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II/15       Photometric Measurements in the UBVr 20 System (Magnenat 1973)
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Catalogue of Photometric Measurements in the UBVr 20 System
    Magnenat P.
    <CDS Internal Report No. 6 (1973)>
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ADC_Keywords: Photometry, UBVr20; Colors

Description:
   In the UBVr photometric system defined by Sandage and Smith (1963), (U-B)20,
   (B-V)20, and (V-r)20 color indices are given for stars from ten reference 
   lists, along with a LID coded number, V magnitude, number of observations and
   reference. A list of weighted means is included for stars appearing on
   more than one list. The reference list and an explanation of the coded
   numbering system are included in separate files.

Introduction:
   The UBVr system is defined by Sandage and Smith (1963). The then recent 
   availability of photomultipliers with S20 cathodes sensitive to the 
   wavelength range 3000 to 8000 A suggested that the customary tricolor
   photometric system could be extended to include a red point close to 6700 A.
   The V-r color index can be employed as a good indicator of effective
   temperature, thanks to its relatively small blanketing effect, compared to
   B-V.

   Sandage and Smith also tried to obtain the U, B and V colors as closely as
   possible to those of Johnson and Morgan's system. In 1960, 64 standard 
   stars of the UBV system (Johnson and Morgan 1953; Johnson and Harris 1954)
   were measured. Comparison of colors obtained in the natural photometric
   system ubvr 20 with colors from Johnson, Morgan and Harris give:

     B-V =   1.100(b-v)20 +   1.023 
          +/-0.004         +-/0.003

     U-B =   1.015(u-b)20 -   1.575
          +/-0.003         +/-0.006    (Sandage and Smith 1963)

   These equations show that the UBVr 20 system is close to the UBV system
   without being identical.

   Means were calculated for stars appearing in multiple references according 
   to the customary manner at CDS, based on the number of measures and the 
   weight of each list. All ten lists were given weight 4.

File Summary:
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 FileName     Lrecl  Records   Explanations
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ReadMe           80        .   This file
obs.dat          80      418   Observations of UBVr 20 colors
wtdmns.dat       80      366   Weighted means for stars in multiple lists
refs.dat         80       42   References to individual lists
codes.dat        80      169   Definition of the coded numbering system
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Byte-by-byte Description of file: obs.dat, wtdmns.dat
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   Bytes Format  Units   Label    Explanations
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   1- 11  F11.8  ---     LID     *Coded number             (see codes.dat)
      12  A1     ---     rem     *Remark
  13- 18  F6.3   mag     U-B20   *? (U-B)20 index
  21- 26  F6.3   mag     B-V20   *? (B-V)20 index
  29- 34  F6.3   mag     V-r20    (V-r)20 index
      37  A1     ---     n_N     *Remark about N           (obs.dat only)
  38- 40  I3     ---     N        ? Number of measurements (obs.dat only)
  43- 49  F7.3   mag     V        ? V magnitude
  76- 80  I5     ---     ref      ? Reference number       (see refs.dat)
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Note on LID:
   Defined in J.Cl. Mermilliod, CDS RISP 5 (see codes.dat)

Note on rem:
   D      = a multiple system
   1 or 2 = only one component of a binary was measured

Note on U-B20:
Note on B-V20:
   If either field is empty, that signifies that the star was not measured on
     the filters in question.

Note on n_N:
   /     = N is unknown (1 is assumed)
   *     = N is a minimum number
   blank = N is exact

Byte-by-byte Description of file: refs.dat
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   Bytes Format  Units   Label    Explanations
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   2-  3  I2     ---     ref      ? Reference number
   6- 80  A75    ---     text     Reference (multiline)
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Byte-by-byte Description of file: codes.dat
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   Bytes Format  Units   Label    Explanations
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   1- 80  A80    ---     text    *Definition of the coded numbering system
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Note on text:
   ampersands "&" in data files have been changed to "+"

Acknowledgement:
   The text of the introduction is taken from P. Magnenat [CDS], translated 
   from French to English by J.A. Watko [SSDOO/ADC].

References:
   Sandage A. and Smith L. 1963, Astrophys. J., 137, 1057.
   Johnson H.L. and Harris D.L.III. 1954, Astrophys. J., 120, 196.
   Johnson H.L. and Morgan W.W. 1953, Astrophys. J., 117, 313.
   Mermilliod J.Cl., CDS RISP 5
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(End)                                  Julie Anne Watko [SSDOO/ADC]  30-MAY-1996