The GALAH+ Survey: A New Library of Observed Stellar Spectra Improves Radial Velocities and Reveals Motions within M67 (original) (raw)
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Monthly Notices of the Royal Astronomical Society, 2021
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 ...
The GALAH survey: accurate radial velocities and library of observed stellar template spectra
Monthly Notices of the Royal Astronomical Society, 2018
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 that 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.
Precise radial velocities of giant stars
2007
Context. The determination of accurate stellar parameters of giant stars is essential for our understanding of such stars in general and as exoplanet host stars in particular. Precise stellar masses are vital for determining the lower mass limit of potential substellar companions with the radial velocity method, but also for dynamical modeling of multiplanetary systems and the analysis of planetary evolution. Aims. Our goal is to determine stellar parameters, including mass, radius, age, surface gravity, effective temperature and luminosity, for the sample of giants observed by the Lick planet search. Furthermore, we want to derive the probability of these stars being on the horizontal branch (HB) or red giant branch (RGB), respectively. Methods. We compare spectroscopic, photometric and astrometric observables to grids of stellar evolutionary models using Bayesian inference. Results. We provide tables of stellar parameters, probabilities for the current post-main sequence evolutionary stage, and probability density functions for 372 giants from the Lick planet search. We find that 81% of the stars in our sample are more probably on the HB. In particular, this is the case for 15 of the 16 planet host stars in the sample. We tested the reliability of our methodology by comparing our stellar parameters to literature values and find very good agreement. Furthermore, we created a small test sample of 26 giants with available asteroseismic masses and evolutionary stages and compared these to our estimates. The mean difference of the stellar masses for the 24 stars with the same evolutionary stages by both methods is only ∆M = M trk. − M Ast. = 0.01 ± 0.20 M. Conclusions. We do not find any evidence for large systematic differences between our results and estimates of stellar parameters based on other methods. In particular we find no significant systematic offset between stellar masses provided by asteroseismology to our Bayesian estimates based on evolutionary models.
Radial Velocities for 889 Late‐Type Stars
The Astrophysical Journal Supplement Series, 2002
We report radial velocities for 844 FGKM-type main-sequence and subgiant stars and 45 K giants, most of which had either low-precision velocity measurements or none at all. These velocities differ from the standard stars of Udry et al. by 0.035 km s À1 (rms) for the 26 FGK standard stars in common. The zero point of our velocities differs from that of Udry et al.: hV Present À V Udry i ¼ þ0:053 km s À1 . Thus, these new velocities agree with the best known standard stars both in precision and zero point, to well within 0.1 km s À1 .
The Astronomical Journal, 2020
We present part 2 of the 6th and final Data Release (DR6 or FDR) of the Radial Velocity Experiment (Rave), a magnitude-limited (9 < I < 12) spectroscopic survey of Galactic stars randomly selected in the southern hemisphere. The Rave mediumresolution spectra (R ∼ 7500) cover the Ca-triplet region (8410 -8795 Å) and span the complete time frame from the start of Rave observations on 12 April 2003 to their completion on 4 April 2013. In the second of two publications, we present the data products derived from 518 387 observations of 451 783 unique stars using a suite of advanced reduction pipelines focussing on stellar atmospheric parameters, in particular purely spectroscopicallyderived stellar atmospheric parameters (T eff , log g, and the overall metallicity), enhanced stellar parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar parametersfor giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [α/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios.The Rave DR6 catalogs are cross matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the Rave Web site a) or the Vizier database.
Stellar parametrization fromGaiaRVS spectra
Astronomy & Astrophysics, 2015
Context. Among the myriad of data collected by the ESA Gaia satellite, about 150 million spectra will be delivered by the Radial Velocity Spectrometer (RVS) for stars as faint as G RVS ∼ 16. A specific stellar parametrization will be performed on most of these RVS spectra, i.e. those with enough high signal-to-noise ratio (S/N), which should correspond to single stars that have a magnitude in the RVS band brighter than ∼14.5. Some individual chemical abundances will also be estimated for the brightest targets. Aims. We describe the different parametrization codes that have been specifically developed or adapted for RVS spectra within the GSP-Spec working group of the analysis consortium. The tested codes are based on optimisation (FERRE and GAUGUIN), projection (MATISSE), or pattern-recognition methods (Artificial Neural Networks). We present and discuss each of their expected performances in the recovered stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) for B-to K-type stars. The performances for determining of [α/Fe] ratios are also presented for cool stars. Methods. Each code has been homogeneously tested with a large grid of RVS simulated synthetic spectra of BAFGK-spectral types (dwarfs and giants), with metallicities varying from 10 −2.5 to 10 +0.5 the solar metallicity, and taking variations of ±0.4 dex in the composition of the α-elements into consideration. The tests were performed for S/N ranging from ten to 350. Results. For all the stellar types we considered, stars brighter than G RVS ∼ 12.5 are very efficiently parametrized by the GSP-Spec pipeline, including reliable estimations of [α/Fe]. Typical internal errors for FGK metal-rich and metal-intermediate stars are around 40 K in T eff , 0.10 dex in log(g), 0.04 dex in [M/H], and 0.03 dex in [α/Fe] at G RVS = 10.3. They degrade to 155 K in T eff , 0.15 dex in log(g), 0.10 dex in [M/H], and 0.1 dex in [α/Fe] at G RVS ∼ 12. Similar accuracies in T eff and [M/H] are found for A-type stars, while the log(g) derivation is more accurate (errors of 0.07 and 0.12 dex at G RVS = 12.6 and 13.4, respectively). For the faintest stars, with G RVS > ∼ 13−14, a T eff input from the spectrophotometric-derived parameters will allow the final GSP-Spec parametrization to be improved. Conclusions. The reported results, while neglecting possible mismatches between synthetic and real spectra, show that the contribution of the RVS-based stellar parameters will be unique in the brighter part of the Gaia survey, which allows for crucial age estimations and accurate chemical abundances. This will constitute a unique and precious sample, providing many pieces of the Milky Way history puzzle with unprecedented precision and statistical relevance.
SEGUE: A Spectroscopic Survey of 240,000 Stars with g= 14-20
The Astronomical …, 2009
The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained ≈240,000 moderateresolution (R ∼ 1800) spectra from 3900 Å to 9000 Å of fainter Milky Way stars (14.0 < g < 20.3) of a wide variety of spectral types, both main-sequence and evolved objects, with the goal of studying the kinematics and populations of our Galaxy and its halo. The spectra are clustered in 212 regions spaced over three quarters of the sky. Radial velocity accuracies for stars are σ (RV) ∼ 4 km s −1 at g < 18, degrading to σ (RV) ∼ 15 km s −1 at g ∼ 20. For stars with signal-to-noise ratio >10 per resolution element, stellar atmospheric parameters are 4377
STELIB: A library of stellar spectra at R?2000
Astronomy and Astrophysics, 2003
We present STELIB, a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution ( < ∼ 3Å) and sampling (1Å). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photometric uncertainty is 3%.
STELIB: A library of stellar spectra at vecRsim2000{\vec R}\sim2000vecRsim2000
Astronomy & Astrophysics, 2003
We present STELIB , a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 Å), with an intermediate spectral resolution (< ∼ 3 Å) and sampling (1 Å). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photometric uncertainty is 3%.