A scaled-up planetary system around a supernova progenitor

Abstract

Context. Virtually all known exoplanets reside around stars with M < 2.3 M either due to the rapid evaporation of the protostellar disks or to selection effects impeding detections around more massive stellar hosts. Aims. To clarify if this dearth of planets is real or a selection effect, we launched the planet-hunting B-star Exoplanet Abundance STudy (BEAST) survey targeting B stars (M > 2.4 M ) in the young (5-20 Myr) Scorpius-Centaurus association by means of the high-contrast spectro-imager SPHERE at the Very Large Telescope. Methods. In this paper we present the analysis of high-contrast images of the massive (M ∼ 9 M ) star µ 2 Sco obtained within BEAST. We carefully examined the properties of this star, combining data from Gaia and from the literature, and used state-of-the-art algorithms for the reduction and analysis of our observations. Results. Based on kinematic information, we found that µ 2 Sco is a member of a small group which we label Eastern Lower Scorpius within the Scorpius-Centaurus association. We were thus able to constrain its distance, refining in turn the precision on stellar parameters. Around this star we identify a robustly detected substellar companion (14.4 ± 0.8 M J ) at a projected separation of 290 ± 10 au, and a probable second similar object (18.5 ± 1.5 M J ) at 21 ± 1 au. The planet-to-star mass ratios of these objects are similar to that of Jupiter to the Sun, and the flux they receive from the star is similar to those of Jupiter and Mercury, respectively. Conclusions. The robust and the probable companions of µ 2 Sco are naturally added to the giant 10.9 M J planet recently discovered by BEAST around the binary b Cen system. While these objects are slightly more massive than the deuterium burning limit, their properties are similar to those of giant planets around less massive stars and they are better reproduced by assuming that they formed under a planet-like, rather than a star-like scenario. Irrespective of the (needed) confirmation of the inner companion, µ 2 Sco is the first star that would end its life as a supernova that hosts such a system. The tentative high frequency of BEAST discoveries is unexpected, and it shows that systems with giant planets or small-mass brown dwarfs can form around B stars. When putting this finding in the context of core accretion and gravitational instability formation scenarios, we conclude that the current modeling of both mechanisms is not able to produce this kind of companion. The completion of BEAST will pave the way for the first time to an extension of these models to intermediate and massive stars.

Making BEASTies: dynamical formation of planetary systems around massive stars

“…In Fig. 2 we show the semimajor axis versus mass of the BEASTies in our simulations, as well as the three observed examples from Janson et al (2021b) and Squicciarini et al (2022). The captured BEASTies in our simulations are shown by the orange triangles, and the stolen BEASTies are shown by the blue circles.…”

“…Planets that are part of a triple system are shown by the open orange triangles. We also show the observed objects from the BEAST project by the red points (Janson et al 2021b;Squicciarini et al 2022).…”

“…Recently, Janson et al (2021a) initiated the B-star Exoplanet Abundance STudy (BEAST) to detect giant planets orbiting massive OB type stars, stars with masses 2.4 M ⊙ . The study immediately bore fruit with the detection of a super-Jupiter-mass planet orbiting at 556 au around b Cen AB, a 6-10 M ⊙ binary star (Janson et al 2021b); and two similar-mass planets orbiting at 21 au and 290 au around µ 2 Sco, a 9 M ⊙ star (Squicciarini et al 2022).…”

Introducing MADYS: the Manifold Age Determination for Young Stars

“…In the latter case, madys can be used in two steps of the chain: to obtain the age of the stellar target -either directly or by exploiting its kinematic neighbors-and to use such information to derive a mass estimate for the companion. A combination of indirect kinematic constraints and literature data was recently applied in Squicciarini et al (2022) to derive age and mass estimates for both the stellar target and its companions.…”

“…A preliminary version of madys has been already used, in in several publications(Janson et al 2021;Bonavita et al 2021;Squicciarini et al 2021Squicciarini et al , 2022 3 The current version on GitHub is an alpha version, only comprising the isochrones used in this paper.…”