Publication detail

A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion

Skarka, M. Liska, J. Dreveny, R. Guggenberger, E. Sodor, A. Barnes, T.G. Kolenberg, K.

Original Title

A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion

Type

journal article in Web of Science

Language

English

Original Abstract

We present a comprehensive study of Z CVn, an RR Lyrae star that shows long-term cyclic variations of its pulsation period. A possible explanation suggested from the shape of the O-C diagram is the light travel-time effect, which we thoroughly examine. We used original photometric and spectroscopic measurements and investigated the period evolution using available maximum times spanning more than one century. If the binary hypothesis is valid, Z CVn orbits around a black hole with minimal mass of 56.5 M-circle dot on a very wide (P-orbit = 78.3 yr) and eccentric orbit (e = 0.63). We discuss the probability of the formation of a black hole-RR Lyrae pair, and, although we found it possible, there is no observational evidence of the black hole in the direction to Z CVn. However, the main objection against the binary hypothesis is the comparison of the systemic radial velocity curve model and spectroscopic observations that clearly show that Z CVn cannot be bound in such a binary. Therefore, the variations of pulsation period are likely intrinsic to the star. This finding represents a discovery/confirmation of a new type of cyclic period changes in RR Lyrae stars. By the analysis of our photometric data, we found that the Blazhko modulation with period of 22.931 d is strongly dominant in amplitude. The strength of the phase modulation varies and is currently almost undetectable. We also estimated photometric physical parameters of Z CVn and investigated their variations during the Blazhko cycle using the inverse Baade-Wesselink method.

Keywords

methods: data analysis; techniques: photometric; techniques: spectroscopic; binaries: general; stars: individual: Z CVn; stars: variables: RR Lyrae

Authors

Skarka, M.; Liska, J.; Dreveny, R.; Guggenberger, E.; Sodor, A.; Barnes, T.G.; Kolenberg, K.

Released

1. 2. 2018

Publisher

OXFORD UNIV PRESS

Location

OXFORD

ISBN

0035-8711

Periodical

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Year of study

474

Number

1

State

United Kingdom of Great Britain and Northern Ireland

Pages from

824

Pages to

837

Pages count

14

URL

https://arxiv.org/abs/1710.06709

BibTex

@article{BUT162179,
  author="Skarka, M. and Liska, J. and Dreveny, R. and Guggenberger, E. and Sodor, A. and Barnes, T.G. and Kolenberg, K.",
  title="A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion",
  journal="MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY",
  year="2018",
  volume="474",
  number="1",
  pages="824--837",
  doi="10.1093/mnras/stx2737",
  issn="0035-8711",
  url="https://arxiv.org/abs/1710.06709"
}