Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
| Sulphur and zinc abundances in Galactic stars and damped Lyα systems
High resolution spectra of 34 halo population dwarf and subgiant starshave been obtained with VLT/UVES and used to derive sulphur abundancesfrom the λ λ 8694.0, 8694.6 and λ λ 9212.9,9237.5 S I lines. In addition, iron abundances have been determined from19 Fe II lines and zinc abundances from the λ λ 4722.2,4810.5 lines. The abundances are based on a classical 1D, LTE modelatmosphere analysis, but effects of 3D hydrodynamical modelling on the[S/Fe], [Zn/Fe] and [S/Zn] ratios are shown to be small. We find thatmost halo stars with metallicities in the range -3.2 < [Fe/H] <-0.8 have a near-constant [S/Fe] ≃ +0.3; a least square fit to[S/Fe] vs. [Fe/H] shows a slope of only -0.04 ± 0.01. Among halostars with -1.2 < [Fe/H] < -0.8 the majority have [S/Fe] ≃+0.3, but two stars (previously shown to have low α/Fe ratios)have [S/Fe] ≃ 0.0. For disk stars with [Fe/H] > -1, [S/Fe]decreases with increasing [Fe/H] . Hence, sulphur behaves like othertypical α-capture elements, Mg, Si and Ca. Zinc, on the otherhand, traces iron over three orders of magnitude in [Fe/H], althoughthere is some evidence for a small systematic Zn overabundance ([Zn/Fe]≃ +0.1) among metal-poor disk stars and for halo stars with [Fe/H]< -2.0. Recent measurements of S and Zn in ten damped Lyαsystems (DLAs) with redshifts between 1.9 and 3.4 and zinc abundances inthe range -2.1 < [Zn/H] < -0.15 show an offset relative to the[S/Zn] - [Zn/H] relation in Galactic stars. Possible reasons for thisoffset are discussed, including low and intermittent star formationrates in DLAs.Based on observations collected at the European Southern Observatory,Chile (ESO No. 67.D-0106).Table A1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/993
| Observations of OB-stars at the former Leiden Southern Station
About 700 stars, mostly OB-stars, were observed by the author at theformer Leiden Southern Station at Hartebeespoortdam, South Africa, inthe observing seasons 1965, 1968, 1969, 1974, 1977, 1978. Observationswere made in the five channels of the Walraven photometric system. Dueto weathering of the telescope mirror the W channel gave no reliableresults for the faintest stars (m = 11 mag); in these cases the U-Wcolour index is not given. The change in sensitivity in the V channel,supposedly having occurred in 1968, was not recognised. Table~5 is onlyavailable 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/qcat?J/A+A/369/527
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Observational status and excitation mechanisms of beta-Cephei variables.
Not Available
| 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.
| A photometric study of β Cephei stars. II. Determination of the degrees L of pulsation modes
The wavelength dependence of photometric amplitudes is used as a meansof identifying the degrees l of pulsation modes of β Cephei starsstudied in an earlier paper. To this end, an expression for thephotometric amplitude of a non-rotating pulsating star is derived interms of the wavelength of the radiation received and the degree of thepulsation mode involved. The derivation differs from earlier derivationsin that the specific radiation intensity is considered instead of theoutward normal radiation flux. Furthermore, the effects of thenon-radial components of the Lagrangian displacement on the localsurface element of the star are taken into account. The angulardependence of the specific radiation intensity is determined by alimb-darkening function. The relative Lagrangian perturbation of thespecific radiation intensity is set equal to the relative Lagrangianperturbation of the outward normal radiation flux. The physicalparameters of the β Cephei stars are estimated by means ofcalibrations of photometric systems. From a comparison of thecalibrations of the Walraven, the Geneva, and the Stroemgren system forearly-type stars, it appears that the most reliable values are obtainedby means of the Walraven system. The influence of the uncertainties onthe physical parameters on the determination of the degrees l ofpulsation modes in β Cephei stars is examined. The expression forthe photometric amplitude of a pulsating star is used for thedetermination of the degree l of a pulsation mode by fitting curves ofthe wavelength dependences of theoretical photometric amplitudes forvarious degrees l to the wavelength dependence of observationallydetermined photometric amplitudes. In this way, values for the degrees lof most of the pulsation modes of the β Cephei stars considered arefound. It appears that not all β Cephei stars pulsate in at leastone radial mode and that multiperiodic β Cephei stars pulsate in avariety of combinations of pulsation modes.
