The GALAH Survey: improving our understanding of confirmed and candidate planetary systems with large stellar surveys

Abstract

Pioneering photometric, astrometric, and spectroscopic surveys are helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy, and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the Gaia satellite, and other data from NASA’s Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs) and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others; Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet, to less than 2.3% and 8.5% respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH’s chemical abundances, we show through chemo-kinematics that there are five planet-hosts that are associated with the galaxy’s thick disc, including NGTS-4, K2-183 and K2-337. Finally, we show there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds.

A Spectroscopic Analysis of a Sample of K2 Planet-host Stars: Stellar Parameters, Metallicities and Planetary Radii

“…The stellar parameters obtained by Petigura et al (2017) were derived using synthetic spectra and the codes SpecMatch and SME@XSEDE; Brewer & Fischer (2018) derived the stellar parameters also using spectral synthesis and the Spectroscopy Made Easy (SME; Piskunov & Valenti 2017) code, while Martinez et al (2019) and Ghezzi et al (2021) adopted a methodology that was based on the classical spectroscopic EW method and used the code MOOG (Sneden 1973). Concerning results for K2 targets, in particular, Petigura et al (2018a), using the same methodology of Petigura et al (2017), analyzed a sample of 141 K2 candidate planet-host stars, while Wittenmyer et al (2020) analyzed a sample of 129 K2 planet candidate host stars whose spectra were observed by the K2-HERMES program (Wittenmyer et al 2018;Sharma et al 2019;Clark et al 2022) in the Galactic Archeology with HERMES (GALAH; Buder et al 2021) survey. In addition, results for a large number of both Kepler 1 and K2 targets were obtained by the low-resolution optical spectroscopic LAMOST survey (Cui et al 2012;Zong et al 2018), as well as the highresolution spectroscopic near-infrared APOGEE survey (Majewski et al 2017; see also Wilson et al 2018).…”