Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The RAdial Velocity Experiment (RAVE): Third Data Release
We present the third data release of the RAdial Velocity Experiment(RAVE) which is the first milestone of the RAVE project, releasing thefull pilot survey. The catalog contains 83,072 radial velocitymeasurements for 77,461 stars in the southern celestial hemisphere, aswell as stellar parameters for 39,833 stars. This paper describes thecontent of the new release, the new processing pipeline, as well as anupdated calibration for the metallicity based upon the observation ofadditional standard stars. Spectra will be made available in a futurerelease. The data release can be accessed via the RAVE Web site.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Distance determination for RAVE stars using stellar models . II. Most likely values assuming a standard stellar evolution scenario
The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of theMilky Way which already collected over 400 000 spectra of ~ 330 000different stars. We use the subsample of spectra with spectroscopicallydetermined values of stellar parameters to determine the distances tothese stars. The list currently contains 235 064 high quality spectrawhich show no peculiarities and belong to 210 872 different stars. Thenumbers will grow as the RAVE survey progresses. The public version ofthe catalog will be made available through the CDS services along withthe ongoing RAVE public data releases. The distances are determined witha method based on the work by Breddels et al. (2010, A&A, 511, A16).Here we assume that the star undergoes a standard stellar evolution andthat its spectrum shows no peculiarities. The refinements include: theuse of either of the three isochrone sets, a better account of thestellar ages and masses, use of more realistic errors of stellarparameter values, and application to a larger dataset. The deriveddistances of both dwarfs and giants match within ~ 21% to theastrometric distances of Hipparcos stars and to the distances ofobserved members of open and globular clusters. Multiple observations ofa fraction of RAVE stars show that repeatability of the deriveddistances is even better, with half of the objects showing a distancescatter of ? 11%. RAVE dwarfs are ~ 300 pc from the Sun, and giantsare at distances of 1 to 2 kpc, and up to 10 kpc. This places the RAVEdataset between the more local Geneva-Copenhagen survey and the moredistant and fainter SDSS sample. As such it is ideal to address some ofthe fundamental questions of Galactic structure and evolution in thepre-Gaia era. Individual applications are left to separate papers, herewe show that the full 6-dimensional information on position and velocityis accurate enough to discuss the vertical structure and kinematicproperties of the thin and thick disks.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://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/522/A54
| Distance determination for RAVE stars using stellar models
Aims: We develop a method for deriving distances fromspectroscopic data and obtaining full 6D phase-space coordinates for theRAVE survey's second data release. Methods: We used stellarmodels combined with atmospheric properties from RAVE (effectivetemperature, surface gravity and metallicity) and (J-Ks)photometry from archival sources to derive absolute magnitudes. Incombination with apparent magnitudes, sky coordinates, proper motionsfrom a variety of sources and radial velocities from RAVE, we are ableto derive the full 6D phase-space coordinates for a large sample of RAVEstars. This method is tested with artificial data, Hipparcostrigonometric parallaxes and observations of the open cluster M 67. Results: When we applied our method to a set of 16 146 stars, wefound that 25% (4037) of the stars have relative (statistical) distanceerrors of <35%, while 50% (8073) and 75% (12 110) have relative(statistical) errors smaller than 45% and 50%, respectively. Our varioustests show that we can reliably estimate distances for main-sequencestars, but there is an indication of potential systematic problems withgiant stars owing to uncertainties in the underlying stellar models. Forthe main-sequence star sample (defined as those with log(g) > 4), 25%(1744) have relative distance errors <31%, while 50% (3488) and 75%(5231) have relative errors smaller than 36% and 42%, respectively. Ourfull dataset shows the expected decrease in the metallicity of stars asa function of distance from the Galactic plane. The known kinematicsubstructures in the U and V velocity components of nearby dwarf starsare apparent in our dataset, confirming the accuracy of our data and thereliability of our technique. We provide independent measurements of theorientation of the UV velocity ellipsoid and of the solar motion, andthey are in very good agreement with previous work. Conclusions:The distance catalogue for the RAVE second data release is available athttp://www.astro.rug.nl/~rave,and will be updated in the future to include new data releases.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Јужна риба |
| Ректацензија: | 22h39m44.05s |
| Deклинација: | -32°04'18.1" |
| Apparent магнитуда: | 11.234 |
| Даљина: | 37.807 parsecs |
| Proper motion RA: | -175.9 |
| Proper motion Dec: | -180.9 |
| B-T magnitude: | 12.863 |
| V-T magnitude: | 11.369 |
Каталог и designations:
|
