The UCAC2 Bright Star Supplement
===============================================================================
The UCAC2 Bright Star Supplement
Urban S.E., Zacharias N., Wycoff G.L.
U.S. Naval Observatory, Washington D.C. 2004
===============================================================================
Contents
--------
Abstract
1) Introduction
2) Combining Hipparcos and Tycho-2 data
3) Identifying UCAC2 BSS stars in the hiptyc2 data set
4) ASCII Data Format
4a) General information (duplicate of section 5a)
4b) Format for ASCII version, bss.dat
5) Binary data formats
5a) General information (duplicate of section 4a)
5b) Format for binary version, main data (Files s01 to s36)
5c) Format for file bsindex.da
5d) Format for file bsindex.txt
6) Description of utility software
Abstract
--------
The UCAC2 Bright Star Supplement is meant to be used with the
Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2) 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 data were extracted from either the Hipparcos Catalogue
or Tycho-2 Catalogue. The data are provided in two formats.
The binary version is very similar in format to the UCAC2 binary
data and much of the same software can be utilized. The ASCII
version contains virtually the same information as the binary
version, with some auxiliary data that did not fit into the
binary data structure.
1) Introduction
---------------
The Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2) has
now been completed and distributed (see CDS catalog I/289). The UCAC2
catalog 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 catalog 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 catalog 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 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.
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. Plots of the sky coverage are found on this
directory in both .ps and .gif formats. The files sky_bss_01.*
show the location of every UCAC2 BSS star, where the files
sky_bss_05.* show every 5th star.
The Hipparcos and Tycho-2 Catalogues provide the best source of data
for the UCAC2 supplement. The combination of the two catalogs
provides excellent astrometry, full-sky coverage, virtually complete
to V=11.0. The first task of the project was to combine the Hipparcos
and Tycho-2 data sets, removing duplicated information from stars
in common.
2) Combining Hipparcos and Tycho-2 data
---------------------------------------
Difficulties and subtleties arise when one considers the Hipparcos
annexes and the Tycho-2 supplements, which should not be neglected for
this type of work. The Hipparcos Double and Multiple Systems Annex
(DMSA), containing the ``component solutions'' of multiple star systems
is the only annex with stars not in the main catalog; this is the only
additional supplementary data needed from Hipparcos beyond that found
in the main catalog. One must understand that it does contain data
that are in the main catalog, so a simple concatenation of the main
catalog and the DMSA cannot be made. In every case, data from the
DMSA for ``C'' solution stars (component solutions) supersede that
from the main catalog in this work.
Unlike the Hipparcos data set, Tycho-2 and its supplements contain
only different stars, hence the combination of the main catalog,
supplement 1 and supplement 2 should contain one record for each star.
The combination of the Hipparcos and Tycho-2 data sets, termed "hiptyc2"
in this write-up, should yield a catalog containing all stars from
Sirius down to about V=11.0. But simply combining them leads to problems
since most Hipparcos stars are in the Tycho-2 catalog although with
slightly different astrometry. Hence, if a concatenation is made,
a multiple entry (defined here as more than one record for the same
star) will appear to be a close double when in reality that is not
the case. Therefore it is important to identify the multiple entries
and remove all but one of the records. Although there is some
cross-referencing information contained in the published Hipparcos
and Tycho-2 catalogs, it was felt positional matching starting from
first principles would be much more complete. The actual matching
was done in several stages, up to a radius of 10 arcsec. In all
cases, the order of precedence was the HIP DMSA, HIP main, then Tycho-2.
The Tycho-2 data were transformed to epoch 1991.25 using the published
proper motions. Where proper motions do not exist, the epoch of
observation was used, which is normally within a year of 1991.25.
3) Identifying UCAC2 BSS stars in the hiptyc2 data set
------------------------------------------------------
To remove the UCAC2 stars in the hiptyc2 data set, the UCAC2 positions
were transformed to epoch 1991.25 using the published UCAC2 proper
motions. A positional search was then performed, and any hiptyc2
star within 3 arcsec of a UCAC2 position was removed. The remaining
set formed the initial UCAC2 BSS list.
The authors decided to retain stars that have a multiplicity code
in the Hipparcos Catalogue (MultFlag field, H59) of G, V, O, or X.
