Transformation coefficients: V,Ic measurements

Observed: 5, 6, 12, 15 Sept 2007

Michel Bonnardeau
18 Sept 2007
Revised 27 Sept 2007

Abstract

The transformation coefficients for my telescope and camera and V,Ic 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,Ic 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-Ic range	Tvi	Cvi	TIv	CIv	Ti	Ci
0	20070905	L110 North	8	1.973	0.97	0.086	0.004	-0.012	0.015	-0.075
1	20070905	L110 South	9	2.147	0.983	0.033	0.004	-0.051	0.006	-0.061
2	20070906	L110 North	8	1.973	0.961	0.081	-0.001	-0.015	0.018	-0.072
3	20070906	L110 South	9	2.154	0.985	0.086	-0.002	-0.101	0.004	-0.173
4	20070912	L110 North	8	1.973	0.977	0.056	0.014	-0.033	0.017	-0.062
5	20070912	L113	7	0.591	0.862	0.110	-0.080	0.058	0.110	-0.098
6	20070912	L95	8	1.168	1.021	0.003	0.003	0.004	-0.021	0.001
7	20070915	L110 North	6	0.830	0.931	0.102	0.042	-0.053	0.131	-0.174

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

V = v + TIv*Tvi*((v-i)-(Vo-Io))
I = V - [(Vo-Io) + Tvi*((v-i)-(Vo-Io))]

or

I= i+ Ti*Tvi*((v-i)-(Vo-Io))
V = I+ (Vo-Io) + Tvi*((v-i)-(Vo-Io))

where Vo,Io are the magnitudes of the comparison star and v,i the observed magnitudes of the star being studied. The only coefficients that are useful for the transformations are then Tvi, TIv*Tvi, Ti*Tvi:







The coefficients are fairly stable; the most discrepant measurements are for runs 5 and 7 that have the smallest V-I range. The adopted values and uncertainties are the average values and the standard deviations:

Tvi = 0.961 +/- 0.047
TIv*Tvi = -0.001 +/- 0.030
Ti*Tvi = 0.032 +/- 0.049

Technical notes

Telescope and camera configuration.

Computer and software configuration.