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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.
| 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 Fornax spectroscopic survey. I. Survey strategy and preliminary results on the redshift distribution of a complete sample of stars and galaxies
The Fornax Spectroscopic Survey will use the Two degree Fieldspectrograph (2dF) of the Anglo-Australian Telescope to obtain spectrafor a complete sample of all 14000 objects with 16.5 <= bj<= 19.7 in a 12 square degree area centred on the Fornax Cluster. Theaims of this project include the study of dwarf galaxies in the cluster(both known low surface brightness objects and putative normal surfacebrightness dwarfs) and a comparison sample of background field galaxies.We will also measure quasars and other active galaxies, any previouslyunrecognised compact galaxies and a large sample of Galactic stars. Byselecting all objects--both stars and galaxies--independent ofmorphology, we cover a much larger range of surface brightness and scalesize than previous surveys. In this paper we first describe the designof the survey. Our targets are selected from UK Schmidt Telescope skysurvey plates digitised by the Automated Plate Measuring (APM) facility.We then describe the photometric and astrometric calibration of thesedata and show that the APM astrometry is accurate enough for use withthe 2dF. We also describe a general approach to object identificationusing cross-correlations which allows us to identify and classify bothstellar and galaxy spectra. We present results from the first 2dF field.Redshift distributions and velocity structures are shown for allobserved objects in the direction of Fornax, including Galactic stars,galaxies in and around the Fornax Cluster, and for the background galaxypopulation. The velocity data for the stars show the contributions fromthe different Galactic components, plus a small tail to high velocities.We find no galaxies in the foreground to the cluster in our 2dF field.The Fornax Cluster is clearly defined kinematically. The mean velocityfrom the 26 cluster members having reliable redshifts is 1560 +/- 80\:km\:s-1. They show a velocity dispersion of 380 +/- 50\:km\:s-1. Large-scale structure can be traced behind thecluster to a redshift beyond z=0.3. Background compact galaxies and lowsurface brightness galaxies are found to follow the general galaxydistribution.
| Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements
New spectral observations for 47 southern galactic red supergiantsobtained with the new RUBIKON spectrophotometer (developed at theAstronomisches Institut der Ruhr-Universitat Bochum) at the Bochum 61-cmtelescope on La Silla are presented. The spectra range from 4800 to 7700A and their resolution is 10 A. The mean error of absolute fluxes is0.028 mag and that of relative fluxes 0.021 mag. The spectra will beavailable at the Strasbourg Stellar Database (CDS). Together with datataken from recently published spectral catalogues, the new observationshave been used to define spectral indices as measures of the strengthsof the following features: Fe i+TiOalpha_1, Mgb+TiOalpha_0,NaD+TiOgamma'_1, TiOgamma'_0 and TiOgamma_1 systems. The indices havebeen checked against errors introduced by reductions, interstellarreddening and different resolutions of different spectral catalogues,and have been found to be very insensitive to all these effects.Therefore, different catalogues may be combined without any loss ofaccuracy and homogeneity. The mean error of a single index has beenfound to be 0.011 mag. For stars from K4 to M7, a strong temperaturedependence is found for all indices. For the Fe i+TiO and especially theMgb+TiO features, a strong dependence on luminosity has also beenobserved. These indices therefore have been combined to form aluminosity index, while the others together form a spectral index. Thecombined indices have been calibrated in terms of MK data using thestepwise linear regression technique, and may be used for quantitativetwo- dimensional spectral classification of late K- and M-type stars.The mean error of the classification is 0.6 of spectral subtype and 0.8of luminosity class, which is much higher than would be expected fromthe uncertainty of the indices alone (which, e.g., for an M4 giantcorrespond to an uncertainty of 0.1 of spectral subtype and 0.3 ofluminosity class). This may be explained by the uncertainty of theoriginal MK classifications and the variability of some programme stars.
| X-Ray and Optical Observations of the COMPTEL Error Box for GRB 910601
We present X-ray and optical observations of the COMPTEL and IPN errorbox of the gamma-ray burst GRB 910601. Our data consists of a 20 ks PSPCROSAT image and optical CCD images and spectra. Thirty X-ray sourceswere identified within the COMPTEL error box. B and V photometry ofobjects within the error boxes of the 12 strongest X-ray sources ispresented as well as optical spectroscopy of several of the brightestoptical sources. Two X-ray sources (#29 and #30) are located within theCOMPTEL 1.5- error box and are also within a few arcmin of the IPN errorannulus for this burst. Source #29 was the strongest X-ray source in thetwo-degree diameter ROSAT field. We have associated this source with thestar SAO 70303, an early G-type star. A fainter star with unusual colorsis located about 16" to the NE of SAO 70303. No obvious opticalcounterpart was found within the ROSAT error circle for #30 to V <=22.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| A new library of stellar optical spectra
Attention is given to a new digital optical stellar library consistingof spectra covering 3510-8930 R at 11-A resolution for 72 differentstellar types. These types extend over the spectral classes O-M andluminosity classes I-V. Most spectra are of solar metallicity stars butsome metal-rich and metal-poor spectra are included. This new library isquantitatively compared to two previously published libraries. It offersseveral advantages over them: it is photometrically well-calibratedindividually and consistently from star to star. Good temperature andluminosity coverage has been achieved. The incorporation of stars withwell-determined temperature, metallicity, and surface gravity parametersincreases the accuracy of the spectral type assigned to each compositelibrary star.
| Hamilton echelle spectra of young stars. I - Optical veiling
An extensive set of veiling measurements of T Tauri stars coveringalmost the entire optical spectrum is presented. These are based onHamilton echelle spectra obtained during 1987-1989. A full range of TTauri stars, from 'weak' to 'continuum' stars is studied; in some cases,several spectra of a given target are seen in which the veiling haschanged, occasionally dramatically. Veilings are determined using twonew methods: one which concentrates on the residual intensities ofselected spectral lines, and the other which compares theautocorrelation functions for a T Tauri star and a veiled standard. Thegeneral shape of the veiling is often as predicted by accretion diskmodels: almost flat in the red and increasing in the blue. Cooler starshave generally higher veiling, implying that the veiling power isrelatively independent of stellar mass. The relation between veiling andthe narrow and broad emission lines supports a nonstellar origin for theveiling and broad line components, and a stellar origin for the narrowlines.
| A library of stellar spectra
Spectra for 161 stars having spectral classes O-M and luminosity classesV, III, and I have been incorporated into a library available onmagnetic tape. The spectra extend from 3510 to 7427 A at a resolution ofabout 4.5 A. The typical photometric uncertainty of each resolutionelement in the spectra is on the order of 1 percent while broad-bandvariations are smaller than 3 percent. Potential uses for the libraryinclude population synthesis of galaxies and clusters, tests of stellaratmosphere models, spectral classification, and the generation of colorindices having arbitrary wavelength and bandpass.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Телец |
| Прямое восхождение: | 04h52m53.01s |
| Склонение: | +27°18'51.2" |
| Видимая звёздная величина: | 9.003 |
| Собственное движение RA: | 12.9 |
| Собственное движение Dec: | -22.9 |
| B-T magnitude: | 10.866 |
| V-T magnitude: | 9.157 |
Каталоги и обозначения:
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