YALO Optical Color Terms
Summary of YALO optical color terms
I use tranformations of the form used by Stetson's CCDSTD program:
O1 = M1 + A0 + A1*I2 + A2*X + A3*T
O2 = M2 + B0 + B1*I2 + B2*X + B3*T
O3 = M3 + C0 + C1*I3 + C2*X + C3*T
O4 = M4 + D0 + D1*I4 + D2*X + D3*T
A3=0.
B3=0.
C3=0.
D3=0.
where X=airmass, T=UT time during the night, I= library index (B-V,V-R, V-I) etc), M= library magnitude (B,V,R,I), and O= observed aperture magnitude.
Put another way, I am solving the following multi-linear equations for the coeffs A0,A1,A2,A3,B0, etc where bvri are the observed mags and BVRI are the tabulated ones:
b_obs = f(B,B-V,X,T)
v_obs = f(V,B-V,X,T)
r_obs = f(R,V-R,X,T)
i_obs = f(I,V-I,X,T)
Thus, if A1 = -0.05, then
b_obs = b0 + B + -0.05*(B-V)
where b_obs is the observed magnitude on the natural system (aperture mag), b0 is the zero-point of the fit (not given here), and B/B-V are the library values of the transformation.
1998
Data taken on three nights, 24/5 - 26/7 Jan 1998
Only 24/5 was really photometric. I reduced the data using a cloudy solution that just calculates the color terms.
A1 = -0.086 0.005 <<
B1 = 0.025 0.005 <<
C1 = -0.403 0.009 << ** Old R filter
D1 = 0.051 0.005 <<
2000
I had data from 7 nights: feb04,feb05,feb06,feb07,feb09,feb11 (all 2000).
Six nights were photometric. New R filter.
The following are the average between the absolute reductions and the cloudy reductions:
A1 = -0.061 0.005
B1 = +0.022 0.005
C1 = -0.017 0.009
D1 = +0.047 0.005
2001
Data taken on feb03,feb04,feb05
feb03 and 05 were photometric and I reduced the data absolutely. Feb04
was not and I used a cloudy solution.
The averaged color terms are:
A1 = -0.079 0.005
B1 = +0.018 0.005
C1 = -0.030 0.005
D1 = +0.045 0.005
The B color term has changed by slightly more than I would have expected.
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