sextractor

Sextractor is a photometry program that builds a catalogue of objects from an astronomical image. Although it is particularly oriented towards reduction of large scale galaxy-survey data, it can perform reasonably well on moderately crowded star fields. A full description can be found at astromatic.net

The program is run by typing: sex myfile.fts, where myfile.fts is a FITS file. There are several configuration files in /usr/local/sectractor that should not need changing. The only file that needs to be specidied in the command line is /usr/local/sextractor/default.sex (this can be copied to the local directory and modified if desired0.

Usage example: sex -c /usr/local/sextractor/default.sex xea12407.fts

----- SExtractor 2.19.5 started on 2016-05-10 at 16:51:10 with 1 thread

----- Measuring from: xea12407.fts

      "V765 Oph" / no ext. header / 1536x1023 / 16 bits (integers)

(M+D) Background: 539.343    RMS: 8.3346     / Threshold: 79.1787

      Objects: detected 868      / sextracted 851

> All done (in 0.2 s: 4773.6 lines/s , 3971.0 detections/s) 

This produces a file test.cat. The first few lines are:

#   1 NUMBER                 Running object number

#   2 FLUX_AUTO              Flux within a Kron-like elliptical aperture                [count]

#   3 FLUXERR_AUTO           RMS error for AUTO flux                                    [count]

#   4 FLUX_BEST              Best of FLUX_AUTO and FLUX_ISOCOR                          [count]

#   5 FLUXERR_BEST           RMS error for BEST flux                                    [count]

#   6 X_IMAGE                Object position along x                                    [pixel]

#   7 Y_IMAGE                Object position along y                                    [pixel]

#   8 X_WORLD                Barycenter position along world x axis                     [deg]

#   9 Y_WORLD                Barycenter position along world y axis                     [deg]

#  10 A_WORLD                Profile RMS along major axis (world units)                 [deg]

#  11 B_WORLD                Profile RMS along minor axis (world units)                 [deg]

#  12 THETA_SKY              Position angle (east of north) (native)                    [deg]

#  13 FWHM_IMAGE             FWHM assuming a gaussian core                              [pixel]

#  14 FWHM_WORLD             FWHM assuming a gaussian core                              [deg]

#  15 FLAGS                  Extraction flags

         1     11535.27     103.0812     11535.27     103.0812    502.7842     19.6134   2.6237934814e+02   6.4359463680e+00  0.000309815  0.000297803 +39.45     1.64  0.000490956   0

         2     10362.92     98.78642     10539.92     193.5643   1076.8123     13.4332   2.6220628757e+02   6.4367849176e+00 0.0003112864 0.0002962685 +71.92     1.54 0.0004617601   3

         3     6376.737      82.2752     6563.514     200.2335   1073.1770      9.7880   2.6220737684e+02   6.4378837116e+00 0.0003069935 0.0002726225 +59.27     1.58 0.0004744338   3

         4     1931.032     59.46868     1931.032     59.46868     17.0698     12.2237   2.6252576133e+02   6.4389724046e+00 0.0002351469 0.0001984784 -50.33     1.76 0.0005264769   0

         5     16211.41      118.092     16211.41      118.092    204.1414      5.7013   2.6246935502e+02   6.4406189704e+00 0.0003178273 0.0003116693 +23.42     1.52 0.0004546758  16

         6     7357.418     89.00897     7357.418     89.00897    507.2009      4.5734   2.6237799067e+02   6.4404452639e+00 0.0003498406 0.0002842087 -44.86     2.31 0.0006918601  16

         7     1805.283     51.16047     1805.283     51.16047    958.0528      3.4720   2.6224207143e+02   6.4399839994e+00 0.0002220735 0.0002073034  +2.21     1.54 0.0004619804  16

© Robert Mutel 2018