I/294A The UCAC2 Bright Star Supplement (Urban+, 2006)
The UCAC2 Bright Star Supplement.
Urban S.E., Zacharias N., Wycoff G.L.
U.S. Naval Observatory, Washington D.C. 2004-2006
<Astron. J. (unpublished) (2004)>
=2009yCat.1294....0U 2009yCat.1294....0U
ADC_Keywords: Positional data ; Proper motions ; Stellar distribution ; Surveys
Keywords: astrometry - stars - fundamental parameters - catalogs -
proper motions - cross identifications
Abstract:
The UCAC2 Bright Star Supplement (UCAC2 BSS) is meant to be used with
the Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2, CDS
Catalogue number I/289) to fill in the missing bright stars and
yet-to-be observed northern regions of the UCAC2. In total 430,000
stars, mostly from the region north of +40 degrees declination, make
up this supplementary data set. All astrometric data were extracted
from either the Hipparcos Catalogue or the Tycho-2 Catalogue;
photometric data were extracted from the Hipparcos, Tycho-2, and 2MASS
catalogues. Cross references between the data sources are given.
Description:
The Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2) has
now been completed and distributed (see CDS catalogue I/289). The
UCAC2 catalogue contains stars in the R ∼ 8-16 magnitude range with
sky coverage from the South Celestial Pole to a ragged northern
boundary between declination +40 to +55 degrees. Details of that
catalogue and project can be found elsewhere (see UCAC web page at
http://ad.usno.navy.mil/ucac/ ).
Two noticeable features of the UCAC2 are its lack of bright stars and
its incomplete sky coverage. The former is a result of the finite
dynamic range of the data acquisition system and observing procedures;
they are optimized for the magnitude range of r∼8-16. The brightest
stars are over-exposed and little astrometric information is gained.
The latter is a result of the on-going nature of the project. The
UCAC2 covers over 85% of the sky; the remaining Northern Celestial
Pole area is currently being observed and reduced. It is expected that
the final UCAC catalogue will be released in 2006. These two features
-- the lack of bright stars and the lack of full sky coverage -- are
the reasoning behind the UCAC2 Bright Star Supplement (UCAC2 BSS).
The UCAC2 BSS is somewhat of a misnomer on two counts. First, there
are no UCAC2 data in it. Instead, all astrometric data were extracted
from the Hipparcos main catalog (HIP), the Hipparcos Double and
Multiple System Annex (DMSA), the Tycho-2 main catalog, or the Tycho-2
Supplement 1. Photometric data were taken from the above catalogues
and the Two-Micron All Sky Survey (2MASS). Second, the UCAC2 BSS
contains not only bright stars, but all stars from the above mentioned
catalogs not found in the UCAC2. This not only includes the spatial
area covered by the UCAC2, but also the far northern regions. For this
reason, most stars in the UCAC2 BSS are north of +40 degrees.
Additional information, including a very extensive catalogue
introduction can be found on the UCAC project website at
http://ad.usno.navy.mil/ucac/ . This website also contains a binary
version of the UCAC2 BSS catalog. This version is very similar in
format to the UCAC2 binary data, therefore much of the same software
can be utilized. The software can be downloaded from the project
webpage.
