Kavli Affiliate: George R. Ricker
| First 5 Authors: Ian Wong, Avi Shporer, George Zhou, Daniel Kitzmann, Thaddeus D. Komacek
| Summary:
We report the discovery of an ultrahot Jupiter with an extremely short
orbital period of $0.67247414,pm,0.00000028$ days ($sim$16 hr). The $1.347
pm 0.047$ $R_{rm Jup}$ planet, initially identified by the Transiting
Exoplanet Survey Satellite (TESS) mission, orbits TOI-2109 (TIC 392476080): a
$T_{rm eff} sim 6500$ K F-type star with a mass of $1.447 pm 0.077$ $M_{rm
Sun}$, a radius of $1.698 pm 0.060$ $R_{rm Sun}$, and a rotational velocity
of $vsin i_* = 81.9 pm 1.7$ km s$^{-1}$. The planetary nature of TOI-2109b
was confirmed through radial velocity measurements, which yielded a planet mass
of $5.02 pm 0.75$ $M_{rm Jup}$. Analysis of the Doppler shadow in
spectroscopic transit observations indicates a well-aligned system, with a
sky-projected obliquity of $lambda = 1overset{circ}{.}7 pm
1overset{circ}{.}7$. From the TESS full-orbit light curve, we measured a
secondary eclipse depth of $731 pm 46$ ppm, as well as phase-curve variations
from the planet’s longitudinal brightness modulation and ellipsoidal distortion
of the host star. Combining the TESS-band occultation measurement with a
$K_s$-band secondary eclipse depth ($2012 pm 80$ ppm) derived from
ground-based observations, we find that the dayside emission of TOI-2109b is
consistent with a brightness temperature of $3631 pm 69$ K, making it the
second hottest exoplanet hitherto discovered. By virtue of its extreme
irradiation and strong planet-star gravitational interaction, TOI-2109b is an
exceptionally promising target for intensive follow-up studies using current
and near-future telescope facilities to probe for orbital decay, detect tidally
driven atmospheric escape, and assess the impacts of H$_2$ dissociation and
recombination on the global heat transport.
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