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gaia data release 3 documentation

20.2 Astrophysical parameter tables

20.2.7 mcmc_samples_gsp_phot

This is the DataLink table hosting Monte-Carlo Markov Chain (MCMC) samples for the posterior probability distribution of all parameters derived from the General Stellar Parametrizer from Photometry (GSP-Phot, see Section 11.3.3 in the online documentation). 2000 MCMC samples are provided for 1) all sources brighter than G=12, 2) a random subset of 0.1% of the sources fainter than G=12. For all other sources fainter than G=12, the sample size is 100 (the last 100 samples in the MCMC).
The table considers the following parameters:

  • effective temperature Teff in K

  • monochromatic extinction at 541.4 nm A0 in mag

  • surface gravity logg

  • metallicity [M/H]

  • G-band extinction in mag

  • absolute magnitude MG in mag

  • distance in pc

  • GBP band extinction ABP in mag

  • GRP band extinction ARP in mag

  • reddening E(GBP-GRP)=ABP-ARP in mag

  • logarithmic posterior probability

  • logarithmic likelihood

  • stellar radius in R


Note this table is not available through the main archive TAP interface. Data are delivered via the Massive Data service indexed by the VO Datalink protocol and described in Chapter 18. For example this can be actioned in the archive user interface by querying the main source catalogue gaia_source and selecting has_mcmc_gspphot = 't'.

Columns description:

solution_id : Solution Identifier (long)

All Gaia data processed by the Data Processing and Analysis Consortium comes tagged with a solution identifier. This is a numeric field attached to each table row that can be used to unequivocally identify the version of all the subsystems that were used in the generation of the data as well as the input data used. It is mainly for internal DPAC use but is included in the published data releases to enable end users to examine the provenance of processed data products. To decode a given solution ID visit https://gaia.esac.esa.int/decoder/solnDecoder.jsp

source_id : Unique source identifier (unique within a particular Data Release) (long)

A unique single numerical identifier of the source obtained from gaia_source (for a detailed description see gaia_source.source_id).

nsamples : Number of samples in the chain from GSP-Phot (short)

The sample size is 100 for most sources, and is set to 2000 for 1) all sources brighter than G=12, 2) a random sample of 0.1% of the sources fainter than G=12.

teff : MCMC samples for Teff from GSP-Phot (float[nsamples] array, Temperature[K])

MCMC samples for posterior probability distribution of the stellar effective temperature from GSP-Phot.

azero : MCMC samples for extinction A0 from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the monochromatic extinction at 541.4 nm A0 from GSP-Phot.

logg : MCMC samples for logg from GSP-Phot (float[nsamples] array, GravitySurface[log cgs])

MCMC samples for posterior probability distribution of the stellar surface gravity logg from GSP-Phot.

mh : MCMC samples for the metallicity from GSP-Phot (float[nsamples] array, Abundances[dex])

MCMC samples for posterior probability distribution of metallicity [M/H] from GSP-Phot.

ag : MCMC samples for extinction in G band from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the extinction in the G band from GSP-Phot.

mg : MCMC samples for MG from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the absolute magnitude in the G band MG from GSP-Phot. The MG value is obtained from isochrones (for details see Section 11.3.3 in the online documentation).

distancepc : MCMC samples for distance from GSP-Phot (float[nsamples] array, Length & Distance[pc])

MCMC samples for posterior probability distribution of the distance from GSP-Phot.

abp : MCMC samples for extinction in GBP band from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the extinction in the GBP band from GSP-Phot.

arp : MCMC samples for extinction in GRP band from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the extinction in the GRP band from GSP-Phot.

ebpminrp : MCMC samples for reddening E(GBP-GRP) from GSP-Phot (float[nsamples] array, Magnitude[mag])

MCMC samples for posterior probability distribution of the reddening E(GBP-GRP)=ABP-ARP from GSP-Phot.

log_pos : MCMC samples for the log-posterior from GSP-Phot (float[nsamples] array)

Logarithmic posterior probability of MCMC samples from GSP-Phot. This can be used in order to replace the GSP-Phot priors by a user-chosen prior using importance sampling (for details see Section 11.3.3 in the online documentation).

log_lik : MCMC samples for the log-likelihood from GSP-Phot (float[nsamples] array)

Logarithmic likelihood of MCMC samples from GSP-Phot. This can be used in order to replace the GSP-Phot priors by a user-chosen prior using importance sampling (for details see Section 11.3.3 in the online documentation).

radius : MCMC samples for stellar radius from GSP-Phot (float[nsamples] array, Length & Distance[Solar Radius])

MCMC samples for posterior probability distribution of the stellar radius from GSP-Phot.