UCAC2 Bright Star Supplement Data Format:
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The data are arranged in 5 degree zones of declination, starting from
the South Celestial Pole, and are sorted by Right Ascension within
each zone. The running ID numbers go from 50,000,001 to 50,430,000;
they are unique, and have no gaps. The start of the ID number at
50,000,001 was chosen so it did not conflict with any UCAC2 ID number.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ucac2bss.dat 218 430000 UCAC Bright Star Supplement
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See also:
http://ad.usno.navy.mil/ucac/ : the UCAC Home Page
I/289 : The UCAC2 Catalogue (Zacharias+ 2003)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
I/259 : The Tycho-2 Catalogue (Hog+ 2000)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
Byte-by-byte Description of file: ucac2bss.dat
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Bytes Format Units Label Explanations
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1- 8 I8 --- ID [50000001,] UCAC2 BSS identifier (1)
10- 21 F12.8 deg RAdeg RA at epoch J2000.0 (ICRS) (2)
23- 34 F12.8 deg DEdeg Dec at epoch J2000.0 (ICRS) (2)
36- 41 F6.2 mas e_RAdeg S.e. of RA at central ep. (*cos DE) (3)
43- 48 F6.2 mas e_DEdeg S.e. of Dec at central epoch (3)
50 A1 --- src Source catalog for astrometry (4)
52- 58 F7.2 yr EpRAm Central epoch for mean RA (5)
60- 66 F7.2 yr EpDEm Central epoch for mean DE (5)
68- 75 F8.2 mas/yr pmRA ? Proper motion in RA (no cos DE) (6)
77- 85 F9.3 mas/yr pmDE ? Proper motion in DE (6)
86- 91 F6.3 mas/yr e_pmRA ? S.e. of pmRA (*cos DE) (7)
92- 96 F5.2 mas/yr e_pmDE ? S.e. of pmDE (7)
98-102 A5 --- q_pmRA Goodness of fit for pmRA (8)
104-108 A5 --- q_pmDE Goodness of fit for pmDE (8)
110-115 F6.3 mag B-V ? Johnson B-V color index (9)
117-120 F4.2 mag V-I ? Cousins V-I color index (10)
122 A1 --- HvarType Variability type (11)
124-129 F6.2 mag Vmag ? Johnson V magnitude (12)
131-136 F6.3 mag BTmag ? Mean Tycho b magnitude (13)
138-143 F6.3 mag VTmag ? Mean Tycho v magnitude (14)
145-150 F6.3 mag Hpmag ? Median mag in Hipparcos system (15)
152 A1 --- VarFlag HIP course variability flag (16)
154-157 I4 --- TYC1 ? Tycho-2 number (17)
158 A1 --- --- [0] (17)
159-163 I5 --- TYC2 ? Tycho-2 number (17)
164 A1 --- --- [0] (17)
165 I1 --- TYC3 ? Tycho-2 number (17)
167 I1 --- r_TYC2 ? Source of Tycho-2 (18)
169-174 I6 --- HIP ? Hipparcos number (19)
176 A1 --- m_HIP HIP component identifier (20)
178-187 I10 --- 2mID ? 2MASS pts_key star id (21)
189-194 F6.3 mag 2mJmag ? 2MASS J magnitude (22)
196-201 F6.3 mag 2mHmag ? 2MASS H magnitude (22)
203-208 F6.3 mag 2mKsmag ? 2MASS Ks magnitude (22)
210-212 A3 --- 2mflags ? 2MASS photo. quality flags (23)
214-216 A3 --- 2mcc ? 2MASS cc_flg (24)
218 A1 --- astflg Warning flag for astrometry (25)
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Note (1): The ID field provides the UCAC2 Bright Star Supplement
identification number. This is a running number that can be used to
link the information between the ASCII version and the binary version.
Notice that this ID number changed between the original version and
this version, see the "History" section below; the old numbering is
available from the on-line version of the catalog if necessary.
Note (2): The RA and DE fields provide positions on the International
Celestial Reference System (ICRS) as represented by the
Hipparcos/Tycho-2 catalogs. The epochs are J2000.0, with conversions
being made (where necessary) using the NOVAS software package. In
cases where there is no proper motion (fields 9 and 10 are " ", or
field 33 is "N"), this position refers to the epoch given in field 4
(for RA) or field 5 (for DE).
Note (3): The e_RAm and e_DEm fields provide the standard errors at the
central epochs.
Note (4): The src field provides the source catalog used for all
astrometric data for that star (position, proper motion and errors).
It has the following meaning:
H = Hipparcos main catalog
D = Hipparcos Double and Multiple Star Annex (DMSA)
T = Tycho-2 main catalog
S = Tycho-2 supplement 1
Note (5): The EpRAm and EpDEm fields provide the central epochs of the
astrometric data.
The central epoch is the epoch with the lowest positional errors
(e_RAm, e_DEm). For all other epochs (including "J2000.0" which
corresponds to the RA, DE positions given), the errors in position
can be computed as:
e_RA (at epoch T) = SQRT ( e_RAm**2 + (e_pmRA * (T-EpRAm))**2)
e_DE (at epoch T) = SQRT ( e_DEm**2 + (e_pmDE * (T-EpDEm))**2)
Thus, for all epochs other than EpRAm or EpDEm, the positional errors
for RA and Dec, respectively, increase going forward or backward in
time. Values for EpRAm and EpDEm are usually not equal due to
different weights assigned to coordinates in the individual catalogs
used in determining the mean positions and proper motions.