This indicates non-linear motion of the object, and such stars may
not be suitable for the highest precision astrometry. These stars
are retained because many of the brightest, well-known stars such
as Sirius, Capella, Antares, and Algol would have been removed if
this criterion were implemented. Instead, these are kept but
a flag indicating compromised astrometry is given. Similarly,
stars with imprecise proper motion and even those stars without
proper motions are retained but flagged.
The only set of stars removed was from the Tycho-2 Supplement 2
data; these stars have a strong likelihood of being bogus.
Following the removal, there remains 430,000 stars (exactly, this
is not a rounded number); these make up the UCAC2 BSS.
4) ASCII Data Format
--------------------
4a) General information (duplicate of section 5a)
--------------------------------------------------
The data are provided in 2 formats. For the ASCII version, a single
file for all stars is given. For the binary version, a set of 36
unformatted (binary) zone files are given, along with some index files
and utility software to facilitate easy access to the data.
The binary zone files are very similar to the UCAC2 main data.
The ASCII file contains more information than the binary files.
For example, the former gives the Hipparcos and Tycho-2 identification
numbers.
The positions in the ASCII file are given in degrees to 8 decimal
places, while those in the binary files are rounded to 1 mas units.
The proper motions are given to different precision in the two
data sets; they are to 0.1 mas/yr in the binary files but 0.01 mas/yr
in the ASCII file. The errors in position and proper motion are
rounded to 1 mas and 0.1 mas/yr units in the binary files, but are
given to 0.01 mas and 0.01 mas/yr in the ASCII file. Otherwise the
data of the ASCII and binary files are the same for the fields given
in both, although in the ASCII version the decimal point is explicit
but in the binary version it is implied. Note that there are cases
where the values are truncated in the binary versions, such as those
stars whose proper motion errors exceed 25.0 mas/yr (217 cases;
values truncated to 25.0 mas/yr in the binary version) and those where
the position error at central epoch exceeds 250 mas (4 cases;
values truncated to 250 mas in the binary version). These are
given to their full precision in the ASCII versions.
The exact same stars are provided in both formats, with the same
running sequence identification number. 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
number goes from 50,000,001 to 50,430,000 is unique, and has no
gaps. This ID number is explicitly provided on the ASCII file and
is generated with the access software from the binary zone and
index files.
4b) Format for ASCII version, bss.dat
-------------------------------------
The following is the format for the ASCII version of the UCAC2
Bright Star Supplement. This remainder of this section is duplicated
in the file bss_ascii.fmt.
The UCAC2 Bright Star Supplement
ASCII version
Fld Cols Fmt Unit Label Explanation Notes
--------------------------------------------------------------------------
1 1- 8 I8 --- ID UCAC2 BSS identifier (1)
2 10- 21 F12.8 deg RA RA at epoch J2000.0 (ICRS) (2)
3 23- 34 F12.8 deg DE Dec at epoch J2000.0 (ICRS) (2)
4 36- 41 F6.2 mas e_RAm S.e. of RA at central ep. (*cos DE) (3)
5 43- 48 F6.2 mas e_DEm S.e. of Dec at central epoch (3)
6 50- 50 A1 --- src Source catalog for astrometry (4)
7 52- 58 F7.2 yr EpRAm Central epoch for mean RA (5)
8 60- 66 F7.2 yr EpDEm Central epoch for mean DE (5)
9 68- 75 F8.2 mas/yr pmRA PM in RA (no cos DE) (6)
10 77- 84 F8.2 mas/yr pmDE PM in DE (6)
11 86- 90 F5.2 mas/yr e_pmRA S.e. of pmRA (*cos DE) (7)
12 92- 96 F5.2 mas/yr e_pmDE S.e. of pmDE (7)
13 98-102 A5 --- q_pmRA Goodness of fit for pmRA (8)
14 104-108 A5 --- q_pmDE Goodness of fit for pmDE (8)
15 110-115 F6.3 mag B-V Johnson B-V color index (9)
16 117-120 F4.2 mag V-I Cousins V-I color index (10)
17 122-122 A1 HvarType Variability type (11)
18 124-129 F6.2 mag Vmag Johnson V magnitude (12)
19 131-136 F6.3 mag B_T Mean Tycho b magnitude (13)
20 138-143 F6.3 mag V_T Mean Tycho v magnitude (14)
21 145-150 F6.3 mag Hpmag Median mag in Hipparcos system (15)
