TOI-836: A super-Earth and mini-Neptune transiting a nearby K-dwarf

Kavli Affiliate: George Ricker

| First 5 Authors: Faith Hawthorn, Daniel Bayliss, Thomas G. Wilson, Andrea Bonfanti, Vardan Adibekyan

| Summary:

We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364)
using data from TESS Sector 11 and Sector 38. TOI-836 is a bright ($T = 8.5$
mag), high proper motion ($sim,200$ mas yr$^{-1}$), low metallicity
([Fe/H]$approx,-0.28$) K-dwarf with a mass of $0.68pm0.05$ M$_{odot}$ and a
radius of $0.67pm0.01$ R$_{odot}$. We obtain photometric follow-up
observations with a variety of facilities, and we use these data-sets to
determine that the inner planet, TOI-836 b, is a $1.70pm0.07$ R$_{oplus}$
super-Earth in a 3.82 day orbit, placing it directly within the so-called
‘radius valley’. The outer planet, TOI-836 c, is a $2.59pm0.09$ R$_{oplus}$
mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that
TOI-836 b has a mass of $4.5pm0.9$ M$_{oplus}$ , while TOI-836 c has a mass
of $9.6pm2.6$ M$_{oplus}$. Photometric observations show Transit Timing
Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are
no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by
an undetected exterior planet.

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