Study of the Mass-Ratio Distribution of Spectroscopic Binaries. II. The Boundaries of the Brown-Dwarf Desert as Seen with the APOGEE Spectroscopic Binaries. (arXiv:1905.13239v1 [astro-ph.SR])

Study of the Mass-Ratio Distribution of Spectroscopic Binaries. II. The Boundaries of the Brown-Dwarf Desert as Seen with the APOGEE Spectroscopic Binaries. (arXiv:1905.13239v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Shahaf_S/0/1/0/all/0/1">Sahar Shahaf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mazeh_T/0/1/0/all/0/1">Tsevi Mazeh</a>

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
$sim 10$ – $30$ days and secondaries with masses in the range of $sim0.01$ –
$0.1, M_{odot}$. 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 $sim0.02$ – $0.2, M_{odot}$. 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 $0.08, M_{odot}$,
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.

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
$sim 10$ – $30$ days and secondaries with masses in the range of $sim0.01$ –
$0.1, M_{odot}$. 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 $sim0.02$ – $0.2, M_{odot}$. 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 $0.08, M_{odot}$,
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.

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