Table 1. Telescope and Camera.
number of lens elements
spectral bandpass of lens
Airy disc diameter (610nm)
usable at eld of view
number of pixels
eld of view
61 61 arcmin
spectral bandpass used
full well capacity
3. The rst catalog
A preliminary catalog (UCAC1) of positions and proper motions of 27 million
stars has been constructed, which is available on CD-ROM from USNO. De-
tails about the project and the this rst catalog can be found in Zacharias et
(2000a). Observations from 13 Feb 1998 through 07 Nov 1999 are included
with a total of over 79,000 CCD frames. The catalog is on the International
Celestial Reference System (ICRS), which is consistent with J2000. This rst
catalog is not complete, e.g. all problem stars have been omitted. The standard
errors in position of UCAC1 are shown in Figure 2.
Proper motions of bright stars (
5) were derived using a combination
of ground-based astrometric catalogs, Hipparcos, and Tycho-2 positions, giving
a typical error of 3 mas/yr. For the fainter stars the USNO A2.0 (Monet et al.,
1998) was used as rst epoch, with typical proper motion errors of 10 and 15
mas/yr. Thus the distribution of UCAC1 proper motion errors is bi-modal, as
shown in Figure 3.
Systematic errors in the UCAC positions are small (10 mas level), as exter-
nal comparisons with SPM 2.0 (Platais et al., 1998) and the Tycho-2 Catalogue
(H g et al., 2000) revealed. Details are found in Zacharias et al. (2000b).
The Full-Sky Astrometric Mapping Explorer (FAME) to be launched in 2004
requires an input catalog for stars to 15th magnitude with a positional standard
error of 100 mas or below. The nal UCAC catalog is expected to be available
at that time. The limiting magnitude of the UCAC (
) will be su cient.
Currently, UCAC is the only project which can meet all requirements for the
FAME input catalog, providing full-sky coverage will be realized in time.