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Photometric studies of three multiperiodic β Cephei stars: β CMa, 15 CMa and KZ Mus
We have carried out single and multisite photometry of the three βCephei stars β and 15 CMa as well as KZ Mus. For the two stars inCMa, we obtained 270h of measurement in the Strömgren uvy andJohnson V filters, while 150h of time-resolved Strömgren uvyphotometry was acquired for KZ Mus. All three stars are multiperiodicvariables, with three (β CMa) and four (15 CMa, KZ Mus) independentpulsation modes. Two of the mode frequencies of 15 CMa are newdiscoveries and one of the known modes showed amplitude variations overthe last 33yr. Taken together, this fully explains the diverse behaviourof the star reported in the literature.Mode identification by means of the amplitude ratios in the differentpassbands suggests one radial mode for each star. In addition, βCMa has a dominant l = 2 mode while its third mode is non-radial withunknown l. The non-radial modes of 15 CMa, which are l <= 3, form analmost equally split triplet that, if physical, would imply that we seethe star under an inclination angle larger than 55°. The strongestnon-radial mode of KZ Mus is l = 2, followed by the radial mode and adipole mode. Its weakest known mode is non-radial with unknown l,confirming previous mode identifications for the pulsations of the star.The phased light curve for the strongest mode of 15 CMa has a descendingbranch steeper than the rising branch. A stillstand phenomenon duringthe rise to maximum light is indicated. Given the low photometricamplitude of this non-radial mode this is at first sight surprising, butit can be explained by the aspect angle of the mode.
| Multiple shock waves in the atmosphere of the Cepheid X Sagittarii?
Context: .Shock waves in Cepheids have often been invoked, both fromobservational and theoretical points of view. However, classical shockwave signatures, such as emission or line doubling, have hardly beendetected. Aims: .In this paper, we suggest that our spectra of theclassical Cepheid X Sgr can be interpreted by means of the passage of 2shock waves per pulsation period. Methods: .We study new,high-resolution (120 000) spectra of X Sgr that show very complicatedpatterns within metallic lines. Results: .Spectra show up to 3components in most of the lines of the spectra during most of thepulsation cycle. These components seem to follow a pulsation motion. Inthe blue wing, the appearance of a new component is observed twice perpulsation period, which can be interpreted by 2 consecutive shock waves,one being apparently related to the classical κ-mechanism at workin these stars. The origin of the second shock is still unclear. Conclusions: .X Sgr is an exceptional Cepheid according to its observedmulti-components behaviour. Additional observations are requested inorder to establish the eventual effect of the binary orbit on thepulsation motion.
| Attempts to measure the magnetic field of the pulsating B star ν Eridani
We report on attempts to measure the magnetic field of the pulsating Bstar ν Eridani with the Musicos spectropolarimeter attached to the 2m telescope at the Pic du Midi, France. This object is one of the mostextensively studied stars for pulsation modes, and the existence of amagnetic field was suggested from the inequality of the frequencyseparations of a triplet in the stars' oscillation spectrum. We showthat the inferred 5-10 kG field was not present during our observations,which cover about one year. We discuss the influence of the strongpulsations on the analysis of the magnetic field strength and set anupper limit to the effective longitudinal field strength and to thefield strength for a dipolar configuration. We also find that theobserved wind line variability is caused by the pulsations.
| Multiperiodicity in the large-amplitude rapidly-rotating β Cephei star HD 203664
Aims.We made a seismic study of the young massive β Cephei star HD203664 with the goal of constraining its interior structure.Methods.Ourstudy is based on a time series of 328 new Geneva 7-colour photometricdata of the star spread over 496.8 days.Results.The data confirm thefrequency of the dominant mode of the star, which we refined tof_1=6.02885 c d-1. The mode has a large amplitude of 37 mmagin V and is unambiguously identified as a dipole mode (&ea;=2) from itsamplitude ratios and non-adiabatic computations. Besides f_1, wediscovered two additional new frequencies in the star with amplitudesabove 4σ: f_2=6.82902 c d-1 and f_3=4.81543 cd-1, or one of their daily aliases. The amplitudes of thesetwo modes are only between 3 and 4 mmag, which explains why they werenot detected before. Their amplitude ratios are too uncertain for modeidentification. Conclusions.We show that the observed oscillationspectrum of HD 203664 is compatible with standard stellar models butthat we have insufficient information for asteroseismic inferences.Among the large-amplitude β Cephei stars, HD 203664 stands out asthe only one rotating at a significant fraction of its critical rotationvelocity (~ 40%).
