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Discovery of a huge magnetic field in the very young star NGC 2244-334 in the Rosette Nebula cluster
During a survey of field strengths in upper main sequence stars in openclusters, we observed the star NGC 2244-334 in the Rosette Nebulacluster and discovered an extraordinarily large mean longitudinal fieldof about -9 kG, the second largest longitudinal field known in anon-degenerate star. This star appears to be a typical Ap He-wk (Si)star of about 4 Mȯ. Spectrum synthesis using a linesynthesis code incorporating the effects of the strong magnetic fieldindicates that He is underabundant by about 1.5 dex, and C, O and Mg byabout 0.1-0.4 dex, while Si, Mn and Fe are overabundant by about 1 dex,and Cr and Ti are nearly 2 dex overabundant.Cluster membership for this star is secure, so its age is about 2×106 yr, which is less than 3% of its main sequence lifetime.This star is one of the very youngest magnetic upper main sequence starswith a well-determined age, and confirms that both magnetic fields andstrong chemical peculiarity can appear in stars which are both extremelyyoung and very close to the ZAMS.This paper is based on data obtained at the European SouthernObservatory VLT during observing runs 70.D-0352 and 270.D-5032.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| 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.
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| Search for low-mass PMS companions around X-ray selected late B stars
We have observed 49 X-ray-detected bright late B-type dwarfs to searchfor close low-mass pre-main sequence (PMS) companions using the EuropeanSouthern Observatory's ADONIS (Adaptive Optics Near Infrared System)instrument. We announce the discovery of 21 new companions in 9binaries, 5 triple, 4 quadruple system and 1 system consisting of fivestars. The detected new companions have K magnitudes between 6.5m and17.3m and angular separations ranging from 0.12 arcsec to 14.1 arcsec(18-2358 AU). Based on observations obtained at the European SouthernObservatory, La Silla, Chile (ESO programme No.~62.I-0477, and Swiss70~cm photometric telescope).
| 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
| Hβ photometry of southern CP2 stars: is the uvbybeta luminosity calibration also valid for peculiar stars?
We present Hβ photometry of 233 southern CP2 stars (covering themagnetic Ap stars according to the definition by Preston 1974) brighterthan V < 8.5 mag from the list of Bidelman & MacConnell (1973).Absolute magnitudes derived from this photometry together with alreadyexisting uvby photometry is confronted with Hipparcos results availablefor a common subset of 152 stars. In order to compare peculiar withnormal stars, we identified a sample of 1147 normal B to F-type starsusing their published uvbybeta and Hipparcos data. For our analysis wedivide both samples into three temperature as well as two Hipparcosparallax accuracy groups. The error distribution of both samples provedto be statistically comparable. As a result the absolute magnitudes forthe B-type CP2 stars show up to be significantly too bright by anaverage of 0.5 mag using the actual photometric calibration. On theother hand, the photometric absolute magnitudes for cool A to F-type CP2stars are up to three magnitudes fainter as compared to Hipparcos. Basedon observations at ESO-La Silla and with the Hipparcos satellite
| Identification of moving groups and member selection using HIPPARCOS data
A new method to identify coherent structures in velocity space - movinggroups - in astrometric catalogues is presented: the Spaghetti method.It relies on positions, parallaxes and proper motions, and is ideallysuited to searching for moving groups in the Hipparcos Catalogue. Noradial-velocity information is required. The method has been testedextensively on synthetic data, and applied to the Hipparcos measurementsfor the Hyades and IC 2602 open clusters. The resulting lists of membersagree very well with those of Perryman et al. for the Hyades and thoseof Whiteoak & Braes for IC 2602.
| 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
| On the near infrared variability of chemically peculiar stars
Some CP stars have recently been discovered by Catalano et al. to bevariable also in the near infrared, although with smaller amplitudesthan in the visible. Hence an observational campaign was started inwhich the infrared light variability of a number of CP2 and CP4 starshas been investigated at the ESO-La Silla Observatory in the bands J, H,and K. As a general result, infrared variations show the same behaviorin all three filters but amplitudes are smaller than in the visible.
| 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
| 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
| Do SI stars undergo any rotational braking?
