79 lines
3.5 KiB
Markdown
79 lines
3.5 KiB
Markdown
# 2MASS Point Source Catalog sample
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`raw/2mass_psc_m31_0p5deg.tbl` is an unmodified IPAC ASCII-table response from the
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NASA/IPAC Infrared Science Archive (IRSA) Gator service, drawn from the **2MASS
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All-Sky Point Source Catalog (PSC)**.
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It is a circular field of view centred on M31:
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- Centre: ICRS/J2000 RA 10.6847083 deg, Dec +41.2687500 deg
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- Cone radius: 0.5 deg
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- Retrieved rows: 9,047
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- Retrieval date: 2026-08-25 (recorded in the table header)
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The all-sky PSC has hundreds of millions of entries, so it is deliberately not
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vendored. This real-survey slice keeps the repository lightweight while
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providing a reproducible replacement for the synthetic latitude/longitude grid.
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Run `bash scripts/download_2mass_psc_m31.sh` from any directory to refresh it.
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The table preserves the service response. Its relevant source fields are:
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| Field | Meaning |
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| --- | --- |
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| `ra`, `dec` | ICRS/J2000 right ascension and declination, in degrees |
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| `j_m`, `h_m`, `k_m` | 2MASS J, H, and Ks default magnitudes, in mag |
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| `dist` | Angular distance from the stated field centre, in arcsec |
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| `rd_flg` | Per-band source/read flag needed to interpret the default magnitudes |
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`j_m`, `h_m`, and `k_m` may be null in the original PSC. No temperature is
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included or inferred: the PSC provides photometry, not source temperatures.
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Do not treat magnitudes as linear fluxes without applying the appropriate 2MASS
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band zero points.
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`processed/2mass_psc_m31_0p5deg_stars.csv` is generated from the raw table by
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`python3 scripts/process_2mass_psc.py`. It retains only `ra_deg`, `dec_deg`,
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`temperature_K`, and `amplitude_sr`. See its directory README for the fitting
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model and quality cut.
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`raw/2mass_psc_m44_1p0deg.tbl` is the corresponding unmodified 1.0-degree
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cone around M44 (Beehive/Praesepe), centred on ICRS/J2000 RA 129.99165 deg and
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Dec +19.54139 deg. It contains 8,790 retrieved PSC rows (2026-08-25) and is
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downloaded by
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`bash scripts/download_2mass_psc_m44.sh`; process it with:
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```sh
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python3 scripts/process_2mass_psc.py \
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--input assets/2mass/raw/2mass_psc_m44_1p0deg.tbl \
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--output assets/2mass/processed/2mass_psc_m44_1p0deg_stars.csv
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```
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The resulting M44 CSV contains 7,802 sources after the documented three-band
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photometry and `rd_flg` selection.
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## Full-sky acquisition
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`scripts/download_2mass_psc_all_sky.py` provides a resumable full-sky
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acquisition without asking IRSA for a cone larger than 1 degree. Inspect its
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storage plan before starting the long download:
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```sh
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python3 scripts/download_2mass_psc_all_sky.py --plan
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python3 scripts/download_2mass_psc_all_sky.py --download --workers 2
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```
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It covers each latitude band with integer-RA cone sectors, wider at high
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latitudes, while outputs are cleaned and retained by unique 1-degree RA/Dec
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ownership cells. Cone overlap cannot create duplicate stars. Temporary raw
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tables and cleaning intermediates are stored under `/tmp/2mass_psc_all_sky/`
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and deleted after each successful cover. The generated full-sky catalogue has
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one CSV per ownership cell under `processed/all_sky/`, named
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`tile_raRRR_decDDD.csv`. `RRR` is
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`floor(RA_deg mod 360)` and `DDD` is `min(179, floor(Dec_deg + 90))`; the
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corresponding range is `[RRR, RRR+1) x [DDD-90, DDD-89)` degrees. It is
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intentionally not a single CSV because that would duplicate a roughly 15--17
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GiB result during merging.
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See that directory's README for restart and raw-retention behavior.
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Provenance: [IRSA Gator program interface](https://irsa.ipac.caltech.edu/docs/howto/gator_prog_interface.html),
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[2MASS PSC column descriptions](https://irsa.ipac.caltech.edu/2MASS/download/allsky/format_psc.html).
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