Constraining planet formation around 6–8 M⊙ stars

Abstract

Identifying planets around O-type and B-type stars is inherently difficult; the most massive known planet host has a mass of only about 3M ⊙ . However, planetary systems which survive the transformation of their host stars into white dwarfs can be detected via photospheric trace metals, circumstellar dusty and gaseous discs, and transits of planetary debris crossing our line-of-sight. These signatures offer the potential to explore the efficiency of planet formation for host stars with masses up to the corecollapse boundary at ≈ 8M ⊙ , a mass regime rarely investigated in planet formation theory. Here, we establish limits on where both major and minor planets must reside around ≈ 6M ⊙ − 8M ⊙ stars in order to survive into the white dwarf phase. For this mass range, we find that intact terrestrial or giant planets need to leave the main sequence beyond approximate minimum star-planet separations of respectively about 3 and 6 au. In these systems, rubble pile minor planets of radii 10, 1.0, and 0.1 km would have been shorn apart by giant branch radiative YORP spin-up if they formed and remained within, respectively, tens, hundreds and thousands of au. These boundary values would help distinguish the nature of the progenitor of metal-pollution in white dwarf atmospheres. We find that planet formation around the highest mass white dwarf progenitors may be feasible, and hence encourage both dedicated planet formation investigations for these systems and spectroscopic analyses of the highest mass white dwarfs.

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

“…For WD J1922+0233, we initially derived T eff ≈ 5800 K and log g ≈ 9.10 using Gaia photometry, which would imply the most massive polluted white dwarf known to date (Koester, Gänsicke & Farihi 2014;Coutu et al 2019;Veras et al 2020). However, a closer inspection of Pan-STARRS photometry reveals non blackbody-like optical fluxes sharply peaking in the g and r bands, with a dropoff in i, z, and y that is sharper than a Rayleigh-Jeans tail.…”

Alkali metals in white dwarf atmospheres as tracers of ancient planetary crusts

“…In contrast, our fit to WD J2317+1830 reveals a mass of 1.00 ± 0.02 M and cooling age of 9.5 ± 0.2 Gyr making it the among most massive white dwarfs detected with signatures of a planetary system 29 . The large mass implies a massive progenitor with a relatively small mainsequence lifetime, leading to a precise total age of 9.7 ± 0.2 Gyr using an empirical initial-to-final mass relation 30 and main-sequence lifetimes 68 .…”

Planetary magnetosphere evolution around post-main-sequence stars

“…We sample 11 initial stellar masses from 1.0M to 7.0M . We justify this range because sub-solar masses take over a Hubble time to evolve, and on the higher end investigating planetary systems with host star masses close to the supernova limit is becoming increasingly relevant (Veras et al 2020;Hollands et al 2021).…”

“…All these planets formed during the protoplanetary disc phase (e.g., Pinte et al 2018) and have since survived stellar evolution to reach the present time. These evolved planets provide valuable benchmarks when tracing the full lifetime of their parent systems (Veras 2016), and, when combined with additional data, can help constrain formation locations in the disc (Harrison et al 2018;Veras et al 2020) and link system chemistry with architecture (Payne et al 2016(Payne et al , 2017 E-mail: d.veras@warwick.ac.uk † STFC Ernest Rutherford Fellow 1 www.lsw.uni-heidelberg.de/users/sreffert/giantplanets Xu et al 2017;Mustill et al 2018;Swan et al 2019;Doyle et al 2021).…”