UCAC2 Catalogue

C2A can read a compiled version of the UCAC2 catalogue (Second U.S. Naval Observatory CCD Astrograph Catalogue). The UCAC2 catalogue, published by the US Naval Observatory, is a high precision high density astrometric catalogue which references around 48 million stars between magnitude 8 and 16 in the Southern hemisphere and a large part of the Northern hemisphere (-90 to+40 degrees of declination). It is the second stage in a project to cover the whole sky. The catalogue gives positions, proper motions, errors in position and proper motion, as well as approximate magnitudes. You select the UCAC2 catalogue as the current catalogue through the Stars tab of the Options dialogue box, or by SHIFT-right-clicking on the map.

C2A takes into account the proper motions given in the UCAC1 catalogue in determining star positions at a date specified by the user (see Advanced Options in the  Stars tab of the options dialogue box).

If you have the original UCAC2 catalogue, the Tools page of the C2A Website provides a tool for compiling it in the C2A format. All the information needed to compile the catalogue is given on that page.

The information reported for each star is in the standard format of the UCAC2 catalogue. The description of the fields given in the UCAC2 documentation is provided below.

Num Bytes Fmt Unit Label Explanation
1 1- 4 I*4 mas RA Right Ascension at epoch J2000.0 (ICRS) (2)
2 5- 8 I*4 mas DE Declination at epoch J2000.0 (ICRS) (2)
3 9-10 I*2 0.01 mag U2Rmag Internal UCAC magnitude (red bandpass) (3)
4 11 I*1 mas e_RAm s.e. at central epoch in RA (*cos DEm)(1,4)
5 12 I*1 mas e_DEm s.e. at central epoch in Dec (1,4)
6 13 I*1 nobs Number of UCAC observations of this star(5)
7 14 I*1 e_pos Error of original UCAC observ. (mas) (1,6)
8 15 I*1 ncat # of catalog positions used for pmRA, pmDC
9 16 I*1 cflg ID of major catalogs used in pmRA, pmDE (7)
10 17-18 I*2 0.001 yr EpRAm Central epoch for mean RA, minus 1975 (8)
11 19-20 I*2 0.001 yr EpDEm Central epoch for mean DE, minus 1975 (8)
12 21-24 I*4 0.1 mas/yr pmRA Proper motion in RA (no cos DE) (9)
13 25-28 I*4 0.1 mas/yr pmDE Proper motion in DE (9)
14 29 I*1 0.1 mas/yr e_pmRA s.e. of pmRA (*cos DEm) (1)
15 30 I*1 0.1 mas/yr e_pmDE s.e. of pmDE (1)
16 31 I*1 0.05 q_pmRA Goodness of fit for pmRA (1,11)
17 32 I*1 0.05 q_pmDE Goodness of fit for pmDE (1,11)
18 33-36 I*4 2m_id 2MASS pts_key star identifier (12)
19 37-38 I*2 0.001 mag 2m_J 2MASS J magnitude (13)
20 39-40 I*2 0.001 mag 2m_H 2MASS H magnitude (13)
21 41-42 I*2 0.001 mag 2m_Ks 2MASS K_s magnitude (13)
22 43 I*1 2m_ph 2MASS modified ph_qual flag (1,14)
23 44 I*1 2m_cc 2MASS modified cc_flg (1,15)

Further information on the UCAC2 catalogue can be found on the UCAC homepage at: http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/ucac.

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