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The kinematics, mean α-elements, and ages of the stars reveal two distinct disc populations observed in the Solar neighbourhood. Although several studies have been carried out to characterize abundances of chemical elements and kinematic identifications in these populations, there are few studies that dealt with the analysis of stellar rotation and characteristics of populations focused on low-mass stars of the F and G types. In this work, we propose a new approach to classify stellar populations from the thin and thick disc for F and G dwarf stars by relating chemical abundance and rotation (v  sin  i) of these stars in the rotational–chemical–plane (v  sin  i –[α/Fe]–[Fe/H] plot). Our results show that the two rotational-chemical sequences disentangled, high- and low-[α/Fe] components, present properties (α-enhanced, ages, kinematics, space velocity gradients, local density ratio) closely linked to the stars of the chemically and kinematically defined as thin and thick disc components. This study has an impact on calibrations that relate ages to rotation (gyro-chronology) as well as age to chemical abundances (chemochronology), as well as sheds light on the understanding of the processes of Galactic disc formation. [ABSTRACT FROM AUTHOR]

Photometric time series gathered by space telescopes such as CoRoT and Kepler allow to detect solar-like oscillations in red giant stars and to measure their global seismic constraints, which can be used to infer global stellar properties (e.g. masses, radii, and evolutionary states). Combining such precise constraints with photospheric abundances provides a means of testing mixing processes that occur inside red-giant stars. In this work, we conduct a detailed spectroscopic and seismic analysis of nine nearby (d < 200 pc) red giant stars observed by Kepler. Both seismic constraints and grid-based modelling approaches are used to determine precise fundamental parameters for those evolved stars. We compare distances and radii derived from Gaia Data Release 3 parallaxes with those inferred by a combination of seismic, spectroscopic, and photometric constraints. We find no deviations within errors bars, however the small sample size and the associated uncertainties are a limiting factor for such comparison. We use the period spacing of mixed modes to distinguish between ascending red-giants and red clump stars. Based on the evolutionary status, we apply corrections to the values of Δν for some stars, resulting in a slight improvement to the agreement between seismic and photometric distances. Finally, we couple constraints on detailed chemical abundances with the inferred masses, radii, and evolutionary states. Our results corroborate previous studies that show that observed abundances of lithium and carbon isotopic ratio are in contrast with predictions from standard models, giving robust evidence for the occurrence of additional mixing during the red-giant phase. [ABSTRACT FROM AUTHOR]

A comprehensive multiwavelength campaign has been carried out to probe stellar activity and variability in the young Sun-like star ι-Horologii. We present the results from long-term spectropolarimetric monitoring of the system by using the ultra-stable spectropolarimeter/velocimeter HARPS at the ESO 3.6-m telescope. Additionally, we included high-precision photometry from the NASA Transiting Exoplanet Survey Satellite (TESS) and observations in the far- and near-ultraviolet spectral regions using the STIS instrument on the NASA/ESA Hubble Space Telescope (HST). The high-quality data set allows a robust characterization of the star's rotation period, as well as a probe of the variability using a range of spectroscopic and photometric activity proxies. By analysing the gradient of the power spectra (GPS) in the TESS light curves, we constrained the faculae-to-spot driver ratio (⁠|$\rm S_{fac}/S_{spot}$|⁠) to 0.510 ± 0.023, which indicates that the stellar surface is spot dominated during the time of the observations. We compared the photospheric activity properties derived from the GPS method with a magnetic field map of the star derived using Zeeman–Doppler imaging (ZDI) from simultaneous spectropolarimetric data for the first time. Different stellar activity proxies enable a more complete interpretation of the observed variability. For example, we observed enhanced emission in the HST transition line diagnostics C  iv and C  iii , suggesting a flaring event. From the analysis of TESS data acquired simultaneously with the HST data, we investigate the photometric variability at the precise moment that the emission increased and derive correlations between different observables, probing the star from its photosphere to its corona. [ABSTRACT FROM AUTHOR]