22 152-152 A1 --- VarFlag HIP course variability flag (16)
23 154-165 I12 --- T2_id Tycho-2 number (17)
24 167-167 I1 --- r_T2_id Source of T2_id (18)
25 169-174 I6 --- HIP Hipparcos number (19)
26 176-176 A1 --- comp_id HIP component identifier (20)
27 178-187 I10 --- 2m_id 2MASS pts_key star id (21)
28 189-194 F6.3 mag 2m_J 2MASS J magnitude (22)
29 196-201 F6.3 mag 2m_H 2MASS H magnitude (22)
30 203-208 F6.3 mag 2m_Ks 2MASS K_s magnitude (22)
31 210-212 A3 --- 2m_ph 2MASS photo. quality flags (23)
32 214-216 A3 --- 2m_cc 2MASS cc_flg (24)
33 218-218 A1 --- astflg Warning flag for astrometry (25)
==========================================================================
Note: In all cases, underscores "_" are inserted for non-existing values.
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.
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)/3600.0
DE (epoch T) = DE + pmDE * (T - 2000.0)/3600.0
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 3600 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 scr 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 scr 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.
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 scr field, the data were
extracted from the Tycho-2 BT field. For stars with "S" in the scr
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 scr field, the data were
extracted from the Tycho-2 VT field. For stars with "S" in the scr
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 T2_id field 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_T2_id 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 K_s
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 undermined.
"*" = star is Hipparcos G,V,O, or X (in H59); or
star's proper motion error in either coordinate is 25.0 mas/yr
or higher; or star is Tycho-2 photocenter solution
"N" = proper motion for this star is not determined
5) Binary data formats
----------------------
5a) General information (duplicate of section 4a)
--------------------------------------------------
The data are provided in 2 formats. For the ASCII version, a single
file for all stars is given. For the binary version, a set of 36
unformatted (binary) zone files are given, along with some index files
and utility software to facilitate easy access to the data.
The binary zone files are very similar to the UCAC2 main data.
The ASCII file contains more information than the binary files.
For example, the former gives the Hipparcos and Tycho-2 identification
numbers.
The positions in the ASCII file are given in degrees to 8 decimal
places, while those in the binary files are rounded to 1 mas units.
The proper motions are given to different precision in the two
data sets; they are to 0.1 mas/yr in the binary files but 0.01 mas/yr
in the ASCII file. The errors in position and proper motion are
rounded to 1 mas and 0.1 mas/yr units in the binary files, but are
given to 0.01 mas and 0.01 mas/yr in the ASCII file. Otherwise the
data of the ASCII and binary files are the same for the fields given
in both, although in the ASCII version the decimal point is explicit
but in the binary version it is implied. Note that there are cases
where the values are truncated in the binary versions, such as those
stars whose proper motion errors exceed 25.0 mas/yr (217 cases;
values truncated to 25.0 mas/yr in the binary version) and those where
the position error at central epoch exceeds 250 mas (4 cases;
values truncated to 250 mas in the binary version). These are
given to their full precision in the ASCII versions.
The exact same stars are provided in both formats, with the same
running sequence identification number. 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
number goes from 50,000,001 to 50,430,000 is unique, and has no
gaps. This ID number is explicitly provided on the ASCII file and
is generated with the access software from the binary zone and
index files.
5b) Format for binary version, main data (Files s01 to s36)
-----------------------------------------------------------
The following is a format for the main binary data of the UCAC2 Bright
Star Supplement. The remainder of this section is duplicated in the
file bss_binary.fmt.
