2.1.1 crowded_field_source
Sources based on Service Interface Function (SIF) images of very dense regions in the sky. These sources build an addon catalogue to the nominal Gaia catalogue. Nominal and SIF detections were not mixed to create these sources. These Sources are thus obtained from SIF image detections only. Sources already present in the nominal catalogue were removed from the SIF addon catalogue.
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
designation : Unique source designation (unique across all Data Releases) (string)
A source designation, unique across all Gaia Data Releases, that is constructed from the prefix ‘Gaia DRx ’ or ‘Gaia FPR ’ followed by a string of digits corresponding to source_id (3 space–separated words in total). Note that the integer source identifier source_id is not guaranteed to be unique across Data Releases; moreover it is not guaranteed that the same astronomical source will always have the same source_id in different Data Releases. Hence the only safe way to compare source records between different Data Releases in general is to check the records of proximal source(s) in the same small part of the sky.
region_name : Name of the designated CrowdedField region in the sky (string)
String, that identifies the SIF CF region in the sky, this source is located in.
Gaia observed 9 regions with SIF CF images. The corresponding String values are:
BAADE_S_WINDOW: Baade’s Window (Bulge region)
SGR_I: Sagittarius window (Bulge region)
LMC: Large Magellanic Cloud, satellite galaxy of the Milky Way
SMC: Small Magellanic Cloud, dwarf irregular galaxy near the Milky Way
NGC104: (aka 47 Tucanae) in the constellation Tucana
NGC4372: (aka Caldwell 108) in the southern constellation of Musca
NGC5139: (aka Omega Centauri or Caldwell 80) in the constellation of Centaurus
NGC6121: (aka Messier 4) in the constellation of Scorpius
NGC6656: (aka Messier 22) in the constellation Sagittarius
source_id : Unique source identifier (unique within a particular Data Release) providing the CrowdedFieldnature of the source via location bit (long)
A unique numerical identifier of the source, encoding the approximate position of the source (roughly to the nearest arcmin), the provenance (data processing centre where it was created), a running number, and a component number following the construction conventions of those in the Gaia DR3 main source catalogue (for a detailed description see gaiadr3.gaia_source.source_id). Note that the Gaia DPAC Data Processing Code provenance value (in bits 33 to 35) is 6 for the crowded field image analysis pipeline, i.e. (source_id $\mathit{>>}32$) & 7 = 6 for sources in crowded_field_source.
ref_epoch : Reference epoch (double, Time[Julian Years])
Reference epoch to which the astrometric source parameters are referred, expressed as a Julian Year in TCB.
ra : Right ascension (double, Angle[deg])
Barycentric right ascension $\alpha $ of the source in ICRS at the reference epoch ref_epoch
ra_error : Standard error of right ascension (float, Angle[mas])
Standard error ${\sigma}_{\alpha *}\equiv {\sigma}_{\alpha}\mathrm{cos}\delta $ of the right ascension of the source in ICRS at the reference epoch ref_epoch.
dec : Declination (double, Angle[deg])
Barycentric declination $\delta $ of the source in ICRS at the reference epoch ref_epoch
dec_error : Standard error of declination (float, Angle[mas])
Standard error ${\sigma}_{\delta}$ of the declination of the source in ICRS at the reference epoch ref_epoch
parallax : Parallax (double, Angle[mas] )
Absolute stellar parallax $\varpi $ of the source at the reference epoch ref_epoch
parallax_error : Standard error of parallax (float, Angle[mas] )
Standard error ${\sigma}_{\varpi}$ of the stellar parallax at the reference epoch ref_epoch
parallax_over_error : Parallax divided by its standard error (float)
Parallax divided by its standard error
pm : Total proper motion (float, Angular Velocity[mas yr${}^{1}$])
The total proper motion calculated as the magnitude of the resultant vector of the proper motion component vectors pmra and pmdec, i.e. ${\text{\U0001d699\U0001d696}}^{2}={\text{\U0001d699\U0001d696\U0001d69b\U0001d68a}}^{2}+{\text{\U0001d699\U0001d696\U0001d68d\U0001d68e\U0001d68c}}^{2}$.
