ABSTRACT
Baade-Wesselink method A method of determining the distance to pulsating stars, which can also be observed spectroscopically. One estimates the surface temperature and hence the surface brightness from the color index (B − V color), based on simultaneous measurements of the blue and visual magnitude at bright and dim epochs in the star’s pulsation. One computes the square root of the ratio of the observed flux to the surface brightness for each of these epochs. This is an estimate of the angular diameter of the star. Spectroscopy yields the surface velocity of the star (via blue and red shifting of spectral lines), which leads to a determination of the total difference in radius of the star between the observations. The combination of these observations allows a determination of the physical size of the star, and thus of its absolute magnitude and distance. The method has also been applied to the expanding envelope of type II supernovae.
