J/PASP/115/413 BVI photometry in the open cluster NGC 6791 (Stetson+, 2003)
Homogeneous photometry. III. A star catalog for the open cluster NGC 6791.
Stetson P.B., Bruntt H., Grundahl F.
<Publ. Astron. Soc. Pac., 115, 413-447 (2003)>
=2003PASP..115..413S 2003PASP..115..413S
ADC_Keywords: Clusters, open ; Photometry, UBVRI ; Photometry, CCD
Abstract:
We present broadband BVI photometry for the open cluster NGC 6791,
based upon analysis of 1764 individual CCD images. Data tables listing
measured magnitudes and standard errors, image-quality indices, a
variability index, and equinox J2000.0 equatorial coordinates for
14,342 stars to V∼24 have been made available to the public through
the services of the Canadian Astronomy Data Centre. Equatorial
coordinates only have been provided for a further 1916 stars, the
photometry for which we were unable to calibrate because of lack of
color information.
Description:
During an eight-night observing run on the 2.5m Nordic Optical
Telescope that took place 2001 July 9-17, we obtained 957 CCD images of
NGC 6791 in the BVI filters (57, 333, and 565 individual exposures,
respectively).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 143 16258 Main data table
crossid.dat 57 10389 Transit table containing star cross-identifications
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See also:
J/PASP/110/533 : BR photometry of Fornax bright stars (Stetson+ 1998)
J/AJ/108/585 : UBVI photometry of NGC 6791 (Montgomery+, 1994)
J/A+AS/114/1 : CCD UBVI photometry of NGC 6791 (Kaluzny+, 1995)
J/AJ/123/3460 : Low-amplitude variables in NGC 6791 (Mochejska+, 2002)
J/AJ/129/656 : Infrared photometry of NGC 6791 (Carney+, 2005)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- SBG Sequential identification number (1)
7- 12 F6.1 pix Xpos X in accompanying image (2)
14- 19 F6.1 pix Ypos Y in accompanying image (2)
21- 26 F6.3 mag Bmag ?=99.999 B-band magnitude
28- 33 F6.4 mag e_Bmag ?=9.9999 σ(B), standard error of the mean
35- 38 I4 --- o_Bmag Number of valid photometric measurements in B
40- 45 F6.3 mag Vmag ?=99.999 V-band magnitude
47- 52 F6.4 mag e_Vmag ?=9.9999 σ(V), standard error of the mean
54- 57 I4 --- o_Vmag Number of valid photometric measurements in V
59- 64 F6.3 mag Imag ?=99.999 I-band magnitude
66- 71 F6.4 mag e_Imag ?=9.9999 σ(I), standard error of the mean
73- 76 I4 --- o_Imag Number of valid photometric measurements in I
79- 84 F6.3 --- chi Mean value of the χ image-quality index (3)
86- 92 F7.3 --- sharp Mean value of the sharp image-quality index (4)
95- 99 F5.2 --- sep ?=99.99 Value of the sep image-isolation index (5)
101-107 F7.3 --- VI Value of the variability index
109-113 F5.1 --- w_VI Weight of the variability index
115-117 I3 h RAh Hour of Right Ascension (J2000.0)
119-120 I2 min RAm Minute of Right Ascension (J2000.0)
122-126 F5.2 s RAs Second of Right Ascension (J2000.0)
128 A1 --- DE- Sign of the Declination (J2000.0)
129-130 I2 deg DEd Degree of Declination (J2000.0)
132-133 I2 arcmin DEm Arcminute of Declination (J2000.0)
135-138 F4.1 arcsec DEs Arcsecond of Declination (J2000.0)
141-144 I4 --- Num Number of images used for the astrometry
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Note (1): Cl* NGC 6791 SBG NNNNN in Simbad
Note (2): Equinox J2000.0, α=19h20min53s, δ=+37°46.5arcmin.
Xpos increases E at 0.5"/pixel and Ypos increases N at 0.5"/pixel
Note (3): The average goodness-of-fit index χ is a dimensionless measure of
the agreement between the perceived brightness profile of any given
object and the model PSF for the frame in which it is measured; it is
essentially the square root of the standard χ2 goodness-of-fit
index, with the fitting residual in each pixel of the profile suitably
weighted by that pixel's expected standard error (derived from readout
and Poisson noise). The perceived range of χ values will tend to
taper inward toward unity at increasingly faint magnitudes.
