The fourth U.S. Naval Observatory CCD Astrograph
Catalog (UCAC4)
2012-10-29T13:38:00Z
1000
UCAC4 is a compiled, all-sky star catalog covering mainly the 8 to
16 magnitude range in a single bandpass between V and R. Positional
errors are about 15 to 20 mas for stars in the 10 to 14 mag range.
Proper motions have been derived for most of the about 113 million
stars utilizing about 140 other star catalogs with significant epoch
difference to the UCAC CCD observations. These data are supplemented
by 2MASS photometric data for about 110 million stars and 5-band
(B,V,g,r,i) photometry from the APASS (AAVSO Photometric All-Sky
Survey) for over 50 million stars. UCAC4 also contains error estimates
and various flags. All bright stars not observed with the astrograph
have been added to UCAC4 from a set of Hipparcos and Tycho-2 stars.
Thus UCAC4 should be complete from the brightest stars to about R=16,
with the source of data indicated in flags.
The UCAC4 release paper (in preparation) should be cited
whenever UCAC data are utilized.
Zacharias, N.; Finch, C. T.; Girard, T. M.;
Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I.
stars
surveys
astrometry
proper-motions
Optical
2000-01-01 2000-01-010/0-118.277e-20 5.369e-19
= 500 mas, >= 50 mas/yr)
- derived PM is larger than 500 mas/yr in either component
- derived central epoch is earlier than 1947
- RA or Dec position difference to CCD data mean position is >= 3 arcsec
These stars are thus added to the group of "no proper motion" stars,
i.e. those which did not match up with other catalogs to even begin the
proper motion calculation. All stars where then checked against the
external set of HPM stars. The PM from the external catalog was used for
stars with no UCAC4 PM solution and for those where the difference in PM
for either component exceeded 40 mas/yr. Thus we trust the external
catalog data more than the UCAC4 derived proper motions in those cases.
Comparions of UCAC4 based astrometric solutions of stars with about
100 mas/yr or more with external data (2MASS, thanks Rae Stiening) indicated
unrealistic proper motions for many such stars in UCAC4 data. Plots of
distribution of number of stars as function of UCAC4 proper motion bins
showed an overdensity around 100 and 200 mas/yr which could be traced back
to blended images or wrong idendifications of stars with NPM and SPM early
epoch data in crowded fields. NPM and SPM plates were exposed twice
(long and short) with offset between exposures and using an objective
grating, enhancing the chances of confusion in crowded fields. In order
to mitigate this problem in UCAC4 new object flags were introduced as
follows. All stars with object type = 0,1,2 (i.e. those with UCAC4 based
solution for proper motions, excluding above described special high proper
motion stars handling, Hipparcos and Tycho data, and supplemented stars)
and a proper motion larger than 80 mas/yr in either coordinate were picked
from the UCAC4. This is a total of about 2.8 million stars. These were
matched with the PPMXL (Roeser et al 2010) using a match radius of 4 arcsec
with both catalog positions at epoch 2000. The UCAC4 stars not matched
with PPMXL in this way were assigned the new object type = 8 (2029306 stars).
For the matched stars the proper motion difference vector lenght was
calcualted and a threshold set to flag discrepant proper motions with
object type = 9. The threshold was set as the lower of 80 mas/yr and
(3 times the combined formal errors + 5 mas/yr systematic error floor).
This way 689470 stars in UCAC4 obtained the ojt = 9 flag, while 140887
stars were found to have consistent proper motions from this set of stars
and no change to UCAC4 data flags were made.
Obviously stars flagged with ojt = 8 or 9 should be handled with caution.
Many of the ojt = 8 objects can be bogus stars and many of the ojt = 9
stars are likely affected by blended images. Unless external data are
consulted to verify UCAC4 results these stars should not be used.
Photometric data
----------------
For each detected image 2 instrumental magnitudes were derived.
First, the model magnitude is based on the flux volume of the best-fit
image profile model which is also used for the center position result.
Second, an aperture photometry magnitude is calculated.
In addition to the systematic error corrections applied for UCAC3
(Finch et al. 2010), for UCAC4 a bias correction was applied as a
function of the pixel x-coordinate of the image. This bias is caused
by the poor charge-transfer efficiency (CTE) of the CCD used for UCAC
observations, resulting in image elongation as a function of x.
