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Documentation

Find information, examples, FAQs and extensive descriptions of the data, curated by the survey teams.

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GALAH

The Galactic Archaeology with HERMES survey is collecting stellar parameters and abundances for one million stars in the Milky Way. GALAH yields a comprehensive view of the formation & evolution of the Galaxy.
Nov. 6, 2020 by J. Simpson
April 26, 2021, 10:15 p.m. S. Sharma

Value-Added Catalogues

GALAH DR3

The GALAH DR3 is accompanied by several value-added-catalogs. On this page we describe these catalogues and their recommended use.

Catalogue name File name File size Description
galah_dr3.vac_gaiaedr3 GALAH_DR3_VAC_GaiaEDR3_v2.fits 338 MB Gaia eDR3 data for all stars in GALAH DR3
galah_dr3.vac_ages GALAH_DR3_VAC_ages_v2.fits 362 MB Ages, masses, distances and other parameters estimated using isochrones
galah_dr3.vac_dynamics GALAH_DR3_VAC_dynamics_v2.fits 554 MB Galactic kinematic and dynamic parameters
galah_dr3.vac_rv GALAH_DR3_VAC_rv_v2.fits 67 MB Collated radial velocity measurements
FGK binary stars Identification of likely for double-lined spectroscopic binaries. This VAC is served on the Centre de Données astronomiques de Strasbourg rather than Data Central.
galahfco target/galahfco_3_public.txt 957 kB List of fields and field configurations. Each field has a unique ra, dec coordinates and field_id. Multiple configurtations can have same field_id.


Data Access for the Value-Added Catalogues

These catalogues can be accessed using the same methods as the main GALAH DR3 table:

For example, if you are interested the ages and masses for stars that could potentially be red clump stars, then the following query could be used:

SELECT
   TOP 100
   *
   FROM galah_dr3.vac_ages
   WHERE age_bstep < 2 and is_redclump_bstep > 0.5


Joining the Value-Added Catalogues and the main GALAH DR3 catalogues

We draw users attentions to the following aspects of the using these Value-Added Catalogues:

The Value-Added Catalogues must be joined with the main GALAH DR3 catalogues using the sobject_id. Do not use Gaia source_id or the star_id for joining catalogues. These value-added catalogues are based upon the extended catalogue which contains measurements per observed spectrum. Some stars were observed multiple times, and therefore have multiple observed spectra. The sobject_id column is our internal ID for each observation and using this column for joining will ensure that you are matching information derived from the same spectrum.

For instance, to join the galah_dr3.main_star to the value-added catalogue of ages (galah_dr3.vac_ages), the following ADQL query could be used:

SELECT
   TOP 100
   g_ms.source_id, g_ages.sobject_id, g_ages.age_bstep, g_ages.e_age_bstep
   FROM galah_dr3.main_star AS g_ms
   JOIN galah_dr3.vac_ages AS g_ages
   	ON g_ms.sobject_id = g_ages.sobject_id

It is also important to pay attention to the flag_sp and flag_fe_h columns for a given spectrum (See the Table Schema page for a full description of the flags)

  • For the values in galah_dr3.vac_ages (stellar age, mass, radius, lumunsoity estimates), it is highly recommended to only use values where flag_sp = 0 and flag_fe_h = 0 in the galah_dr3.main_star or galah_dr3.main_spec catalogues, as the values in galah_dr3.vac_ages depend on the teff, logg, fe_h from the main catalogues.
  • For the galah_dr3.vac_dynamics catalogue, we have used the Gaia eDR3 astrometry, so it is important that you consider the reliability of the Gaia eDR3 astrometry for a given star. Note that the flag_sp value in the main catalogues has its first bit set if there is unreliable Gaia DR2 astrometry (defined as ruwe_dr2>1.4) as this was used in the GALAH DR3 stellar parameter and abundance analysis.

