MBCAA Observatory

Transformation coefficients: V, Rc measurements

Observed: 24 Dec 2006, 12 Jan, 19 July, 5 Aug, 5, 6, 12, 15 Sept 2007

Michel Bonnardeau
18 Sept 2007

Abstract

The transformation coefficients for my telescope and camera and V,Rc filters are measured.

Introduction

For an introduction to transformation equations and coefficients for differential photometry, see HERE.

The transformation coefficients for my telescope and camera and V,Rc filters are derived by multiple observations of Landolt's fields (1992, VizieR II/183A), spanning over several nights. The stability of these coefficients can then be assessed.

Observations

Run Session Field Nb of
stars
V-Rc
range
Tvr Cvr Tv Cv Tr Cr
0 20061224 L98 8 0.607 1.118 -0.053 -0.050 0.001 -0.143 0.042
1 20070112 L95 9 0.663 1.026 -0.022 -0.014 0.017 -0.041 0.039
2 20070719 L110 7 1.038 1.154 -0.079 0.041 -0.042 -0.111 0.038
3 20070805 L111 3 0.730 1.135 -0.090 -0.054 0.042 -0.173 0.121
4 20070905 L110 North 8 1.038 1.105 -0.054 0.004 -0.010 -0.107 0.049
5 20070905 L110 South 9 1.148 1.157 -0.144 0.006 -0.049 -0.145 0.084
6 20070906 L110 North 8 1.038 1.105 -0.075 -0.008 -0.012 -0.115 0.063
7 20070906 L110 South 9 0.999 1.131 -0.141 -0.001 -0.103 -0.132 0.031
8 20070912 L110 North 8 1.038 1.132 -0.096 0.021 -0.030 -0.109 0.063
9 20070912 L113 7 0.362 0.979 0.006 -0.116 0.038 -0.049 0.012
10 20070912 L95 8 0.644 1.097 -0.062 0.005 0.004 -0.085 0.061
11 20070915 L110 North 6 0.462 1.184 -0.091 0.071 -0.048 -0.073 0.024

There is only one subfield observed per session, except for 20070112 which has 2 subfields.

The transformed V,R magnitudes of the star being studied are computed the following way:

V = v + Tv*Tvr*((v-r)-(Vo-Ro))
R = V - [(Vo-Ro) + Tvr*((v-r)-(Vo-Ro))]

or

R = r + Tr*Tvr*((v-r)-(Vo-Ro))
V = R + (Vo-Ro) + Tvr*((v-r)-(Vo-Ro))

where Vo,Ro are the magnitudes of the comparison star and v,r the observed magnitudes of the star being studied. The only coefficients that are useful for the transformations are then Tvr, Tv*Tvr, Tr*Tvr:







The coefficients are fairly stable. The adopted values and uncertainties are the average values and the standard deviations:

Tvr = 1.110 +/- 0.057
Tv*Tvr = -0.007 +/- 0.052
Tr*Tvr = -0.120 +/- 0.047

Technical notes

Telescope and camera configuration.

Computer and software configuration.



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