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Testing Stellar Models with an Improved Physical Orbit for 12 Bootis
In a previous paper we reported on the binary system 12 Bootis and itsevolutionary state. In particular, the 12 Boo primary component is in arapid phase of evolution; hence accurate measurement of its physicalparameters makes it an interesting test case for stellar evolutionmodels. Here we report on a significantly improved determination of thephysical orbit of the double-lined spectroscopic binary system 12 Boo.We have a 12 Boo interferometry data set spanning 6 yr with the PalomarTestbed Interferometer, a smaller amount of data from the Navy PrototypeOptical Interferometer, and a radial velocity data set spanning 14 yrfrom the Harvard-Smithsonian Center for Astrophysics. We have updatedthe 12 Boo physical orbit model with our expanded interferometric andradial velocity data sets. The revised orbit is in good agreement withprevious results, and the physical parameters implied by a combined fitto our visibility and radial velocity data result in precise componentmasses and luminosities. In particular, the orbital parallax of thesystem is determined to be 27.72+/-0.15 mas, and masses of the twocomponents are determined to be 1.4160+/-0.0049 and 1.3740+/-0.0045Msolar, respectively. These mass determinations are moreprecise than those in the previous report by a factor of 4-5. Asindicated in the previous publication, even though the two componentsare nearly equal in mass, the system exhibits a significant brightnessdifference between the components in the near-infrared and visible. Weattribute this brightness difference to evolutionary differences betweenthe two components in their transition between main-sequence and giantevolutionary phases, and based on theoretical models, we can estimate asystem age of approximately 3.2 Gyr. Comparisons with stellar modelssuggest that the 12 Boo primary may be just entering the Hertzsprunggap, but that conclusion is highly dependent on details of the models.Such a dynamic evolutionary state makes the 12 Boo system a unique andimportant test for stellar models.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| 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}
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| The Visual Orbit and Evolutionary State of 12 Bootis
We report on the determination of the visual orbit of the double-linedspectroscopic binary system 12 Bootis with data obtained by the PalomarTestbed Interferometer in 1998 and 1999. 12 Boo is a nearly equal-massdouble-lined binary system whose spectroscopic orbit is well known. Wehave estimated the visual orbit of 12 Boo from our interferometricvisibility data fitted both separately and in conjunction with archivaland CORAVEL radial velocity data. Our 12 Boo orbit is in good agreementwith the spectroscopic results, and the physical parameters implied by acombined fit to our visibility data and radial velocity data result inprecise component masses. In particular, the orbital parallax of thesystem is determined to be 27.09+/-0.41 mas, and masses of the twocomponents are determined to be 1.435+/-0.023 Msolar and1.409+/-0.020 Msolar, respectively. Somewhat remarkably, eventhough the two components are nearly equal mass, the system exhibits asignificant brightness difference between the components in thenear-infrared and visible. We attribute this brightness difference toevolutionary differences between the two components in their transitionbetween main-sequence and giant evolutionary phases, and based ontheoretical isochrones we can estimate a system age. Further, becausethe atmospheres of the two components are becoming more convective, wesuggest the system components are currently at or near synchronousrotation, and the system orbit is in the process of circularizing.
| Accuracy of two-dimensional spectral classes derived through DDO photometry.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..832Y&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Boote |
| Ascensione retta: | 14h08m15.86s |
| Declinazione: | +24°18'54.2" |
| Magnitudine apparente: | 6.559 |
| Distanza: | 204.082 parsec |
| Moto proprio RA: | -24.5 |
| Moto proprio Dec: | 2.9 |
| B-T magnitude: | 8.515 |
| V-T magnitude: | 6.721 |
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