Abstract
Abstract GALAH+ is a magnitude-limited survey of high resolution stellar spectra obtained by the HERMES spectrograph at the Australian Astronomical Observatory. Its third data release provides reduced spectra with new derivations of stellar parameters and abundances of 30 chemical elements for 584,015 dwarfs and giants, 88 per cent of them in the Gaia magnitude range 11 < G < 14. Here we use these improved values of stellar parameters to build a library of observed spectra which is useful to study variations of individual spectral lines with stellar parameters. This and other improvements are used to derive radial velocities with uncertainties which are generally within 0.1 km s−1 or ∼25 per cent smaller than in the previous release. Median differences in radial velocities measured here and by the Gaia DR2 or APOGEE DR16 surveys are smaller than 30 m s−1, a larger offset is present only for Gaia measurements of giant stars. We identify 4483 stars with intrinsically variable velocities and 225 stars for which the velocity stays constant over ≥3 visits spanning more than a year. The combination of radial velocities from GALAH+ with distances and sky plane motions from Gaia enables studies of dynamics within streams and clusters. For example, we estimate that the open cluster M67 has a total mass of ∼3300 M⊙ and its outer parts seem to be expanding, though astrometry with a larger time-span than currently available from Gaia eDR3 is needed to judge if the latter result is real.
Highlights
Galactic archaeology (Freeman & Bland-Hawthorn 2002) aims to decipher the structure and formation of our Galaxy as one of the typical galaxies in the Universe through detailed measurements of stellar kinematics and chemistry of their atmospheres
In this paper we presented the construction of a new library of observed median spectra observed by the GALAH+ survey, based on parameters of its DR3 data release (B20)
The observed median spectra are virtually noise-free so that their radial velocity (RV) versus synthetic spectra can be computed over many wavelength intervals which may contain only weak lines
Summary
Galactic archaeology (Freeman & Bland-Hawthorn 2002) aims to decipher the structure and formation of our Galaxy as one of the typical galaxies in the Universe through detailed measurements of stellar kinematics and chemistry of their atmospheres. Recent studies of Galactic dynamics show that the disc is not an axisymmetric equilibrium structure, but dynamically young and perturbed, by the on-going passages of the Sagittarius dwarf galaxy (Antoja et al 2018; Helmi et al 2018; Bland-Hawtorn et al 2019; Helmi 2020) Such perturbations inflict variations in stellar positions and velocities which are much smaller than their nominal values. Steinmetz et al (2020) present the final data release of the 10-yr RAVE survey It reports RVs of 518 387 spectra with a typical accuracy of 1.4 km s−1. The cornerstone are new values of effective temperature, surface gravity, metallicity, and α-enhancement for 584 015 spectra from the third data release of the GALAH+ survey (Buder et al 2021, hereafter B20) which presents an unprecedented set of measurements of abundances of 30 chemical elements ([X/Fe]) for the same stars.
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