Revised Architecture and Two New Super-Earths in the HD 134606 Planetary System

Abstract

Multi-planet systems exhibit a diversity of architectures that diverge from the solar system and contribute to the topic of exoplanet demographics. Radial velocity (RV) surveys form a crucial component of exoplanet surveys, as their long observational baselines allow searches for more distant planetary orbits. This work provides a significantly revised architecture for the multi-planet system HD 134606 using both HARPS and UCLES RVs. We confirm the presence of previously reported planets b, c, and d with periods $12.0897_{-0.0018}^{+0.0019}$, $58.947_{-0.054}^{+0.056}$, and $958.7_{-5.9}^{+6.3}$ days, and masses $9.14_{-0.63}^{+0.65}$, $11.0\pm 1$, and $44.5\pm 2.9$ Earth masses respectively, with the planet d orbit significantly revised to over double that originally reported. We report two newly detected super-Earths, e and f, with periods $4.31943_{-0.00068}^{+0.00075}$ and $26.9_{-0.017}^{+0.019}$ days, and masses $2.31_{-0.35}^{+0.36}$ and $5.52_{-0.73}^{+0.74}$ Earth masses, respectively. In addition, we identify a linear trend in the RV time series, and the cause of this acceleration is deemed to be a newly detected sub-stellar companion at large separation. HD 134606 now displays four low mass planets in a compact region near the star, one gas giant further out in the Habitable Zone, an additional massive companion in the outer regime, and a low mass M dwarf stellar companion at large separation, making it an intriguing target for system formation/evolution studies. The location of planet d in the Habitable Zone proves to be an exciting candidate for future space-based direct imaging missions, whereas continued RV observations of this system are recommended for understanding the nature of the massive, long period companion.

23 pages, 10 figures, 4 tables, accepted for publication in the Astronomical Journal