AIMS Provenance: NOIRLab Source Catalog DR2

Draft for review. This page describes the current AIMS handling of NOIRLab Source Catalog DR2 detections.

Source summary

The NOIRLab Source Catalog (NSC) is a catalog built from public imaging in NOIRLab’s Astro Data Archive. NSC DR2 includes public imaging primarily from CTIO-4m/DECam, KPNO-4m/Mosaic3, and Bok-2.3m/90Prime.

Publisher summary for DR2:

about 35,273 square degrees of sky coverage;
412,116 exposures;
3,932,838,064 unique objects;
67,822,619,019 individual measurements;
depths of roughly 23rd magnitude in many broad bands;
reported photometric calibration accuracy of roughly 1—2%;
reported astrometric zero-point accuracy of roughly 2 mas.

The NSC project describes source extraction, calibration, combination, quality assurance, and use cases in the NSC Data Lab documentation and the NSC DR2 paper.

How AIMS accesses NSC

AIMS queries NSC DR2 through NOIRLab Data Lab query services. The AIMS source query joins:

nsc_dr2.object for object-level motion and detection-count fields;
nsc_dr2.meas for individual source measurements;
nsc_dr2.exposure for exposure timing, duration, filter, and instrument fields.

AIMS partitions the ingest by UTC day and uses chunked subqueries within each day to keep large Data Lab requests reliable.

AIMS date range and observatories

The AIMS NSC DR2 surface is treated as a frozen historical dataset:

AIMS partition start: 2012-09-23;
AIMS partition end: 2019-11-16 inclusive.

AIMS maps NSC instrument labels to MPC observatory codes:

NSC instrument	AIMS/MPC observatory code
`c4d`	`W84`
`ksb`	`V00`
`k4m`	`695`

Rows without a recognized instrument-to-observatory mapping should be reviewed before publication or use.

AIMS filtering

AIMS does not ingest the full NSC DR2 measurement table. It filters the NSC measurements to retain detections more likely to be useful for moving-object searches.

For each NSC row group, AIMS computes total proper motion:

pm = sqrt(pmra^2 + pmdec^2)

The NSC proper-motion units are milliarcseconds per year. AIMS converts this to arcseconds per day, then keeps measurements satisfying at least one of:

converted proper motion is >= 0.3 arcsec/day;
ndet == 1 (single-detection object, no reliable motion estimate);
deltamjd <= 1 day (detections close enough in time that slow apparent motion may be misleading).

This filter is intentionally tuned for moving-source and precovery use cases. It excludes most static sources but can still include high-proper-motion stars or other non-solar-system sources.

AIMS-derived and normalized values

AIMS field	NSC source or derivation
`observation_id`	`meas.measid` converted to string.
`exposure_id`	`meas.exposure`.
`dataset_id`	Constant `nsc`.
`observatory_code`	Derived from NSC `instrument` using the mapping above.
Observation time	Exposure midpoint, computed as `exposure.mjd + exposure.exptime / 2 / 86400`.
`ra_deg`, `dec_deg`	`meas.ra`, `meas.dec`.
`ra_sigma_deg`, `dec_sigma_deg`	`meas.raerr`, `meas.decerr` converted from arcseconds to degrees.
`mag`, `mag_sigma`	`meas.mag_auto`, `meas.magerr_auto`.
`filter`	`meas.filter`.
`healpixel`	Derived by AIMS from RA/Dec at nside=128 NESTED.

Known limitations and interpretation notes

AIMS stores a moving-source subset of NSC DR2, not the full source catalog.
The NSC source catalog is object-centric, while AIMS is detection-centric. AIMS uses the meas rows but relies on object motion/detection-count metadata for filtering.
NSC proper motions are useful for filtering but do not prove solar-system origin.
AIMS preserves NSC photometry and filters as source measurements; it does not cross-calibrate NSC photometry onto a shared AIMS photometric system.
NSC data are historical/frozen in AIMS; later NOIRLab catalog releases should be documented separately if added.