pmra : Proper motion in right ascension direction (double, Angular Velocity[mas yr${}^{1}$])
Proper motion in right ascension ${\mu}_{\alpha *}\equiv {\mu}_{\alpha}\mathrm{cos}\delta $ of the source in ICRS at the reference epoch ref_epoch. This is the local tangent plane projection of the proper motion vector in the direction of increasing right ascension.
pmra_error : Standard error of proper motion in right ascension direction (float, Angular Velocity[mas yr${}^{1}$] )
Standard error ${\sigma}_{\mu \alpha *}$ of the local tangent plane projection of the proper motion vector in the direction of increasing right ascension at the reference epoch ref_epoch
pmdec : Proper motion in declination direction (double, Angular Velocity[mas yr${}^{1}$] )
Proper motion in declination ${\mu}_{\delta}$ of the source at the reference epoch ref_epoch. This is the projection of the proper motion vector in the direction of increasing declination.
pmdec_error : Standard error of proper motion in declination direction (float, Angular Velocity[mas yr${}^{1}$] )
Standard error ${\sigma}_{\mu \delta}$ of the proper motion component in declination at the reference epoch ref_epoch
ra_dec_corr : Correlation between right ascension and declination (float)
Correlation coefficient $\rho (\alpha ,\delta )$ between right ascension and declination. This is a dimensionless quantity in the range [1,+1].
ra_parallax_corr : Correlation between right ascension and parallax (float)
Correlation coefficient $\rho (\alpha ,\varpi )$ between right ascension and parallax, a dimensionless quantity in the range [1,+1].
ra_pmra_corr : Correlation between right ascension and proper motion in right ascension (float)
Correlation coefficient $\rho (\alpha ,{\mu}_{\alpha *})$ between right ascension and proper motion in right ascension, a dimensionless quantity in the range [1,+1].
ra_pmdec_corr : Correlation between right ascension and proper motion in declination (float)
Correlation coefficient $\rho (\alpha ,{\mu}_{\delta})$ between right ascension and proper motion in declination, a dimensionless quantity in the range [1,+1].
dec_parallax_corr : Correlation between declination and parallax (float)
Correlation coefficient $\rho (\delta ,\varpi )$ between declination and parallax, a dimensionless quantity in the range [1,+1].
dec_pmra_corr : Correlation between declination and proper motion in right ascension (float)
Correlation coefficient $\rho (\delta ,{\mu}_{\alpha *})$ between declination and proper motion in right ascension, a dimensionless quantity in the range [1,+1].
dec_pmdec_corr : Correlation between declination and proper motion in declination (float)
Correlation coefficient $\rho (\delta ,{\mu}_{\delta})$ between declination and proper motion in declination, a dimensionless quantity in the range [1,+1].
parallax_pmra_corr : Correlation between parallax and proper motion in right ascension (float)
Correlation coefficient $\rho (\varpi ,{\mu}_{\alpha *})$ between parallax and proper motion in right ascension, a dimensionless quantity in the range [1,+1].
parallax_pmdec_corr : Correlation between parallax and proper motion in declination (float)
Correlation coefficient $\rho (\varpi ,{\mu}_{\delta})$ between parallax and proper motion in declination, a dimensionless quantity in the range [1,+1].
pmra_pmdec_corr : Correlation between proper motion in right ascension and proper motion in declination (float)
Correlation coefficient $\rho ({\mu}_{\alpha *},{\mu}_{\delta})$ between proper motion in right ascension and proper motion in declination, a dimensionless quantity in the range [1,+1].
n_scans : Number of CrowdedField scans of the source location (short)
Number of SIF scans or images covering the source location. When compared to the number of matched detections, it will allow to assess the quality/reliability of the source.
astrometric_n_obs_al : Total number of observations in the alongscan (AL) direction (short)
Total number of AL observations (= CCD transits) used in the astrometric solution of the source, independent of their weight. Note that some observations may be strongly downweighted (see astrometric_n_bad_obs_al).
astrometric_n_obs_ac : Total number of observations in the acrossscan (AC) direction (short)
Total number of AC observations (= CCD transits) used in the astrometric solution of the source, independent of their weight (note that some observations may be strongly downweighted). Nearly all sources having G $$ will have AC observations from 2d windows, while fainter than that limit only $\sim 1$% of transit observations (the so–called ‘calibration faint stars’) are assigned 2d windows resulting in AC observations.
