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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.
| The active binary star II Pegasi with it BeppoSAX
II Peg is an ideal target to study stellar activityand flares, since intense and long lasting flares have been frequentlydetected from this system at all wavelengths. We report here about aBeppoSAX observation of II Peg. We followed thesystem for ~ 19 hours on December 5 and 6 1997 with BeppoSAX and theX-ray light curve resembles the typical behavior of a decay phase of along-lasting flare. The spectral analysis shows that the IIPeg X-ray spectrum is described by a two-temperaturecomponents, with the two dominant temperatures centered in the range of9-11 and 24-26 MK. The derived coronal metal abundance is low ( Z ~ 0.2Z_sun) compared to recent determinations of the photospheric abundance(Z ~ 0.6 Z_sun). Some possible explanations for this phenomenology arereviewed. As for most other stellar coronal sources observed withBeppoSAX, we find that in order to fit the BeppoSAX spectra aninterstellar column density about a factor ten higher than previouslydetermined is required.
| The photospheric filling factor of the active binary II Pegasi
UBV and JHK photometry of the active single-lined binary II Peg, weperformed in 1995, is presented. A method to determine the fraction ofthe photosphere covered by spots (filling factor) and to check theaccuracy of generally assumed values of photospheric parameters has beendeveloped. The procedure is based on the comparison between multibandfluxes and low resolution synthetic spectra weighted on the base of thespot filling factor and scaled with the ratio between the star radiusand distance (R/d), so that we can also estimate the R/d ratio. A chi2 fit has been performed for II Peg observations close to thelight maximum and minimum by assuming reliable values of thephotospheric parameters. Although a unique solution cannot be reached,we found clear indication for a spot filling factor at light maximum>= 40%. We find that the same set of parameters that gives us thebest fit solutions at light maximum also provides the best fit at lightminimum. The resulting solutions are consistent with the observedamplitude of the photometric wave, and with the commonly accepted valueof R, unspotted V magnitude and spectral classification for II Pegasi.
| The photosphere and chromosphere of the RS Canum Venaticorum star, II Pegasi. II. A multi-wavelength campaign in August/September 1992
We describe multi-wavelength, simultaneous observations of the RS CVnstar, II Pegasi, most of which were obtained during the first threeweeks of September 1992. These observations were made using optical andinfra-red broad-band photometry, ultraviolet and optical spectroscopyand microwave monitoring. We have detected photospheric spots andchromospheric flares, as well as deriving a description of meanconditions in the quiet chromosphere. One of the flares, observed inoptical photometry and ultraviolet spectroscopy is one of the mostenergetic ever observed on this star. We demonstrate that in its``quiescent'' state II Peg is continually variable in most of itschromospheric emissions, as well as in its coronal output.
| The photosphere and chromosphere of the RS Canum Venaticorum star, II Pegasi I. Spots and chromospheric emission in 1991.
We report on high-resolution spectroscopy of the RSCVn binary IIPeg,along with contemporaneous UBV(RI)_KC_ photometry, including partlysimultaneous U-band flare monitoring, during the third quarter of 1991.The spectroscopy was taken at two epochs separated by more than 6(1)/(2)weeks or seven rotations of IIPeg. At the first epoch we have observedthe three chromospheric lines, Hα, Hβ and HeID_3_, over asingle rotation and at the second epoch we observed almost the entirevisible region, for a substantial fraction of one rotation, includingHα-Hɛ and CaIIH. Our photometric results show that therewas an unusually complicated spot distribution at this epoch, with atleast three centres of activity discernable. We demonstrate, for thefirst time on a spotted late-type star, that these centres of spotactivity have significantly different mean temperatures from oneanother. Furthermore, our derived spot temperatures are markedly lowerthan those previously derived from such multicolour photometry and moresimilar to those derived spectroscopically. Using multiple repeatexposures on each spectral line within each night, we are confident thatwe have derived a mean, non-flaring spectrum at each observationalphase. Furthermore, the line flux variations at the two epochs repeatvery well, suggesting that the mean global chromospheric structures arestable on a 1(1)/(2) months time scale. We discuss the implications ofthe mean spectra for the non-flaring atmosphere of IIPeg and concludethat, in the region of formation of the Hα line, velocity fieldsare required to account for the line profile. These results suggestupward motions of the deep chromosphere with a less dramatic downflow inthe high chromosphere. We examine the variation of the chromosphericline fluxes as a function of spot visibility and conclude that there isonly a very loose spatial correlation of chromsopheric heating withspots. The motions suggested from the Hα profile variations appearto be spot-associated.
| Dynamic phenomena on the RS Canum Venaticorum binary Pi Pegasi in August 1989. I - Observational data
Observational results are given for two flares in Pi Pegasi that weredetected by the GINGA and IUE satellites, as well as by ground-basedJohnson U-band photometry and optical spectroscopy. The best-fittingresults were obtained for a combination of a single-temperature plasmatogether with a power law; for a two-temperature model, the temperatureof the second component was very high due to the tail in the photondistribution.
| UBV Observations of II Peg in 1988-1989
Not Available
| The 1986 Light Curve of II Peg
Not Available
| Coordinated Ultraviolet, Optical and Radio Observations of RS CVn and Flare Stars
Not Available
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Miembro de los siguientes grupos:
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Datos observacionales y astrométricos
| Constelación: | Pegaso |
| Ascensión Recta: | 23h54m29.69s |
| Declinación: | +29°38'17.7" |
| Magnitud Aparente: | 8.507 |
| Distancia: | 61.162 parsecs |
| Movimiento Propio en Ascensión Recta: | 0.5 |
| Movimiento Propio en Declinación: | -192.3 |
| B-T magnitude: | 9.479 |
| V-T magnitude: | 8.588 |
Catálogos y designaciones:
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