galah_dr3.vac_gaiaedr3

GALAH_DR3_VAC_GaiaEDR3_v2.fits

Gaia eDR3 data for all stars in GALAH DR3

This provides a cross-match GALAH DR3 and Gaia eDR3. This catalogue contains an entry for every star in GALAH DR3 that we identified a match in Gaia eDR3. The vac_gaiaedr3 catalogue consists of:

  • GALAH DR3 sobject_id and star_id
  • All columns from gaiaedr3.gaia_source (with source_id renamed dr3_source_id)
  • All columns from gaiaedr3.dr2_neighbourhood:
    • e.g., angular_distance, magnitude_difference, proper_motion_propagation
  • Photogeometric and Geometric Distances from Bailer-Jones et al. (2020)
  • Zeropoints from Lindegren et al. (2020)

Some notes and caveats about the cross-match between GALAH DR3 and Gaia eDR3:

  • This cross-match used the previously identified Gaia DR2 source_id for each GALAH DR3 star, and the gaiaedr3.dr2_neighbourhood table created by the Gaia team. The Gaia DR2 source_id had been found using the gaiadr2.tmass_best_neighbour table and the 2MASS ID of each GALAH star. In the future, we suggest to perform this crossmatch via GALAH's 2MASS ID and the yet-to-come match of Gaia EDR3 and 2MASS identifiers.
  • All galah_dr3.vac_gaiaedr3 entries have an angular distance between their Gaia DR2 and eDR3 sources smaller than 160 mas, and 99.9 per cent are within 20 mas.
  • There is a Gaia eDR3 source for every entry in the galah_dr3.main_star table.
    • There are 111 entries in the galah_dr3.main_spec table that lack a Gaia source_id as we have not attempted to find them in Gaia eDR3 and they never had a Gaia DR2 source_id. Of these 38 are bright stars and do have a parallax from Hipparcos,
  • 17654 stars had more than one Gaia eDR3 match (98 per cent two matches and the remainder with 3 or 4 matches). For simplicity we have chosen the match with the smallest angular distances between the Gaia DR2 and Gaia eDR3 position as reported by the gaiaedr3.dr2_neighbourhood.
    • For over 99 per cent of stars the closest match had an angular distance <10 mas, and second closest match was >600 mas.
    • There is likely source confusion for <100 stars. For instance, for 57 of the 17000 stars with multiple matches in the gaiaedr3.dr2_neighbourhood table, the second closest match in angular distance has a smaller magnitude difference between GaiaDR2 and eDR3.


galah_dr3.vac_ages

GALAH_DR3_VAC_ages_v2.fits

Ages, masses, distances and other parameters estimated using isochrones

To estimate stellar properties like age, mass, and distance we use the Bayesian Stellar Parameter Estimation code (BSTEP) from Sharma et al. (2018). BSTEP provides a Bayesian estimate of intrinsic stellar parameters from observed parameters by making use of stellar isochrones.

For details of the adopted priors see Sharma et al. (2018). Briefly, a flat prior on age and metallicity was used and for density distribution of stars a combination of an exponential stellar disc and a diffuse stellar halo was used. For results presented in this paper, we use the PARSEC release v1.2S + COLIBRI stellar isochrone (Marigo et al. 2017). We use the following observables, Teff , log g, [Fe/H], [alpha/Fe] , 2MASS J and Ks photometry, and parallax from Gaia. The effective observed metallicity, log(Z/Z⊙), was estimated from [Fe/H] and [alpha/Fe] using the formula by Salaris (2006). This was compared with the surface metallicity reported by the isochrones, which takes the evolutionary changes in surface metallicity Z into account.

The code provides an estimate of age, actual mass, initial mass, initial metallicity, surface metallicity, radius, distance, extinction E(B-V), luminosity, surface gravity, temperature and the probability of being a red clump star. For each estimated parameter we report a mean value and the 16th, 50th, and 84th percentiles.


galah_dr3.vac_dynamics

GALAH_DR3_VAC_dynamics_v2.fits

Galactic kinematic and dynamic information

NOTE: The distance to star reported in the galah_dr3.vac_dynamics table may differ from the distance used in the stellar parameter and abundance determination. This is because the GALAH DR3 analysis was done prior to the release of Gaia eDR3, and so used GALAH DR2-derived distances.