Different bias models were derived for the model and aperture photometry.
The APASS 5-band photometry of over 9 million stars (DR2) was utilized
to "flatten" the UCAC instrumental magnitudes. The raw instrumental
magnitudes are not linear with offsets up to about 0.5 and 0.3 mag at
the bright and faint end, respectively. From color-color plots a linear
model was adopted to predict UCAC bandpass magnitudes from APASS r and V.
The predicted minus observed (model and aperture mags handled separately)
UCAC magnitudes were then plotted as fucntion of magnitude and inter-
polation polynomials derived. These corrections were then applied to
all UCAC instrumental magnitudes.
All corrected, instrumental magnitudes were then transformed into the
system of Tycho-2 by a simple zero-point correction (Finch et al. 2010),
the same way as with UCAC3 data. Photometric results were averaged for
stars with multiple CCD observations to arrive at the UCAC4 catalog
entries. Nights with poor photometric quality were flagged and
not used in the average, unless no other data are available.
Note, that "poor photometric" quality for UCAC4 means "really bad"
nights, with significant transparency variations due to clouds.
The goal was to obtain approximate magnitudes, maybe reliable on
the 10% level with differential magnitudes good to about 5%.
UCAC is *not* a photometric catalog.
The UCAC4 data are supplemented by 2MASS near-IR magnitudes and
APASS 5-band optical photometry up to its data release DR6 (June 2012).
Properties of the catalog and important notes for the user
==========================================================
Sky coverage
------------
UCAC4 is an all-sky catalog with at least about 40 stars per square
deg anywhere on the sky. The average density of this catalog is over
2000 stars per square deg. See a
`color-coded all-sky plot called `_
showing the logarithm of the number of stars per box of 0.5 by 0.5 deg on the
sky. Blue is low density, red high with green and yellow in between.
Completeness
------------
UCAC4 like UCAC3 is more complete than UCAC2, including previously
omitted "problem" stars and double stars, many of which could be new
discoveries. A paper is in preparation about a sample of new double
stars found in UCAC4 and the rate of confirmation by speckle observations.
For preliminary results see (Hartkopf et al. 2010). The separation limit
for double stars in UCAC4 varies as function of brightness of the
components and brightness difference. However, some doubles with
separations of under 2 arcsec in UCAC3 have been confirmed as real.
Those cases are rare and objects within 2 arcsec of each other have
generally been merged to at least a blended image in UCAC4. Some 12,000
sources with a separation of less than 2 arcsec remain in UCAC4, of which
about half entered through the Hipparcos/Tycho-2 supplement data, which
includes double star annex catalogs. Stars fainter than R = 10 with
separations larger than 2 arcsec are likely real double stars in UCAC4.
UCAC4 also contains observations of some bright stars, as they happened
to make it through the pipeline. However, poor data have been substituted
by FK6, Hipparcos and Tycho-2 data (in that order of available data).
For reduction details on this see section 2b above. Thus UCAC4 should
be complete from the brightest naked eye stars to about 16th mag.
The following table gives some general statistics about UCAC4 stars:
=========== ==========================================================
113780093 total number of stars in UCAC4 (incl. supplement stars)
109921682 with 2MASS identification
106689821 with proper motions
81897551 with 2 epoch PM
27245403 with 3 or more epoch PM
80806744 with 2 or more images from "good fit" CCD observations
48323349 matched with UCAC2
54690 matched with LEDA galaxies
76020 matched with 2MASS extended source catalog
8925 supplemented stars (no CCD obs.)
121350 UCAC4 entries with a matched Hipparcos star ID
104681 UCAC4 entries with CCD obs. substituted by FK6/Hip/Tycho-2
=========== ==========================================================
If the computed position error of a star exceeds 500 mas in either
coordinate it was set to 500 mas but the star was kept, if at least
2 observations from different CCD observations were matched or the
star is either in the 2MASS, SPM or NPM data files.
Similarly, the error in proper motion was truncated to 50 mas/yr
but respective stars kept in UCAC4 by the same criteria as for large
positional errors. Obviously all large error objects need to be
handled with caution, and some of these are simply nonexistent.
