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λ Bootis stars with composite spectra
We examine the large sample of λ Boo candidates collected inTable 1 of Gerbaldi et al. (\cite{Gerbaldi2003}) to see how many of themshow composite spectra. Of the 132 λ Boo candidates we identify22 which definitely show composite spectra and 15 more for which thereare good reasons to suspect a composite spectrum. The percentage ofλ Boo candidates with composite spectra is therefore >17% andpossibly considerably higher. For such stars the λ Booclassification should be reconsidered taking into account the fact thattheir spectra are composite. We argue that some of the underabundancesreported in the literature may simply be the result of the failure toconsider the composite nature of the spectra. This leads to thelegitimate suspicion that some, if not all, the λ Boo candidatesare not chemically peculiar at all. A thorough analysis of even a singleone of the λ Boo candidates with composite spectra, in which thecomposite nature of the spectrum is duly considered, which woulddemonstrate that the chemical peculiarities persist, would clear thedoubt we presently have that the stars with composite spectra may not beλ Boo stars at all.Based on observations collected at ESO (Echelec spectrograph) and at TBL(Telescope Bernard Lyot) of the Pic du Midi Observatory (France).
| Rotational Velocities of B, A, and Early-F Narrow-lined Stars
Projected rotational velocities for 58 B, A, and early-F stars have beendetermined from high-resolution spectroscopic observations made at KittPeak National Observatory with the coudé feed telescope. All thestars are slowly rotating with vsini<60 km s-1. Because oftheir low rotational velocities, 15 of the stars have been observed asprospective, early-type, radial velocity standards.
| The heterogeneous class of lambda Bootis stars
We demonstrate that it is arduous to define the lambda Boo stars as aclass of objects exhibiting uniform abundance peculiarities which wouldbe generated by a mechanism altering the structure of their atmosphericlayers. We collected the stars classified as lambda Boo up to now anddiscuss their properties, in particular the important percentage ofconfirmed binaries producing composite spectra (including our adaptiveoptics observations) and of misclassified objects. The unexplained RVvariables (and thus suspected binaries), the known SB for which we lackinformation on the companion, the stars with an UV flux inconsistentwith their classification, and the fast rotating stars for which noaccurate abundance analysis can be performed, are also reviewed.Partly based on observations collected at the CFH Telescope (Hawaii) andat TBL of the Pic du Midi Observatory (France).Table \ref{tab5} is only available in electronic form athttp://www.edpsciences.org
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| How many lambda Bootis stars are binaries?
In the attempt to shed new light on the lambda Boo phenomenon weanalyzed the astrometric, photometric and spectroscopic characteristicsof stars out of a list of recently selected lambda Boo candidates. Weshow that the class is still ill-defined and discuss the possibilitythat some, if not most stars presently classified as lambda Boo, are infact binary pairs and that peculiar abundances may not correspond toactual values if the average values of the atmospheric parameters{Teff} and log g are assumed and the effect of veiling is nottaken into account. Partly based on data from the ESA Hipparcosastrometry satellite.
| Late A-type stars: new Strömgren photometric calibrations of absolute magnitudes from HIPPARCOS
Hipparcos trigonometric parallaxes have been used to derive aphotometric absolute magnitude calibration of main-sequence late A-typestars in terms of Strömgren photometric indices - accounting fortemperature, evolution and metallicity effects - and projectedequatorial rotational velocities. The derived calibrations are valid formain-sequence normal A3-A9 and metallic Am stars, showing residuals of0.22 and 0.20 magnitudes, respectively. One of the fitting methods used(BCES) allows the derivation of the observational ZAMS in this spectralrange, showing an excellent accordance with theoretical evolutionarymodels. The evolutionary state of the Am stars is also discussed.Table~A1 is only available in electronic form from CDS via anonymous ftp130.79.128.5, and by e-mail: request to cesca@am.ub.es
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| New lambda Bootis stars with a shell
We publish here the second part of our spectroscopic survey at highdispersion of some known and suspected lambda Bootis stars with a viewto detecting circumstellar shell features. Eight stars of our sampleexhibit such features. These stars are fast rotators, a result which isin line with Hohlweger and Rentzsch-Holm's study (1995). The analysis ofthe photometric data has allowed us to confirm the exclusion of a fewstars misclassified from the lambda Bootis group.
