Abstract

We used photometric data from the WASP (Wide‐Angle Search for Planets) survey to explore the possibility of detecting eclipses and transit signals of brown dwarfs, gas giants and terrestrial companions in close orbit around white dwarfs. We performed extensive Monte Carlo simulations and we found that for Gaussian random noise WASP is sensitive to companions as small as the Moon orbiting a V∼12 white dwarf. For fainter stars WASP is sensitive to increasingly larger bodies. Our sensitivity drops in the presence of co‐variant noise structure in the data, nevertheless Earth‐size bodies remain readily detectable in relatively low S/N data. We searched for eclipses and transit signals in a sample of 194 white dwarfs in the WASP archive however, no evidence for companions was found. We used our results to place tentative upper limits to the frequency of such systems. While we can only place weak limits on the likely frequency of Earth‐sized or smaller companions; brown dwarfs and gas giants (radius≃RJup) with periods ⩽0.2 days must certainly be rare (<10%). More stringent constraints requires significantly larger white dwarf samples, higher observing cadence and continuous coverage. The short duration of eclipses and transits of white dwarfs compared to the cadence of WASP observations appears to be one of the main factors limiting the detection rate in a survey optimised for planetary transits of main sequence stars.

Highlights

  • The transit technique involves searching for periodic dips in stellar light-curves due to the orbital revolution of a transiting body, blocking a fraction of the stellar light

  • We have investigated the detection limits for sub-stellar and planetary companions to white dwarfs using in the WASP survey

  • Application of our modified BLS algorithm to search for companions to White dwarfs (WD) in our sample of 194 stars available in the WASP archive, did not reveal any eclipsing or transiting sub-stellar or planetary companions

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Summary

INTRODUCTION

The transit technique involves searching for periodic dips in stellar light-curves due to the orbital revolution of a transiting body, blocking a fraction of the stellar light. At the time of writing only three wide white dwarf + brown dwarf (WD+BD) systems have been spectroscopically confirmed, GD 165 (Becklin and Zuckerman 1988), PHL5038 (Steele et al 2009), and LSPM 1459 + 0857 AB (Day-Jones et al 2010) and two detached, non-eclipsing, short-period WD+BD systems are currently known, WD0137 −349 (Maxted et al 2006, Burleigh et al 2006, P≈116mins), and GD1400 (Farihi and Christopher 2004, Dobbie et al 2005, Burleigh et al 2010, P≈9.9h) The latter, is currently the lowest mass (∼50M jup) object known to have survived CE evolution. The detection of short period sub-stellar and planetary mass companions to white dwarfs, will open an exciting chapter in the study of exoplanet evolution, constraining theoretical models of CE evolution and helping us to understand the ultimate fate of hot Jupiter systems as well as the fate of our own solar system in the post main-sequence phase.

CHARACTERISTICS OF THE TRANSIT SIGNAL
Detecting transit signals
SEARCHING FOR TRANSIT SIGNALS IN WASP SURVEY DATA
Findings
CONCLUSION
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