J and H Band Color Transformation

Introduction
To produce quality data from your J and H band observations and to allow your data to be combined with data obtained by others, your observational data must be reduced to the Standard System using calibrated color coefficients for your instrumentation.

J and H Band Filter Responses

J Band response 1170 - 1340 nm
H Band response 1500 - 1780 nm

Objective

To determine r (J band color transformation coefficient) and l ((J - H) color transformation coefficient).

Note: Some books use epsilon and mu for the color transformation coefficients for J and (J - H) bands. Because the symbols are used in the UBV bands the symbols rho and lambda are used in this paper for the color transformation coefficients for J and (J - H) respectively. Determining the color transformation coefficients and zero points depends on using the equation for a straight line Y = MX + B where M is the slope and B is the Y intercept ( point where line croses the Y axis when X = 0.

The key is to get the coefficient equations in the form of Y= MX + B.

Use stars that have a wide range of (J - H). Try to observe the stars as close to the zenith as possible.

Measure multiple stars close to the zentih that have a wide range of (J - H) values . The values j and h are raw instrurmental magnitudes.

Note: Corrected counts are counts normalized to 1 second integration and unity gain. Sky readings have been subtracted.

Note: Air Mass X of each observation must be determined. Determining air mass is somewhat involved and covered in another white paper.

For each star:

j = - 2.5 log10 (J corrected counts) Equation 1
h= - 2.5 log10 (H corrected counts) Equation 2

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Present Page Version as of 1 November 2006

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