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UVOTBSCAT: Help
OverviewThis 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.ReferencesThere is no published reference for this catalog to the HEASARC's knowledge.ProvenanceThis 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.DescriptionThe 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 <= 9.5Most 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 CatalogsFurther 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
Dec
LII
BII
Vmag
Bmag
Source_Catalog
Mag_Flag Contact PersonQuestions regarding the UVOTBSCAT database table can be addressed to the HEASARC User Hotline. |
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