Detectable close-in planets around white dwarfs through late unpacking

Abstract

Although 25%-50% of white dwarfs (WDs) display evidence for remnant planetary systems, their orbital architectures and overall sizes remain unknown. Vibrant close-in (≃ 1R ⊙ ) circumstellar activity is detected at WDs spanning many Gyrs in age, suggestive of planets further away. Here we demonstrate how systems with 4 and 10 closely-packed planets that remain stable and ordered on the main sequence can become unpacked when the star evolves into a WD and experience pervasive inward planetary incursions throughout WD cooling. Our full-lifetime simulations run for the age of the Universe and adopt main sequence stellar masses of 1.5M ⊙ , 2.0M ⊙ and 2.5M ⊙ , which correspond to the mass range occupied by the progenitors of typical present-day WDs. These results provide (i) a natural way to generate an ever-changing dynamical architecture in post-main-sequence planetary systems, (ii) an avenue for planets to achieve temporary close-in orbits that are potentially detectable by transit photometry, and (iii) a dynamical explanation for how residual asteroids might pollute particularly old WDs.

Destruction of Refractory Carbon in Protoplanetary Disks

“…The strong gravitational forces of white dwarfs are expected to deplete heavier elements from their photospheres on relatively short timescales. Therefore, heavy elements observed in the atmospheres of white dwarfs are believed to have originated in rocky bodies that are destroyed near the tidal radius and accreted by the star (Zuckerman et al 2007;Veras & Gänsicke 2015). Elemental measurements reveal these bodies to be carbon-poor with C/Fe ratios similar to those measured in chondritic meteorites in our own solar system (Jura & Young 2014;Farihi et al 2016;Wilson et al 2016).…”

The fate of exomoons in white dwarf planetary systems

“…As seen in Fig. 2, many moons remain bound after the 10 8 yr modelled here, yet planet-planet scattering around WDs continues over Gyr time-scales (Veras & Gänsicke 2015), providing further opportunity for liberation of moons. Hence, the prevalence of moons in inner regions is likely to increase as these systems are tracked over longer timespans.…”

“…We rely on simulations from both of these studies, in which Veras & Gänsicke (2015) adopted equal-mass planets, and Veras et al (2016a) investigated unequal-mass planets within the same system. In these simulations, packed systems of planets were integrated for >10 10 yr, with the central star initially being on the main sequence, then passing through the giant branch (and hence losing mass), before settling into the white dwarf phase.…”

“…As planet-planet scattering around WDs can occur over Gyr time-scales (far longer than examined here, see fig. 1 of Veras & Gänsicke 2015), many more close encounters will occur, making it extremely likely that yet more moons will be liberated from their parent planets at future times. We note that the fine details of an individual planet-planet scattering encounter (e.g.…”

Does a Differentiated, Carbonate-Rich, Rocky Object Pollute the White Dwarf SDSS J104341.53+085558.2?

“…Simulation work suggests that it is unlikely that a full-fledged planet (Mars-like or more massive) would be delivered to the tidal destruction radius of a white dwarf star (e.g., Debes & Sigurdsson 2002;Jura 2008;Mustill et al 2014;Veras & Gänsicke 2015;Veras et al 2016). As discussed by Zuckerman et al (2011), it is not necessary to deliver an entire planet-sized object into the tidal destruction radius of a polluted white dwarf star, even when there is evidence for the material to have come from particular layers of a differentiated rocky body.…”