BEAST begins: sample characteristics and survey performance of the B-star Exoplanet Abundance Study

Abstract

While the occurrence rate of wide giant planets appears to increase with stellar mass at least up through the A-type regime, B-type stars have not been systematically studied in large-scale surveys so far. It therefore remains unclear up to what stellar mass this occurrence trend continues. The B-star Exoplanet Abundance Study (BEAST) is a direct imaging survey with the extreme adaptive optics instrument SPHERE, targeting 85 B-type stars in the young Scorpius-Centaurus (Sco-Cen) region with the aim to detect giant planets at wide separations and constrain their occurrence rate and physical properties. The statistical outcome of the survey will help determine if and where an upper stellar mass limit for planet formation occurs. In this work, we describe the selection and characterization of the BEAST target sample. Particular emphasis is placed on the age of each system, which is a central parameter in interpreting direct imaging observations. We implement a novel scheme for age dating based on kinematic sub-structures within Sco-Cen, which complements and expands upon previous age determinations in the literature. We also present initial results from the first epoch observations, including the detections of ten stellar companions, of which six were previously unknown. All planetary candidates in the survey will need follow up in second epoch observations, which are part of the allocated observational programme and will be executed in the near future.

The Scorpion Planet Survey: Wide-Orbit Giant Planets Around Young A-type Stars

“…Finally, our results offer a complementary sample to past studies that were largely focused on lower-mass stellar hosts in the solar neighborhood, and also to other ongoing surveys of both higher and lower-mass stars in Sco OB2. Taken in combination with GPIES (Nielsen et al 2019) and SHINE (Vigan et al 2021), the BEASTS survey of B-type stars (Janson et al 2021), and YSES survey (Bohn et al 2020(Bohn et al , 2021 of solar-type stars (both also focused on Sco OB2), these surveys provide a rich and comprehensive view of wide-orbit giant plants around nearby young stars. Together, they inform our understanding of exoplanet demographics, and perhaps of equal importance, enable the yield of future exoplanet imaging surveys to be enhanced by targeting stars around which detectable planets are more likely to exist.…”

Unveiling the star formation history of the Upper Scorpius association through its kinematics

“…The tool, to be shortly made publicly available, constitutes a development of the age determination tool already employed in 2020), are computed for simplicity at a fixed 𝑑 = 160 pc, encompassing ∼ 90% of the sample. Janson et al (2021). We describe in this Section the results of the kinematic analysis of our samples.…”

“…The discipline of star formation, in all of its aspects, has always been of paramount importance in astrophysics: lying at the interception of several fields of studies, it stretches from the grandest scale of galactic evolution, passing through the intricate web of the interstellar medium, to the dusty scenery of primordial discs, where stellar furnaces mildly begin to shimmer and glow. The presence of active stellar formation in our Galaxy (Evans 1999) provides the opportunity to gaze at the process while it unfolds before our eyes: during the last years, several surveys have been performed to study the environment of galactic star-forming regions (e.g., Churchwell et al 2009), the formation of multiple systems (e.g., Kraus et al 2011), or even to directly test the predictions from models of planetary formation (e.g., Janson et al 2021).…”

“…Spanning an enormous area of approximately 80 • × 40 • in the sky, this very young (𝑡 < 20 Myr, Pecaut et al 2012) region comprises a few regions still actively forming stars (Wilking et al 2008). The exquisite concoction of closeness, youth and low extinction, allowing detection of members down to the brown dwarf regime, has made it the target of many studies in the last decades (e.g., de Zeeuw et al 1999;Mamajek et al 2002) involving binaries (e.g., Janson et al 2013), primordial discs (e.g., Carpenter et al 2006), high mass (Chen et al 2012), Sun-like (e.g., Pecaut et al 2012) and low-mass stars (e.g., Lodieu 2013), and even young planets (e.g., Janson et al 2021).…”

A scaled-up planetary system around a supernova progenitor

“…On the other hand, as already mentioned, massive planets at large separations can be detected through direct imaging provided that they are young enough. Past high-contrast imaging surveys (e.g., Rameau et al 2013;Bowler 2016;Chauvin et al 2017;Nielsen et al 2019;Vigan et al 2021) have focused on stars of spectral type A or later (M 2.4M ); to fill in the gap, in 2018 we started the B-star Exoplanet Abundance STudy (BEAST) survey (Janson et al 2021b), exploiting the capabilities of the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument (Beuzit et al 2019) at the Very Large Telescope (VLT): its scientific goal is to look for exoplanets around a sample of 85 B stars in the young (5-20 million years) Scorpius-Centaurus OB association (Sco-Cen), the nearest region of ongoing stellar formation. While the survey is still in progress, we recently reported the discovery of a 10.9 ± 1.6M J planet around the stellar binary b Cen, whose total mass reaches 6-10 M (Janson et al 2021a).…”