Intercontinental simultaneous survey of the unique cepheid HR 7308 inphotometry and radial velocity.

A simultaneous monitoring in photometry and radial velocity was organized in August 1984 on the unique cepheid HR 7308 (V473 Lyr). The data were obtained by using ten telescopes located in six different countries in Europe and North America. Three different versions of the Baade-Wesselink method have been applied and the results (5O ± 15R_sun, 41 ± 11R_sub, 32 ± 10R_sun) are in favour of a mean radius larger than 30 R_sun. The photometric analysis confirms that the star has a normal solar abundance. HR 7308 is most probably a classical cepheid pulsating in the second (or higher) overtone. However, the possibility that the star is a Population II cepheid and/or that it is pulsating in the fundamental mode or the first overtone cannot yet be ruled out definitively.