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Multi-periodic photospheric pulsations and connected wind structures in HD 64760
We report on the results of an extended optical spectroscopic monitoringcampaign on the early-type B supergiant HD 64760(B0.5 Ib) designed to probe the deep-seated origin of spatial windstructure in massive stars. This new study is based on high-resolutionechelle spectra obtained with the Feros instrument at ESO La Silla. 279spectra were collected over 10 nights between February 14 and 24, 2003.From the period analysis of the line-profile variability of thephotospheric lines we identify three closely spaced periods around 4.810h and a splitting of ±3%. The velocity - phase diagrams of theline-profile variations for the distinct periods reveal characteristicprograde non-radial pulsation patterns of high order corresponding topulsation modes with l and m in the range 6{-}10. A detailed modeling ofthe multi-periodic non-radial pulsations with the Bruce and Kyliepulsation-model codes (Townsend 1997b, MNRAS, 284, 839) favors eitherthree modes with l=-m and l=8,6,8 or m=-6 and l=8,6,10 with the secondcase maintaining the closely spaced periods in the co-rotating frame.The pulsation models predict photometric variations of 0.012{-}0.020 magconsistent with the non-detection of any of the spectroscopic periods byphotometry. The three pulsation modes have periods clearly shorter thanthe characteristic pulsation time scale and show small horizontalvelocity fields and hence are identified as p-modes. The beating of thethree pulsation modes leads to a retrograde beat pattern with tworegions of constructive interference diametrically opposite on thestellar surface and a beat period of 162.8 h (6.8 days). This beatpattern is directly observed in the spectroscopic time series of thephotospheric lines. The wind-sensitive lines display features ofenhanced emission, which appear to follow the maxima of the photosphericbeat pattern. The pulsation models predict for the two regionsnormalized flux amplitudes of A=+0.33,-0.28, sufficiently large to raisespiral co-rotating interaction regions (Cranmer & Owocki 1996, ApJ,462, 469). We further investigate the observed Hα wind-profilevariations with a simple rotating wind model with wind-densitymodulations to simulate the effect of possible streak lines originatingfrom the localized surface spots created by the NRP beat pattern. It isfound that such a simple scenario can explain the time scales and somebut not all characteristics of the observed Hα line-profilevariations.
| Influence of the Coriolis force on the instability of slowly pulsating B stars
This paper explores the effect of rotation on the κ-mechanisminstability of slowly pulsating B stars. A new non-adiabatic code, whichadopts the so-called traditional approximation to treat the Coriolisforce, is used to investigate the influence exerted by rotation over thestability of stellar models covering the mass range2.5Msolar<=M*<= 13.0Msolar. Theprincipal finding is that, for all modes considered apart from theprograde sectoral (PS) class, rotation shifts the κ-mechanisminstability toward higher luminosities and effective temperatures; theseshifts are accompanied by broadenings in the extent of instabilitystrips. Such behaviour is traced to the shortening of mode periods underthe action of the Coriolis force. Instability strips associated with PSmodes behave rather differently, being shifted to marginally lowerluminosities and effective temperatures under the influence of rotation.The implications of these results are discussed in the context of theobservational scarcity of pulsation in B-type stars having significantrotation; various scenarios are explored to explain the apparentdichotomy between theory and observations. Furthermore, the possiblesignificance of the findings to Be stars is briefly examined.
| 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.
| A semi-analytical formula for the light variations due to low-frequency g modes in rotating stars
Through the adoption of the so-called `traditional approximation', a newsemi-analytical formula is derived for the light variations produced bylow-frequency g modes in uniformly rotating stars. The formula is usedto examine the influence of rotation on the variability produced by astellar model representative of the slowly pulsating B-type class.It is found that, for all apart from prograde sectoral modes, theCoriolis force acts to trap pulsation within an equatorial waveguide.Towards rapid rotation and/or low pulsation frequency, this waveguidebecomes so narrow that only a thin band around the stellar equator makesany appreciable contribution toward flux changes. As a result, unlessviewed from near the poles, the variability exhibited by the starbecomes very small, possibly explaining why recent photometricobservations of rapidly rotating stars have failed to find much evidencefor the presence of low-frequency modes.It is further demonstrated that the ratio between the variabilityamplitude in pairs of passbands depends, with the introduction ofrotation, both on the azimuthal order of a mode, and on the location ofthe observer in relation to the rotation axis of the star. This meansthat the standard photometric techniques used to identify modes innon-rotating stars cannot easily be applied to systems where rotation issignificant.
