Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| XMM-Newton observations of the supernova remnant RX J0852.0-4622/GRO J0852-4642
RX J0852.0-4622 is a supernova remnant discovered in the ROSAT all-skysurvey. Spatially coincident 1.157 MeV γ-ray line emission wasdetected with the COMPTEL instrument on-board CGRO. The analysiscombining the X-ray and γ-ray data suggests that RX J0852.0-4622is a close-by and young supernova remnant. Follow-up observations withASCA show that the two brightest sections of the limb have non-thermalspectra, which make an independent assessment of the age and distanceusing the Sedov equations for the evolution of the remnant almostimpossible. We have observed three rim sections of RX J0852.0-4622 withXMM-Newton and confirm the power-law type spectra measured with ASCA. Wealso confirm the presence of an emission-line like feature at 4.45± 0.05 keV, which we suggest to be emission from Ti and Scexcited by atom/ion or ion/ion high velocity collisions. The highvelocity is in agreement with the width of the 1.157 MeV γ-rayline. The X-ray line flux expected from such an interaction isconsistent with the 1.157 MeV γ-ray line flux measured by COMPTEL.This consistency of the X-ray line flux and the γ-ray line fluxlends further support to the existence and amounts of Ti in RXJ0852.0-4622 claimed by Iyudin et al. (\cite{Iyudin98}, Nature, 396,142) and to the suggestion that RX J0852.0-4622 is young and nearby(Aschenbach et al. \cite{Aschenbach99}, A&A, 350, 997). Iyudin etal. (\cite{Iyudin98}) quote a very large broadening of the 1.157 MeVγ- ray line which would indicate a large velocity of the emittingmatter of about 15 000 km s-1. Such high ejecta velocity forTi is found only in explosion models of sub-Chandrasekhar type Iasupernovae (Woosley & Weaver \cite{Woosley94}, ApJ, 423, 371; Livne& Arnett \cite{Livne95}, ApJ, 452, 62). In this case no compactremnant is expected. The obvious, remaining questions are what thenature and the origin of the central compact source CXOUJ085201.4-461753 are and why the absorption column density apparentlyassociated with RX J0852.0-4622 is much greater than the typical columnfor the Vela SNR.
| Shocked Clouds in the Vela Supernova Remnant
Unusually strong high-excitation C I has been detected in 11 lines ofsight through the Vela supernova remnant (SNR) by means of UV absorptionline studies of IUE data. Most of these lines of sight lie near thewestern edge of the bright X-ray region of the SNR in a spatiallydistinct band approximately 1° by 4° oriented approximatelynorth-south. The high-excitation C I (denoted C I* and C I**) isinterpreted as evidence of a complex of shocked dense clouds interactingwith the SNR, because of the high pressures indicated in this region. Tofurther analyze the properties of this region of enhanced C I* and CI**, we present new HIRES-processed IRAS data of the entire Vela SNR. Atemperature map calculated from the HIRES IRAS data, based on atwo-component dust model, reveals the signature of hot dust at severallocations in the SNR. The hot dust is anticorrelated spatially withX-ray emission, as would be expected for a dusty medium interacting witha shock wave. The regions of hot dust are strongly correlated withoptical filaments, supporting a scenario of dense clouds interior to theSNR that have been shocked and are now cooling behind the supernovablast wave. With few exceptions, the lines of sight to the stronghigh-excitation C I pass through regions of hot dust and opticalfilaments. Possible mechanisms for the production of the unexpectedlylarge columns of high-excitation C I are discussed. Dense clouds on theback western hemisphere of the remnant may explain the relatively lowX-ray emission in the western portion of the Vela SNR due to the slowerforward shock velocity in regions where the shock has encountered thedense clouds. An alternate explanation for the presence of ground-stateand excited-state neutrals, as well as ionized species, along the sameline of sight is a magnetic precursor that heats and compresses the gasahead of the shock.
| Masses and other parameters of massive binaries
Binary stars provide us with the means to measure stellar mass. Here Ipresent several lists of known O-type stars with reliable mass estimatesthat are members of eclipsing, double-lined spectroscopic binaries. Themasses of young, unevolved stars in binaries are suitable for testingthe predictions of evolutionary codes, and there is good agreementbetween the observed and predicted masses (based upon temperature andluminosity) if the lower temperature scale from line-blanketed modelatmospheres is adopted. A final table lists masses for systems in awide variety of advanced evolutionary stages.
