Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| Close binary stars in ob-association regions i. preliminary investigation
We performed a sample of O- and B-eclipsing binary stars inOB-association regions and obtained the preliminary list of 147 binariesin 45 OB-association regions. We tried to elucidate the question whether(or not) the close binaries belong to corresponding OB-associations,from the commonness of their proper motions, radial velocities anddistances. Based on the completeness of the data,the binaries aredevided into three groups and the scheme for calculation of degree ofbelonging of stars to OB-associations is developed. Necessary data arenot available for nine systems and they are given in a specific table.For 12 cases, the binaries project onto the regions of two associations.We show that 33 (22.3%) close binary stars are members, 65 (43.9%) areprobable members and 39 (26.4%) are less probable members of theOB-associations. We find that 11 binaries belong to the Galaxybackground. The comparison of the distributions of orbital periods forthe binaries in OB-associations and for O-, B-binaries of the Galaxybackground shows their considerable differences in the vicinity of thetwo-day period.
| IC 2395 and BH 47: Only one open cluster in the Vela constellation
We report UBV photoelectric photometry for 273 stars in the fields ofthe open clusters IC 2395 and BH 47. Our postulate is that, rather thantwo different clusters in this region of Vela, there is only one, whichwe call IC 2395 = BH 47. The cluster is centered at about alpha =8{h} 42fm 5, delta = -48degr 06farcm 8 (2000), itsangular diameter being ~ 19'. The analysis of the photometric datayields 61 probable cluster members and 16 possible members. Photometricmembership probabilities show good agreement with those obtained from aproper motion study for 21 stars in common. The reddening across thecluster appears to be uniform, the mean E(B-V) value being 0.09 +/-0.02. The true distance modulus is (V-MV)0 = 9.52+/- 0.10, corresponding to a distance from the Sun of (800 +/- 40) pcand 48 pc below the Galactic plane. The cluster age, determined byfitting isochrones with core overshooting, turns out to be (6 +/- 2)Myr. There is a strong likelihood that IC 2395 = BH 47 is physicallyconnected to the Vela OB1C association.
| Intermediate- and High-Velocity Ionized Gas toward ζ Orionis
We combine near-UV spectra obtained with the Hubble Space Telescope GHRSechelle with far-UV spectra obtained with the Interstellar MediumAbsorption Profile Spectrograph and Copernicus to study the abundancesand physical conditions in the predominantly ionized gas seen at highvelocity (-105 km s-1<~vsolar<~-65 kms-1) and at intermediate velocity (-60 kms-1<~vsolar<~-10 km s-1) alongthe line of sight to the star ζ Ori. We have high-resolution(FWHM~3.3-4.5 km s-1) and/or high signal-to-noise ratiospectra for at least two significant ions of C, N, Al, Si, S, andFe-enabling accurate estimates for both the total N(H II) and theelemental depletions. C, N, and S have essentially solar relativeabundances; Al, Si, and Fe appear to be depleted by about 0.8, 0.3-0.4,and 0.95 dex, respectively, relative to C, N, and S. While various ionratios would be consistent with collisional ionization equilibrium (CIE)at temperatures of 25,000-80,000 K, the widths of individualhigh-velocity absorption components indicate that T~9000+/-2000 K-so thegas is not in CIE. Analysis of the C II fine-structure excitationequilibrium, at that temperature, yields estimates for the densities(ne~nH~0.1-0.2 cm-3), thermal pressures(2nHT~2000-4000 cm-3 K), and thicknesses (0.5-2.7pc) characterizing the individual clouds. We compare the abundances andphysical properties derived for these clouds with those found for gas atsimilar velocities toward 23 Ori and τ CMa and also with severaldifferent models for shocked gas. While the shock models can reproducesome features of the observed line profiles and some of the observed ionratios, there are also significant differences between the models andthe data. The measured depletions suggest that roughly 10% of the Al,Si, and Fe originally locked in dust in the preshock medium may havebeen returned to the gas phase, consistent with recent predictions forthe destruction of silicate dust in a 100 km s-1 shock. Theobserved near-solar gas-phase abundance of carbon, however, appears tobe inconsistent with the predicted longer timescales for the destructionof graphite grains. Based in part on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high-resolution (R~75,000), high signal-to-noise (S/N~100) CaII λ3933.663 and Na I λλ5889.951, 5895.924 spectraof 68 stars in the direction of the Vela supernova remnant. The spectracomprise the most complete high-resolution, high S/N optical survey ofearly-type stars in this region of the sky. A subset of the sight lineshas been observed at multiple epochs, 1993/1994 and 1996. Of the 13stars observed twice, seven have spectra revealing changes in theequivalent width and/or velocity structure of lines, most of which arisefrom remnant gas. Such time variability has been reported previously forthe sight lines toward HD 72089 and HD 72997 by Danks & Sembach andfor HD 72127 by Hobbs and coworkers. We have confirmed the ongoing timevariability of these spectra and present new evidence of variability inthe spectra of HD 73658, HD 74455, HD 75309, and HD 75821. We havetabulated Na I and Ca II absorption-line information for the sight linesin our sample to serve as a benchmark for further investigations of thedynamics and evolution of the Vela SNR. Based on observations obtainedat the European Southern Observatory, La Silla, Chile.
