Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Spectroscopy, Photometry and Micro-arcsec Astrometry of Binaries with the GAIA Space Mission and with the RAVE Experiment
The GAIA astrometric mission of ESA will be very efficient indiscovering binary and multiple stars with any orbital period, fromminutes to millions of years. The main parameters of the revised missiondesign are presented. Next we estimate the fraction of binary starsdiscovered by means of astrometry, photometry and on-board spectroscopy.Finally we summarize observations that confirm the ability to measurephysical parameters like masses, radii and spectroscopic distance fromGAIA data alone. GAIA will fly only in 2010, but the radial velocityexperiment (RAVE) has started this year. We show that its spectroscopicobservations have the capacity to discover a large fraction of so farunknown binary systems.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are 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/418/989
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| Asiago eclipsing binaries program. I. V432 Aurigae
The orbit and physical parameters of the previously unsolved eclipsingbinary V432 Aur, discovered by Hipparcos, have been derived with errorsbetter than 1% from extensive Echelle spectroscopy and B, V photometry.Synthetic spectral analysis of both components has been performed,yielding Teff and log g in close agreement with the orbitalsolution, a metallicity [Z/Zȯ] = -0.6 and rotationalsynchronization for both components. Direct comparison on thetheoretical L, Teff plane with the Padova evolutionary tracksand isochrones for the masses of the two components (1.22 and 1.08Mȯ) provides a perfect match and a 3.75 Gyr age. Themore massive and cooler component is approaching the base of the giantbranch and displays a probable pulsation activity with an amplitude ofΔ V = 0.075 mag and Δrad.vel. = 1.5 km s-1. Witha Teff = 6080 K it falls to the red of the nearby instabilitystrip populated by δ Sct and γ Dor types of pulsatingvariables. Orbital modeling reveals a large and bright surface spot onit. The pulsations activity and the large spot(s) suggest the presenceof macro-turbulent motions in its atmosphere. They reflect in a linebroadening that at cursory inspection could be taken as indication of arotation faster than synchronization, something obviously odd for anold, expanding star.
| δ Sct-type pulsations in eclipsing binary systems: RZ Cas
We present the results of a three-continent multisite photometriccampaign carried out on the Algol-type eclipsing binary system RZ Cas,in which the primary component has recently been discovered to be aδ Sct-type pulsator. The present observations include, for thefirst time, complete simultaneous Strömgren uvby light curvestogether with a few Crawford Hβ data collected around the orbitalphase of the first quadrature. The new observations confirm thepulsational behaviour of the primary component. A detailed photometricanalysis, based on these observations, is presented for both binarityand pulsation. The results indicate a semidetached system where thesecondary fills its Roche lobe. The appearance of the light curvesreveals the presence of the mass stream from the secondary component anda hotspot where this stream impacts on the surface of the primary star.There are also some indications of chromospheric activity in thesecondary. On the other hand, the pulsational behaviour out-of-primaryeclipse can be well described with only one frequency at 64.1935cd-1 similar to the main peak found by Ohshima et al. Theexistence of multiperiodicity is not confirmed in our data. Concerningthe mode identification, our results indicate non-radial pulsation in ahigh radial order (n= 6), with l= 2, |m|= 1, 2 as the most suitable.However, additional effects must be taken into account in thepredictions. Moreover, the pulsation amplitude in the u band is largerthan in b and v, which is unusual among the δ Sct-type variables.This can be explained as due to pulsation in a high n value and close tothe blue edge of the δ Sct region. On the other hand, the earlydata of Ohshima et al. have also been analysed and similar results arefound concerning the frequency content and pulsational amplitude.Finally, a revision of all the photometric out-of-primary-eclipse datasets available in the literature is made together with some additionalunpublished data leading to interesting findings relative to changestaking place in the pulsation amplitudes and frequencies from season toseason. Furthermore, multiperiodicity is probably present in someepochs.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 171: HD 152028 and HDE 284195 (GK Dra and V1094 Tau)