| Interstellar Silicon Abundance
We present 34 measurements of silicon gas phase column densities in theinterstellar medium. We have used spectra containing the SiII 1808 Angline which were obtained with the Goddard High Resolution Spectrograph(GHRS) aboard the Hubble Space Telescope (HST). Extinction curveparameters are determined for analyzed lines of sight and relationbetween Si/H ratio and extinction parameters is discussed. We find theabundance of gas phase silicon in diffuse clouds to be lower than thesolar value by a factor of four.
| 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.
| The early-type multiple system QZ Carinae
We present an analysis of the early-type quadruple system QZ Car,consisting of an eclipsing and a non-eclipsing binary. The spectroscopicinvestigation is based on new high dispersion echelle and CAT/CESspectra of H and He lines. The elements for the orbit of thenon-eclipsing pair could be refined. Lines of the brighter component ofthe eclipsing binary were detected in near-quadrature spectra, whilesignatures of the fainter component could be identified in only fewspectra. Lines of the primary component of the non-eclipsing pair and ofboth components of the eclipsing pair were found to be variable inposition and strength; in particular, the He ii 4686 emission line ofthe brighter eclipsing component is strongly variable. An ephemeris forthe eclipsing binary QZ Car valid at present was derived Prim. Min. =hel. JD 2448687.16 + 5fd9991 * E. The relative orbit of the two binaryconstituents of the multiple system is discussed. In contrast to earlierinvestigations we found radial velocity changes of the systemicvelocities of both binaries, which were used - together with an O-Canalysis of the expected light-time effect - to derive approximateparameters of the mutual orbit of the two pairs. It is shown that thisorbit and the distance to QZ Car can be further refined by minima timingand interferometry. Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile.
| The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
| 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.
| Interstellar Carbon Abundance
We present 10 new measurements of carbon gas phase column density in theinterstellar medium. We have used spectra made with the Goddard HighResolution Spectrograph aboard the Hubble Space Telescope containing theCII 1334.5 Ang and CII* 1335.7 Ang lines. The continuum reconstructionmethod has been used to obtain the carbon column density from theLorentzian damped lines. Extinction curve parameters are determined inselected directions and relation between C/H ratio and extinctionparameters is discussed. A correlation has been found between C/H andthe strength of the 2175 Ang bump. Unlike previous results, we noticethat C/H changes with fractional abundance of molecular hydrogen,f(H_2). The average value of C/H=3.55*10^{-4} for lines of sight withf(H_2)<1*10^{-3} is the same as solar photospheric abundance fromGrevese and Noels (1993) and may represent the real cosmic carbonabundance.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Visible neutral helium lines in main sequence B-type stars: observations and NLTE calculations
Spectra in the visible range 410 - 710 nm have been obtained for asample of main sequence B-type stars to determine the behavior ofneutral helium lines with effective temperature and gravity. Equivalentwidths have been compared with new calculations which combine thecapabilities of LTE atmospheric models of including millions of linescontributing to the opacity and accurate NLTE treatment of the lineformation. The latter take advantage of accurate atomic cross-sections.We find a satisfactory agreement between theory and observations withdifferences probably due to the microturbulence. We also investigate theeffects of blending and find that the Hei412.1nm is severely blendedwith oxygen lines for spectral types earlier than B3.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| 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 early-type binary KX Velorum.
A spectroscopic study of the double-lined OB-type binary system KX Velis presented. Radial velocities were measured on 20 new CCD spectra and4 high dispersion IUE SWP images. From a combination with earlyphotographic data, the orbital period was found to be 26.306d. The highprecision radial velocity curve of the evolved primary component allowedfor an accurate determination of the highly eccentric orbit (e=0.59)using a SIMPLEX based fit procedure. The less luminous secondary mainsequence component could be identified in spectra taken at phasesshortly before and after the periastron passage, at which the highopposite radial velocities of both components made a deconvolution ofthe line blends possible. The combination of an earlier eclipsemeasurement with the new spectroscopic elements yields an ephemeris forexpected future eclipse minima. Further spectroscopic observations(close to periastron phases) and photometric measurements (at eclipseepochs) are suggested to derive the absolute dimensions of the binarycomponents of this detached close binary system.