| Far-Ultraviolet and Optical Observations of BW Vulpeculae
We have compared the behavior of 39 Far-Ultraviolet SpectroscopicExplorer spectra through the pulsation cycle of the very large amplitudeβ Cephei star BW Vul with optical and UV (IUE) spectra, as well asoptical photometry. The FUSE light curve suggests a temperatureamplitude of about 4000 K, while the radial velocity curve is similar tocorresponding optical curves, except that the famous ``stillstand''feature, due to a shock wave caused by returning infall to theatmosphere from a previous cycle, is slightly weakened. We haveperformed line syntheses on a number of features in various spectralregions. We find that profiles of the red He I lines (λ6678 andλ5876) at ``faint star'' and ``bright star'' phases can besynthesized with standard Kurucz model atmospheres by assuming moderateand high microturbulences, respectively. For the faint-star profile, theline profiles are too deep to be explained other than by lowering theboundary temperature of a standard Kurucz model by 1000-2000 K. Thisresult is confirmed by line syntheses of the far-UV spectra at bothphases, which show that fits can be best achieved with models havingeffective temperatures 4000 K hotter than models fitting optical lines.This result is robust against non-LTE effects. The combined optical andfar-UV results suggest that the temperature distributions of both thelower and upper atmosphere are steeper than those computed in (static)Kurucz models. With ad hoc modifications to the atmospheric temperaturedistribution, we simulated the weakening of the temperature-sensitive CII λλ6578-6583 doublet during shock passages byintroducing a uniform shallow temperature gradient through the lineformation region. This result agrees with published hydrodynamic resultsthat these shocks produce a plateau-like elevation in gas variablesthrough the atmosphere.
| 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.
| Pulsating Stars in the ASAS-3 Database. I. beta Cephei Stars
We present results of an analysis of the ASAS-3 data for short-periodvariables from the recently published catalog of over 38000 stars. Usingthe data available in the literature we verify the results of theautomatic classification related to \beta Cep pulsators. In particular,we find that 14 stars in the catalog can be classified unambiguously asnew beta Cep stars. By means of periodogram analysis we derive thefrequencies and amplitudes of the excited modes. The main modes in thenew beta Cep stars have large semi-amplitudes, between 35 and 80 mmag.Up to four modes were found in some stars. Two (maybe three) new betaCep stars are members of southern young open clusters: ASAS164409-4719.1 belongs to NGC 6200, ASAS 164630-4701.2 is a member ofHogg 22, and ASAS 164939-4431.7 could be a member of NGC 6216.We also analyze the photometry of four known beta Cep stars in theASAS-3 catalog, namely IL Vel, NSV 24078, V1449 Aql and SY Equ. Finally,we discuss the distribution of beta Cep stars in the Galaxy.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
| Hydrodynamic models for β Cephei variables. I. BW Vulpeculae revisited
A hydrodynamical model is generated for the high-amplitude β Cepheistar BW Vulpeculae, and the spectral line profiles are calculated fordifferent pulsational phases. The pulsational characteristics and lineprofiles are compared with recent observational data obtained duringseven consecutive nights in August 2000. We found a generally goodagreement in the basic photometric and spectral parameters. Two strongshock waves appear during one period, and the ``stillstand'' is due tothe gas dynamics between the passages of these shocks. Note that thisgood agreement suppose a metallicity Z=0.03, while a metallicity Z=0.02does not lead to the correct amplitudes and shapes of the curves.
