THE POSSIBILITY OF ESTIMATING PHOTOSPHERIC EXTENSIONS FOR RED GIANTS FROM BROAD-BAND PHOTOMETRY

A method of stepwise multiple linear regression was applied in order t o estimate extensions of red giant atmospheres. It is shown that a set of five color indices enables one to find photospheric extensions ove r a wide range of stellar parameters and for large differences in chem ical abundances, with an accuracy sufficient for statistical studies. If the star's effective temperature is known, three color indices are enough to determine photospheric extensions with an r.m.s. error of le ss than 0.05.