The GALAH survey: accurate radial velocities and library of observed stellar template spectra

Abstract

GALAH is a large-scale magnitude-limited southern stellar spectroscopic survey. Its second data release (GALAH DR2) provides values of stellar parameters and abundances of 23 elements for 342,682 stars (Buder et al.). Here we add a description of the public release of radial velocities with a typical accuracy of 0.1 km s −1 for 336,215 of these stars, achievable due to the large wavelength coverage, high resolving power and good signal to noise ratio of the observed spectra, but also because convective motions in stellar atmosphere and gravitational redshift from the star to the observer are taken into account. In the process we derive medians of observed spectra which are nearly noiseless, as they are obtained from between 100 and 1116 observed spectra belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly released 1181 median spectra have a resolving power of 28,000 and trace the well-populated stellar types with metallicities between −0.6 and +0.3. Note that radial velocities from GALAH are an excellent match to the accuracy of velocity components along the sky plane derived by Gaia for the same stars. The level of accuracy achieved here is adequate for studies of dynamics within stellar clusters, associations and streams in the Galaxy. So it may be relevant for studies of the distribution of dark matter.

The gravitational force field of the Galaxy measured from the kinematics of RR Lyrae in Gaia

“…Many nonaxisymmetric motions are obvious in the new data from Gaia (e.g. Katz et al 2019;Antoja et al 2018;Hunt et al 2018), and we expect the value of V c (R 0 ) to soon be clarified with this data. Indeed our inferred value of the circular velocity at the Sun is quite close to the value of V c (R 0 ) = 229 km s −1 ±2% very recently measured using the combination of Gaia DR2 and APOGEE data by Eilers et al (2019).…”

Gaia Data Release 2

“…In each case, only a subset of these catalogues has been selected, 3 Arenou et al (2018) also compared the Gaia DR2 radial velocities to the first GALAH data release (Kos et al 2017;Martell et al 2017). The second GALAH data release (Buder et al 2018;Zwitter et al 2018) was published after the completion of the validation of Gaia DR2.…”

“…The A&A 622, A205 (2019) In the past 15 yr, spectroscopic surveys have delivered radial velocities, as well as stellar parameters and abundances for large stellar samples. Examples are the Geneva-Copenhagen-Survey (Nordström et al 2004) with ∼17 000 stars, SEGUE (Yanny et al 2009) with ∼240 000 stars, APOGEE (Holtzman et al 2015) with ∼150 000 stars, APOGEE-2 (Majewski et al 2017;Abolfathi et al 2018) with ∼263 000 stars, RAVE (Steinmetz et al 2006;Kunder et al 2017) with ∼460 000 stars in DR5, the Gaia-ESO-Survey (Gilmore et al 2012;Sacco et al 2014;Jackson et al 2015) with ∼50 000 stars in DR3, LAMOST (Cui et al 2012;Zhao et al 2012) with ∼5.3 million stars in DR5, and GALAH (Buder et al 2018;Zwitter et al 2018) with ∼340 000 stars in DR2. In continuity of these large surveys, Gaia DR2 contains median radial velocities for 7 224 631 stars with T eff in the range [3550,6900] K that are distributed throughout the entire celestial sphere.…”

The GALAH survey and Gaia DR2: Linking ridges, arches, and vertical waves in the kinematics of the Milky Way

“…This internal release includes non-LTE corrections on [Fe/H] but not on [α/Fe]. For the kinematics of this dataset, we make use of the parallax and proper motion (ω, µ α , µ δ ) from Gaia DR2, but use the highly precise radial velocities from GALAH, which have typical error of 0.1 km s −1 (Zwitter et al 2018). Since we are mainly interested in nearby stars, we restrict our GALAH sample only to dwarfs, by applying a surface gravity cut of (log g> 3), which results in a final sample of 258289 stars.…”