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assets/2mass/README.md

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+# 2MASS Point Source Catalog sample
+
+`raw/2mass_psc_m31_0p5deg.tbl` is an unmodified IPAC ASCII-table response from the
+NASA/IPAC Infrared Science Archive (IRSA) Gator service, drawn from the **2MASS
+All-Sky Point Source Catalog (PSC)**.
+
+It is a circular field of view centred on M31:
+
+- Centre: ICRS/J2000 RA 10.6847083 deg, Dec +41.2687500 deg
+- Cone radius: 0.5 deg
+- Retrieved rows: 9,047
+- Retrieval date: 2026-08-25 (recorded in the table header)
+
+The all-sky PSC has hundreds of millions of entries, so it is deliberately not
+vendored.  This real-survey slice keeps the repository lightweight while
+providing a reproducible replacement for the synthetic latitude/longitude grid.
+Run `bash scripts/download_2mass_psc_m31.sh` from any directory to refresh it.
+
+The table preserves the service response.  Its relevant source fields are:
+
+| Field | Meaning |
+| --- | --- |
+| `ra`, `dec` | ICRS/J2000 right ascension and declination, in degrees |
+| `j_m`, `h_m`, `k_m` | 2MASS J, H, and Ks default magnitudes, in mag |
+| `dist` | Angular distance from the stated field centre, in arcsec |
+| `rd_flg` | Per-band source/read flag needed to interpret the default magnitudes |
+
+`j_m`, `h_m`, and `k_m` may be null in the original PSC.  No temperature is
+included or inferred: the PSC provides photometry, not source temperatures.
+Do not treat magnitudes as linear fluxes without applying the appropriate 2MASS
+band zero points.
+
+`processed/2mass_psc_m31_0p5deg_stars.csv` is generated from the raw table by
+`python3 scripts/process_2mass_psc.py`.  It retains only `ra_deg`, `dec_deg`,
+`temperature_K`, and `amplitude_sr`.  See its directory README for the fitting
+model and quality cut.
+
+`raw/2mass_psc_m44_1p0deg.tbl` is the corresponding unmodified 1.0-degree
+cone around M44 (Beehive/Praesepe), centred on ICRS/J2000 RA 129.99165 deg and
+Dec +19.54139 deg. It contains 8,790 retrieved PSC rows (2026-08-25) and is
+downloaded by
+`bash scripts/download_2mass_psc_m44.sh`; process it with:
+
+```sh
+python3 scripts/process_2mass_psc.py \
+  --input assets/2mass/raw/2mass_psc_m44_1p0deg.tbl \
+  --output assets/2mass/processed/2mass_psc_m44_1p0deg_stars.csv
+```
+
+The resulting M44 CSV contains 7,802 sources after the documented three-band
+photometry and `rd_flg` selection.
+
+Provenance: [IRSA Gator program interface](https://irsa.ipac.caltech.edu/docs/howto/gator_prog_interface.html),
+[2MASS PSC column descriptions](https://irsa.ipac.caltech.edu/2MASS/download/allsky/format_psc.html).

assets/2mass/processed/README.md

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+# 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
+
+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`).
+
+## 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](https://irsa.ipac.caltech.edu/data/2MASS/docs/releases/allsky/doc/sec1_6b.html),
+[2MASS zero points](https://www.ipac.caltech.edu/2mass/releases/allsky/faq.html).