A Variation on the Baade-Wesselink Technique

Authors

Norman R. Simon, University of Nebraska - LincolnFollow

Document Type

Article

Date of this Version

1986

Citation

Bulletin of the American Astronomical Society, Vol. 18 (1986), p.964.

Comments

Copyright 1986 American Astronomical Society. Provided by the NASA Astrophysics Data System

Abstract

Consider a radially pulsating star. Expand the radius variation in a Fourier series: R = R_O+A_icos(i_wt+ϕi) [summation convention]. The velocity is v=--iwA_isin(iwt+ϕ_i). The ratio of the radii at two phases of the cycle may be written

(R₁/R₂)² = (L₁ T₂⁴) / (L₂ T₁⁴)/(L₂ T₁⁴) = α

Setting R = Ro + Δr (Δr/R_o « 1), we obtain R_o = 2(αΔr₂ - rΔ_l ) / (1-α). The radial excursion Δr at any phase of the pulsation may be determined from a Fourier fit to the observed velocity curve. Assuming highly accurate velocity data (e.g. CORAVEL data), this can be done very precisely. If we choose phase 2 to be that for which Δr₂ = O, we have

α = (2/R_o) Δr₁ + 1.