Search for giant planets in M 67 V: A warm Jupiter orbiting the turn-off star S1429

¹ Universitäts-Sternwarte München, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 München, Germany
e-mail: lthomas@usm.lmu.de
² Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
³ ESO-European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁴ Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Arcetri, 50125 Firenze, Italy
⁵ GEPI, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, 92190 Meudon, France
⁶ Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, Campus Universitário, Natal, RN, 59072-970, Brazil
⁷ Georg-August-Universität, Institut für Astrophysik und Geophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁸ Instituto Nazionale di Astrofisica, Osservatorio Astronomico di Padova, 35122 Padova, Italy
⁹ Instituto Nazionale di Astrofisica, Osservatorio Astronomico di Roma, via Frascati 33, Monte Porzio Catone, Italy

Received: 15 January 2024
Accepted: 28 February 2024

Abstract

Context. Planets orbiting members of open or globular clusters offer a great opportunity to study exoplanet populations systematically, as stars within clusters provide a mostly homogeneous sample, at least in chemical composition and stellar age. However, even though there have been coordinated efforts to search for exoplanets in stellar clusters, only a small number of planets have been detected. One successful example is the seven-year radial velocity (RV) survey ‘Search for giant planets in M 67’ of 88 stars in the open cluster M 67, which led to the discovery of five giant planets, including three close-in (P < 10 days) hot-Jupiters.

Aims. In this work, we continue and extend the observation of stars in M 67, with the aim being to search for additional planets.

Methods. We conducted spectroscopic observations with the Habitable Planet Finder (HPF), HARPS, HARPS-North, and SOPHIE spectrographs of 11 stars in M 67. Six of our targets showed a variation or long-term trends in their RV during the original survey, while the other five were not observed in the original sample, bringing the total number of stars to 93.

Results. An analysis of the RVs reveals one additional planet around the turn-off point star S1429 and provides solutions for the orbits of stellar companions around S2207 and YBP2018. S1429 b is a warm-Jupiter on a likely circular orbit with a period of ${77.48}_{-0.19}^{+0.18}$ days and a minimum mass of M sin i = 1.80 ± 0.2 M_J. We update the hot-Jupiter occurrence rate in M 67 to include the five new stars, deriving ${4.2}_{-2.3}^{+4.1}\mathrm{\%}$ when considering all stars, and ${5.4}_{-3.0}^{+5.1}\mathrm{\%}$ if binary star systems are removed.