ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir

Monthly Notices of the Royal Astronomical Society

Dhillon

et al. 2011

Self Cite

146

We present high‐speed, three‐colour photometry of the eclipsing cataclysmic variables CTCV J1300−3052, CTCV J2354−4700 and SDSS J115207.00+404947.8. These systems have orbital periods of 128.07, 94.39 and 97.52 min, respectively, placing all three systems below the observed ‘period gap’ for cataclysmic variables. For each system we determine the system parameters by fitting a parametrized model to the observed eclipse light curve by χ2 minimization. We also present an updated analysis of all other eclipsing systems previously analysed by our group. The updated analysis utilizes Markov chain Monte Carlo techniques which enable us to arrive confidently at the best fits for each system with more robust determinations of our errors. A new bright‐spot model is also adopted, that allows better modelling of bright‐spot dominated systems. In addition, we correct a bug in the old code which resulted in the white dwarf radius being underestimated, and consequently both the white dwarf and donor mass being overestimated. New donor masses are generally between 1σ and 2σ of those originally published, with the exception of SDSS 1502 (−2.9σ, ΔMr=−0.012 M⊙) and DV UMa (+6.1σ, ΔMr=+0.039 M⊙). We note that the donor mass of SDSS 1501 has been revised upwards by 0.024 M⊙ (+1.9σ). This system was previously identified as having evolved past the minimum orbital period for cataclysmic variables, but the new mass determination suggests otherwise. Our new analysis confirms that SDSS 1035 and SDSS 1433 have evolved past the period minimum for cataclysmic variables, corroborating our earlier studies. We find that the radii of donor stars are oversized when compared to theoretical models, by approximately 10 per cent. We show that this can be explained by invoking either enhanced angular momentum loss, or by taking into account the effects of star spots. We are unable to favour one cause over the other, as we lack enough precise mass determinations for systems with orbital periods between 100 and 130 min, where evolutionary tracks begin to diverge significantly. We also find a strong tendency towards high white dwarf masses within our sample, and no evidence for any He‐core white dwarfs. The dominance of high‐mass white dwarfs implies that erosion of the white dwarf during the nova outburst must be negligible, or that not all of the mass accreted is ejected during nova cycles, resulting in the white dwarf growing in mass.

Section: Resultssupporting

confidence: 82%

Section: Discussionmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 99%

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Cataclysmic variables below the period gap: mass determinations of 14 eclipsing systems

Savoury

Monthly Notices of the Royal Astronomical Society

Dhillon

et al. 2011

Self Cite

146

“…Data reduction was carried out using the ULTRACAM pipeline reduction software (see Feline et al 2004). A nearby, bright and photometrically stable comparison star was used to correct for any transparency variations during observations.…”

Section: O B S E Rvat I O N Smentioning

confidence: 99%

Using Gaussian processes to model light curves in the presence of flickering: the eclipsing cataclysmic variable ASASSN-14ag

McAllister

Mon. Not. R. Astron. Soc.

Dhillon

et al. 2016

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The majority of cataclysmic variable (CV) stars contain a stochastic noise component in their light curves, commonly referred to as flickering. This can significantly affect the morphology of CV eclipses and increases the difficulty in obtaining accurate system parameters with reliable errors through eclipse modelling. Here we introduce a new approach to eclipse modelling, which models CV flickering with the help of Gaussian processes (GPs). A parameterised eclipse model -with an additional GP component -is simultaneously fit to 8 eclipses of the dwarf nova ASASSN-14ag and system parameters determined. We obtain a mass ratio q = 0.149 ± 0.016 and inclination i = 83.4 +0.9 −0.6• . The white dwarf and donor masses were found to be M w = 0.63 ± 0.04 M and M d = 0.093 +0.015 −0.012 M , respectively. A white dwarf temperature T w = 14000 +2200 −2000 K and distance d = 146 +24 −20 pc were determined through multicolour photometry. We find GPs to be an effective way of modelling flickering in CV light curves and plan to use this new eclipse modelling approach going forward.

“…Data reduction was carried out using the ULTRACAM pipeline reduction software (see Feline et al 2004). A nearby, photometrically stable comparison star was used to correct for any transparency variations during observations.…”

Section: O B S E Rvat I O N Smentioning

confidence: 99%

PHL 1445: an eclipsing cataclysmic variable with a substellar donor near the period minimum

McAllister

Monthly Notices of the Royal Astronomical Society

Baraffe

et al. 2015

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We present high-speed, three-colour photometry of the eclipsing dwarf nova PHL 1445, which, with an orbital period of 76.3 min, lies just below the period minimum of ∼82 min for cataclysmic variable stars. Averaging four eclipses reveals resolved eclipses of the white dwarf and bright spot. We determined the system parameters by fitting a parameterised eclipse model to the averaged lightcurve. We obtain a mass ratio of q=0.087 ± 0.006 and inclination i=85.2 ± 0.9 • . The primary and donor masses were found to be M w =0.73 ± 0.03 M and M d =0.064 ± 0.005 M , respectively. Through multicolour photometry a temperature of the white dwarf of T w =13200 ± 700 K and a distance of 220 ± 50 pc were determined.The evolutionary state of PHL 1445 is uncertain. We are able to rule out a significantly evolved donor, but not one that is slightly evolved. Formation with a brown dwarf donor is plausible; though the brown dwarf would need to be no older than 600 Myrs at the start of mass transfer, requiring an extremely low mass ratio (q=0.025) progenitor system. PHL 1445 joins SDSS 1433 as a sub-period minimum CV with a substellar donor. These existence of two such systems raises an alternative possibility; that current estimates for the intrinsic scatter and/or position of the period minimum may be in error.