This approach, different to UCAC2, was taken in order to drive up the
completeness of UCAC3 and UCAC4 at the expense of slightly greater
contamination. For UCAC4 also a lower threshold than for UCAC3
was adopted in image size for failed image profile fit objects.
In particular, the larger limits in positional errors deemed acceptable
for UCAC3 and UCAC4 accommodate the fainter limiting magnitude, which
was possible mainly due to superior handling of dark subtraction in the
pixel data. This allowed many low signal-to-noise, real stars to enter
the catalog, although with expected large random errors, as compared to
UCAC2.
Reference frame
---------------
The astrometry provided in UCAC4 is on the Hipparcos system, i.e.
the International Celestial Reference System (ICRS), as represented
by the Tycho-2 catalog. Contrary to earlier UCAC releases, the UCAC4
processing included a down-weighting of Tycho-2 stars with V-magnitude
fainter than 11.5 by a factor of 1.5 w.r.t. their nominal weight.
Any possible deviations of the Tycho system with respect to Hipparcos
or the extragalactic radio reference frame are still under investigation.
Positions in UCAC4 are given at the standard epoch of Julian date 2000.0,
thus the UCAC4 is a compiled catalog. In order to be able to calculate
positional errors at any epoch, the central epoch, i.e. the weighted mean
epoch of the data (UCAC + early epoch other catalogs) is given. At the
central epoch (which varies from star to star and is also different for
RA and Dec) the positional error has its smallest value; the one given
in the catalog for "sigma position". In most cases this central epoch
will be close to the UCAC observational epoch due to the relatively large
weight given to the UCAC observations. However, a fair number of stars
have a vastly different mean epoch, ranging back to about 1947. Proper
motion solutions with central epoch earlier than that were defined as
invalid and substituted by other catalog results if available, or only
the observed CCD position is reported with no proper motion.
The proper motions are given at the central epoch. Positional errors
of stars increase according to the errors in the proper motions when
going forward or backward in time from the central epoch.
Magnitudes
----------
UCAC4 observational data (CCD exposures) covers the magnitude range of
about R = 8 to 16.3 in a 579-642 nm bandpass. However, data from
FK6, Hipparcos, and Tycho-2 were used to supplement UCAC4 to create
a star catalog complete from brightest stars to about 16th magnitude.
The UCAC bandpass is between visual (V) and red (R). The limiting
magnitude can vary by about +-0.3 mag from field to field.
UCAC4 gives center fit-model magnitudes as well as aperture photometry
derived from the same pixel data reductions already performed for UCAC3.
Systematic errors in these magnitudes are believed to be below 0.1 mag,
which is a significant improvement over the UCAC2 release. Non-linearity
of the instrumental magnitudes were calibrated out using APASS photometry
for UCAC4. Tycho-2 stars (excluding the faint end) were used to determine
the zero-point of the corrected, instrumental magnitudes on a frame by
frame basis. However, UCAC observations often were performed in non-
photometric sky conditions. Mean magnitudes were derived from CCD frames
with indications of "acceptable photometric quality", which is about 50%
of the observations.
Additional photometry
---------------------
The UCAC4 observational data are supplemented with 5-band photometry (B,V,
g,r,i) from the APASS project (Henden, private comm.) as well as with IR
photometry (J,H,K_s) from the Two Micron All Sky Survey, 2MASS (Skrutskie
et al. 2006). In addition, magnitudes errors and some flags are provided.
For more details see http://www.aavso.org/apass and
http://www.ipac.caltech.edu/2mass/releases/allsky/ .
Non-stellar data
----------------
The UCAC4 contains some galaxies, particularly at the faint end.
No flag indicating a galaxy or star has been derived from the CCD
pixel data; however, a cross reference to the LEDA galaxies (Paturel
et al. 2005) and the 2MASS extended source catalog (Skrutskie et al.
2006) has been made and corresponding information is put into the
UCAC4 release. The procedure is the same as for UCAC3.
Observations of asteroids have been identified and taken out of the
main UCAC4 catalog. Individual epoch observations of about 1000
asteroids at multiple epochs have been prepared for publication, but
are not part of the UCAC4 release. The observing schedule explicitly
avoided all minor planets brighter than about R = 12, except for
special observing campaigns to derive masses of asteroids.
