TOI-969: a late-K dwarf with a hot mini-Neptune in the desert and an eccentric cold Jupiter

Abstract

The current architecture of a given multi-planetary system is a key fingerprint of its past formation and dynamical evolution history. Long-term follow-up observations are key to complete their picture. In this paper we focus on the confirmation and characterization of the components of the TOI-969 planetary system, where TESS detected a Neptune-size planet candidate in a very close-in orbit around a late K-dwarf star. We use a set of precise radial velocity observations from HARPS, PFS and CORALIE instruments covering more than two years in combination with the TESS photometric light curve and other ground-based follow-up observations to confirm and characterize the components of this planetary system. We find that TOI-969 b is a transiting close-in ($P_b\sim 1.82$ days) mini-Neptune planet ($m_b=9.1_{-1.0}^{+1.1}$ M${}_{\oplus }$, $R_b=2.765_{-0.097}^{+0.088}$ R${}_{\oplus }$), thus placing it on the {lower boundary} of the hot-Neptune desert ($T_{\mathrm{eq},\mathrm{b}}=941\pm 31$ K). The analysis of its internal structure shows that TOI-969 b is a volatile-rich planet, suggesting it underwent an inward migration. The radial velocity model also favors the presence of a second massive body in the system, TOI-969 c, with a long period of $P_c=1700_{-280}^{+290}$ days and a minimum mass of $m_c\sin i_c=11.3_{-0.9}^{+1.1}$ M${}_{\mathrm{Jup}}$, and with a highly-eccentric orbit of $e_c=0.628_{-0.036}^{+0.043}$. The TOI-969 planetary system is one of the few around K-dwarfs known to have this extended configuration going from a very close-in planet to a wide-separation gaseous giant. TOI-969 b has a transmission spectroscopy metric of 93, and it orbits a moderately bright ($G=11.3$ mag) star, thus becoming an excellent target for atmospheric studies. The architecture of this planetary system can also provide valuable information about migration and formation of planetary systems.

arXiv commentAccepted for publication in A&A. 25 pages, 15 figures, 12 tables

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