TOI 560: Two Transiting Planets Orbiting a K Dwarf Validated with iSHELL, PFS, and HIRES RVs
Authors: El Mufti Mohammed , Plavchan Peter P. , Isaacson Howard , Cale Bryson L. , Feliz Dax L. , Reefe Michael A. , Hellier Coel , Stassun Keivan , Eastman Jason , Polanski Alex , Crossfield Ian J. M. , Gaidos Eric , Kostov Veselin , Wittrock Justin M. , Villaseñor Joel , Schlieder Joshua E. , Bouma Luke G. , Collins Kevin I. , Zohrabi Farzaneh , Lee Rena A. , Sohani Ahmad , Berberian John , Vermilion David , Newman Patrick , Geneser Claire , Tanner Angelle , Batalha Natalie M. , Dressing Courtney , Fulton Benjamin , Howard Andrew W. , Huber Daniel , Kane Stephen R. , Petigura Erik A. , Robertson Paul , Roy Arpita , Weiss Lauren M. , Behmard Aida , Beard Corey , Chontos Ashley , Dai Fei , Dalba Paul A. , Fetherolf Tara , Giacalone Steven , Hill Michelle L. , Hirsch Lea A. , Holcomb Rae , Lubin Jack , Mayo Andrew , Močnik Teo , Akana Murphy Joseph M. , Rosenthal Lee J. , Rubenzahl Ryan A. , Scarsdale Nicholas , Stockdale Christopher , Collins Karen , Cloutier Ryan , Relles Howard , Tan Thiam-Guan , Scott Nicholas J , Hartman Zach , Matthews Elisabeth , Ciardi David R. , Gonzales Erica , Matson Rachel A. , Beichman Charles , Bieryla Allyson , Furlan E. , Gnilka Crystal L. , Howell Steve B. , Ziegler Carl , Briceño César , Law Nicholas , Mann Andrew W. , Rabus Markus , Johnson Marshall C. , Christiansen Jessie , Kreidberg Laura , Berardo David Anthony , Deming Drake , Gorjian Varoujan , Morales Farisa Y. , Benneke Björn , Dragomir Diana , Wittenmyer Robert A. , Ballard Sarah , Bowler Brendan P. , Horner Jonathan , Kielkopf John , Liu Huigen , Shporer Avi , Tinney C. G. , Zhang Hui , Wright Duncan J. , Addison Brett C. , Mengel Matthew W. , Okumura Jack 
Published: December 2022

Abstract
We validate the presence of a two-planet system orbiting the 0.15–1.4 Gyr K4 dwarf TOI 560 (HD 73583). The system consists of an inner moderately eccentric transiting mini-Neptune (TOI 560 b,

P
=

6.3980661

−
0.0000097

+
0.0000095

days,

e
=

0.294

−
0.062

+
0.13

,

M
=

0.94

−
0.23

+
0.31

M

Nep

) initially discovered in the Sector 8 Transiting Exoplanet Survey Satellite (TESS) mission observations, and a transiting mini-Neptune (TOI 560 c,

P
=

18.8805

−
0.0011

+
0.0024

days,

M
=

1.32

−
0.32

+
0.29

M

Nep

) discovered in the Sector 34 observations, in a rare near-1:3 orbital resonance. We utilize photometric data from TESS Spitzer, and ground-based follow-up observations to confirm the ephemerides and period of the transiting planets, vet false-positive scenarios, and detect the photoeccentric effect for TOI 560 b. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with the iSHELL spectrograph at the NASA Infrared Telescope Facility and the HIRES Spectrograph at Keck Observatory to validate the planetary nature of these signals, which we combine with published Planet Finder Spectrograph RVs from the Magellan Observatory. We detect the masses of both planets at >3σ significance. We apply a Gaussian process (GP) model to the TESS light curves to place priors on a chromatic RV GP model to constrain the stellar activity of the TOI 560 host star, and confirm a strong wavelength dependence for the stellar activity demonstrating the ability of near-IR RVs to mitigate stellar activity for young K dwarfs. TOI 560 is a nearby moderately young multiplanet system with two planets suitable for atmospheric characterization with the James Webb Space Telescope and other upcoming missions. In particular, it will undergo six transit pairs separated by <6 hr before 2027 June.