astrometric_n_good_obs_al : Number of good observations in the alongscan (AL) direction (short)
Number of AL observations (= CCD transits) that were not strongly downweighted in the astrometric solution of the source. Strongly downweighted observations (with downweighting factor $$) are instead counted in astrometric_n_bad_obs_al. The sum of astrometric_n_good_obs_al and astrometric_n_bad_obs_al equals astrometric_n_obs_al, the total number of AL observations used in the astrometric solution of the source.
astrometric_n_bad_obs_al : Number of bad observations in the alongscan (AL) direction (short)
Number of AL observations (= CCD transits) that were strongly downweighted in the astrometric solution of the source, and therefore contributed little to the determination of the astrometric parameters. An observation is considered to be strongly downweighted if its downweighting factor $$, which means that the absolute value of the astrometric residual exceeds 4.83 times the total uncertainty of the observation, calculated as the quadratic sum of the centroiding uncertainty, excess source noise, and excess attitude noise.
astrometric_gof_al : Goodness of fit statistic of model wrt alongscan observations (float)
Goodnessoffit statistic of the astrometric solution for the source in the alongscan direction. This is the ‘gaussianized chisquare’, which for good fits should approximately follow a normal distribution with zero mean value and unit standard deviation. Values exceeding, say, $+3$ thus indicate a bad fit to the data.
This statistic is computed according to the formula
$\mathtt{\text{astrometric\_gof\_al}}={(9\nu /2)}^{1/2}[{\text{\U0001d69b\U0001d69e\U0001d6a0\U0001d68e}}^{2/3}+2/(9\nu )1]$
where ruwe is the renormalised unit weight error and
$\nu =\mathtt{\text{astrometric\_n\_good\_obs\_al}}N$
is the number of degrees of freedom for a source update. Here $N=5$ for 2parameter and 5parameter solutions (respectively astrometric_params_solved = 3 or 31) and 6 for 6parameter solutions (astrometric_params_solved = 95).
Note that only ‘good’ (i.e. not strongly downweighted) observations are included in $\nu $. For further details please see Lindegren et al. (2021).
astrometric_chi2_al : AL chisquare value (float)
Astrometric goodnessoffit (${\chi}^{2}$) in the AL direction.
${\chi}^{2}$ values were computed for the ‘good’ AL observations of the source, without taking into account the astrometric_excess_noise (if any) of the source. They do however take into account the attitude excess noise (if any) of each observation.
astrometric_excess_noise : Excess noise of the source (float, Angle[mas])
This is the excess noise ${\u03f5}_{i}$ of the source. It measures the disagreement, expressed as an angle, between the observations of a source and the bestfitting standard astrometric model (using five astrometric parameters). The assumed observational noise in each observation is quadratically increased by ${\u03f5}_{i}$ in order to statistically match the residuals in the astrometric solution. A value of 0 signifies that the source is astrometrically wellbehaved, i.e. that the residuals of the fit statistically agree with the assumed observational noise. A positive value signifies that the residuals are statistically larger than expected.
The significance of ${\u03f5}_{i}$ is given by astrometric_excess_noise_sig ($D$). If $D\le 2$ then ${\u03f5}_{i}$ is probably not significant, and the source may be astrometrically wellbehaved even if ${\u03f5}_{i}$ is large.
The excess noise ${\u03f5}_{i}$ may absorb all kinds of modelling errors that are not accounted for by the observational noise (image centroiding error) or the excess attitude noise. Such modelling errors include LSF and PSF calibration errors, geometric instrument calibration errors, and part of the highfrequency attitude noise. These modelling errors are particularly important in the early data releases, but should decrease as the astrometric modelling of the instrument and attitude improves over the years.
Additionally, sources that deviate from the standard fiveparameter astrometric model (e.g. unresolved binaries, exoplanet systems, etc.) may have positive ${\u03f5}_{i}$. Given the many other possible contributions to the excess noise, the user must study the empirical distributions of ${\u03f5}_{i}$ and $D$ to make sensible cutoffs before filtering out sources for their particular application.
