Far beyond the Sun: I. The beating magnetic heart in Horologium

Abstract

A former member of the Hyades cluster, $\iota$ Horologii ($\iota$ Hor) is a planet-hosting Sun-like star which displays the shortest coronal activity cycle known to date ($P_{\mathrm{cyc}}\sim$ 1.6 yr). With an age of $\sim$$625$ Myr, $\iota$ Hor is also the youngest star with a detected activity cycle. The study of its magnetic properties holds the potential to provide fundamental information to understand the origin of cyclic activity and stellar magnetism in late-type stars. In this series of articles, we present the results of a comprehensive project aimed at studying the evolving magnetic field in this star and how this evolution influences its circumstellar environment. This paper summarizes the first stage of this investigation, with results from a long-term observing campaign of $\iota$ Hor using ground-based high-resolution spectropolarimetry. The analysis includes precise measurements of the magnetic activity and radial velocity of the star, and their multiple time-scales of variability. In combination with values reported in the literature, we show that the long-term chromospheric activity evolution of $\iota$ Hor follows a beating pattern, caused by the superposition of two periodic signals of similar amplitude at $P_1\simeq 1.97\pm 0.02$ yr and $P_2\simeq 1.41\pm 0.01$ yr. Additionally, using the most recent parameters for $\iota$ Hor b in combination with our activity and radial velocity measurements, we find that stellar activity dominates the radial velocity residuals, making the detection of additional planets in this system challenging. Finally, we report here the first measurements of the surface longitudinal magnetic field strength of $\iota$ Hor, which displays varying amplitudes within $\pm 4$ G and served to estimate the rotation period of the star ($P_{\mathrm{rot}}=7.70_{-0.67}^{+0.18}$ d).

14 pages, 7 Figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

References in corpus (11)

• Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
• The HARPS search for southern extra-solar planets. X. A m sin i = 11 Mearth planet around the nearby spotted M dwarf GJ 674
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• The Gaia FGK Benchmark Stars - High resolution spectral library
• The Mount Wilson Observatory S-index of the Sun
• Discovery of a 1.6-year Magnetic Activity Cycle in the Exoplanet Host Star iota Horologii
• Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri
• The connection between stellar activity cycles and magnetic field topology
• First Zeeman Doppler imaging of a cool star using all four Stokes parameters
• The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster
• A possible long-term activity cycle for ι Horologii: First results from the HKα & SPI-HKα projects