| β Cep stars from a spectroscopic point of view
In this review we present the current status of line-profile-variationstudies of β Cep stars. Such studies have been performed for 26bright members of this class of pulsating stars in the past 25 years. Wedescribe all these currently available data and summarize theinterpretations based on them in terms of the excited pulsation modes.We emphasize that line-profile variations offer a much more detailedpicture of the pulsational behaviour of pulsating stars compared toground-based photometric data. The latter, however, remain necessary tounravel the often complex frequency pattern and to achieve unambiguousmode identification for multiperiodic β Cep stars and also toderive the pulsational properties of the faint members of the class. Wehighlight the statistical properties of the sample of 26 stars for whichaccurate spectroscopic studies are available and point out some futureprospects.
| No Random Cycle-to-Cycle Period Changes in the β Cephei Star BW Vulpeculae
We show, using the formalism of Eddington & Plakidis, that thenonevolutionary period changes in the β Cephei star BW Vul are notthe result of random cycle-to-cycle period fluctuations, as they are inseveral cooler types of pulsating variables. The fractional fluctuationper cycle is less than 0.002.
| IUE observations of beta Cephei stars. Paper 2: Beta Cephei
Not Available
| Spectral response of the pulsationally induced shocks in the atmosphere of BW Vulpeculae
BW Vulpeculae (BW Vul) is remarkable for exciting an extremely strongradial pulsation mode which grows through its outer envelope and formsvisible shock features in the atmosphere. Material propelled upwards bythe shock returns violently to the lower photosphere where it creates asecond shock just before the start of the next cycle. We have obtainedthree nights of echelle data for this star over about five pulsationcycles (P= 0.201 d) in 2000 September in order to investigate theeffects of atmospheric shocks on important lines in the optical redspectrum. These lines include HeIλ5875 and λ6678,CIIλλ6578-83 doublet, and other moderate and highexcitation lines. To these data we have added 37 archival IUE/SWPechelle spectra obtained in 1994. We have investigated the equivalentwidths and shapes of the optical lines for evidence of inter alia lagsand have compared our results to the IUE fluxes extracted from thefar-ultraviolet continuum, HeIIλ1640, and several resonancelines.A comparison of HeIλ5875 and λ6678 line profiles duringthe peak of the infall activity suggests that differences in thedevelopment of a second blue lobe in the profile at this time are due toheating and a short-lived formation of an optically thin layer above theregion compressed by the infall. This discovery and the well-knowndecreases in equivalent widths of the CII doublet at the two shockphases further suggest that shock heating flattens the atmospherictemperature gradient.Except for evidence of wind absorption in the far blue wings of theultraviolet resonance lines, we find no evidence for a shock delayarriving at different photospheric strata (i.e., a `Van Hoof effect').Line-to-line differences in the relative strengths of double lobes canbe false indicators arising from varying degrees of desaturation ofmultiple lines, such as for the red HeI lines.
| Statistics of the Instability Strip of β Cephei Stars
We present a study of the β Cephei instability strip based on asample of 49 stars of this type. After deriving their effectivetemperatures and luminosities from their observed (B-V), (U-B) colorsand parallaxes we find their positions in the HR diagram to be mostlyconfined to the main sequence, and their masses to lie between 7Mȯ and 30 Mȯ. Their distribution on theHR diagram matches well with our previous theoretical instability stripwhich has an upper bound in the luminosity and rather tight boundariesin the effective temperature.
| Abundances and radial velocity analysis of BW Vulpeculae
We present the results of the analysis of 56 échelle spectra ofthe beta Cephei star BW Vulpeculae. The data were obtained during threenights with the SOFIN spectrograph at the Nordic Optical Telescope andcover a wavelength range from 3650 Å to 7340 Å. We comparethe observed spectrum with a synthetic spectrum calculated from a modelatmosphere for this star utilizing the program ATLAS9 by Kurucz. Fromthis, we determine a projected rotational velocity, v sin i, of 24 kms-1.Detailed spectral line identification and an abundance analysis for thisstar are performed. From these analyses we find that Ne, Si, He, and Arare over-abundant in BW Vulpeculae, while the abundances for N, S, O,Fe, C, and Al are solar.Finally, a comparison of radial velocity curves from six differentlayers of BW Vulpeculae's atmosphere is presented, corresponding to theformation depths of different elements. We show that at least six ofthese layers move independently from each other.Based on observations made with the Nordic Optical Telescope, operatedon the island of La Palma jointly by Denmark, Finland, Iceland, Norway,and Sweden, in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| IUE observations of beta Cephei stars. Paper 1: BW Vulpeculae
Not Available
| Short-period line profile and light variations in the Beta Cephei star 19 Monocerotis
We present an analysis of 555 high-dispersion echelle spectra of 19 Monobtained from two sites as well as 115 Strömgren uvby observations.We show that three periodicities are present at 5.22994, 0.17019 and4.88956cycled-1. The first periodicity has by far the largestamplitude. Photometric amplitude ratios and phase differences indicatean l=2 mode, while the line profile variations unequivocally point tol=2,m=-2. Because of the low amplitudes of the other two modes, verylittle can be said concerning them. Although 19 Mon was originallyselected on the basis of its classification as a marginal Be star, theBe nature of the star is not supported by our observations.
