Gyrochronological dating of the stellar moving group Group X

Abstract

Context. Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. Aims. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. Methods. We extracted the light curves of all candidate members from the TESS full frame images and measured their rotation periods using different period search methods. Results. We measured the rotation period of 168 of a total of 218 stars and compared their period-colour distribution with those of two age-benchmark clusters, the Pleiades (125 Myr) and Praesepe (625 Myr), as well as with the recently characterised open cluster NGC 3532 (300 Myr). Conclusions. As result of our analysis, we derived a gyro age of 300 ± 60 Myr. We also applied as independent methods the fitting of the entire isochrone and of the three brightest candidate members individually with the most precise stellar parameters, deriving comparable values of 250 Myr and 290 Myr, respectively. Our dating of Group X allows us to definitively rule out the previously proposed connection with the nearby but much older Coma Berenices cluster.

The GAPS Programme at TNG

“…The rotation period vs color for TOI-1807, TOI-2076 and the other comoving objects (see Fig. 7) matches well the sequence of Group X recently obtained by Messina et al (2022). Group X is a sparse association overlapping on the sky with the Coma Ber open cluster, but with distinct kinematics and age.…”

“…Group X is a sparse association overlapping on the sky with the Coma Ber open cluster, but with distinct kinematics and age. Messina et al (2022) derived an age of 300±60 Myr for this group, considering both the rotation sequence and isochrone fitting of turn-off members, making it an ideal reference for objects with age intermediate between Hyades and Pleiades. From the overall similitude to Group X age, we adopted 300±80 Myr for TOI-1807.…”

“…We obtained the light curves of these stars from the Full Frame Images (FFIs) by using the PATHOS pipeline described in detail by Nardiello et al (2019) and also reported in Section 2.1. We selected the best aperture for each target comparing their mean rms distributions, as described in detail by Nardiello et al (2020) and Messina et al (2022).…”

“…We analyzed the TESS light curves of all 55 stars to measure the rotation period. Details on the procedure can be found in Messina et al (2022). Briefly, we used three different methods: Generalized Lomb-Scargle (GLS; Zechmeister & Kürster 2009), CLEAN (Roberts et al 1987) and AutoCorrelation Function (ACF; McQuillan et al 2013) in order to provide a "grade" of confidence on the correctness of the measured rotation periods ("A" if the three methods provided a similar value; "B" when only two methods found a similar value; "C" when period estimates differed across all three methods).…”

Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars

“…Several of our targets have ages between Hyades and Pleiades. In this range, we took advantage of the recently derived rotation sequence for Group X at an age of 300 Myr (Messina et al 2022). When applicable, we considered the age indicators for physical companions outside the SPHERE field of view and, for close binaries, we deblended photometric colors for binarity, to improve the reliability of the derived ages.…”