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Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is 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/430/165}
| 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 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.
| Rotational modulation and flares on the RS Canum Venaticorum binary II Pegasi in July/September 1990: Spots and flares on II Peg
During ultraviolet spectroscopic observations of the RS CVn star II Pegin September 1990 a long duration (greater than or = 3 hrs.) flare wasobserved. During the early stage of the event, a feature at 1354 A waspresent, however, within the spectral resolution of the data it is notpossible to identify this line. A contribution from the hot coronal ionFe XXI is suspected. From line diagnostic ratios, the electron pressureat flare peak was estimated to be 1017/cu cm K, decreasing to1016/cu cm K towards the end of the flare. One other flarewas observed with IUE, and three optical flares (unfortunately none ofthese were observed simultaneously). The chromospheric and transitionregion losses from the larger of the two IUE flares was approx. 3 x1031 erg/s at flare maximum, with totalchromospheric/transition region radiative losses over the duration ofthe event being approx. 1.5 x 1035 erg. Continuum radiativelosses over the wavelength region 1150A to 1950A were approximately 3%of the above figure. At flare maximum, the N V 1240 A line showed anenhancement factor of approx. 3 over the preflare value compared to 9for the C IV 1550 A line. We interpret this difference as due to anunderabundance of nitrogen during the flare, possibly related tophotoionization of lower chromospheric material by soft X-ray photonssometime prior to the flare. No evidence of rotational modulation waspresent in any of the transition region lines, although thechromospheric lines did show a phase variation. However, these lines(H-alpha, Ca II K and Mg II h&k) were not consistent with oneanother although it is clear that the H-alpha equivalent width showedvariations faster than the star's rotation period, being perhaps relatedto the decay/activation of individual active regions.
| 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
| 1988-89 Observations of II Peg
Not Available
| 1987 Amplitude Changes of II Peg Light Curve
Not Available
| The 1986 Light Curve of II Peg
Not Available
| Infrared and visible photometry of the RS CVn-star II Peg
Infrared photometry in J, H, K, L, M bands carried out in differentyears from 1983 to 1986, and U, B, V, R, I quasi-simultaneous to 1984are presented. Although the amplitude of the minima decrease as thewavelength increase, the infrared light curves show a similar behaviorto that observed in visible. Since no variations in the averagemagnitudes are noted from 1983 to 1986, it is assumed that the activityof II Peg is not increasing. Also from the light curves a concentrationprocess of the spots seems to have taken place from 1984 to 1986. In theanalysis of the infrared colors an excess attributable to circumstellardust emission is found.
| 1986 J, K Light Curves of II Peg
Not Available
| 1984 UBVRI Photometry of II Peg
Not Available
| Photometric Observations of Active Chromosphere Stars: II Peg, HD 175742, HD 199178
Not Available
| Coordinated Ultraviolet, Optical and Radio Observations of RS CVn and Flare Stars
Not Available
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Pegasus |
| Ascensió Recta: | 23h55m01.34s |
| Declinació: | +29°27'01.8" |
| Magnitud Aparent: | 8.237 |
| Distancia: | 2380.952 parsecs |
| Moviment propi RA: | -0.8 |
| Moviment propi Dec: | -11.5 |
| B-T magnitude: | 9.853 |
| V-T magnitude: | 8.371 |
Catàlegs i designacions:
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