תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
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.
| Variable Na I Absorption toward ρ Leonis: Biased Neutral Formation in the Diffuse Interstellar Medium?
We present multiepoch KPNO coudé feed telescope observations ofinterstellar Na I and Ca II absorption toward the bright star ρ Leo.Comparisons of the Na I profiles observed over a period of 8 yr revealsignificant temporal variations in the Na I column in at least onecomponent, implying that there is ``structure'' at scales on the orderof the proper motion (~12 AU). Archival Hubble Space Telescope (HST)Goddard High Resolution Spectrograph observations of the C Ifine-structure excitation in the variable component suggest that thedensity is <~20 cm-3, significantly lower than thedensities inferred in past H I 21 cm and Na I studies. We suggest thatthe bulk of the trace neutral species are in the density peaks within aninterstellar cloud. The patchy distribution of these species naturallygives rise to the large fluctuations seen on scales of 10-1000 AU inpast temporal and binary studies. This picture predicts that the scalesover which fluctuations will be observed vary as a function of theionization rate of a species.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedfrom the data archive at the Space Telescope Science Institute. STScI isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS 5-26555.
| 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.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| An ultra-high-resolution study of the interstellar medium towards Orion
We report ultra-high-resolution observations (R~9×105)of NaI, CaII, KI, CH and CH+ for interstellar sightlinestowards 12 bright stars in Orion. These data enable the detection ofmany more absorption components than previously recognized, providing amore accurate perspective on the absorbing medium. This is especially sofor the line of sight to the Orion nebula, a region not previouslystudied at very high resolution. Model fits have been constructed forthe absorption-line profiles, providing estimates for the columndensity, velocity dispersion and central velocity for each constituentvelocity component. A comparison between the absorption occurring insightlines with small angular separations has been used, along withcomparisons with other studies, to estimate the line-of-sight velocitystructures. Comparisons with earlier studies have also revealed temporalvariability in the absorption-line profile of ζ Ori, highlightingthe presence of small-scale spatial structure in the interstellar mediumon scales of ~10au. Where absorption from both Na0 andK0 is observed for a particular cloud, a comparison of thevelocity dispersions measured for each of these species providesrigorous limits on both the kinetic temperature and turbulent velocityprevailing in each cloud. Our results indicate the turbulent motions tobe subsonic in each case. Na0/Ca+ abundance ratiosare derived for individual clouds, providing an indication of theirphysical state.
| Variable Interstellar Absorption toward the Halo Star HD 219188: Implications for Small-Scale Interstellar Structure
Within the last 10 yr, strong, narrow Na I absorption has appeared atvsolar~-38 km s-1 toward the halo star HD 219188;that absorption has continued to strengthen, by a factor of 2-3, overthe past 3 yr. The line of sight appears to be moving into/through arelatively cold, quiescent intermediate-velocity (IV) cloud, because ofthe 13 mas yr-1 proper motion of HD 219188; the variations inNa I probe length scales of 2-38 AU yr-1. UV spectra obtainedwith the Hubble Space Telescope GHRS in 1994-1995 suggestN(Htot)~4.8×1017 cm-2, ``halocloud'' depletions, nH~25 cm-3, andne~0.85-6.2 cm-3 (if T~100 K) for the portion ofthe IV cloud sampled at that time. The relatively high fractionalionization, ne/nH>~0.034, implies that hydrogenmust be partially ionized. The N(Na I)/N(Htot) ratio is veryhigh; in this case, the variations in Na I do not imply large localpressures or densities. Based in part on observations with the NASA/ESAHubble Space Telescope, obtained from the data archive at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| Rapid Temporal Variations of Interstellar Absorption Lines in the Carina Nebula
Two observations of the complex interstellar absorption-line profiles inthe UV spectrum of CPD -59°2603, obtained 22 months apart in theR~110,000 mode of the Space Telescope Imaging Spectrograph on the HubbleSpace Telescope, reveal substantial variations in the intensities ofseveral high-velocity components, including the virtual disappearance ofone of them. These are the first observations of interstellar temporalvariations in dominant ions to our knowledge. The most probableinterpretation is motion across the line of sight of discrete absorbingfeatures in the near foreground of the O-type star, within the CarinaNebula. Ground-based survey data also indicate that the extremeinterstellar profiles throughout this region originate relatively nearthe most massive stars, suggesting an origin related to their stellarwinds. The morphological similarity of these profiles to alow-ionization, narrow-line system in a quasi-stellar object (QSO)spectrum is pointed out. Time variability may provide a critical testamong different interpretations of such QSO systems. Based onobservations with the NASA/ESA Hubble Space Telescope obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| 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
| Evidence of Interstellar NA I Structure at Scales Down to 15 AU in Low-Density Gas
We present high-resolution Hubble Space Telescope/Space TelescopeImaging Spectrograph and multiepoch KPNO coudé feed observationsof multiple interstellar lines toward the binary system HD 32039/40.Comparisons of the Na I profiles observed over a period of 4.25 yrreveal significant temporal variation in the Na I column in at least onecomponent, implying that there is structure at scales on the order ofthe proper motion (~15-21 AU). Large differences are also observed amongmultiple components in the profiles of the neutral species between thebinary sight lines (5060 AU separation). In addition, significantdifferences in the S II profile are seen between the stars-the firstoptical/UV detection of small-scale variations in a dominant ion.Measurements of the C I fine-structure excitation in the variablecomponents suggest that the densities in these components are ~20-200cm-3, significantly lower than the densities inferred in pastH I 21 cm and Na I studies. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| 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 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Observations of Ubiquitous Small-Scale Structure in the Diffuse Interstellar Medium
We present results of a study of the Na I D interstellar absorptiontoward 17 binary and/or common proper-motion systems (including twotriples). The stars range in spectral type from O6 to A5, lie atdistances between 85 and 1200 pc, and have stellar separations between480 and 29,000 AU. We compare the Na I absorption present in each of thetwo (or three) lines of sight and find that the line strength and/orprofile varies for all 17 of the systems examined. We infer thatsmall-scale structure in clouds containing Na I is ubiquitous anddiscuss the implications of that conclusion.