The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

Solar analogues are important stars to study for understanding the properties of the Sun. Combined with seismic and spectroscopic analysis, evolutionary modelling becomes a powerful method to characterize stellar intrinsic parameters, such as mass, radius, metallicity and age. However, these characteristics, relevant for other aspects of astrophysics or exoplanetary system physics, for example, are difficult to obtain with high precision and/or accuracy. The goal of this study is to characterize the two solar analogues, HD 42618 and HD 43587, observed by CoRoT. In particular, we aim to infer their precise mass, radius and age, using evolutionary modelling constrained by spectroscopic, photometric and seismic analysis. These stars show evidence of being older than the Sun but with a relatively large lithium abundance. We present the seismic analysis of HD 42618, and the modelling of the two solar analogues, HD 42618 and HD 43587 using the cestam stellar evolution code. Models were computed to reproduce the spectroscopic (effective temperature and metallicity) and seismic (mode frequency) data, and the luminosity of the stars, based on Gaia parallaxes. We infer very similar values of mass and radius for both stars compared with the literature, within the uncertainties, and we reproduce correctly the seismic constraints. The modelling shows that HD 42618 is slightly less massive and older than the Sun, and that HD 43587 is more massive and older than the Sun, in agreement with previous results. The use of chemical clocks improves the reliability of our age estimates. [ABSTRACT FROM AUTHOR]

We present a study of the evolutionary state of a few lithium-rich giant stars based on the Gaia Data Release 2 (DR2) parallaxes and photometry. We also investigate the chromospheric activity, the presence of a surface magnetic field, and the radial velocity for our sample stars. We analysed both archive and new data. We gathered archive spectra from several instruments, mainly ELODIE and NARVAL, and we added new data acquired with the spectrograph MUSICOS. We applied the least-squares deconvolution technique to obtain Stokes V and I mean profiles to compute longitudinal magnetic field for a subset. Moreover, for the same subset, we analysed the Ca  ii  H&K emission lines to calculate the S -index. We also derived atmospheric parameters and Li abundances for all 18 stars of our sample. We found that stars previously classified as red giant branch (RGB) may actually be at a different evolutionary state. Furthermore, we identified that most stars in our sample with detection of surface magnetic field show at least moderate rotation velocities, but none the less, we could not detect a magnetic field in two fast rotators. Because of our small sample of magnetic giants, it is difficult to determine if the presence of surface magnetic field and the Li-rich giant phenomena could be somehow linked. The large variation of the radial velocity of part of our sample indicates that some of them might have a binary companion, which may change the way we look at the Li problem in giant stars. [ABSTRACT FROM AUTHOR]

Context. One of the most enigmatic phenomena related to solar activity is the so-called Maunder minimum phase. It consists in the lowest sunspot count ever registered for the Sun and has not been confirmed for other stars to date. Since the spectroscopic observations of stellar activity at the Mount Wilson Observatory, the solar analog HD 43587 has shown a very low and apparently invariant activity level, which makes it a Maunder minimum candidate. Aims. We aim to analyze the chromospheric activity evolution of HD 43587 and its evolutive status, with the intention of unraveling the reasons for this low and flat activity. Methods. We used an activity measurements dataset available in the literature, and computed the S-index from HARPS and NARVAL spectra to infer a cycle period. Additionally, we analyzed the CoRoT light curve of HD 43587, and applied gyrochronology and activity calibrations to determine its rotation period. Finally, based on an evolutionary model and the inferred rotation period, we used the EULAG-MHD code to perform global MHD simulations of HD 43587 to get some insight into its dynamo process. Results. We confirm the almost flat activity profile, with a cycle period Pcyc = 10.44 ± 3.03 yr deduced from the S-index time series, and a long-term trend that might be a period of more than 50 yr. It was impossible to define a rotation period from the light curve, however gyrochronology and activity calibrations allow us to infer an indirect estimate of ¯Prot = 22.6 ± 1.9 P ¯ rot = 22.6 ± 1.9 $ \overline{P}_{\mathrm{rot}} = 22.6 \pm 1.9 $ d. Furthermore, the MHD simulations confirm an oscillatory dynamo with a cycle period in good agreement with the observations and a low level of surface magnetic activity. Conclusions. We conclude that this object might be experiencing a "natural" decrease in magnetic activity as a consequence of its age. Nevertheless, the possibility that HD 43587 is in a Maunder minimum phase cannot be ruled out. [ABSTRACT FROM AUTHOR]