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| Radial-velocity measurements in 20 young open clusters
The further results of a program to determine the radial velocities ofyoung open clusters are presented. Using the KPNO coude spectrographcoupled with the 1-m feed and 2.1-m telescopes, radial velocities havebeen measured for nearly one hundred stars, most of which are ofspectral type B and A, in 20 young clusters. The combination ofinstruments and the use of cross-correlation techniques show that radialvelocities of B and A type stars as faint as 10th magnitude can bedetermined with an internal precision of less than about 2 km/s. Asexpected, the uncertainties in the velocity determination for the youngclusters are dominated by spectroscopic binary stars in these clusters.A third of the stars in the sample are found to be spectroscopicbinaries, but with a large variation in the frequency of binaries fromcluster to cluster. Because the time coverage is still limited, thisshould be considered a lower limit to the binary frequency. Clustervelocities are determined after eliminating binaries and known nonmemberstars. The new velocities are compared with a model galactic rotationcurve, as well as with previous velocity determinations.
| Miscellaneous spectroscopic notes
Results of slit-spectrograph observations are reported for approximately260 stars. The data presented range from recognition of many new Ap, Am,and other unusual stars to H-alpha observations of early-typesupergiants and Be stars. The material discussed was obtained over thepast 40 years at a number of U.S. observatories and at the DominionAstrophysical Observatory in Victoria, B.C.
| Starbursts, binary stars, and blue stragglers in local superclusters and groups. I - The very young disk and young disk populations
The distributions in the HR diagram with theoretical time-constant locifor stars in several young clusters and superclusters are compared todemonstrate that 'blue stragglers' in these aggregates are mostfrequently simply single massive (mode B) stars formed in bursts of starformation that occur at discrete intervals in time following theformation of the bulk of the low-mass (mode A) stars in the aggregate.The characteristics of the close binary systems in these aggregates areexamined to show that, in several cases, mass transfer by Roche lobeoverflow has or will occur and that, in some instances, the system wouldhave appeared as a blue straggler prior to the mass-transfer event, and,in other instances, mass transfer will lead to the identification of thesystem as a blue straggler. Thus, it is concluded that the bluestraggler phenomenon has at least two distinct physical origins: it mayoriginate from delayed formation (starbursts) or from 'delayedevolution' in some close binaries (mass transfer from an evolvedprimary).
| A catalogue of Fe/H determinations, 1984 edition
The present version of the Cayrel de Strobel et al. (1981) catalog ofFe/H abundance ratio determinations contains 1921 values for 1035 stars,which represents an augmentation over the previous publication of 48 and47 percent, respectively. In addition, the literature search conductedis complete up to December, 1983. Stellar metal abundance, effectivetemperature, spectroscopic gravity, spectral type, and photometricindices are covered.
| The A0 stars
A photometric grid, standardized on MK spectral standards, has been usedto compare spectral types and luminosity classes obtainedphotometrically with those in two extensive spectral surveys coveringthe entire sky. Major discrepancies include the spectroscopicclassification of B9.5, which may indicate an otherwise unrecognizedspectral peculiarity, a different A0/A1 spectral type boundary in thetwo samples involved, the well-known misclassification of weak heliumstars, and an appreciable percentage of stars which are called dwarfsspectroscopically but are of higher photometric luminosity. The spacemotion vectors of these stars for which radial velocities are available,and excluding the minimum of 25 percent that are spectroscopic binarieswithout orbital elements, show structure in their distribution in the(U, V)-plane, with members of the Local Association and the Hyades andSirius superclusters forming obvious concentrations. The members of theLocal Association in the samples are mainly old (more than 200 millionyears) mode A stars, although a few much younger stars are included. Themembers of the Hyades and Sirius superclusters contain many bluestragglers, including several peculiar stars of the Hg, Mn, and Sivarieties.
