TOI 560 : Two Transiting Planets Orbiting a K Dwarf Validated with iSHELL, PFS and HIRES RVs

Kavli Affiliate: Avi Shporer

| First 5 Authors: Mohammed El Mufti, Peter P. Plavchan, Howard Isaacson, Bryson L. Cale, Dax L. Feliz

| Summary:

We validate the presence of a two-planet system orbiting the 0.2–1.4 Gyr K4
dwarf TOI 560 (HD 73583). The system consists of an inner moderately eccentric
transiting mini-Neptune (TOI 560 b, $P = 6.397438 pm 0.000037$ days,
$e=0.294^{0.13}_{0.062}$) initially discovered in the Sector 8 tess mission
observations, and a transiting mini-Neptune (TOI 560 c, $P = 18.8779 pm
0.0016$ days) discovered in the Sector 34 observations, in a rare 1:3 orbital
resonance. We utilize photometric data from tess, textit{Spitzer}, and
ground-based follow-up observations to confirm the ephemerides and period of
the transiting planets and vet false positive scenarios. 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 PFS RVs from Magellan Observatory. We place upper limits
on the masses of both planets of $<$2.1 and $<$4.1 M$_{Nep}$ for b and c,
respectively. We apply a Gaussian Processes (GP) model to the tess light
curves to place priors on a chromatic radial velocity GP model to constrain the
stellar activity of the TOI 560 host star. TOI 560 is a nearby moderately young
multi-planet system with two planets suitable for atmospheric characterization
with James Webb Space Telescope (JWST) and other upcoming missions. In
particular, it will undergo six transit pairs separated by $<$6 hours before
June 2027.

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