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gaia early data release 3 documentation

8.3 External catalogues matched with Gaia EDR3

8.3.1 Panstarrs 1.1

Reference papers:
Chambers et al. 2016;
Magnier et al. 2016a;
Waters et al. 2016;
Magnier et al. 2016c;
Magnier et al. 2016b;
Flewelling et al. 2016.

The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is a system for wide-field astronomical imaging developed and operated by the Institute for Astronomy at the University of Hawaii. Pan-STARRS1 (PS1) is the first part of Pan-STARRS to be completed and is the basis for Data Release 1 (DR1).
The PS1 survey used a 1.8 meter telescope and its 1.4 Gigapixel camera to image the sky in five broadband filters (g, r, i, z, y).

The current table contains a filtered subsample of the 10 723 304 629 entries listed in the original ObjectThin table.

A description of the original ObjectThin and MeanObjects tables can be found at: this link

Data curation and catalogue preparation

We used only ObjectThin and MeanObject tables to extract panstarrs1_original_valid table, this means that objects detected only in stack images are not included here. The main reason for us to avoid the use of objects detected in stack images is that their astrometry is not as good as the mean objects astrometry: “The stack positions (raStack, decStack) have considerably larger systematic astrometric errors than the mean epoch positions (raMean, decMean).” The astrometry for the MeanObject positions uses Gaia DR1 as a reference catalogue, while the stack positions use 2MASS as a reference catalogue.

In details, we filtered out all objects where:

  • nDetections = 1;

  • no good quality data in Pan-STARRS, objInfoFlag 33554432 not set;

  • mean astrometry could not be measured, objInfoFlag 524288 set;

  • stack position used for mean astrometry, objInfoFlag 1048576 set;

  • error on all magnitudes equal to 0 or to –999;

  • all magnitudes set to –999;

  • error on RA or DEC greater than 1 arcsec.

The number of objects in panstarrs1_original_valid is 2 264 263 282.

The panstarrs1_original_valid table contains only a subset of the columns available in the combined ObjectThin and MeanObject tables.

Catalogue cleaning and Join table

The results of a search of the nearest neighbour (neglecting additional neighbours except for the nearest) around each allWISE object are shown in Marrese et al. (2019, Appendix A).
The distribution of nearest neighbours (i.e. the source separation distribution) shows the presence of nearest neighbours much closer than the catalogue angular resolution. They are most probably multiples (objects with exactly the same astrometry) or suspected duplicates (objects much closer than the catalogue angular resolution). It was thus decided not to consider multiple/duplicates when calculating the cross-match.
A convenience table is available that can be used to join Pan-STARRS1 DR1.1 catalogue with the cross-match results. The table links the external catalogue original sourceId ( original_ext_sourceId) to the corresponding the additional numerical identifier ( clean_Panstarrs1_oid).

Both original_ext_sourceId and cleanPanstarrs1Oid are present in the cross-match output tables ( panstarrs1- BestNeighbour and panstarrs1Neighbourhood).

However, in case there are suspected duplicates in the external catalogue, different original_ext_sourceId will correspond to the same cleanPanstarrs1Oid.

In the cross-match output table only the original_ext_sourceId of the source with the best astrometry among the suspected duplicates is be listed.

In practice, users may use the original_ext_sourceId in the original catalogue to find the matching source with the best astrometry. Users interested to find all matching suspected duplicates should instead use the clean_panstarrs1_oid in the join with the cross-match result tables.

Cross-match algorithm

According to the definition used in this work, Pan-STARRS1 is a dense survey, in the cross-match algorithm Gaia is the leading catalogue, this means that Gaia objects matches are searched for in Pan-STARRS1.
For this catalogue special treatment was done for a) the sources which are resolved in Gaia, b) the possible underestimation of astrometric errors in Pan-STARRS1, and c) small issues in Gaia astrometry, especially for bright stars.