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UVOTBSCAT: Help

UVOTBSCAT - UVOT Bright Star Catalog


Overview

This catalog was compiled from 4 catalogues: Tycho-2, GVCS III, NGC, and the Yale Bright Star Catalog. All catalogs were preprocessed before compiling this catalog to achieve uniform columns and units. Next, they were merged into one catalogue before eliminating "red" objects and precessing all coordinates to epoch 2000.0. The catalog was then corrected for missing decimal points. Finally, the catalog was sorted by R.A. for ease of locating objects within the catalogue. The original catalog contained 239,853 objects brighter than 12.0 mags.

References

There is no published reference for this catalog to the HEASARC's knowledge.

Provenance

This table was originally created by the HEASARC in July 2008 based on an input table supplied by the Swift Project which was compiled by Elizabeth Auden at MSSL. It was renamed to UVOTBSCAT in January 2009.

Description

The aim of this catalog is to prevent the Swift UVOT from looking at very bright objects, particularly in the blue range. Therefore, some fainter objects deemed "too red" to harm the UVOT have been eliminated from the catalog. This process was done through an awk script that retained objects in the catalog according to these limits:
A. B-V < -0.3            V <= 12.0
B. -0.3  <= B-V < -0.17  V <= 11.0
C. -0.17 <= B-V <  0.01  V <= 10.0
D.  0.01 <= B-V          V <= 9.5
Most faint objects with V higher than B could be thrown out according to these rules. This reduced the number of objects in this catalog by almost half.

All missing V or B magnitudes were generated in preprocessing. If V was missing, V was set to "B - 0.3"; likewise, missing B was set to "V + 0.3". These values were chosen to indicate that the object could be "very blue". A "B - V" value of less than "-0.3" causes the object to be retained in the UVOT catalog after the "red" objects are eliminated. Even if this "B - V" value is invented, the UVOT monitor is prevented from looking at potentially bright objects.

Just over 800 of the stars from the Tycho-2 catalogue gave data in epoch 1991.5, while around 3000 variable stars from the GCVS gave information in epoch 1950 coordinates. An awk script precessed right ascension and declination, both given in degrees, using these equations:

"RA_new" = "RA_old" + (15/3600)years(3.074+1.336*sin((pi/360)* "RA_old")*tan((pi/360)* "Dec_old"))
"Dec_new" = "Dec_old"  + (1/3600)years(20.038*cos((pi/360)* "RA_old"))
where "years" is the number of years between 2000.0 and the epoch given. This precession equation produces values accurate to < 1 second of right ascension and 5 arcseconds of declination. The equation was found on an Arizona State University astronomy class webpage:

http://ircamera.as.arizona.edu/astr_250/ProblemSets/tele_solv.html


Component Catalogs

Further information on the procedure in which entries from the component catalogs were amalgamated to make this table is given in the file uvotbscat_doc.txt.

Parameters

RA
The Right Ascension of the source in the selected equinox. The RA was provided in J2000.0 equatorial coordinates to a variety of implied precisions in the original table.

Dec
The Declination of the source in the selected equinox. The Declination was provided in J2000.0 equatorial coordinates to a variety of implied precisions in the original table.

LII
The Galactic Longitude of the source.

BII
The Galactic Latitude of the source.

Vmag
The V magnitude (Johnson System) of the source.

Bmag
The B magnitude (Johnson System) of the source.

Source_Catalog
The reference catalog from which the source was taken: GCVS, Hipparcos (for Hipparcos Project Tycho-2 Catalog or the Yale Bright Star Catalog), or NGC.

Mag_Flag
This flag parameter is set to 'B' if the B magnitude value for the source was invented: see the above Description section for more details on this procedure.


Contact Person

Questions regarding the UVOTBSCAT database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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