|Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*|
We present the results of a magnetic survey of a sample of eightβCephei stars and 26 slowly pulsating B (SPBs) stars with the FOcalReducer low dispersion Spectrograph at the Very Large Telescope. A weakmean longitudinal magnetic field of the order of a few hundred Gauss isdetected in the βCephei star ξ1CMa and in 13 SPBstars. The star ξ1CMa becomes the third magnetic staramong the βCephei stars. Before our study, the star ζCas wasthe only known magnetic SPB star. All magnetic SPB stars for which wegathered several magnetic field measurements show a field that varies intime. We do not find a relation between the evolution of the magneticfield with stellar age in our small sample. Our observations imply thatβCephei and SPB stars can no longer be considered as classes ofnon-magnetic pulsators, but the effect of the fields on the oscillationproperties remains to be studied.
|Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT|
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
|Photometric modelling of slowly pulsating B stars|
The photometric characteristics of slowly pulsating B stars areinvestigated using a numerical approach. Stability calculations areperformed for a set of stellar models representative of the mid-B type,using a non-radial non-adiabatic pulsation code. The results from thesecalculations are used to synthesize photometry, in several commonsystems, for unstable modes of harmonic degrees l=1...4. Focusing on theGeneva system for illustrative purposes, a variety of techniques areemployed to analyse and visualize the synthetic data, including the useof multicolour-amplitudes and amplitude-phase diagnostic diagrams. Oneoutstanding aspect of the analysis is the discovery, for the l=2...4modes, of `inter-term cancellation' (ITC) - the process of destructiveinterference between the flux variations originating from surfacetemperature perturbations and those arising from radius perturbations.The ITC can be severe enough that a mode may be excited to a significantamplitude, and yet exhibit levels of photometric variability that fallbelow typical observational detection thresholds. Furthermore, it canaffect not only the light variations in a given photometric passband,but also the variations of the bolometric flux. However, thecancellation is dependent on wavelength, and will not occur to the samedegree in more than one passband. Therefore, simultaneous observation ina multitude of passbands represents the best approach to ensuring thatno modes are overlooked during searches for variability in B-type stars.A consequence of ITC is that ratios between the variability amplitude,in differing passbands, become very sensitive towards mode-to-modechanges in the pulsation. This increased sensitivity will tend tocomplicate any attempts at identifying the harmonic degrees of the modesresponsible for observed variability. However, the cancellation alsointroduces significant phase differences between the light variations ineach passband, especially for the l=3 and l=4 modes. On the grounds thatcorrespondingly large phase differences are not seen in observationaldata, it is argued that the variability seen in slowly pulsating B starscan tentatively be attributed to l=1 and l=2 modes.
|A study of bright southern slowly pulsating B stars. II. The intrinsic frequencies|
We present the results of detailed frequency analyses of a sample ofthirteen confirmed slowly pulsating B stars. Our analysis is based on acombination of elaborate photometric and spectroscopic data-sets. Theoriginal sample consists of a mixture of five confirmed slowly pulsatingB stars and twelve candidate slowly pulsating B stars discovered thanksto the photometric measurements of the HIPPARCOS satellite. HD 55522 andHD 131120 turn out to be chemically peculiar stars. HD 169978 and HD69144 are two ellipsoidal variables for which no intrinsic variabilityis found. At least nine of the thirteen studied slowly pulsating B starsare multi-periodic. For HD 74195, HD 85953, HD 123515 and HD 215573, theobserved frequency spacings suggest that we are dealing with frequencymultiplets. For the apparent mono-periodic binary HD 24587, it is notclear if the observed variations are induced by stellar pulsation and/orby rotation modulation. We highlight the statistical character of theobserved pulsational properties of our sample. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile Full Tables 2-4, 6-15 are only availablein electronic form at the CDS via anounymous ftp to cdsarc.u-strasbg.fr(188.8.131.52) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/965
|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 (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|A study of bright southern slowly pulsating B stars. I. Determination of the orbital parameters and of the main frequency of the spectroscopic binaries|
In 1996, we started a long-term spectroscopic and photometric study of17 southern Slowly Pulsating B-stars. In this paper, we report ourfinding that at least 8 of them turn out to be spectroscopic binaries.We present the results of the determination of the orbits from thespectroscopic data. There is a great variety in the derived orbits.HD123515 and HD140873 were known as single-lined spectroscopic binaries,but both turn out to be double-lined. All the others binaries aresingle-lined. For HD140873 and HD177863, we find orbits with a largeeccentricity of respectively e=0.731 +/- 0.006 and e=0.603 +/- 0.007.HD69144, HD92287 and HD169978 are three circular binaries with a veryshort orbital period (a few days). Since their photometric measurementsare dominated by a (close to) sinusoidal variation with twice theorbital frequency, these stars are ellipsoidal variables. Their orbitalperiods are of the same order of magnitude as the periods of pulsation.After removing the orbit, we find the same first frequency in theresidual radial velocities as in the gathered photometric measurementsfor 6 stars. For HD69144 and HD169978 we did not yet succeed in derivingan intrinsic period, although HD69144 has prominent line profilevariations. HD169978 was misclassified as an SPB. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile
