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/catalogs/8/8004/

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2. Get the data files via anonymous FTP. (See Note.)

VIII/4        Fourth Cambridge Survey (4C)      (Pilkington+ 1965; Gower+ 1967)
================================================================================
A survey of radio sources between declinations 20 and 40.
     Pilkington J.D.H., Scott P.F.
    <Mem. Roy. Astron. Soc. 69, 183 (1965)>
    =1965MmRAS..69..183P
A survey of radio sources in the declination ranges -07 to 20 and 40 to 80.
     Gower J.F.R., Scott P.F., Wills D.
     <Mem. Roy. Astron. Soc. 71, 49 (1967)>
    =1967MmRAS..71...49G
================================================================================
ADC_Keywords: Surveys; Radio sources

Description:
    The Fourth Cambridge Radio Survey (4C) Catalogue contains all survey
    data from the papers of Pilkington and Scott (1965MmRAS..69..183P) and
    Gower, Scott and Wills (1967MmRAS..71...49G). These data result from a
    survey of radio sources between declinations -07 and +80 degrees using
    the large Cambridge interferometer at 178 MHz. The computerized
    catalog contains for each source the 4C number, 1950 position,
    measured flux density, accuracy class, galactic coordinates, and
    remarks. For some sources miscellaneous brief comments such as cross
    identifications to the 3C catalog or remarks on contamination from
    nearby sources are given at the ends of the data records. A flag (*)
    is included if there are additional remarks in the published catalog.

File Summary:
--------------------------------------------------------------------------------
  FileName      Lrecl  Records   Explanations
--------------------------------------------------------------------------------
ReadMe             80        .   This file
radio4c.dat        72     4844   Fourth Cambridge Radio Survey Data
--------------------------------------------------------------------------------

Byte-by-byte Description of file: radio4c.dat
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  Bytes  Format  Units   Label    Explanations
--------------------------------------------------------------------------------
  1- 8   A8      ---     4C       *The 4C number
 11-12   I2      h       RAh      *Right ascension equinox 1950.0
 14-15   I2      min     RAm      R.A. in minutes
 17-20   F4.1    s       RAs      R.A. in seconds
    23   A1      ---     DE-      Sign of declination equinox 1950.0
 24-25   I2      deg     DEd      Dec.
 27-30   F4.1    arcmin  DEm      Dec.
 34-40   F7.1    Jy      FluxDen  *Flux density (1.0E-26 W/m2/Hz) at 178 MHz
 43-44   I2      ---     ErrClas1 *Position and flux error class (in number)
 48-52   F5.1    deg     GLON     Galactic longitude, System II.
 55-59   F5.1    deg     GLAT     Galactic latitude, System II.
 61-63   A3      ---     ErrClas2 *Position & flux error class (character form)
 65-72   A8      ---     com      *Remarks
--------------------------------------------------------------------------------

Note on 4C:
    The 4C number. The first byte contains the zone sign; the first two
    digits give the zone, while the last two sequentially number the
    source in the zone (there are no sequential numbers over 100). Bytes
    7-8 contain the characters ".1" only for source 4C+25.56.1, which was
    added by Pilkington and Scott (1965MmRAS..69..183P) after publication
    of the catalog.

Note on RAh, RAm, RAs:
    The positions were determined from interference pattern phases (see
    Pilkington and Scott 1965MmRAS..69..183P).

Note on FluxDen:
    See source references for additional information. Byte 40 is blank for
    sources having lower accuracy data.

Note on ErrClas1:
    Numerical code for position and flux density error class. The codes
    having e's and l's plus *'s are assigned the same numerical codes as
    those without the asterisks (i.e. be* = be = 21). The codes are as
    follows:
         1 = a          11 = ae        14 = blank
         2 = b          21 = be        15 = [1]
         3 = c          31 = ce
        13 = a*         12 = al
        23 = b*         22 = bl
        33 = c*         32 = cl
    [1] a special code indicating that a character class is listed in
    the published catalog, but the flux density is from 3C only and is
    enclosed in parentheses.

