MINI REVIEW article
Front. Astron. Space Sci.
Sec. Stellar and Solar Physics
This article is part of the Research TopicTime Domain Astronomy: Insights into Variable and Transient SourcesView all 4 articles
Type II Cepheids: Period-Luminosity-Metallicity relations for the Population II distance scale
Provisionally accepted
- 1Inter University Centre for Astronomy and Astrophysics, Savitribai Phule Pune University, Pune, India
- 2Osservatorio Astronomico di Capodimonte, Naples, Italy
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Type II Cepheids are a class of pulsating variable stars that play a critical role in our understanding of stellar evolution, distance measurement and tracing the structure and kinematics of old stars in nearby galaxies. This review provides a comprehensive summary of the current state of research on Type II Cepheids, including their observed properties, pulsation mechanisms and their distinction from other variable stars. These pulsating variable stars, found primarily in older stellar populations, exhibit well-defined period-luminosity relations but with an added advantage that they exhibit weak or negligible dependence on metallicity. We explore their relevance in the context of their role as distance indicators and potential calibrators of the first rung of the extragalactic distance ladder. Finally, the review highlights recent advancements in theoretical models, observations across different wavelengths and ongoing debates concerning their classification.
Keywords: Cepheid, Population II, Period-luminosity relation, Variable - stars, Low mass stars, Cosmic distance scale
Received: 04 Oct 2025; Accepted: 18 Nov 2025.
Copyright: © 2025 Das, Bhardwaj and Marconi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Susmita Das, susmita.das@iucaa.in
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