Note (4): The index sharp is based upon the pixel-by-pixel residuals from the
fitting of the model PSF to the data for any given star, except in
this case it is a measure of the degree to which the negative
brightness residuals are more or less centrally concentrated than the
positive residuals. In essence, it is a first-order estimate of the
intrinsic angular radius of a resolved source; assuming that the PSF
has a characteristic radius sPSF and the measured image profile has
a characteristic radius sobsi, sharp2~|sobs2-sPSF2|.
If sobs>sPSF, then sharp is assigned a positive value and
if sobs<sPSF, then sharp is assigned a negative value.
Note (5): The surface brightness produced by a star of specified apparent
magnitude and centroid position can be determined at any point within
the field. We can evaluate the local surface brightness at the
position of the centroid of that star. At the same time, we can
evaluate and sum up the surface brightnesses produced by all the other
stars in the field at the position of the centroid of the star in
question. The ratio of these two surface brightnesses - the central
surface brightness of the star in question as compared to the summed
surface brightnesses of all other stars in the list evaluated at the
same position - expressed as a magnitude, constitutes our "separation
index" sep. For instance, a computed value sep=5 implies that at its
centroid the star is about 100 times brighter than the summed profiles
of all other stars in the field, and we conclude that the star is
contaminated at a level of ∼1%. Conversely, a value sep<0 implies that
the central surface brightness of the star in question is fainter than
the summed wings of all the other stars at that position, and the
detection is possibly spurious or, at best, a poor measurement of a
badly crowded object.
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Byte-by-byte Description of file: crossid.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- SBG Source name
7- 12 A6 --- K65 Object number in Kinman, T. D.,
1965ApJ...142..655K 1965ApJ...142..655K
14- 15 A2 --- HC Object number in Harris & Canterna
1981AJ.....86.1332H 1981AJ.....86.1332H (1)
17- 19 I3 --- ATT ? Object number in Anthony-Twarog & Twarog
1985ApJ...291..595A 1985ApJ...291..595A (2)
21- 24 I4 --- K90 ? Object number in Kaluzny, J.
1990MNRAS.243..492K 1990MNRAS.243..492K
26- 29 I4 --- KU ? Object number in Kaluzni & Udalski
1992AcA....42...29K 1992AcA....42...29K (3)
31- 33 A3 --- GVZH Object number in Garnavich et al.
1994AJ....107.1097G 1994AJ....107.1097G (4)
35- 38 I4 --- MJP ? Object number in Montgomery et al.
1994, Cat. J/AJ/108/585 (5)
40- 42 A3 --- KUB Object number in Kaluzny & Rucinski
1995, Cat. J/A+AS/114/1 (6)
44- 47 I4 --- KR1 ? Object number in Kaluzny & Rucinski
1995, Cat. J/A+AS/114/1 (7)
49- 53 I5 --- KR2 ? Object number in Kaluzni & Rucinski
1995, Cat. J/A+AS/114/1 (8)
55- 57 A3 --- KR Object number in Mochejska, B. J.
2002, Cat. J/AJ/123/3460 (9)
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Note (1): Cl* NGC 6791 HC SN in Simbad
Note (2): Cl* NGC 6791 ATT NNN
Note (3): Cl* NGC 6791 KU NNNN in Simbad
Note (4): Cl* NGC 6791 GVZH RNN in Simbad
Note (5): Cl* NGC 6791 MJP NNNN
Note (6): Cl* NGC 6791 KU BNN in Simbad
Note (7): Cl* NGC 6791 KR 1-NNNN in Simbad
Note (8): Cl* NGC 6791 KR 2-NNNNN in Simbad
Note (9): Cl* NGC 6791 KR VNN or Cl* NGC 6791 BU BNN in Simbad
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History:
Copied from http://cadcwww.hia.nrc.ca/stetson/NGC6791/
References:
Stetson et al., Paper I, 1998PASP..110..533S 1998PASP..110..533S, Cat. J/PASP/110/533
Stetson, Paper II, 2000PASP..112..925S 2000PASP..112..925S
(End) Marianne Brouty [CDS] 14-Oct-2005