Study of the Mass-Ratio Distribution of Spectroscopic Binaries. II. The Boundaries of the Brown-Dwarf Desert as Seen with the APOGEE Spectroscopic Binaries

Abstract

Analysis of APOGEE DR12 stellar radial-velocities by Troup et al. (2016) affirmed the existence of the well-known Brown-Dwarf Desert (BDD). They detected a dearth of spectroscopic binaries (SB) with periods shorter than ∼ 10-30 days and secondaries with masses in the range of ∼ 0.01-0.1 M . We reconsider here their sample of binaries, focusing on 116 systems on the main sequence of the Gaia color-magnitude diagram, with mostly K-dwarf primaries. Using our recently devised algorithm to analyze the mass-ratio distribution of a sample of SBs we confirm the BDD existence and delineate its boundaries. For the K-dwarf APOGEE 1-25 days binaries, the companion-mass range of the BDD is ∼ 0.02-0.2 M . The mass ratio distribution of the long-period (25-500 days) binaries does not show any dearth at the q-range studied. Instead, their distribution displays a linear increase in log q, implying a tendency towards low-q values. The limits of the BDD do not coincide with the frequently used mass limits of the brown-dwarf population, sometimes defined as 0.013 and 0.08 M , based on theoretically derived stellar minimum masses for burning deuterium and hydrogen in their cores. Trying to draw the boundaries of the desert, we suggest either a wedged or trapezoidal shape. We discuss briefly different scenarios that can account for the formation of the BDD, in terms of differentiating between stellar secondaries and planets in particular, and compare this desert to the Neptunian desert that can distinguish between Jovian planets and super Earths of short periods.

Impact of Binary Stars on Planet Statistics -- I. Planet Occurrence Rates, Trends with Stellar Mass, and Wide Companions to Hot Jupiter Hosts

“…M-type (Dieterich et al 2012;Duchêne & Kraus 2013), solar-type (Grether & Lineweaver 2006;Santerne et al 2016), and A-type (Murphy et al 2018) primaries all exhibit an intrinsic dearth of close brown dwarf companions (M2 0.08 M⊙) commonly known as the brown dwarf desert. The brown dwarf desert is observed within a 1 au (Grether & Lineweaver 2006;Csizmadia et al 2015;Santerne et al 2016;Murphy et al 2018;Shahaf & Mazeh 2019), and only ≈ 2% of stars have brown dwarf companions across intermediate separations of a ≈ 10 -100 au (Kraus et al 2008(Kraus et al , 2011Dieterich et al 2012;Wagner et al 2019;Nielsen et al 2019). Even if brown dwarf companions are capable of suppressing planet formation, their contribution is statistically insignificant compared to close stellar companions.…”

Formation of close binaries by disc fragmentation and migration, and its statistical modelling

“…Binaries that formed early have, on average, migrated to shorter periods and have larger q. Various surveys have demonstrated that solar-type primaries exhibit a dearth of close brown dwarf companions within P 100 days, commonly known as the brown dwarf desert, but that the frequency of brown dwarf companions increases with increasing separation (Grether & Lineweaver 2006;Kraus et al 2008Kraus et al , 2011Csizmadia et al 2015;Wagner et al 2019;Shahaf & Mazeh 2019). Our model naturally reproduces the brown dwarf desert, as it is very difficult for very low-mass companions to migrate within P 100 days without also accreting above M2 > 0.08 M⊙.…”

3D Selection of 167 Substellar Companions to Nearby Stars

“…Recently, more and more BDs have been found to reside in this desert (e.g., Persson et al 2019;Carmichael et al 2019Carmichael et al , 2020Acton et al 2021). As suggested by Shahaf & Mazeh (2019), characterization of the shape of the brown dwarf desert in the period-mass diagram by a large sample of circumstellar BDs can improve our understanding of its origin.…”