Format for binary version of the UCAC2 Bright Star Supplement (BSS)
The binary version of the UCAC2 BSS is extremely similar to the UCAC2
main catalog. However, the user should be aware of the following
differences between the two:
- BSS zones are 5 degree wide, instead of 0.5 degree as for UCAC2
- BSS covers all sky, i.e. there are 36 zones
- the name of the zone files is "s01" through "s36"
- for BSS the "UCAC2 magnitude" (field #3) contains either the
Tycho V magnitude, Hipparcos median magnitude, or Tycho B magnitude
- for BSS, the source of the magnitude (Tycho-V, Median Hipparcos,
or Tycho-B) is given in field #6; for UCAC2, this field was used
for the number of UCAC observations
- for BSS the central epoch (fields #10, 11) is given in 1/100 year,
instead of 1/1000 year as for UCAC2
- BSS fields #7 and 8 are set to zero (no UCAC observational data)
- for BSS the "cflg" (field #9) is -1 through -7, and provides the
catalog from which the astrometry was taken and warnings about
poor or non-existent proper motions (see note 7 below)
The rest of the information (by column, format and units) is identical
for the UCAC2 BSS and the main UCAC2 release data.
All items are (signed) integer. "I*1" means the data for these items are
contained in 1 byte, "I*2" means 2 bytes, etc. The order of bytes is for
an Intel processor. Each record contains the data for one star, totaling
23 items. The record length is 44 bytes, with no additional "end of
line" or unformatted leading or trailing bytes. In Fortran this is
known as a direct access, fixed record length, unformatted file.
(Note, some compilers specify the record length as a multiple of
4-byte segments, thus RECL=11 is required in that case, instead
of RECL=44 which applies to other compilers. RECL=44 is used in the
utility software provided with the BSS release).
============================================================================
Format for binary version
Fld Bytes Fmt Unit Label Explanation Notes
-----------------------------------------------------------------------------
1 1- 4 I*4 mas RA Right Ascension at epoch J2000.0 (ICRS) (2)
2 5- 8 I*4 mas DE Declination at epoch J2000.0 (ICRS) (2)
3 9-10 I*2 0.01 mag mag Mean magnitude (3)
4 11 I*1 mas e_RAm S.e. at central epoch in RA (*cos DE) (1,4)
5 12 I*1 mas e_DEm S.e. at central epoch in Dec (1,4)
6 13 I*1 magsrc Source of magnitude (5)
7 14 I*1 mas e_pos Error of original UCAC observ. (6)
8 15 I*1 ncat # of catalog posit. for pmRA, pmDC (6)
9 16 I*1 cflg ID of cats. used for astrometry fields (7)
10 17-18 I*2 0.01 yr EpRAm Central epoch for mean RA, minus 1975 (8)
11 19-20 I*2 0.01 yr EpDEm Central epoch for mean DE, minus 1975 (8)
12 21-24 I*4 0.1 mas/yr pmRA Proper motion in RA (no cos DE) (9)
13 25-28 I*4 0.1 mas/yr pmDE Proper motion in DE (9)
14 29 I*1 0.1 mas/yr e_pmRA S.e. of pmRA (*cos DE) (1,10)
15 30 I*1 0.1 mas/yr e_pmDE S.e. of pmDE (1,10)
16 31 I*1 0.05 q_pmRA Goodness of fit for pmRA (1,11)
17 32 I*1 0.05 q_pmDE Goodness of fit for pmDE (1,11)
18 33-36 I*4 2m_id 2MASS pts_key star identifier (12)
19 37-38 I*2 0.001 mag 2m_J 2MASS J magnitude (13)
20 39-40 I*2 0.001 mag 2m_H 2MASS H magnitude (13)
21 41-42 I*2 0.001 mag 2m_Ks 2MASS K_s magnitude (13)
22 43 I*1 2m_ph 2MASS modified ph_qual flag (1,14)
23 44 I*1 2m_cc 2MASS modified cc_flg (1,15)
-----------------------------------------------------------------------------
Example:
As an example, the data of the first 3 stars from s01 are
printed here in ASCII. These are the numbers obtained when
using the bssdumpz.f program.
item 1 2 3 4 5 6 7 8 9 10 11 12
6854506 -309739533 738 1 1 0 0 0 -1 1625 1625 3290
11379804 -314290944 1105 40 43 0 0 0 -2 934 711 44333
34875774 -307484785 783 1 1 0 0 0 -1 1625 1625 -10799
item 13 14 15 16 17 18 19 20 21 22 23
70 6 5 20 20 1085334238 7323 7387 7360 000 000
37 16 16 28 26 1329017546 9623 9259 9189 000 000
-288 6 6 20 20 1181015501 6399 6068 5956 000 000
Note (1): In order to fit within the range of a 1 byte (signed)
integer (-127 to +127), some items have an offset value of -127
applied. These are fields #4,5 (e_RAm, e_DEm),
#14-17 (e_pmRA, e_pmDE, q_pmRA, q_pmDE), and #22,23 (2m_ph, 2m_cc).