In this work, we simulate the evolution of the solar wind along its main-sequence lifetime and compute its thermal radio emission. To study the evolution of the solar wind, we use a sample of solar mass stars at different ages. All these stars have observationally reconstructed magnetic maps, which are incorporated in our 3D magnetohydrodynamic simulations of their winds. We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionary time-scales, although they can vary in a magnetic cycle time-scale. Stellar winds are known to emit radiation in the form of thermal bremsstrahlung in the radio spectrum. To calculate the expected radio fluxes from these winds, we solve the radiative transfer equation numerically from first principles. We compute continuum spectra across the frequency range 100 MHz to 100 GHz and find maximum radio flux densities ranging from 0.05 to 2.2 |$\mu$| Jy. At a frequency of 1 GHz and a normalized distance of d  = 10 pc, the radio flux density follows 0.24 (Ω/Ω⊙)0.9 (d /[10pc])-2 |$\mu$| Jy, where Ω is the rotation rate. This means that the best candidates for stellar wind observations in the radio regime are faster rotators within distances of 10 pc, such as κ1 Ceti (0.73 |$\mu$| Jy) and χ1 Ori (2.2 |$\mu$| Jy). These flux predictions provide a guide to observing solar-type stars across the frequency range 0.1–100 GHz in the future using the next generation of radio telescopes, such as ngVLA and Square Kilometre Array. [ABSTRACT FROM AUTHOR]

Tidal interaction governs the redistribution of angular momentum in close binary stars and planetary systems and determines the systems evolution towards the possible equilibrium state. Turbulent friction acting on the equilibrium tide in the convective envelope of low-mass stars is known to have a strong impact on this exchange of angular momentum in binaries. Moreover, theoretical modelling in recent literature as well as presented in this paper suggests that the dissipation of the dynamical tide, constituted of tidal inertial waves propagating in the convective envelope, is weak compared to the dissipation of the equilibrium tide during the red giant phase. This prediction is confirmed when we apply the equilibrium-tide formalism developed by Zahn, Verbunt & Phinney, and Remus, Mathis & Zahn on to the sample of all known red giant binaries observed by the NASA Kepler mission. Moreover, the observations are adequately explained by only invoking the equilibrium tide dissipation. Such ensemble analysis also benefits from the seismic characterization of the oscillating components and surface rotation rates. Through asteroseismology, previous claims of the eccentricity as an evolutionary state diagnostic are discarded. This result is important for our understanding of the evolution of multiple star and planetary systems during advanced stages of stellar evolution. [ABSTRACT FROM AUTHOR]

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos. [ABSTRACT FROM AUTHOR]

We investigate how the observed large-scale surface magnetic fields of low-mass stars (∼0.1–2 M⊙), reconstructed through Zeeman–Doppler imaging, vary with age t, rotation and X-ray emission. Our sample consists of 104 magnetic maps of 73 stars, from accreting pre-main sequence to main-sequence objects (1 Myr ≲ t ≲ 10 Gyr). For non-accreting dwarfs we empirically find that the unsigned average large-scale surface field is related to age as t−0.655 ± 0.045. This relation has a similar dependence to that identified by Skumanich, used as the basis for gyrochronology. Likewise, our relation could be used as an age-dating method (‘magnetochronology’). The trends with rotation we find for the large-scale stellar magnetism are consistent with the trends found from Zeeman broadening measurements (sensitive to large- and small-scale fields). These similarities indicate that the fields recovered from both techniques are coupled to each other, suggesting that small- and large-scale fields could share the same dynamo field generation processes. For the accreting objects, fewer statistically significant relations are found, with one being a correlation between the unsigned magnetic flux and rotation period. We attribute this to a signature of star–disc interaction, rather than being driven by the dynamo. [ABSTRACT FROM AUTHOR]

Context. We present rotation period measurements for subgiants observed by CoRoT. Interpreting the modulation of stellar light that is caused by star-spots on the time scale of the rotational period depends on knowing the fundamental stellar parameters. Aims. Constraints on the angular momentum distribution can be extracted from the true stellar rotational period. By using models with an internal angular momentum distribution and comparing these with measurements of rotation periods of subgiant stars we investigate the agreement between theoretical predictions and observational results. With this comparison we can also reduce the global stellar parameter space compatible with the rotational period measurements from subgiant light curves. We can prove that an evolution assuming solid body rotation is incompatible with the direct measurement of the rotational periods of subgiant stars. Methods. Measuring the rotation periods relies on two different periodogram procedures, the Lomb-Scargle algorithm and the Plavchan periodogram. Angular momentum evolution models were computed to give us the expected rotation periods for subgiants, which we compared with measured rotational periods. Results. We find evidence of a sinusoidal signal that is compatible in terms of both phase and amplitude with rotational modulation. Rotation periods were directly measured from light curves for 30 subgiant stars and indicate a range of 30 to 100 d for their rotational periods. Conclusions. Our models reproduce the rotational periods obtained from CoRoT light curves. These new measurements of rotation periods and stellar models probe the non-rigid rotation of subgiant stars. [ABSTRACT FROM AUTHOR]

