Table information for 'gdr3spec.ssameta'


Table Description: SSA Metadata for the Monte Carlo-sampled Gaia DR3 XP spectra

This table is available for ADQL queries and through the TAP endpoint.

Resource Description:

This is a re-publication the Gaia DR3 RP/BP spectra in the IVOA Spectral Data Model. It presents the continous spectra in sampled form, using a Monte Carlo scheme to decorrelate errors, elaborated in this resource's reference URL. The underlying tables are also available for querying through TAP, which opens some powerful methods for mass-analysing the data.

For a list of all services and tables belonging to this table's resource, see Information on resource 'Gaia DR3 RP/BP (XP) Monte Carlo sampled spectra'

Citing this table

This table has an associated publication. If you use data from it, it may be appropriate to reference 2022arXiv220800211G (ADS BibTeX entry for the publication) either in addition to or instead of the service reference.

To cite the table as such, we suggest the following BibTeX entry:

  title={Gaia DR3 RP/BP (XP) Monte Carlo sampled spectra},
  author={Demleitner, M. and Andrae, R.},
  howpublished={{VO} resource provided by the {GAVO} Data Center},
  doi = {10.21938/W:hWbPah3wBabuqewQULTA}

Resource Documentation

In Gaia's DR3, most BP/RP spectra come in “continuous” form only, that is, as coefficients of Gauss-Hermite polynomials. These can be turned into a “sampled” representation using GaiaXPy; however, since the errors are given in the form of covariance matrices for the polynomial coefficients, the errors in the resulting spectra are strongly correleated, which can sometimes result in artefacts in the signal.

To get approximately decorrelated errors and hence sampled spectra usable with less caution, we apply a scheme of Monte Carlo-sampling different realisations from the error model of the coefficients. Specifically, given the covariance matrix C defined through the Xp_coefficient_errors and Xp_coefficient_correlations column in the DR3 xp_continuous_mean_spectrum table, and noting that for a unit normal-distributed random variable u

u.uT⟩ = 1

holds (x denotes the expectation), we can re-write the covariance matrix using a Cholesky decomposition into LLT as

C =  LLT  =  Lu.uTLT  =  Lu.uTLT  =  x.xT

Hence, x = Lu is a realisation of the errors satisfying the covariance matrix. To come up with a sampled spectrum, we now draw (in this case) 10 samples of the coefficients and have GaiaXPy convert them to a sampled spectrum.

The source code we used for that is

To be on the conservative side of the resolution and the bandwidth, and also to keep storage requirements modest, we have chosen a relatively rough grid over the optical band, that is, bins of 10 nm over the spectral range between 400 and 800 nm.


Sorted by DB column index. [Sort alphabetically]