Star identification numbers (name)
----------------------------------
Official UCAC4 star ID numbers should be utilized for identification
purposes and for communication with the UCAC team: the UCAC4 star
number is of the following format::
UCAC4-zzz-nnnnnn
where zzz is the 3 digit zone number (form 001 to 900) and nnnnnn the
the 6-digit running record number along the zone file. The cross-
identification to UCAC2 stars follows the same pattern with zone and
record number of the UCAC2 release given in the UCAC4 data.
Note, zones numbers in UCAC4 run from 1 to 900 (0.2 deg wide), while
zone numbers in UCAC2 run from 1 to 360 (0.5 deg wide), in both cases
beginning at the South Celestial Pole (i.e. in order of declination).
Acknowledgments
===============
In a project such as this that has spanned over more than a decade and
two continents, many people have been involved. Here we list people
and their main contributions to the project.
Norbert Zacharias
Principle Investigator, observer, responsible for
UCAC position reductions (from pixels to positions on the sky),
observing schedule, and external position comparisons, re-processing
of pixel data and development of reduction pipeline, Star-Scan plate
measure reductions.
Ted Rafferty
former project lead, instrumentation specialist, observer,
main author of the astrograph history document.
Charlie Finch
re-reduction of CCD x,y to RA,Dec, including systematic
error control, high proper motion stars, match to 2MASS and
photometric calibration.
Marion Zacharias
quality control, observer, early position reductions,
extragalactic link program.
Terry Girard
SPM data reductions, from x,y plate data to RA,Dec,
incl. systematic error handling (magnitude equations) and all
related reduction pipeline development.
Bill van Altena
for many years of collaboration in astrometry.
Burton Jones, Bob Hanson, and Arnold Klemola
NPM data.
Arne Henden
for sharing unpublished APASS data and photometric consulting.
Dave Monet
measurements of SPM and NPM plates on PPM at NOFS.
Nigel Hambly
for collaboration on high proper motion stars and big
contributions to UCAC3 proper motions.
Gary Wycoff
proper motions data preparation, star identifications (up to UCAC3).
Sean Urban
proper motions of UCAC2 release, preparation of
other position catalogs including systematic error removal
and compiling a merged catalog of Hipparcos and Tycho data.
Valeri Makarov
reduction of AGK2 and other StarScan plate measures
from global x,y to individual RA,Dec positions.
Jennifer Bartlet
assisting in taking out original PMM x,y measures
mapping parameters to arrive at raw x,y data of NPM plates
Brian Mason, Bill Hartkopf
new double star speckle observations with USNO 26in and data reductions.
Bill Hartkopf and Marion Zacharias
preparing the history section of the UCAC4 DVD release.
David Hall
verification of tape archive, early data handling.
Marvin Germain
telescope control system software development,
software-to-hardware interface including electronics.
Ellis Holdenried
telescope control system software maintenance
and extension of user interface for telescope operation.
Lars Winter
basis for astrometric CCD reduction software.
Greg Hennessy
computer administration support (USNO-DC)
Danilo Castillo
observer, Cerro Tololo, Chile
Mauricio Martinez
observer, Cerro Tololo, Chile
Sergio Pizarro
observer, Cerro Tololo, Chile
Oscar Saa
telescope manager, Cerro Tololo, Chile
Trudy Tilleman
observer, U.S. Naval Observatory Flagstaff Station,
assist with data reductions.
Stephanie Potter
observer, U.S. Naval Observatory Flagstaff Station.
Dominic Marcello
observer, U.S. Naval Observatory Flagstaff Station.
Gary Wieder
telescope upgrades, relocation, maintenance, and troubleshooting.
John Pohlman
telescope upgrades, maintenance, and troubleshooting.
John Bowles
telescope upgrades and maintenance (USNO-DC).
Dave Smith
telescope upgrades and maintenance (USNO-DC).
Tie Siemers
telescope upgrades and maintenance (USNO-DC).
Mike Divittorio
telescope maintenance and troubleshooting (NOFS).
Steve Sell
telescope maintenance and troubleshooting (NOFS).
Albert Rhodes
telescope maintenance and troubleshooting (NOFS).