The excess source noise is further explained in Sections 3.6 and 5.1.2 of
Lindegren et al. (2012).
astrometric_excess_noise_sig : Significance of excess noise (float)
A dimensionless measure ($D$) of the significance of the calculated astrometric_excess_noise (${\u03f5}_{i}$). A value $D>2$ indicates that the given ${\u03f5}_{i}$ is probably significant.
For good fits in the limit of a large number of observations, $D$ should be zero in half of the cases and approximately follow the positive half of a normal distribution with zero mean and unit standard deviation for the other half. Consequently, $D$ is expected to be greater than 2 for only a few percent of the sources with wellbehaved astrometric solutions.
In the early data releases ${\u03f5}_{i}$ will however include instrument and attitude modelling errors that are statistically significant and could result in large values of ${\u03f5}_{i}$ and $D$. The user must study the empirical distributions of these statistics and make sensible cutoffs before filtering out sources for their particular application.
The excess noise significance is further explained in Section 5.1.2 of
Lindegren et al. (2012).
astrometric_params_solved : Which parameters have been solved for? (byte)
The seven bits of astrometric_params_solved indicate which parameters have been estimated in AGIS for this source. A set bit means the parameter was updated, an unset bit means the parameter was not updated. The leastsignificant bit corresponds to ra. The table below shows the values of astrometric_params_solved for relevant combinations of the parameters.
The radial proper motion (${\mu}_{r}$) is formally considered to be one of the astrometric parameters of a source, and the sixth bit is therefore reserved for it. It is also in principle updatable in AGIS, but in practice it will always be computed from a spectroscopic radial velocity and the estimated parallax, in which case the bit is not set.
$C$ is the pseudocolour of the source, i.e. the astrometrically estimated effective wavenumber.
astrometric_params_solved  ra  dec  parallax  pmra  pmdec  ${\mu}_{r}$  $C$ 

${0000011}_{2}=3$  ✓  ✓  
${0000111}_{2}=7$  ✓  ✓  ✓  
${0011011}_{2}=27$  ✓  ✓  ✓  ✓  
${0011111}_{2}=31$  ✓  ✓  ✓  ✓  ✓  
${0111111}_{2}=63$  ✓  ✓  ✓  ✓  ✓  ✓  
${1011111}_{2}=95$  ✓  ✓  ✓  ✓  ✓  ✓ 
In practice all the sources in DR3 have only values of 3, 31 or 95 for the $\mathrm{\U0001d68a\U0001d69c\U0001d69d\U0001d69b\U0001d698\U0001d696\U0001d68e\U0001d69d\U0001d69b\U0001d692\U0001d68c}\mathrm{\_}\mathrm{\U0001d699\U0001d68a\U0001d69b\U0001d68a\U0001d696\U0001d69c}\mathrm{\_}\mathrm{\U0001d69c\U0001d698\U0001d695\U0001d69f\U0001d68e\U0001d68d}$, corresponding to twoparameter (position), fiveparameter (position, parallax, and proper motion) and sixparameter (position, parallax, proper motion and astrometrically estimated effective wavenumber) solutions.
pseudocolour : Astrometrically estimated pseudocolour of the source (float, Misc[$\mu {m}^{1}$])
Effective wavenumber of the source estimated in the final astrometric processing.
The pseudocolour is the astrometrically estimated effective wavenumber of the photon flux distribution in the astrometric ($G$) band, measured in $\mu $m${}^{1}$. The value in this field was estimated from the chromatic displacements of image centroids, calibrated by means of the photometrically determined effective wavenumbers (${\nu}_{\text{eff}}$) of primary sources.
The field is empty when chromaticity was instead taken into account using the photometrically determined ${\nu}_{\text{eff}}$ given in the field nu_eff_used_in_astrometry.
pseudocolour_error : Standard error of the pseudocolour of the source (float, Misc[$\mu {m}^{1}$])
Standard error ${\sigma}_{\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b}}$ of the astrometrically determined pseudocolour of the source.
