00003 days. The phase of the emission line strengths lags that of the velocities by 0.237 +/- 0.013 cycle, consistent with the quarter-cycle offset expected if emission arises from the side of the secondary facing the hot white dwarf. EUVE J1016-053 is another example of an extreme ultraviolet (EUV) illumination-effect binary, which only recently emerged from a common-envelope phase of binary evolution. Based on spectroscopic measurements and new BVR photometry, we find that the M-dwarf secondary's contribution to the combined light is smaller than previously reported, probably because of the difficulty of avoiding contamination from a third star 3.2" distant. The velocity of the weak He II absorption is in antiphase to the emission, suggesting that it originates in the white dwarf photosphere. The mass function implied by the emission line motion is f(M) = 0.28 +/- 0.08 M_o. Assuming the He II absorption does follow the white dwarf, the mass ratio M_WD / M_dM is 1.8 +/- 0.5, and the gravitational redshift is 45 +/- 14 km/s. The modulation of the emission lines suggests the inclination i > 40 deg, but plausible masses demand the inclination be well above this value.
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