HD 38858: a solar-type star with an activity cycle of ∼10.8 yr

Abstract

Context. The detection of chromospheric activity cycles in solar-analogue and twin stars can be used to place the solar cycle in a wider context. However, relatively few of these stars with activity cycles have been detected. It is well known that the cores of the Ca II H&K lines are modulated by stellar activity. The behaviour of the Balmer and other optical lines with stellar activity is not yet completely understood. Aims. We search for variations in the Ca II H&K, Balmer, and Fe II lines modulated by stellar activity. In particular, we apply a novel strategy to detect possible shape variations in the Hα line. Methods. We analysed activity signatures in HD 38858 using HARPS and CASLEO spectra obtained between 2003 and 2017. We calculated the Mount Wilson index (SMW), log(R′HK), and the statistical moments of the Ca II H&K, Balmer, and other optical lines. We searched for periodicities using the generalized Lomb-Scargle periodogram. Results. We detect a long-term activity cycle of 10.8 yr in Ca II H&K and Hα in the solar-analogue star HD 38858. In contrast, this cycle is marginally detected in the Fe II lines. We also detect a noticeable variation in radial velocity that seems to be produced by stellar activity. Conclusions. HD 38858 is the second solar-analogue star where we find a clear activity cycle that is replicated in the Balmer lines. Spectral indexes based on the shape of Hα line seem to be more reliable than the fluxes in the same line for detecting activity variations. The cyclic modulation we detected gives place to a variation in radial velocity that previously has been associated with a super-Earth planet. Finally, due to the similarity of HD 38858 with the Sun, we recommend to continue monitoring this star.

The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515

“…Furthermore, Flores et al (2016) showed observational evidence of modulations (∼2 mÅ) of the equivalent widths (hereafter EW) of Fe II lines with the chromospheric cycle of the solar twin HIP 45184 (with ∼5.1 yr activity cycle and S = 0.173). However, Flores et al (2018) were not able to find the similar modulations in HD 38858 (∼10.8 yr activity cycle). Precise spectroscopic measurements in the Sun over more than three decades (Livingston et al 2007), show small but measurable variations in some spectral lines (including some strong Fe I lines), but their dependence on the solar activity cycle is not well-established yet.…”

Solar activity and responses observed in Balmer lines

“…Recent multi-year long-term surveys of sizeable samples of F-M (Cincunegui et al 2007) and F-G-K stars (Gomes da Silva et al 2014) provide a perplexingly wide variety of cases, from well-correlated to independent and even anticorrelated behavior of the CaII and Hα line fluxes (Cincunegui et al 2007). For example, in two solar analogs, HD 45184 (Flores et al 2016) and HD 38858 (Flores et al 2018), the rising line-core fluxes (line-filling and shallowing in a typical reaction to a rising stellar activity) in the CaII H&K doublet lead to a stronger (deeper) profile of the Balmer Hβ line.…”

Detecting prolonged activity minima in binary stars

“…The most significant CLEAN periods are indicated in each panel. Baliunas et al 1995;Metcalfe et al 2010;Gomes da Silva et al 2011;Flores et al 2018b), enables us to reduce the rotational scatter originated by individual active regions. Following Zechmeister & Kürster (2009), we computed the Generalised Lomb-Scargle periodogram (hereafter GLS) and the false-alarm probability (hereafter FAP, see their equation 24) of each significant peak present in the periodograms.…”