ra_pseudocolour_corr : Correlation between right ascension and pseudocolour (float)
Correlation coefficient $\rho (\alpha ,\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b})$ between right ascension ra and pseudocolour, a dimensionless quantity in the range [1,+1]
dec_pseudocolour_corr : Correlation between declination and pseudocolour (float)
Correlation coefficient $\rho (\delta ,\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b})$ between declination dec and pseudocolour, a dimensionless quantity in the range [1,+1]
parallax_pseudocolour_corr : Correlation between parallax and pseudocolour (float)
Correlation coefficient $\rho (\varpi ,\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b})$ between parallax and pseudocolour, a dimensionless quantity in the range [1,+1]
pmra_pseudocolour_corr : Correlation between proper motion in right asension and pseudocolour (float)
Correlation coefficient $\rho ({\mu}_{\alpha *},\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b})$ between proper motion in right ascension pmra and pseudocolour, a dimensionless quantity in the range [1,+1]
pmdec_pseudocolour_corr : Correlation between proper motion in declination and pseudocolour (float)
Correlation coefficient $\rho ({\mu}_{\delta},\mathrm{\U0001d699\U0001d69c\U0001d68e\U0001d69e\U0001d68d\U0001d698\U0001d68c\U0001d698\U0001d695\U0001d698\U0001d69e\U0001d69b})$ between proper motion in declination pmdec and pseudocolour, a dimensionless quantity in the range [1,+1]
astrometric_matched_transits : Matched FOV transits used in the AGIS solution (short)
The number of field–of–view transits matched to this source, counting only the transits containing CCD observations actually used to compute the astrometric solution.
This number will always be equal to or smaller than matched_transits, the difference being the FOV transits that were not used in the astrometric solution because of bad data or excluded time intervals.
visibility_periods_used : Number of visibility periods used in Astrometric solution (short)
Number of visibility periods used in the astrometric solution.
A visibility period is a group of observations separated from other groups by a gap of at least 4 days. A source may have from one to tens of field–of–view transits in a visibility period, but with a small spread in time, direction of scanning, and parallax factor. From one visibility period to the next these variables have usually changed significantly. A high number of visibility periods is therefore a better indicator of an astrometrically well–observed source than a large number of field–of–view transits (matched_transits or astrometric_matched_transits) or CCD observations (astrometric_n_obs_al). A small value (e.g. less than 10) indicates that the calculated parallax could be more vulnerable to errors, e.g. from the calibration model, not reflected in the formal uncertainties. See Lindegren et al. (2018) for a discussion of this and other astrometric quality indicators.
astrometric_sigma5d_max : The longest semimajor axis of the 5d error ellipsoid (float, Angle[mas])
The longest principal axis in the 5dimensional error ellipsoid.
This is a 5dimensional equivalent to the semimajor axis of the position error ellipse and is therefore useful for filtering out cases where one of the five parameters, or some linear combination of several parameters, is particularly illdetermined. It is measured in mas and computed as the square root of the largest singular value of the scaled $5\times 5$ covariance matrix of the astrometric parameters. The matrix is scaled so as to put the five parameters on a comparable scale, taking into account the maximum alongscan parallax factor for the parallax and the time coverage of the observations for the proper motion components. If $C$ is the unscaled covariance matrix, the scaled matrix is $SCS$, where $S=\text{diag}(1,1,\mathrm{sin}\xi ,T/2,T/2)$, $\xi ={45}^{\circ}$ is the solar aspect angle in the nominal scanning law, and $T$ the time coverage of the data used in the solution.
astrometric_sigma5d_max is given for all the solutions, as its size is one of the criteria for accepting or rejecting the 5 or 6parameter solution. In case of a 2 parameter solution (astrometric_params_solved = 3) it gives the value for the rejected 5 or 6parameter solution, and can then be arbitrarily large.
matched_transits : The number of transits matched to this source (short)
The total number of field–of–view transits matched to this source.
ipd_gof_harmonic_amplitude : Amplitude of the IPD GoF versus position angle of scan (float)
This statistic measures the amplitude of the variation of the Image Parameter Determination (IPD) goodness–of–fit (GoF; reduced chisquare) as function of the position angle of the scan direction. A large amplitude indicates that the source has some nonisotropic spatial structure, for example a binary or galaxy, that is at least partially resolved by Gaia. The phase of the variation is given by the parameter ipd_gof_harmonic_phase.
