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B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Extending the radio spectrum of magnetic chemically peculiar stars to the mm range
Magnetic chemically peculiar (MCP) stars can present radio emission atcentimetre wavelengths. The steep decrement of the dominant dipolarcomponent of the photospheric magnetic field results in each radiofrequency being mainly emitted in a well localised shell of thecircumstellar region. To explore the most internal regions of themagnetosphere, observations of a sample of eleven MCP stars known to beradio sources in the 1.4-22.5 GHz range were carried out at 87.7 GHzwith the IRAM interferometer. Millimeter emission, with a flux densityat about 4× the sensitivity limit of our observations, wasdetected towards two of the stars: HD 35298 and HD 124224. Combiningour mm-observations with previous cm-observations, it appears that MCPstars with a relatively weak magnetic field present a radio spectrumthat increases with frequency up to 22.5 GHz and then decreases towardsthe mm range. In presence of strong fields, the radio spectrum is alwaysdecreasing with frequency. A comparison of the observed cm-mm spectrumof HD 124224 with results of numerical simulations of thegyrosynchrotron emission suggests that circumstellar regions emitting inthe mm-range cannot present magnetic fields larger than 1-2 kG.Based on observations carried out with the IRAM Plateau de BureInterferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany)and IGN (Spain).
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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
| 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
| Magnesium abundance in main sequence B-type and magnetic chemically peculiar stars.
The abundance of magnesium for a sample of 19 main sequence B-type and41 magnetic chemically peculiar stars has been derived by spectrumsynthesis analysis of the MgII448.1nm line under the LTE assumption. Thelogarithm of the average Mg abundance for the main sequence stars is log(N(MgII)/N(Tot))=-4.28+/-0.19. Comparing magnetic chemically peculiar(Cp) and main sequence stars with equal effective temperature andgravity, one finds that the magnesium abundance tends to be lower inpeculiar stars with the exception of helium rich stars where thiselement can be overabundant. In Cp stars with effective temperature ofabout 14000K, the magnesium abundance does not depend on gravity,microturbulent velocity or rotational period. There appears to exist acorrelation between the magnesium abundance and the surface magneticfield, with the stars poorest in magnesium presenting the strongestmagnetic fields. In accord with the theory of magnetically controlleddiffusion - which predicts a non-homogeneous distribution of magnesiumover the stellar surface and stratification in the photosphere - somepeculiar stars show evidence of spectral variability with the rotationalphase; the respective magnesium abundances of the HgMn stars HD49606 andHD78316 depend on optical depth.
| 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.
| Radial velocities and axial rotation for a sample of chemically peculiar stars.
As part of a systematic project we have determined radial velocities andprojected rotational velocities for a sample of 186 chemically peculiarstars which have been observed by the Hipparcos' satellite. The purposeis to provide necessary data to study the space velocities of peculiarstars.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| A spectroscopic study of the suspected chemically peculiar star HD210424.
HD210424 is a suspected Chemically Peculiar star in The generalcatalogue of Ap and Am stars by Renson et al. (1991). To investigate ifHD210424 is really a CP star, we obtained time-resolved high-resolutionspectra of this star in the 482-513nm region. The Hbeta_ linecan be matched by an ATLAS9 (Kurucz 1993) model with solar abundances,T_eff_=13200K and logg=4.0. The overall flux distribution between 150and 600nm can be reproduced by a unique ATLAS9 model with T_eff_=13450Kand logg=4.0. Abundances, obtained using WIDTH9 (Kurucz, priv. comm.),are typical of a normal B-type star. Spectral line variations,characterizing CP stars, are absent on a seven day time scale.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Radio Emission from Magnetic Chemically Peculiar Stars - Results of the 1992 VLA Survey
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994A&A...283..908L&db_key=AST
| Far-ultraviolet stellar photometry: A field in Orion
Far-ultraviolet photometry for 625 objects in Orion is presented. Thesedata were extracted from electrographic camera images obtained duringsounding rocket flights in 1975 and 1982. The 1975 images were centeredclose to the belt of Orion while the 1982 images were centeredapproximately 9 deg further north. One hundred and fifty stars fell inthe overlapping region and were observed with both cameras. Sixty-eightpercent of the objects were tentatively identified with known starsusing the SIMBAD database while another 24% are blends of objects tooclose together to separate with our resolution. As in previous studies,the majority of the identified ultraviolet sources are early-type stars.However, there are a significant number for which no such identificationwas possible, and we suggest that these are interesting objects whichshould be further investigated. Seven stars were found which were brightin the ultraviolet but faint in the visible. We suggest that some ofthese are nearby white dwarfs.
