Cold Giant Planets Evaporated by Hot White Dwarfs

Abstract

Atmospheric escape from close-in Neptunes and hot Jupiters around sun-like stars driven by extreme ultraviolet (EUV) irradiation plays an important role in the evolution of exo-planets and in shaping their ensemble properties. Intermediate and low mass stars are brightest at EUV wavelengths at the very end of their lives, after they have expelled their envelopes and evolved into hot white dwarfs. Yet the effect of the intense EUV irradiation of giant planets orbiting young white dwarfs has not been assessed. We show that the giant planets in the solar system will experience significant hydrodynamic escape caused by the EUV irradiation from the white dwarf left behind by the Sun. A fraction of the evaporated volatiles will be accreted by the solar white dwarf, resulting in detectable photospheric absorption lines. As a large number of the currently known extra-solar giant planets will survive the metamorphosis of their host stars into white dwarfs, observational signatures of accretion from evaporating planetary atmospheres are expected to be common. In fact, one third of the known hot single white dwarfs show photospheric absorption lines of volatile elements, which we argue are indicative of ongoing accretion from evaporating planets. The fraction of volatile contaminated hot white dwarfs strongly decreases as they cool. We show that accretion from evaporating planetary atmospheres naturally explains this temperature dependence if more than 50 per cent of hot white dwarfs still host giant planets.

Orbit decay of 2–100 au planetary remnants around white dwarfs with no gravitational assistance from planets

“…Challenges to this canonical theory of the dynamical origin of pollution have arisen from the alternate ideas of second-generation formation (Perets 2011;Perets & Kenyon 2013;Bear & Soker 2014;Schleicher & Dreizler 2014;Völschow et al 2014;Hogg et al 2018), evaporation of planetary atmospheres (Schreiber et al 2019), and impact ejecta from collisions with planets (Veras & Kurosawa 2020). However, second-generation formation around single white dwarfs is feasible only for high disc masses (> 10 23 kg) (van Lieshout et al 2018), and the other two ideas still require the presence of planets.…”

Gaia white dwarfs within 40 pc – I. Spectroscopic observations of new candidates

“…With increasing distances, further rare examples of stellar or planetary evolution are being discovered, such as double white dwarf merger remnants (Hollands et al 2020;Kawka, Vennes & Ferrario 2020b), extremely low mass white dwarfs that will most likely merge (Brown et al 2016;Kawka et al 2020a), or stellar remnants with transiting planetesimals and planets on closein orbits (Vanderburg et al 2015;Gänsicke et al 2019;Manser et al 2019). Hot white dwarfs might even serve to study the composition of gas giant planet atmospheres (Schreiber et al 2019). A proper characterization of the occurrence of these systems requires the definition of larger volume-complete samples.…”

TESS Asteroseismic Analysis of the Known Exoplanet Host Star HD 222076

“…Here, we explore this possibility by applying the same procedure as in Campante et al (2019), which is based on the dynamical tidal formalism of Zahn (1977) that was implemented in Villaver et al (2014), with the added adiabatic assumption of stellar mass loss (Veras et al 2011) and wind velocity and density prescriptions from Veras et al (2015). We do not consider atmospheric evaporation (Schreiber et al 2019), or the possibility of another hidden planet in the system or any other dynamical process which may affect the planet's post-main-sequence evolution (Veras 2016).…”