Документ взят из кэша поисковой машины. Адрес оригинального документа : http://xmm.vilspa.esa.es/docs/documents/CAL-SRN-0195-1-0.ps.gz Дата изменения: Fri Sep 30 18:43:51 2005 Дата индексирования: Mon Oct 1 22:36:38 2012 Кодировка: Поисковые слова: п п п п п п п п п п п п п п п п п п п п п п п п п п п п

XMM-Newton CCF Release Note
XMM-CCF-REL-195
OM Photometry:
Zero points, AB System and ux conversion factors
A. Talavera
September 19, 2005
1 CCF components
Name of CCF VALDATE List of Blocks
changed
CAL VERSION XSCS ag
OM COLORTRANS 0010 2000-01-01T00:00:00 Header keywords No
2 Changes
The zero points used to compute the magnitudes in OM aperture photometry are given as keywords
contained in the FITS header of the OM COLORTRANS CCF. These values have been recomputed
taken into consideration two recently implemented corrections in the OM data processing by SAS:
the point spread function for the OM UV lters and the time sensitivity degradation correction.
The corresponding ZPTlter keywords have been updated.
A widely used magnitude system, AB magnitude, has been dened for OM. Its corresponding
zero points have been included as keywords as well, ABM0lter.Flux conversion factors have been
dened within the AB system. They allow the user to convert the count rates derived by SAS
into uxes at the eective wavelength of each lter. These conversion factors, ABF0lter,are new
keywords in the header of OM COLORTRANS 0010.CCF.
Finally, the existing ux conversion factors FCFlter, based in the observations of white dwarfs
standard stars, have also been updated taken into consideration the PSF correction for UV lters
and the time sensitivity degradation correction..
1

XMM-Newton CCF Release XMM-CCF-REL-195 Page: 2
3 Scientic Impact of this Update
The OM photometric system is now better than before, since it takes into consideration and applies
corrections for more eects present in the OM data.
In addition the newly implemented (SAS 6.5) AB system will allow the users to compare their
data with other instruments, since is usage is becoming more extended.
4 Estimated Scientic Quality
As it was pointed out before, OM photometry improves with these new reference values, which
include more and better corrections to the obtained data.
5 Test procedures
Whenever we make a change or update in the OM photometric calibration, the test procedure
consists in reprocessing some data sets for which we have also calibrated ground based observations.
Some of those correspond to what is known as standard elds. This is applicable to the OM optical
lters (U, B, V).
In the UV (OM lters UVW1, UVM2, UVW2) there is no standard photometric system. There-
fore we have compared OM AB magnitudes of several stars (some of them spectrophotometric
standards) with data from the literature.
6 Summary of the test results
In next table we can see the comparison of OM AB magnitudes with some other determinations for
several stars. It should be noted that in spite that an exact comparison is impossible because the
lters are not equal in the dierent systems, the OM values agree very well with other sources.
HZ2
OM filter lambda AB_OM AB_Oke 1974
U 3440. 13.6605 13.74
B 4500. 13.6567 13.72
V 5430. 13.8325 14.04
LBB227
OM filter lambda AB_OM AB_Oke 1974

XMM-Newton CCF Release XMM-CCF-REL-195 Page: 3
V 5430. 15.2684 15.24
G93-48
OM filter lambda AB_OM Galex(2271A)
UVW2 2120. 12.3650
UVM2 2310. 12.3820 12.39
UVW1 2910. 12.5384
HZ43
OM filter lambda AB_OM Galex(2271A)
UVW2 2120. 11.2396
UVM2 2310. -- 11.36
UVW1 2910. 12.7067
BD+33 2642
OM filter lambda AB_OM Galex(2271A)
UVW2 2120. 10.4329
UVM2 2310. 10.4522 10.47
UVW1 2910. 10.3756
7 Expected updates
No updates are expected in the near future.