| Studies of the ISM in the Vela Supernova Remnant
Recent observations of the Vela SNR in the ISM species Ca II and Na Iare presented and discussed in the context of the ``break-down'' of theSpitzer-Routly effect. Variations in line profiles with time aredemonstrated, eventually through a statistical approach a description ofcloud structure will be possible. The IS lines in ~ 70 sightlines areused to determine an accurate distance to the Vela SNR of 250 +/- 30 pc.Finally a discussion of future observations are given relatinginformation obtained from measurements of near-by ISM to more distantintergalactic medium.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward delta Orionis by the Interstellar Medium Absorption Profile Spectrograph
Studies of the abundances of deuterium in different astrophysical sitesare of fundamental importance to answering the question about how muchdeuterium was produced during big bang nucleosynthesis and what fractionof it was destroyed later. With this in mind, we used the InterstellarMedium Absorption Profile Spectrograph (IMAPS) on the ORFEUS-SPAS IImission to observe at a wavelength resolution of 4 km s^-1 (FWHM) theLydelta and Lyepsilon absorption features produced by interstellaratomic deuterium in the spectrum of delta Ori A. A chi^2 analysisindicated that 0.96
| A common resonance of delta SCT stars and ellipsoidal binaries.
Not Available
| 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
| On rotation of ellipsoidal binary systems.
Not Available
| A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| The Composition of the Diffuse Interstellar Medium
Recent Goddard High Resolution Spectrograph measurements of Si, S, Cr,Mn, Fe, and Zn in interstellar clouds along lines of sight in theGalactic disk and into the lower halo are discussed. The gas-phaseabundance of S relative to H in the interstellar clouds appears to beindistinguishable from the solar value. For the other elements, we findwell-defined upper limits in the gas-phase abundances at significantlysubsolar values. For Fe, Mn, and Cr (and probably Ti), there are noconvincing cases in which the relative gas-phase abundances exceedroughly -0.5 dex, i.e., these elements are not seen in interstellar gaswith an abundance greater than about one-third solar. For Si, the limitis roughly -0.15 dex, and for Zn a constant abundance of -0.13 dex isfound from seven clouds along one halo sight line. These subsolarmaximum abundances have two possible interpretations: (1) they indicatethe presence of an essentially indestructible component of interstellardust, which contains about two-thirds of the Ti, Mn, Cr, and Fe andabout one-third of the Si (based on solar composition), or (2) theyindicate that the true total abundances of these elements aresubstantially less than in the Sun.
| Speckle Interferometry of Southern Double Stars.I.First Results of the Yale-San Juan Speckle Interferometry Program
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1681H&db_key=AST
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| A Search for r-Process Elements in the VELA Supernova Remnant
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..688W&db_key=AST
| High-Velocity Gas in the VELA Supernova Remnant
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2627D&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.
