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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.
|An empirical temperature calibration for the Δ a photometric system . I. The B-type stars|
We establish an empirical effective temperature calibration of mainsequence, luminosity class V to III B-type stars for the Δ aphotometric system which was originally developed to detect magneticchemically peculiar objects of the upper main sequence (early B-type toearly F-type) at 5200 Å. However, this system provides the index(g_1-y) which shows an excellent correlation with (B-V) as well as (b-y)and can be used as an indicator of the effective temperature. This issupplemented by a very accurate color-magnitude diagram, y or V versus(g_1-y), which can be used, for example, to determine the reddening,distance and age of an open cluster. This makes the Δ aphotometric system an excellent tool to investigate theHertzsprung-Russell-Diagram (HRD) in more detail. Using thereddening-free parameters and already established calibrations withinthe Strömgren uvbyβ, Geneva 7-color and Johnson UBV systems, apolynomial fit of third degree for the averaged effective temperaturesto the individual (g_1-y)0 values was derived. For thispurpose, data from the literature as well as new observations were takenresulting in 225 suitable bright normal B-type objects. The statisticalmean of the error for this sample is 238 K which is sufficient toinvestigate the HRD of distant galactic open clusters as well asextragalactic aggregates in the future.
|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 (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|A three-year Strömgren photometric survey of suspected beta Pictoris-like stars|
We carried out a Strömgren photometric survey of thirteen southernbright stars, including beta Pictoris itself, during three years,d'Astrophysique de Paris, in order to detect possible weak photometricvariations. beta Pictoris presents a small long-term variation with achange of brightness by -2.1 10-3 mag per year, over abouttwo years from beginning of 1996, a situation relatively similar to theone about 18 years ago. Among the other stars, only HD 38392 presentsweak photometric variations with a period of 21.4 days, probably relatedto the star rotation period. The negative result concerning photometricvariations of all other stars suggests that those stars are actuallyreally stable and strengthens the reality of the variations discoveredin the case of beta Pictoris and HD 38392. Based on observationsobtained at the Danish 50 cm telescope (SAT) at ESO, La Silla, Chile.
|Observations of BN and AN stars: New Be stars|
From a survey of spectra of Bn/An stars, we have detected seven new Bestars: HR 1056 (A0Vn), 1544 (A1Vn), 2191 (A0Vnn), 2300 (B8Vn), 3134(B9.5 Vn), 3878 (B0.5 IIIn) and 4552 (B9IIIpSi). H_alpha profiles ofthese stars are presented. Measured values of equivalent widths, fullwidths at half intensity maximum, and the peak-separations of theH_alpha emission profiles are also tabulated in this paper. We have alsocomputed the radii of emission disks of the newly detected Be stars.
|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 22.214.171.124 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).|
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
|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.
|The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation|
In the fourth and final of a series of papers on the late B to the earlyF type stars, we refine the Morgan Keenan (MK) spectral classificationsystem for the late B type stars and consider the effect of rotation onboth spectral classification and Stroemgren photometry of these stars.We extend the work of Morgan by establishing self-consistent sequencesof narrow and broadlined standards. We reclassify a number of Bp stars,compare these classifications with Stroemgren photometry and considerthe question of whether all Bp stars are main-sequence objects.
|An Einstein Observatory SAO-based catalog of B-type stars|
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
|Observation of fine structure in the cold phase of the local interstellar medium using K I absorption|
The K I 7699-A resonance absorption line was used to observe a group of18 early-type stars within a 200-pc radius of the sun with asignal-to-noise ratio of 50-250. The interstellar absorptions provide away to 'tag' a cloud via its radial velocity to within +/-1.5 km/s.Based on the hypothesis of pressure confinement, the temperatures of theclouds are estimated at 100 K or less. The mass fraction of the localinterstellar medium (LISM) is found to be high in these clouds, at least80 percent of the total, whereas the filling factor is low, well below10 percent of the total LISM volume. One cloud with high densities andlower temperatures was detected which is thought to be on the edge ofatomic-molecular equilibrium.
|The EXOSAT high Galactic latitude survey|
This study presents a survey of serendipitous sources performed in thevery soft X-ray band (0.05-2.0 keV) using the Exosat imaging telescopes.It covers 783 sq deg of high Galactic latitude sky and includes 210serendipitous sources which define a complete (flux-limited) sample. Twohundred of the 210 detected sources are identified via extensive opticaland radio observations together with cross-correlations with catalogs ofknown objects. The log N-log S relation was found to be consistent withthat of the Einstein extended Medium-Sensitivity Survey (EMSS) and withthe 'Euclidean' value of 1.5. The normalization of the relation is astrong function of the assumed spectral slope of AGN. It is inferredfrom the consistency with the EMSS results that the average (energy)slope of extragalactic sources in the soft X-ray band is very steep(approximately 1.5). An analysis of the association between AGNdetection and Galactic N(H) also shows that the average slope is steepand inconsistent with the canonical value of 0.7.