κ1 Cet (HD 20630, HIP 15457, d = 9.16 pc, V = 4.84) is a dwarf star approximately 30 light-years away in the equatorial constellation of Cetus. Among the solar proxies studied in the Sun in Time, κ1 Cet stands out as potentially having a mass very close to solar and a young age. On this study, we monitored the magnetic field and the chromospheric activity from the Ca II H & K lines of κ1 Cet. We used the technique of Least-Square-Deconvolution (LSD, Donati et al. 1997) by simultaneously extracting the information contained in all 8,000 photospheric lines of the echelogram (for a linelist matching an atmospheric model of spectral type K1). To reconstruct a reliable magnetic map and characterize the surface differential rotation of κ1 Cet we used 14 exposures spread over 2 months, in order to cover at least two rotational cycles (Prot ~9.2 days). The Least Square deconvolution (LSD) technique was applied to detect the Zeeman signature of the magnetic field in each of our 14 observations and to measure its longitudinal component. In order to reconstruct the magnetic field geometry of κ1 Cet, we applied the Zeeman Doppler Imaging (ZDI) inversion method. ZDI revealed a structure in the radial magnetic field consisting of a polar magnetic spot. On this study, we present the fisrt look results of a high-resolution spectropolarimetric campaign to characterize the activity and the magnetic fields of this young solar proxy. [ABSTRACT FROM PUBLISHER]

Using spectropolarimetric data acquired with the ESPaDOnS and NARVAL instruments at CFHT and at TBL, we present a detailed spectral synthesis analysis of HD 232 862, a field giant classified as a G8II star hosting a magnetic field. This star is the first lithium-rich field giant hosting a magnetic field. Stellar evolution models suggest that HD 232 862 should be a 1.5 to 2.0 M⊙ star at the bottom of the red giant branch. Its unsually high lithium content (A(Li) = 2.45 ± 0.25 dex) is even more puzzling and challenges our understanding of the evolution of this star. [ABSTRACT FROM PUBLISHER]

We explore the non-standard mixing history of five solar twins to determine as precisely as possible their mass and age. For this, we computed a grid of evolutionary models with non-standard mixing at given metallicities with the Toulouse-Geneva code for a range of stellar masses. We choose the evolutionary model that best fit the low lithium abundances observed in the solar twins. Our best model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. Li depletion due to the additional mixing in solar-twins is strongly mass dependent. An accurate lithium abundance measurement connected with non-standard models provides a more precise information about the age and mass better than that determined only by classical methods. [ABSTRACT FROM PUBLISHER]

From spectropolarimetric data and spectral synthesis analysis, we report the serendipitous discovery of an unusually high lithium content field giant. HD 232862, classified as a G8II star, appears to be the first Lithium-rich field giant star hosting a surface magnetic field. [ABSTRACT FROM PUBLISHER]

We describe the behavior of the rotational velocity in metal-poor stars ([Fe/H] ~ −0.5 dex) at different evolutionary stages, based on v sin i values from the literature. Our sample is composed of stars in the field and in some Galactic globular clusters, including stars on the main sequence (MS), red-giant branch (RGB), and horizontal branch (HB). The metal-poor stars are mainly slow rotators, and their v sin i distribution along the Hertzsprung–Russell diagram is quite homogeneous. Nevertheless, a few moderate to high values of v sin i are found for stars located on the MS and the HB. We show that the overall distribution of v sin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating MS stars in our sample exhibit similar rotation rates as their metal-rich counterparts, suggesting that some may actually be fairly young, in spite of their low metallicity, or else that at least some would be better classified as blue straggler stars. We do not find significant evidence of evolution in v sin i values as a function of position on the RGB. In particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue-HB stars has been suggested as due to angular-momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and v sin i values. [ABSTRACT FROM PUBLISHER]