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The CCD photometric study of the newly identified RS CVn binary star DV Piscium
This paper presents new CCD BVRI light curves of the newly discovered RSCVn eclipsing binary star DV Psc. From the asymmetric light curvesoutside the eclipse, we find there are two depressions in the phaseranges 0.3-0.45 and 0.6-0.9, respectively. By analyzing thelight curves using the Wilson-Devinney program, the fourphotometric solutions of the system are obtained and the starspotparameters are also derived. It turns out that the case of two spotsbeing on the primary is most successful in reproducing the light curvedistortion of DV Psc. Moreover, analysis the longitudes of spotssuggests that there are two active longitude belts (one is about90°, the other is about 270°). At the same time, on 22 November2008, the first flare-like event was detected on DV Psc at phase 0.35whose duration was about 13.5 min. These findings reveal that DV Psc hasa high degree of magnetic activity.
| Starspots
Starspots are created by local magnetic fields on the surfaces of stars,just as sunspots. Their fields are strong enough to suppress theoverturning convective motion and thus block or redirect the flow ofenergy from the stellar interior outwards to the surface andconsequently appear as locally cool and therefore dark regions againstan otherwise bright photosphere (Biermann in Astronomische Nachrichten264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots areobservable tracers of the yet unknown internal dynamo activity and allowa glimpse into the complex internal stellar magnetic field structure.Starspots also enable the precise measurement of stellar rotation whichis among the key ingredients for the expected internal magnetictopology. But whether starspots are just blown-up sunspot analogs, we donot know yet. This article is an attempt to review our current knowledgeof starspots. A comparison of a white-light image of the Sun (G2V, 5Gyr) with a Doppler image of a young solar-like star (EK Draconis;G1.5V, age 100 Myr, rotation 10 × ? Sun) and witha mean-field dynamo simulation suggests that starspots can be ofsignificantly different appearance and cannot be explained with ascaling of the solar model, even for a star of same mass and effectivetemperature. Starspots, their surface location and migration pattern,and their link with the stellar dynamo and its internal energytransport, may have far reaching impact also for our understanding oflow-mass stellar evolution and formation. Emphasis is given in thisreview to their importance as activity tracers in particular in thelight of more and more precise exoplanet detections around solar-like,and therefore likely spotted, host stars.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Multiple and changing cycles of active stars. II. Results
Aims. We study the time variations in the cycles of 20 active starsbased on decade-long photometric or spectroscopic observations. Methods:A method of time-frequency analysis, as discussed in a companion paper,is applied to the data. Results: Fifteen stars definitely show multiplecycles, but the records of the rest are too short to verify a timescalefor a second cycle. The cycles typically show systematic changes. Forthree stars, we found two cycles in each of them that are not harmonicsand vary in parallel, indicating a common physical mechanism arisingfrom a dynamo construct. The positive relation between the rotationaland cycle periods is confirmed for the inhomogeneous set of activestars. Conclusions: Stellar activity cycles are generally multiple andvariable.
| Multiple and changing cycles of active stars. I. Methods of analysis and application to the solar cycles
Context: Long-term observational data have information on the magneticcycles of active stars and that of the Sun. The changes in the activityof our central star have basic effects on Earth, such as variations inthe global climate, so that understanding the nature of these variationsis extremely important. Aims: The observed variations related tomagnetic activity cannot be treated as stationary periodic variations,therefore methods like Fourier transform or different versions ofperiodograms only give partial information on the nature of the lightvariability. We demonstrate that time-frequency distributions provideuseful tools for analysing the observations of active stars. Methods: We tested and used different methods, such as short-termFourier transform, wavelet, and generalised time-frequencydistributions, for analysing temporal variations in timescales ofobservational data. Results: With test data we demonstrate thatthe observational noise has practically no effect on the determinationin the long-term changes of time-series observations of active stars.The rotational signal may modify the determined cycles, therefore it isadvisable to remove it from the data. Wavelets are less powerful inrecovering complex long-term changes than other distributions that arediscussed. By applying our technique to the sunspot data we find acomplicated, multi-scale evolution in the solar activity.
