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README file for the GB6 FTP directory

J. J. Condon

95/10/16 version
The Green Bank 4.85 GHz (~6 cm wavelength) survey was made with the (former) 91 m telescope during November 1986 and October 1987 (Condon et al. 1994). The final set of sky maps covering the declination band from 0 to +75 deg was constructed with data from both epochs. Its noise and position errors are nearly a factor of sqrt(2) smaller than in the epoch 1987 maps, from which the 87GB catalog of 54,579 sources stronger than S ~ 25 mJy (Gregory & Condon 1991) was extracted. We therefore used the new maps to make the GB6 catalog (Gregory et al. 1996) of 75,162 discrete sources with angular sizes < 10.5 arcmin and flux densities above S ~ 18 mJy. This catalog is available in machine-readable versions with either B1950 or J2000 positions and as a printed book with peak flux densities and B1950 positions only. The digital catalog format is described in detail by Gregory & Condon (1991) and is illustrated by the first source in the list, GB6 0000+1833:

000004.7 0.7 +183324 11 -42.5 107.2    64    7      1.06 0.94  79   0  937  388

Bytes (01--02).--- Hours of right ascension, format I2
Bytes (03--04).--- Minutes of right ascension, format I2
Bytes (05--08).--- Seconds of right ascension, format F4.1
Bytes (09--12).--- RMS uncertainty in right ascension (s), format F4.1
Byte  (14).    --- Sign of declination, format A1
Bytes (15--16).--- Degrees of declination, format I2
Bytes (17--18).--- Arcminutes of declination, format I2
Bytes (19--20).--- Arcseconds of declination, format I2
Bytes (22--23).--- RMS uncertainty in declination (arcsec), format I2
Bytes (25--29).--- Galactic latitude (deg), format F5.1
Bytes (31--35).--- Galactic longitude (deg), format F5.1
Bytes (37--41).--- 4.85 GHz peak flux density (mJy), format I5
Bytes (43--46).--- RMS uncertainty in peak flux density (mJy), format I4
48             --- Bflag [B] for sources near the border (1)
Byte  (49).    --- Flag "E" for significant extension, format A1
Byte  (50).    --- Flag "W" for warning, format A1
Byte  (51).    --- Flag "C" for confusion, format A1
Bytes (53--56).--- Normalized FWHM major axis, format F4.2
Bytes (58--61).--- Normalized FWHM minor axis, format F4.2
Bytes (63--65).--- Fitted major-axis position angle (deg east of north),
                   format I3
Bytes (67--69).--- Local sky level (mJy), format I3
Bytes (71--74).--- Map pixel column number counted from left, format I4
Bytes (76--79).--- Map pixel row number counted from bottom, format I4


Condon, J. J., Broderick, J. J., Seielstad, G. A., Douglas, K., & Gregory, P. C. 1994, AJ, 107, 1829
Gregory, P. C., & Condon, J. J. 1991, ApJS, 75, 1011
Gregory, P. C., Scott, W. K., Douglas, K., & Condon, J. J. 1996, ApJS, submitted
The digital catalogs may be copied by FTP as follows:

     login: anonymous
     password:               (type your full email address here)
     cd pub/gb6              (to access the GB6 public directory)
     ls                      (to list the directory contents)
     get README              (to get a printed copy of this file)
     binary                  (to copy binary files)
     get B1950.gz            (to get the B1950 catalog in compressed form)
     get J2000               (to get the J2000 catalog in uncompressed form)
Compression: The catalogs are stored as text files compressed in GNU zip (gzip) format, the .gz at the end of the name denoting this compression. If you want an uncompressed version, simply omit the ".gz" when requesting the file from ftp. Gzipped files can be uncompressed by "gunzip" which is available for most computer systems. For more details see file pub/nvss/compress.txt. The uncompressed catalog is 6 Mbytes in size; the compressed version is only 2 Mbytes.
If you would like to order the printed catalog or have any questions, comments, or special requests, please contact Jim Condon by e-mail at Internet address "" or by telephone at (804) 296-0322.