The two stars that form the subject of this paper are both short-perioddouble- lined eclipsing binaries having non-circular orbits despitetheir short periods. Although the HD type of HD 152028 is G0, theintegrated spectral type of the system must actually be much earlier:the B-V colour index is only about 0.37 mag and the parallax indicatesan integrated absolute magnitude as bright as +1.4 mag. A publishedphotometric investigation suggests that the primary star exhibits deltaScuti pulsations, with a period of 0.1138 days. That period is notpresent in the radial velocities, but we have identified a comparableperiodicity in the initially excessive residuals (sigma of the order of2 km/s) in the radial velocities of the primary star: there is anasymmetrical pulsational velocity curve with a semi-amplitude of about 3km/s and a period of 0.1178 days. HDE 284195 was not observed byHipparcos, but its HDE type of G0 is in reasonable agreement with itscolour and the nature of its radial-velocity traces. The rotations ofboth stars appear to be pseudo-synchronized to the orbit. The orbitalinclinations are not formally determined but they must be veryhigh,however and there is specific evidence that the inclination of HD152028 is very close to 90 degrees,so it is permissible to assume thatthe masses are scarcely above the minimum values, which in the case ofHD 152028 are 1.78 and 1.42 solar mass and in that of HDE 284195 are1.10 and 1.01 solar mass, with uncertainties below 1%.(ABRIDGED)
| Evaluating GAIA performances on eclipsing binaries . II. Orbits and stellar parameters for V781 Tau, UV Leo and GK Dra
The orbits and physical parameters of three close, double-lined G0eclipsing binaries have been derived combining H_P, V_T, B_T photometryfrom the Hipparcos/Tycho mission with 8480-8740 Å ground-basedspectroscopy. The setup is mimicking the photometric and spectroscopicobservations that should be obtained by GAIA. The binaries consideredhere are all of G0 spectral type, but each with its own complications:V781 Tau is an overcontact system with components of unequaltemperature, UV Leo shows occasional surface spots and GK Dra contains adelta Scuti variable. Such peculiarities will be common among binariesto be discovered by GAIA. We find that the values of masses, radii andtemperatures for such stars can be derived with a 1-2% accuracy usingthe adopted GAIA-like observing mode.
| V1154 Tau: a New Eclipsing Star within a Triple System
V1154 Tau has been discovered by Hipparcos as a a low amplitude variableof unsolved nature. We have carried out extensive B,V photometry fromDec 2002 to February 2003 and discovered that V1154 Tau is an eclipsingsystem with an orbital period of 1.7678805 days. The system is triplewith the third component on an extremely wide orbit, 0.355 arcsec away,or 90 AU at the system distance, contributing 21 of the total systemlight. The orbit of the eclipsing binary is eccentric and the totalcolor difference between primary and secondary eclipse is 0.02 mag inB-V, both being total with flat bottom.
| GK Dra: a delta Scuti Star in a New Eclipsing System Discovered by Hipparcos
GK Dra has been discovered by the Hipparcos mission as a 17 dayseclipsing binary. We present here the first ground-based study of thisstar, based on extensive BV photoelectric photometry. We found a periodof 9.974 days, equal depth primary and secondary eclipse (m=0.35 mag),no color variation in eclipse, and one of the components being a Sctstar with an amplitude of 0.04 mag and a period of about 2.7 hours.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Dragón |
| Ascensión Recta: | 16h45m41.18s |
| Declinación: | +68°15'30.9" |
| Magnitud Aparente: | 8.778 |
| Distancia: | 296.736 parsecs |
| Movimiento Propio en Ascensión Recta: | -5.6 |
| Movimiento Propio en Declinación: | 12.8 |
| B-T magnitude: | 9.188 |
| V-T magnitude: | 8.812 |
Catálogos y designaciones:
|
