תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
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
| 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
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The ROSAT Galactic Plane Survey: Analysis of a low latitude sample area in Cygnus
The analysis of the part of the ROSAT all-sky survey covering thegalactic plane is the scope of a dedicated project called the ROSATGalactic Plane Survey. In order to statistically understand the natureof the ~14,000 sources discovered by ROSAT at |b| <= 20 degrees, anumber of sample areas have been chosen for follow-up opticalidentification. In this paper we present the X-ray and optical materialgathered in a region located in the Cygnus constellation, centered at l= 90 degrees, b = 0 degrees and covering an area of 64.5deg2. A total of 95 and 128 sources are detected with amaximum likelihood larger than 10 and 8 respectively. With a typicalsurvey exposure time of the order of 700 to 900 s the flux completenesslevel is ~0.02 cnts s^{-1} corresponding to ~2 10^{-13} erg cm^{-2}s^{-1}. The position of the sample area allows to investigate the softX-ray content of a rather typical region of the galactic plane. In thispaper we describe the details of the observational procedures and datareduction. For each ROSAT source we list the main X-ray characteristicstogether with those of the proposed optical identification. Whenappropriate, we also show optical spectra and finding charts. The fullanalysis and discussion of these data are presented in a companion paper(\cite[Motch et al. 1997]{ref13}). Tables 2 to 6 are also available inelectronic form at the CDS via anonymous ftp cdsarc.u-strasbg.fr.Figures are only published electronically and are made available athttp://www.ed-phys.fr/Abstract.html.
| The ROSAT galactic plane survey: analysis of a low latitude sample area in Cygnus.
We present the analysis of the point source content of a low galacticlatitude region selected from the ROSAT all-sky survey. The test fieldis centered at l=90deg, b=0deg and has an area of 64.5deg^2^. A total of128 soft X-ray sources are detected above a maximum likelihood of 8.Catalogue searches and optical follow-up observations show that in thisdirection of the galactic plane, 85% of the sources brighter than 0.03PSPC cts/s are identified with active coronae. F-K type stars represent67%(+/-13%) of the stellar identifications and M type stars account for19%(+/-6%). A small but significant number of X-ray sources areassociated with A type stars on the basis of positional coincidence.These results together with those of similar optical campaignsdemonstrate that the soft X-ray population of the Milky Way is largelydominated by active stars. We show that the density and distribution influx and spectral type of the active coronae detected in X-rays areconsistent with the picture drawn from current stellar population modelsand age dependent X-ray luminosity functions. The modelling of thispopulation suggests that most of the stars detected by ROSAT in thisdirection are younger than 1Gyr. This opens the possibility to extractin a novel way large samples of young stars from the ROSAT all-skysurvey. The small number of unidentified sources at low X-ray flux putrather strong constraints on the hypothetical X-ray emission from oldneutron stars accreting from the interstellar medium. Our observationsclearly rule out models which assume no dynamical heating for thispopulation and a total number of N_ns_=10^9^ neutron stars in theGalaxy. If accretion on polar caps is the dominant mode then our upperlimit may imply N_ns_=~10^8^. Among the non coronal identifications arethree white dwarfs, a Seyfert 1 active nucleus, two early type stars andone cataclysmic variable. We also report the discovery of a Me + WDclose binary system with P_orb_=~12h.
| Kinematics of Sandage-Fouts stars in three cardinal directions
V and (B - V) for 429, 442, and 427 stars are observed in the directionsof the anticenter, Cygnus, and the NGP, respectively, and DDO colors forthose stars G0 and later. The samples observed are ones for whichSandage and Fouts (1987) have published radial velocities. W, V, and Wcomponents of space velocity are derived from DDO distances withavailable proper motions. A clear correlation was found to exist betweenthe velocity dispersions and Fe/H with the dispersions decreasing asFe/H increases to about + 0.00, where V then becomes significantlynegative. The 'thick disk' component is clearly recognized, with sigma(W) approximately equal to 36 km/sec. In the 'old thin disk' and the'young thin disk', 43 percent and 42 percent of the stars have negativeV values, respectively.
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h49m36.72s |
| סירוב: | +51°18'51.5" |
| גודל גלוי: | 6.657 |
| מרחק: | 63.694 פארסק |
| תנועה נכונה: | 9.1 |
| תנועה נכונה: | -45.2 |
| B-T magnitude: | 7.076 |
| V-T magnitude: | 6.692 |
קטלוגים וכינוים:
|