We provide a value-added-catalog with kinematic and dynamic information, that builds upon the 5D astrometric information by Gaia eDR3, and primarily radial velocities determined from GALAH spectra.

The radial velocity values were primarily (83 per cent of spectra) from values calculated by Zwitter et al (2020) from the GALAH DR3 spectra. Of the remainder, 13 per cent use the radial velocity calculated as part of the stellar parameter and abundance determination, 2 per cent use the Gaia DR2 value (which was not updated in Gaia eDR3), and 2 per cent have no radial velocity value. The method used for a given spectrum is provided by the use_rv_flag in the galah_dr3.vac_dynamics (or galah_dr3.vac_rv) catalogue.

For the vast majority of stars (96 per cent), we use distance_bstep from the vac_ages catalogue, calculated by the Bayesian Stellar Parameter Estimation code (BSTEP) from Sharma et al. (2018). For the other 4 per cent of the stars we mostly use the photogeometric distances from Bailer-Jones et al. (2020) (r_med_photogeo in the vac_gaiaedr3 catalogue). The method used for a given spectrum is provided by the use_dist_flag in the galah_dr3.vac_dynamics table.

The galah_dr3.vac_dynamics catalogue provides columns calculated from the "best" input values:

  • Heliocentric cartesian coordinate (X_XYZ, Y_XYZ, Z_XYZ) and velocity frames (U_UVW, V_UVW, W_UVW)
  • Galactocentric cylindrical coordinate (R_Rzphi, z_Rzphi, phi_Rzphi) and velocity frames (vR_Rzphi, vz_Rzphi, vT_Rzphi)
    • Note that we report vT_Rzphi rather than vR_Rzphi. The initial release of this table did report vphi_Rzphi. We changed to vT_Rzphi because due to the normalisation within galpy the notation was confusing.
    • If vphi_Rzphi is desired, it can be calculated as vphi_Rzphi = vT_Rzphi * (8.21 kpc) / R_Rzphi
  • Orbital angles (angle_R, angle_phi, angle_z) and frequencies (omega_R, omega_phi, omega_z)
  • Actions (J_R, L_Z, J_Z)
  • eccentricity (ecc)
  • maximum Galactocentric orbit height (zmax), pericenter and apocenter radii (R_peri, R_ap)
  • Orbit energies (Energy)

For each estimated parameter we also report a mean value and the 5th, 50th, and 95th percentiles (these have the suffixes _5, _50, _95).

For the calculation of orbit information we use version 1.6 of the python package galpy (Bovy 2015). To estimate actions, eccentricity, maximum orbit Galactocentric height, and apocenter/pericenter radii, we use the Staeckel fudge via the galpy module actionAngleStaeckel with a focus of 0.45. We use the following potentials and observed properties of the Galaxy:

  • The best fitting axisymmetric potential by McMillan (2017);
  • A solar radius of 8.21 kpc, consistent with the latest measurement by Gravity Collaboration et al. (2019) of 8.178 ± 0.013(stat.) ± 0.022(sys.) kpc;
  • A circular velocity at this radius of 233.1 km/s;
  • The total motion of the Sun in the V-direction of 248.27 km/s by evaluation the proper motion measurements from Reid & Brunthaler (2004) at our chosen Solar radius;
  • The Sun placed 25 pc above the plane (Jurić et al. 2008);
  • The peculiar solar velocities U = 11.1 km/s and W=7.25 km/s by Schönrich et al (2020) but V=15.17 km/s.