Blaize Canzian
network and computer system support (NOFS).
Sumit Dutta
summer student working on separating out minor planet observations
and streak artifacts.
Aleida Young
summer student working on identification of high proper motion stars.
Danley Hsu
summer student working on UCAC3 release, and providing
the UCAC3 access code, assist with checking of UCAC4.
References
==========
This list includes items cited in the above text and is supplemented by
listing all publications related to UCAC production and presentations.
Many of the papers listed here can be found in the "papers" subdirectory
on the distribution DVD with the aim to document the history of the project.
Boyd,M.R., Winters,J.G., Henry,T.J., et al. 2011,
"The solar neighborhood XXV. Discovery of new proper motion stars
with 0.40 "/yr > mu > 0.18 "/yr between declinations -47 and 00",
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Deacon,N. R., Hambly,N. C., Cooke,J. A. 2005
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proper motion stars from first full hemisphere scan"
A&A, 435, 363
ESA 1997,
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Finch,Charlie T., Henry,Todd J., Subasavage,John P., Jao,Wei-Chun,
Hambly,Nigel C., 2007,
"The Solar Neighborhood. XVIII. Discovery of New Proper-Motion
Stars with 0.40" yr-1 > µ >= 0.18" yr-1 between Declinations -90°
and -47°", AJ, 133, 2898
Finch,C., Zacharias,N., Girard,T., Wycoff,G.L., Zacharias,M.I. 2009,
"UCAC3 is coming!"
AAS
Finch,C., Zacharias,N., Wycoff,G., 2010,
"UCAC3 atrometric reductions", AJ 139, 2200
Finch,C., Zacharias,N., Henry,T., 2010
"UCAC3 Proper Motion Survey. I. Discovery of New Proper Motion
Stars in UCAC3 with 0."40 yr-1 > µ = 0.0018 yr^-1 between Declinations
-90 degrees and -47 degrees", AJ 140, 844
Finch, C.T., Zacharias, N., Boyd, M.R., Henry, T.J., Hambly, N.C., 2012
"UCAC3 Proper Motion Survey. II. Discovery Of New Proper Motion Stars In
UCAC3 With 0.40" yr^-1 > mu >= 0.18" yr^-1 Between Declinations -47 deg
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Gauss,F.S. Zacharias,N. Rafferty,T.J. Germain,M.E. Holdenried,E.R.
Pohlman,J.W. and Zacharias,M.I., 1996,
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Bull.AAS 28, No.4, p.1282
Girard,T. M., Platais,I., Kozhurina-Platais,V., van Altena, W. F.,
Lopez, C. E. 1998,
"The Southern Proper Motion Program. I. Magnitude-Equation Correction",
AJ 115, 855.
Girard,T.M., van Altena,W.F., Zacharias,N., Viera,K., Casetti-Dinescu,D.I.,
Castillo,D., Herrera,D., Lee,Y.S., Beers,T.C., Monet,D.G., Lopez,C.E. 2011,
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AJ 142, 15
Hartkopf,W.I., Mason,B.D., Wycoff,G.L., Finch,C.T., Zacharias,N., 2010,
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Bastian,U., 2000,
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stars", A&A 355L, 27 (short paper)
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Wicenec,A., Urban,S., Corbin,T., Wycoff,G., 2000,
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A&A 357, 367 (long paper)
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Lawrence,A. 2001,
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Hambly,N. C., Davenhall,A. C., Irwin,M. J., MacGillivray, H. T. 2001,
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Henry,Todd J., Subasavage,John P., Brown,Misty A., Beaulieu,Thomas D.,
Jao,Wei-Chun, Hambly,Nigel C. 2004,
"The Solar Neighborhood. X. New Nearby Stars in the Southern Sky
and Accurate Photometric Distance Estimates for Red Dwarfs",
AJ. 128, 2460
Jones, B. F., Hanson, R. B., and Klemola, A. R., 2000,
"Lick Northern Proper Motion Program: NPM2", AAS meeting 196
abstract 53.02
Kovalevsky,J., Lindegren,L., Perryman,M.A.C. et al. 1997,
"The Hipparcos Catalogue as a realisation of the extragalactic
reference system", A&A 323, 620
Lepine,S., Shara,M.M. 2005,
"A Catalog of Northern Stars with Annual Proper Motions Larger than
0.15" (LSPM-NORTH Catalog)", AJ. 129, 1483
Lepine,S., 2008