Note (6): The fields pmRA and pmDE provide the proper motion in
right ascension and declination, respectively, referred to the central
epoch. Note that pmRA is without cos(DE), thus these values can be
large for stars close to the pole. This is done so the units for pmRA
and RA are similar, thus facilitating easy computation to change
epochs. Both pmRA and pmDE can directly be used to update a star's
position for proper motion by:
RA (epoch T) = RA + pmRA * (T - 2000.0)/3.6e6
DE (epoch T) = DE + pmDE * (T - 2000.0)/3.6e6
Note, values for RA, and DE provided here are in degrees, while the
pmRA and pmDE provided here are in mas/yr, thus the factor 3600000 in
the equations. Also note that the above formulas do not account for
so-called "second-order" effects, such as the change in the apparent
direction of the pole as seen from a star as proper motion is applied
or the apparent acceleration of a proper motion due to the distance to
a star changing. The first effect is negligible in most instances
unless a star has a very high proper motion and is very close to the
pole and that proper motion is being applied for many years. The
second effect is negligible in most cases unless a star is nearby and
has a large radial velocity (often this is unknown). Where no proper
motions exist, these fields are " ".
Note (7): e_pmRA and e_pmDE are the standard errors of pmRA, pmDE
respectively. Note e_pmRA does include cos(DE), which makes both
e_pmRA and e_pmDE of comparable size in the tangential plane. Where no
proper motions exist, these fields are "_"
Note (8): The q_pmRA and q_pmDE fields provide "goodness-of-fit"
parameters to give the user some idea of how well determined the
astrometry is.
For stars with "H" in the src field, the values were extracted from
field H30; values above +3 indicate a poor fit to the data.
For stars with "D" in the src field, the values were extracted from
field DC5. For these records, "A" indicates a good solution, "B"
indicates a fair, moderately reliable solution, "C" indicates a poor,
less reliable solution, and "D" indicates an uncertain solution.
For stars with "T" in the src field, the data gives information on how
well the computed proper motions actually fit the catalog positions
used to compute them. The values q_pmRA and q_pmDE are actually
ratios, "scatter error pm"/e_pmRA (or e_pmDC). Thus, when the actual
fit of the proper motion to the catalog positions is better than the
formal, model errors (e_pmRA, e_pmDE), the ratio is smaller than 1.
In the opposite case, the ratio is larger than 1. Stars with q_pmRA
or q_pmDE values exceeding 5 should be used with caution. Values
exceeding 9.9 are truncated to 9.90.
Note, this value is only defined when the number of catalog positions
used to compute the proper motions is greater than 2, else an
underscore is given.
Note (9): The B-V field provides the Johnson B-V color index.
It is only given for stars with an "H" in the src field; it was
extracted from HIP field H37.
Note (10): The V-I field provides the Cousins V-I color index.
It is only given for stars with an "H" in the src field; it was
extracted from HIP field H40.
Note (11): The HvarType field provides the Hipparcos variability type.
It is only given for stars with an "H" in the src field; it was
extracted from HIP field H52 and means:
C = no variability detected ("constant")
D = duplicity-induced variability
M = possibly micro-variable (amplitude < 0.03mag)
P = periodic variable
R = V-I colour index was revised due to variability analysis
U = unsolved variable which does not fall in the other categories
Note (12): The Vmag field provides the Johnson V magnitude.
It is only given for stars with an "H" in the src field; it was
extracted from HIP field H5.
Note (13): The B_T field provides the mean Tycho b magnitude.
For stars with "H" in the src field, the data were extracted from HIP
field H32.
For stars with "D" in the src field, the data were extracted from DMSA
field DC11. For stars with "T" in the src field, the data were
extracted from the Tycho-2 BT field. For stars with "S" in the src
field, the data were extracted from the Tycho-2 BT field.
The users should note that stars from HIP, DMSA, and Tycho-2
Supplement 1 use the initial Tycho magnitudes, whereas the
Tycho-2 stars use the Tycho-2 magnitudes.
Note (14): The V_T field provides the mean Tycho v magnitude.
For stars with "H" in the src field, the data were extracted from HIP
field H34. For stars with "D" in the src field, the data were
extracted from DMSA field DC13. For stars with "T" in the src field,
the data were extracted from the Tycho-2 VT field. For stars with "S"
in the src field, the data were extracted from the Tycho-1 VT field.
