Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983a%26a...121...29m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 121, no. 1, May 1983, p. 29-34.
Astronomy and Astrophysics
Astrophysics
96
Accretion Disks, Dwarf Novae, Periodic Variations, Stellar Models, Atmospheric Density, Stellar Atmospheres, Stellar Mass Accretion, Surface Properties, Viscosity
Scientific paper
Recent models relate the outbursts of dwarf novae to convective outer regions of accretion disks around the primary white dwarf. Such regions disappear for accretion rates above a critical value M(crit). By means of disk structure computations we show that the accretion rate in Z Cam is near M(crit). It is suggested that in standstills it is slightly higher than this value while in the cyclic phase it is slightly lower. This is explained as an effect of irradiation of the secondary's surface producing higher mass overflow rates in steady standstills than in cyclic phases and enabling the system to remain in either state. In the long run an imbalance between the mean accretion rate (forced on the system by loss of angular momentum, say) and the actual accretion rate in either state forces the system to alternate between its two states in form of a relaxation oscillation. With this model the Z Cam system falls between the U Gem subgroup (regular outburst cycles, low accretion rate) and the UX Uma subgroup (steady light curve, high accretion rate). Observational evidence or the model is discussed.
Meyer Fernand
Meyer-Hofmeister Emmi
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