The young HD 73583 (TOI-560) planetary system: two 10-M-circle plus mini-Neptunes transiting a 500-Myr-old, bright, and active K dwarf

Abstract

We present the discovery and characterization of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterize the system. We found that HD73583 is a young (~500 Myr) active star with a rotational period of 12.08 ± 0.11 ?d, and a mass and radius of 0.73 ± 0.02 M? and 0.65 ± 0.02 R?, respectively. HD?73583?b (Pb = 6.3980420+0.0000067-0.0000062 d) has a mass and radius of 10.2+3.4-3.1 M? and 2.79 ± 0.10 R?, respectively, which gives a density of 2.58+0.95-0.81 gcm-3?. HD?73583?c (Pc = 18.87974+0.00086-0.00074 d) has a mass and radius of 9.7+1.8-1.7 M? and 2.39+0.10-0.09 R?, respectively, which translates to a density of 3.88+0.91-0.80 gcm-3?. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.