Multi-wavelength variability of the young solar analog ι Horologii

Abstract

Context. Chromospheric activity cycles are common in late-type stars; however, only a handful of coronal activity cycles have been discovered. ι Hor is the most active and youngest star with known coronal cycles. It is also a young solar analog, and we are likely facing the earliest cycles in the evolution of solar-like stars, at an age (∼ 600 Myr) when life appeared on Earth. Aims. Our aim is to confirm the ∼1.6 yr coronal cycle and characterize its stability over time. We use X-ray observations of ι Hor to study the corona of a star representing the solar past through variability, thermal structure, and coronal abundances. Methods. We analyzed multi-wavelength observations of ι Hor using XMM-Newton, TESS, and HST data. We monitored ι Hor throughout almost seven years in X-rays and in two UV bands. The summed RGS and STIS spectra were used for a detailed thermal structure model, and the determination of coronal abundances. We studied rotation and flares in the TESS light curve. Results. We find a stable coronal cycle along four complete periods, more than covered in the Sun. There is no evidence for a second longer X-ray cycle. Coronal abundances are consistent with photospheric values, discarding any effects related to the first ionization potential. From the TESS light curve we derived the first photometric measurement of the rotation period (8.2 d). No flares were detected in the TESS light curve of ι Hor. We estimate the probability of having detected zero flares with TESS to be ∼ 2%. Conclusions. We corroborate the presence of an activity cycle of ∼1.6 yr in ι Hor in X-rays, more regular than its Ca ii H&K counterpart. A decoupling of the activity between the northern and southern hemispheres of the star might explain the disagreement. The inclination of the system would result in an irregular behavior in the chromospheric indicators. The more extended coronal material would be less sensitive to this effect.

Characterizing X‐ray activity cycles of young solar‐like stars with solar observations

“…Since the underlying cause for cyclic brightness variations in all layers of the atmosphere are magnetic fields, it is expected that the X‐ray luminosity (representing the corona) varies in line with the chromospheric Ca II emission. Up to date, the X‐ray satellite XMM‐Newton revealed the presence of X‐ray activity cycles in seven solar‐like stars: Cen A and B (15 and 8.8 year; Robrade et al 2012; Wargelin et al 2017), 61 Cyg A and B (7.3 and 11.3 year; Hempelmann et al 2006; Robrade et al 2012), HD 81809 (8 year; Favata et al 2008; Orlando et al 2017), Hor (1.6 year; Sanz‐Forcada et al 2019, 2013) and Eri (2.95 year; Coffaro et al 2020). All stars were monitored in the chromosphere and the variation of their X‐ray fluxes coincides with that of the S‐index.…”

Evidence of a Clear Atmosphere for WASP-62b: The Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone

“…We fit European Photon Imaging Camera (EPIC) spectra using a one-temperature coronal model to calculate an X-ray luminosity (0.12−2.48 keV) of L X = 6.0×10 28 erg s −1 (S/N=5.8), for a Gaia DR2 distance of 176.53±0.41 pc. The resulting = -L L log 5.1 X bol measurement indicates that the star has a moderate activity level, similar to the young solar analog ιHor (G0V) in which X-ray variability is present but flares are not frequently observed (Sanz-Forcada et al 2019). Furthermore, the X-ray and UV light curves taken with the XMM-Newton EPIC (∼1−124 Å) and the Optical Monitor (OM)/UVM2 filter (2070−2550 Å) show some level of variability.…”

Evidence of a Clear Atmosphere for WASP-62b: the Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone

“…We fit European Photon Imaging Camera (EPIC) spectra using a onetemperature coronal model to calculate an X-ray luminosity (0.12−2.48 keV) of L X = 6.0 × 10 28 erg s −1 (S/N=5.8), for a Gaia DR2 distance of 176.53±0.41 pc. The resulting log L X /L bol = −5.1 measurement indicates that the star has a moderate activity level, similar to the young solar analog ι Hor (G0V) in which X-ray variability is present but flares are not frequently observed (Sanz-Forcada et al 2019).…”