GALAH DR3 Kinematics and Dynamics

This plot is taken from Buder et al. (2020) and shows the coverage of stellar kinematics (space velocities) and dynamics (actions) for the stars observed as part of GALAH. Panel a) shows a Galactocentric version of the Toomre diagram (compare to e.g. Bonaca et al. 2017; Feuillet et al. 2020), panel b) Galactic space velocities (compare to e.g. Belokurov et al. 2018; Feuillet et al. 2020), panel c) two actions (compare to e.g. Trick et al. 2019; Feuillet et al. 2020), and panel d) the distribution of actions (compare to e.g. Vasiliev 2019). The vast majority of stars in GALAH DR3 has both azimuthal / transversal Galactocentric velocities and angular momenta very similar to the Sun.


galah_dr3.vac_rv

GALAH_DR3_VAC_rv_v2.fits

Collated radial velocity measurements

The rv_galah value in galah_dr3.main_star, galah_dr3.main_spec and galah_dr3.rv catalogues reports our best value for the radial velocity of each spectrum. The radial velocity values were primarily (83 per cent of spectra) from values calculated by Zwitter et al (2020) from the GALAH DR3 spectra. Of the remainder, 13 per cent use the radial velocity calculated as part of the stellar parameter and abundance determination, 2 per cent use the Gaia DR2 value (which was not updated in Gaia eDR3), and 2 per cent have no radial velocity value. The method used for a given spectrum is provided by the use_rv_flag in the galah_dr3.vac_dynamics (or galah_dr3.vac_rv) catalogue (see the Table Schema page).

The galah_dr3.vac_rv catalogue contains the possible radial velocities for the star, described here in descending order of preference:

  • rv_obst and rv_nogr_obst (and their error columns)
    • Zwitter et al (2020) created essentially noiseless observed spectra for stars are created by creating median spectra for all GALAH DR3 stars belonging to the same bin with a width of 50 K in temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. The observed spectra are then cross-correlated with these noiseless spectra to measure radial velocities with a typical accuracy of 0.1 km/s. The rv_nogr_obst reports the value without the gravitational redshift correction.
  • rv_sme_v2 (and its error columns)
    • The radial velocity calculated by SME as part of the stellar parameter and abundance determination.
    • There is also a rv_sme_v1 column which was the value found in the original GALAH DR3 release which had an incorrect barycentric correction.
  • dr2_radial_velocity (and its error columns)
    • Radial velocity from Gaia DR2
    • This value is also listed as rv_gaia_dr2 in galah_dr3.main_spec and galah_dr3.main_star.


FGK binary stars

Binary stellar systems represent a significant fraction of stars in our Galaxy. Therefore, their effect on observations, as well as their impact on the Galactic environment, have to be properly taken into account when studying Galactic structure and evolution. To this end, we present a sample of 12760 binary systems for which the properties of their stellar components were derived in a separate analysis from the main DR3 analysis.

The details of the analysis are described in Traven et al. (2020), and the catalogue of derived parameters is available at CDS.


galahfco

List of fields and field cofiguations. Each field is specified by its location (ra, dec) and has a unique identifier field_id. Each row describes a field configuration. There can be multiple rows with same field_id indicating different configurations that the field can be observed in, e.g., fields observed with different magnitude ranges specified by (vmin ,vmax). Description of the available columns is given below.

  • field_id: (int) Unique field identifier
  • ra: (deg)
  • dec: (deg)
  • radius: (deg) Ranging from 0 to 1.0
  • selfunc: (int) Selection function
  • vmin: Minimum V(J,K) magnitude
  • vmax: Maximum V(J,K) magnitude
  • vsplit: V(J,K) mag used for complicated selection functions
  • vexp: V(J,K) magnitude used to set exposure time.
  • progname: (str) one of the following ['bright', 'galah', 'galah_faint', 'galah_ufaint', 'k2', 'ocluster', 'repeat0', 'tess']
  • fco_id: field configiration identifier, row number in the table
  • priority: (int) 0 or 1 (for internal use)
  • active: (int) 0 or 1 (for internal use)
  • special: (int) 0 or 1 (for internal use)
Nov. 6, 2020 by J. Simpson
April 26, 2021, 10:15 p.m. S. Sharma