| The chromospherically active binary star EI Eridani: II. Long-term Doppler imaging
Data from 11 years of continuous spectroscopic observations of theactive RS CVn-type binary star EI Eridani - gained at NSO/McMath-Pierce,KPNO/Coudé Feed and during the MUSICOS 98 campaign - were used toobtain 34 Doppler maps in three spectroscopic lines for 32 epochs, 28 ofwhich are independent of each other. Various parameters are extractedfrom our Doppler maps: average temperature, fractional spottedness, andlongitudinal and latitudinal spot-occurrence functions. We find thatnone of these parameters show a distinct variation nor a correlationwith the proposed activity cycle as seen from photometric long-termobservations. This suggests that the photometric brightness cycle maynot necessarily be due to just a cool spot cycle. The general morphologyof the spot pattern remains persistent over the whole period of 11years. A large cap-like polar spot was recovered from all our images. Ahigh degree of variable activity was noticed near latitudes of?60-70° where the appendages of the polar spot emerged anddissolved.
| 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.
| A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| Chromospheric activity on the RS Canum Venaticorum binary SZ Piscium
Aims. We present the new high-resolution echelle spectra of SZ Psc,obtained in Nov. 2004 and Sep.-Dec. 2006, and study its chromosphericactivity. Methods: By means of the spectral subtraction technique, weanalyze our spectroscopic observations including several opticalchromospheric activity indicators (the He I D{3}, Na I D{1}, D{2},Hα, and Ca II infrared triplet lines). Results: All indicatorsshow that the chromospheric activity of the system is associated withthe cooler component. We find that the values ofEW8542/EW8498 are in the range 1-3, whichindicates optically thick emission in plage-like regions. The 2006 datasuggest the presence of active longitude phenomena. For the Ca II 8542and 8662 and the Hα lines, it seems that the excess emission isstronger near the two quadratures of system. This may be anti-correlatedwith the behavior of the Na I D{1} line. The absorption features aredetected in the subtracted Hα lines, which could be explained byprominence-like extended material seen on the stellar disk or by masstransfer from the cooler component to the hotter one.
| Mg II h+k emission lines as stellar activity indicators of main sequence F-K stars
Context: The largest dataset of stellar activity measurements availableat present is the one obtained at the Mount Wilson Observatory, wherehigh-precision Ca II H+K fluxes have been measured from 1966 for about2200 stars. Since the Mg II h and k lines at λ2800 Å areformed in a similar way to the Ca II H+K emission lines, they are alsogood indicators of chromospheric structure. The InternationalUltraviolet Explorer (IUE) provides a large database of UV spectra inthe band 1150-3350 Å from 1978 to 1995, which can also be used tostudy stellar activity. Aims: The main purpose of this study is to usethe IUE spectra in the analysis of magnetic activity of main sequenceF-K stars. Combining IUE observations of Mg II and optical spectroscopyof Ca II, the registry of activity of stars can be extended in time. Methods: We retrieved all the high-resolution spectra of F, G, and Kmain sequence stars observed by IUE (i.e. 1623 spectra of 259 F to Kdwarf stars). We obtained the continuum surface flux near the Mg II h+klines near λ2800 Å and the Mg II line-core surface fluxfrom the IUE spectra. Results: We obtained a relation between the meancontinuum flux near the Mg II lines with the colour B-V of the star. Fora set of 117 nearly simultaneous observations of Mg II and Ca II fluxesof 21 F5 to K3 main sequence stars, we obtained a colour dependentrelation between the Mount Wilson Ca II S-index and the Mg II emissionline-core flux. As an application of this calibration, we computed theMount Wilson index for all the dF to dK stars which have high resolutionIUE spectra. For some of the most frequently observed main sequencestars, we analysed the Mount Wilson index S from the IUE spectra,together with the ones derived from visible spectra. We confirm thecyclic chromospheric activity of ɛ Eri (HD 22049) and βHydri (HD 2151), and we find a magnetic cycle in α Cen B (HD128621)Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/483/903
| 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.
| Changing stellar activity cycles
We investigated continuous long-term photometric datasets of thirteenactive stars, Ca II variability of one single main-sequence star, and10.7cm radio data of the Sun, with simple Fourier- and time-frequencyanalysis. The data reflect the strength of the activity manifested inmagnetic spots. All studied stars show multiple (2 to 4) cycles ofdifferent lengths. The time-frequency analysis reveals, that in severalcases of the sample one or two of the cycles exhibit continuous changes(increase or decrease). For four stars (V711 Tau, IL Hya, HK Lac, HD100180) and for the Sun we find that the cycle length changes arestrong, amounting to 10-50% during the observed time intervals. Thecycle lengths are generally longer for stars with longer rotationalperiods.
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Starspot activity in late stars: Methods and results
Three types of methods for studying the surface inhomogeneities of coolstars and the results of their use on type BY Dra, RS CVn, FK Com, and TTau variables are discussed. The current relevance of traditionalphotometric methods and the advantages of the zonal spottedness modelare pointed out. Dependences of the maximum total areas, averagelatitudes, and temperatures of spots on the global parameters of thestars are given. Analogs of the solar cycle in the variations of theareas and latitudes of starspots are examined, as well as the effects ofdifferential rotation and active longitudes.
