Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...303..127g&link_type=abstract
Astronomy and Astrophysics, v.303, p.127
Astronomy and Astrophysics
Astrophysics
93
Accretion, Binaries: Close, Stars: Atmospheres, Stars: Individual: Am Her, Ultraviolet: Stars, X-Rays: Stars
Scientific paper
We present orbital phase-resolved UV spectroscopy of AM Herculis in its high and low state obtained with the IUE satellite. We derive the effective temperatures and sizes of the accretion-heated polecap in both states. We also estimate the effective temperature and radius of the white dwarf. The spot is hotter in the high state, but always covers a large fraction f~0.1 of the white-dwarf surface. We discuss the energy balance of accretion-induced irradiation of the white dwarf and re-emission in the UV. From two quasi-simultaneous sets of IUE and ROSAT observations, we find that the UV flux is consistent with being produced by reprocessing of hard X-ray and cyclotron emission from the hot post-shock plasma. The bulk of the soft X-ray emission does not enter this energy balance. Our finding partly resolves the soft X-ray puzzle. We re-determine the distance to AM Her to be d=91^+18^_-15_pc. The low-state accretion rate is ~10^-11^Msun_/yr.
Beuermann Klaus
de Martino Domitilla
Gänsicke Boris T.
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