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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 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.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| The orbit of the close spectroscopic binary \varepsilon Lup and the intrinsic variability of its early B-type components
We subjected 106 new high-resolution spectra of the double-linedspectroscopic close binary \varepsilon Lup, obtained in a time-span of17 days from two different observatories, to a detailed study of orbitaland intrinsic variations. We derived accurate values of the orbitalparameters. We refined the sidereal orbital period to 4.55970d days andthe eccentricity to e=0.277. By adding old radial velocities, wediscovered the presence of apsidal motion with a period of the rotationof apses of about 430 years. Such a value agrees with theoreticalexpectations. Additional data is needed to confirm and refine thisvalue. Our dataset did not allow us to derive the orbit of the thirdbody, which is known to orbit the close system in 64 years. We presentthe secondary of \varepsilon Lup as a new β Cephei variable, whilethe primary is a β Cephei suspect. A first detailed analysis ofline-profile variations of both primary and secondary led to detectionof one pulsation frequency near 10.36 c d-1 in thevariability of the secondary, while no clear periodicity was found inthe primary, although low-amplitude periodicities are still suspected.The limited accuracy and extent of our dataset did not allow any furtheranalysis, such as mode-identification.
| A study of bright southern slowly pulsating B stars. III. Mode identification for singly-periodic targets in spectroscopy
We present the results of the mode identification for a sample of 7bright southern slowly pulsating B stars showing one pulsation frequencyin the λλ 413 nm Si II profiles. We combined the resultsfrom (1) the method of photometric amplitudes; (2) the moment method;and (3) the amplitude and phase variation across the profile to searchfor the ℓ and m values of the modes best fitting the data. It is thefirst time that the applicability of these techniques is tested to asample of main-sequence g-mode pulsators. Combining the moment methodwith the amplitude and phase variations across the observed line profilegives an improvement in spectroscopic identification of low degree ℓg-mode pulsations. Using the variations of the higher order even moments< v4> and < v6> of the moment methodsolutions can also help. For HD 181558, HD 24587, HD 140873 and HD177863, the photometric and spectroscopic results are compatible andpoint towards (ℓ,m) = (1, +1) sectoral modes. For HD 215573, HD53921 and HD 92287, the results are inconclusive. Our proposedmethodology for mode identification is also applicable to γDoradus stars.Based on observations collected with the CAT Telescope of the EuropeanSouthern Observatory and with the Swiss Photometric Telescope of theGeneva Observatory, both situated at La Silla in Chile.
| HD 207651: A Triple System with δ Scuti and Ellipsoidal Variations But No γ Doradus Pulsations
We examine HD 207651 as a possible example of a star exhibiting bothγ Doradus and δ Scuti type pulsations. We find photometricperiods of 0.06479 and 0.06337 days with peak-to-peak amplitudes inJohnson B of 21 and 13 mmag, respectively, clearly indicating δScuti pulsations. Additional light variation with a period of 0.73540days and an even larger amplitude of 31 mmag is within the range ofγ Doradus pulsation periods but results instead from theellipticity effect. HD 207651 has a composite spectrum with a weak,narrow absorption line superposed near the center of each broad metalline. The broad-lined component is the primary of a short-period,single-lined binary, which has a period of 1.4708 days, twice the periodof the ellipsoidal variations seen in the photometry. We determine theprimary to be an A8 giant and estimate the unseen secondary of theshort-period binary to be a mid-M dwarf. The narrow-lined star, an F7:dwarf, shows velocity variability with a period of months or perhapsyears. It is thus a more distant companion to the binary, making HD207651 a triple system. All light variations come from the A8 giantprimary star. Since the 0.73540 day variation results from theellipticity effect, HD 207651 is not an example of a star that exhibitsboth δ Scuti and γ Doradus pulsations. The growing number ofconfirmed γ Doradus stars that also occur within the δ Scutiinstability strip but fail to show additional δ Scuti variabilitymakes it increasingly unlikely that the two types of pulsation cancoexist in the same star.
