"Astronomers have discovered five transiting companions near the
hydrogen-burning mass limit in close orbits around main-sequence stars
TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. A defining characteristic of brown dwarfs is their relative low
occurrence rate (less than 1%) in close orbits (less than 5 AU) around
main-sequence stars compared to giant planets and other stars, or the
‘brown dwarf desert.’
“Brown dwarfs are supposed to shrink over time as they burn up their
deuterium reserves and cool down,” said Professor François Bouchy.
“We found that the two oldest objects, TOI-148b and TOI-746b, have a
smaller radius, while the two younger companions have larger radii.”
With an effective temperature of 9800 ± 200 K, TOI-587 is the hottest
known main-sequence star to host a transiting brown dwarf or very
low-mass star. We found evidence of spin-orbit synchronization for
TOI-148 and TOI-746 as well as tidal circularization for TOI-148.
“Even with these additional objects, we still lack the numbers to
draw definitive conclusions about the differences between brown dwarfs
and low-mass stars,” Dr. Grieves said.
TOI-681 has been previously reported to be a member of the open star cluster NGC 2516...TOI-681 is relatively hot (Teff = 7440
K) and fast rotating (Prot∕sin i
= 2.61 ± 0.13 days) star, which can create enhanced magnetic fields
from spin-orbit tidal synchronization for short period systems and has
been thought to cause inflated radii of similar low-mass companions.
However, given its relatively long period of 15.78 days TOI-681b is unlikely to have reached spin-orbit
synchronization.
TOI-746 .... with a companion on a moderately eccentric e
= 0.199 ± 0.003 orbit. As discussed, tidal torques can drive a star’s
rotation rate toward a tidally locked state where the tidal torques fix
the rotation period Prot to the equilibrium rotation period Peq. Tidal models can predict Peq including the “constant phase lag” equilibrium tidal model. Following Barnes (2017) and Fleming et al. (2019) the CPL model permits a 1:1 and 3:2 spin-orbit state by:
Using the second case we find Peq = 7.32 days for TOI-746 and with an upper limit on the rotation period of Prot∕sin i
= 7.9 ± 1.6 days TOI-746 may be in a supersychronous 3:2 spin-orbit
state. We also consider the system may be in a pseudo-synchronous
rotation state that approximates spin-orbit synchronization around the time of periastron. Zimmerman explored possible pseudosynchronization for heartbeat binary stars with Kepler lightcurves but found generally that their sampleclustered around 
times the pseudosynchronization period indicating that they have
plateaued prematurely in their synchronization. We roughly estimate this
using Kepler’s third law to determine what the period would be if the
companion was in a circular orbit at the periastron distance:
Assuming this circular orbit at periastron we find Pperi
= 7.88 ± 0.05 days which is very similar to the upper limit of the
rotation period suggesting TOI-746 may be in a pseudo-synchronous
rotation at periastron.
TOI-1213 ... star with a companion on an eccentric e = 0.498
orbit. We find Peq = 18.14 days for TOI-1213, and with Prot∕sin i = 12.0 ± 3.6 days TOI-1213 does not appear to have spin-orbit synchronization.
TOI-148,which is on the upper end of v sin i* distributions for stars of similar mass, indicating TOI-148’s stellar rotation period may be affected by tidal torques with its companion.
TOI-587 is a very hot star which is outside the range of temperatures in
the spectral library of SpecMatch-Emp. TOI-587 also falls outside the
valid temperature range for the MARCS model atmospheres and we instead
use the ATLAS9 model atmosphere..... TOI-587 is the hottest main-sequence host star of a transiting brown dwarf or low-mass star below 150 MJup with a Teff = 
K.
The sample of transiting brown dwarfs and low-mass stars we analyzed is
still too small to make significant statistical claims; however, their
eccentricity and metallicity distributions are still consistent with
previous suggestions of two separate populations for lower and higher
mass brown dwarfs." SciNews/ecosciences
Maybe they were CREATED as two different star Populations... Which commandeth the sun, and it riseth not; and sealeth up the stars. Job 9:7