| 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.
| Influence of non-adiabatic temperature variations on line profile variations of slowly rotating beta Cephei stars and SPBs. II. Simulations of line profile time series
We investigate to what extent non-adiabatic temperature variations atthe surface of slowly rotating non-radially pulsating beta Cephei starsand slowly pulsating B stars affect silicon line profile variations. Weuse the non-adiabatic amplitudes of the effective temperature andgravity variation presented in Dupret et al. (\cite{Dupret02}), togetherwith a Kurucz intensity grid, to compute time series of line profilevariations. Our simulations point out that the line shapes do not changesignificantly due to temperature variations. We find equivalent widthvariations of at most two percent of the mean equivalent width. Weconfront our results with observational equivalent width variations andwith photometrically obtained effective temperature variations. Based onobservations obtained with the Swiss photometric telescope and with theESO/CAT telescope, at La Silla in Chile.
| Ultraviolet Spectrophotometry of Variable Early-Type Be and B Stars Derived from High-Resolution IUE Data
High-dispersion IUE data encode significant information about aggregateline absorptions that cannot be conveniently extracted from individualstellar spectra. Here we apply a new technique in which fluxes from eachechelle order of a short-wavelength IUE spectrum are binned together toconstruct low-resolution spectra of a rapidly varying B or Be star. Thedivision of binned spectra obtained during a ``bright-star'' phase byspectra from a ``faint-star'' phase leads to a ratioed spectrum thatcontains information about the mechanism responsible for a star'svariability. The most likely candidate mechanisms are either theperiodic or episodic occultations of the star by ejected matter or achange in photospheric structure, e.g., from pulsation. We model thevariations caused by these mechanism by means of model atmosphere andabsorbing-slab codes. Line absorptions strength changes are rathersensitive to physical conditions in circumstellar shells and ``clouds''at temperatures of 8000-13,000 K, which is the regime expected forcircumstellar structures of early B stars. To demonstrate proofs of thisconcept, we construct spectral ratios for circumstellar structuresassociated with flux variability in various Be stars: (1) Vela X-1 has abow-shock wind trailing its neutron star companion; at successive phasesand hence in different sectors, the wind exhibits spectrophotometricsignatures of a 13,000 or 26,000 K medium; (2) 88 Her undergoes episodic``outbursts'' during which its UV flux fades, followed a year later by adimming at visible wavelengths as well; the ratioed spectrum indicatesthe ``phase lag'' is a result of a nearly gray opacity that dominatesall wavelengths as the shell expands from the star and cools, permittingthe absorptions in the visible to ``catch up'' to those in the UV; and(3) ζ Tau and 60 Cyg exhibit periodic spectrum and flux changes,which match model absorptions for occulting clouds but are actually mosteasily seen from selective variations of various resonance lines. Inaddition, ratioed UV spectra of radial and large-amplitude nonradialpulsating stars show unique spectrophotometric signatures, which can besimulated with model atmospheres. An analysis of ratioed spectraobtained for a representative sample of 18 classical Be stars known tohave rapid periodic flux variations indicates that 13 of them haveratioed spectra that are relatively featureless or have signatures ofpulsation. Ratioed spectra of three others in the sample exhibitsignatures that are consistent with the presence of corotating clouds.
