出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present high speed photometric observations of the eclipsing dwarf nova IP Peg taken with the triple-beam camera ULTRACAM mounted on the William Herschel Telescope. We obtained eighteen observations of the eclipse in 2004/2005, simultaneous in the Sloan u′, g′ and r′ bands. By phase-folding and averaging our data we make the first significant detection of the white dwarf ingress in this system and thus make the most secure photometric determinations of the binary parameters in this system to date, which are in agreement with the best spectroscopic determinations. The white dwarf temperature is more difficult to determine, since the white dwarf is seen to vary significantly in flux, even between consecutive eclipses. This is seen particularly in the u′-band, and is probably the result of absorption by disc material. Our best estimate of the temperature is 10,000 – 15,000K, which is much lower than would be expected for a CV with this period, and implies a mean accretion rate that is more than 40 times lower than the expected rate. Unless the mass transfer in IP Peg has begun very recently, these findings imply either that CVs can sustain accretion rates well below the expected rate for very long periods of time, or that the classical picture whereby the long-term accretion rate scales with period is not correct.
