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这是Tycho I/239,I/250,I/259的英文摘要：
----- Tycho I/239星表 ------------------------------------------------------------
I/239 The Hipparcos and Tycho Catalogues (ESA 1997)
Description:
The Hipparcos and Tycho Catalogues are the primary products of the
European Space Agency's astrometric mission, Hipparcos. The satellite,
which operated for four years, returned high quality scientific data
from November 1989 to March 1993.
Each of the catalogues contains a large quantity of very high quality
astrometric and photometric data. In addition there are associated
annexes featuring variability and double/multiple star data, and solar
system astrometric and photometric measurements. In the case of the
Hipparcos Catalogue, the principal parts are provided in both printed
and machine-readable form (on CDROM). In the case of the Tycho
Catalogue, results are provided in machine-readable form only (on
CDROM). Although in general only the final reduced and calibrated
astrometric and photometric data are provided, some auxiliary files
containing results from intermediate stages of the data processing, of
relevance for the more-specialised user, have also been retained for
publication. (Some, but not all, data files are available from the
Centre de Donnees astronomiques de Strasbourg.)
The global data analysis tasks, proceeding from nearly 1000 Gbit of
raw satellite data to the final catalogues, was a lengthy and complex
process, and was undertaken by the NDAC and FAST Consortia, together
responsible for the production of the Hipparcos Catalogue, and the
Tycho Consortium, responsible for the production of the Tycho
Catalogue. A fourth scientific consortium, the INCA Consortium, was
responsible for the construction of the Hipparcos observing programme,
compiling the best-available data for the selected stars before launch
into the Hipparcos Input Catalogue. The production of the Hipparcos
and Tycho Catalogues marks the formal end of the involvement in the
mission by the European Space Agency and the four scientific
consortia.
----- TRC I/250 星表 -------------------------------------------------------
I/250 The Tycho Reference Catalogue (Hog+ 1998)
Abstract:
The Tycho Reference Catalogue (TRC) contains high-quality positions
and proper motions for 990182 stars of the Tycho Catalogue. The proper
motions were derived from Tycho positions and Astrographic Catalogue
positions reduced to the Hipparcos system. The median accuracy of the
TRC position components is 40 mas at J1991.25. The median accuracy of
the proper motion is about 2.5 mas/yr. Systematic errors are less than
about 1.0 mas(/yr). The quality of the proper motions in TRC is
assessed by comparison with the Hipparcos and Tycho Catalogues.
Comparison with the recent ACT Catalogue which is based on an
independent reduction of the same observations as used for
constructing the TRC is reported.
------ Tycho2 I/259 星表 ------------------------------------------------------
I/259 The Tycho-2 Catalogue (Hog+ 2000)
Abstract:
The Tycho-2 Catalogue is an astrometric reference catalogue containing
positions and proper motions as well as two-colour photometric data
for the 2.5 million brightest stars in the sky. The Tycho-2 positions
and magnitudes are based on precisely the same observations as the
original Tycho Catalogue (hereafter Tycho-1; see Cat. <I/239>))
collected by the star mapper of the ESA Hipparcos satellite, but
Tycho-2 is much bigger and slightly more precise, owing to a more
advanced reduction technique. Components of double stars with
separations down to 0.8 arcsec are included. Proper motions precise to
about 2.5 mas/yr are given as derived from a comparison with the
Astrographic Catalogue and 143 other ground-based astrometric
catalogues, all reduced to the Hipparcos celestial coordinate system.
Tycho-2 supersedes in most applications Tycho-1, as well as the ACT
(Cat. <I/246>) and TRC (Cat. <I/250>) catalogues based on Tycho-1.
Supplement-1 lists stars from the Hipparcos and Tycho-1 Catalogues
which are not in Tycho-2. Supplement-2 lists 1146 Tycho-1 stars which
are probably either false or heavily disturbed.
For more information, please consult the Tycho-2 home page:
http://www.astro.ku.dk/~erik/Tycho-2
Catalogue Characteristics:
The principal characteristics of the Tycho-2 Catalogue are
summarized below. By means of proper motions the positions
are transferred to the year 2000.0, the epoch of the catalogue.
The median values of internal standard errors are given.
------------------------------------------------------------
Mean satellite observation epoch ~J1991.5
Epoch of the Tycho-2 Catalogue J2000.0
Reference system ICRS
coincidence with ICRS (1) +/-0.6 mas
deviation from inertial (1) +/-0.25 mas/yr
Number of entries 2,539,913
Astrometric standard errors (2)
V_T_ < 9 mag 7 mas
all stars, positions 60 mas
all stars, proper motions 2.5 mas/yr
Photometric std. errors (3) on V_T_
V_T_ < 9 mag 0.013 mag
all stars 0.10 mag
Star density
b= 0 deg 150 stars/sq.deg.
b= +/-30 deg 50 stars/sq.deg.
b= +/-90 deg 25 stars/sq.deg.
Completeness to 90 per cent V ~ 11.5 mag
Completeness to 99 per cent V ~ 11.0 mag
Number of Tycho observations ~300 10^6^
------------------------------------------------------------
Note (1): about all 3 axes
Note (2):
ratio of external to internal standard errors is ~1.0
for positions and for proper motions. Systematic errors
are less than 1 mas and 0.5 mas/yr
Note (3):
ratio of photometric external to internal standard errors
at V_T_ > 9 mag is below 1.5
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