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Survey. Iv. Completion of the Southern Survey and 170 Additional Stars
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Fouque,P., Mamon,G. 2005,
"A catalog of LEDA galaxies with DENIS measurements"
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Platais,I., Girard,T. M., Kozhurina-Platais,V., van Altena,W. F.,
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Rafferty,T., Zacharias,N. 1999,
"USNO CCD Astrograph Catalog - South",
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Roeser,S., Demleitner,M., Schilbach,E. 2010,
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AJ 139, 2440
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Salim S., Gould A. 2003
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Springer Science Library, Vol. 350
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the HIPPARCOS Catalogue"
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Urban, S.E., Wycoff, G.L., Makarov, V.V., 2000,
"Comparisons of Tycho-2 Catalogue Proper Motions with Hipparcos
and ACT", AJ 120, 501
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Fabricius, C., 2000,
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"The Yale/San Juan Southern Proper Motion Program",
AAS DDA meeting #31, #10.04
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1999, "Sixth Catalogue of Fundamental stars (FK6)",
Veroeff. Astron. Rechen-Inst. Heidelberg 35, 1
Winter, L. 1999
Ph.D thesis, University of Hamburg (in German), CCD image reductions
Zacharias, N. 1997,
"Astrometric Quality of the USNO CCD Astrograph (UCA)", AJ 113, 1925
Zacharias, N., Germain, M.E., Rafferty, T.J., 1997,
"UCAC-S: a New High Precision, High Density Astrometric Catalog in
the Southern Hemisphere", in: Proceedings "Hipparcos Venice 97",
ESA publication SP-402, p.177
Zacharias,N.
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IAU GA 1997, JD7, invited review talk
in Highlights of Astronomy, Vol.11A, p.300-303,
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Zacharias,N. Corbin,T.E. Zacharias,M.I Rafferty,T.J.
Seidelmann,P.K. Gauss,F.S., 1998 (BAAS 30 No.4, p.1368)
"High Precision Astrometry for the Hubble Deep Field - South",
poster preseted at the AAS meeting #193, Austin, TX, Jan. 1999
Zacharias, N. Zacharias, M.I., 1999,
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]]>
Time TT "cepra"
Position ICRS Epoch J2000.0 "raj2000" "dej2000" Error "sigra" "sigdec"
Velocity "pmra" "pmde" Error "sigpmr" "sigpmd"
band, ucd
J, phot.mag;em.IR.J
H, phot.mag;em.IR.H
K_s, phot.mag;em.IR.K
band, ucd
B, phot.mag;em.opt.B
V, phot.mag;em.opt.V
g, phot.mag;em.opt.V
r, phot.mag;em.opt.R
i, phot.mag;em.opt.I
Positions are on the International Celestial Reference
System (ICRS) as represented by the Hipparcos / Tycho-2 catalogs.
The epoch for the positions of all stars is J2000.0; the weighted
mean catalog position was updated using the provided proper
motions. The observational UCAC position is but one of several
going into these values and is not given in the UCAC4; thus the
original UCAC observation cannot be recovered from these data.
Systematic errors are expected to be below 0.1 mag for magm, maga
photometric results obtained from the UCAC CCD pixel data. The aperture
photometry is considered more robust, particularly for "odd" cases, while
the model fit magnitude is expected to be more accurate for "well behaved"
stars.
For many stars a photometric error based on the scatter from
individual observations of that star on different CCD frames
could be obtained. A model error was also attempted to be
assigned, based on the S/N ratio. The error quoted here is
the larger of the 2. If that error exceeds 0.9 mag the error
was set to 0.9 mag
The object type flag is used to identify possible problems
with a star or the source of data. Of the individual image flags
the one with the largest value (worst problem case) is propagated
into this object type flag, unless it is superseded by an overriding
flag at the combined image stage.