NameTable Head DescriptionUnitUCD
phot_g_mean_mag m_G Mean magnitude in the G band. This is computed from the G-band mean flux applying the magnitude zero-point in the Vega scale. To obtain error estimates, see phot_g_mean_flux_over_error. mag phot.mag;em.opt;stat.mean
phot_bp_mean_mag Mag BP Mean magnitude in the integrated BP band. This is computed from the BP-band mean flux applying the magnitude zero-point in the Vega scale. To obtain error estimates, see phot_bp_mean_flux_over_error. mag phot.mag;em.opt.B
phot_rp_mean_mag Mag RP Mean magnitude in the integrated RP band. This is computed from the RP-band mean flux applying the magnitude zero-point in the Vega scale. To obtain error estimates, see phot_rp_mean_flux_over_error. mag phot.mag;em.opt.R
source_id Source Id Gaia DR3 unique source identifier. Note that this *cannot* be matched against the DR1 or DR2 source_ids. [Note id] N/A;meta.main
ra RA (ICRS) Barycentric Right Ascension in ICRS at epoch J2016.0 deg pos.eq.ra;meta.main
dec Dec (ICRS) Barycentric Declination in ICRS at epoch J2016.0 deg pos.eq.dec;meta.main
preview Preview URL of a preview for the dataset N/A meta.ref.url;meta.preview
accref Product key Access key for the data N/A meta.ref.url;meta.dataset
owner Owner Owner of the data N/A N/A
embargo Embargo ends Date the data will become/became public a N/A
mime Type MIME type of the file served N/A meta.code.mime
accsize File size Size of the data in bytes byte N/A
ssa_dstitle Title A compact and descriptive designation of the dataset. N/A meta.title;meta.dataset
ssa_creatorDID C. DID Dataset identifier assigned by the creator N/A
ssa_pubDID P. DID Dataset identifier assigned by the publisher N/A meta.ref.ivoid
ssa_cdate Proc. Date Processing/Creation date N/A time;meta.dataset
ssa_pdate Pub. Date Date last published. N/A N/A
ssa_bandpass Bandpass Bandpass (i.e., rough spectral location) of this dataset; this should be the most appropriate term from the vocabulary N/A instr.bandpass
ssa_cversion C. Version Creator assigned version for this dataset (will be incremented when this particular item is changed). N/A meta.version;meta.dataset
ssa_targname Object Common name of object observed. N/A;src
ssa_targclass Ob. cls Object class (star, QSO,...; use Simbad object classification if at all possible) N/A src.class
ssa_redshift z Redshift of target object N/A src.redshift
ssa_targetpos Obj. pos Equatorial (ICRS) position of the target object. N/A pos.eq;src
ssa_snr SNR Signal-to-noise ratio estimated for this dataset N/A stat.snr
ssa_location Location ICRS location of aperture center deg pos.eq
ssa_aperture Aperture Angular diameter of aperture deg phys.angSize;instr.fov
ssa_dateObs Date Obs. Midpoint of exposure (MJD) d time.epoch
ssa_timeExt Exp. Time Exposure duration s time.duration
ssa_specmid Mid. Band Midpoint of region covered in this dataset m instr.bandpass
ssa_specext Bandwidth Width of the spectrum m instr.bandwidth
ssa_specstart Band start Lower value of spectral coordinate m em.wl;stat.min
ssa_specend Band end Upper value of spectral coordinate m em.wl;stat.max
ssa_length Length Number of points in the spectrum N/A N/A
ssa_model Model Data model name and version N/A N/A
ssa_csysName Sys System RA and Dec are given in N/A N/A
ssa_timeSI [Time] Time conversion factor in Osuna-Salgado convention. N/A N/A
ssa_spectralSI [Spectral] Spectral conversion factor in Osuna-Salgado convention N/A N/A
ssa_spectralucd UCD(spectral) UCD of the spectral column in the spectra served; when you have wavelengths, use em.wl for vacuum wavelengths, em.wl;obs.atmos for air wavelengths. N/A meta.ucd
ssa_spectralunit unit(spectral) Unit of the spectral column N/A meta.unit
ssa_fluxSI [Flux] Flux/magnitude conversion factor in Osuna-Salgado convention N/A N/A
ssa_fluxucd UCD(flux) UCD of the flux column N/A meta.ucd
ssa_fluxunit unit(flux) Unit of the flux column N/A meta.unit
ssa_dstype Data type Type of data (spectrum, time series, etc) N/A N/A
ssa_publisher Publisher Publisher of the datasets included here. N/A meta.curation
ssa_creator Creator Creator of the datasets included here. N/A N/A
ssa_collection Collection A short handle naming the collection this spectrum belongs to. N/A N/A
ssa_instrument Instrument Instrument or code used to produce these datasets N/A;instr
ssa_datasource Src Method of generation for the data (one of survey, pointed, theory, custom, artificial). N/A N/A
ssa_creationtype Using Process used to produce the data (archival, cutout, filtered, mosaic, projection, spectralExtraction, or catalogExtraction) N/A N/A
ssa_reference Ref. URL or bibcode of a publication describing this data. N/A meta.bib.bibcode
ssa_fluxStatError Err. flux Statistical error in flux N/A stat.error;phot.flux.density;em
ssa_fluxSysError Sys. Err flux Systematic error in flux N/A stat.error.sys;phot.flux.density;em
ssa_fluxcalib Calib Flux Type of flux calibration (ABSOLUTE, CALIBRATED, RELATIVE, NORMALIZED, or UNCALIBRATED). N/A N/A
ssa_binSize Spect. Bin Bin size in wavelength m em.wl;spect.binSize
ssa_spectStatError Err. Spect Statistical error in wavelength m stat.error;em
ssa_spectSysError Sys. Err. Spect Systematic error in wavelength m stat.error.sys;em
ssa_speccalib Calib. Spect. Type of wavelength calibration N/A meta.code.qual
ssa_specres Spec. Res. Resolution (in meters of wavelength) on the spectral axis m spect.resolution;em.wl
ssa_spaceError Err. Spc Statistical error in position deg stat.error;pos.eq
ssa_spaceCalib Calib. Spc Type of calibration in spatial coordinates N/A meta.code.qual
ssa_spaceRes Res. Spc Spatial resolution of data deg pos.angResolution
ssa_region Coverage Rough coverage based on location and aperture N/A N/A

Columns that are parts of indices are marked like this.


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Copyright and such:

This data is derived from public Gaia DR3 data. Please take note of ESAC's guide on how to acknowledge and cite Gaia results.