Publisher source
SkyMapper Southern Survey DR2 was released on 27 February 2019. The publisher describes observations from March 2014 through March 2018, more than 4.7 billion detections over 21,000 square degrees, AB photometry, and reduced images plus object and per-image/CCD photometry tables.
SkyMapper provides public web, cone-search, image-cutout, and TAP/ADQL access. AIMS uses staged DR2 image metadata and per-image photometry for its normalization path.
What AIMS selects
The source transform joins:
- image metadata containing image id, observation date, exposure time, and filter;
- per-image photometry containing image id, position, PSF magnitude and uncertainty, and object id;
- an object-id mask built from a Gaia crossmatch.
The mask begins with valid SkyMapper object ids as keepable, then removes ids whose Gaia best-neighbor distance is less than 1.5 arcsec. Rows with null, negative, or out-of-range object ids are excluded before the mask lookup.
AIMS also stores null rather than invalid magnitudes for NaN values or values outside -10 to 30.
The Gaia mask reduces the dominant static-star population. It is not a definitive solar-system classifier and its selection behavior depends on both SkyMapper object association and Gaia crossmatch completeness.
Coverage and observatory
AIMS treats SkyMapper DR2 as a frozen historical source:
- coverage: 2014-03-15 through 2018-03-31, inclusive;
- observatory code:
Q55.
Normalization into AIMS
| AIMS field | SkyMapper source or derivation |
|---|---|
observation_id | Deterministic q55v2:<object_id>:<image_id>:<ra_scaled>:<dec_scaled>. |
exposure_id | image_id. |
dataset_id | Constant skymapper. |
observatory_code | Constant Q55. |
| Observation time | Image date plus half the exposure time. |
filter | Image filter. |
ra_deg, dec_deg | Photometry ra_img, decl_img. |
ra_sigma_deg, dec_sigma_deg | Unavailable from this AIMS source path and stored as null. |
mag, mag_sigma | mag_psf, e_mag_psf, after magnitude sanitization. |
healpixel | Derived from RA/Dec at nside=128 NESTED. |
The identifier scales RA/Dec by 1,000,000,000 and rounds them to integers, avoiding unstable raw floating-point strings while retaining deterministic source identity.
Published AIMS products
In the AIMS BigQuery dataset, normalized SkyMapper rows are written to aims_skymapper, copied into aims_detections_hot, and exposed through the aims_detections_unified view with dataset_id = skymapper.
The same normalized rows are exported to Google Cloud Storage through the daily aims_detections_parquet product. AIMS also derives aims_frames_unified BigQuery rows and aims_frames_parquet search indexes grouped by SkyMapper image and spatial cell. Complete detection/frame pairs are listed in aims_unified_parquet_catalog/catalog.json for consumers such as Precovery. There is no separate SkyMapper-only runtime Parquet product.
Scientific validity and limitations
- The retained per-image positions and PSF photometry preserve SkyMapper DR2 measurements apart from documented time, identifier, magnitude, and indexing transformations.
- The Gaia-based mask makes the product useful for moving-source search but does not define a complete or unbiased moving-object sample. It can remove or retain detections according to Gaia and SkyMapper association behavior.
- This path does not provide per-detection RA/Dec uncertainty or correlation. AIMS does not substitute object-level master-catalog values for missing per-image covariance, so consumers must treat both fields as unavailable.
- SkyMapper DR2 has publisher caveats around flags, neighbors, bright stars, PSF behavior, and known release issues; those remain applicable to AIMS rows.
- AIMS treats this source as frozen DR2. A later SkyMapper release would require separate selection and provenance review.