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| Observing roAp Stars with WET: A Primer
We give an extensive primer on roAp stars -- introducing them, puttingthem in context and explaining terminology and jargon, and giving athorough discussion of what is known and not known about them. Thisprovides a good understanding of the kind of science WET could extractfrom these stars. We also discuss the many potential pitfalls andproblems in high-precision photometry. Finally, we suggest a WETcampaign for the roAp star HR 1217.
| A review of the O-C method and period change.
The classical O--C curves are discussed in different cases in whichvarious period changes involved. Among them, the analytic O--C curveswith frequency, amplitude modulations and with double modes are closelyinspected, respectively. As a special, the light-time effect isillustrated. The features of period change noise and period change tometallicity are added at the end.
| Long-term period and amplitude variations in beta Cephei stars.
Not Available
| Ultraviolet and Optical Line Profile Variations in the Spectrum of ɛ Persei
The rapid variable star, ɛ Per (B0.5 IV-III), displays thelargest amplitude profile fluctuations known among the growing number ofmassive, spectrum-variable stars. Here we present an analysis of acontinuous 5 day run of IUE UV spectroscopy, and we show for the firsttime that the systematic, blue-to-red moving patterns observed inhigh-quality optical spectra are also present in the UV photosphericlines. We present cross-correlation functions of the individual spectrawith that of a narrow-lined standard that produce a high signal-to-noiseratio representation of the blue-to-red moving bump patterns found inindividual lines. We then use time series analysis methods to determinethe periodic components of the profile variations (after reregisteringthe spectra to correct for binary motion). There are at least sixperiods present (ranging from 8.46 to 2.27 hr), and most of thesesignals are also found in optical line variations observed in 1986(although the relative amplitudes have changed significantly).Furthermore, analysis of a shorter time series of IUE spectra from 1984shows that similar periods were present then. We also present Hαand He I λ6678 profiles obtained with the Georgia StateUniversity Multi-Telescope Telescope, which were made simultaneouslywith IUE, and we show that the profile variations are essentiallyidentical in the UV and optical ranges. We rule out rotationalmodulation and circumstellar gas obscuration as possible causes, and wesuggest instead that the variations are the result of photosphericnonradial pulsations of relatively low degree (l=3-5). There weresignificant changes (~10%) in the equivalent widths of the UV stellarwind lines during the IUE run, and we suggest that wind strengtheningevents are related to episodes of large-amplitude, constructiveinterference between the NRP modes. Thus, intermode beating may play animportant role in promoting wind loss from massive stars.
| Changes and Absorption Features in the Ultraviolet Spectrum of the PG 1159-Type Central Star RX J2117+3412
Comparison of IUE high- and low-dispersion spectra for the PG 1159-typecentral star of RX J2117+3412 indicates that the stellar continuum leveland some absorption features decreased between 1993 and 1995. Theseobserved changes may represent a new phenomenon not previously known tooccur in PG 1159-type DO degenerates. The definite detection of O Vlambda1371 in co-added 1993 IUE spectra suggests that T_eff for the starmay have been even higher than 170,000 K in 1993. Radial velocities andequivalent widths were measured for more than 60 photospheric andcircumstellar/interstellar features, some of which are compared withpublished data obtained from HST GHRS and IUE.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Period Changes of BW Vulpeculae: the Influence of Motion in a Binary System
This paper presents the reduced photoelectric observational data on thevariable star BW Vulpeculae obtained at Timisoara AstronomicalObservatory. Using the moments of the observed minima and others fromreferences, we computed a quadratic ephemeris describing a secularevolution. Removing the evolutionary term, from the O-C diagram, itstill remains a periodicity. Assuming this due to the light-time effectin a binary system, these residuals allowed us to compute the orbitalelements. Finally we concluded that the period variation is described bythe superposition of two separate physical effects: the evolution of thepulsating star and the orbital motion in a binary system.
| High-resolution spectroscopy of the beta Cephei stars BW Vulpeculae and gamma Pegasi
We obtained time-series high-resolution spectra of two beta Cephei stars(BW Vulpeculae and gamma Pegasi) covering several periods of theirpulsation cycle. A total of 67 stellar spectra covering the wavelengthrange from 3531 to 7039 Angstroms with a spectral resolutionlambda/Delta<~mbda 30,000 is presented.
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