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Dense clumps of ionized gas near Pi Scorpii, as revealed by the fine-structure excitation of N II
The column density and the emission of the ionized gas along the line ofsight toward the B1 V + B2 V binary star Pi Sco are measured on thebasis of the fine-structure absorption lines of the ground state N II.It is found that the bulk of this ionized gas must be clumped on alength scale of 0.025 pc, which is far smaller than the observed size ofthe diffuse H II region surrounding Pi Sco of about 6 pc. The observedcolumn density of S III toward Pi Sco yields an upper limit on thedistance of the absorbing, clumped gas from the star of less than about0.02 pc, assuming that both the N II and S III absorption arise from thesame gas. The possibility that the ionized gas originates from aphotoevaporating circumstellar disk directly surrounding Pi Sco isexcluded, since such a disk would have an unusual size of order 0.025 pcand would have had to survive for the estimated age of Pi Sco of 5-8Myr. The derived mean density of the clumped gas is of order 40/cu cm,so that the gas is at a pressure that far exceeds the mean pressure inthe H II region. It is concluded that the ionized gas could originatefrom evaporation flows off a cluster of compact neutral objects thatevaporate due to the ionizing radiation of Pi Sco.
| CCD observations of additional interstellar lines in stars associated with the VELA Remnant and Eta Carinae nebulosity
Nine stars from the Vela Remnant and seven stars in the Eta Carinaecomplex are examined with CCD spectrograms with high signal-to-noiseratios for data regarding the optical interstellar lines. These data aresupplemented by observations of objects with known high-velocitycomponents and substantial interstellar Ti II lines. The CCDspectrograms have signal-to-noise ratios of 100-300, a 2-pixel resolvingpower of 20,000, and cover features of Na I, Ti II, Ca I, CH(+), and CHin the 3200-4400-A range. The Ca I line confirms the high H density inVela, and the Ti II lines show evidence of shock-induced grainevaporation. Weak shocks are thought to contribute to the CH(+)component, and a high H I density in some clouds is inferred from the CHline. The high H I density is supported by IUE data on Ca I and on thefine-structure carbon lines. The data point to a significant differencein spectroscopic morphology between the two groups of stars, and theneed for theoretical support is underscored.
| Fine structure lines of C(+) and N(+) in the galaxy
The emissivity of the local interstellar medium in the forbidden C II158-micron, forbidden N II 205-micron, and forbidden N II 122-micronlines is derived from the column densities of these ions in theirfine-structure excited levels, estimated from Copernicus observations oftheir UV lines. A comparison with recent larger-scale observations ofthe visible and FIR lines of N(+) suggests that the local emissivitiesare anomalously high, especially if they are due to the diffuse ionizedmedium. It is shown that the Galactic emission in the N(+) FIR lines isdominated by H II regions. The origin of the C(+) is also discussed. Thedata under consideration are consistent with the Galactic ratio of 10between the 158- and 105-micron lines observed by the COBE satellite.
| A search for rapid photometric variations in southern Be and BN stars
Fifteen Be, 5 Bn, and 1 B stars were monitored during 10 nights inMarch-April 1988 by means of photoelectric ubvy photometry. At least 80percent of the Be stars were found variable. Tentative periods between0.3 and 4.3 days were derived for 13 stars of this entire sample. In allcases, the stars are bluest when brightest. Variations in B0-B5e starsare, in average, of larger amplitude than in B5-B9e stars. Bn starsshow, in general, variations of smaller amplitude than Be stars. Theseresults are discussed in terms of the current models on short-termphotometric variability. In addition, from the observed perioddistribution the existence of intrinsically slow Be rotators arededuced. The rotation of slightly displaced poles of a weak globaldipolar magnetic field is proposed as being responsible for the rapidperiodic light variations.
| Long Slit Observations of Emitting Gas in the VELA Supernova Remnant
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.245..701W&db_key=AST
| ICCD speckle observations of binary stars. V - Measurements during 1988-1989 from the Kitt Peak and the Cerro Tololo 4 M telescopes
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..965M&db_key=AST
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Yelken |
| Sað Açýklýk: | 08h42m16.00s |
| Yükselim: | -48°05'57.0" |
| Görünürdeki Parlaklýk: | 5.51 |
| Uzaklýk: | 518.135 parsek |
| özdevim Sað Açýklýk: | -3 |
| özdevim Yükselim: | 1.3 |
| B-T magnitude: | 5.236 |
| V-T magnitude: | 5.438 |
Kataloglar ve belirtme:
|
INHABITED SKY
