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Calibración y Eficiencia 

M67 Dipper Asterism stars are used to calibrate the UBVRI filter set. The following set of equations are used:

V - v0 = av + bv(B-V)
U - u0 = au + bu(U-B)
B - b0 = ab + bb(B-V)
R - r0  = ar + br(V-R)
I  - i0  = ai + bi(V-I)

where UBVRI are standard magnitudes of Chevalier, C & Ilovaisky, S.A. 1991, (A& AS, 90, 225) (U from ...). v0, u0, b0, r0  and i0 are extinction corrected instrumental magnitudes defined as

v0 = -2.5log10(counts/sec) - kvXv,

where kv and Xv are extinction coefficient and airmass for the V-band image.

a and b are the "zeropoint" and "color coefficient" respectively. Zeropoint is defined as the magnitude that gives 1 count/sec (or equivalently 1.85 e-/sec) in the system for a star of zero color (A0). The derived values of the coefficients are given in the following table:

 

Transformation coefficients of the UBVRI filter set
Filter a b Eta (%)
V 23.77 0.0715 14.5
B 23.24 -0.1368 6.8
R 22.91 -0.2859 22.6
I 23.33 0.0257 8.0
U 21.04    

Eta in the table is the net efficiency of the system; Eta = Etatel*Etafil*EtaCCD (see McLean 1989 Textbook Electronic and Computer Aided Astronony for details).

 


Last Update:
26-11-2008 a las 16:25 by

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