Handling of magnitude systems

The handling of magnitude systems was a bit confuse in version 2.0. We now use (for versions >=2.2) a more comprehensive scheme. In fitmodel.card, each magnitude system is identified by a key referencing a description file in the data directory. For instance, @VEGA MagSys/BD17-snls3.dat As for previous versions, the key has to be mentionned in the light curves, along with the instrument name and the pass band. For instance,

@MAGSYS VEGA

The description file contains the path to a calibrated spectrum of a reference star ( in ergs/s/cm2/A), and a list of magnitudes for this star for various instruments and pass-bands. For instance, BD17-snls3.dat contains:

# 2009 release of CALSPEC 
@SPECTRUM MagSys/bd_17d4708_stisnic_002.ascii
# Magnitudes in the Landolt system : Landolt & Uomoto (2007)
STANDARD U 9.724
STANDARD B 9.907
STANDARD V 9.464
STANDARD R 9.166
STANDARD I 8.846

# Magnitudes in the Megacam local natural system : Regnault et al (2009), Table 7
MEGACAM u 9.7688 # annexe papier calib08
MEGACAM g 9.6906
MEGACAM r 9.2183
MEGACAM i 8.9142
MEGACAM z 8.7736

The labels for instruments has to be the same as in the fitmodel.card file: @STANDARD Instruments/SNLS3-Landolt-model The pass bands have to match those in the instrument filter wheel file.

In $PATHMODEL/Instruments/SNLS3-Landolt-model/instrument.cards

...
@FILTERS FilterWheel
...

In $PATHMODEL/Instruments/SNLS3-Landolt-model/FilterWheel

U U_bessel sux-shifted.dat
B B_bessel sb-shifted.dat
V V_bessel sv-shifted.dat
R R_bessel sr-shifted.dat
I I_bessel si-shifted.dat

The only exception is the AB magnitude system which directly implemented in the C++ code.