Let $\psi $ be the position angle of the scan direction. The following expression is fitted to the IPD GoF for the accepted AF observations of the source:
$$\mathrm{ln}(\mathrm{GoF})={c}_{0}+{c}_{2}\mathrm{cos}(2\psi )+{s}_{2}\mathrm{sin}(2\psi )$$ 
The amplitude and phase of the variation are calculated as
$$\mathtt{\text{ipd\_gof\_harmonic\_amplitude}}=\sqrt{{c}_{2}^{2}+{s}_{2}^{2}}$$ 
$$\mathtt{\text{ipd\_gof\_harmonic\_phase}}=\frac{1}{2}\mathrm{atan2}({s}_{2},{c}_{2})\phantom{\rule{1em}{0ex}}(+{180}^{\circ})$$ 
where atan2 returns the angle in degrees. In the last expression 180 is added for negative values, so that ipd_gof_harmonic_phase is always between 0 and 180${}^{\circ}$. Only the AF observations accepted by the astrometric solution are used to compute the amplitude and phase, thus for example outliers and observations in the early Ecliptic Pole Scanning Law phase are not used.
The GoF variation is modelled as a periodic function of $2\psi $ because a source with fixed structure is normally expected to give fits of similar quality when scanned in opposite directions ($\psi $ differing by 180${}^{\circ}$). See ipd_gof_harmonic_phase for the interpretation of the phase.
ipd_gof_harmonic_phase : Phase of the IPD GoF versus position angle of scan (float, Angle[deg])
This statistic measures the phase of the variation of the IPD GoF (reduced chisquare) as function of the position angle of the scan direction. See the description of ipd_gof_harmonic_amplitude for details on the computation of the phase.
The interpretation of this parameter is nontrivial because of the complex interaction between the source structure and the IPD. At least the following different scenarios could occur:

•
For a binary with separation $\lesssim 0.1$ arcsec the GoF is expected to be higher when the scan is along the arc joining the components than in the perpendicular direction, in which case ipd_gof_harmonic_phase should indicate the position angle of the binary modulo 180${}^{\circ}$. Such a binary will normally have negligible ipd_frac_multi_peak (less than a few per cent).

•
For a resolved binary the GoF may instead have a minimum when the scan is along the arc joining the two components, in which case ipd_gof_harmonic_phase differs from the position angle of the binary (modulo 180${}^{\circ}$) by approximately $\pm {90}^{\circ}$. Such a binary will normally have a large ipd_frac_multi_peak.

•
For a bright binary ($G\lesssim 13$) the GoF refers to the fitting of a twodimensional PSF, which could further complicate the intrepretation.

•
For a galaxy with elongated intensity distribution, the IPD may give a smaller GoF when the scan is along the major axis of the image, resulting in an offset of approximately $\pm {90}^{\circ}$ between the ipd_gof_harmonic_phase and the position angle of the major axis (modulo 180${}^{\circ}$).
scan_direction_strength_k1 : Degree of concentration of scan directions across the source (float)
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 quantify the distribution of AL scan directions across the source. scan_direction_strength_k1 (and similarly 2,3,4) are the absolute value of the trigonometric moments ${m}_{k}=\u27e8\mathrm{exp}(ik\theta )\u27e9$ for $k=1,2,3,4$ where $\theta $ is the position angle of the scan and the mean value is taken over the astrometric_n_good_obs_al observations contributing to the astrometric parameters of the source. $\theta $ is defined in the usual astronomical sense: $\theta =0$ when the FoV is moving towards local North, and $\theta ={90}^{\circ}$ towards local East.
N.B. When astrometric_n_obs_ac $>0$ the scan direction attributes are not provided at Gaia DR3. Hence for all sources brighter than G $\approx 13$, and for a tiny fraction of fainter sources ($\approx 1$%), these 8 scan direction fields will be NULL.
The scan_direction_strength_k1…4 are numbers between 0 and 1, where 0 means that the scan directions are well spread out in different directions, while 1 means that they are concentrated in a single direction (given by the corresponding scan_direction_mean_k1…4).