| 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.
| 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 spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| An IRAS/ISSA Survey of Bow Shocks Around Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2914V&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.
| 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.
| An IUE survey of interstellar H I LY alpha absorption. 2: Interpretations
We present an analysis of interstellar neutral hydrogen column densitiesobtained from archival Ly alpha absorption line data toward the completesample of B2 and hotter stars observed at high spectral resolution withthe IUE satellite. The full sample includes 554 stars and more thandoubles the number of lines of sight previously observed. Many of the B2and B1.5 stars exhibit contamination from stellar Ly alpha absorption,and were excluded from the subsequent analysis. The final working sampleincludes 393 stars. We present statistical averages for a number ofquantities derived for the sample. The stars range in distance from 0.12to 11 kpc with an average distance of 2.1 kpc. Values for averagesight-line density range from 0.017 to 8.62 atoms cm-3, withan overall average of 0.23 atoms cm-3. Neutral hydrogen anddust are well correlated, with N(H I)/E(B - V) = 4.93 x 1021cm-2 mag-1, and N(H I)/E(Bump) = 2.17 x1021 cm-2 mag-1. There is an increasein the H I to dust ratios for the densest sight lines. Evidently, the HI to dust ratios in dense clouds are higher than in the lower densitymedium between the clouds and in interarm directions. The effect isprobably an indication of dust modification in the dense clouds. The H Ito dust ratios are approx. 17% smaller for the sight lines to O starscompared to the ratios found toward B stars. We have identified sightlines with anomalously large and small values of N(H I)/E(B - V) and H(HI)/E(Bump). Some of these sight lines are well-known examples ofpeculiar extinction (i.e., HD 147933 and HD 37061 (NU Ori)). Others areless well known and may provide important new examples of regions withhighly modified dust. The number of stars with anomalously low H I todust ratios is disproportionately larger than the number of stars withanomalously high H I to dust ratios. The distribution of the gas awayform the Galactic plane for the sample of objects is complex. For thesubset of 375 stars whose lines of sight have a statistically lowprobablility of intersecting a large cloud, the distribution may beroughly approximated by an exponential density distribution, with amidplane density of 0.366 atoms cm-3, a scale height of 195pc, and a random logarithmic scattering parameter sigma p of0.159 dex.
| Ultraviolet FeIII lines in the spectra of high galactic latitude early-type stars
Using high resolution spectral data from the International UltravioletExplorer satellite, we present qualitative and quantitative comparisonsof blends of Fe III absorption lines in the region1890A<=λ<=1930A for a sample of fifteen high latitudeB-type and standard stars. Standard and halo stars were matched ineffective temperature and surface gravity using Stroemgren [c_1_] andHβ photometry, and LTE model atmosphere codes were used toinvestigate whether they had similar iron abundances. We conclude thatwhile most of the halo stars have Population I iron abundances and maybe young objects, one star, HD 177566, has significant iron and silicondepletions and is most probably an old, evolved star. In view of thecoincidence of the atmospheric parameters of this star with those ofyoung B-type stars, we consider a post-AGB evolutionary status to belikely for HD 177566.
| The distribution of interstellar dust in the solar neighborhood
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
| Rotational velocity of Be stars correlated with extinction law
The paper presents the comparison of the extinction curves extractedfrom spectra of 35 Be stars. It is suggested that high rotationalvelocity relates to 'peculiar' shape of extinction curve i.e., the lackof the 2200 A bump. This phenomenon occurs only if the total reddeningis not very high. We assume that such extinction curves originate solelyin circumstellar disks surrounding the high rotational velocity stars.Other objects are probably also obscured by some additional interstellarclouds.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Vitorla |
| Rektaszcenzió: | 08h50m33.50s |
| Deklináció: | -46°31'45.0" |
| Vizuális fényesség: | 5.1 |
| Távolság: | 826.446 parszek |
| RA sajátmozgás: | -3.4 |
| Dec sajátmozgás: | 3 |
| B-T magnitude: | 4.829 |
| V-T magnitude: | 5.07 |
Katalógusok és elnevezések:
|
