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تسجيل مستخدم جديدSolar analogues in open clusters: The case of M67
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K. Biazzo
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Solar analogues are fundamental targets for a better understanding of our Sun and our Solar System. Usually, this research is limited to field stars, which offer several advantages and limitations. In this work, we present the results of a research of solar twins performed for the first time in a open cluster, namely M67. Our analysis allowed us to find five solar twins and also to derive a solar colour of (B-V)0=0.649+/-0.016 and a cluster distance modulus of 9.63+/-0.08. This study encourages us to apply the same method to other open clusters, and to do further investigations for planet search in the solar twins we find.
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The solar analogues are fundamental targets for a better understanding of our Sun and Solar System. Notwithstanding the efforts, this research is usually limited to field stars. The open cluster M67 offers a unique opportunity to search for solar ana
logues because its chemical composition and age are very similar to those of our star. In this work, we analyze FLAMES@VLT spectra of about one hundred of M67 main sequence stars with the aim to identify solar analogues. We first determine cluster members which are likely not binaries, by combining both proper motions and radial velocity measurements. Then, we concentrate our analysis on the determination of stellar effective temperature, using the analyzes of line-depth ratios and Halpha wings. Finally, we also compute lithium abundance for all the stars. Thanks to the our analysis, we find ten solar analogues, which allow us to derive a solar color (B-V)=0.649+/-0.016 and a cluster distance modulus of 9.63+/-0.08, very close to values found by previous authors. Among them, five are the best solar twins with temperature determinations within 60 K from the solar values. Our results lead us to do further spectroscopic investigations because the solar analogues candidates are suitable for planet search.
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Mixing mechanisms bring the Li from the base of the convective zone to deeper and warmer layers where it is destroyed. These mechanisms are investigated by comparing observations of Li abundances in stellar atmospheres to models of stellar evolution.
Observations in open cluster are especially suitable for this comparison, since their age and metallicity are homogeneous among their members and better determined than in field stars. In this work, we compare the evolution of Li abundances in three different clusters: the Hyades, NGC752, and M67. Our models are calculated with microscopic diffusion and transport of chemicals by meridional circulation, and calibrated on the Sun. These comparisons allow us to follow the evolution of Li abundance as a function of stellar mass in each cluster and as a function of the age by comparing this evolution in each cluster. We evaluate the efficiency of the mixing mechanisms used in the models, and we try to identify the lacking mechanisms to reproduce the observed evolution of Li abundance.
Lithium abundances in open clusters provide an effective way of probing mixing processes in the interior of solar-type stars and convection is not the only mixing mechanism at work. To understand which mixing mechanisms are occurring in low-mass star
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Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. Their occurrence rates and energy distributions trace stellar characteristics such as mass and age. But before flares can be used
to constrain stellar properties, the flaring-age-mass relation requires proper calibration. This work sets out to quantify flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Drawing from the complete K2 archive, we searched 3435 $sim 80$ day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6 Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690 Myr) to the sample as a comparison cluster to Praesepe (750 Myr), the 2.6 Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. The flare energy distribution was similar in the entire parameter space, following a power law relation with exponent $alphaapprox 1.84-2.39$. The flaring rates declined with age, and declined faster for higher mass stars. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 days, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. (abridged)
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