| Abstract : | Classical pulsators are immensely important astrophysical objects. The existence of their well-
defined period-luminosity relations make them useful extragalactic distance estimators. RR Lyraes
(RRLs), classical and type II Cepheids (T2Cs) are a few of the most important classical pulsators
and the focus of my thesis. My research combines modern observational data with the state-of-the-
art theoretical models to provide stringent constraints for the stellar evolution and pulsation models,
and to improve calibration of these stars for the extragalactic distance measurements.
The specific applications discussed in my thesis include (i) theoretical and empirical investigations
into the pulsation properties of classical pulsators, viz., period-colour, amplitude-colour and period-
luminosity relations at multiple wavelengths, (ii) modelling observed pulsational properties of
classical pulsators and thereby understanding the impact of composition and convective efficiency
on the pulsation of these stars and (iii) probing the stellar structures to understand the microphysics
of the outer envelopes of the pulsating variables. We used the RRL light curve model fitting
approach to estimate μLMC=18.51 ± 0.07, in good agreement with published results. We also probed
the HIF-stellar photosphere interaction theory from observational and theoretical aspects and
demonstrated that the theory holds true across a broad spectrum of variable stars in different
evolutionary stages. Lastly, we tested for the effect of metallicity and convection parameters on the
PL and PR relations for a grid of BLHer models and found significant effect of metallicity on PL in
U and B-bands and negligible effect in infrared. No significant metallicity effects were seen in the
PR relations. |
