41 lines
1.9 KiB
Markdown
41 lines
1.9 KiB
Markdown
# Renderer-facing 2MASS star catalog
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`2mass_psc_m31_0p5deg_stars.csv` is made from the corresponding table in
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`../raw/` by `python3 scripts/process_2mass_psc.py`.
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The processor accepts `--input` and `--output`, so the same documented quality
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selection and fit are used for the M44 comparison field.
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The CSV is intentionally compatible with the current four-column catalog
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loader: `ra_deg,dec_deg,temperature_K,amplitude_sr`. RA and Dec are ICRS/J2000
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degrees. The loader treats them as longitude and latitude when constructing
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the source-sky direction.
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## Quality selection
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All three J/H/Ks magnitudes must be finite and every character of `rd_flg` must
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be `1`, `2`, or `3`. These are the 2MASS default-magnitude origins that
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generally indicate the best detections, photometry, and astrometry. Thus the
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script rejects nondetections/upper limits (`0`), poor aperture photometry (`4`),
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inconsistent band deblends (`6`), and missing brightness estimates (`9`).
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## Two-parameter fit
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For J, H, Ks effective wavelengths 1.235, 1.662, and 2.159 micrometres and
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Vega zero points 1594, 1024, and 666.7 Jy, respectively, each magnitude is
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converted to flux density using `F_nu = F_nu,0 * 10^(-0.4 m)`.
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The script then performs an unweighted least-squares fit in `log(F_nu)` to
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`F_nu = amplitude_sr * B_nu(T)`.
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`temperature_K` is constrained to 300--100000 K; `amplitude_sr` is the fitted
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apparent solid angle in steradians. The fit treats each band as monochromatic
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at its effective wavelength and does not deredden the source. This is the
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same two-parameter thermal-source reduction described qualitatively in the
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reference paper, but the paper does not publish its fit implementation; this
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script therefore records the numerical choice explicitly.
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References: [2MASS `rd_flg` definitions](https://irsa.ipac.caltech.edu/data/2MASS/docs/releases/allsky/doc/sec1_6b.html),
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[2MASS zero points](https://www.ipac.caltech.edu/2mass/releases/allsky/faq.html).
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