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The chromospherically active binary star EI Eridani: I. Absolute dimensions
We present a detailed determination of the astrophysical parameters ofthe chromospherically active binary star EI Eridani. Our new radialvelocities allow to improve the set of orbital elements and reveallong-term variations of the barycentric velocity. A possible third-bodyorbit with a period of {? 19} years is presented. Absoluteparameters are determined in combination with the {Hipparcos} parallax.EI Eri's inclination angle of the rotational axis is confined to 56.0 °± 4.5 °, its luminosity class {IV} is confirmed by its radius of{2.37 ± 0.12} R_{?}. A comparison to theoreticalstellar evolutionary tracks suggests a mass of 1.09 ± 0.05M_{?} and an age of ? 6.15 Gyr. The presentinvestigation is the basis of our long-term Doppler imaging study of itsstellar surface.
| Long-term magnetic activity in close binary systems. I. Patterns of color variations
Aims.This is the first of a series of papers in which we present theresults of a long-term photometric monitoring project carried out atCatania Astrophysical Observatory aimed at studying magnetic activity inlate-type components of close binary systems, its dependence on globalstellar parameters, and its evolution on different time scales from daysto years. In this first paper, we present the complete observationdataset and new results of an investigation into the origin ofbrightness and color variations observed in the well-known magneticallyactive close binary stars: AR Psc, VYAri, UX Ari, V711 Tau,EI Eri, V1149 Ori, DHLeo, HU Vir, RS CVn,V775 Her, AR Lac, SZPsc, II Peg and BY Dra Methods: About 38 000 high-precision photoelectric nightly observationsin the U, B and V filters are analysed. Correlation and regressionanalyses of the V magnitude vs. U-B and B-V color variations are carriedout and a comparison with model variations for a grid of active regiontemperature and filling factor values is also performed. Results: Wefind the existence of two different patterns of color variation. Eightstars in our sample: BY Dra, VYAri, V775 Her, II Peg,V1149 Ori, HU Vir, EIEri and DH Leo become redder when theybecome fainter, as is expected from the presence of active regionsconsisting of cool spots. The other six stars show the oppositebehaviour, i.e. they become bluer when they become fainter. ForV711 Tau this behaviour could be explained by theincreased relative U- and B-flux contribution by the earlier-typecomponent of the binary system when the cooler component becomesfainter. On the other hand, for AR Psc, UXAri, RS CVn, SZ Psc andAR Lac the existence of hot photospheric faculae mustbe invoked. We also found that in single-lined and double-lined binarystars in which the fainter component is inactive or much less active theV magnitude is correlated to B-V and U-B color variations in more than60% of observation seasons. The correlation is found in less than 40% ofobservation seasons when the fainter component has a non-negligiblelevel of activity and/or hot faculae are present but they are eitherspatially or temporally uncorrelated to spots.I dedicate this paper to the memory of the P.I. of this project, Prof.Marcello Rodonò, who suddenly passed away on October 23, 2005. Tohim my sincere estimation and deepest gratitude.Based onobservations collected at INAF-Catania Astrophysical Observatory, Italy.
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Long-term monitoring of active stars. IV. UBV(RI)_c_ observations obtained at La Silla in December 1989.
High-precision UBV(RI)_c_ photometry of 23 selected acitve stars,collected at the European Southern Observatory (La Silla, Chile) overthe period 9-28 December 1989, is presented. This paper is part of alarger program focusing on the global properties and evolution of activestars and is aimed at establishing a time-extended database which cangive important clues on topics such as the stability of the spottedareas, differential rotation and solar-like cycles. Significantevolution of the wave-like light curves, period variations and, in mostcases, evidence for long-term variability of the global degree ofspottedness are found for the observed stars. Some spectralclassifications are rediscussed and evidence for a newly discoveredvariable star is given.
| Long-term monitoring of active stars. I - 1988-89 UBV photometry with the PHOENIX APT
As part of a large program aimed at studying the global properties andevolution of active star atmospheres, high-precision UBV photometry ofselected RS CVn, BY Dra, and FK Com-type systems has been carried outsince early 1988 by using the Phoenix 25-cm Automatic PhotoelectricTelescope at Whipple Observatory on Mt. Hopking (USA, AZ). We presentthe results of systematic obsrvations of nine active stars monitoredduring the years 1988 and 1989. Significant evolution of the wave-likelight curves for most of the observed stars, both in amplitude andshape, is found. These photometric data can give important clues on thelifetimes of spotted areas and associated magnetic structures,differential rotation and solar-like cycles, and are required to addressthe question of spatial and physical correlations between confinedstructures in active star photospheres and outer atmospheres, the latterderived from chromospheric and transition region spectral signatures atother wavelengths. Evidence of long-term variability for most of theobserved stars is also presented.
| Photoelectric photometry of the RS CVn binary EI Eridani = HD 26337
Differential UBV(RI)sub KC and UBVRI photometry of the RS CVn binary EIEridani obtained during December 1987 and January 1988 at fourteendifferent observatories is presented. A combined visual bandpass lightcurve, corrected for systematic errors of different observatories,utilizes the photometric period of 1,945 days to produce useful results.The analysis shows the visual light curve to have twin maxima, separatedby about 0.4 phase, and a full amplitude of approximately 0.06 mag forthe period of observation, a smaller amplitude than reported in thepast. The decrease in amplitude may be due to a decrease orhomogenization of spot coverage. To fit the asymmetrical light curve, astarspot model would have to employ at least two spotted regionsseparated in longitude.
| Observations of active chromosphere stars
It is pointed out that spectroscopic signatures of stellar chromosphericactivity are readily observable. The present study is concerned with newphotometric and spectroscopic observations of active-chromosphere RSCVn, BY Dra, and FK Com stars. Attention is given to the first resultsof a synoptic monitoring program of many active chromosphere stars.During the time from 1980 to 1982, photometric and spectroscopicobservations of 10 known or suspected active-chromosphere objects weremade. The results regarding the individual stars are discussed. Sevenstars observed with the International Ultraviolet Explorer (IUE) are allspectroscopic binaries.
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