The mass accretion rate in quiescent cataclysmic variables (CVs) and ex-novae.
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- Created: Monday, 25 January 2016 12:22
Pierluigi Selvelli - OATS-INAF Elena Mason - OATS-INAF Roberto Gilmozzi - ESO-Garching.
CVs are semi-detached binaries in which the white dwarf (WD) primary star accretes material from the low main sequence companion. Novae are a class of CVs that displays thermonuclear runaway driven outbursts. Other different classes of CVs are identified depending on the mechanism driving and controlling the transfer of material between the companion and the WD. Theory predicts that, during their lifetime, all CVs evolve from long to short orbital periods and, as they do so, the mass accretion rate decline. Hence, the mass accretion rate is a very important parameter since it characterizes both the evolutionary phase of a system and the recurrence time of nova outbursts. While the period -- mass-accretion relation appears almost univocal in theoretical models, observationally a large range of mass accretion rates is reported for a given orbital period. Observationally, the determination of the mass accretion rate heavily relays on the knowledge of the system distance and the UV spectral energy distibution, where the bulk of the accretion luminosity is emitted (at least for the case of non strongly magnetic CVs). Unlike other CVs, novae have more reliable distances determined from empirical methods. Searching archival (IUE and STIS) UV data of old novae and nova distance determination in the literature, we obtained a fiducial sample of 18 novae for which we could estimate the UV luminosity and the mass accretion rate with relatively high accuracy. Our preliminary results suggest that, contrarily to the expectation, there is no correlation between the mass accretion rate and the orbital period in old novae. While a number of speculations can be brought up to explain the discrepancy, the analysis should be extended to a larger sample of novae as well as to other CVs. This will be possible in the near future with the accurate distances that will be soon available from the GAIA project, in combination with archive UV observations of CVs by IUE, GALEX, HST and other experiments.
Contact person: Pierluigi Selvelli