INAOE | Astrophysics | Observatories | OAGH | Direct Imaging Camera | Calibration and Efficiency

Calibración y Eficiencia

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

V - v_{0} = a_{v} + b_{v}(B-V)

U - u_{0} = a_{u} + b_{u}(U-B)

B - b_{0} = a_{b} + b_{b}(B-V)

R - r_{0} = a_{r} + b_{r}(V-R)

I - i_{0} = a_{i} + b_{i}(V-I)

where UBVRI are standard magnitudes of Chevalier, C & Ilovaisky, S.A. 1991, (A& AS, 90, 225) (U from ...). v_{0}, u_{0}, b_{0}, r_{0} and i_{0} are extinction corrected instrumental magnitudes defined as

v_{0} = -2.5log10(counts/sec) - k_{v}X_{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:

Transformation coefficients of the UBVRI filter set | |||
---|---|---|---|

Filter | a | b | Eta (%) |

V |
23.77 | 0.0715 | 14.5 |

B |
23.24 | -0.1368 | 6.8 |

R |
22.91 | -0.2859 | 22.6 |

I |
23.33 | 0.0257 | 8.0 |

U |
21.04 |

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).

Last Update:

26-11-2008 a las 16:25 by

26-11-2008 a las 16:25 by

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