Abstract

Secondary stars in cataclysmic variables (CVs) follow a well-defined period-density relation. Thus, canonical donor stars in CVs are generally low-mass stars of spectral type M. However, several CVs have been observed containing secondary stars that are too hot for their inferred masses. This particular configuration can be explained if the donor stars in these systems underwent significant nuclear evolution before they reached contact. In this paper, we present SDSS J001153.08-064739.2 as an additional example belonging to this peculiar type of CV and discuss in detail its evolutionary history. We perform spectroscopic and photometric observations and make use of available Catalina Real-Time Transient Survey photometry to measure the orbital period of SDSS J001153.08-064739.2 as 2.4 hr and estimate the white dwarf (M-wd > 0.65 M-circle dot) and donor star (0.21 M-circle dot < M-don < 0.45 M-circle dot) masses, the mass ratio (q = 0.32 +/- 0.08), the orbital inclination (47 degrees < i < 70 degrees); derive an accurate orbital ephemeris (T-0 = 2453383.578(1) + E x 0.10028081(8)); and report the detection of an outburst. We show that SDSS J001153.08-064739.2 is one of the most extreme cases in which the donor star is clearly too hot for its mass. SDSS J001153.08-064739.2 is therefore not only a peculiar CV containing an evolved donor star, but also an accreting CV within the period gap. Intriguingly, approximately half of the total currently observed sample of these peculiar CVs are located in the period gap with nearly the same orbital period.