| A Photometric and Spectroscopic Study of 3 Vulpeculae: An Observer's Nightmare
We describe photometry of 3 Vulpeculae obtained with the Four CollegeAutomated Photoelectric Telescope and spectroscopy obtained with the1.22 m telescope of the Dominion Astrophysical Observatory. We haveanalyzed differential uvby photometric observations obtained over 7 yr.Three main frequencies (f1=0.9719, f2=0.7923, andf3=0.8553 cycles day-1) were found, as well as asum frequency (f1+f2=1.76420 cyclesday-1). A study of the photographic region usinghigh-dispersion spectrograms obtained with a Reticon detector at thecoudé spectrograph confirms the variable nature of 3 Vul as a 53Persei star and indicates that the star's abundances are normal formain-sequence band B stars. The new spectra were combined with thosepreviously published to confirm an orbital period very close to 1 yr.Finally, comparison with models yielded both a mass (4.16Msolar) and an age (25 Myr), and a mass range for thecompanion (0.6-1.1 Msolar). With an orbital period of almost1 yr and a pulsation period of almost 1 day, this star is indeed anobserver's nightmare.
| 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
| 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.
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Surface trapping and leakage of low-frequency g modes in rotating early-type stars - II. Global analysis
A global analysis of the surface trapping of low-frequency non-radial gmodes in rotating early-type stars is undertaken within the Cowling,adiabatic and traditional approximations. The dimensionless pulsationequations governing these modes are reviewed, and the boundaryconditions necessary for solution of the equations are considered; inparticular, an outer mechanical boundary condition, which does notenforce complete wave trapping at the stellar surface, is derived anddiscussed in detail. The pulsation equations are solved for a7-Msolar model star over a range of rotation rates, using anumerical approach. The results of the calculations confirm the findingsof the preceding paper in the series: modes with eigenfrequencies belowa cut-off cannot be fully trapped within the star, and exhibit leakagein the form of outwardly propagating waves at the surface. The dampingrates resulting from leakage are calculated for such `virtual' modes,and found to be appreciably larger than typical growth rates associatedwith opacity-driven pulsation. Furthermore, it is demonstrated that thesurface perturbations generated by virtual modes are significantlychanged from those caused by fully trapped modes; the latter resultsuggests differences in the line-profile variations exhibited by thesetwo types of mode. The findings are discussed in the context of the 53Per, SPB and pulsating Be classes of variable star. Whilst wave leakagewill probably not occur for overstable g modes in the 53 Per and slowlyrotating SPB stars, the adoption of the new outer mechanical boundarycondition may still affect the pulsational stability of these systems.Wave leakage for overstable modes remains a possibility in Be stars andthe more rapidly rotating SPB stars.
| A Proposal for Multicolor WET Photometric Campaign on roAp Stars.
A review of the asteroseismology of the rapidly oscillating Ap (roAp)stars based on the simultaneous or multicolor photometry is presented.So far, multicolor photometric studies of roAp stars are based on singlefrequencies. In this paper we propose simultaneous multicolorphotometric study on multi-mode roAp stars such as HR 1217. HR 1217 hassix modes, three of which are of comparable and large enough amplitudesto be detectable in several wavelengths. With a WET campaign on a starlike HR 1217, we could resolve the individual modes, and monitor each indifferent colors for amplitude and phase information. This study is alsowell suited for mode-identification.
