Data Central uses cookies to make your browsing experience better. By using Data Central you agree to its use of cookies. Learn more I agree

Documentation

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

GALAH logo

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.
Feb. 7, 2021 by J. Simpson
March 17, 2021, 10:59 a.m. J. Simpson

Using the GALAH Catalogues

GALAH DR3

On this page we provide advice and instructions for using the GALAH DR3 catalogues. We would recommend taking the time to read Buder et al. (2020), which supplies even more information and quality assessment of GALAH DR3. Sven Buder has created iPython notebooks tutorials for GALAH DR3 which are available here.

On this page:

  • Recommended catalogue and set of stars
  • Recommended columns
  • Gaia data included with GALAH DR3 catalogues
  • How to join tables in GALAH DR3


Recommended catalogue and set of stars

We highly recommend using the galah_dr3.main_star catalogue if you want to work with the GALAH DR3 stellar parameters and elemental abundances. This catalogue contains one entry per star and is a cleaned version of the extended galah_dr3.main_spec. Details on accessing the data can be found on the Catalogue Data Access page. If you just want the entire table, it can be directly downloaded from here (it has the file name GALAH_DR3_main_allstar_v2.fits), or by using wget (removing the --spider flag):

wget --spider https://cloud.datacentral.org.au/teamdata/GALAH/public/GALAH_DR3/GALAH_DR3_main_allstar_v2.fits

We make two strong recommendations about flags in GALAH DR3. Full details of the flags are found on the Table Schema page.

  • By default, we recommend that users only consider stellar parameters (Teff, logg, [Fe/H], broadening velocity, radial velocity) for stars with flag_sp == 0 and flag_fe_h == 0. The flag_sp folds in many potential sources of errors in the input values (e.g., unreliable astrometry, very low signal spectra, reduction problems, possibly binarity). A non-zero flag_fe_h indicates problems with the stellar parameter determination.
  • As for all of our previous GALAH releases, we want to stress that we discourage the use of flagged element abundances without consideration of the possible systematics that these flagged measurements can introduce. We strongly recommend only considering the abundance of element X when flag_X_fe == 0. Further, we would recommend considering only stars with a signal to noise snr_c3_iraf > 30.


Recommended columns

As well as the main_star catalogue, there are a number of value-added catalogues. Details on accessing the data can be found on the Catalogue Data Access page. The value-added catalogues are fully described on the Value-Added Catalogues page. Briefly the catalogues of GALAH DR3 are:

  • main_star: The main result catalogue. Our recommended table about stellar parameters and elemental abundance. One entry per star observed. Radial velocity, stellar parameters and abundance data.
  • main_spec: One entry per observation (about 50000 stars have been observed at least twice). Radial velocity, stellar parameters for each observation. Also contains abundances derived for each individual line.
  • vac_ages: Ages, distances, luminosities, masses, metallicities, radii and other parameters calculated from isochrones by the Bayesian Stellar Parameter Estimation code (BSTEP) from Sharma et al. (2018).
  • vac_rv: Collated radial velocity measurements
  • vac_gaiaedr3: Gaia eDR3 data for all stars in GALAH DR3
  • vac_dynamics: Galactic kinematic and dynamic parameters

Full details of all the columns and their descriptions is found on the Table Schema page.

Across these catalogues for many parameters we provide only one value, e.g., for the α-element abundance, we provide one value: alpha_fe. However, some parameters have multiple values calculated by different methods. We tabulate and discuss below these parameters and in most cases make a recommendation on the value to use. Generally we do not recommend values found only in the main_spec catalogue as these are only for expert use and are typically for diagnostic purposes.