|The 74th Special Name-list of Variable Stars|
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
|Selection of a sample of bright southern Slowly Pulsating B Stars for long-term photometric and spectroscopic monitoring|
The photometric experiment on Hipparcos has led to the discovery of,among other types of variables, a large amount of new Slowly Pulsating BStars. We have selected twelve bright southern stars of this sample,together with five previously known Slowly Pulsating B Stars, forspectroscopic and photometric monitoring. These seventeen stars havespectral types ranging from B 2 up to B 9 and thus fully cover theinstability strip. We here present the results of a preliminary analysisof our data and show that our sample is an extremely important one toperform seismology of intermediate-massive stars. In particular, we findthat all but one of the selected stars exhibit clear line-profilevariability. The broader-lined Slowly Pulsating B Stars tend to havemore complex line-profile variations. One of the previously known SlowlyPulsating B stars was known to be a binary. Besides this star, anothersix of the selected Slowly Pulsating B stars turn out to be multiplesystems. Five of these seven binaries have large rotational velocitiesand complicated line-profile variations with moving subfeatures. It isnot yet clear whether or not the binarity results in a particularspectrum of excited modes. Based on observations collected with the CATTelescope of the European Southern Observatory and with the SwissPhotometric Telescope of the Geneva Observatory, both situated at LaSilla in Chile
|Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars|
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
|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.
|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.
|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.
|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.
|UBV photometry for southern OB stars|
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
|Spectral classification from the ultraviolet line features of S2/68 spectra. V - Supplement series|
The paper presents the ultraviolet classification of more than 450 B-Aand F spectra obtained with the sky survey telescope mounted on the TD1satellite. Concerning abnormal objects, attention is given to the Bestars, the binary stars, the helium weak stars, and the lambda Booobjects. With regard to Be stars, it is concluded that the 1930 Awavelength feature is linked to the existence of either shell structuresor Fe II emission lines in the visual spectral range. In addition, it issuggested that stellar spectra at wavelengths of 1410, 1610-20 and 2400A are equivalent to the He-weak group in the classical range.
|On the period-luminosity relation of Beta Cephei stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....84..374J&db_key=AST
|On the 4430 A interstellar band - A visual classification|
A system of visual classification of the strength of the interstellarband 4430 A has been developed, based on spectra taken at spectralclassification dispersion. The intensity of the band was divided into 8main classes, defined by a group of selected standard stars. The systemwas applied to 1,111 southern OB stars contained in the catalog ofspectral types by Garrison, Hiltner, and Schild (1977). The mean errorin the classification was estimated to be plus or minus 1 class.Equivalent widths were measured for 100 stars; an excellent correlationwith the visual estimations was obtained. A calibration between thesetwo parameters is given.
|A search for Beta Cephei stars. III - Photometric studies of southern B-type stars|
The result of a photometric search for Beta Cephei stars among a groupof 37 southern B-type stars is presented. Beside two new Beta Cepheistars, one eclipsing binary, one helium-weak variable, and ten slowvariables were found.
|Space velocities and ages of nearby early-type stars|
Photometric distances and space velocities have been calculated for 458B0-A0 stars with apparent magnitudes not exceeding 6.5. UsingStromgren's ubvy-beta photometry the effective temperature and theposition in bolometric magnitude over the zero-age main sequence of thestars were derived. These quantities were used to obtain age and massfor 423 of the stars by interpolation in the models of stellar evolutionfor the chemical composition (X Z) = (0.7, 0.03). A relation forderiving interstellar reddening for normal stars in the intermediategroup is given.
|MK spectral classifications for southern OB stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...35..111G&db_key=AST
|Search for Beta Cephei stars south of declination -20 deg. I - Incidence of light variability among early B giants and subgiants: Summer objects|
|The spatial distribution of young stars in VELA (l=250 to 284).|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27..343D&db_key=AST
|Structure and age of the local association /Pleiades group/|
Intermediate-band indices are used to derive luminosities for some 500early-type stars with well-determined proper motions and radialvelocities. Space motion vectors and galactic coordinates are computedfor the stars considered. It is found that the local association membersare mainly concentrated in the Sco-Cen region in the Southern Hemisphereand the Cas-Tau region in the north.
|New kinematical data for bright southern OB-stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..129L&db_key=AST
|Four-color and H-beta photometry for bright B-type stars in the southern hemisphere.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..621C&db_key=AST
|MK Spectral Types for Bright Southern OB Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..313H&db_key=AST
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967MNRAS.137..337D&db_key=AST
|A Survey of Southern Be Stars|
|Spectral types and luminosities of B, A and F southern stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957MNRAS.117..449D&db_key=AST