II/15 Photometric Measurements in the UBVr 20 System (Magnenat 1973)
Catalogue of Photometric Measurements in the UBVr 20 System
Magnenat P.
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.
See also:
GCPD/69 : The General Catalogue of Photometric Data, maintained
by Lausanne-Geneva
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
mean.dat 80 366 Weighted means for stars in multiple lists
refs.dat 78 32 References to individual lists
codes.txt 80 169 Definition of the coded numbering system
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Byte-by-byte Description of file: obs.dat mean.dat
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Bytes Format Units Label Explanations
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1-11 F11.8 --- LID Coded number (see codes.txt)
12 A1 --- m_LID [D12] Multiplicity code (1)
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_Nobs Remark about Nobs (2)
38-40 I3 --- Nobs [0/29]? Number of measurements
43-49 F7.3 mag Vmag ? V magnitude
76-80 I5 --- ref [9001/9010]? Reference number (see refs.dat)
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Note (1):
D = a multiple system
1 or 2 = only one component of a binary was measured
Note (2):
/ = N is unknown (1 is assumed)
* = N is a minimum number
blank = N is exact
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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2-5 I4 --- ref [9001/9010] Reference number
6-80 A75 --- text Reference (multiline)
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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. =1963ApJ...137.1057S 1963ApJ...137.1057S
Johnson H.L. and Harris D.L.III. =1954ApJ...120..196J 1954ApJ...120..196J
Johnson H.L. and Morgan W.W. =1953ApJ...117..313J 1953ApJ...117..313J
Mermilliod J.Cl., CDS RISP 5
(End) Julie Anne Watko [SSDOO/ADC] 30-May-1996