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| Zonal Model of Starspots. Application to RS CVn Systems
Model results on starspots in 15 chromospherically active type RS CVnbinary systems are presented. The dependences of the parameters of thespots on the principal characteristics of the stars (spectral class,luminosity class, rotation, Rossby number) are examined. Latitudinaldrift of the spots, cycles in the spot activity, and differentialrotation are found in 9 of the stars.
| Photometric observations from theoretical flip-flop models
Some active stars show a so-called flip-flop phenomenon in which themain spot activity periodically switches between two active longitudesthat are 180° apart. In this paper we study the flip-flop phenomenonby converting results from dynamo calculations into long-term syntheticphotometric observations, which are then compared to the real stellarobservations. We show that similar activity patterns as obtained fromflip-flop dynamo calculations, can also be seen in the observations. Thelong-term light-curve behaviour seen in the synthesised data can be usedfor finding new stars exhibiting the flip-flop phenomenon.
| Spurious `active longitudes' in parametric models of heavily spotted eclipsing binaries
In this paper, the size distributions of starspots extrapolated from thecase of the Sun are modelled on the eclipsing binary SV Cam tosynthesize images of stellar photospheres with high spot fillingfactors. These spot distributions pepper the primary's surface withspots, many of which are below the resolution capabilities ofeclipse-mapping and Doppler-imaging techniques. The light curvesresulting from these modelled distributions are used to determine thelimitations of image reconstruction from photometric data. Surfacebrightness distributions reconstructed from these light curves showdistinctive spots on the primary star at its quadrature points. It isconcluded that two-spot modelling or chi-squared minimization techniquesare more susceptible to spurious structures being generated bysystematic errors, arising from incorrect assumptions about photosphericsurface brightness, than simple Fourier analysis of the light curves.
| Flip-flop phenomenon: observations and theory
In many active stars the spots concentrate on two permanent activelongitudes which are 180 ° apart. In some of these stars thedominant part of the spot activity changes the longitude every fewyears. This so-called flip-flop phenomenon has up to now been reportedin 11 stars, both single and binary alike, and including also the Sun.To explain this phenomenon, a non-axisymmetric dynamo mode, giving riseto two permanent active longitudes at opposite stellar hemispheres, isneeded together with an oscillating axisymmetric magnetic field. Here wediscuss the observed characteristics of the flip-flop phenomenon andpresent a dynamo solution to explain them.
| Stellar activity cycles: observing the dynamo?
The enormous complexity of the atmospheric structure observed on the Sunmakes it very difficult to compare the Sun with ``solar-type stars''.Clearly, we need to identify parameters that can be observed on the Sunas well as on other stars which can be interpreted unambiguously. Themost widely accepted dynamo signature is the presence of an activitycycle, well documented for the Sun and for main-sequence stars due tothe Mount Wilson Ca II H&K project. Only recently have we detectedspatial information, differential rotation and possibly meridional flowson other stars and thereby adding another constraint for itsinterpretation within a dynamo theory. Again, the picture is notcomplete yet, despite that there is just a single main ingredient thatacts as the driving mechanism for activity in all atmospheric layers andthe convective envelope of a solar-type star: the dynamo-relatedmagnetic field. I stress the importance of mapping stellar surfaces asfingerprints of the underlying dynamo action over long periods of time.
| Direct Evidence for a Polar Spot on SV Camelopardalis
We have used spectrophotometric data from the Hubble Space Telescope(HST) to eclipse-map the primary component of the RS CVn binary SV Camover nine HST orbits. We find from these observations and the Hipparcosparallax that the surface flux in the eclipsed low-latitude region ofthe primary is about 30% lower than that computed from a PHOENIX modelatmosphere at the effective temperature that best fits the spectralenergy distribution of the eclipsed flux. This can only be accounted forif about a third of the primary's surface is covered with unresolveddark starspots. Extending this to the full surface of the primary, wefind that, even taking into account this spot-filling factor, there isan additional flux deficit on the primary star. This can only beexplained if there is a large polar spot on the primary star extendingfrom the pole to latitude 48deg+/-6deg.