The different orders $k$ are statistics of the scan directions modulo ${360}^{\circ}/k$. For example, at first order ($k=1$), $\theta ={10}^{\circ}$ and $\theta ={190}^{\circ}$ count as different directions, but at second order ($k=2$) they are the same. Thus, scan_direction_strength_k1 is the degree of concentration when the sense of direction is taken into account, while scan_direction_strength_k2 is the degree of concentration without regard to the sense of direction. A large value of scan_direction_strength_k4 indicates that the scans are concentrated in two nearly orthogonal directions.
scan_direction_strength_k2 : Degree of concentration of scan directions across the source (float)
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_strength_k1 for further details.
scan_direction_strength_k3 : Degree of concentration of scan directions across the source (float)
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_strength_k1 for further details.
scan_direction_strength_k4 : Degree of concentration of scan directions across the source (float)
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_strength_k1 for further details.
scan_direction_mean_k1 : Mean position angle of scan directions across the source (float, Angle[deg])
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source. scan_direction_mean_k1 (and similarly for $k=2,3,4$) is $1/k$ times the argument of the trigonometric moments ${m}_{k}=\u27e8\mathrm{exp}(ik\theta )\u27e9$, where $\theta $ is the position angle of the scan and the mean value is taken over the astrometric_n_good_obs_al observations contributing to the astrometric parameters of the source. $\theta $ is defined in the usual astronomical sense: $\theta =0$ when the FoV is moving towards local North, and $\theta ={90}^{\circ}$ towards local East.
N.B. When astrometric_n_obs_ac $>0$ the scan direction attributes are not provided at Gaia DR3. Hence for all sources brighter than G $\approx 13$, and for a tiny fraction of fainter sources ($\approx 1$%), these 8 scan direction fields will be NULL.
scan_direction_mean_k1 (and similarly for $k=2,3,4$) is an angle between ${180}^{\circ}/k$ and $+{180}^{\circ}/k$, giving the mean position angle of the scans at order $k$.
The different orders $k$ are statistics of the scan directions modulo ${360}^{\circ}/k$. For example, at first order ($k=1$), $\theta ={10}^{\circ}$ and $\theta ={190}^{\circ}$ count as different directions, but at second order ($k=2$) they are the same. Thus, scan_direction_mean_k1 is the mean direction when the sense of direction is taken into account, while scan_direction_mean_k2 is the mean direction without regard to the sense of the direction. For example, scan_direction_mean_k1 = 0 means that the scans preferentially go towards North, while scan_direction_mean_k2 = 0 means that they preferentially go in the NorthSouth direction, and scan_direction_mean_k4 = 0 that they preferentially go either in the NorthSouth or in the EastWest direction.
scan_direction_mean_k2 : Mean position angle of scan directions across the source (float, Angle[deg])
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_mean_k1 for further details.
scan_direction_mean_k3 : Mean position angle of scan directions across the source (float, Angle[deg])
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_mean_k1 for further details.
scan_direction_mean_k4 : Mean position angle of scan directions across the source (float, Angle[deg])
The scan_direction_strength_k1…4 and scan_direction_mean_k1…4 attributes quantify the distribution of AL scan directions across the source.
See the description for attribute scan_direction_mean_k1 for further details.
astrometric_primary_flag : Primary or secondary (boolean)
Flag indicating if this source was used as a primary source (true) or secondary source (false). Only primary sources contribute to the estimation of attitude, calibration, and global parameters. The estimation of source parameters is otherwise done in exactly the same way for primary and secondary sources.
phot_g_n_obs : Number of observations contributing to G photometry (short)
Number of observations (CCD transits) that contributed to the G mean flux (phot_g_mean_flux) and mean flux error (phot_g_mean_flux_error).
phot_g_mean_flux : Gband mean flux (double, Flux[e${}^{}$ s${}^{1}$])
Mean flux in the Gband.
phot_g_mean_flux_error : Error on Gband mean flux (float, Flux[e${}^{}$ s${}^{1}$])
Standard deviation of the Gband fluxes divided by the square root of the number of observations (phot_g_n_obs).
phot_g_mean_flux_over_error : Gband mean flux divided by its error (float)
Mean flux in the Gband phot_g_mean_flux divided by its error phot_g_mean_flux_error.
phot_g_mean_mag : Gband mean magnitude (float, Magnitude[mag])
Mean magnitude in the G band. This is computed from the Gband mean flux (phot_g_mean_flux ) applying the magnitude zeropoint in the Vega scale (see Gaia DR3 online documentation and references therein).
