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Spectroscopic and Decade-long Photometric Observations of the Contact Binary V2790 Ori: Evidence for a Brown Dwarf Companion and a Solar-like Magnetic Activity Cycle

Si-Rui Wang, Kai Li, Qi-Qi Xia, Dong-Yang Gao, Xiang Gao, Jing-Yi Wang, Ya-Ni Guo, Xing Gao, Guo-You Sun

Abstract

We present 22 sets of light curves and one radial velocity curve for the W UMa-type total eclipse contact binary system V2790 Ori, derived by combining all available public photometric data, the photometric data in previous studies, and our own spectroscopic and decade-long photometric observations. Our simultaneous analysis of the light curves and radial velocity curve shows that V2790 Ori is a W-subtype contact binary with a mass ratio of $q = 0.322(\pm0.001)$ and a shallow contact degree of $14.8(\pm0.6)\%$. The orbital period analysis based on 445 eclipsing minima reveals a secular decrease at a rate of $\dot P = -3.18 (\pm 0.75) \times 10^{-8}\mathrm{d~yr^{-1}}$, superimposed with a cyclic variation with an amplitude of $A = 8.98 (\pm 2.19) \times 10^{-4}~\mathrm{d}$ and a period of $ P_3 = 7.44 (\pm 0.52)~\mathrm{yr}$. The secular decrease is caused by AML via magnetic braking, while the cyclic period variation is explained by the light-travel time effect due to a third body, which is likely to be a brown dwarf. Furthermore, our analysis indicates a mass transfer from the more massive component to the less massive one at a rate of $1.22(\pm0.29) \times 10^{-8}~\mathrm{M_{\odot}~yr^{-1}}$. A model with a cool spot on each component was adopted to fit the O'Connell effect observed in the light curves. Since the O'Connell effect varies over time, we identified a solar-like magnetic activity cycle with a period of approximately 5.4 yr by analyzing the magnitude difference ($Δm$) at the two light maxima and the O'Connell effect ratio. In addition, evolutionary analysis suggests that V2790 Ori is a newly formed contact binary that evolved from a detached phase into the present contact configuration.

Spectroscopic and Decade-long Photometric Observations of the Contact Binary V2790 Ori: Evidence for a Brown Dwarf Companion and a Solar-like Magnetic Activity Cycle

Abstract

We present 22 sets of light curves and one radial velocity curve for the W UMa-type total eclipse contact binary system V2790 Ori, derived by combining all available public photometric data, the photometric data in previous studies, and our own spectroscopic and decade-long photometric observations. Our simultaneous analysis of the light curves and radial velocity curve shows that V2790 Ori is a W-subtype contact binary with a mass ratio of and a shallow contact degree of . The orbital period analysis based on 445 eclipsing minima reveals a secular decrease at a rate of , superimposed with a cyclic variation with an amplitude of and a period of . The secular decrease is caused by AML via magnetic braking, while the cyclic period variation is explained by the light-travel time effect due to a third body, which is likely to be a brown dwarf. Furthermore, our analysis indicates a mass transfer from the more massive component to the less massive one at a rate of . A model with a cool spot on each component was adopted to fit the O'Connell effect observed in the light curves. Since the O'Connell effect varies over time, we identified a solar-like magnetic activity cycle with a period of approximately 5.4 yr by analyzing the magnitude difference () at the two light maxima and the O'Connell effect ratio. In addition, evolutionary analysis suggests that V2790 Ori is a newly formed contact binary that evolved from a detached phase into the present contact configuration.

Paper Structure

This paper contains 12 sections, 16 equations, 7 figures.

Table of Contents

  1. Introduction
  2. OBSERVATIONS AND DATA REDUCTION
  3. Photometric Observations
  4. Spectroscopic Observations
  5. RADIAL VELOCITY AND LIGHT CURVE ANALYSIS
  6. ORBITAL PERIOD INVESTIGATION
  7. DISCUSSIONS AND CONCLUSIONS
  8. Orbital Period Variations and Their Physical Origins
  9. Secular Period Decrease
  10. Cyclic Period Variation
  11. O’Connell effect variation
  12. Evolutionary State

Figures (7)

  • Figure 1: Theoretical light curves (solid lines) fitted by W-D program compared to observed ones for V2790 Ori. The fitted residuals are displayed at the bottom of each panel. All figures of 22 sets of light curves are available in the online journal.
  • Figure 2: Radial velocity and fitted curves of V2790 Ori. The black triangular represents the radial velocity of the less massive component, and the black circular represents the radial velocity of the more massive component. The blue lines show the theoretical curves of the less massive components, and the red lines show the theoretical curves of the more massive components.
  • Figure 3: $O-C$ curves of V2790 Ori. (a) Fitting result of Q+L model. (b) Fitting result of Q+S model. The top panel shows the $(O-C)_1$ curve determined by the new linear ephemeris of Equation (\ref{['eq5']}). The $(O-C)_2$ values, which remove the quadratic term from the $(O-C)_1$ curve, are plotted in the middle panel. The residuals from the full ephemeris of Equation (\ref{['eq6']}) or (\ref{['eq7']}) are displayed in the lower panel.
  • Figure 4: Possible cyclic variations for $\Delta m$ and OER. The solid lines represent the sinusoidal fit with Equation (\ref{['16']}) and Equation (\ref{['17']}). The periods determined are presented in the top left corner of each panel.
  • Figure 5: (a) The relation of M-L. (b) The relation of M-R. The zero-age main sequence (ZAMS) and terminal-age main sequence (TAMS), generated using the binary star evolution code from 2002MNRAS.329..897H, are plotted as solid and dashed black lines, respectively. Circular and square symbols represent W-subtype and A-subtype contact binaries, respectively, and are taken from 2021AJ....162...13L. Solid symbols denote the more massive primary components, while open symbols represent the less massive secondary components. The positions of the components of V2790 Ori are marked with red squares. (c) The relation between orbital angular momentum and total mass for detached and contact binaries. The dashed boundary line between detached and contact binaries and detached binaries are adopted from 2006MNRAS.373.1483E. The samples of contact binaries are taken from 2021AJ....162...13L. Open circular and solid square symbols represent A-subtype and W-subtype contact binaries, respectively. The position of V2790 Ori is marked with a red solid square.
  • ...and 2 more figures