What is a ultraviolet proxy?

What is a ultraviolet proxy?

A UV proxy is a model used to convert the brightness temperature of an object back to its surface temperature.

One example of a UV proxy is the Johnson-Kron-Cousins system, which can be used to estimate a star's spectral type using its temperature. The Johnson-Kron-Cousins system uses two filters, G and N, on the Johnson-Cousins system (ie Cousins & Luyten 1979; Jeffery 1990). Each filter consists of a single narrow-band filter covering only a small wavelength range. The G filter starts at 380nm with a 3nm bandwidth and extends from 379nm to 383nm, while the N filter extends from 394nm to 402nm with 3nm bandwidth. The filters are placed so that both filters fall across the U and B bands, as these two bands are where the Balmer jump and Paschen Jump is found in most stars of the cool, luminous class, Ia (eg Bessell et al. 2011; Dopita & Sutherland 2010; Pauldrach 2001).

The method that we use to find UV proxies for F, G, and K spectral types is very simple. First, we simply convert the measured UV flux of each filter to an equivalent UV flux using the filter transmission curves, T (Fig. 1). These transmission curves can be thought of as a function that returns a measure of the UV flux that would be measured through a given filter and atmosphere. For example, if a star has a measured flux of fg = 5,000 ergs s1 cm2, and a transmission curve of T = 10%, this implies a flux measured through G as G0 = 4500 ergs s1 cm2. Next, we convert the measured flux into a temperature. We used the filter temperature response function (FTF) and the atmospheric properties that represent the spectrum of a star for the corresponding temperature.