Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/docs/documents/Appendix/omphot_jan01/igor_vg/vg1.ps.gz Дата изменения: Tue Jan 9 12:35:53 2001 Дата индексирования: Sat Dec 22 15:36:04 2007 Кодировка: Поисковые слова: туманность андромеды

Photometric calibration based on ground based observations
Current status
Important: current ground based observations are in the WFI natural system!
The OM frames currently used in UBV calibration:
Field/Filter u b v
EXO 0748-67 1 2 5
Abell 2690 1 1 1
BPM 16274 1 1 1
G158-100 1 1 1
The eld GD153 is reduced but not included yet. Comparing to the initial
transformation based on the EXO 0748-67 eld, the number of stars upon which
the transformation is based increased as follows:
U: 67 ! 101
B,V: 106 ! 157
The transformation formulae have changed insignicantly:
U-u = -6.513 - 0.134*(u-b) (old)
0.034 0.032
U-u = -6.502 - 0.143*(u-b) (new)
0.045 0.042
----------------------------------------------------
B-b = -5.876 - 0.370*(b-v) (old)
0.012 0.023
B-b = -5.850 - 0.356*(b-v) (new)
0.008 0.017
----------------------------------------------------
V-v = -6.976 + 0.098*(b-v) (old)
0.013 0.025
V-v = -6.992 + 0.049*(b-v) (new)
0.007 0.012

SAS photometry
1.Raw cts measurement.
Allow for a circular aperture.
The user should be able to specify a circular aperture of a given raduis. If the
default raduis (currently 6 arcsec) is chosen then proceed with the coincidence
loss correction. Put the value of the default radius into the CCF. If non-default
radius is chosen the task must scale the ux measured within this aperture to
the default aperture using the information about the PSF. PSF shape should
be a function of the star brightness and coordinates.
Think about implementation a PSF-tting mode for crowded elds? If stel-
lar objects of interest have optical companions close than 1/2 FWHM of the
PSF the aperture photometry will fail. Or just let the user to use external
software like daophot? Then the user should be allowed to extract the PSF,
the coincidence loss correction function and other necessary information in a
form suitable for using with the external package (or in a form allowing the
necessary conversion - ascii being the simplest and best?).
2.Coincidence loss correction.
Use the empirical formulae.
At the moment, the theoretical formula is being used. I'd suggest to allow
the user to choose between 2 options: (i)use theoretical formula; (ii)use the
empirical formula (the default). (i) is simply because it is already coded in;
who knows, maybe it will be of some use :) As for the empirical formula, put
its parameters into the CCF le.
3.Instrumental magnitude.
Seems ok.
4.Colour transformation.
Change the transforamtion formulae for the colours? Allow for more than one
transformation per a colour range?
No reason to use the second-order xed transformation. No reason to write
the transformations in the Harris et al.-like style. I suggest the following re-
placement for (14) and (15) in CAL omGetColorTrans:
n
MAG1-MAG2 = sum k(i)*(mag1-mag2)**i (14)
i=0
n
MAG2 = sum l(i)*(mag1-mag2)**i +mag2 (15)
i=0