| Analysis of Ten Years of APT Observations of 53 Persei
The non-radially pulsating star, 53 Persei, has been observed for thelast ten years by the Four-College Consortium Automatic PhotoelectricTelescope (APT). During the first six seasons the telescope was locatedon Mt. Hopkins in southern Arizona. For the last four seasons it hasbeen at the Fairborn Observatory in Washington Camp, Arizona. In thispaper we present a comparison of our analysis of the first six years ofdata with a separate analysis of the last four years. We have eliminatedobservations not passing various observational checks that have beendevised to eliminate APT observations obtained under non-photometricconditions. Our current data set runs from the Fall of 1990 through theSpring of 2000. Our analysis of these observations shows that the twofrequencies (0.46 c/d and 0.59 c/d) identified by Smith, et. al. (Ap. J.282, 226, 1984) and confirmed by Huang, et. al. (Ap. J. 431, 850, 1994)are present. The additional frequency at 0.47 c/d which we earlierreported (BAAS, 190, #26.04. 1997) to be a close doublet appears to be asingle term in the latter set. We find another three frequencies ( 0.57c/d, 1.055 c/d, and 0.52 c/d) present in both essentially independentdata sets. We note that the 1.05 term is the sum of the two strongestterms. Finally, the strongest frequencies show a significant (u-b) colorvariation. This work has been supported in part by NSF grants#AST86-16362, #AST91-15114, #AST95-28906, and #AST-0071260 to theCollege of Charleston.
| The observational status of the Slowly Pulsating B star iota Herculis
New spectroscopic and photometric measurements are presented concerningthe SPB binary star iota Her. Our observations are spread over 10 years,and consist of 10 spectroscopic nights in 1985, 7 spectroscopic nightsand 22 photometric nights in 1987, and 15 spectroscopic nights in 1995.In addition, we analysed the photometric observations provided byHipparcos (1990-1993) as well as all published radial velocities. Weused all the spectroscopic data to refine the binary ephemeris. It wastherefore possible to study the pulsation variability properly. Despiteour large data set, only one frequency has been clearly established: nu1=0.28671 c.d-1, for which an ephemeris isprovided. Three other frequencies are detected: nu 2=0.43c.d-1, nu 3=0.77 c.d-1 and nu4=0.2483 c.d-1. The nu 2 frequency ispresent in most data sets, nu 4 is detected only in Hipparcosdata (longtime basis of homogeneous data set), while nu 3 isdetected in only one data set. The precision on the value of nu1 allowed us to estimate the phase-lag between photometricand spectroscopic variations for the first time in an SPB star. The lagof the photometric maxima with respect to those of velocity is around0.64 period i.e., significantly different from what is measured in theclasses of variable stars surrounding the SPB stars. The pulsationamplitude has varied in a complex way during the last 10 years. It hasincreased during the 3 years of photometric observations by Hipparcos,while a decrease by a factor 2 was observed in spectroscopic databetween 1985 and 1995. Periodograms of both photometric andspectroscopic variations show faint peaks in the [6;8] c.d-1and [15;25] c.d-1 frequency regions. However, one of our datasets, providing a good precision on the velocity variations, shows arather flat periodogram after 5 c.d-1, with no detectablepeak having an amplitude above 0.05 km s-1. Therefore, theserelatively high frequencies may have a transient nature. Although iotaHer is one of the best observed SPB star, its variability behaviour isstill uncertain, and long term monitoring is needed. Partially based onobservations obtained at the Observatoire de Haute Provence
| Spatial wavelet analysis of line-profile variations
The technique of wavelet analysis is discussed in the context ofline-profile variations in rapidly rotating stars undergoing non-radialpulsation. This technique may be used to determine the harmonic degree lof the pulsation using isolated residual spectra; it is able to handlespectra with relatively low signal-to-noise ratio levels, and is wellsuited to extracting previously unobtainable information fromlow-quality, patchy data. A demonstration of the technique is presentedusing data generated from a spectral synthesis code.
