Physical properties of IP Pegasi: an eclipsing dwarf nova with an unusually cool white dwarf

Abstract

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. The primary eclipse in this system was observed twice in 2004, and then a further sixteen times over a three week period in 2005. Our observations were 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 find the phase width φ of the white dwarf eclipse to be 0.0935 ± 0.0003, significantly higher than the previous best value of 0.0863 < φ < 0.0918. The mass ratio is found to be q = M 2 /M 1 = 0.48 ± 0.01, consistent with previous measurements, but we find the inclination to be 83.8 ± 0.5 deg, significantly higher than previously reported. We find the radius of the white dwarf to be 0.0063 ± 0.0003R ⊙ , implying a white dwarf mass of 1.16 ± 0.02M ⊙ . The donor mass is 0.55 ± 0.02M ⊙ . 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 of < 5 × 10 −11 M ⊙ yr −1 , more than 40 times lower than the expected rate.

A 62-minute orbital period black widow binary in a wide hierarchical triple

“…HiPERCAM light curve analysis Modelling the HiPERCAM light curve of ZTF J1406+1222 is challenging for three reasons: 1. We lack kinematic constraints and thus the binary mass ratio and the scale of the semi-major axis are not constrained; 2. the two modelling codes we used, LCURVE 39 and ICARUS 40 , lack the physics needed to fully describe the behaviour we see in the light curve, in particular, contributions from the wind near minimum flux and the phase shift seen at maximum; and 3. the cool subdwarf companion contributes some amount of light in each band and its assumed spectral energy distribution greatly impacts the amplitude of the modulation, especially in the redder filters. We introduce a correction for this contribution in our ICARUS model.…”

Liverpool telescope 2: a new robotic facility for rapid transient follow-up

“…Similarly the cadences of Gaia photometric monitoring will be sufficient to identify eclipsing binaries and extrasolar planets (Zwitter, 2003), but detailed modelling (e.g. Littlefair et al 2008;Copperwheat et al 2010Copperwheat et al , 2011 will require high-cadence follow-up observations.…”

ULTRACAM observations of SDSS J0926+3624: The first known eclipsing AM CVn star

“…The phase-folded and superhump-subtracted light curves and model fits are plotted in Figure 3. We modelled the light curve with LCURVE, a code developed to fit light curves characteristic of eclipsing dwarf novae and detached white dwarf / M dwarf binary stars [3]. In this code the binary is defined by four components: a white dwarf primary, a Roche-lobe filling secondary star, accretion disc and bright-spot.…”

“…We first obtained an initial fit to each light curve using the simplex and Levenberg-Marquardt methods [17]. We then used a Markov Chain Monte Carlo (MCMC) algorithm for minimisation and determination of uncertainties [3]. A more complete description of these model fits is given in [4].…”

“…In 2006 and 2009 we took high time resolution observations of SDSS 0926 with the fast CCD camera ULTRACAM. The aim of these observations was to determine precise system parameters for this system, using techniques we have in the past successfully applied to normal CVs (e.g., [10,3]).…”