The GAPS Programme at TNG XL: A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422
Creators: name: Naponiello, L.
name: Mancini, L.
name: Damasso, M.
name: Bonomo, A. S.
name: Sozzetti, A.
name: Nardiello, D.
name: Biazzo, K.
name: Stognone, R. G.
name: Lillo-Box, J.
name: Lanza, A. F.
name: Poretti, E.
name: Lissauer, J. J.
name: Zeng, L.
name: Bieryla, A.
name: Hébrard, G.
name: Basilicata, M.
name: Benatti, S.
name: Bignamini, A.
name: Borsa, F.
name: Claudi, R.
name: Cosentino, R.
name: Covino, E.
name: de Gurtubai, A.
name: Delfosse, X.
name: Desidera, S.
name: Dragomir, D.
name: Eastman, J. D.
name: Essack, Z.
name: Fiorenzano, A. F. M.
name: Giacobbe, P.
name: Harutyunyan, A.
name: Heidari, N.
name: Hellier, C.
name: Jenkins, J. M.
name: Knapic, C.
name: König, P. -C.
name: Latham, D. W.
name: Magazzù, A.
name: Maggio, A.
name: Maldonado, J.
name: Micela, G.
name: Molinari, E.
name: Molinaro, M.
name: Morgan, E. H.
name: Moutou, C.
name: Nascimben, V.
name: Pace, E.
name: Pagano, I.
name: Pedani, M.
name: Piotto, G.
name: Pinamonti, M.
name: Quintana, E. V.
name: Rainer, M.
name: Ricker, G. R.
name: Seager, S.
name: Twicken, J. D.
name: Vanderspek, R.
name: Winn, J. N.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We investigate the exoplanet candidate TOI-1422b, which was discovered by the TESS space telescope around the high proper-motion G2V star TOI-1422 ($V=10.6$ mag), 155pc away, with the primary goal of confirming its planetary nature and characterising its properties. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 years to precisely quantify its radial velocity variation. The radial velocity measurements are analyzed jointly with TESS photometry and we also check for blended companions through high-spatial resolution images using the AstraLux instrument. We estimate that the parent star has a radius and a mass of $R^*=1.019_{-0.013}^{+0.014} R_{\odot}$, $M^*=0.981_{-0.065}^{+0.062} M_{\odot}$, respectively. Our analysis confirms the planetary nature of TOI-1422b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422c, which is not detected in TESS light curves. The inner planet, TOI-1422b, orbits on a period $P_{\rm b}=12.9972\pm0.0006$ days and has an equilibrium temperature $T_{\rm eq, b}=867\pm17$ K. With a radius of $R_{\rm b}=3.96^{+0.13}_{-0.11} R_{\oplus}$, a mass of $M_{\rm b}=9.0^{+2.3}_{-2.0} M_{\oplus}$ and, consequently, a density of $ρ_{\rm b}=0.795^{+0.290}_{-0.235}$ g cm$^{-3}$, it can be considered a warm Neptune-size planet. Compared to other exoplanets of similar mass range, TOI-1422b is among the most inflated ones and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around $10\%-25\%$ of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422c, has an orbital period of $P_{\rm c}=29.29^{+0.21}_{-0.20}$ days, a minimum mass, $M_{\rm c}\sin{i}$, of $11.1^{+2.6}_{-2.3} M_{\oplus}$, an equilibrium temperature of $T_{\rm eq, c}=661\pm13$ K and, therefore, if confirmed, it could be considered as another warm Neptune.
description: 22 pages, 20 figures, 6 tables. Accepted for publication in Astronomy &amp; Astrophysics on July 7, 2022. Abstract abridged