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Survival of a brown dwarf after engulfment by a red giant star

Abstract

Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics1,2,3,4,5 but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass1,4,5. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants—that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models6,7. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion8 but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.

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Figure 1: Trailed spectrograms of WD 0137–349.
Figure 2: Infrared flux distribution of WD 0137–349.

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Acknowledgements

This Letter is based on observations collected at the European Southern Observatory, Chile, and makes use of data products from the Two Micron All Sky Survey (2MASS). P.D.D. is supported by PPARC. R.N. and M.R.B. acknowledge the support of PPARC Advanced Fellowships. Author Contributions P.F.L.M. analysed and interpreted the data from which the orbital period and other properties of the system were measured. R.N. identified WD 0137–349 as a strong candidate for a brown dwarf companion to a white dwarf from observations obtained as part of the SPY programme, of which he is the principal investigator. M.R.B. and P.D.D. analysed the 2MASS data for this object. All authors discussed and interpreted the results and commented on the manuscript.

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Correspondence to P. F. L. Maxted.

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Maxted, P., Napiwotzki, R., Dobbie, P. et al. Survival of a brown dwarf after engulfment by a red giant star. Nature 442, 543–545 (2006). https://doi.org/10.1038/nature04987

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