SLR has been used in a number of research initiatives. Stellar locus regression (SLR) was a method developed to eliminate the need for standard star observations in photometric calibrations, except highly infrequently (once a year or less) to measure color terms. Such methods take advantage of the fundamental distribution of stellar colors in our galaxy across the vast majority of the sky, and the fact that observed stellar colors (unlike apparent magnitudes) are independent of the distance to the stars. The color-color diagram of stars can be used to directly calibrate or to test colors and magnitudes in optical and infrared imaging data. This can be useful to recover information on the filters usedfor the case of old data, when logs are not conserved and filter information has been lost.Īpplications Photometric calibration Ī schematic illustration of the stellar locus regression method of photometric calibration in astronomy. It can be used to measure the effective wavelength midpoint of an unknown filter too, by using two well known filters. Note that the slope of the straight line depends only on the effective wavelength, not in the filter width.Īlthough this formula cannot be directly used to calibrate data, if one has data well calibrated for two given filters, it can be used to calibrate data in other filters. Therefore, in most cases the straight feature of the stellar locus can be described by Ballesteros' formula deduced for pure blackbodies:Ĭ − D = ν c − ν d ν a − ν b ( A − B ) + k, These divergences can be more or less evident depending on the filters used: narrow filters with central wavelength located in regions without lines, will produce a response close to the black body one, and even filters centered at lines if they are broad enough, can give a reasonable blackbody-like behavior. The divergences with the straight line are due to the absorptions and emission lines in the stellar spectra. If stars were perfect black bodies, the stellar locus would be a pure straight line indeed. In the stellar locus, stars tend to align in a more or less straight feature. This feature leads to applications within various wavelength bands. As such, color-color diagrams can be used as a means of representing the stellar population, much like a Hertzsprung–Russell diagram, and stars of different spectral classes will inhabit different parts of the diagram. Thus by comparing the magnitude of the star in multiple different color indices, the effective temperature of the star can still be determined, as magnitude differences between each color will be unique for that temperature.
Obtaining complete spectra for stars through spectrometry is much more involved than simple photometry in a few bands. Thus, observation of a stellar spectrum allows determination of its effective temperature. The overall shape of a black-body curve is uniquely determined by its temperature, and the wavelength of peak intensity is inversely proportional to temperature, a relation known as Wien's Displacement Law. Stars emit less ultraviolet radiation than a black body with the same B−V index.Īlthough stars are not perfect blackbodies, to first order the spectra of light emitted by stars conforms closely to a black-body radiation curve, also referred to sometimes as a thermal radiation curve. Effective temperature of a black body compared with the B−V and U−B color index of main sequence and supergiant stars in what is called a color-color diagram.