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Spectroscopic survey of post-AGB star candidates
Aims.Our goal is to establish the true nature of post-AGB starcandidates and to identify new post-AGB stars. Methods: We used lowresolution optical spectroscopy and we compared the spectra of thecandidate post-AGB stars with those of stars in the library spectaavailable in the literature and with spectra of "standard" post-AGBstars, and direct imaging in narrow-band filters. Results: Spectra wereobtained for 16 objects: 14 objects have not been observed previouslyand 2 objects are already known post-AGB stars used as "standards" foridentification. From the spectra we identify: six new post-AGB starswith spectral types between G5 and F5, two H ii regions the morphologyof which is revealed in the direct images for the first time, a G giantwith infrared emission, a young stellar object, a probable post-AGB starwith emission lines and three objects for which the classification isstill unclear. As a whole, our results provide new, reliableidentifications for 10 objects among listed post-AGB star candidates.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC), and at the Observatorio de Sierra Nevada, whichis operated by the Consejo Superior de InvestigacionesCientíficas through the Instituto de Astrofísica deAndalucía (Granada, Spain). Appendices A-D are only available inelectronic form at http://www.aanda.org
| Spectroscopic survey of field stars : A search for metal-poor stars
We have undertaken a spectroscopic survey of field stars to finemetal-poor objects among them. Though the main objective of the surveyis to find new metal-poor stars, stellar parameterization is carried outfor all the sample stars so that the other categories of interestingobjects like composite stars, weak or strong CN, CH stars etc. can alsobe identified. Observations are carried out using OMR spectrographattached to VBT, Kavalur. The sample of candidate stars are chosen fromprismatic survey of Beers and his collaborators covering a large part ofthe Galaxy. At the first phase of this project, the analysis ofcompleted for a set of 19 relatively hot stars (Teff in 6000 to 8000Krage). The metallicities of the program stars are derived bysynthesizing the spectrum in the wavelength range 4900 to 5400 Åfor different metallicities and matching them with the observed spectra.This spectral region contains strong feature of Fe I at 5269 Å andone moderately strong Fe I blend at 5228 Å. These features weregenerally relied upon for Fe/H determination. More than half of thecandidate stars were found to show (Fe/H) in -0.7 to -1.2 range. Twomost metal-poor stars have (Fe/H) values of -1.3 and -1.8. It appearsthat metal-poor candidates suggested by Beers et al. from theirprismatic survey has a very significant fraction of metal-poor stars.The significantly metal-poor stars found so far would be studied indetail using high resolution spectra to understand nucleosynthesisprocesses that might have occurred in early Galaxy.
| 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
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| A Supergiant-Dominated Starburst in the Nucleus of NGC 4569
The Virgo spiral NGC 4569 has a very compact optical nucleus whosespectrum is highly composite, which strong Balmer absorption indicatingthat A stars dominate the optical light. Recent HST imaging shows thatthe nucleus is extremely compact in the mid-ultraviolet, so that eitherthere must be a central AGN or an extraordinarily luminous and compactcentral star cluster. I present here IUE and ground-basedspectrophotometry and high-resolution optical spectra, which are used todecompose the nucleus into possible stellar and AGN contributions.Accounting for the asymmetric contamination by Balmer emission, at avelocity different from the stellar absorption lines, removes theapparent discrepancy between radial velocities for different stellarcomponents. The nuclear spectrum shows contributions from ordinary bulgelight and from a young population. This young component has effectivespectral type of mid-A, and the Balmer lines are so narrow that A-typesupergiants are the most important contributors to the optical light.The young population is therefore much younger than the spectral typewould suggest if interpreted as a main-sequence turnoff age, and theasociated OB stars might account for much of the UV flux. In this case,the nucleus contains an extraordinarily bright star cluster about aslarge as the core of 30 Doradus but more than 6 magnitudes brighter.While some less luminous supergiant-dominated star clusters have beenfound, current models of starburst evolution do not give a naturalexplanation for such a bunching in effective temperature. Evidence foran AGN is equivocal; M/L arguments show that only for the most extremeconditions of timing and burst duration could stars alone give a smallenough value to satisfy the observational limit on velocity dispersion,and this condition would be eased if some of the UV radiation and theionization of the nuclear gas can be attributed to an AGN. While, forvery favorable conditions the Balmer absorption might be interpreted ascoming from an unusually extensive and face-on accretion disk (ratherthan stars), the small linewidths and dominance of a single photospherictemperature place very stringent geometric and size constraints on thispossibility. (SECTION: Galaxies)
| 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.
| 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.
| The complicated giant binary SX Cas.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..500K&db_key=AST
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| קבוצת-כוכבים: | קאסיופיאה |
| התרוממות ימנית: | 00h13m00.35s |
| סירוב: | +55°51'32.5" |
| גודל גלוי: | 7.96 |
| מרחק: | 1086.957 פארסק |
| תנועה נכונה: | -2.9 |
| תנועה נכונה: | 1.7 |
| B-T magnitude: | 8.548 |
| V-T magnitude: | 8.009 |
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