| The chemically peculiar star HD 37808
A photometric and spectroscopic study of the chemically peculiar star HD37808 is presented. On the basis of uvby photometry of the period oflight variability has been improved to the value 1.09909 +/- 0.00003 d.Near infrared photometry shows that light variations with the sameperiod are present up to 2.2 micrometers. From high resolutionspectroscopy in the 482-513 nm region the effective temperature, thegravity (by matching the hydrogen beta line profile) and the abundancesof some elements are estimated. Equivalent line width variations ofsilicon, chromium, and iron are also studied, and their phase relationwith the near infrared variations is established. As to HD 37808, lineblocking as a possible origin of the infrared variations is ruled out.
| 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.
| 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.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Absolute dimensions of eclipsing binaries. XVI - V 1031 Orionis
The high-dispersion spectroscopic observations of the triple system V1031 Orionis are presented, including catalog data, radial-velocityobservations, spectral lines, and orbital elements. Photometric data arediscussed with emphasis on the method of observation, ephemeris, andphotometric elements. Absolute dimensions are analyzed, and theevolutionary models of the system are outlined, along with rotation ofthe components. It is noted that despite the complications produced bythe presence of a visually unresolved companion, the absolute masses andradii of the eclipsing components of the system are determinedaccurately, and that the system properties are matched by standardevolutionary models. The radii indicate that the components of V 1031Orionis are near the end of their main-sequence evolution, and thesecomponents rotate slower than the synchronous rate observed in similarsystems.
| Effective temperatures and angular diameters of Bp-Ap SI stars and B and A normal stars - (u-b) and Delta(m2100)0 calibrations
The JHKLM photometric calibrations of Johnson (1966), Hayes (1979) andWamsteker (1981) are compared in computing empirical T(eff) and angulardiamters for nine standard stars and 12 Bp-Si stars from totalintegrated fluxes by the method of Blackwell et al. (1980). The resultsare presented in extensive tables and discussed in detail. It is foundthat the Hayes calibration gives the most consistent T(eff) values fromJ and K, and that T(eff) is overestimated by 700-1100 K if thenormal-star calibration is applied to peculiar stars. T(eff) is thendetermined from the (u-b) and Delta(m2100)0 calibrations for 10 standardand 39 peculiar stars, and it is confirmed that the Balmer jump ofpeculiar stars decreases with Si abundance and is smaller than that ofnormal stars of the same T(eff).
| 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.
| Statistical Investigation of Chemically Peculiar Stars - Part Two - the Stars with the Dispersion of Continuum Spectrum at Lambda 5200A
Not Available
| Statistical Investigation of Chemically Peculiar Stars - Part One - the Stars with Known Periods
Not Available
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| On the shape of the UVBY lightcurves of CP stars
Light curves in the Stroemgren system are presented for 56 CP stars. Theobservational data have been fitted by a sine wave and its firstharmonic. The least-square parameters are tabulated, and it is shownthat such a fit describes very well the CP variations in most cases, theonly exceptions being due to observational uncertainties.
| New period determinations for variable CP stars
Periods, or improved determinations of periods, are presented for 29 CPstars observed at La Silla in 1977-1982. The PHOT2 program's algorithmmakes possible the bringing together of different observing runs,through an improved reduction of the data to a common standard system.It is noted that, in many instances, magnetic observations would berequired for the resolution of ambiguities, especially in the presenceof quasi-symmetric double waves.
| Effective temperature of AP stars - A comparison between several photometric estimators
Effective temperatures are inferred for 28 Bp stars with theBlackwell-Shallis method. They are compared to photometric estimations,which are made with Delta-m(2100), (B-V)j, (B2-G), (R-I)c, and (J-K). Itis shown that (B2-G) and (R-I)c are the most interesting temperatureestimators for peculiar stars. A new calibration of (B2-G)0 is thenprovided for Si and He weak stars. Linear radii of Bp stars are found tobe similar to those of main sequence late B-type stars.
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| Takýmyýldýz: | Avci |
| Sað Açýklýk: | 05h40m46.00s |
| Yükselim: | -10°24'34.0" |
| Görünürdeki Parlaklýk: | 6.52 |
| Uzaklýk: | 164.474 parsek |
| özdevim Sað Açýklýk: | -0.6 |
| özdevim Yükselim: | 0 |
| B-T magnitude: | 6.3 |
| V-T magnitude: | 6.422 |
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