4.1. Merged Catalogues
In addition to astrometric header information, SCAMP can write out “merged”
catalogues (one per field group). These catalogues contain the calibrated coordinates
and magnitudes of a union of all detections from input catalogues that passed the SCAMP
acceptation criteria (S/N, flags).
Merged coordinates and magnitudes are computed using a weighted average of all overlapping
measurements, and are accompanied by estimates of formal errors and 1-sigma uncertainties
on individual measurements.
The MERGEDOUTCAT_TYPE configuration parameter sets the format of the merged catalogue;
it is set to NONE by default, which means that no catalogue is created.
The available formats are ASCII (pure ASCII table), ASCII_HEAD (ASCII table with
a small header describing the column content), and FITS_LDAC (FITS binary table).
FITS_LDAC is the recommended format; FITS_LDAC files are smaller, carry the data
with full precision, and can be read with popular software such as fv and TOPCAT.
They can be converted to ASCII format with the ldactoasc command-line utility,
which is part of the SExtractor package.
The columns present in the file are:
| Name: | SOURCE_NUMBER |
|---|
| Content: | Source ID, the same as in “full” catalogue |
|---|
| Unit: | - |
|---|
| Name: | NPOS_TOTAL |
|---|
| Content: | Total number of overlapping positions |
|---|
| Unit: | - |
|---|
| Name: | NPOS_OK |
|---|
| Content: | Number of overlapping positions kept for astrometry |
|---|
| Unit: | - |
|---|
| Name: | ALPHA_J2000 |
|---|
| Content: | (Weighted-)average Right-Ascension |
|---|
| Unit: | deg |
|---|
| Name: | DELTA_J2000 |
|---|
| Content: | (Weighted-)average Declination |
|---|
| Unit: | deg |
|---|
| Name: | ERRA_WORLD |
|---|
| Content: | Position uncertainty (RMS) along major world axis
(may include additional uncertainty computed by SCAMP) |
|---|
| Unit: | deg |
|---|
| Name: | ERRB_WORLD |
|---|
| Content: | Position uncertainty (RMS) along minor world axis
(may include additional uncertainty computed by SCAMP) |
|---|
| Unit: | deg |
|---|
| Name: | ERRTHETA_WORLD |
|---|
| Content: | Position angle of error ellipse (CCW/world-x)
(The current estimation of error ellipse parameters is still done very crudely) |
|---|
| Unit: | deg |
|---|
| Name: | DISPALPHA_J2000 |
|---|
| Content: | Measured dispersion (RMS) of position along Right-Ascension |
|---|
| Unit: | deg |
|---|
| Name: | DISPDELTA_J2000 |
|---|
| Content: | Measured dispersion (RMS) of position along Declination |
|---|
| Unit: | deg |
|---|
| Name: | PMALPHA_J2000 |
|---|
| Content: | Apparent proper motion along Right-Ascension |
|---|
| Unit: | mas/yr |
|---|
| Name: | PMDELTA_J2000 |
|---|
| Content: | Apparent proper motion along Declination |
|---|
| Unit: | mas/yr |
|---|
| Name: | PMALPHAERR_J2000 |
|---|
| Content: | Proper motion uncertainty (RMS) along Right Ascension |
|---|
| Unit: | mas/yr |
|---|
| Name: | PMDELTAERR_J2000 |
|---|
| Content: | Proper motion uncertainty (RMS) along Declination |
|---|
| Unit: | mas/yr |
|---|
| Name: | PARALLAX_WORLD |
|---|
| Content: | Trigonometric parallax |
|---|
| Unit: | mas |
|---|
| Name: | PARALLAXERR_WORLD |
|---|
| Content: | Trigonometric parallax uncertainty |
|---|
| Unit: | mas |
|---|
| Name: | CHI2_ASTROM |
|---|
| Content: | Reduced chi2 per d.o.f. of the proper motion/parallax fit |
|---|
| Unit: | - |
|---|
| Name: | EPOCH |
|---|
| Content: | (Astrometrically-)weighted-average of observation dates |
|---|
| Unit: | yr |
|---|
| Name: | EPOCH_MIN |
|---|
| Content: | Earliest observation date |
|---|
| Unit: | yr |
|---|
| Name: | EPOCH_MAX |
|---|
| Content: | Latest observation date |
|---|
| Unit: | yr |
|---|
| Name: | NMAG |
|---|
| Content: | Number of magnitude measurements in each photometric instrument” |
|---|
| Unit: | - |
|---|
| Name: | MAG |
|---|
| Content: | Vector of ( ux-weighted-)average magnitudes |
|---|
| Unit: | mag |
|---|
| Name: | MAGERR |
|---|
| Content: | Vector of magnitude uncertainties |
|---|
| Unit: | mag |
|---|
| Name: | MAG_DISP |
|---|
| Content: | Vector of measured magnitude dispersions (RMS) |
|---|
| Unit: | mag |
|---|
| Name: | COLOR |
|---|
| Content: | Composite colour index computed by SCAMP |
|---|
| Unit: | mag |
|---|
| Name: | SPREAD_MODEL |
|---|
| Content: | (Weighted-)average of ``SPREAD_MODEL``s |
|---|
| Unit: | - |
|---|
| Name: | SPREADERR_MODEL |
|---|
| Content: | SPREAD_MODEL uncertainty |
|---|
| Unit: | - |
|---|
| Name: | FLAGS_EXTRACTION |
|---|
| Content: | Arithmetic OR of SExtractor flags over overlapping detection |
|---|
| Unit: | - |
|---|
| Name: | FLAGS_SCAMP |
|---|
| Content: | SCAMP flags for this detection |
|---|
| Unit: | - |
|---|
4.2. Full Catalogues
Other catalogues which can be produced by SCAMP are the “full” catalogues (one per field
group). These catalogues contain the raw and calibrated coordinates and magnitudes of all
individual detections that passed the SCAMP acceptation criteria. Each detection is linked to
a parent source through to the SOURCE_NUMBER identifier, also present in the merged output
catalogue. The CATALOG_NUMBER identifier link the detected source to its catalogue (as SCAMP
could receive more than one input catalogue), CATALOG_NUMBER set to 0 beeing reserved to the
reference catalogue.
