Gaia and Hipparcos data from 63,254 stars place the brown dwarf desert at a mass ratio of about 2%
A preprint analysing astrometry of 63,254 stars finds companions depleted at a fixed mass ratio rather than a fixed mass, across hosts from M dwarfs to B stars.
A preprint on arXiv · preprint, not yet peer reviewed, analyses Hipparcos and Gaia DR2/DR3 astrometry for 63,254 stars. The authors report that the brown dwarf desert, the scarcity of companions between giant planets and stars, sits at a fixed companion-to-star mass ratio q of about 2%, and a desert at fixed companion mass is excluded arxiv.org
arXiv · препринтarxiv.orgOpen source ↗. The sample covers companions on 3–94 yr orbits (about 2–20 au) around hosts from M dwarfs to B stars.
According to the authors, the sample is 1–2 orders of magnitude larger than those of previous wide-orbit demographic studies. They describe it as the first single survey to measure occurrence rates of both planetary and stellar companions on such orbits across this range of host masses.
Astrometry and a population model instead of a detection list
A companion pulls the photocenter of its star along an ellipse around the common center of mass, and Hipparcos and Gaia can register this shift. Sensitivity drops only when the orbital period exceeds the time baseline of the data. It is fairly uniform across spectral types, because no spectral lines are needed for a Doppler shift.
Most candidate companions have poorly constrained periods, and few can be confirmed independently. The authors therefore set no detection threshold. A hierarchical model propagates each system's uncertainty over the number of companions and their parameters, and infers the population that best explains all stars at once. The input is the G23H catalog of posteriors from Gaia DR2, DR3 and Hipparcos. Host masses span 0.16–8.1 solar masses, with 99% between 0.54 and 5.1; they are constrained with Gaia photometry and MIST isochrone grids arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
Two populations on either side of the desert
Companions are strongly depleted at q of about 2% independent of stellar mass from M to B stars. Below the desert, occurrence rises with host metallicity; above it, occurrence falls with metallicity.
The authors suggest that the desert separates two populations, plausibly two formation channels, each scaling with stellar mass. The lightest stellar-like companions of K stars (about 13 Jupiter masses) are lighter than the heaviest planet-like companions of B stars (about 27 Jupiter masses). The planet-like population continues well beyond the deuterium-burning limit. On this basis the authors conclude that mass ratio, not mass, is the physically meaningful boundary between planets and their stellar-like counterparts.
The study was done ahead of the Gaia DR4 epoch astrometry release, from which thousands of planet detections are expected arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
