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Spots, plages, and flares on λ Andromedae and II Pegasi
Aims.We present the results of a contemporaneous photometric andspectroscopic monitoring of two RS CVn binaries, namelyλ And and II Peg. The aimof this work is to investigate the behavior of surface inhomogeneitiesin the atmospheres of the active components of these systems that havenearly the same temperatures but different gravities. Methods: Thelight curves and the modulation of the surface temperature, as recoveredfrom line-depth ratios (LDRs), were used to map the photospheric spots,while the Hα emission was used as an indicator of chromosphericinhomogeneities. The spot temperatures and sizes were derived from aspot model applied to the contemporaneous light and temperature curves. Results: We find larger and cooler spots on II Peg (T_sp ≃ 3600 K)than on λ And (T_sp ≃ 3900 K); this could be the result ofboth the difference in gravity and the higher activity level of theformer. Moreover, we find a clear anti-correlation between the Hαemission and the photospheric diagnostics (temperature and lightcurves). We have detected a modulation in the intensity of the He I D3line with the star rotation, suggesting surface features also in theupper chromosphere of these stars. A rough reconstruction of the 3Dstructure of their atmospheres was also performed by applying aspot/plage model to the light and temperature curves and to the Hαflux modulation. In addition, a strong flare affecting the Hα, theHe I D3, and the cores of Na I D{1,2} lines has been observed on II Peg. Conclusions: The spot/plage configuration has been reconstructed in thevisible component of λ And and II Peg, which have nearly the sametemperature but very different gravities and rotation periods. A closespatial association of photospheric and chromospheric active regions, atthe time of our observations, was found in both stars. Larger and coolerspots were found on II Peg, the system with the active component ofhigher gravity and a higher activity level. The area ratio of plages tospots seems to decrease when the spots get bigger. Moreover, with boththis and literature data, a correlation between the temperaturedifference Δ T = T_ph-T_sp and the surface gravity is alsosuggested.Based on observations collected at Catania Astrophysical Observatory(Italy) and Ege University Observatory (İzmir, Turkey).
| Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data
Context: .This paper is the last in a series devoted to the analysis ofthe binary content of the Hipparcos Catalogue. Aims: .Thecomparison of the proper motions constructed from positions spanning ashort (Hipparcos) or long time (Tycho-2) makes it possible to uncoverbinaries with periods of the order of or somewhat larger than the shorttime span (in this case, the 3 yr duration of the Hipparcos mission),since the unrecognised orbital motion will then add to the propermotion. Methods: .A list of candidate proper motion binaries isconstructed from a carefully designed χ2 test evaluatingthe statistical significance of the difference between the Tycho-2 andHipparcos proper motions for 103 134 stars in common between the twocatalogues (excluding components of visual systems). Since similar listsof proper-motion binaries have already been constructed, the presentpaper focuses on the evaluation of the detection efficiency ofproper-motion binaries, using different kinds of control data (mostlyradial velocities). The detection rate for entries from the NinthCatalogue of Spectroscopic Binary Orbits (S_B^9) is evaluated, as wellas for stars like barium stars, which are known to be all binaries, andfinally for spectroscopic binaries identified from radial velocity datain the Geneva-Copenhagen survey of F and G dwarfs in the solarneighbourhood. Results: .Proper motion binaries are efficientlydetected for systems with parallaxes in excess of ~20 mas, and periodsin the range 1000-30 000 d. The shortest periods in this range(1000-2000 d, i.e., once to twice the duration of the Hipparcos mission)may appear only as DMSA/G binaries (accelerated proper motion in theHipparcos Double and Multiple System Annex). Proper motion binariesdetected among S_B9 systems having periods shorter than about400 d hint at triple systems, the proper-motion binary involving acomponent with a longer orbital period. A list of 19 candidate triplesystems is provided. Binaries suspected of having low-mass(brown-dwarf-like) companions are listed as well. Among the 37 bariumstars with parallaxes larger than 5 mas, only 7 exhibit no evidence forduplicity whatsoever (be it spectroscopic or astrometric). Finally, thefraction of proper-motion binaries shows no significant variation amongthe various (regular) spectral classes, when due account is taken forthe detection biases.Full Table [see full textsee full text] is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/377
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| II Pegasi Reached The Largest Amplitude Up To Now
Not Available
| The magnetic activity cycle of II Pegasi: results from twenty-five years of wide-band photometry
We present an analysis of a sequence of light curves of the RS CVn-typebinary II Pegasi extending from 1974 to 1998. The distribution of thespotted area versus longitude is derived by Maximum Entropy and Tikhonovregularized maps, assuming a constant spot temperature (Lanza et al.1998a). The spot pattern on the active K2 IV star can be subdivided intoa component uniformly distributed in longitude and a second unevenlydistributed component, which is responsible for the observed photometricmodulation. The uniformly distributed component appears to be possiblymodulated with an activity cycle of ~ 13.5 yr. The unevenly distributedcomponent is mainly concentrated around three major active longitudes.The spot activity appears practically permanent at one longitude, butthe spot area changes with a cycle of ~ 9.5 yr. On the contrary, thespot activity is discontinuous at the other two longitudes, and itswitches back and forth between them with a cycle of ~ 6.8 yr. However,before each switching is completed, a transition phase of ~ 1.05 yr,during which both longitudes are active, occurs. After this transientphase, spot activity remains localized at one of the two longitudes for~ 4.7 yr untill another switching event occurs, which re-establishesspot activity at the other longitude. The longitude separation betweenthe permanent and the switching active longitudes is closest during theswitching phases and it varies along the ~ 6.8 yr cycle. Different timescales characterize the activity at the permanent longitude and at theswitching longitudes: a period of ~ 9.5 yr is related to the activitycycle at the permanent longitude, and a period of ~ 4.3 yr characterizesthe spot life time at the switching longitudes in between switchingevents. The photometric period of the active star changes from season toseason with a relative amplitude of 1.5% and a period of ~ 4.7 yr. Sucha variation of the photometric period may be likely associated with thephase shift of the light curves produced by the switching of spotactivity from one active longitude to the other. The permanently activelongitude shows a steady migration towards decreasing orbital phases,with an oscillating migration rate along the 9.5 yr cycle period andnearly in phase with the variation of its spotted area. The amplitude ofthe differential rotation derived from such a behaviour is of the orderof ~ 0.023%, about one order of magnitude smaller than estimated byHenry et al. (1995). The other two active longitudes migrates alsotowards decreasing orbital phase, but at a discontinuous rate. Thereappears to be no correlation between the location of the activelongitudes with respect to the line joining the two components of thesystem and their activity level.
| 1984 UBVRI Photometry of II Peg
Not Available
| I.A.U. Archives of Unpublished Observations of Variable Stars - 1981-1984 Data
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