| 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 Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| 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.
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| Small-scale structure in the diffuse interstellar medium
The initial results of a study to probe the small-scale structure in thediffuse interstellar medium (ISM) through IUE and optical observationsof interstellar absorption lines toward both components of resolvablebinary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linearseparations ranging from 5700 to 700 Au. Except for Kappa CrA, thestrengths of the interstellar absorption lines toward both components ofthese binaries agree to within 10 percent. In the case of Kappa CrA, theoptically thin interstellar Mg I and Mn II lines are about 50 percentstronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolutionobservations of interstellar Ca II show that this difference isconcentrated in the main interstellar component at V(LSR) = 9 + or - 2km/s. Interestingly, this velocity corresponds to an intervening cloudthat may be associated with the prominent Loop I shell in the local ISM.Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, theline strength variations indicate that this cloud has structure onscales of 2800 AU or less.
| 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.
| A Note about the Comparison Between the Old and New Slettebak Systems of Axial Rotational Velocities
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984RMxAA...9....9G&db_key=AST
| Ages and uvbybeta photometry of wide visual binaries. II
Visual magnitudes and color indices b-y, m1, c1 and beta have beenobtained for the members of 39 double or multiple systems containingstars with magnitudes greater than 4m. Relationships between stellarages, spectral types and photometric indices are given from a sample ofabout 3,500 stars. Data is presented with regard to MK spectral types,the separation, and absolute magnitudes; also tabulated are the meanvalues of photometric unreddened indices with their standard deviationfor intervals of 0.2 in log age. From calculations for each binary ofthe relative difference in the ages of the components and the differencein the effective temperatures, an increase in the relative differencesin ages with the differences in temperatures is noted.
| About the Consistency of Absolute Luminosity Calibrations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....82..370H&db_key=AST
| 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.
| UVBY photometry of wide visual double stars with B, A and F spectral type- I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
| 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
| The influence of rotation and stellar winds upon the Be phenomenon
A number of rapidly rotating B stars, not previously known as Be stars,were observed spectroscopically at H alpha. These results were thencombined with existing data to show that the spectral type of a star andthe minimum velocity at which it must rotate in order to become a Bestar are related. The trend of this relationship is found to have anatural explanation in terms of stellar winds.
| Rotational velocities and spectral types for a sample of binary systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...19...91L&db_key=AST
| The manganese stars
Ultraviolet spectrograms of 194 middle and late B-type stars wereobtained in a search for Mn stars. The 24 Mn stars found in this searchlay within the limited temperature range from 0.33 to 0.48. Theirobserved rate of incidence and rotational velocity distributionsubstantiate the hypothesis that the Mn stars constitute a considerablefraction of the slowly rotating stars in this temperature range. If theatmospheres of these stars are sufficiently stable for diffusionprocesses to be effective, then it also becomes possible to account forthe temperature range in which the Mn overabundance occurs.
| Statistical Studies in Stellar Rotation. II. a Method of Analyzing Rotational Coupling in Double Stars and an Introduction to its Applications
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...177..161B&db_key=AST
| Four-color and Hβ photometry for the brighter AO type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..109C&db_key=AST
| The Spectra and Axial Rotational Velocities of the Components of 116 Visual Double-Star Systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963ApJ...138..118S&db_key=AST
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אוריון |
| התרוממות ימנית: | 05h00m33.90s |
| סירוב: | +03°36'58.0" |
| גודל גלוי: | 6.66 |
| מרחק: | 42.863 פארסק |
| תנועה נכונה: | 10.5 |
| תנועה נכונה: | -18.2 |
| B-T magnitude: | 6.516 |
| V-T magnitude: | 6.592 |
קטלוגים וכינוים:
|
INHABITED SKY
