תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Asphericity and clumpiness in the winds of Luminous Blue Variables
We present the first systematic spectropolarimetric study of LuminousBlue Variables (LBVs) in the Galaxy and the Magellanic Clouds, in orderto investigate the geometries of their winds. We find that at least halfof our sample show changes in polarization across the strong Hαemission line, indicating that the light from the stars is intrinsicallypolarized and therefore that asphericity already exists at the base ofthe wind. Multi-epoch spectropolarimetry on four targets revealsvariability in their intrinsic polarization. Three of these, AG Car, HRCar and P Cyg, show a position angle (PA) of polarization which appearsrandom with time. Such behaviour can be explained by the presence ofstrong wind-inhomogeneities, or “clumps” within the wind.Only one star, R 127, shows variability at a constant PA, and henceevidence for axi-symmetry as well as clumpiness. However, if viewed atlow inclination, and at limited temporal sampling, such a wind wouldproduce a seemingly random polarization of the type observed in theother three stars. Time-resolved spectropolarimetric monitoring of LBVsis therefore required to determine if LBV winds are axi-symmetric ingeneral. The high fraction of LBVs (>50%) showing intrinsicpolarization is to be compared with the lower ~20-25% for similarstudies of their evolutionary neighbours, O supergiants and Wolf-Rayetstars. We anticipate that this higher incidence is due to the lowereffective gravities of the LBVs, coupled with their variabletemperatures within the bi-stability jump regime. This is alsoconsistent with the higher incidence of wind asphericity that we find inLBVs with strong Hα emission and recent (last ~10 years) strongvariability.
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| V382 Velorum
IAUC 7184 available at Central Bureau for Astronomical Telegrams.
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| A Minisurvey of Interstellar Titanium from the Southern Hemisphere
We describe the results of a minisurvey of interstellar Ti II and Ca IIabsorption toward 42 early-type stars observed from the southernhemisphere at a spectral resolution of 4.5 km s-1. Results are alsopresented for the Na I ultraviolet line (3302 Angstroms) detected towardnine of these targets. We examine the dependence of the integratedcolumn densities of N(Ti II), N(Ca II), and N(Na I) on distance,reddening, neutral hydrogen column density, and their Galactic elementalabundance. Our findings support the proposition that Ti II and Ca IIabsorption originates in the same regions of the pervasive, warm, andneutral intercloud gas of the interstellar medium. We have observed acorrelation of decreasing Ti and Ca abundance with increasingline-of-sight gas density. The Ti II/Ca II abundance ratio has beenfound to be essentially constant under all the interstellar densityconditions we have sampled. Thus, we conclude that the generalabsorption properties of titanium (and calcium) are similar throughoutthe entire disk of our Galaxy.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| 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.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&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.
| The position corrections of 1400 stars observed with PA II in San Juan.
Not Available
| Vilnius Photometric System - Part Two - the Bright Southern Standard Stars
Not Available
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
| Spectral synthesis in the ultraviolet. IV - A library of mean stellar groups
A library of mean UV stellar energy distributions is derived from IUEspectrophotometry of 218 stars. The spectra cover 1230-3200 A with aspectral resolution of about 6 A. They have been corrected forinterstellar extinction and converted to a common flux and wavelengthscale. Individual stars were combined into standard groups according totheir continuum colors, observed UV spectral morphology, MK luminosityclass, and metal abundance. The library consists of 56 groups: 21dwarf(V), 8 subgiant(IV), 16 giant(III), and supergiant(I + II) groups,covering O3-M4 spectral types. A metal-poor sequence is included,containing four dwarf and two giant groups, as is a metal-enhancedsequence with a single dwarf, subgiant, and giant group. Spectralindices characterizing the continuum and several strong absorptionfeatures are examined as temperature, luminosity, and abundancediagnostics. The library is intended to serve as a basis forinterpreting the composite UV spectra of a wide variety of stellarsystems, e.g., elliptical galaxies, starburst systems, and high-redshiftgalaxies.
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| Santiago declination catalogue. II - A declination catalogue of 493 FK5 stars (equinox J2000.0)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&AS...90..109C&db_key=AST
| Second Rio Grande catalogue (RG2).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990RMxAA..21..286H&db_key=AST
| Physical data of the fundamental stars.
Not Available
| Spectral synthesis in the ultraviolet. III - The spectral morphology of normal stars in the mid-ultraviolet
The morphology of 218 mid-UV spectra of stars ranging from O through Kin spectral type is examined. Several new line and continuum indices aredefined and their usefulness as temperature, luminosity, and metallicitydiscriminants is discussed. Mid-UV stellar continua are found to bemarkedly affected by abundance. A UV excess, delta(2600-V), is computedwhich is more sensitive by a factor of 10 to (Fe/H) than is delta(U-B).The relative strength of spectral lines in the mid-UV is not as stronglyaffected by abundance. Mid-UV spectra are much more sensitive to thetemperature of the stellar population than to either metallicity or thedwarf/giant ratio. Mg II 2800 shows unexpected behavior, displaying nosensitivity to abundance for cool stars and a reversed sensitivity in FGdwarfs such that metal-poor stars have stronger Mg II strengths at thesame temperature than more metal-rich stars.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| The spectral energy distribution of early-type stars. II - The extinction law towards O-type stars
Photometric measurements through different pass-bands are used todetermine the color-excess E(B-V) for O-type stars in the UV and IRspectral regions. The results are used to examine the extinctioncharacter of the stars. It is found that, in the UV, each O-type starhas its own extinction character. In general, the visual and NIRextinction in the direction of O-type stars are normal.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
| The UV silicon spectra of early B stars
Equivalent widths of UV silicon lines obtained from high dispersion IUESWP spectra for a sample of 37 mid- to early B stars are presented.These are compared to other atmospheric diagnostics and to modelatmosphere calculations. It is found that some of the UV silicon linesare extremely sensitive to stellar temperature and luminosity over therange B5-B0.5, or roughly a factor of two in effective temperature. Thepotential usefulness of these lines is stressed, and it is demonstratedthat they could determine temperatures and surface gravities to the sameaccuracy as other commonly used diagnostics once adequate models becomeavailable. Although the available models fail to predict thequantitative behavior of the line strengths, they do, in most instances,describe their qualitative behavior. Since the existing models aresomewhat out of date, the results suggest that models based upon morecomplete opacity tables may be quite reliable.
| The UV silicon spectra of early B stars
The UV silicon spectra of mid to early B stars are examined and comparedto models. It is found that lines are extremely sensitive to stellartemperature and luminosity. Although the models fail to predict thequantitative behavior of the line strengths, they do, in most instances,describe their qualitative behavior.
| Energy Distribution in the Stellar Spectra of Different Spectral Types and Luminosities - Part Five - Normal Stars
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | מפרש |
| התרוממות ימנית: | 09h56m51.80s |
| סירוב: | -54°34'04.0" |
| גודל גלוי: | 3.54 |
| מרחק: | 591.716 פארסק |
| תנועה נכונה: | -13 |
| תנועה נכונה: | 1.4 |
| B-T magnitude: | 3.402 |
| V-T magnitude: | 3.5 |
קטלוגים וכינוים:
|