| Search for activity-induced variability in AR Lac, KT Peg, KZ And, II Peg and EI Eri in autumn 1997
We report on a search for activity-induced variability in the SB2systems AR Lac, KT Peg and KZ And as well as in the SB1 systems II Pegand EI Eri in the September 1997 season. The study of Hα lineprofiles, Na I 5889Angstrom doublet, Ca II IRT lines and TiO7055Angstrom absorption band is presented. The spot properties wereestimated for the systems AR Lac and II Peg. The former possesses spotsat intermediate stellar latitudes on the primary component while thelatter shows these surface inhomogeneities at low latitudes. In bothcases, the spots cooler than the surrounding photosphere were revealed.Significant variability in the hydrogen Hα line profile wasobserved on II Peg and EI Eri, and the evidence of a rotationalmodulation was found in KT Peg and II Peg.
| Mg II chromospheric radiative loss rates in cool active and quiet stars
The Mg II k emission line is a good indicator of the level ofchromospheric activity in late-type stars. We investigate the dependenceof this activity indicator on fundamental stellar parameters. To thispurpose we use IUE observations of the Mg II k line in 225 late-typestars of luminosity classes I-V, with different levels of chromosphericactivity. We first re-analyse the relation between Mg II k lineluminosity and stellar absolute magnitude, performing linear fits to thepoints. The ratio of Mg II surface flux to total surface flux is foundto be independent of stellar luminosity for evolved stars and toincrease with decreasing luminosity for dwarfs. We also analyse the MgII k line surface flux-metallicity connection. The Mg II k emissionlevel turns out to be not dependent on metallicity. Finally, the Mg II kline surface flux-temperature relation is investigated by treatingseparately, for the first time, a large sample of very active and normalstars. The stellar surface fluxes in the k line of normal stars arefound to be strongly dependent on the temperature and slightly dependenton the gravity, thus confirming the validity of recently proposedmodels. In contrast, data relative to RS CVn binaries and BY Dra stars,which show very strong chromospheric activity, are not justified in theframework of a description based only on acoustic waves and uniformlydistributed magnetic flux tubes so that they require more detailedmodels.
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| The science case of the PEPSI high-resolution echelle spectrograph and polarimeter for the LBT
We lay out the scientific rationale for and present the instrumentalrequirements of a high-resolution adaptive-optics Echelle spectrographwith two full-Stokes polarimeters for the Large Binocular Telescope(LBT) in Arizona. Magnetic processes just like those seen on the Sun andin the space environment of the Earth are now well recognized in manyastrophysical areas. The application to other stars opened up a newfield of research that became widely known as the solar-stellarconnection. Late-type stars with convective envelopes are all affectedby magnetic processes which give rise to a rich variety of phenomena ontheir surface and are largely responsible for the heating of their outeratmospheres. Magnetic fields are likely to play a crucial role in theaccretion process of T-Tauri stars as well as in the acceleration andcollimation of jet-like flows in young stellar objects (YSOs). Anotherarea is the physics of active galactic nucleii (AGNs) , where themagnetic activity of the accreting black hole is now believed to beresponsible for most of the behavior of these objects, including theirX-ray spectrum, their notoriously dramatic variability, and the powerfulrelativistic jets they produce. Another is the physics of the centralengines of cosmic gamma-ray bursts, the most powerful explosions in theuniverse, for which the extreme apparent energy release are explainedthrough the collimation of the released energy by magnetic fields.Virtually all the physics of magnetic fields exploited in astrophysicsis somehow linked to our understanding of the Sun's and the star'smagnetic fields.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| Stellar surface imaging: mapping brightness and magnetic fields
Rapidly rotating late-type stars typically display signs of magneticactivity that exceed those seen on the Sun by over two orders ofmagnitude. The techniques of Doppler imaging and Zeeman Doppler imaginghave been instrumental in unveiling magnetic activity patterns at thephotospheres of these active stars. Essentially, these techniques workby inverting time-series of high resolution spectra to producetemperature, brightness and/or magnetic field maps at the surfaces ofstars. I will describe how these techniques work and review what theyhave taught us about the nature of magnetic activity in rapid rotatorsover the last 20 years. Finally, I will conclude by outlining thecapabilities of these techniques in light of new instrumentation that isnow becoming available.
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Osservazione e dati astrometrici
| Costellazione: | Eridano |
| Ascensione retta: | 04h09m40.89s |
| Declinazione: | -07°53'34.3" |
| Magnitudine apparente: | 7.047 |
| Distanza: | 56.18 parsec |
| Moto proprio RA: | 36.3 |
| Moto proprio Dec: | 105.1 |
| B-T magnitude: | 7.867 |
| V-T magnitude: | 7.115 |
Cataloghi e designazioni:
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