The OPTical IDentification ( OPTID
) database was developed at the
Infrared Processing and Analysis Center ( IPAC
), in collaboration with
the Royal Observatory Edinburgh ( ROE
) and the Naval Research Lab ( NRL
),
to provide users of the IRAS
Faint Source Survey ( FSS
) with reliable
optical star and galaxy identifications for all infrared sources in
the FSS
. Two publicly available large-area optical catalogs,
derived from archival
Schmidt plate material using automatic plate measuring engines, were used
to generate the optical identifications to the infrared sources:
The COSMOS
/ UKST
Southern Sky Object Catalogue ( COSCAT
: Yentis et al.
1992)
covers the sky south of 
and above galactic latitude
and contains stars and galaxies to 
or fainter,
and the Guide Star Catalog version 1.1 ( GSC
;
Jenkner et al.
1990, Lasker et al.
1990, Russell et al.
1990), which covers the
entire sky and is complete for stars to B=14--16th mag. In addition, the
completeness and accuracy of
OPTID
for bright stellar identifications has been increased by use of
the Tycho Input Catalog ( TIC
; Egret et al.
, 1992), which is a merger of
the Hipparcos Input Catalogue Consortium ( INCA
) Data Base with the
GSC
version 1.0. The TIC
was merged at IPAC
with the GSC
version 1.1;
the combined catalog is referred to as the GSC/TIC
in this document.
Since the COSCAT
goes to much fainter magnitudes than the GSC/TIC
the
current release of OPTID
provides a much more complete set of optical
identifications to the FSS
in the southern equatorial hemisphere
(
) than in the north. In particular, many extragalactic
IRAS sources north of this declination and fainter than about 0.5 Jy at
60
m do not have identifications in OPTID
because the GSC/TIC
is
severely incomplete for galaxies fainter than 
mag.
In addition, galaxy magnitudes are
systematically too bright by up to 5 magnitudes in the GSC/TIC
compared
to COSCAT
because the GSC
magnitude system is tuned to stars.
OPTID employs a new, robust method to estimate the identification probabilities of candidate optical matches to the FSS . This method follows previous approaches based on positional coincidence but also utilizes a random matching method, which operates as an effective control and calibration for the matching process.
The optical catalogs
provide multiple candidate matches for nearly every FSS
object
within their coverage. OPTID
provides, for each candidate match,
an estimate of the probability that it is the correct
identification, 
, and, for each FSS
object, the probability
that no identification exists in the optical catalog, 
. Many other
parameters related to the infrared source, to each optical object that
is a candidate identification for each infrared source, and to the goodness
of match of each candidate optical identification, are also available in the
database. OPTID
also provides a finding chart service.
Finally, OPTID
parameters can be used to revise the reliability of
low SNR infrared sources.