Abstract
Pulsating stars, like Cepheids or RR Lyrae stars, are ones of the most important distance indicators. They are also key objects for testing the predictions of stellar evolution and stellar pulsation theory. In the Araucaria Project we have studied these objects since 2002, measuring distances to the galaxies in the Local Group and beyond.In 2010 we have for the first time confirmed spectroscopically the existence of a classical Cepheid in an eclipsing binary system. This has opened an opportunity to study in great details and with high accuracy (better than 1%) the physical parameters of these very important objects. First dynamical mass determination (M cep = 4.16 ± 0.03 M ⊙ ) let us solve the long-standing mass discrepancy problem. Since then we have measured masses for 6 classical Cepheids in binary systems and determined projection factors for three of them. One of the analyzed systems was confirmed to consist of two first-overtone Cepheids.Type II Cepheids are recently becoming more important as distance indicators and astrophysics laboratory, although our knowledge of these stars is quite limited. Their evolutionary status is also not well understood and observational constraints are needed to confirm the current theories. We are presenting here our first results of the spectroscopic analysis of 4 of these systems. The masses of type II Cepheids seem consistent with the expected 0.5 − 0.6 M⊙. We also present first results of the fully modeled pulsator originally classified as peculiar W Vir star. The mass of this star is 1.51 ± 0.09 M ⊙ and the p-factor 1.3 ± 0.03. It was eventually found not to belong to any typical Cepheid group.
Highlights
The Araucaria Project, started in 2000, is a collaboration between astronomers from institutions in Chile, the United States and Europe
Its principal aim is to provide an improved calibration of the local extragalactic distance scale
The principal reason for this persisting difficulty is in the ill-known dependencies of stellar standard candles, used to measure the distances of nearby galaxies, on the environmental properties of their host galaxies
Summary
The Araucaria Project, started in 2000, is a collaboration between astronomers from institutions in Chile, the United States and Europe. Its principal aim is to provide an improved calibration of the local extragalactic distance scale. In the process of setting up the extragalactic distance scale, the greatest difficulty leading to the currently largest contribution on the systematic uncertainty of the Hubble constant lies in the determination of accurate absolute distances to nearby galaxies. The principal reason for this persisting difficulty is in the ill-known dependencies of stellar standard candles, used to measure the distances of nearby galaxies, on the environmental properties of their host galaxies (metallicity, age of the stellar populations). The Araucaria Project is an effort to remedy this situation for several of the most important stellar candles, including Cepheid variables, RR Lyrae stars, red clump giants, and blue supergiants which all have the potential to provide accurate distance determinations to nearby galaxies once their environmental dependencies are well calibrated
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have