The GALAH Survey: Using Galactic Archaeology to Refine our Knowledge of TESS Target Stars

Abstract

An unprecedented number of exoplanets are being discovered by the Transiting Exoplanet Survey Satellite (TESS ). Determining the orbital parameters of these exoplanets, and especially their mass and radius, will depend heavily upon the measured physical characteristics of their host stars. We have cross-matched spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the TESS Input Catalog and Gaia Data Release 2, to create a curated, self-consistent catalog of physical and chemical properties for 47,285 stars. Using these data we have derived isochrone masses and radii that are precise to within 5%. We have revised the parameters of three confirmed, and twelve candidate, TESS planetary systems. These results cast doubt on whether CTOI-20125677 is indeed a planetary system since the revised planetary radii are now comparable to stellar sizes. Our GALAH-TESS catalog contains abundances for up to 23 elements. We have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si and Fe/Mg, to assist in determining the composition and structure of planets with R p < 4R ⊕ . From these ratios, 36 % fall within 2 sigma of the Sun/Earth values, suggesting that these stars may host rocky exoplanets with geological compositions similar to planets found within our own Solar system.

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

“…There is an overall good agreement between the catalogs, with a mean difference between Teff values from GALAH and TIC of −11 +121 −127 K, and Gaia of 32 +281 −163 K, with an RMS difference of 10 and 21 K, respectively. Just as Hardegree-Ullman et al ( 2020) and Clark et al (2020) showed in their work, we also find a horizontal structure within our Gaia T eff comparison near 5000 K. This further suggests that Gaia T eff values preferentially converge onto some T eff values over others. For our comparison of TIC T eff values, we only compare GALAH's values to those found with the TIC that have been derived photometrically and not spectroscopically.…”

“…There are twelve CTOIs that have radii comparable to substellar and stellar objects, being larger than our 2R P limit. Of these Clark et al (2020) also found the planetary radii values for CTOI 201256771.01, CTOI 201256771.02 and CTOI 300903537.01 to be too large for a planetary object. The two candidates orbiting TIC 141622065 both have radii of 344.62±6.50R ⊕ and 339.57±6.40R ⊕ , with an orbital period separation of 0.05 days.…”

“…To derive the physical parameters of these host stars from the GALAH catalog, we use a similar approach to Clark et al (2020), implementing the Python package (Morton 2015). derives physical parameters from observed stellar parameters using the stellar evolution grid, MESA Isochrones & Stellar Tracks (MIST; Choi et al 2016).…”

“…Similarly, the radii for all candidates in the CTOI 91369561 system including TIC 91369561.02 and TIC 91369561.03 have radii comparable to FGK type stars. CTOI 140830390.01 and CTOI 220402290.02 have planetary radii on the cusp of the "planetarylimit" of ∼22R ⊕ , but was further suggested in Clark et al (2020) that the candidate events within the CTOI 220402290 system are also from a single object, which is likely caused by a sub-stellar or stellar companion. CTOIs 31869740.01 and 219322317.01 are both recorded as having sub-stellar radius values of 31.61R ⊕ and 39.24±2.64R ⊕ respectively on TFOP.…”

“…The resulting dataset is a treasuretrove of information that is of vital importance to the exoplanet community. In particular, the GALAH stellar abundances can assist in determining the compositions of the planets these stars might host (Bitsch & Battistini 2020;Clark et al 2020;Unterborn et al 2018a;Dorn et al 2017Dorn et al , 2015Rogers & Seager 2010), and even the types of planets the stars could potentially host (Hinkel et al 2019). At the same time, the Gaia spacecraft is taking incredibly precise distance measurements of the stars being surveyed by GALAH (surveying up to ∼ 2% of all stars in the Galaxy).…”