The old question of rotational braking of Ap Si stars is revisited onthe empirical side, taking advantage of the recent Hipparcos results.Field stars with various evolutionary states are considered, and it isshown that the loose correlation between their rotational period andtheir surface gravity is entirely compatible with conservation ofangular momentum. No evidence is found for any loss of angular momentumon the Main Sequence, which confirms earlier results based on lessreliable estimates of surface gravity. The importance of reliable,fundamental T_eff determinations of Bp and Ap stars is emphasized. Basedon data from the ESA Hipparcos satellite
| 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.
| An X-ray study of the young open cluster IC 2602.
We present the results of ROSAT PSPC observations of the 30Myr old IC2602 cluster; for the X-ray detected objects the results of a CCDphotometric survey are also given. In X-rays, we detect a total of 110objects within a 11deg^2^ area, above a threshold of typically3-5x10^28^erg/sec. 68 of the detected objects have been identified withat least one optical counterpart; 44 of these are new optical candidatesfor cluster membership provided by our CCD photometry. Stars of allspectral types have been detected, from the very early- types to thelate-M dwarfs. Soft X-ray luminosities range between about 10^29^erg/secto a few 10^30^erg/sec, with the maximum and average L_X_ decreasingwith spectral type for B-V larger than ~0.8. Many of the stars redderthan B-V~0.8 show a L_X_/L_bol_ ratio at about the saturation level of10^-3^. We construct X-ray luminosity distribution functions for objectsin different color ranges and we compare them with those for thePleiades. F, G, and early-K type candidates in IC 2602 appear to be moreX-ray luminous than in the Pleiades, while no significant difference isseen among late-K and M dwarfs. Under the assumption that our IC 2602sample is not severely affected by incompleteness, we argue that theabove finding is related to the distribution of rotational velocities inthe two clusters, with most of the late-type stars being fast rotatorsin both clusters, while, due to different spin-down timescales, theearlier type stars in IC 2602 are likely to rotate more rapidly thantheir counterparts in the Pleiades.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Some problems of non-reversive CP stars. I. Spatial distribution.
Not Available
| Catalogue of CP stars with references to short time scale variability
A catalogue was compiled which contains all references in the literaturesince 1962 related to variations of CP stars on time scales shorter thanthe rotation period. The role of this catalogue lies in the unbiasedlisting of all available references, and not in a critical evaluation.
| UBV photometry of the Eta Carinae complex in 1980 and 1991
UBV photometric observations of the seven hot stars in the Eta Carcomplex are reported. The variability of the objects on time scales from1 d to 11 yr is investigated. Eta Car itself has exhibited increasedbrightness by 0.33, 0.28, and 0.25 mag in U, B, V, respectively, overthe 11-yr period. No periodicity in Eta Car was found. CPD-59 deg 2603shows two levels of brightness, which differ by about 0.3 mag in allfilters. The remaining stars, including HD 93162 (WN7 + abs), do notexhibit light variability above 0.02 mag.
| The Gaii Lines in the Red Spectrum of Ap-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...272..465L&db_key=AST
| Effective temperature of AP and AM stars from Geneva photometry
The determination of the effective temperature of different kinds ofchemically peculiar stars from Geneva photometry is rediscussed. Wepropose an improved method of determining T(eff) of Ap stars fromGeneva's reddening-free X and Y parameters or from the B2-G index. Theeffect of duplicity on the determination of T(eff) of Am stars isdiscussed.
