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Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| Prospects for population synthesis in the H band: NeMo grids of stellar atmospheres compared to observations
Context: .For applications in population synthesis, libraries oftheoretical stellar spectra are often considered an alternative totemplate libraries of observed spectra, because they allow a completesampling of stellar parameters. Most of the attention in publishedtheoretical spectral libraries has been devoted to the visual wavelengthrange.Aims.The goal of the present work is to explore the near-infraredrange where few observed fully calibrated spectra and no theoreticallibraries are available.Methods.We make a detailed comparison oftheoretical spectra in the range 1.57-1.67 μm for spectral types fromA to early M and for giant and dwarf stars, with observed stellarspectra at resolutions around 3000, which would be sufficient todisentangle the different groups of late-type stars. We selected theNeMo grids of stellar atmospheres to perform this comparison.Results.Wefirst demonstrate that observed spectral flux distributions can bematched very well with theoretical ones for almost the entire parameterrange covered by the NeMo grids at moderate resolution in the visualrange. In the infrared range, although the overall shape of the observedflux distributions still matches reasonably well, the individualspectral features are reproduced by the theoretical spectra only forstars earlier than mid F type. For later spectral types the differencesincrease, and theoretical spectra of K type stars have systematicallyweaker line features than those found in observations. Thesediscrepancies are traced back to stem primarily from incomplete data onneutral atomic lines, although some of them are also related tomolecules.Conclusions.Libraries of theoretical spectra for A to early Mtype stars can be successfully used in the visual regions for populationsynthesis, but their application in the infrared is restricted to earlyand intermediate type stars. Improving atomic data in the near infraredis a key element in making the construction of reliable libraries ofstellar spectra feasible in the infrared.
| 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.
| Stellar populations in active galactic nuclei. II. Population synthesis
The relationship of an AGN to its host galaxy is one crucial question inthe study of galaxy evolution. We present a method to estimate thestellar contribution in active galactic nuclei. We perform stellarpopulation synthesis in the central regions of a sample of 12 galaxiesof different levels of activity: normal galaxies, starburst galaxies,LINERs, Seyfert 2 and Seyfert 1 galaxies. Quantification of the stellarcontribution is carried out in the visible range (5000 to 8800 Ä)using the equivalent widths of the absorption features throughout thespectrum. The synthesis is done by a variant of the new GPG method(Pelat, 1997). This method, contrary to previous ones, gives a uniquesolution. We find quite different stellar populations for the differenttypes of activity, which seems to be indicative of an age sequence. Thestarburst galaxies present the youngest populations of the sample. TheSeyfert 2 nuclei and NGC 1275, a Seyfert 1 with signs of interaction andwhere young stellar clusters have been found, also show the contributionof a young population, less intense than in the starburst galaxies butmetal rich. NGC 3516, a typical Seyfert 1, has a normal populationcharacteristic of galaxies of the same Hubble type and finally theLINERs show the oldest populations in the sample, metal rich, withlittle star formation still going on. It is found that a strong CaIItriplet, even though these lines are sensitive to gravity, does notimply necessarily a stellar population dominated by supergiant stars.Based on observations collected at the Canadian-French-HawaiianTelescope, Hawaii, and Observatoire de Haute Provence, France.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A new method to solve stellar population synthesis problems with the use of a data base
In this paper, we present a new solution of the stellar populationsynthesis problem using as primary information the equivalent width ofthe absorption lines observed in the spectra of, say, a galaxy. It isshown that this problem leads to a formulation akin to the maximumentropy method so successfully applied in image analysis and elsewhere.Emphasis is placed on the fact that it is a certain type of inverseproblem for which many local solutions do exist. Among these localsolutions there generally exists a global solution which is difficult toobtain in practice. A new method to search for this solution isproposed. First we solve a problem that is slightly different from theoriginal one but which possesses a unique solution. Then we return tothe original problem using that solution as a starting point of a localexploration. Because the change between the two formulations getssmaller as the errors in the data get smaller, we have great confidencethat the solution we find in this way is an efficient one. As thissolution may not be physical, we argue that either (1) the errors in theobservations are too big for any method to work properly or (2) it isthe signature of an inadequate stellar base. We then explore allboundaries by removing one or more stars from the data base and retainonly those truncated data bases for which the solution is physical. Thefinal solution (called the GPG solution) is that solution whichminimizes a certain distance criterion. We have tested our methodagainst noise in the data by Monte Carlo simulations and found it to begenerally unbiased and to have a small dispersion around the true valuefor signal-to-noise ratio as low as 10. This property holds true at verylow signal-to-noise ratio for stellar contributions greater thanapproximately 10 per cent. An example of the new method for the study ofthe active galaxy NGC 5643 is given.
| Spectra of late type stars from 4800 to 9000A.
We present optical spectra of 21 stars from 4800 to 8920A, coveringessentially the late spectral types, G, K, M and the luminosity classesI and III. Half of the stars are super metal rich (SMR) ones. Thespectra were obtained at a resolution of 1.25A using the Aureliespectrograph, equipped with a linear array CCD-like detector, attachedto the OHP 1.52m telescope. Also presented are the spectra of 7 stars,covering the region 5000-9783A at a resolution of 8.5A, observed at theCFHT with the Herzberg spectrograph. The spectral types are F, G, K, Mand the luminosity classes III and V. Five stars are SMR. These spectrahave been obtained with the aim of extending existing libraries used forpopulation synthesis purposes. The inclusion of SMR stars in a stellarlibrary dedicated to the study of stellar populations in the centralpart of galaxies is crucial as abundance gradients have been observed inthe optical range.
| A library of H band stellar spectra for stellar population analysis purposes.
A sample of 37 stars of luminosity classes I, III, V, including few SMRstars observed in the H band with a medium resolution (R=1500-2000) ispresented. This sample of flux calibrated spectra is intended to widenexisting stellar libraries. A new IR spectrograph, ISIS/IR, foreseen forCFHT has been used. Its main characteristics are briefly described.Stellar spectra obtained with this new spectrograph are compared tosimilar data obtained with the ESO NTT IRSPEC spectrograph. Thebehaviour of some prominent features is described and it is shown thatthe COλ1.60/SiIλ1.60 line ratio is a good luminosityindicator for stellar types later than K0.
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| Csillagkép: | Szextáns |
| Rektaszcenzió: | 10h49m31.69s |
| Deklináció: | -06°46'10.6" |
| Vizuális fényesség: | 9.106 |
| RA sajátmozgás: | -201.8 |
| Dec sajátmozgás: | 51.4 |
| B-T magnitude: | 10.223 |
| V-T magnitude: | 9.199 |
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