When using the provided software, the data items are converted to
I*4 and automatically corrected for this offset on the required
items. For some of the fields this is not necessary for the
Bright Star Supplement; however, this -127 offset has been applied
anyway to be consistent with the main UCAC2 data files.
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 (field 9 equals -7), this
position refers to the epoch given in field 10 (for RA) or
field 11 (for DE).
Note (3): The mag field provides the mean V magnitude. Users should
note that this is different than what is found in the main UCAC2 data
for this same field, although this is the most similar data to the UCAC
observed magnitudes found in the Hipparcos and Tycho data files.
The order of priority was the Tycho-V magnitude if it exists, next
the median Hipparcos magnitude if it exists, else the Tycho-B
magnitude. Utilizing these three sources, magnitudes for all stars
could be provided. The source of magnitudes is found in
field 6, magsrc.
The users should note that stars with astrometry from HIP and
DMSA use the initial Tycho magnitudes, whereas the Tycho-2 stars
use the Tycho-2 magnitudes.
Note (4): The e_RAm and e_DEm fields provide the standard errors at the central
epochs, not at epoch J2000 (see Note 8 below).
Note (5): The magsrc field provides the source of magnitude given in
field 3.
0 = Tycho-V magnitude
-1 = Median Hipparcos magnitude
-2 = Tycho-B magnitude
Note (6): The e_pos and ncat fields are zero for all BSS stars.
These fields are kept for consistency with the data structure of
the main UCAC2 files.
Note (7): The field cflg provides the identifier of the source catalog
used for all astrometric data of that star (position, proper motion
and errors). It also has data to warn users of imprecise or non-existent
proper motions. It has the following meaning:
-1 = Hipparcos main catalog
-2 = Tycho-2 catalog
-3 = Hipparcos Double and Multiple Star Annex (DMSA)
-4 = Hipparcos main catalog, proper motion warning (see below)
-5 = Tycho-2 catalog, proper motion warning (see below)
-6 = Hipparcos DMSA, proper motion warning (see below)
-7 = Tycho-2 catalog, no proper motion given
Proper motion warning is given when this field is -4, -5, or -6.
This warning arises when the star is Hipparcos G,V,O, or X
(in H59), or the star's proper motion error in either coordinate
is 25.0 mas/yr or higher, or the star's proper motion is from a
photocenter solution.
Note (8): The EpRAm and EpDEm fields provide the central epochs of the
astrometric data in 1/100 year minus 1975.00.
For the Hipparcos stars this is 1991.25 (which translates to the
number 1625 in this field (on the binary files). The access
software multiplies that number by 10 to show 16250 in the output
tables, consistent with the 1/1000 year unit for the UCAC2 main data.
For the BSS binary data the 1/100 year unit was required to fit that
value in the I*2 number, because several stars had a very early
central epoch.
The central epoch is the epoch with the lowest positional errors
(e_RAm, e_DEm). For all other epochs, T, (including "J2000.0" which
corresponds to the RA, DE positions given here), the errors in
position can be computed as:
EpRA_central = EpRAm/100.0 + 1975.0
EpDE_central = EpDEm/100.0 + 1975.0
e_RA (at epoch T) = SQRT( e_RAm**2 + (e_pmRA*(T-EpRA_central))**2)
e_DE (at epoch T) = SQRT( e_DEm**2 + (e_pmDE*(T-EpDE_central))**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 (9): pmRA and pmDE are 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 be directly used to update a star's position
for proper motion by:
RA (epoch T) = RA + pmRA * (T - 2000.0)/10.0
DE (epoch T) = DE + pmDE * (T - 2000.0)/10.0
Note, values for RA, and DE provided here are in mas, while the
pmRA and pmDE provided here are in units of 0.1 mas/yr. 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
affect is negligible in most cases unless a star is nearby and
has a large radial velocity (often this is unknown). Values
of 0.0 are given for undetermined proper motions (indicated by
a value of -7 in field 9, cflg).