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
| Metallicities of the SPB stars from the IUE ultraviolet spectra
We derived the stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddenings for 20 SPB and34 reference stars observed during the IUE satellite mission. Theparameters were derived by means of an algorithmic procedure of fittingtheoretical flux distributions to the low-resolution IUE spectra andoptical spectrophotometric observations. Since the metallicity [m/H] hasa special importance for pulsating B type stars, we focused ourattention on that parameter. We found that the mean value of themetallicity of the considered SPB and reference stars amounts to [m/H] ~-0.20. The results only slightly depend on the reduction procedure usedfor the IUE images (NEWSIPS and INES). The metal abundances obtained inthis paper are in accordance with the average value of -0.2 dex forstars in the solar neighborhood recently reported by otherinvestigators.Tables 3-7 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/689
| The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel
We report new radial velocity observations of GP Vel / HD 77581, theoptical companion to the eclipsing X-ray pulsar Vela X-1. Using dataspanning more than two complete orbits of the system, we detect evidencefor tidally induced non-radial oscillations on the surface of GP Vel,apparent as peaks in the power spectrum of the residuals to the radialvelocity curve fit. By removing the effect of these oscillations (tofirst order) and binning the radial velocities, we have determined thesemi-amplitude of the radial velocity curve of GP Vel to beKo = 22.6 +/- 1.5 km s-1. Given the accuratelymeasured semi-amplitude of the pulsar's orbit, the mass ratio of thesystem is 0.081 +/- 0.005. We are able to set upper and lower limits onthe masses of the component stars as follows. Assuming GP Vel fills itsRoche lobe then the inclination angle of the system, i, is70.1deg +/- 2.6deg. In this case we obtain themasses of the two stars as Mx = 2.27 +/- 0.17 Msunfor the neutron star and Mo = 27.9 +/- 1.3 Msunfor GP Vel. Conversely, assuming the inclination angle isi=90deg, the ratio of the radius of GP Vel to the radius ofits Roche lobe is beta = 0.89 +/- 0.03 and the masses of the two starsare Mx = 1.88 +/- 0.13 Msun and Mo =23.1 +/- 0.2 Msun. A range of solutions between these twosets of limits is also possible, corresponding to other combinations ofi and beta . In addition, we note that if the zero phase of the radialvelocity curve is allowed as a free parameter, rather than constrainedby the X-ray ephemeris, a significantly improved fit is obtained with anamplitude of 21.2 +/- 0.7 km s-1 and a phase shift of 0.033+/- 0.007 in true anomaly. The apparent shift in the zero phase of theradial velocity curve may indicate the presence of an additional radialvelocity component at the orbital period. This may be anothermanifestation of the tidally induced non-radial oscillations andprovides an additional source of uncertainty in the determination of theorbital radial velocity amplitude.
| Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295*
We have discovered both intermediate-order gravity mode and low-orderpressure mode pulsation in the same star, HD 209295. It is thereforeboth a γ Doradus and a δ Scuti star, which makes it thefirst pulsating star to be a member of two classes. The analysis of our128h of multisite spectroscopic observations carried out over twoseasons reveals that the star is a single-lined spectroscopic binarywith an orbital period of 3.10575+/-0.00010d and an eccentricity of0.352+/-0.011. Only weak pulsational signals are found in both theradial velocity and line-profile variations, but we have succeeded inshowing that the two highest-amplitude γ Doradus pulsation modesare consistent with l=1 and |m|=1. These two modes dominated our 280h ofBVIC multisite photometry, also obtained over two seasons. Wedetected altogether ten frequencies in the light variations, one in theδ Scuti regime and nine in the γ Doradus domain. Five of theγ Doradus frequencies are exact integer multiples of the orbitalfrequency. This observation leads us to suspect they are tidallyexcited. Attempts to identify modes from the multicolour photometryfailed. We performed model calculations and a stability analysis of thepulsations. The frequency range in which δ Scuti modes are excitedagrees well with observations. However, our models do not showexcitation of γ Doradus pulsations, although the damping issmaller in the observed range. We also investigated tidal excitation ofγ Doradus modes. Some of the observed harmonics of the orbitalperiod were found to be unstable. The observed orbital harmonics whichare stable in the models can be understood as linear combinations of theunstable modes. We could not detect the secondary component of thesystem in infrared photometry, suggesting that it may not be amain-sequence star. Archival data of this star show that it has a strongultraviolet (UV) excess, the origin of which is not known. The orbit ofthe primary is consistent with a secondary mass ofM>1.04Msolar, which is indicative of a neutron star,although a white dwarf companion is not ruled out.