| Simultaneous photometry and spectroscopy of the Be star 28 (omega) CMa - II. Line profile modelling
We analyse a series of high-resolution line profiles of He I 6678 in theperiodic Be star 28 CMa. A simple zeroth-order approximation to theeigenfunctions is used to model the line profile variations in terms ofnon-radial pulsation. In addition, we use the best available theory forthe eigenfunction in a rotating star. In all cases the calculated fitsto the observed profiles are poor. We conclude that non-radial pulsationis almost certainly not responsible for the line profile variations inthis star. In an attempt to understand the very large line profilechanges, but negligible light variation, we consider a `patch' model.This consists of a circular area on the photosphere having the sametemperature, but a different intrinsic line width. A simple model ofthis kind produces a good fit to the line profile variations and to thephotometry. We conclude that modulation of the profile by a patch on, orclose to, the photosphere may offer a plausible starting point forunderstanding the periodic variations in some Be stars.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| New observations of 53 Persei
We gathered 37 new spectra of the B star 53 Persei spread overapproximately 2 years. On these data, we performed a frequency and amode analysis. We determined the physical parameters of 53 Persei andplaced the star in the theoretical SPB instability strip. We alsoanalysed the 110 photometric observations of the Hipparcos satellite.Our results show the presence of the two frequencies often quoted in theliterature nu_1 = 0.461 c/d, nu_2 = 0.594 c/d and a third frequency nu_3= 0.471 c/d which was first proposed by Mills & Dukes (1994). It isthe first time that two studies result in the same third frequency basedon two different data sets. The mode analysis provides evidence for l_1= 1 or l_1 = 2 for the dominant mode, supporting the conclusions ofSmith & Huang (1994).
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Variable stars in astronomical research, education, and development.
Not Available
| Rotation modulation or/and pulsation in O Andromedae. I. The photometric results of an international multisite multitechnique campaign
We present the photometry of a month-long international campaign on thevariable Be star o Andromedae. Excellent time coverage and photometricprecision permit a critical comparison for the first time between thepulsational and the rotational modulation hypotheses. A multiperiodicanalysis of data taken many years apart shows sets of close frequencies.The amplitude ratio between the ultraviolet and visible variations iswhat is expected for early-type star pulsation. But, the total amplitudeand the order of importance of the frequencies is very different betweenobservation campaigns. A simple double wave periodic curve accounts formost of the light variation: a rotation/modulation model is considered,with activity variations in or just above the photosphere. Any modelmust explain the observed changes in the amplitudes of the frequencecorresponding to the period and its first harmonic. A very simple modelwith two stable photospheric activity "features" is insufficient toexplain the small variations observed around the mean values of theperiod and its light amplitude. Thus we propose that the photosphere,which is very probably oblate and seen almost equator-on, is dividedinto zonal bands undergoing differential rotation.
| 53 Persei: a slowly pulsating B star
A new investigation of the behaviour of the star 53Per was performed.New photometric observations allow to confirm two dominant periodsp_1=2.16d, p_2= 1.67d. A third one p_3= 3.64d is detected. These longperiod variations are present in our radial velocities data and in oldequivalent width data. The amplitude of the p_1 = 2.16d period increasesfrom 1977 to 1991, while the amplitude of the 1.67d period remainsconstant. Considering the observational characteristics of the starsince 1997, 53Per clearly belongs to the Slowly Pulsating B stars groupas defined by Waelkens (1991) and North & Paltani (1994).spectroscopic observations performed at the Haute Provence Observatory
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Stellar Pulsations Across the HR Diagram: Part 2
Stars over essentially the whole mass domain can become pulsationallyunstable during various stages of their evolution. They will appear asvariable stars with characteristics that are of much diagnostic value toastronomers. The analysis of such observations provides a challengingand unique approach to study aspects of the internal constitution andevolutionary status of these objects that are not accessible otherwise.This review touches on most classes of known pulsating variable starsand tries to elucidate connections to stellar physical aspects. To aidfuture investigations, we stress questions and problems that we believeare yet to be resolved satisfactorily.
| 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.
| HR1328: a cool edge "Slowly Pulsating B Star".
