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Abundance analysis of 5 early-type stars in the young open cluster IC 2391
Aims.It is unclear whether chemically peculiar stars of the upper mainsequence represent a class completely distinct from normal A-type stars,or whether there exists a continuous transition from the normal to themost peculiar late F- to early B-type stars. A systematic abundanceanalysis of open cluster early-type stars would help to relate theobserved differences of the chemical abundances of the photospheres toother stellar characteristics, without being concerned by possibledifferent original chemical composition. Furthermore, if a continuoustransition region from the very peculiar to the so called normal A-Fstars exists, it should be possible to detect objects with mildpeculiarities. Methods: .As a first step of a larger project, anabundance analysis of 5 F-A type stars in the young cluster IC 2391 wasperformed using high resolution spectra obtained with the UVESinstrument of the ESO VLT. Results: .Our targets seem to follow ageneral abundance pattern: close to solar abundance of the lightelements and iron peak elements, heavy elements are slightlyoverabundant with respect to the sun, similar to what was found inprevious studies of normal field A-type stars of the galactic plane. Wedetected a weakly chemically peculiar star, HD 74044. Its elementpattern contains characteristics of CP1 as well as CP2 stars, enhancedabundances of iron peak elements and also higher abundances of Sc, Y, Baand Ce. We did not detect a magnetic field in this star (detection limitwas 2 kG). We also studied the star SHJM 2, proposed as a pre-mainsequence object in previous works. Using spectroscopy we found a highsurface gravity, which suggests that the star is very close to theZAMS.
| Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
| X-ray spectral and timing characteristics of the stars in the young open cluster IC 2391
We present X-ray spectral and timing analysis of members of the youngopen cluster IC 2391 observed with the XMM-Newton observatory. Wedetected 99 X-ray sources by analysing the summed data obtained fromMOS1, MOS2 and pn detectors of the EPIC camera; 24 of them are members,or probable members, of the cluster. Stars of all spectral types havebeen detected, from the early-types to the late-M dwarfs. Despite thecapability of the instrument to recognize up to 3 thermal components,the X-ray spectra of the G, K and M members of the cluster are welldescribed with two thermal components (at kT1 0.3-0.5keV and kT2 1.0-1.2 keV respectively) while the X-rayspectra of F members require only a softer 1-T model. TheKolmogorov-Smirnov test applied to the X-ray photon time series showsthat approximately 46% of the members of IC 2391 are variable with aconfidence level >99%. The comparison of our data with those obtainedwith ROSAT/PSPC, nine years earlier, and ROSAT/HRI, seven years earlier,shows that there is no evidence of significant variability on thesetime scales, suggesting that long-term variations due to activity cyclessimilar to that on the Sun are not common, if present at all, amongthese young stars.
| Data mining in the young open cluster IC2391
Large-scale astrometric and photometric data bases have been used tosearch for and confirm stellar membership of the open cluster IC2391.125 stars were found that satisfied criteria for membership based onproper motion components and BRI photometry from the United States NavalObservatory B (USNO-B) catalogue and JHK photometry from the Two MicronAll Sky Survey (2MASS) catalogue. This listing was compared with othersrecently published. A distance to the cluster of 147.7 +/- 5.5 pc wasfound with mean proper motion components, from the Tycho2 catalogue of(-25.04 +/- 1.53 masyr-1+23.19+/-1.23 masyr-1). Arevised Trumpler classification of II3r is suggested. Luminosity andmass functions for the candidate stars were constructed and comparedwith those of field stars and other clusters.
| On the evolutionary status of chemically peculiar stars of the upper main sequence
We present further evidence that the magnetic chemically peculiar stars(CP2) of the upper main sequence already occur at very early stages ofthe stellar evolution, significantly before they reach 30% of theirlife-time on the main sequence. This result is especially important formodels dealing with dynamo theories, angular momentum loss during thepre- as well as main sequence and evolutionary calculations for CP2stars. Results from the literature either derived for objects in theHyades and the UMa cluster or from the Hipparcos mission contradict eachother. A way out of this dilemma is to investigate young open clusterswith known ages and accurate distances (error <10%), including CP2members. Up to now, four open clusters fulfill these requirements: IC2391, IC 2602, NGC 2451 A and NGC 2516. In total, 13 CP2 stars can befound within these clusters. We have used the measurements andcalibrations of the Geneva 7-color photometric system to deriveeffective temperatures and luminosities. Taking into account the overallmetallicity of the individual clusters, isochrones and evolutionarytracks were used to estimate ages and masses for the individual objects.The derived ages (between 10 and 140 Myr) are well in line with those ofthe corresponding clusters and further strengthen the membership of theinvestigated CP2 stars.Based on observations by the Hipparcos satellite.
