תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| An extensive library of 2500 10 500 Å synthetic spectra
We present a complete library of synthetic spectra based on Kurucz'scodes that covers the 2500 10 500 Å wavelength range at resolvingpowers R{P}=20 000, 11 500 (≡GAIA), 8500 (≡RAVE),2000 (≡SLOAN) and uniform dispersions of 1 and 10 Å/pix. Thelibrary maps the whole HR diagram, exploring 51 288 combinations ofatmospheric parameters spanning the ranges: 3500 ≤ T_eff ≤ 47500 K, 0.0≤ log g ≤ 5.0 , -2.5 ≤ [M/H] ≤ 0.5, [α/Fe] = 0.0,+0.4, ξ = 1, 2, 4 km s-1, 0 ≤ V_rot≤ 500 km s-1. The spectra are available both as absolutefluxes as well as continuum normalized. Performance tests andspectroscopic applications of the library are discussed, includingautomatic classification of data from spectroscopic surveys like RAVE,SLOAN, GAIA. The entire library of synthetic spectra is accessible viathe web.
| Spectroscopic survey of the Galaxy with Gaia- II. The expected science yield from the Radial Velocity Spectrometer
The Gaia mission is designed as a Galaxy explorer, and will measuresimultaneously, in a survey mode, the five or six phase-space parametersof all stars brighter than 20th magnitude, as well as providing adescription of their astrophysical characteristics. These measurementsare obtained by combining an astrometric instrument with micro-arcsecondcapabilities, a photometric system giving the magnitudes and colours in15 bands and a medium-resolution spectrograph named the Radial VelocitySpectrometer (RVS). The latter instrument will produce spectra in the848- to 874-nm wavelength range, with a resolving power R= 11500, fromwhich radial velocities, rotational velocities, atmospheric parametersand abundances can be derived. A companion paper has presented thecharacteristics of the RVS and its performance. The present paperdetails the outstanding scientific impact of this important part of theGaia satellite on some key open questions in present-day astrophysics.The unbiased and simultaneous acquisition of multi-epoch radialvelocities and individual abundances of key elements in parallel withthe astrometric parameters is essential for the determination of thedynamical state and formation history of our Galaxy. Moreover, for starsbrighter than V~= 15, the resolving power of the RVS will giveinformation about most of the effects that influence the position of astar in the Hertzsprung-Russell diagram, placing unprecedentedconstraints on the age, internal structure and evolution of stars of alltypes. Finally, the RVS multi-epoch observations are ideally suited tothe identification, classification and characterization of the manytypes of double, multiple and variable stars.
| Aus der Sektion Bedeckungsveranderliche.
Not Available
| 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.
| Evaluating GAIA performances on eclipsing binaries. III. Orbits and stellar parameters for UW LMi, V432 Aur and CN Lyn
The orbits and physical parameters of three detached F and G-typeeclipsing binaries have been derived combining Hipparcos HPphotometry with 8480-8740 Å ground-based spectroscopy, simulatingthe photometric + spectroscopic observations that the GAIA mission willobtain. Tycho BT and VT light curves are too noisyto be modeled for the three targets, and only mean Tycho colors areretained to constrain the temperature. No previous combinedphotometric+spectroscopic solution exists in the literature for any ofthe three targets. Quite remarkably, CN Lyn turned out to be anequal-masses F5 triple system. Distances from the orbital solutionsagree within the astrometric error with the Hipparcos parallaxes.
| Neue Anmerkungen zu NN Delphini.
Not Available
| 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.
| V432 Aur: a New Eclipsing System
V432 Aur has been discovered by the Hipparcos mission as a low amplitudevariable of unsolved nature. We have carried out extensive B, Vphotometry from Dec. 1998 to Feb. 2002 and discovered that V432 Aur isan eclipsing system with an orbital period of 3.08175 days. The primaryeclipse is about 0.37 mag deep. The secondary is well centered at phase0.5 and is about 0.26 mag deep. Both primary and secondary eclipses areflat bottomed with totality lasting about 0.035 of the orbital period.The secondary star is cooler by Delta (B-V)=0.05 (Delta T(eff) about210K) and appears to be intrinsically variable by some Delta V=0.05 mag.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | עגלון |
| התרוממות ימנית: | 05h37m32.51s |
| סירוב: | +37°05'12.3" |
| גודל גלוי: | 8.056 |
| מרחק: | 118.624 פארסק |
| תנועה נכונה: | -40.8 |
| תנועה נכונה: | 34.6 |
| B-T magnitude: | 8.7 |
| V-T magnitude: | 8.11 |
קטלוגים וכינוים:
|
