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V965 Cephei revisited: evidence for a binary system

Maksym Pyatnytskyy

TL;DR

V965 Cep is a high-amplitude Delta Scuti (HADS) star, and the study addresses whether its observed timing variations arise from intrinsic period changes or a light-time effect due to a companion. The authors extend the O-C diagram by including all available Johnson V data and unfiltered observations, deriving times of maxima via a Fourier-model fit and testing for periodic structure. They find that a periodic component with $\Pi = 13.4 \pm 0.9$ yr and semi-amplitude $0.00249 \pm 0.00014$ d can explain the residuals, implying a companion with minimum mass $\approx 0.1\,M_\odot$ in a roughly 7 AU orbit around a $\sim 1.8\,M_\odot$ primary. They also report BV photometry yielding $B-V = 0.48 \pm 0.05$ at maximum and $0.57 \pm 0.05$ at minimum, consistent with a modest color variation during pulsation. Overall, the results provide evidence for a binary companion to V965 Cep and highlight the usefulness of extended O-C analyses in discriminating period modulation mechanisms for Delta Scuti stars.

Abstract

We extended the $O-C$ diagram for V965 Cep with all currently available observations in the Johnson V filter and added unfiltered ones. The new, up-to-date $O-C$ diagram shows that the seeming period change previously revealed by the author does not occur uniformly. Instead, the near-parabolic part of the $O-C$ diagram can be a part of a periodic curve. This could be a sign of the second body in the system. Based on our observations, we also estimated the $B-V$ index of the star to be $0.48 \pm 0.05$ at maximum brightness and $0.57 \pm 0.05$ at minimum brightness.

V965 Cephei revisited: evidence for a binary system

TL;DR

V965 Cep is a high-amplitude Delta Scuti (HADS) star, and the study addresses whether its observed timing variations arise from intrinsic period changes or a light-time effect due to a companion. The authors extend the O-C diagram by including all available Johnson V data and unfiltered observations, deriving times of maxima via a Fourier-model fit and testing for periodic structure. They find that a periodic component with yr and semi-amplitude d can explain the residuals, implying a companion with minimum mass in a roughly 7 AU orbit around a primary. They also report BV photometry yielding at maximum and at minimum, consistent with a modest color variation during pulsation. Overall, the results provide evidence for a binary companion to V965 Cep and highlight the usefulness of extended O-C analyses in discriminating period modulation mechanisms for Delta Scuti stars.

Abstract

We extended the diagram for V965 Cep with all currently available observations in the Johnson V filter and added unfiltered ones. The new, up-to-date diagram shows that the seeming period change previously revealed by the author does not occur uniformly. Instead, the near-parabolic part of the diagram can be a part of a periodic curve. This could be a sign of the second body in the system. Based on our observations, we also estimated the index of the star to be at maximum brightness and at minimum brightness.

Paper Structure

This paper contains 8 sections, 2 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. The Author's Observations
  4. Deriving Times of Maxima
  5. Results and Discussion
  6. The BV photometry
  7. The $O-C$ Diagram
  8. Conclusion

Figures (5)

  • Figure 1: The phase diagram for the observations in the "clear" filter conducted by the author during 2023 and up to June 18, 2024. The Fourier model is shown with the light-color line.
  • Figure 2: The phase diagrams for the author's observations in the V and B bands.
  • Figure 3: The phase diagram for the B-V model curve.
  • Figure 4: The O-C diagram for V965 Cep.
  • Figure 5: Folded $O-C$ (period $13.4 yr$) diagram after removing a linear trend. The smooth curve is a sinusoidal model.