Transformation coefficients (with weights): Rc,Ic measurements

Observed: 7 Jan 2005, 5, 6, 12, 15 Sept 2007

Michel Bonnardeau
9 Oct 2007

Abstract

The transformation coefficients for my telescope and camera and Rc,Ic filters are measured and computed from weighted averages and weighted standard deviations.

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	Rc-Ic range	Tri		Tr		TRi
					value	error	value	error	value	error
0	20050107	L95	14	1.007	0.880	0.047	-0.083	0.009	0.043	0.041
1	20070905	L110 North	8	0.935	0.855	0.005	-0.117	0.001	0.034	0.007
2	20070905	L110 South	9	0.999	0.840	0.003	-0.153	0.004	0.015	0.001
3	20070906	L110 North	8	0.935	0.846	0.004	-0.125	0.001	0.043	0.005
4	20070906	L110 South	9	1.297	0.861	0.005	-0.142	0.001	0.001	0.007
5	20070912	L110 North	8	0.935	0.849	0.005	-0.119	0.001	0.041	0.006
6	20070912	L113	7	0.229	0.739	0.110	-0.173	0.084	0.206	0.141
7	20070912	L95	8	0.524	0.956	0.113	-0.089	0.036	-0.044	0.084
8	20070915	L110 North	6	0.368	0.752	0.037	-0.065	0.030	0.273	0.035

There are 3 subfields for the run 0.

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

R= r+ Tr*Tri*((r-i)-(Ro-Io))
I = R- [(Ro-Io) + Tri*((r-i)-(Ro-Io))]

or

I= i+ TRi*Tri*((r-i)-(Ro-Io))
V = I+ (Ro-Io) + Tri*((r-i)-(Io-Io))

where Ro,Io are the magnitudes of the comparison star and r,i the observed magnitudes of the star being studied. The only coefficients that are useful for the transformations are then Tri, Tr*Tri, TRi*Tri:







The coefficients are fairly stable; the most discrepant measurements are for runs 6 and 8 that have the smallest R-I range. The adopted values and uncertainties are the weighted average values and the weighted standard deviations:


(m

(N the number of runs, Ti the transformation coefficient for run i, deltaTi the uncertainty/error)

Tri = 0.847 +/- 0.009
Tr*Tri = -0.106 +/- 0.010
TRi*Tri = 0.022 +/- 0.011

Technical notes

Telescope and camera configuration.

Computer and software configuration.