High-precision distance measurements with classical pulsating stars
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Ó Indian Academy of Sciences Sadhana(0123456789().,-volV)FT3 ](0123456789().,-volV)
REVIEW
High-precision distance measurements with classical pulsating stars ANUPAM BHARDWAJ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871, China. E-mail: [email protected] MS received 4 May 2020; accepted 29 June 2020 Abstract. Classical Cepheid and RR Lyrae variables are radially pulsating stars that trace young and oldage stellar populations, respectively. These classical pulsating stars are the most sensitive probes for the precision stellar astrophysics and the extragalactic distance measurements. Despite their extensive use as standard candles thanks to their well-defined Period–Luminosity relations, distance measurements based on these objects suffer from their absolute primary calibrations, metallicity effects, and other systematic uncertainties. Here, I present a review of classical Cepheid, RR Lyrae and type II Cepheid variables starting with a historical introduction and describing their basic evolutionary and pulsational properties. I will focus on recent theoretical and observational efforts to establish absolute scale for these standard candles at multiple wavelengths. The application of these classical pulsating stars to high-precision cosmic distance scale will be discussed along with observational systematics. I will summarize with an outlook for futher improvements in our understanding of these classical pulsators in the upcoming era of extremely large telescopes. Keywords. Stars: variables: Cepheids—RR Lyrae—Type II Cepheids—stars: evolution—stars: oscillations— cosmology: distance scale.
1. Introduction Stars are primary engines of cosmic evolution and play a crucial role in our understanding of the Universe. Variable stars, in particular, provide information about the stellar properties including physical parameters, internal and external envelope structure and composition, and probe both the stellar evolution and cosmic distances. The first variable star was discovered more than four centuries back in 1596 by David Fabricius which was later named as Omicron Ceti or Mira and now represents one of the subclasses belonging to the long-period variables. The short-period, typically fainter, variable stars were not wellknown until two British astronomers, Edward Pigott and John Goodricke started observations of b Persei (Algol) in 1782 (Goodricke 1783). A few years later, Pigott detected the variability in g Aquilae, the first
known Cepheid variable. At the same time, Goodricke discovered d Cephei (Goodricke 1786), which represents classical Cepheid variables as one of the most important classes of pulsating variables in the modern astronomy. About a century later the first variable stars within a Galactic globular cluster (GGC) were discovered by Wilhelmina Flemming and reported in Pickering (1889). Following this discovery, Solon Bailey initiated a search for variable stars in the GGCs from the Harvard College Observatory in 1893 and
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