of BATC Photomeric System
magnitude of standard stars
||8, Running program
The information from head of image
|4, Extinction curve
||10, Test by TA03 field
of the extinction
||11, New TEST Quality of calibration
by TA03 field
of variation of extinction
||12, diferencial check of standard
Because left of Zheng Zhong-yuan and I am not familiar with
system of IRAF, we need to develop a new software to treat the data of
photometric night used for BATC flux calibration. The method
1, BATC magnitude of
4 standard star of Oke & Gunn(1983) are used for BATC flux calibration.
They are: BD+17d4708, BD+26d2606, HD19445, and
HD84937. The absolute fluxes of these stars are taken from Fukugita
et al.(1996). The definition of BATC magnitude and the method for get the
magnitudes from absolute flux was described by Yan et al. (1999). Table
1 of gives the magnitude of the 4 standards (Yan et al. 1999).
As we done before (Yan,1999), a radius of 15 pixel aperture is used for
make aperture photometry. Bertin's photometric code, Source Extractor is
used for calculation. The parameter set are listed in dingbiao.set. The
file bindbiao.param gives the contents in output catalogs "dingbiao.cat".
Note: The output catalogue "dingbiao.cat" is a temporary file, it is deleted
after it being used. In the output catalog, the central brightest star
is regard as standard stars. It will be used for comparing with standard
BATC magnitude of standards. Before do that, the instrumental magnitudes
are normalized to the magnitude with exposure time of 300 second.
3, The information
from head of image
By reading head of the image treated, we can get coordinates (RA and DEC),
observation date and time and exposure duration. The RA, DEC and observing
time are used for calculate the Air mass of the image. exposure time is
used for normalize the instrumental magnitude.
4, Extinction curve
The diagrams of magnitude vs airmass shows the extinction curves. The magnitude
is the difference of instrumental magnitude M_inst and BATC magnitude of
By fitting a straight line we can get the extinction coefficient of
the filter K and the instrumental zero point:
M_inst-M_batc = K X + C
here X is airmass of the image.
K and C is derived by median fitting of the data points with straight
line. A program from Numerical Recipe, "medfit" is used for fitting.
5, Variation of the extinction
As supposed the changing of the instrumental zero point is very small within
a short time (in scale of few hours), the main variation in calibration
with time is variation of the weather. We need a time dependent item to
trace the variation of the condition of the earth atmosphere. As our previous
works, a correction on zero point C, named f(ut) was used. It independent
from airmass and color of the filters bands. It can be regard as mean variation
of all possible reason with the time. As shown in paper of Yan et al.(1999),
it can much reduce the fitting error and gives K and C good enough for
In my present work, for make things better, I considered the difference
of wavelength and airmass. I use a variation item on extinction coefficient
K instead of zero point. Two kind of variation is given in my programs.
One is variation of the extinction coefficient of single filter band dK_band.
the other is mean variation of all filter bands, dk_mean.
6, Fitting of variation
Different from we have done before, I used a smoothed continue curve to
trace the variation instead of several jointed straight lines. Each fit
point is the mean value of all observing points with 2 hours. I give a
higher weight to nearby points in time.
here T_fit is fitting time point and T_obs is times of each observation
point. They are in unit of hour.
A good trace of extinction variation need a set of good estimation of mean
extinction coefficient K and instrumental zero point C. And a good estimation
of K and C need information of the variation. Few iterations are done on
determination of K, C and variation. Fortunately, almost all the nights,
the iteration can be convergent within 4 iterations. For security, 10 iterations
are run before stop.
8, Running program
Two similar codes, dingbiao_ds and dingbiao_qs
are used for situation of single band variation and mean variation respectively.
Here we use dingbiao_ds to show how to use
the two codes.
Tape dingbiao_ds without any arguments,
we can see a simple one line help:
This shows the 4 function of the program. The program can distinct the
different functions by the input arguments.
i, Read original data and make calculation of K, C and variation
dingbiao_ds image-directory figur-format
there are two argument in this case. The first is the directory where
the piplined images locate. The another argument is figure display window
or output figure format. There 3 kind of format usually used:
xw : output the figures to a new x-window
gif : Output figure in gif format same
as the figure files of this web page.
ps : Output the figures as postscript
files. It can be used for printing or called by latex. If "xw"
is selected, we need to click the figure window to change figure and go
to next step of calculation. The intermediate result are written in file
of result.dat and stdxxxx.dat.
xxxx is Julian date of the observation.
First column is the filter name. The second column is time of the image
in UT. The third column is airmass and the 4'th column is differential
magnitude between instrumental and BATC standard magnitude.
ii, Checking the Processing and the Result
For checking, several figures will shown during calculation. We can also
check again the calculation from result of photometry "result.dat"
dingbiao_ds plot figure-format
In this case only figure-format can be changed. Five kind of figure are
shown during the calculation.
First figure is primary fitting of extinction curves (figures/pf11127.gif)
Second figure is variation of extinction on zero point as f(ut) of Yan(1999)
Third figure is variation of extinction processed (figures/rK91127.gif)
The 4'th figure is variation of extinction with fitting curve (figures/rKf91127.gif)
the Last figure is the next fitting of extinction curve (figures/nf91127.gif)
In the same time of figure showing, the result of calculation of each
iteration is listed.
iii, Get K and C of indicated filter and time
From the result of photometry stdxxxx.dat
(again, xxxx is Julian date), we make calculation and give the extinction
coefficient and the zero point of indicated filter band and time (in UT).
dingbiao_ds filter-band Julian-date UT
Still, used JD1127 as an example. After run:
dingbiao_ds d 1127 16.35
iv, Get calibrated magnitude
By the given parameters of filter band, Julian date, observing time (UT),
airmass, exposure time and instrumental magnitude, the program can give
the calibrated magnitude.
dingbiao_ds Filter J.day U.T. AirMs Exposur M_inst
Again, used JD1127 as an example. After run:
dingbiao_ds d 1127 16.35 1.20 600 17.3
we get "M_batc" as calibrated magnitude :
By using the new calibration codes, I have checked all the BATC data CDs.
There are 77 days from JD0 9648 to JD1 1525 make standard observations.
(The period is 11525-9648=1877days or 15/year). From these 77 days data,
I found 58 days (about 12/year) are useful for BATC calibration by using
code "dingbiao_ds" and "dingbiao_qs". All good days are listed in following
table. By click on day of the table, we can find the figures of the fitting.
There are 1849 image of BATC field were obtained during these 58 photometric
nights. I get the zero magnitude ( M_zero ) and fitting error (RMS) for
all these images. The result are listed in img2cali.dat
. The zero magnitude means the BATC magnitude for a star of 0 instrumental
A program developed for do this work:
Separately, there are two table for TA03 field
and T329 field.
10, Test by TA03 field
TA03 field was used for check new codes by JIANG
Zhao-ji. His works were done in following steps:
1, Combine the TA03 field images band by band. The result is 15 combined
images of 15 color.
2, Use BATC pip2 to make photometry with method of PSF fitting. We obtained
3, Make aperture photometry on all the images obtained during the photometric
nights. We got magnitude of total flux with aperture magnitude and a growth
curve of the image, M_ap. Only isolate, non saturated bright star are measured.
4, Star by star, we got a mean magnitude difference between combined image
and single image of photometric night. M_pip2-ap.
5, We check the value of M_pip2-ap-Mag_zero of all single photometric night
images. It should be equal to a common constant.
M_pip2-ap-Mag_zero is zero magnitude of combined