| Nonadiabatic observables in beta Cephei models
Using results of linear nonadiabatic calculations for oscillations ofbeta Cephei star models, we calculate amplitudes and phases for light,color and radial velocity for the unstable modes of low harmonicdegrees, l. The nonadiabatic observables are the amplitude ratios andthe phase differences for various oscillating parameters. We constructtheoretical diagrams involving these observables as well as pulsationperiods and compare them with the stellar data. Balona & Stobie(1979) showed that the diagrams based on two-color photometric data maybe used to determine the l-value of an observed mode. Our use of resultsof nonadiabatic calculations improves their method. We show, inparticular, that the diagrams employing the satellite ultravioletmeasurements are the best for discrimination between the l = 0, 1 and 2cases. The clearest separation of the domains for the three l-valuesoccurs in the diagram making use of both photometric and the radialvelocity data. The observational points fall into three theoretricaldomains and an assignment of the l-value is unambiguous. A comparison ofthe theory with the observations is also made using the Period versusAmplitude ratios diagrams in various photometric systems. The agreementis very satisfactory and, in most cases, the l-value can be determined.The nonadiabtic observables are useful not only to determine l but alsothe radial order of the observed modes as well as for constrain meanstellar parameters. As an example we consider the case of delta Ceti-asingle mode beta Cephei star. Our results point to the significantmulticolor photometric and spectroscopic data for asteroseismology.
| Chemical abundances in early B-type stars. 5: Metal abundances and LTE/NLTE comparison
Chemical abundances of neon, magnesium, aluminum, sulfur, and iron arederived for a sample of 21 unevolved B-stars in the local field andnearby associations. While aluminum, sulfur, and iron are underabundantin nearly all stars, near solar abundances are found for magnesium andneon. In agreement with earlier results for carbon, nitrogen, oxygen,and silicon (Kilian 1992), the present results show no correlation withsurface gravities or evolutionary states, which indicates that the metalabundances reflect the original composition of the interstellar medium.The results are supplemented by a comparison of local thermodynamicequilibrium (LTE) and non-LTE (NLTE) abundances for C, N, O, Si, Mg, andAl. In most cases the differences amount to +/- (0.1-0.2) dex, whichslightly exceeds the estimated accuracy of the NLTE abundancedetermination. However, a clear temperature gradient is evident for mostelements, which indicates systematic LTE abundance errors with a maximumamplitude of 0.4 dex between 21 000 K and 31 000 K.
| Beta Cephei stars from a photometric point of view
This is an observational review, with an emphasis on photometric dataand their interpretation. Two lists are presented, one containing BetaCephei stars and the other Beta Cephei suspects. These lists then serveas a basis for discussing such topics as the location of Beta Cepheistars in the observational and theoretical H-R diagrams, theevolutionary state of these stars, the period-luminosity andperiod-luminosity-color relations, and observational identification ofpulsation modes. The paper also includes references to recent workconnected with the theoretical discovery that an opacity mechanism isresponsible for the excitation of Beta Cephei-star pulsations. Finally,observational programs for verifying the consequences of this discoveryare suggested.
| Evolutionary Variations of Nitrogen and Helium Abundances in Early B-Type Main Sequence Stars - an Analysis of New Data
Not Available
| Observations of interstellar NA I and CA II towards five southern stars and some comments on the location of the denser diffuse clouds in the southern Milky Way
High-resolution observations (3.6 km/s FWHM) of interstellar Na I and CaII lines toward five southern early-type stars are presented. All fivestars have strong absorption lines with low LSR radial velocities (notgreater than 5 km/s) which are interpreted as arising in materialassociated with the ridge of local molecular clouds identified by Dameet al. (1987). It is argued that the strong, low-velocity, atomic andmolecular lines observed toward other southern stars close to theGalactic plane also arise in this material, and special reference ismade to the foreground interstellar spectrum of the Sco OB1 association.Four of the observed stars also have absorption components consistentwith an origin in the Sagittarius-Carina spiral arm, and two (HD 111904and 164402) have highly negative velocity components (v(lsr) not greaterthan -40 km/s) which are interpreted as arising in expanding shellscentered on the Cen OB1 and Sgr OB1 associations, respectively.
| Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
| A photometric study of Beta Cephei stars. I - Frequency analyses
A frequency analysis is presented for both new photometric data andolder radial-velocity measurements for 33 Beta Cephei stars. While thepresent results are largely in agreement with those of Cuypers (1985)and Engelbrecht (1986), marked differences are noted. A tabulation isgiven of the pulsation frequencies of the stars that are generallyaccepted to be Beta Cephei variables.
