COLOR GRADIENTS IN GALAXIES - USE OF A SMALL AREA DETECTOR

A method is described which enables objective quantitative information on color gradients to be obtained using a small area detector such as a CCD, without any knowledge of the background sky level. The technique relies on the linearity of the data. The color gradient is estimated by means of the curvature in an I(lambda1) VS I(lambda2) diagram. A completely model independent observable is described, as well as a versatile and robust parameterization. We demonstrate consistency with traditional analysis procedures and provide transformations between different systems. Traditional methods result in uncertainties on derived color gradients of almost-equal-to 0.04 mag per decade in radius, while the new proposed method, with the same data, can provide color gradients with an accuracy of 0.01-0.02 mag per decade in radius.