Hot planets around cool stars - two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
Fridlund, M.; Guenther, E. W.; Barragán, O.; Gandolfi, D.; Hirano, T.; Korth, J.; Grziwa, S.; Albrecht, S.; Smith, A. M. S.; Cochran, W. D.; Palle, E.; Persson, C. M.; Van Eylen, V.; Nowak, G.; Winn, J. N.; Knudstrup, E.; Serrano, L. M.; Collins, K. A.; Deeg, H. J.; Esposito, M.; Goffo, E.; Jenkins, J. M.; Lam, K. W. F.; Luque, R.; Osborne, H. L. M.; Redfield, S.; Ricker, G. R.; Seager, S.; Twicken, J. D.; Bieryla, A.; Latham, D. W.; Vanderspek, R.; Brasseur, C. E.; Csizmadia, Sz; Furlan, E.; Carleo, I.; Crossfield, I. J. M.; Gonzales, E.; Kane, S. R.; Stassun, K. G.; Kabáth, P.; Guerra, P.; Jensen, E. L. N.; Howell, S. B.; Matthews, E. C.; Livingston, J.; Levine, A. M.; Schlieder, J. E.; Tenenbaum, P.; Quinn, S. N.; Scott, N. J.; Gan, T.; Matson, R. A.; Paegert, M.; Ciardi, D.; Georgieva, I. Y.; Locci, D.; McDermott, S.; Colon, K. D.
Sweden, United Kingdom, Spain, Netherlands, Italy, United States, Japan, Switzerland, Denmark, Germany, China, Czech Republic
Abstract
We present the discovery and characterization of two sub-Neptunes in close orbits, as well as a tentative outer planet of a similar size, orbiting TOI-1260 - a low metallicity K6 V dwarf star. Photometry from Transiting Exoplanet Survey Satellite(TESS) yields radii of Rb = 2.33 ± 0.10 and Rc = 2.82 ± 0.15 R⊕, and periods of 3.13 and 7.49 d for TOI-1260 b and TOI-1260 c, respectively. We combined the TESS data with a series of ground-based follow-up observations to characterize the planetary system. From HARPS-N high-precision radial velocities we obtain Mb = $8.6 _{ - 1.5 } ^ { + 1.4 }$ and Mc = $11.8 _{ - 3.2 } ^ { + 3.4 }$ M⊕. The star is moderately active with a complex activity pattern, which necessitated the use of Gaussian process regression for both the light-curve detrending and the radial velocity modelling, in the latter case guided by suitable activity indicators. We successfully disentangle the stellar-induced signal from the planetary signals, underlining the importance and usefulness of the Gaussian process approach. We test the system's stability against atmospheric photoevaporation and find that the TOI-1260 planets are classic examples of the structure and composition ambiguity typical for the 2-3 R⊕ range.