Two substellar survivor candidates; one found and one missing by N. Walters et al. on Tuesday 29 November

This study presents observations of two possible substellar survivors of

post-main sequence engulfment, currently orbiting white dwarf stars. Infrared

and optical spectroscopy of GD 1400 reveal a 9.98 h orbital period, where the

benchmark brown dwarf has $M_2=68\pm8$ M$_{\rm Jup}$, $T_{\rm eff}\approx2100$

K, and a cooling age under 1 Gyr. A substellar mass in the lower range of

allowed values is favoured by the gravitational redshift of the primary.

Synthetic brown dwarf spectra are able to reproduce the observed CO bands, but

lines below the bandhead are notably overpredicted. The known infrared excess

towards PG 0010+281 is consistent with a substellar companion, yet no radial

velocity or photometric variability is found despite extensive searches. Three

independent stellar mass determinations all suggest enhanced mass loss

associated with binary evolution, where the youngest total age for an isolated

star is $7.5\pm2.5$ Gyr. A possible solution to this conundrum is the

cannibalization of one or more giant planets, which enhanced mass loss

post-main sequence, but were ultimately destroyed. PG 0010+281 is likely

orbited by a debris disk that is comfortably exterior to the Roche limit,

adding to the growing number of non-canonical disks orbiting white dwarfs. At

present, only L-type (brown) dwarfs are known to survive direct engulfment

during the post-main sequence, whereas T- and Y-type substellar companions

persist at wide separations. These demographics indicate that roughly 50

M$_{\rm Jup}$ is required to robustly avoid post-main sequence annihilation,

suggesting all closely-orbiting giant planets are consumed, which may

contribute to mass loss and magnetic field generation in white dwarfs and their

immediate progenitors.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2207.07022v2