• DOI:10.3847/0004-637X/821/2/74
• Corpus ID: 118651905

A 12-Year Activity Cycle for HD 219134

@article{Johnson2016A1A,
  title={A 12-Year Activity Cycle for HD 219134},
  author={Marshall C. Johnson and Michael Endl and William D. Cochran and Stefano Meschiari and Paul Robertson and P. Macqueen and Erik J. Brugamyer and Caroline Caldwell and A. P. Hatzes and Iv'an Ram'irez and Robert A. Wittenmyer},
  journal={arXiv: Earth and Planetary Astrophysics},
  year={2016}
}

• Marshall C. Johnson, M. Endl, +8 authors R. Wittenmyer
• Published 16 February 2016
• Physics, Geology
• arXiv: Earth and Planetary Astrophysics

The nearby (6.5 pc) star HD 219134 was recently shown by Motalebi et al. (2015) and Vogt et al. (2015) to host several planets, the innermost of which is transiting. We present twenty-seven years of radial velocity observations of this star from the McDonald Observatory Planet Search program, and nineteen years of stellar activity data. We detect a long-period activity cycle measured in the Ca II $S_{HK}$ index, with a period of $4230 \pm 100$ days (11.7 years), very similar to the 11-year Solar activity cycle. Although the period of the Saturn-mass planet HD 219134 h is close to half that of the activity cycle, we argue that it is not an artifact due to stellar activity. We also find a significant periodicity in the $S_{HK}$ data due to stellar rotation with a period of 22.8 days. This is identical to the period of planet f identified by Vogt et al. (2015), suggesting that this radial velocity signal might be caused by rotational modulation of stellar activity rather than a planet. Analysis of our radial velocities allows us to detect the long-period planet HD 219134 h and the transiting super-Earth HD 219134 b. Finally, we use our long time baseline to constrain the presence of longer-period planets in the system, excluding to $1\sigma$ objects with $M\sin i>0.36 M_J$ at 12 years (corresponding to the orbital period of Jupiter) and $M\sin i>0.72 M_J$ at a period of 16.4 years (assuming a circular orbit for an outer companion).