RR-Lyrae variable stars


What are they

RR-Lyrae variables are located on the horizontal branch of the HR diagram

They are relatively old stars (at least ~9 Gyr old)

Their periods are less than 1.5 days

Their variability allows us to use them as standard candles



Period-luminosity relation

measure period => derive luminosity => compare with apparent luminosity => distance


Why study them

To derive the local distance scale




RR Lyrae in NGC6426


Study of RR-Lyrae Variable Stars at Skinakas Observatory





Discovery of RR Lyrae variables in Globular clusters

Construction of light-curves and Fourier analysis of them

Scientific Aim:

dependence of period—amplitude relation on metal abundance affects age determination of GC

determination of distances – distance scale (RR-Lyrae variables are good standard candles)

internal stellar structure of RR-Lyrae variables