Note (10): 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.
Values exceeding 25.0 are truncated to 25.0; these stars have
a value of -4, -5, or -6 in field 9 (cflg). For stars with
undetermined proper motions, a value of 25.0 is also given; these
stars have a value of -7 in field 9 (cflg).
Note (11): 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 the binary data, only stars whose astrometry is from Tycho-2
(cflg=-2) are included. Else a value of 1.0 is given in the
q_pmRA and q_pmDE fields.
These values give information on how well the computed
proper motions actually fit the catalog positions used to compute
them, termed "scatter error". 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. If the ratio is larger than 9.9
it is set to 9.9. Note, this value is only defined when the number
of catalog positions used to compute the proper motions is greater than 2.
Else a value of 1.0 is given in the q_pmRA and q_pmDE fields.
The actual integer numbers coded in the data file for q_pmRA and
q_pmDE are multiplied by 20 and then have 127 subtracted from them
(see Note (1)). Thus, for example, a q_pmRA value of +13 means
the value is (13+127)/20, equaling a ratio of 7.0, a value of -107
is (-107+127)/20, equaling 1.0.
Note (12): 2m_id is the "pts_key" star identification number found
in the 2MASS point source catalog. It is a unique 4-byte integer
number greater than 0. If no unique match to the 2MASS point source
catalog was found, 2m_id was set to 0.
Note (13) 2m_J, 2m_H, 2m_Ks are the J, H, and K_s magnitudes taken
directly from the 2MASS catalog with full precision (in units of
1/1000 of a magnitude. No error estimates on these magnitudes
are given here, but they can be extracted from the 2MASS catalog.
For stars not matched, all three magnitudes are set to 30.0
(a value of 30000 on the binary record).
Note (14): 2m_ph is a modified 2MASS "ph_qual" flag, which is the
photometric quality flag given in the 2MASS catalog. For each
color (J, H, K_s) one digit is given and has the following meaning:
0 = ph_qual in 2MASS is A or B, meaning good detections (snr > 7)
1 = ph_qual in 2MASS is C or D, meaning weak detections
2 = ph_qual in 2MASS is something else and the 2MASS documentation
should be consulted.
Note that the values in 2m_ph also have 127 subtracted from them
(see Note (1)). For example 2m_ph =-115 is decoded to (-115+127)
= 012, meaning good detection in J, weak in H, and a problem in K.
Note (15): 2m_cc is a modified 2MASS "cc_flg", which indicates the
amount of contamination and confusion seen in the 2MASS data.
Similar to 2m_ph (see Note (14)), each color (J, H, K_s) is
assigned one digit which has the following meaning:
0 = cc_flg in 2MASS is 0, no artifacts or contamination seen
1 = cc_flg in 2MASS is "c", confusion with nearby brighter source
2 = cc_flg in 2MASS is something else and the 2MASS documentation
should be consulted.
Note that the values in 2m_cc also have 127 subtracted from them
(see Note (1)). For example 2m_cc = 83 is decoded to (83+127)
= 210, meaning a problem in J, contamination in H, and no
contamination seen in K.
============================================================================
5c) Format for file bsindex.da
---------------------------------------------------------------------------
This binary file is very similar to the ASCII file 'bsindex.txt'.
It contains the "nxb" array, which contains information
regarding the number of stars in each area of sky. These areas are
arranged in declination zones (each zone is 5 degrees wide, numbering
starts at the South Celestial Pole) further divided by 0.1 hour bins
in RA. There are 36 declination zones covering the entire sky up to
+90 degrees declination. There are 240 bins along RA, thus a total of
36 by 240 = 8640 bins.
This binary file is used by some of the utility software and is
expected to be in the same directory as the binary data files.
nxb (36,240) = on 36 direct access records;
each record of 240 x 4 bytes (RECL=960);
total = 34,560 bytes
nxb (z,jj) = accumulated number of stars for zone z and RA bin jj
This information can also be obtained from the bsindex.txt file.