The object type flag has the following meaning:
0
good, clean star (from MPOS), no known problem
1
largest flag of any image = near overexposed star (from MPOS)
2
largest flag of any image = possible streak object (from MPOS)
3
high proper motion (HPM) star, match with external PM file (MPOS)
4
actually use external HPM data instead of UCAC4 observ.data
(accuracy of positions varies between catalogs)
5
poor proper motion solution, report only CCD epoch position
6
substitute poor astrometric results by FK6/Hip/Tycho-2 data
7
added supplement star (no CCD data) from FK6/Hip/Tycho-2 data,
and 2 stars added from high proper motion surveys
8
high proper motion solution in UCAC4, star not matched with PPMXL
9
high proper motion solution in UCAC4, discrepant PM to PPMXL (see
discussion of flags 8,9 in redcution section 2e above)
The number of stars with those flags is:
=== =========
0 103080317
1 2785787
2 15519
3 97042
4 35073
5 5004704
6 34473
7 8925
8 2028600
9 689653
=== =========
The cdf flag is a combined double star flag used to indicate
the type/quality of double star fit. It is a combination of 2 flags,
cdf = 10 * dsf + dst
with the following meaning:
dsf = double star flag, overall classification
=== ====================================
0 single star
1 component #1 of "good" double star
2 component #2 of "good" double star
3 blended image
=== ====================================
dst = double star type, from pixel data image profile fits,
largest value of all images used for this star
=== ==============================================================================================
0 no double star, not sufficient #pixels or elongation to even call double star fit subroutine
1 elongated image but no more than 1 peak detected
2 2 separate peaks detected -> try double star fit
3 secondary peak found on each side of primary
4 case 1 after successful double fit (small separ. blended image)
5 case 2 after successful double fit (most likely real double)
6 case 3 after successful double fit (brighter secondary picked)
=== ==============================================================================================
A word of caution: often a dsf= 1 or 2 image is paired with a dsf= 3.
If for a star any of the several images reveals a "blended image",
that higher dsf=3 flag is carried into the output file. This can
happen for a regular double star with unique components 1 and 2.
A flag dsf=3 means this could be component 1 or 2 but at least on
one CCD frame a blended image was detected. This blend could be
with the other component, or a spurious image or artifact.
The double star flags need to be interpreted with caution; anything
but a zero means "likely some double star component or blended image".
If the astrometric data for a star was substituted from an external
catalog like Hipparcos, Tycho or high proper motion data, a mean
error in position and proper motion depending on the catalog and
magnitude of the star was adopted.
A zero for the number of used images indicates that all images
have some "problem" (such as overexposure). In that case an unweighted
mean over all available images (na) is taken to derive the mean
position, while normally a weighted mean was calculated based on
the "good" images, excluding possible problem images (u <= na).
10 AND [jhk]cmsig<0.10857
6 ph_qual 2MASS B, valid measurement, [jhk]snr> 7 AND [jhk]cmsig<0.15510
7 ph_qual 2MASS C, valid measurement, [jhk]snr> 5 AND [jhk]cmsig<0.21714
8 ph_qual 2MASS D, valid measurement, no [jhk]snr OR [jhk]cmsig req.
=== ========================================================================
For example icqflg = 05 is decoded to be cc_flg=0, and ph_qual=5, meaning
no artifacts or contamination from cc_flg and 2MASS qual flag = "A" .
]]>
The photometric errors from 2MASS were rounded by 1 digit
here.
These data were taken from the j_msigcom, h_msigcom, and k_msigcom columns
of the 2MASS point source catalog.
These data are from the AAVSO Photometric all-sky survey (APASS)
DR6 plus single observation stars kindly provided by A.Henden.
For bright stars the magB and magV columns contain the
Hipparcos/Tycho Bt and Vt mags respectively, whenever there is no
APASS B or V available and valid Bt or Vt mags were found.
For the bright supplement stars the same was done. All thses cases
are identified by the respective errors being NULL.
For over 10,000 stars no Vt mag was available and the V mag from Tycho
was used instead.
The following number of stars have entries in the APASS photometry:
======== ========================================
51862350 some valid data in either of the columns
51070044 B mag
51861015 V mag
45799843 g mag
45615993 r mag
41491953 i mag
======== ========================================
The original data release distinguishes between error estimates from
the APASS data release (for objects with at least two observations)
and formal, S/N estimated errors. This distinction is not carried
over here.
