Astron. Astrophys. 343, 909-915 (1999)

6. Brief review of QPOs in MV Lyr

Rapid light variations with a timescale of 1-30 min and amplitude about were first found by Walker (1954).

The 47-min QPOs have been observed by Borisov (1992) and Skillman et al. (1995) and 18-21 min by Andronov et al. (1992) in the high brightness state. In the low state the behaviour of MV Lyr is fairly quiet and short-period variations (as well as single flares) are rather rare events. It seems, that they could appear with a probability of . Thus Robinson in one of five nights observed min light variations with an amplitude of (Robinson et al. 1981). Pavlenko in 3 of 30 nights detected a single flare with typical time min, and during one night a series of QPOs with a period of 37.6 min and amplitude (Pavlenko 1998b).

So, comparing all previous studies of MV Lyr, we have found that all the observed quasi-periodic oscillations (QPOs) occurred at the some preferred frequencies. They do not depend on the brightness state. However, in the low state such QPOs are very rare events, whereas in the high state one could detect if not one then the other listed QPOs.

The nature of the periods is unknown. Several approaches for explanation are possible.

1. The QPOs are caused by an inhomogeneous disk structure. If we suppose that the periods correspond to Keplerian orbits, the inhomogeneities are located at the middle and outer regions of the disk ().

2. QPOs are connected with oscillations of the ionizaton front near the inner Lagrange point, causing variations in the mass transfer rate about (King 1989). This value in our case is equal to p=9.6 min. The most prominent QPOs whenever detected occured at 19.2 min, or 29 min, or 38 min, or 47 min (or at both periods), suggesting 2p, 3p, 4p, and 5p! But a QPO at p itself was never observed, despite having adequate time resolution.

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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