| Atlas of extinction curves derived from ultraviolet spectra of the TD-1 satellite
The collection of 166 extinction curves derived from the publishedlow-resolution spectra acquired with the aid of the spectrometer onboard the TD-1 satellite is presented. The observed variety ofextinction laws is apparently due to the varied physical parameters ofinterstellar clouds; for example, the bright stars, included in thesample of TD-1 material, are very likely to be obscured by single clouds(interstellar or circumstellar). The system of standards constructedwith the aid of a special procedure allowing the possible effects ofspectral mismatch to be avoided and making possible the derivation ofextinction curves even in cases of very small E(B-V)S, was applied. Thecurves are presented in the form of plots, normalized to E(B-V) = 1.
| Chemical abundances in early B-type stars. III - NLTE temperature and gravity determination
Effective temperatures Teff and gravities log g of l9 unevolved B starsin the local field and nearby associations are given. Determinations ofTeff due to non-LTE analyses of silicon line formation and non-LTEanalyses of helium line formation are compared, and a reasonableagreement is obtained. Small differences were observed for four B starsonly. The temperature calibration of some important photometricobservables is discussed, with particular emphasis on a comparison withsynthetic spectral indices. Temperatures obtained from thenonthermodynamic ionization equilibria of helium and silicon were foundto be systematically higher by 2000 K than those calculated fromsynthetic photometry and LTE assumptions.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Catalogue of i and w/w crit values for rotating early type stars
Not Available
| Chemical abundances in early B-type stars. I - Sample and metal line equivalent widths
Equivalent widths for over 100 lines of C, N, O, Ne, Mg, Al, Si, S andFe of 21 unevolved B-stars in the local field and nearby associationsare given. The spectra cover the wavelength range 406-506 nm. Data forsharp unblended lines are accurate to 5 percent or better, for otherlines the error lies between 5 and 10 percent. The tables containequivalent widths and standard deviations for all lines measured in all21 stars.
| 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.
| UVBY photometry of southern B- and A stars
uvby differential photometry is presented for a number of southern earlytype variable stars. With the exception of Sigma Sco, all stars werepreviously observed during Jerzykiewicz and Sterken's (1977) searchprogram for new southern Beta Cephei type variables. Mean values of thestandard uvby magnitudes and color indices are also provided.
| HD 126859 - A low-amplitude multiperiodic Delta Scuti star
Based on observations obtained with the uvby photometer on the 50-cm ESOtelescope in Chile, the A6V star HD 126859 is found to be a normal mainsequence Delta Scuti star with low amplitude pulsation. A primary periodof 0.0528489 d with an associated full light range of 0.015 m in V isderived, and the secondary period being 0.059694, the period ratio of0.89 suggests either nonradial or high overtone pulsation. No evidencefor a change of the periods in time is found.
| Kinematics and distribution of interstellar H I in the region 290 L 320, +3 B +17.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985RMxAA..10..159O&db_key=AST
| The 67th Name-List of Variable Stars
Not Available
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| 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.
| Two new multiperiodic Beta Cephei candidates in the Scorpius complex
The discovery of two hitherto unknown Beta Cephei candidates isreported. The photometric variations of both stars indicate the presenceof at least three frequencies. The periods of HD 147985 are 0.13231 d,0.14493 d, and 0.15666 d; the periods of HD 15662 are 0.16890 d, 0.18861d, and 0.16978 d. Both variables belong to the Scorpius complex. Unlikethe Beta Cephei candidates discovered in NGC 6231 (Balona and Shobbrook,1983), they fit into the classical instability strip. It thus seemsunlikely that the peculiar position in the HR diagram of the variablesin NGC 6231 is related to the galactic location of the cluster. Thepossibility of a more extended instability strip is discussed in view ofthe results of recent surveys in the solar neighborhood. It is foundthat the actual instability strip closely parallels the main sequence.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Zirkel |
| Right ascension: | 14h45m10.90s |
| Declination: | -55°36'07.0" |
| Apparent magnitude: | 6.1 |
| Distance: | 529.101 parsecs |
| Proper motion RA: | -8.6 |
| Proper motion Dec: | -7.9 |
| B-T magnitude: | 6.001 |
| V-T magnitude: | 6.077 |
Catalogs and designations:
|
