TOI-1235 b: a keystone super-Earth for testing radius valley emergence models around early M dwarfs
Creators: name: Cloutier, Ryan
name: Rodriguez, Joseph E.
name: Irwin, Jonathan
name: Charbonneau, David
name: Stassun, Keivan G.
name: Mortier, Annelies
name: Latham, David W.
name: Isaacson, Howard
name: Howard, Andrew W.
name: Udry, Stéphane
name: Wilson, Thomas G.
name: Watson, Christopher A.
name: Pinamonti, Matteo
name: Lienhard, Florian
name: Giacobbe, Paolo
name: Guerra, Pere
name: Collins, Karen A.
name: Beiryla, Allyson
name: Esquerdo, Gilbert A.
name: Matthews, Elisabeth
name: Matson, Rachel A.
name: Howell, Steve B.
name: Furlan, Elise
name: Crossfield, Ian J. M.
name: Winters, Jennifer G.
name: Nava, Chantanelle
name: Ment, Kristo
name: Lopez, Eric D.
name: Ricker, George
name: Vanderspek, Roland
name: Seager, Sara
name: Jenkins, Jon M.
name: Ting, Eric B.
name: Tenenbaum, Peter
name: Sozzetti, Alessandro
name: Sha, Lizhou
name: Ségransan, Damien
name: Schlieder, Joshua E.
name: Sasselov, Dimitar
name: Roy, Arpita
name: Robertson, Paul
name: Rice, Ken
name: Poretti, Ennio
name: Piotto, Giampaolo
name: Phillips, David
name: Pepper, Joshua
name: Pepe, Francesco
name: Molinari, Emilio
name: Mocnik, Teo
name: Micela, Giuseppina
name: Mayor, Michel
name: Fiorenzano, Aldo F. Martinez
name: Mallia, Franco
name: Lubin, Jack
name: Lovis, Christophe
name: López-Morales, Mercedes
name: Kosiarek, Molly R.
name: Kielkopf, John F.
name: Kane, Stephen R.
name: Jensen, Eric L. N.
name: Isopi, Giovanni
name: Huber, Daniel
name: Hill, Michelle L.
name: Harutyunyan, Avet
name: Gonzales, Erica
name: Giacalone, Steven
name: Ghedina, Adriano
name: Ercolino, Andrea
name: Dumusque, Xavier
name: Dressing, Courtney D.
name: Damasso, Mario
name: Dalba, Paul A.
name: Cosentino, Rosario
name: Conti, Dennis M.
name: Colón, Knicole D.
name: Collins, Kevin I.
name: Cameron, Andrew Collier
name: Ciardi, David
name: Christiansen, Jessie
name: Chontos, Ashley
name: Cecconi, Massimo
name: Caldwell, Douglas A.
name: Burke, Christopher
name: Buchhave, Lars
name: Beichman, Charles
name: Behmard, Aida
name: Beard, Corey
name: Murphy, Joseph M. Akana
Publisher: name: arXiv
Year: 2020
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Small planets on close-in orbits tend to exhibit envelope mass fractions of either effectively zero or up to a few percent depending on their size and orbital period. Models of thermally-driven atmospheric mass loss and of terrestrial planet formation in a gas-poor environment make distinct predictions regarding the location of this rocky/non-rocky transition in period-radius space. Here we present the confirmation of TOI-1235 b ($P=3.44$ days, $r_p=1.738^{+0.087}_{-0.076}$ R$_{\oplus}$), a planet whose size and period are intermediate between the competing model predictions thus making the system an important test case for emergence models of the rocky/non-rocky transition around early M dwarfs ($R_s=0.630\pm 0.015$ R$_{\odot}$, $M_s=0.640\pm 0.016$ M$_{\odot}$). We confirm the TESS planet discovery using reconnaissance spectroscopy, ground-based photometry, high-resolution imaging, and a set of 38 precise radial-velocities from HARPS-N and HIRES. We measure a planet mass of $6.91^{+0.75}_{-0.85}$ M$_{\oplus}$, which implies an iron core mass fraction of $20^{+15}_{-12}$% in the absence of a gaseous envelope. The bulk composition of TOI-1235 b is therefore consistent with being Earth-like and we constrain a H/He envelope mass fraction to be $&lt;0.5$% at 90% confidence. Our results are consistent with model predictions from thermally-driven atmospheric mass loss but not with gas-poor formation, suggesting that the former class of processes remain efficient at sculpting close-in planets around early M dwarfs. Our RV analysis also reveals a strong periodicity close to the first harmonic of the photometrically-determined stellar rotation period that we treat as stellar activity, despite other lines of evidence favoring a planetary origin ($P=21.8^{+0.9}_{-0.8}$ days, $m_p\sin{i}=13.0^{+3.8}_{-5.3}$ M$_{\oplus}$) that cannot be firmly ruled out by our data.
description: Accepted to The Astronomical Journal. 8 figures &amp; 5 tables. Table 2 is provided in the arXiv source code