  • For effective temperature, surface gravity, iron abundance ([Fe/H]), broadening velocity, we strongly recommend teff, logg, fe_h, vbroad respectively from the main_star catalogue. These are inferred as part of the spectrum fitting and abundance determination. The other provided values of these are either calculated during an intermediary analysis step (e.g., teff_guess), or as part of a value-added catalogues (e.g., teff_bstep).
  • Distinct from the iron abundance ([Fe/H]) calculated from the spectra, the value-added catalogue of values from BSTEP includes the initial and current metallicity of the star. These values were not used as part of the abundance analysis.
  • For stellar mass and age, we recommend age_bstep, mass_bstep from the vac_ages catalogue, the values found in the vac_ages catalogue, rather than the mass and age found in the main_spec table.
  • For parallax, the GALAH DR3 catalogues has the parallax values from both the Gaia DR2 and eDR3 values (the former being called parallax_dr2 in our catalogues). We have also calculated the eDR3 parallax corrected for the zeropoint offset as prescribed in Lindegren et al (2020), called parallax_corr in our tables. We do not have any strong recommendation on the best parallax value to use.
  • For distance, as with parallax, we include values derived from both Gaia DR2 and eDR3. In addition, we also have distance_bstep, calculated as part of the estimation of age, mass, radius etc found in the vac_ages catalogue. We recommend this distance_bstep value from the vac_ages catalogue. Note that for the calculation of Galactic kinematic and dynamic parameters in vac_dynamics, distance_bstep was used for the vast majority of stars (96 per cent). For the other 4 per cent of the stars we mostly use the photogeometric distances r_med_photogeo in the vac_gaiaedr3 catalogue as calculated by Bailer-Jones et al. (2020). The distance used for a given spectrum is provided by the use_dist_flag in the galah_dr3.vac_dynamics table.
  • For radial velocity, we strongly recommend the rv_galah from the main_star catalogue. The source of this value differs for each star. For 83 per cent of stars rv_galah == rv_obst (found in the vac_rv table), the radial velocity measured by Zwitter et al (2020) from our observed spectra. The remaining stars will have rv_galah == rv_sme_v2, the value measured by SME during the analysis process. The rv_obst value has errors typically five times smaller than the SME-measured value. Consult the use_rv_flag for each star to identify the source of the radial velocity for rv_galah. The other radial velocity values available are either from Gaia DR2, or are diagnostic values measured during the analysis (e.g., rv_6708 is the RV measured from just the Li6708 line). See the section of the Value-added catalogues documentation page on the vac_rv catalogue for more details.
  • For reddening, we recommend the ebv value from the main_star catalogue. This is from Schlegel et al (1998) and was used as part of the estimation of the bolometric corrections.


These above recommendations are summarised below

(This table has seven columns; you may need to widen your browser window if you cannot see the vac_gaiaedr3 column on the far right).

Parameter Recommended value main_star main_spec vac_ages vac_rv vac_gaiaedr3
Effective Temperature teff teff, irfm_teff teff, irfm_teff, init_teff, teff_guess teff_bstep
Surface gravity logg logg logg, init_logg, logg_guess logg_bstep
[Fe/H] fe_h fe_h, fe_h_atmo fe_h, fe_h_atmo, init_fe_h_atmo, feh_guess
Metallicity meh_act_bstep, meh_ini_bstep
Broadening velocity vbroad vbroad vbroad, init_ vbroad
Stellar mass m_act_bstep mass m_act_bstep, m_ini_bstep
Stellar age age_bstep age age_bstep
Parallax parallax_dr2 parallax_dr2 parallax , parallax_corr
Distance Consult the use_dist_flag for each star r_est_dr2 r_est_dr2 distance_bstep r_med_geo, r_med_photogeo
Radial velocity rv_galah (Consult the use_rv_flag for each star to identify the source of the radial velocity) rv_galah, rv_gaia_dr2 rv_galah, rv_gaia_dr2, rv_guess, rv_5854, rv_6708, rv_6722 rv_galah, rv_sme_v2, rv_sme_v1, rv_obst, rv_nogr_obst, dr2_radial_velocity dr2_radial_velocity
E(B-V) ebv ebv, irfm_ebv ebv, irfm_ebv ebv_bstep


Gaia data included with GALAH DR3 catalogues

The results from the Gaia mission are integral to GALAH DR3. Our analysis makes use of Gaia DR2 results, in particular using a parallax-derived distance estimate for each star to provide a first estimate of its surface gravity. In galah_dr3.main_star and galah_dr3.main_spec, all Gaia data is from Gaia DR2, except for the Gaia eDR3 source_id (dr3_source_id). The Gaia DR2 columns provide the Gaia data that was used for the GALAH DR3 analysis and we have added "dr2" to their column names to indicate their source (e.g., parallax and ruwe from Gaia DR2 are parallax_dr2 and ruwe_dr2). Any data from the Gaia mission that does not have a "dr2" in the column name can be assumed to come from Gaia eDR3. Full details of all the columns and their source is found on the Table Schema page. A full description of the included Gaia data and our method of cross-matching is found on the caveats page.


How to join tables in GALAH DR3

The catalogues of GALAH DR3 must be joined or cross-matched 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. About 50000 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
Feb. 7, 2021 by J. Simpson
March 17, 2021, 10:59 a.m. J. Simpson