The Donor Stars of Cataclysmic Variables

By C. Knigge. 2006

294 citations recorded by the source corpus.

We construct a complete, semi-empirical donor sequence for CVs with orbital periods less than 6 hrs. All key physical and photometric parameters of CV secondaries (along with their spectral types) are given as a function of P_orb along this sequence. The main observational basis for our donor sequence is an empirical mass-radius relation for CV secondaries. We present an optimal estimate for this relation that ensures consistency with the observed locations of the period gap and the period minimum. We also present new determinations of these periods, finding P_{gap, upper edge} = 3.18 +/- 0.04 hr, P_{gap, lower edge} = 2.15 +/- 0.03 hr and P_{min} = 76.2 +/- 1.0 min. We then test the donor sequence by comparing observed and predicted spectral types (SpTs) as a function of orbital period. To this end, we update the SpT compilation of Beuermann et al. and show explicitly that CV donors have later SpTs than main sequence (MS) stars at all orbital periods. The semi-empirical donor sequence matches the observed SpTs very well, implying that the empirical M2-R2 relation predicts just the right amount of radius expansion. We finally apply the donor sequence to the problem of distance estimation. Based on a sample of 22 CVs with trigonometric parallaxes, we show that the donor sequence correctly traces the envelope of the observed M_{JHK}-P_{orb} distribution. Thus robust lower limits on distances can be obtained from single-epoch infrared observations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0503c2e2283588bd61f1422b2b269e3f8cc27be6

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Citations in the corpus

THE EVOLUTION OF CATACLYSMIC VARIABLES AS REVEALED BY THEIR DONOR STARS (2011, background): “Until recently, the latter was usually estimated to be around Pmin 75 minutes, based on the observed cutoff in the period distribution of the then available CV sample (e.g., Knigge 2006, hereafter K06).”
LISA verification binaries with updated distances from Gaia Data Release 2 (2018, background): “A large number of AM CVn systems have indirect constraints on the mass ratio (q) from the empirical relation of the superhump excess (Knigge 2006). q = (0.114 ± 0.005) + (3.97 ± 0.41) × ( − 0.025) (1) MNRAS 000, 1–9 (2015) where = Psh−PorbPorb is the superhump excess.”
Post-common-envelope binaries from SDSS. IX: Constraining the common-envelope efficiency (2010, background): “…the gap seem to be slightly expanded compared to mainsequence stars, which is consistent with the donor stars being driven out of thermal equilibrium (Knigge 2006); and (5) we find the fraction of PCEBs among WDMS binaries to be significantly decreasing towards higher masses at the fully…”
Design Considerations for a Ground-Based Transit Search for Habitable Planets Orbiting M Dwarfs (2007, background): “However, as pointed out by Knigge (2006), this improvement appears to be somewhat at the expense of accuracy in I K colors, which the original NextGen models reproduce well.”
SDSS unveils a population of intrinsically faint cataclysmic variables at the minimum orbital period (2009, background): “Confronting theory and observations, it is clear that such a spike is absent in the period distribution of the known CVs (Patterson 1998; Gänsicke, Hagen & Engels 2002; Knigge 2006).”