The users should note that stars from HIP, DMSA, and Tycho-2
Supplement 1 use the initial Tycho magnitudes, whereas the Tycho-2
stars use the Tycho-2 magnitudes.
Note (15): The Hpmag field provides the median magnitude in the
Hipparcos photometric system. For stars with "H" in the src field, the
data were extracted from HIP field H44. For stars with "D" in the src
field, the data were extracted from DMSA field DC9. There is no
comparable magnitude in the Tycho-2 data, so stars with "T" or "D" in
the src field are filled with underscores.
Note (16): The VarFlag field provides the Hipparcos course variability flag.
It is only given for stars with an "H" in the src field; it was
extracted from HIP field H6. A flag in this field indicates the star
is a variable in the Hipparcos photometric system at the following
level:
1 = < 0.06 mag
2 = 0.06 - 0.6 mag
3 = > 0.6 mag
Note (17): The TYC-2 field (bytes 162-165) provides the Tycho-2 number.
It is extracted from the Tycho-2 catalog fields "TYC1", "TYC2", and
"TYC3". Zeros are embedded where blanks existed in the Tycho-2
catalog, therefore all IDs are 12 digits in length.
Note (18): The r_TYC-2 field provides the source of the Tycho-2 number.
It shows whether it was extracted from the main catalog or a supplement.
" " = no Tycho-2 number
0 = extracted from Tycho-2 main catalog
1 = extracted from Tycho-2 Supplement 1
Note (19): The HIP field provides the Hipparcos number. For stars
with an "H" in the src field, it was extracted from HIP field H1.
For stars with a "D" in the src field, it was extracted from DMSA
field DC8. For stars with "T" or "S" in the src field, it was
extracted from the HIP field of the respective catalog.
Note (20): The comp_id field provides the Hipparcos component identifier.
It is only provided for those stars with a "D" in the src field. It
was extracted from DMSA field DC7.
Note (21): The 2m_id field provides the 2MASS identifier.
Given is the "pts_key" star identification number found in the 2MASS
point source catalog.
Note (22): The 2m_J, 2m_H, and 2m_Ks fields provide the J, H, and Ks
magnitudes of 2MASS. They are extracted directly from the 2MASS catalog.
Note (23): The 2m_ph field provides the 2MASS photometric quality flags
as extracted from the 2MASS catalog. For each color (J, H, K_s) one
letter is given. Specific meanings can be found in the 2MASS
documentation. General meanings are:
A or B = good detections (snr > 7)
C or D = weak detections
other = the 2MASS documentation should be consulted.
Note (24): The 2m_cc field provides the 2MASS contamination and confusion
flags as extracted from the 2MASS point source catalog. They indicate
the amount of contamination and confusion seen in the 2MASS data.
For each color (J, H, K_s) one value is given. Specific meanings can
be found in the 2MASS documentation. General meanings are:
0 = no artifacts or contamination seen
c = confusion with nearby brighter source
other = the 2MASS documentation should be consulted.
Note (25): The astflg provides the user with a warning if a star is
known to have either non-linear astrometry (in the case of orbit
stars, for example), the proper motion was based on photocenter data,
the proper motion error in either coordinate is 25.0 mas/yr or higher,
or the proper motion is undetermined.
"*" = star is Hipparcos G,V,O, or X (in H59); or
star's proper motion error in either coordinate is 25.0mas/yr
or higher; or star is Tycho-2 photocenter solution
"N" = proper motion for this star is not determined
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Acknowledgements:
The UCAC team is pleased to acknowledge the great effort by the
Hipparcos team, the Tycho-2 team, and the Two-Micron All Sky Survey
team. Without the great products that they produced, the UCAC2 Bright
Star Supplement would not exist.
History:
* 12-Mar-2004: Original version, from Sean Urban
* 14-Oct-2009: Installation of the 2006 version having the same
set of stars, but with different ID numbers in the same range
50000001-50430000. The change followed a re-work of BSS at USNO.
References:
Urban S.E., Zacharias, N, and Wycoff, G.L., 2004, AJ, in preparation
The UCAC2 Bright Star Supplement
(End) Sean Urban [USNO, USA] 14-Oct-2009