The g-flag from the Yale San Juan first epoch Southern
Proper Motion data (YSJ1, SPM) has the following meaning:
=== ========================================
0 no info
1 matched with 2MASS extended source list
2 LEDA galaxy
3 known QSO
=== ========================================
The c-flag from the Yale San Juan first epoch Southern
Proper Motion data (YSJ1, SPM) indicates which input catalog
has been used to identify stars for pipeline processing:
=== ===============================================================
1 Hipparcos
2 Tycho2
3 UCAC2
4 2MASS psc
5 2MASS xsc (extended sources, largely (but not all!) galaxies)
6 LEDA (confirmed galaxies, Paturel et al. 2005)
7 QSO (Veron-Cetty & Veron 2006)
=== ===============================================================
Catalog match flags, compiled into a single number, formed as::
icf = hiptyc*10^8
+ AC2000*10^7
+ AGK2 Bonn*10^6
+ AGK2 Hamburg*10^5
+ Zone Astrog.*10^4
+ Black Birch*10^3
+ Lick Astrog.*10^2
+ NPM Lick*10^1
+ SPM YSJ1
The meaning of hiptyc is:
=== ==============================================================
0 not a Hip. or Tycho star
1 Hipparcos 1997 version main catalog (not in UCAC4 data files)
2 Hipparcos double star annex
3 Tycho-2
4 Tycho annex 1
5 Tycho annex 2
6 FK6 position and proper motion (instead of Hipparcos data)
7 Hippparcos 2007 solution position and proper motion
8 FK6 only PM substit. (not in UCAC4 data)
9 Hipparcos 2007, only proper motion substituted
=== ==============================================================
The remaining flags are provided for major catalogs used
in the computation of the proper motions. Each match is analyzed
for multiple matches of entries of the 1st catalog to 2nd catalog
entries, and the other way around. Matches are also classified
by separation and difference in magnitude to arrive at a confidence
level group. In each case the codes mean:
=== ======================================================================
0 star not matched with this catalog
1 unique-unique match, not involving a double star
2 ... same, but involving a flagged double star
3 multiple match but unique in high confidence level group, no double
4 ... same, but involving a flagged double star
5 closest match, not involving a double, likely o.k.
6 ... same, but involving a flagged double star
7 maybe o.k. smallest sep. match in both directions, no double
8 ... same, but involving a flagged double star
=== ======================================================================
Where given, this gives the apparent total diameter for I-band
(object size) information copied from the LEDA catalog (galaxies).
A size value of less than 1 has been rounded up to 1. The original
source gives the log10 of this value in units of 0.1 arcmin; this means
that this is a rough measure rather than the actual LEDA value.
This flag is either NULL (no match) or contains the length of
the semi-major axis of the fiducial ellipse at the K-band
(object size) information copied from the 2MASS extended source
catalog.
This unique star identification number is between 200001
and 321640 for Hipparcos stars, and between 1 and 9430 for non-
Hipparcos stars supplemented to the UCAC4 catalog (no CCD observ.).
For all other stars this unique star identification number is the
internal mean-position-file (MPOS) number + 1 million.
For both the Hipparcos and the supplement stars there is an entry
on the u4supl.dat file providing more information, including the
original Hipparcos star number. Note, there are several thousand
cases where different UCAC4 stars link to the same Hipparcos star
number due to resolved binary stars with each component being a
separate star entry in UCAC4.
This info provides a cross reference to UCAC2. Both zn2
and rn2 are NULL if the UCAC4 star could not be found in UCAC2.
ucac4 scs
314.998278055556
35.2673475
label, item
good star, 1
near overexposure, 2
possible streak, 3
use external HPM data (accuracy varies), 4
poor proper motion solution, 5
substitute poor results by FK6/Hip/Tycho-2 data, 6
supplement star from FK6/Hip/Tycho-2, 7
high proper motion solution; not matched with PPMXL, 8
high proper motion solution, 9
s/scs.xml
row = self.getFirstVOTableRow(rejectExtras=False)
self.assertAlmostEqual(row["magi"], 13.397, places=5)
self.assertAlmostEqual(row['_r'], 1.22555451700773e-06)
self.assertEqual(row['icqflgK_s'], 5)