# 13.5.2 gaia_universe_model

Table of simulated galactic stars according to the Gaia Universal Model Simulation (GUMS). True values of the intrinsic simulated quantities (astrometry, photometry and physical parameters) for the sources generated by GOG using the Universe Model are given. No errors are added.

Columns description:

source_extended_id : Extended source identifier (string)

Unique object String identifier describing:

• the object type. Here only stars or stellar systems are present, code =“*”

• the HTM region of the object (0-268435455)

• the object number in this region (0-262143)

• the multiplicity (Washington Double Stars Catalogue -WDS- type, 7 components, 4 hierarchical levels max)

• a variability flag (“V”)

Example: *000000455-000035Ab2V is a variable star and component Ab2 in a 3-level system. This system is the 35th of the HTM region 455. Such a system as at least 7 sources present in the GUMS table: *000000455-000035+ (the system), *000000455-000035A+, *000000455-000035B, *000000455-000035Aa, *000000455-000035Ab+, *000000455-000035Ab1, *000000455-000035Ab2V

source_id : Long Identifier (long)

A unique source identifier composed by the type of source, the sky region where the source is located and a sequential number inside this region (as the source_extended_id).

In the source_id information is coded within the 64 bit long integer. The celestial position is encoded via a level 12 Hierarchical Triangular Mesh, covering roughly one square arc minute size on the average:

• The 4 most significant bits contain the object type: (0: Unknown; 1: Stellar; 2: Galaxy; 3: QSO; 4: Supernova; 5: Exoplanet; 6: Noise or PPE; 7: Cluster; 8: Planetary Nebulae; 9: HII Region; 10: GRB; 11: Asteroid; 12: Comet; 13: Planet; 14: Satellite; 15: User Source; -1: Not identified)

• The 28 following bits contain the HTM index at level 12 (note the use of HTM as opposed to HEALPix in source_id in gaia_source)

• One bit indicates the variability,

• One bit indicates whether this is a multiple system (i.e. not a component).

• The 4 next groups of 3 bits are the 4 hierarchical levels for a multiple system. It is based on the fact that the maximum multiplicity of a hierarchical multiple system currently known is 7 (i.e. 3 bits are needed) with a 4 levels depth. The components in a level are sequential (i.e. non-hierarchical).

• The 18 least significant bits concern the object number in the region.

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 where 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

ra : Right Ascension (double, Angle[deg])

Right ascension of the barycentre at J2010 reference epoch in ICRS frame

dec : Declination (double, Angle[deg])

Declination of the barycentre at J2010 reference epoch in ICRS frame

barycentric_distance : Barycentric distance to the simulated source (float, Length & Distance[pc])

Distance from the barycenter of the Solar System to the barycenter of the source at J2010 reference epoch

pmra : Proper motion along right ascension (float, Angular Velocity[mas/year] )

Proper motion along right ascension at J2010 reference epoch: $\mu_{\alpha*}\equiv\mu_{\alpha}\cos\delta$. This is the local tangent plane projection of the proper motion vector in the direction of increasing right ascension.

pmdec : Proper motion along declination (float, Angular Velocity[mas/year] )

Proper motion along declination at J2010 reference epoch. This is the projection of the proper motion vector in the direction of increasing declination.

Spectroscopic radial velocity in the solar barycentric reference frame at J2010 reference epoch.

mag_g : Mean Apparent G magnitude (float, Magnitude[mag])

Mean apparent magnitude in the G band in the Vega scale.

mag_bp : Mean Apparent BP magnitude (float, Magnitude[mag])

Mean Apparent magnitude in the integrated BP band in the Vega scale.

mag_rp : Mean Apparent RP magnitude (float, Magnitude[mag])

Mean Apparent magnitude in the integrated RP band in the Vega scale.

mag_rvs : Mean Apparent RVS magnitude (float, Magnitude[mag])

Mean Apparent magnitude in the integrated RVS band in the Vega scale.

v_i : (V-I) color (float, Magnitude[mag])

Intrinsic V-I color (Johnson-Cousins)

mean_absolute_v : Mean Absolute V magnitude (float, Magnitude[mag])

Mean Absolute V (Johnson) magnitude

ag : Absorption in G (float, Magnitude[mag])

line-of-sight interstellar absorption in the G band

av : Absorption in V (float, Magnitude[mag])

line-of-sight interstellar absorption in the V band

teff : Effective temperature (float, Temperature[K] )

Stellar effective temperature.

spectral_type : spectral class + luminosity class (string)

Stellar MK classification

logg : Surface gravity (float, GravitySurface[log cgs])

Stellar surface gravity log g

feh : Metallicity (float, Abundances[dex])

Stellar metallicity [Fe/H]

alphafe : Alpha elements (float, Abundances[dex])

Abundance of alpha-elements with respect to iron [$\alpha$/Fe]

mbol : Absolute bolometric magnitude (float, Magnitude[mag])

Mean absolute bolometric magnitude

age : Age (float, Time[Gyear])

Age of the stellar source (Gyr)

mass : Mass (float, Mass[Solar Mass])

Stellar mass

Stellar radius (mean value for variable pulsating stars)

vsini : Rotational velocity (float, Velocity[km/s] )

Projected rotational velocity

population : Population (int)

Galactic stellar population: 1=thin disc, 2=thick disc, 3=spheroid, 4=bulge

has_photocenter_motion : Boolean describing if the photocenter has or not motion (boolean)

Field to describe if the photocenter has or not stellar hotspot induced motion

nc : Number of components (int)

nb of components (a component can be either one star or a system)

nt : Total number of object (int)

total number of objects (stars, brown dwarfs or exoplanets) in the system

semimajor_axis : Semi major axis (float, Length & Distance[AU] )

semi-major axis of the orbit of the component (for multiple systems)

eccentricity : Eccentricity (float)

Eccentricity of the orbit of the component (for multiple systems)

inclination : Inclination (float, Angle[deg] )

Inclination of the orbit of the component (for multiple systems)

longitude_ascending_node : Longitude of ascending node (float, Angle[deg] )

Longitude of the ascending node of the orbit of the component (for multiple systems)

orbit_period : Period of the orbit (float, Time[day])

Period of the orbit of the component (for multiple systems)

periastron_date : Date of periastron (float, Time[day])

Periastron date of the orbit of the component (for multiple systems)

periastron_argument : Periastron argument (float, Angle[deg] )

Periastron argument of the orbit of the component (for multiple systems)

variability_type : Variability type (string)

Stellar variability type : ACV, be, cepheid, classicalnovae, deltascuti, dwarfnovae, DYPer, emission, Flaring, gammador, microlens, mira, RCrBs, RRab, RRc, roAp, semiregular, ZZceti

variability_amplitude : Amplitude of variability (float, Magnitude[mag])

Photometric variability amplitude in V magnitude

variability_period : Period of variability (float, Time[day])

Photometric variability period.

variability_phase : Phase of variability (float)

Photometric variability phase at J2010 reference epoch

r_env_r_star : Envelope characterisic for Be stars (float)

Envelope characteristic parameter for Be stars