Monte Carlo radiation transfer in CV disk winds: application to the AM CVn prototype

Kusterer, D.-J.; Nagel, T.; Hartmann, S.; Werner, K.; Feldmeier, A.

Context: AM CVn systems are ultracompact binaries in which a (semi-) degenerate star transfers helium-dominated matter onto a white dwarf. They are effective gravitational-wave emitters and potential progenitors of Type Ia supernovae.

Aims: To understand the evolution of AM CVn systems it is necessary to determine their mass-loss rate through their radiation-driven accretion-disk wind. We constructed models to perform quantitative spectroscopy of P Cygni line profiles that were detected in UV spectra.

Methods: We performed 2.5D Monte Carlo radiative transfer calculations in hydrodynamic wind structures by making use of realistic NLTE spectra from the accretion disk and by accounting for the white dwarf as an additional photon source.

Results: We present first results from calculations in which LTE opacities are used in the wind model. A comparison with UV spectroscopy of the AM CVn prototype shows that the modeling procedure is potentially a good tool for determining mass-loss rates and abundances of trace metals in the helium-rich wind.

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