EDP Sciences
Free access
Volume 403, Number 2, May IV 2003
Page(s) 683 - 691
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030410

A&A 403, 683-691 (2003)
DOI: 10.1051/0004-6361:20030410

Distance and mass of pulsating stars from multicolour photometry and atmospheric models

S. Barcza

Konkoly Observatory, PO Box 67, 1525 Budapest, XII, Hungary
(Received 15 October 2002 / Accepted 27 February 2003)

For determining distance and mass of pulsating stars a new, purely photometric method is described in which radial velocity observations are not needed. From multicolour photometry the variation of angular diameter is determined in a conventional way by using the surface brightness of the theoretical atmospheric models ATLAS of Kurucz (1997). As a function of phase the following two parameters are introduced in the Navier-Stokes equation: gravity (of the appropriate static ATLAS model), and angular diameter. Distance and mass are derived from phases of standstill. Conclusions are drawn on the hydrodynamic behaviour of the atmosphere. The new method is compared with the Baade-Wesselink (BW) method. As an example the RR Lyrae variable SU Dra is given: using $UBVR_{\rm C}$ photometry, a distance of $647\pm 16$ pc, and a mass of $0.66\pm .03~{\cal M}_{\odot}$ were found. In addition to the radius change $(4.58{-}5.51)~R_{\odot}$ radius undulations have been found with amplitude $\approx$ $0.2~R_{\odot}$ and period  P/5, which are synchronized with the main period $P=0\fd 66042$. The present method has confirmed the distance value from the BW method; thus, in the problem of different distance scales from BW and other methods the short extragalactic distance scale has been bolstered by an independent argument. The mass is some 30 percent larger than the value from the equation of pulsation of van Albada & Baker (1971).

Key words: stars: variables: RR Lyr -- stars: fundamental parameters: distance, mass -- stars: atmospheres -- stars: individual: SU Dra

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