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

Abstract

Abstract. 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 C photometry, a distance of 647 ± 16 pc, and a mass of 0.66 ± .03 M were found. In addition to the radius change (4.58−5.51) R radius undulations have been found with amplitude ≈0.2 R and period P/5, which are synchronized with the main period P = 0. d 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).

Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models - I. Theory and practical implementation

“…A first attempt to derive d and of an RR star from the over‐simplified version (1) of (3) was described by Barcza (2003). The present results for the distance and mass of SU Dra differ only slightly from the previous d = (647 ± 16) pc and .…”

“…The averaged surface gravity for the whole pulsation cycle is log g e = 2.73, which is in excellent agreement with log g e = 2.69, 2.72 from uvby and UBV(RI) C photometry (Siegel 1982;Liu & Janes 1990), respectively. The averaged effective temperature of T e = 6778 K is significantly higher than T e = 6433, 6400, 6490 K (Siegel 1982;Liu & Janes 1990;Barcza 2003). The minimal, averaged and maximal angular radii are (1.519, 1.669, 1.801) × 10 −10 rad corresponding to R min = (4.46, 4.90, 5.29) R , respectively.…”

“…The bolometric corrections and UBV ( RI ) C physical fluxes of a model with given T e , log g e , [ M ], E ( B − V ) are available in a tabular form (Kurucz 1997), and they allow us to determine the angular radius of the star defined by Technical details of finding the appropriate model and determining ϑ at a phase ϕ are given in Barcza (2003) and Barcza & Benkő (2009) 1…”

“…Technical details of finding the appropriate model and determining ϑ at a phase ϕ are given in Barcza (2003) and Barcza & Benkő (2009). 1 On the scale provided by the Kurucz atmospheric models, the above procedure offers a possibility of determining reddening and atmospheric metallicity from photometry without using spectroscopy.…”

Hysteresis of atmospheric parameters of 12 RR Lyrae stars based on multichannel simultaneous Strömgren photometry

“…The CoRoT data do not have the 0.02 phase resampling rhythm. Barcza (2003) found in the RR Lyr star SU Dra from photometry an "undulation"' of P/5. It is unclear what the cause of these periodicities is.…”