Kavli Affiliate: Michael Fausnaugh
| First 5 Authors: Laurel Kaye, Shreyas Vissapragada, Maximilian N. Gunther, Suzanne Aigrain, Thomas Mikal-Evans
| Summary:
We present ground and space-based photometric observations of TOI-270
(L231-32), a system of three transiting planets consisting of one super-Earth
and two sub-Neptunes discovered by TESS around a bright (K-mag=8.25) M3V dwarf.
The planets orbit near low-order mean-motion resonances (5:3 and 2:1), and are
thus expected to exhibit large transit timing variations (TTVs). Following an
extensive observing campaign using 8 different observatories between 2018 and
2020, we now report a clear detection of TTVs for planets c and d, with
amplitudes of $sim$10 minutes and a super-period of $sim$3 years, as well as
significantly refined estimates of the radii and mean orbital periods of all
three planets.
Dynamical modeling of the TTVs alone puts strong constraints on the mass
ratio of planets c and d and on their eccentricities. When incorporating
recently published constraints from radial velocity observations, we obtain
masses of $M_{mathrm{b}}=1.48pm0.18,M_oplus$, $M_{c}=6.20pm0.31,M_oplus$
and $M_{mathrm{d}}=4.20pm0.16,M_oplus$ for planets b, c and d,
respectively. We also detect small, but significant eccentricities for all
three planets : $e_mathrm{b} =0.0167pm0.0084$, $e_{c} =0.0044pm0.0006$ and
$e_{d} = 0.0066pm0.0020$. Our findings imply an Earth-like rocky composition
for the inner planet, and Earth-like cores with an additional He/H$_2$O
atmosphere for the outer two. TOI-270 is now one of the best-constrained
systems of small transiting planets, and it remains an excellent target for
atmospheric characterization.
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