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SEFStars Catalog Format

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William Forney edited this page Mar 10, 2026 · 1 revision

Fixed Star Catalog Format (sefstars.txt)

This document describes the text format of the sefstars.txt fixed-star catalog file. The format was established by empirical analysis of the file contents.

This file is external data, not included in this repository.

Overview

sefstars.txt is a comma-delimited text catalog of ~1,400 fixed stars. Each non-comment line encodes the star's position at epoch J2000.0, proper-motion rates, parallax, radial velocity, and apparent magnitude.

Line Format

Comment Lines

Lines beginning with # are comments and must be skipped.

Data Lines

common_name , bayer_desig , frame , ra_h , ra_m , ra_s , dec_d , dec_m , dec_s , pm_ra , pm_dec , radvel , parallax , mag [, color_index , catalog_no]

All fields are comma-delimited; leading and trailing whitespace within each field should be trimmed.

Column Field Type Unit Notes
1 common_name string — E.g., Aldebaran, Sirius
2 bayer_desig string — Bayer designation, e.g., alTau, alCMa
3 frame string — Coordinate frame: ICRS, FK5, or 2000 (= FK5 J2000)
4 ra_h integer hours Right ascension — hours component
5 ra_m integer minutes Right ascension — minutes component
6 ra_s decimal seconds Right ascension — seconds component
7 dec_d integer degrees Declination — degrees (sign included, e.g., +16, -26)
8 dec_m integer arcmin Declination — arcminutes
9 dec_s decimal arcsec Declination — arcseconds
10 pm_ra decimal mas/yr Proper motion in RA already multiplied by cos(Dec)
11 pm_dec decimal mas/yr Proper motion in Dec
12 radvel decimal km/s Radial velocity (positive = receding)
13 parallax decimal mas Annual trigonometric parallax
14 mag decimal mag Visual (V-band) apparent magnitude
15 color_index integer — Optional; spectral colour index
16 catalog_no integer — Optional; catalogue number

Column 7 sign: The degrees field carries a leading + or − sign for the declination. Arcminutes and arcseconds are always positive; the sign from degrees propagates to the full Dec.

Converting to Decimal Degrees

Right Ascension

RA_degrees = (ra_h + ra_m / 60.0 + ra_s / 3600.0) × 15.0

Declination

sign   = −1 if dec_d starts with '−', else +1
Dec    = sign × (|dec_d| + dec_m / 60.0 + dec_s / 3600.0)

Proper-Motion Correction

To apply proper motion and advance positions from J2000.0 to a target Julian Day JD:

dt_years = (JD − 2451545.0) / 365.25

RA_corrected  = RA_J2000  + (pm_ra  / 3600000.0) × dt_years / cos(Dec_rad)
Dec_corrected = Dec_J2000 + (pm_dec / 3600000.0) × dt_years

Note: pm_ra in the file already includes the cos(Dec) factor; divide it back out when applying the RA shift in degrees. Alternatively, directly shift in RA × cos(Dec) space and then divide by cos(Dec) at the end.

Parallax Correction

The parallax gives the annual trigonometric parallax π in mas. To shift the star from barycentric to geocentric, the maximum positional shift is π / 1000.0 / 3600.0 degrees (sub-arcsecond for all but the nearest stars).

For most purposes the parallax correction is negligible and may be omitted.

Example Lines

Aldebaran  ,alTau,ICRS,04,35,55.2387,+16,30,33.485,62.78,-189.35,54.26,50.09,0.985, 16,  629
Sirius     ,alCMa,ICRS,06,45,08.9173,-16,42,58.017,-546.05,-1223.14,-7.6,379.21,-1.47,-16, 1591
Polaris    ,alUMi,ICRS,02,31,49.0837,+89,15,50.794,44.22,-11.75,-17.4,7.56,2.005, 88,    8

For Sirius (alCMa):

  • RA = (6h 45m 08.9173s) = 101.2872°
  • Dec = −16° 42′ 58.017″ = −16.7161°
  • pm_ra = −546.05 mas/yr (× cos(Dec)); pm_dec = −1223.14 mas/yr
  • parallax = 379.21 mas ≈ 2.64 pc
  • mag = −1.47

References

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