The bsindex.da file is used for faster access with the utility programs.
Both index files (the ASCII and the binary versions) can be re-created
by the user by running the bsschk program (see Section 6).
5d) Format for file bsindex.txt
----------------------------------------------------
This file is very similar to the binary file 'bsindex.da'.
This ASCII file contains information regarding the number of
stars in each area of sky. These areas are arranged in declination
zones (each zone is 5 degrees wide, numbering starts at the South
Celestial Pole) further divided by 0.1 hour bins in RA. There are
36 declination zones covering the entire sky up to +90 degrees
declination. There are 240 bins along RA, thus a total of
36 by 240 = 8640 bins.
The first few lines in the bsindex.txt file give a short explanation
followed by the main table records like:
nsbin naz nat zn jj DCmax RAmax
-------------------------------------------
0 0 0 1 1 -89.5 0.1
1 1 1 1 2 -89.5 0.2
1 2 2 1 3 -89.5 0.3
0 2 2 1 4 -89.5 0.4
0 2 2 1 5 -89.5 0.5
The following format is used for the main table records in bsindex.txt:
Num Bytes Fmt Units Label Explanation
1 1- 6 I6 nsbin number of stars in that bin (zn,jj)
2 7-14 I6 naz number of stars accumulated within zone zn
3 15-23 I9 nat number of stars accumulated total
4 24-27 I4 zn zone number
5 28-31 I4 jj Right ascension index (0.1 hour wide boxes)
6 32-37 F6.1 deg DCmax largest Declination in bin (zn,jj)
7 38-42 F5.1 hour RAmax largest right ascension in bin (zn,jj)
6) Description of utility software
----------------------------------
Some software is provided to facilitate use of the binary version of the
UCAC2 BSS. Note, the use of this software is not required but may be
helpful. Those familiar with using the UCAC2 will find much of this
similar. No software is given for use of the ASCII version.
The source code (Fortran, F77 + extensions) of all programs can be
found in the this directory. More explanations are provided as comments
in the source code files as well as in the interactive output when
running the programs. For some compilers, you need to substitute
the declaration BYTE with INTEGER*1. If writing
your own software, you might want to take advantage of the low-level
access routines open_bfile and read_bsline in the bssub.f file.
For a combined access of UCAC2 and BSS, the subroutines are in
ubsub.f, which is also required for the ubaccess.f main program.
bssub.f: contains various subroutines used in the following
utility programs, could be used for basic level access
in user software. Notes contained in that file explain
the individual subroutines and their functions.
Use this with bsdumpz.f and bsaccess.f (however not
for ubaccess.f).
bschk.f: - reads all zone files of BSS
- checks if byte flip is required
- gets statistics and histograms of data items per star
- outputs summary to ASCII file
- option: generate index files (ASCII -- bsindex.txt --
and binary -- bsindex.da -- were generated this way).
bsdumpz.f: - reads all data of a single zone of the BSS
- dumps integer values to ASCII file, all columns
- option is available for user-selected limiting magnitude
bsdumpz.f is a short, simple program and serves as an
example of how to use the basic level routines.
bsaccess.f: - interactive access to BSS data by area in the sky
- select box in RA, Dec or center + width of box
- select mag range (V_T)
- sort output by any of the 23 items (columns)
- update of positions and errors to desired epoch
- output stars in ASCII, various formats
- user may define additional output formats
sorti.f: - general subroutine to sort a 2-index integer array
ubsub.f: - subroutines for combined access of BSS and main
UCAC2 data files
ubaccess.f - main program for combined access of BSS and UCAC2,
output to single array, combined sort
bsaccess - executable files for Linux PC (Pentium processor)
ubaccess - executable files for Linux PC (Pentium processor)
bsdumpz - executable files for Linux PC (Pentium processor)
bsaccess.exe - executable files for Windows (DOS)
ubaccess.exe - executable files for Windows (DOS)
bsdumpz.exe - executable files for Windows (DOS)
No guarantee can be made for this software, nor can any kind of
support be provided. Users are encouraged to take segments of these
examples and build their own software.