Note on ErrClas2:
    Position and flux density error class in character form (lower case
    letters) corresponding to numerical code in bytes 43-44. The symbols
    have the following meanings:
    a,b,c:  Error class of source; estimated standard errors for sources
            in various ranges of flux density are given in Tables II and
            III of the respective source references.
    e:      Possible right ascension lobe-shift earlier.
            The magnitude of the lobe shift for each 1 degree interval is
            given in Tables I of the source references.
    l:      Possible right ascension lobe-shift later.
    *:      The source is confused by a weaker uncatalogued one.  The
            weaker source will usually lie within 30' and have a flux
            density at least 1/3 of the main source. The quoted error
            class for each source includes the effect of such
            confusing sources.

Note on com:
    Remarks. Only cross identifications to the Revised 3C Catalogue
    (Bennett 1962MmRAS..68..163B) are actually given in the remarks field;
    however, additional remarks given in the published catalog, for which
    there is insufficient room in the 8-byte field, are indicated by an
    asterisk. Asterisks can occur alone or with 3C numbers.
--------------------------------------------------------------------------------

Remarks and Modifications:
    The machine-readable version of the 4C catalog was received on
    magnetic tape from Dr. G. G. Pooley of Mullard Radio Astronomy
    Observatory, Cambridge on 1 March 1983. As received, the file
    consisted of 80-byte card images with a blank record following every
    fifth data record. The following modifications were made so that the
    data structures conform more closely to those of other computerized
    catalogs and so that the data are easier to process and to interpret.

    1. Blank records, clearly a problem for data processing, searching and
       sorting, were removed.

    2. The 4C numbers in the machine file were written as positive and
       negative integers (e.g. 7901, -105, -7) rather than as real numbers
       in the form +/-xx.xx, as they are normally written in the literature.
       The integers were converted to the present form.

    3. Negative declinations had minus signs on both degrees and minutes.
       The latter were removed, while minus signs were moved to all occur
       in byte 23 and plus signs were added for positive declinations
       (previously blank). Signs were also moved or added to byte 55 in the
       Galactic latitude field. Preceding zeros were added to these fields
       to make uniform numbers.

    4. The file was sorted by 4C number to correspond exactly with the
        published catalog. The error classes (in character form) and
        remarks were keyed to a separate data set on disk. After interval
        checks throughout the then 4843 records, the newly keyed records
        were added to the original data set. The numerical and character
        coded classes should be equivalent in all cases. The file was then
        resorted by 4C number, South to North.

    5. There were only 3623 sources in the printed 1967 catalog, while
       3624 records are contained in the machine version. Source 4C+48.61,
       found in the machine catalog, is missing from the published version.
       The character class for 4C+48.61(a) was obtained from the machine
       version and inserted. The source 4C+25.56.1, added as an addendum
       to the 1965 publication, was in the machine version as a duplicate
       of 4C+25.56. The ".1" was added to the 4C number (bytes 7-8) for
       this record.

    6. The logical record length was changed from 80 bytes to 72 bytes,
       since bytes 72-80 were never used.

    7. Numerical codes for 4C-02.07, 4C+21.19 and 4C+29.58 did not agree
       with the published catalog, so they were corrected in the machine
       version. The character and numerical codes have not been checked
       entirely, so additional disagreements may be found. In these cases,
       reference should be made to the source papers.

    8. Some sources having numerical class code 14 were found to have
       non-blank character codes in the published catalog. These sources
       have only 3C flux densities enclosed in parentheses. To distinguish
       them from published sources with blank class codes, a new numerical
       code of 15 was defined and added to the appropriate records.

Acknowledgements:
  The original ADC documentation by Wayne H. Warren, Jr. (1983) was used
  to create this ReadMe file.

History:
  * 27-Aug-2001: Declination of 4C+16.12 corrected, thanks to E. Davoust
  * 03-Sep-2001: 3C counterpart of 4C+02.41 changed to 3C327 (ibid)

References:
  Bennett, A. S. 1962, Mem. Roy. Astron. Soc. 68, 163 (1962MmRAS..68..163B)
  Gower, J. F. R., Scott, P. F. and Wills D. 1967, Mem. Roy. Astron. Soc.
    71, 49. (1967MmRAS..71...49G)
  Pilkington, J. D. H. and Scott, P. F. 1965, Mem. Roy. Astron. Soc. 69, 183.
    (1965MmRAS..69..183P)
================================================================================
(End)                      C.-H. Joseph Lyu [Hughes STX/NASA]        02-Apr-1996