Related papers: HD 4915: A Maunder Minimum Candidate
The long-term solar magnetic activity and its cyclical behaviour, which is maintained by a dynamo mechanism, are both still challenging for the astrophysics. In particular, an atypical event occurred between 1645 and 1715 when the solar…
HD 166620 was recently identified as a Maunder Minimum candidate based on nearly 50 years of Ca II H & K activity data from Mount Wilson and Keck-HIRES (Baum et al. 2022). These data showed clear cyclic behavior on a 17-year timescale…
We present five decades of chromospheric activity measurements in 59 Sun-like stars as time series. These include and extend the 35 yr of stellar chromospheric activity observations by the Mount Wilson Survey (1966--2001), and continued…
As the only known unambiguous star in a Maunder minimum-like chromospheric activity state, the properties of HD 166620 can provide valuable insight into the behaviour of the Sun during the historic extended low-states of its activity cycle.…
We report intensive monitoring of the activity variability in the H$\alpha$ line for 10 Sun-like stars using the 1.88-m reflector at Okayama Branch Office, Subaru Telescope, during the last four years 2019-2022. Our aim was to investigate…
Context. It is well known that from 1645 to 1715 solar activity was notably low and the number of sunspots was extremely reduced. This epoch is known as the Maunder Minimum (MM). The study of stars in prolonged activity minima like the MM…
We present new Hubble Space Telescope (HST) UV spectra of the K2 V star HD 166620, the first star clearly recognized to be in a "magnetic grand minimum" state analogous to the Sun's "Maunder Minimum" in the late 1600's. The stellar H I…
The solar analogs of M67 let us glimpse the probable behavior of the Sun on time scales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun.…
We present the results from high-resolution spectroscopic measurements to determine metallicities and activities of bright stars in the southern hemisphere. We have measured the iron abundances ([Fe/H]) and chromospheric emission indices…
One of the most enigmatic phenomena related to solar activity is the so-called Maunder minimum phase. It consists of the lowest sunspot's counting ever registered for the Sun, and never so far confirmed for other stars. Since the…
Aims: Although the time of the Maunder minimum (1645--1715) is widely known as a period of extremely low solar activity, claims are still debated that solar activity during that period might still have been moderate, even higher than the…
We report the results of our study of magnetic fields in a sample of 15 Be stars using spectropolarimetric data obtained at the European Southern Observatory with the multi-mode instrument FORS1 installed at the 8m Kueyen telescope. We…
High-resolution spectra of the magnetic star HD191612 were acquired using the Chandra X-ray observatory at both maximum and minimum emission phases. We confirm the flux and hardness variations previously reported with XMM-Newton,…
Aims: We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena. Methods: We discuss…
The Sun has a steady 11-year cycle in magnetic activity most well-known by the rising and falling in the occurrence of dark sunspots on the solar disk in visible bandpasses. The 11-year cycle is also manifest in the variations of emission…
M dwarfs are prime targets for planet search programs, particularly of those focused on the detection and characterization of rocky planets in the habitable zone. Understanding their magnetic activity is important because it affects our…
Most stars previously identified as Maunder minimum stars are old stars evolved off of the main sequence. Analysis of activity measurements from the California and Carnegie Planet Search program stars and Hipparcos parallaxes implies that…
The solar cycle periodically reshapes the magnetic structure and radiative output of the Sun and determines its impact on the heliosphere roughly every 11 years. Besides this main periodicity, it shows century-long variations (including…
Activity studies of solar-type stars, especially with reference to the status of our current Sun among them, have exposed the importance of (1) homogeneously selecting the sample stars and (2) reliably evaluating their activities down to a…
We present the initial results from our XMM program aimed at searching for X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat more evolved than the Sun, and with a less massive companion) with a pronounced 8.2…