| Chemical abundances in Hg-Mn stars
An abundance analysis has been conducted of 21 elements in 21 Hg-Mn, twoSi-Cr, and six normal stars using model atmospheres and high-dispersionspectroscopy in the visible and UV. Manganese line strengths implyabundances that correlate well with stellar effective temperature.Within the studied sample of Hg-Mn stars there appears to be nocorrelation of abundances of any element with projected rotationalvelocity. Abundances in several Hg-Mn stars show patterns that areprobably consistent with diffusion but difficult to reconcile withequilibrium nucleosynthesis. In general, no combination of gross stellarphysical parameters is sufficient to characterize the patterns of linestrengths observed in Hg-Mb Hg-Mn stars.
| Late B-type stars - Rotation and the incidence of HgMn stars
High-dispersion spectrograms for an unbiased sample of 256 late B-typestars are examined in an attempt to determine whether slow rotation isnecessary and sufficient for the appearance of HgMn anomalies innonmagnetic stars. The peculiar stars in the sample are identified,values of v sin i are derived for all the stars observed, and theradial-velocity variations of the identified HgMn stars are analyzed.The distribution of rotational velocities for late B-type stars isobtained, and the role of rotation in producing extended envelopes isevaluated. The binary frequency and mass-ratio distribution are derivedfor systems containing HgMn components, the effect of duplicity on thedistribution of rotational velocities is estimated, and the role of suchfactors as rotation, age, and binary characteristics in determiningwhether HgMn anomalies are present is investigated. The results clearlyshow that HgMn stars occur only within a limited temperature range, thatall such stars rotate slowly, but that rotation, effective temperature,age, surface gravity, and binary properties do not serve to determinewhether a star will exhibit abundance anomalies.
| Duplicity of late B-type stars
High-dispersion spectroscopic observations of 83 stars are used todetermine the binary characteristics of late B-type stars. For a randomsample of such objects, including peculiar as well as normal stars, thefrequency of binaries with mass ratios m2/m sub 1 greaterthan 0.1 and orbital periods less than 100 days is estimated to be about24%, and the frequency of binaries decreases with decreasingm2/m sub 1. In both respects, the late B-type stars aresimilar to early B-, late A-, and solar-type stars. For the majority ofstars with an orbital period greater than 4 days, the observedrotational velocity exceeds the value that corresponds to synchronism ofrotation and revolution, but the ratio of the observed to thesynchronous rotational velocity seldom exceeds a factor of 2 even forperiods as long as 15 days. An additional 20% of the stars surveyedexhibit low amplitude-velocity variations that, if due to orbitalmotion, correspond to m2 m1 less than 0.1. Themost likely explanation is that these systems are close binary remnantsthat have already passed through the mass-transfer phase, with thepresent secondary being a white dwarf.
| Spectral classification from the ultraviolet line features of S2/68 spectra. III - Early A-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33...15C&db_key=AST
| Space velocities and ages of nearby early-type stars
Photometric distances and space velocities have been calculated for 458B0-A0 stars with apparent magnitudes not exceeding 6.5. UsingStromgren's ubvy-beta photometry the effective temperature and theposition in bolometric magnitude over the zero-age main sequence of thestars were derived. These quantities were used to obtain age and massfor 423 of the stars by interpolation in the models of stellar evolutionfor the chemical composition (X Z) = (0.7, 0.03). A relation forderiving interstellar reddening for normal stars in the intermediategroup is given.
| Is star formation bimodal ? II. The nearest early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
| Four-color and Hβ photometry for the brighter AO type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..109C&db_key=AST
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Kis Róka |
| Rektaszcenzió: | 20h39m10.60s |
| Deklináció: | +21°49'02.0" |
| Vizuális fényesség: | 6.08 |
| Távolság: | 284.091 parszek |
| RA sajátmozgás: | 31.6 |
| Dec sajátmozgás: | 15.3 |
| B-T magnitude: | 6.017 |
| V-T magnitude: | 6.067 |
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INHABITED SKY