|High-resolution observations of interstellar NA I and K I absorptions towards giants within 200 PC from the sun|
The first results of a program of observations designed to probe thestructure and kinematics of the Local Interstellar Medium (LISM) usingthe Queen's University of Belfast Echelle Spectrograph (QUBES) on the4.2 m William Herschel Telescope are reported. The observations show thepotential of the instrument for measuring small column densities and forprecise velocity structure analysis.
|Highly ionized species and circumstellar shells in B8-A1 stars|
The nature of the C IV and Si IV absorption seen in the spectra ofapparently normal late-type B and early-type A stars located within 200pc of the sun was investigated by examining a total of 93 archival IUEspectra of 41 stars. In three of these objects, variable or asymmetric CIV profiles indicate that the absorption features have a stellar origin.One star, HD 119921, showed shortward-shifted discrete C IV and Si IVabsorption components similar to those observed in Be stars. All of thestars with detected C IV in their spectra had large values of v sin i.Four of the stars showing C IV and Si IV also showed sharp absorptionfeatures in Si II, with two of these stars displaying variable Si IIfeatures. These results strongly suggest that these stars areunidentified Be/Ae and shell stars.
|The reflection nebula around HD 26676|
The gaseous component of the reflection nebula surrounding HD 26676 isinvestigated by comparing the UV spectrum of the star with that of theforeground star HD 26793. The physical properties of the cloud areconstrained under the assumption of Mg photoionization and H ionizationby cosmic rays and taking into account the effect of the stellarradiation field on the Mg(0) ionization rate. The average ionizationrate is obtained as a function of the extension of the nebula along theline of sight to the embedded star (R). The values determined for thetemperature, the mean density, and R for a cosmic ray ionization rate ofabout 10 to the -16th/s are found to be typical of diffuse H-I regions.
|C IV and SI IV in IUE spectra of normal B8-A0 stars: UV identified Be/Ae stars|
Archival IUE high dispersion spectra of 42 B6-A2 stars within 200 pcwere surveyed. Five of the program stars show significant C IV and Si IVabsorption. All of the stars with detected C IV have v sin i less thanor = 190 km/sec. Sharp absorption cores are present in Si II lambda 1533in 3 of the objects, indicating that these are previously unrecognizedshell stars. Three of the stars have variable or asymmetric C IVprofiles which are consistent with the C IV and Si IV being produced instellar winds. One star has C IV in the form of a shortward-shifteddiscrete absorption component, similar to those observed in Be stars.The data are compared with similar data for Be and B shell stars.
|Two-colour diagrams for differentially rotating stars|
|Carbon and nitrogen in B2 to A2 main-sequence stars|
Carbon abundances are derived from the C II resonance doublet at 1335 Ain 108 main-sequence stars between 9000 and 21000 K from IUE archivaldata. Only alpha Leo and psi sq 2 Aqr are strongly carbon deficient(factors 14 and 50, resp.). The N I lines at 1493 and 1495 A weremeasured in 28 sharp-lined stars below 16500 K. Nitrogen anomalies arefound in 5 stars, but seem uncorrelated to the C abundances. Fourmechanisms for the depletion of carbon are discussed, but none issatisfactory.
|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.
|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.
|Four-colour and H-beta photometry of B stars in Fehrenbach and Burnage radial velocity fields at B about -30 deg|
Observations in uvby and H-beta are presented for 39 stars classified asB-type in seven 4 x 4-deg fields studied by Fehrenbach and Burnage(1981, 1982) at b about -30 deg. About half the stars arephotometrically little-evolved B stars; most of the rest areintermediate A stars. Intrinsic color and absolute-magnitudecalibrations are applied: that of Hilditch et al. (1983) forintermediate A stars is estimated to be much less certain than those forother types. Maps of reddening along lines of sight indicate that littlereddening occurs within 100 pc of the sun, that essentially allreddening has occurred within z = + or - 150-200 pc, and that the totalreddening is essentially consistent with values given by the Bursteinand Heiles (1982) HI/GC method. The luminosities of some faint early Bstars cannot be usefully constrained by placing them within thereddening structure. One of the two program stars with very large radialvelocities is a horizontal branch object; the other has peculiar colors.
|A new list of 617 radial velocities in four galactic fields|
Four stellar fields in the -30 deg galactic latitude have been surveyedfor radial velocities, using a 62 cm objective prism. Exact positions,spectral types, and approximate magnitudes are provided for 617 stars infour different 4 x 4 deg fields. B to F4 stars were found which haveGaussian velocity distributions.
|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.
|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
|Catalogue of early-type stars measured in a narrow-band photometric system|
A compilation of the photoelectric measurements in the Barbier-Morguleffsystem is presented. The catalogue includes data for 773 stars ofspectral type 08 to F6. 706 stars have been measured at least twice.
|Four-color and H beta photometry for the bright B8 and B9 type stars north of declination -10 degre.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..738C&db_key=AST
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