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تسجيل مستخدم جديدThe chromospherically active binary star EI Eridani I. Absolute dimensions
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We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long-term variations of the barycentric velocity. A possible third-body orbit with a period of approximately 19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eris inclination angle of the rotational axis is confined to 56.0 plus/minus 4.5 degrees, its luminosity class IV is confirmed by its radius of 2.37 plus/minus 0.12 R_Sun. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 plus/minus 0.05 M_Sun and an age of approximately 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface.
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RAVE, the unbiased magnitude limited survey of the southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the CaII IRT range which is a known indicator of chromospheric activity. Our previous work (
Matijeviv{c} et al. 2012) classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-LTE profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5AA wide interval and their sum EW_IRT for ~44,000 candidate active dwarf stars with S/N>20 and with no respect to the source of their emission flux. From these ~14,000 show a detectable chromospheric flux with at least 2sigma confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and in some cases radial velocities of active stars derived from automatic pipeline suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre main-sequence cases. The catalogue will be publicly available with the next RAVE public data releases.
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