| 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.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/965
| Tidally induced radial-velocity variations in close binaries
A theoretical framework for the determination of tidally inducedradial-velocity variations in a component of a close binary ispresented. Both the free and the forced oscillations of the componentare treated as linear, isentropic perturbations of a sphericallysymmetric star. Resonances between dynamic tides and free oscillationmodes are taken into account by means of the formalism developed by{{Smeyers} et al.} (\cite{SWV1998}). The amplitude of the tidallyinduced radial-velocity variations seen by the observer depends on theorbital eccentricity and on the orbital inclination. The amplitudeincreases with increasing orbital eccentricity and is most sensitive tothe value of the orbital inclination when 20o <~ i <~70o. In the case of a 5 Msun ZAMS star with a 1.4Msun compact companion, it is shown that resonant dynamictides can lead to radial-velocity variations with amplitudes largeenough to be detected in observations. The shape of the tidally inducedradial-velocity curves varies from very irregular for orbital periodsaway from any resonances with free oscillation modes to sinusoidal fororbital periods close to a resonance with a free oscillation mode. Ourinvestigation is concluded with an application to the slowly pulsating Bstar HD 177863 showing the possibility of resonant excitation of ahigh-order second-degree g+-mode in this star.
| 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
| On the Variability of Late B III-V Stars
We investigate the Hipparcos Satellite photometry of luminosity classIII-V B6-B9 stars. Most are relatively non-variable. Candidates forwhich further study is desirable are identified.
| 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.
| 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
| 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
| 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.
| HD 37151: A new 'slowly pulsating B star'
We report the discovery of non-radial pusations with at least 5 periodsin the B8V star HD 37151, a probable member of the Orion OB1association. This result is based on 465 photometric measurements in 7colors spanning 12 years. In addition, 30 high-resolution spectra weretaken in the Mg II lambda 4481 region: they show a small projectedrotational velocity and slight variations of the line profiles where atleast two out of the five photometric periods can be identified.Although this star was once classified B8Vp(Si), all available data showit is a normal star instead. Therefore, this object in not anotherexample (after ET And) of a pulsating silicon star, but entirely matchesthe characteristics of Waelkens' 'Slowly Pulsating B stars' (SPB). Itoffers the interest of being the second coolest member of this class,helping to define empirically the cool border of the related instabilitydomain. The ratio of color to visual amplitudes A(sub(u-v)/Avof the known SPB stars is nicely correlated with Teff, ingood agreement with theoretical expectations for non-radial pulsationswith order less than or = 2.
| The Opacity Mechanism in B-Type Stars - Part Two - Excitation of High-Order G-Modes in Main Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..588D&db_key=AST
| The 71st Name-List of Variable Stars
Not Available
| Slowly pulsating B stars
Photometric data obtained during several years of observations of sevenB-type stars are analyzed, including HD 74195 (Omicron Velorum), HD74560 (HD 3467), HD 123515 (HR 5296), HD 143309, HD 160124, HD 177863(HR 7241), and HD 181558 (HR 7339). Results indicate that all sevenstars are multiperiodic variables with periods of the order of days. Twoperiods were identified for HD 177863, three periods for HD 74560 and HD181558, four periods for HD 123515, five periods for HD 74195, sixperiods for HD 143309, and eight periods for HD 160124. Themultiperiodicity and the amplitude behavior of these stars point towardpulsation in high-radial-order g-modes in the stars. It is suggestedthat these stars form a distinct group of early-type variables, whichare named here 'slowly pulsating B 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.
| 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.
| Photometric variability of mid-B stars
An extended systematic study was carried out of photometric variationsof B-type main sequence stars. The campaign was performed using theseven-color instrument at La Silla. The survey covered 30 stars andshowed that the objects could be typified by the 53 Per variables. Theobserved variabilities may arise from pulsations in nonradial g-modeswith high radial wavenumbers. The motions detected occur in the outerstellar layers, i.e., in the second He ionization zone, a situation withsignificance for classifications of variable OB stars and supergiants,as opposed to mid-B stars. Another 10 yr of observations would berequired to derive the frequency spectra with an accuracy as high asthat available for white dwarfs.
| 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.
| Is star formation bimodal ? II. The nearest early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
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Dades d'Observació i Astrometria
| Constel·lació: | Sagittarius |
| Ascensió Recta: | 19h07m08.50s |
| Declinació: | -18°44'16.0" |
| Magnitud Aparent: | 6.29 |
| Distancia: | 222.222 parsecs |
| Moviment propi RA: | -2.7 |
| Moviment propi Dec: | -16.8 |
| B-T magnitude: | 6.233 |
| V-T magnitude: | 6.285 |
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