| A study of magnetic fields in AP SI and He weak stars
A survey of 44 Ap and Bp Si and He-weak stars for the presence ofdetectable longitudinal magnetic fields (Be) is reported. Fields havebeen detected in about half of the sample, with typical standard errorsin the range of 100-400 G. In 11 stars, fields have been detected forthe first time. For most of the stars with detected fields, thevariation of Be with rotational phase has been determined at leastapproximately. In a number of cases the phase relationship withphotometric or spectroscopic variations have also been established.Several of the newly detected fields are relatively large, with rmsvalues between 1 and 4 kG, and thus may be especially suitable fordetailed mapping and modelling. A particularly interesting result ofthese observations is the identification of at least four stars in whichextrema of the photometric or spectroscopic variations do not coincidewith the magnetic extrema, which implies that the distribution ofchemical elements over the stellar surface that leads to photometricvariations is definitely not symmetric about the magnetic axis of thestar.
| On the determination of effective temperature and surface gravity of B, A, and F stars using Stromgren UVBY beta photometry
The determination of stellar temperatures and surface gravities by meansof the Stromgren uvby beta photometric system is examined in the regionof main sequence stars. We used a sample of stars with independentlyderived temperatures and gravities. In particular, the calibrations ofMoon & Dworetsky (1985), Lester et al. (1986), and Balona (1984) arediscussed. We compare our results with Castelli (1991) and present newtemperature calibrations for normal, Johnson, and Ap stars. The use ofintegrated fluxes and especially the infrared flux method fordetermining stellar temperatures is discussed. Surface gravities of Band A stars, derived by fitting theoretical profiles to the Balmerlines, are used to check the calibrations.
| Liste des étoiles Ap et Am dans les amas ouverts (édition révisée)
Not Available
| On the origin of the statistical correlation between rotation periods and apparent radii for CP 2 stars
Apparent rotational velocities and rotation periods for CP 2 stars areused to study the 'apparent' radius distribution of R sin i. It impliesa distribution for the radii of CP 2 stars which is almost normal fortheir temperatures when compared to main sequence stars. However, astatistical correlation exists between rotation period P and R sin i. Itis argued that, at least in the case of silicon stars, neitherconservation of angular momentum on the main sequence, nor bias in themeasured v sin i values are able to induce a correlation of the observedstrength. Thus, one has to postulate either additional rotationalbraking depending statistically on R, or a detection bias dependingstatistically on i. It is shown that the correlation might be explainedin both ways and the implications of each possibility are discussed.
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| The binary companion of the classical Cepheid AW Per
An analysis of IUE spectra of the companion of AW Per shows it to be anextreme BpSi/HeW star with a spectral type of B7 V to B8 V. The flux ofthe composite spectrum from 1200 A through V is found to be well matchedby F7 Ib and B8 V standard stars with Delta M(V) = 3.1 mag. The resultssuggest that the mass of the Cepheid must be greater than 4.7 solarmasses. The flux distribution of the star and the mass limits from theorbit are consistent with a companion that is itself a binary.
| Radii and space orientation of the rotational axes of AP stars
The inclination of the rotation axis to the line of sight (i) has beendetermined for a carefully selected sample of Ap stars with reliablevalues of periods of rotation, and values of the stellar radius (R)times sin i have been compared with values of normal main-sequencestars. The findings that none of the obtained R x sin i values aresignificantly larger than the upper limit for the radius of a mainsequence stars and that the mean radius of Ap stars is close to thenormal main sequence value suggest that most Ap stars are main-sequenceobjects. The observed i distribution implies that the distribution ofthe rotational axes of Ap stars in space is random.
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| Takýmyýldýz: | Karina |
| Sað Açýklýk: | 10h40m11.30s |
| Yükselim: | -65°06'02.0" |
| Görünürdeki Parlaklýk: | 5.52 |
| Uzaklýk: | 142.857 parsek |
| özdevim Sað Açýklýk: | -17 |
| özdevim Yükselim: | 12.9 |
| B-T magnitude: | 5.299 |
| V-T magnitude: | 5.474 |
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