Astrofísica

Calibración y Eficiencia:

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

V - v₀ = a_v + b_v(B-V)
U - u₀ = a_u + b_u(U-B)
B - b₀ = a_b + b_b(B-V)
R - r₀  = a_r + b_r(V-R)
I  - i₀  = a_i + b_i(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) - k_vX_v,

where k_v and X_v 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:

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