Updates to systems around sdB binaries

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Updates to systems around sdB binaries

Post by Lazarus on 13th November 2017, 1:25 pm

Pulley et al. "The quest for stable circumbinary companions to post-common envelope sdB eclipsing binaries Does the observational evidence support their existence?"
https://arxiv.org/abs/1711.03749

The case for circumbinary companions in these systems appears to be far from secure. The systems which have had exoplanet claims:

  • NSVS 14256825 remains consistent with the single circumbinary brown dwarf hypothesis, but data only covers one orbital period. Given the issues with other binaries, claiming a detection of a companion is likely premature.

  • NY Virginis is departing from previous models. As noted in the text:
    In early 2013 NY Vir began to show a departure from the predictions of Lee et al. (2014). These changes were noted by both Kilkenny (2014) and ourselves (Pulley et al. (2016a). Our new data does not rule out the possibility of circumbinary planets but does raise questions as to whether the 21 years of observations is sufficient to base predictions on.

  • NSVS 07826147 - was claimed to have a planet with minimum mass 4.7 MJupiter (not sure if we have a thread on this one), the new data indicate that while there is scatter in the O-C times, there does not seem to be any long-term variation.

The spectre of an Applegate-type mechanism remains:
Although the spectral types of sdB companions are not tightly constrained, we are, however, in general agreement with Bours that larger values of RMS of residuals are generally found with companions of spectral type M5/6 or earlier. This is the boundary where a star becomes fully convective and may be indicative that significant LTT effects are being driven by magnetic processes within the companion star, possibly from a modified Applegate type mechanism. There are some possible anomalies, e.g. EC10246-2707 and NSVS 07826147, which are both classified as M5 but show little LTT effects.
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