2.1 KiB
Renderer-facing 2MASS star catalog
2mass_psc_m31_0p5deg_stars.csv is made from the corresponding table in
../raw/ by python3 scripts/process_2mass_psc.py.
The processor accepts --input and --output, so the same documented quality
selection and fit are used for the M44 comparison field.
The CSV is intentionally compatible with the current four-column catalog
loader: ra_deg,dec_deg,temperature_K,amplitude_sr. RA and Dec are ICRS/J2000
degrees. The loader treats them as longitude and latitude when constructing
the source-sky direction.
Quality selection
RA/Dec must be finite and inside their ICRS ranges; all three J/H/Ks magnitudes
must be finite; and every character of rd_flg must be 1, 2, or 3.
These are the 2MASS default-magnitude origins that generally indicate the best
detections, photometry, and astrometry. Thus the script rejects
nondetections/upper limits (0), poor aperture photometry (4), inconsistent
band deblends (6), and missing brightness estimates (9).
The IPAC literal null is treated as a missing numeric value, the same as a
blank field, and is therefore rejected by these finite-value checks.
Two-parameter fit
For J, H, Ks effective wavelengths 1.235, 1.662, and 2.159 micrometres and
Vega zero points 1594, 1024, and 666.7 Jy, respectively, each magnitude is
converted to flux density using F_nu = F_nu,0 * 10^(-0.4 m).
The script then performs an unweighted least-squares fit in log(F_nu) to
F_nu = amplitude_sr * B_nu(T).
temperature_K is constrained to 300--100000 K; amplitude_sr is the fitted
apparent solid angle in steradians. The fit treats each band as monochromatic
at its effective wavelength and does not deredden the source. This is the
same two-parameter thermal-source reduction described qualitatively in the
reference paper, but the paper does not publish its fit implementation; this
script therefore records the numerical choice explicitly.
References: 2MASS rd_flg definitions,
2MASS zero points.