Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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}
| HD 207651: A Triple System with δ Scuti and Ellipsoidal Variations But No γ Doradus Pulsations
We examine HD 207651 as a possible example of a star exhibiting bothγ Doradus and δ Scuti type pulsations. We find photometricperiods of 0.06479 and 0.06337 days with peak-to-peak amplitudes inJohnson B of 21 and 13 mmag, respectively, clearly indicating δScuti pulsations. Additional light variation with a period of 0.73540days and an even larger amplitude of 31 mmag is within the range ofγ Doradus pulsation periods but results instead from theellipticity effect. HD 207651 has a composite spectrum with a weak,narrow absorption line superposed near the center of each broad metalline. The broad-lined component is the primary of a short-period,single-lined binary, which has a period of 1.4708 days, twice the periodof the ellipsoidal variations seen in the photometry. We determine theprimary to be an A8 giant and estimate the unseen secondary of theshort-period binary to be a mid-M dwarf. The narrow-lined star, an F7:dwarf, shows velocity variability with a period of months or perhapsyears. It is thus a more distant companion to the binary, making HD207651 a triple system. All light variations come from the A8 giantprimary star. Since the 0.73540 day variation results from theellipticity effect, HD 207651 is not an example of a star that exhibitsboth δ Scuti and γ Doradus pulsations. The growing number ofconfirmed γ Doradus stars that also occur within the δ Scutiinstability strip but fail to show additional δ Scuti variabilitymakes it increasingly unlikely that the two types of pulsation cancoexist in the same star.
| Probing the stellar surface of HD 209458 from multicolor transit observations
Multicolor photometric observations of a planetary transit in the systemHD 209458 are analyzed. The observations, made in the Strömgrenphotometric system, allowed a recalculation of the basic physicalproperties of the star-planet system. This includes derivation of linearlimb-darkening values of HD 209458, which is the first time that alimb-darkening sequence has observationally been determined for a singlelate main-sequence star beyond the Sun. As the derived physicalproperties depend on assumptions that are currently known with limitedprecision only, scaling relations between derived parameters andassumptions are given. The observed limb-darkening is in good agreementwith theoretical predictions from evolutionary stellar models combinedwith ATLAS model atmospheres, verifying these models for the temperature(Teff~6000 K), surface gravity (/log g~4.3) and mass (~1.2Msolar) of HD 209458.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| UBV photometry of stars whose positions are accurately known.
Photometric indices V, B-V, and U-B were measured for about 560 stars ofthe AGK3R and NPZT catalogs between BD declinations 11 deg and 23 deg,using the 40-cm Cassegrain telescope of the Kvistaberg Observatory fromApril 1986 to May 1987. The observation procedure and the reductiontechnique were the same as in the earlier papers of this series by Oja(1984, 1985, 1986, and 1987). The mean errors were calculated from theinternal consistency of the data. The accuracy was found to be the sameas for the earlier parts of the survey.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kanatli At |
| Sað Açýklýk: | 21h58m59.69s |
| Yükselim: | +19°01'13.1" |
| Görünürdeki Parlaklýk: | 6.499 |
| Uzaklýk: | 63.776 parsek |
| özdevim Sað Açýklýk: | 77.9 |
| özdevim Yükselim: | -32.3 |
| B-T magnitude: | 7.801 |
| V-T magnitude: | 6.607 |
Kataloglar ve belirtme:
|