| Seven-Color Photoelectric Photometry of the Omicron Velorum Cluster
Photoelectric observations in the Vilnius seven-color photometric systemof 36 stars in the magnitude range 3.6 < V < 10.7 in the opencluster around the star o Velorum are presented. Photometric spectraland luminosity classes are determined for each star from which the meandistance modulus of the cluster is found to be 5.94+/-0.02 mag and themean color excess EY-V = 0.00+/-0.02 mag. The membership ofthe cluster stars is discussed.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| A Deep X-Ray Image of IC 2391
A 56 ks soft X-ray image of the IC 2391 star cluster has been acquiredwith the ROSAT High Resolution Imager, resulting in the detection of 34sources above a 3 sigma detection level of L_X~=4x10^28 ergs s^-1. Wereport source coordinates and fluxes plus identifications and broadbandBVRI photometry for optical counterparts to each source. We comparethese results with X-ray source fluxes from a ROSAT PSPC image of thesame region, which we obtained 2 yr earlier. The largest change in X-raybrightness for any of the known or suspected G, K, and M cluster membersis 0.43 dex, i.e., a factor of ~3. Given this modest amplitude in X-rayvariability, we conclude that the broad (factor of 20) dispersion inX-ray luminosities within IC 2391 is unrelated to short- orintermediate-term cycles of the stellar dynamo. We further show that theeffects of source confusion on the PSPC X-ray luminosity function, fordistance scales of 5"-30", are relatively small and are thus negligiblefor the purpose of comparing IC 2391 with older clusters and forstudying the evolution of coronal X-ray emission in solar-type stars.The greater part of the observed scatter in X-ray luminosity within IC2391 still awaits explanation.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Effective temperatures of AP stars
A new method of determination of the effective temperatures of Ap starsis proposed. The method is based on the fact that the slopes of theenergy distribution in the Balmer continuum near the Balmer jump for``normal" main sequence stars and chemically peculiar stars with thesame Teff are identical. The effective temperaturecalibration is based on a sample of main sequence stars with well knowntemperatures (\cite[Sokolov 1995]{sokolov}). It is shown that theeffective temperatures of Ap stars are derived by this method in goodagreement with those derived by the infrared flux method and by themethod of \cite[Stepien & Dominiczak (1989)]{stepien}. On the otherhand, the comparison of obtained Teff with Teffderived from the color index (B2-G) of Geneva photometry shows a largescatter of the points, nevertheless there are no systematicaldifferences between two sets of the data.
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| The Evolution of Rotation and Activity in Young Open Clusters: IC 2391
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..489P&db_key=AST
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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 new list of effective temperatures of chemically peculiar stars. II.
Not Available
| The Evolution of Stellar Coronae: Initial Results from a ROSAT PSPC Observation of IC 2391
Not Available
| Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
Not Available
| HgMn stars, good or bad for optical soundings in the Milky Way?
Ten mercury-manganese stars from the Michigan Catalogue are examined toassess the consistency of their spectral appearance in sample groupsfrom Galactic optical soundings. The search for classification criteriayields no clear parameters for HgMn stars, and most stars withparticular rotational velocities and temperature ranges exhibit thecharacteristics of HgMn stars. Systematic errors in optical soundingscan be avoided by obtaining samples of stars in the actual temperaturerange used for calibration of absolute magnitude and intrinsic colorsand anticipating a significant fraction of unrevealed HgMn objects.
| The IC 2391 supercluster
Sixty-three field stars and the sparse cluster IC 2391 have beenidentified as members of the IC 2391 supercluster. The members have atleast 95 percent of their space motion, directed toward (A,D) = (5.82h,- 12.44d). Like members of the very similar Pleiades supercluster, theIC 2391 supercluster contains objects of two ages: t = 8 x 19 exp 7 and2.5 x 10 exp 8 yr. A prototype very active chromosphere star and theenigmatic giant variable TZ For are supercluster members together withtwo A-type stars suspected of possessing particulate disks. Anespecially interesting member is the system of Xi Cep (HR 8417) in whichthe two brightest components are greatly undermassive.
| Second supplement to the catalogue of observed periods of AP stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&AS...87...59C&db_key=AST
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| Giant CP stars?
This study is part of an investigation of the possibility of usingchemically peculiar (CP) stars to map local galactic structure. Correctluminosities of these stars are therefore crucial. CP stars aregenerally regarded as main-sequence or near-main-sequence objects.However, some CP stars have been classified as giants. A selection ofstars, classified in the literature as CP giants, are compared to normalstars in the same effective temperature interval and to ordinary'nongiant' CP stars. No clear confirmation of a higher luminosity for'CP giants' than for CP stars in general is found. In addition, CPcharacteristics seem to be individual properties not repeated in acomponent star or other cluster members.
| Radial velocities in the open cluster IC 2391
Radial velocities have been determined for 31 stars in the field of theopen cluster IC 2391, and the percentage of probable radial-velocityvariables is derived. The orbit of one previously known spectroscopicbinary is improved, and the existence of two double-line binaries isconfirmed. The membership to the cluster and the average cluster radialvelocity are discussed and the incidence of short-period binaries amongthe Main-Sequence members of IC 2391 is compared with the incidence forother clusters with similar average axial rotation of its members.
| Chemically peculiar stars in open clusters. I - The catalog
The largest existing compilation is presented of Ap and Am open clusterstars. The catalog contains information on 381 chemically peculiar (CP)stars of the upper main sequence in 79 open clusters. The catalog iscomposed of the following tables: (1) the main body, which lists CP (orsuspected CP) stars which are kinematical (or suspected kinematical)members of open clusters; (2) the list of CP (or suspected CP) starssometimes numbered among cluster members but which are actuallykinematical nonmembers; (3) the list of stars sometimes designated as'peculiar' but, in fact, probably not CP; (4) references for numberingsystems of cluster stars; (5) references for membership; and (6)references for spectral and/or peculiarity types.
| Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
| First supplement to the catalog of observed periods of AP stars
Supplementary data on the periods of Ap stars with references arepresented; 58 new stars are introduced for which periodic variabilityhas been discovered since 1983. For some of these stars periodicity wasknown before 1983 but they were not reported in the previous catalog.Recently attributed variable star names are also reported.
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| Сазвежђа: | Једра |
| Ректацензија: | 08h42m18.90s |
| Deклинација: | -53°06'00.0" |
| Apparent магнитуда: | 5.52 |
| Даљина: | 148.148 parsecs |
| Proper motion RA: | -21.8 |
| Proper motion Dec: | 24.3 |
| B-T magnitude: | 5.309 |
| V-T magnitude: | 5.453 |
Каталог и designations:
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INHABITED SKY