The FULLOUTCAT_TYPE configuration parameter sets the format of the full catalogue; the choice
of options is the same as for MERGEDOUTCAT_TYPE.
The columns present in the file are:
| Name: | SOURCE_NUMBER |
|---|
| Content: | Source ID, the same as in “merged” catalogue |
|---|
| Unit: | - |
|---|
| Name: | CATALOG_NUMBER |
|---|
| Content: | Catalogue ID, 0 beeing reserved to the reference catalogue |
|---|
| Unit: | - |
|---|
| Name: | EXTENSION |
|---|
| Content: | FITS extension of the parent image (always set to 1 for single extension images) |
|---|
| Unit: | - |
|---|
| Name: | ASTR_INSTRUM |
|---|
| Content: | Astrometric instrument (context) ID |
|---|
| Unit: | - |
|---|
| Name: | PHOT_INSTRUM |
|---|
| Content: | Photometric instrument (context) ID |
|---|
| Unit: | - |
|---|
| Name: | X_IMAGE |
|---|
| Content: | x pixel coordinate of centroid |
|---|
| Unit: | pixel |
|---|
| Name: | Y_IMAGE |
|---|
| Content: | y pixel coordinate of centroid |
|---|
| Unit: | pixel |
|---|
| Name: | ERRA_IMAGE |
|---|
| Content: | Position uncertainty (RMS) along major error ellipse axis |
|---|
| Unit: | pixel |
|---|
| Name: | ERRB_IMAGE |
|---|
| Content: | Position uncertainty (RMS) along minor error ellipse axis |
|---|
| Unit: | pixel |
|---|
| Name: | ERRTHETA_IMAGE |
|---|
| Content: | Position angle of error ellipse (forced to 0 by current versions of
SCAMP which isotropise input uncertainties.) |
|---|
| Unit: | deg |
|---|
| Name: | ALPHA_J2000 |
|---|
| Content: | Calibrated Right-Ascension of centroid in the ICRS (at epoch of observation) |
|---|
| Unit: | deg |
|---|
| Name: | DELTA_J2000 |
|---|
| Content: | Calibrated Declination of centroid in the ICRS (at epoch of observation) |
|---|
| Unit: | deg |
|---|
| Name: | ERRA_WORLD |
|---|
| Content: | Position uncertainty (RMS) along major world axis
(may include additional uncertainty computed by SCAMP) |
|---|
| Unit: | deg |
|---|
| Name: | ERRB_WORLD |
|---|
| Content: | Position uncertainty (RMS) along minor world axis
(may include additional uncertainty computed by SCAMP) |
|---|
| Unit: | deg |
|---|
| Name: | ERRTHETA_WORLD |
|---|
| Content: | Position angle of error ellipse (CCW/world-x)
(The current estimation of error ellipse parameters is still done very crudely) |
|---|
| Unit: | deg |
|---|
| Name: | EPOCH |
|---|
| Content: | Julian date at start of observation |
|---|
| Unit: | yr |
|---|
| Name: | MAG |
|---|
| Content: | Calibrated magnitude |
|---|
| Unit: | mag |
|---|
| Name: | MAGERR |
|---|
| Content: | Magnitude uncertainty (may include additional uncertainty computed by
SCAMP.) |
|---|
| Unit: | mag |
|---|
| Name: | MAG_DISP |
|---|
| Content: | Vector of measured magnitude dispersions (RMS) |
|---|
| Unit: | mag |
|---|
| Name: | SPREAD_MODEL |
|---|
| Content: | SPREAD_MODEL parameter |
|---|
| Unit: | - |
|---|
| Name: | SPREADERR_MODEL |
|---|
| Content: | SPREAD_MODEL uncertainty |
|---|
| Unit: | - |
|---|
| Name: | FLAGS_EXTRACTION |
|---|
| Content: | SExtractor flags |
|---|
| Unit: | - |
|---|
| Name: | FLAGS_SCAMP |
|---|
| Content: | SCAMP flags for this detection |
|---|
| Unit: | - |
|---|