J/AcA/50/421 OGLE-II DIA BUL_SC1 field (Wozniak, 2000)
Difference Image Analysis of the OGLE-II bulge data. I. The method.
Wozniak P.R.
<Acta Astron., 50, 421 (2000)>
=2000AcA....50..421W 2000AcA....50..421W
ADC_Keywords: Gravitational lensing ; Photometry
Keywords: techniques: photometric - methods: data analysis
Abstract:
We present an implementation of the difference image photometry based
on the Alard and Lupton optimal PSF matching algorithm. The most
important feature distinguishing this method from the ones using
Fourier divisions is that equations are solved in real space and the
knowledge of each PSF is not required for determination of the
convolution kernel. We evaluate the method and software on 380G B of
OGLE-II bulge microlensing data obtained in 1997-1999 observing
seasons. The error distribution is Gaussian to better than 99% with
the amplitude only 17% above the photon noise limit for faint stars.
Over the entire range of the observed magnitudes the resulting scatter
is improved by a factor of 2-3 compared to DoPhot photometry,
currently a standard tool for massive stellar photometry in
microlensing searches. For testing purposes the photometry of approx
4600 candidate variable stars and sample difference image data are
provided for BUL_SC1 field. In the candidate selection process, very
few assumptions have been made about the specific types of flux
variations, which makes this data set well suited for general
variability studies, including the development of the classification
schemes.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 106 4597 *The Bulge-SC1 catalog of candidate variables
detected on difference frames
calib.dat 56 4597 *Calibration data for fluxes
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Note on catalog.dat: Please note that the photometry in this file is a
crude photometry on the reference image without the modeling of the
neighboring stars
Note on calib.dat: The DIA light curves are flux differences between each
frame and the reference frame. The reference flux is sometimes needed.
Therefore I cross-identified DoPhot output with my DIA variables. The
closest match is provided for every variable. Because sometimes the
variable is not detected on the reference image it is not obvious that
the closest match is what actually varied (in some cases definitely
not). That is why I keep it separately and leave it to user's
judgement.
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See also:
J/AcA/51/175 : OGLE-II DIA microlensing events (Wozniak+, 2001)
http://astro.Princeton.EDU/~wozniak/dia/bul_sc1 : All data
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Star sequential number (OGLE BUL-SC1 NNNN)
7- 13 F7.2 pix Xpos X template coordinate (1)
15- 21 F7.2 pix Ypos Y template coordinate (1)
25- 33 F9.3 --- PFlux Flux-profile photometry
38- 42 F5.2 --- e_PFlux error in Flux-profile photometry
46- 54 F9.3 --- AFlux Flux-aperture photometry
59- 63 F5.2 --- e_AFlux error in Flux-aperture photometry
67- 73 F7.3 --- Backg Background
74- 81 F8.2 --- chi2 chi2 per pixel of the PSF fit
(usually a bad fit due to local crowding)
85- 90 F6.3 --- Corr Correlation coefficient with the PSF
94 I1 --- bad Number of bad pixels within the fitting
radius (3.0 pix)
97- 98 I2 --- Var Variability type (2)
100-102 I3 --- Nfr Number of frames used in centroid calculation
106 I1 --- Flag [0/1] Crowding flag (0 - uncrowded)
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Note (1): 0.0 for center of the first pixel
Note (2): 1: transient, 10: continuous variable, 11: both
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Byte-by-byte Description of file: calib.dat
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Bytes Format Units Label Explanations
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1- 4 I4 ---- Seq Star sequential number (OGLE BUL-SC1 NNNN)
9- 16 F8.2 --- rFlux Rough estimate of the reference flux from
DIA catalog
21- 25 F5.2 pix Dist Distance between the variable and the closest
DoPhot star
30- 36 F7.3 mag mag ?=-99.999 DoPhot magnitude of the closest match
40- 47 F8.2 --- ArFlux ?=-1.00 Accurate reference flux (converted from
DoPhot mag)
52- 56 F5.2 --- mag0 Magnitude zero point for that star (same for
all variables in each subframe)
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History:
Copied at http://astro.Princeton.EDU/~wozniak/dia/bul_sc1
(End) Patricia Bauer [CDS] 03-Feb-2003