We report on the discovery of a photometric variability (in Stroemgren uand v filters) of HR 1328, a B8 main-sequence star. Two periods areeasily derived, of the order of 0.61d and 0.77d. From the position ofthis star in the HR diagram together with other pulsationalcharacteristics, HR 1328 can be classified as a Slowly Pulsating B star(SPB). Although these stars are found to oscillate in high-order g-modesthe relatively short pulsation periods of HR 1328 point towardslower-order g-modes in this case. Together with HD 123515, HR 1328extends and precises the observational cool edge of the SPB'sinstability strip.
| Kuhle Gasringe um heisse veranderliche Sterne. Teil 2 : Die Variationen der Be-Sterne und die Erklarung der Ringbildung.
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| Dynamic processes in Be star atmospheres. 3: Rapid multiwavelength variability in gamma Cassiopeiae
A review of the characteristics of X-ray emission from gamma Cassuggests various weaknesses with conventional scenarios that invoke Bewind interactions with a putative binary companion. To explore whetherthis emission might arise instead from sporadic high-energy events onthe Be star itself, we have examined the temporal behavior of Voyager 1FUV spectra and He I lambda 6678 line profiles. The FUV continuum lightcurves show a continuous rapid variability with a range of greater thanor = 0.2 mag over a timescale of approximately 1 hr. All indications arethat this variability is real. The difference spectrum of the inferredfluctuating component is identical to the photospheric spectrum, rulingout an origin much hotter than the star's effective temperature. Ahistogram of flux differences formed from consecutive observations showsa flat-topped distribution out to 0.2 mag. This result bears a strikingresemblance to histograms constructed from EXOSAT and Ginga data,suggesting that the X-ray and FUV variabilities could have a commonorigin. Evidence is also presented of rapid variability in opticalspectral lines associated with the stars photosphere. Time series ofdifference profiles of the lambda 6678 line confirm the existence ofmigrating subfeatures reported by earlier studies. The comoving averageof these profiles shows that these features have a shape resembling asymmetrical 'wave-packet'. Wave packets appear to be preceeded andrejuvenated by a sharp central absorption feature. We also report atransient emission feature in lambda 6678 that is similar to briefemissions once reported by Slettebak & Snow in UV resonance lineprofiles of Si IV and Mg II. We argue that the FUV and opticalvariability may find an explanation in terms of magnetic flares. Solarwhite-light flares offer a possible paradigm. However, problems remainwith such explanations, in particular their high mean energy, frequency,and temperature.
| 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 star at the frontier between p- and g-modes: ιHerculis.
Six nights have been devoted to an intensive spectroscopic study (410spectra in the Hδ domain) of the star ιHer. Our data samplingis not suitable to undertake a period determination, but none of theprevious published periods seem to be valid to represent the variationswe observe. This is certainly due to a multiperiodic phenomenon. Thanksto the short exposure time, we strongly suspect a short time scalevariability in addition to the longer periods. Therefore, two timescales would be involved, one being of the order of a day, the otherbeing of the order of an hour, this latter having a 2K-amplitude around0.8km/s, slightly varying. The short time scale is clearly detected atleast in 5 nights, and concerns all the studied lines. Thenight-to-night variations (frequency, amplitude) measured are certainlydue to the beat-modulation with the longer periods. From the pulsationtheory, the long and short time scales can respectively be attributed tohigh-order g- and p-modes. Indeed, ιHer lies in the HR diagram atthe frontier where p- and g-modes are excited due to the metal opacitybump mechanism.
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| Takýmyýldýz: | Kahraman |
| Sað Açýklýk: | 04h21m33.20s |
| Yükselim: | +46°29'56.0" |
| Görünürdeki Parlaklýk: | 4.85 |
| Uzaklýk: | 142.248 parsek |
| özdevim Sað Açýklýk: | 21.6 |
| özdevim Yükselim: | -32.7 |
| B-T magnitude: | 4.746 |
| V-T magnitude: | 4.803 |
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