No error is provided for this quantity as the error distribution is only symmetric in flux space. This converts to an asymmetric error distribution in magnitude space which cannot be represented by a single error value.
phot_g_flux_uwv : Unit weight variance of fluxes (double)
The unit weight variance of the flux values.
phot_g_flux_median : Median flux (float, Flux[e${}^{}$ s${}^{1}$])
Median of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_skewness : Measure of the skewness of the flux distribution (float)
Measure of the skewness of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_kurtosis : Measure of the kurtosis of the flux distribution (float)
Kurtosis of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_mad : MAD of the flux distribution (float, Flux[e${}^{}$ s${}^{1}$])
Median Absolute Deviation (MAD) of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_first_quartile : First quartile of the flux distribution (float, Flux[e${}^{}$ s${}^{1}$])
First ($25\%$) quartile of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_third_quartile : Third quartile of the flux distribution (float, Flux[e${}^{}$ s${}^{1}$])
Third ($75\%$) quartile of the flux distribution.
When an insufficient number of observations are available to compute these quantities, the corresponding field will be set to Float.NaN.
phot_g_flux_min : Minimum flux value (float, Flux[e${}^{}$ s${}^{1}$])
Minimum flux value.
phot_g_flux_max : Maximum flux value (float, Flux[e${}^{}$ s${}^{1}$])
Maximum flux value.
phot_proc_mode : Photometry processing mode (byte)
This flag indicates the photometric calibration process used for the source. For nominal processing, this process is determined by the availability of colour information derived from the internally calibrated mean BP and RP source spectra. The following values are defined for Gaia DR3:

•
0: this corresponds to the ‘gold’ photometric dataset. Sources in this dataset have complete colour information.

•
1: this corresponds to the ‘silver’ photometric dataset. Sources in this dataset have incomplete colour information and therefore were calibrated using an iterative process that estimated the missing colour information from the source mean G and either BP or RP photometry (depending on which band had full colour information available) using empirical relationships derived from the gold dataset.

•
2: this corresponds to the ‘bronze’ photometric dataset. Sources in this dataset had insufficient colour information and therefore were calibrated using default colour information derived from the gold dataset.

•
16: this data was not produced with the nominal PhotPipe code, but with a dedicated photometric overlap calibration performed for SIF CF Focussed Product Release using calibrated DR3 sources as reference.
Because the process of generating the mean BP and RP spectra and the process of producing mean BP and RP integrated photometry are very different and have different requirements it is possible for gold sources to be missing any of the bands, i.e. gold does not imply anything about the availability of mean G, BP and RP photometry. Similarly for silver and bronze sources it is possible to have photometry available in any bands (and possible combinations).
More details about the different calibration procedures are available in Chapter 5 of the Gaia DR3 online documentation and in Riello et al. (2021) and references therein.
l : Galactic longitude (double, Angle[deg])
Galactic Longitude of the object at reference epoch ref_epoch.
b : Galactic latitude (double, Angle[deg])
Galactic Latitude of the object at reference epoch ref_epoch.
ecl_lon : Ecliptic longitude (double, Angle[deg])
Ecliptic Longitude of the object at reference epoch ref_epoch, obtained from the equatorial coordinates using the transformation defined in Volume 1, Section 1.5.3 of ESA (1997).
Note that in the transformation applied here the ICRS origin is shifted in the equatorial plane from $\mathrm{\Gamma}$ by $\varphi =0.05542$ arcsec, positive from $\mathrm{\Gamma}$ to the ICRS origin (Chapront et al. 2002). The ICRS has an unambiguous definition with an origin in the ICRF equator defined by the realisation of the ICRF. The ecliptic system is less welldefined, potentially depending on additional conventions in dynamical theories. The transformation employed here corresponds to the inertial mean ecliptic with obliquity and $\mathrm{\Gamma}$ defined by reference to the ICRS equator. Both the obliquity and the position of $\mathrm{\Gamma}$ on the ICRS equator with respect to the ICRS origin have been obtained from Lunar Laser Ranging measurements. This has no time dependence – there is no secular variation of the obliquity and no precession – and it simply defines the relative situation of the various planes at J2000.
ecl_lat : Ecliptic latitude (double, Angle[deg])
Ecliptic Latitude of the object at reference epoch ref_epoch. For further details see the description for attribute ecl_lon.