Connections between Tilted Accretion Disksaround White Dwarfs and SubstellarCompanions

摘要

Accretion disks in white dwarf systems arc believed to be tilted. In a recent publication, the lift force has been suggested to be a source to disk tilt, a source that is likely relevant to all accretion disk systems. Lift is generated by slightly different supersonic gas stream speeds flowing over and under the disk at the bright spot. In this conference proceeding, we focus on whether a brown dwarf donor star accreting onto a white dwarf primary has enough mass to contribute to disk tilt. We also would like to obtain whether a white dwarf - brown dwarf close binary system has enough mass to induce and maintain a disk tilt of four degrees. We adopt SDSS 103533.03+055158.4 as our model system which has a mass transfer rate of (10±2) x 10~(-12) M_⊙ yr~(-1). We find that the brown dwarf in SDSS 1035 does not have enough mass to contribute to disk tilt. We find a gross magnitude of the minimum mass transfer rate to be ～ 10~(-10)M_⊙yr~(-1). We conclude that SDSS 1035 does not seem to have a high enough mass transfer rate to induce and maintain an observable disk tilt. Hence one reason why brown dwarf donor systems may be so difficult to find could be due to their low mass transfer rates which do not induce observable dynamical effects that is typical in white dwarf-red dwarf CVs.