Abstract
Context. The multiplicity of classical Cepheids (CCs) and RR Lyrae stars (RRLs) is still imperfectly known, particularly for RRLs. Aims. In order to complement the close-in short orbital period systems presented in Paper I, our aim is to detect the wide, spatially resolved companions of the targets of our reference samples of Galactic CCs and RRLs. Methods. Angularly resolved common proper motion pairs were detected using a simple progressive selection algorithm to separate the most probable candidate companions from the unrelated field stars. Results. We found 27 resolved, high probability gravitationally bound systems with CCs out of 456 examined stars, and one unbound star embedded in the circumstellar dusty nebula of the long-period Cepheid RS Pup. We found seven spatially resolved, probably bound systems with RRL primaries out of 789 investigated stars, and 22 additional candidate pairs. We report in particular new companions of three bright RRLs: OV And (companion of F4V spectral type), RR Leo (M0V), and SS Oct (K2V). In addition, we discovered resolved companions of 14 stars that were likely misclassified as RRLs. Conclusions. The detection of resolved non-variable companions around CCs and RRLs facilitates the validation of their Gaia DR2 parallaxes. The possibility to conduct a detailed analysis of the resolved coeval companions of CCs and old population RRLs will also be valuable to progress on our understanding of their evolutionary path.
Highlights
Classical Cepheids (CCs) and RR Lyrae stars (RRLs) are essential standard candles for Galactic (e.g., Drake et al 2013) and extragalactic (e.g., Riess et al 2016) distance determinations
A variation in the γ-velocity of δ Cep A reported by Anderson et al (2015) revealed the presence of the close-in orbiting companion δ Cep Ab. δ Cep exhibits a strong proper motion anomaly (PMa) in the Hipparcos and GDR2 catalogs, at S/N levels of ∆Hip = 7.0 and
We reported in Paper I the presence of a strong PMa on AX Cir induced by its close-in orbiting companion (Jaschek & Jaschek 1960; Petterson et al 2004) of spectral type B6V (Evans 1994)
Summary
Classical Cepheids (CCs) and RR Lyrae stars (RRLs) are essential standard candles for Galactic (e.g., Drake et al 2013) and extragalactic (e.g., Riess et al 2016) distance determinations These pulsating stars are the subject of several studies following the first (Gaia Collaboration 2017; Iorio et al 2018) and second (Clementini et al 2019; Muraveva et al 2018; Rimoldini et al 2018) Gaia data releases. In Paper I (Kervella et al 2019), we searched for companions of CCs and RRLs from the signature of the presence of a companion on their proper motion (PM) For this purpose, we used the positions measured by the Hipparcos and Gaia spacecrafts at two epochs separated by 24.25 yr to determine the PM of their center of mass.
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