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

Multiplanet 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 for searches for more distant planetary orbits. This work provides a significantly revised architecture for the multiplanet system HD 134606 using both HARPS and UCLES RVs. We confirm the presence of previously reported planets b, c, and d with periods of12.0897_(−0.0018)^(+0.0019),58.947_(−0.054)^(+0.056), and958.7_(−5.9)^(+6.3)days and masses of9.14_(−0.63)^(+0.65), 11.0 ± 1, and 44.5 ± 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 of4.31943_(−0.00068)^(+0.00075)and26.9_(−0.017)^(+0.019)days and masses of2.31_(−0.35)^(+0.36)and5.52_(−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 massive companion with a very long orbital period. 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 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. ; © 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of theCreative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation ...