DBCIRCLE

      Find sources in a database within specified radius of specified center

      Database must include items named 'RA' (in hours) and 'DEC' (in degrees)
      and must have previously been opened with DBOPEN

     list = DBCIRCLE( ra_cen, dec_cen, [radius, dis, sublist, /SILENT,
                                          TO_B1950, /TO_J2000 ] )

       RA_CEN - Right ascension of the search center in decimal HOURS, scalar
       DEC_CEN - Declination of the search center in decimal DEGREES, scalar
               RA_CEN and DEC_CEN should be in the same equinox as the
               currently opened catalog.

       RADIUS - Radius of the search field in arc minutes, scalar.
               DBCIRCLE prompts for RADIUS if not supplied.
       SUBLIST - Vector giving entry numbers in currently opened database
               to be searched.  Default is to search all entries

     LIST - Vector giving entry numbers in the currently opened catalog
            which have positions within the specified search circle
            LIST is set to -1 if no sources fall within the search circle
            !ERR is set to the number sources found.

       DIS -  The distance in arcminutes of each entry specified by LIST
               to the search center (given by RA_CEN and DEC_CEN)

       /SILENT - If this keyword is set, then DBCIRCLE will not print the
               number of entries found at the terminal
       /TO_J2000 - If this keyword is set, then the entered coordinates are
               assumed to be in equinox B1950, and will be converted to
               J2000 before searching the database
       /TO_B1950 - If this keyword is set, then the entered coordinates are
               assumed to be in equinox J2000, and will be converted to
               B1950 before searching the database
               NOTE: The user must determine on his own whether the database
               is in B1950 or J2000 coordinates.

       A DBFIND search is first performed on a square area of given radius.
       The list is the restricted to a circular area by using GCIRC to
       compute the distance of each object to the field center.

       Find all Hipparcos stars within 40' of the nucleus of M33
       (at J2000 1h 33m 50.9s 30d 39' 36.7'')
       IDL> dbopen,'hipparcos'
       IDL> list = dbcircle( ten(1,33,50.9), ten(3,39,36.7), 40)

       BPRECESS, DBFIND(), DBEXT, DB_INFO(), GCIRC, JPRECESS

      Written W. Landsman     STX           January 1990
      Fixed search when crossing 0h         July 1990
      Spiffed up code a bit     October, 1991
      Converted to IDL V5.0   W. Landsman   September 1997
      Leave DIS vector unchanged if no entries found W. Landsman July 1999
      Use maximum declination, rather than declination at field center to
      correct RA for latitude effect    W. Landsman   September 1999

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