We undertake another attempt towards seismic modelling of the most intensive studied main sequence pulsators of the early B spectral type, $ν$ Eridani. Our analysis is extended by a requirement of fitting not only pulsational frequencies but also the complex amplitude of the bolometric flux variation, $f$, related to each mode frequency. This approach, called {\it complex asteroseismology}, provides a unique test of stellar parameters, atmospheres and opacities. In particular, the concordance of the empirical and theoretical values of $f$ we obtained for the high-order g mode opens a new gate in seismic studies of the main-sequence hybrid pulsators. The most intriguing and challenging result is that whereas an agreement of the theoretical and empirical values of $f$ for the radial mode can be achieved only with the OPAL data, a preference for the OP tables is derived from the analysis of the high-order gravity mode.
MOST time-series photometry of mu Eri, an SB1 eclipsing binary with a rapidly-rotating SPB primary, is reported and analyzed. The analysis yields a number of sinusoidal terms, mainly due to the intrinsic variation of the primary, and the eclipse light-curve. New radial-velocity observations are presented and used to compute parameters of a spectroscopic orbit. Frequency analysis of the radial-velocity residuals from the spectroscopic orbital solution fails to uncover periodic variations with amplitudes greater than 2 km/s. A Rossiter-McLaughlin anomaly is detected from observations covering in…
We present a comprehensive seismic study of the three pulsating stars of $β$ Cep/SPB type: $ν$ Eridani, 12 Lacertae and $γ$ Pegasi. Models with the modified mean opacity profile are constructed in order to account for both the observed frequency range and the values of some individual frequencies. To decrease the number of possible solutions, we make use of the non-adiabatic parameter $f$, whose value is very sensitive to subphotospheric layers where pulsations are driven. This complex seismic modelling show the need for a significant modification of the opacity profile.
Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric behavior, the upper main-sequence B-type stars are assigned to different groups, such as beta Cep stars and slowly pulsating B (SPB) stars, He-rich and He-deficient Bp stars, Be stars, BpSi stars, HgMn stars, or normal B-type stars. All these groups are characterized by different magnetic field geometry and strength, from fields below the detection limit of a few Gauss up to tens of kG. Our c…
We determine the fundamental parameters of SPB and Beta Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators by comparing newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE and check for NLTE effects for the hottest stars. For comparison, we determine Teff independently from fitting the spectral energy distribution of the stars obtained from the available photometry. We determine Teff, log(g), micro-turbulent velocity, vsin(i), metallicity, and elemental abundance fo…
We report a simultaneous ground and space-based photometric study of the Beta Cephei star Nu Eridani. Half a year of observations have been obtained by four of the five satellites constituting BRITE-Constellation, supplemented with ground-based photoelectric photometry. We show that carefully combining the two data sets virtually eliminates the aliasing problem that often hampers time-series analyses. We detect 40 periodic signals intrinsic to the star in the light curves. Despite a lower detection limit we do not recover all the pressure and mixed modes previously reported in the literature, …
We present results of a search for identification of modes responsible for the six most significant frequency peaks detected in the rapidly rotating SPB star $μ$ Eridani. All published and some unpublished photometric data are used in our new analysis. The mode identification is carried out with the method developed by Daszyńska-Daszkiewicz et al. employing the phases and amplitudes from multi-band photometric data and relying on the traditional approximation for the treatment of oscillations in rotating stars. Models consistent with the observed mean parameters are considered. For the five fr…
Large-scale magnetic fields at the surface of massive stars do not only influence the outer-most layers of the star, but also have consequences for the deep interior, only observationally accessible through asteroseismology. We performed a detailed characterization of the dipolar magnetic field at the surface of the B3.5V star HD 43317, a SPB/$β$ Cep hybrid pulsator, by studying the rotationally modulated magnetic field of archival and new Narval spectropolarimetry. Additionally, we employed a grid-based approach to compare the Zeeman signatures with model profiles. By studying the rotational …
Slowly Pulsating B and $β$ Cephei are $κ$ mechanism driven pulsating B stars. That $κ$ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in the area of $\log T \approx 5.3$. Theoretical results predict very few SPBs and no $β$ Cep to be encountered in low metallicity environments such as the Small Magellanic Cloud. However recent variability surveys of B stars in the SMC reported the detection of a significant number of SPB and $β$ Cep candidates. Though the iron content plays a major role in the excitation of $β$ Cep and SPB…
Recently announced magnetic models for four SPB and β Cep stars, along with magnetic detections for two additional stars, have potentially doubled the number of known magnetic SPB and βCep stars (see Grunhut et al., these proceedings). We have reanalyzed the published data and re-reduced archival low resolution spectropolarimetry collected with the FORS1/2 instruments at VLT on which the models were based, and compare them with high resolution data from the ESPaDOnS spectropolarimeter at CFHT, investigating previously noted inconsistencies between results from the two instruments.
Results of mode identification and seismic modelling of the $β$ Cep/SBP star 12 Lacertae are presented. Using data on the multi-colour photometry and radial velocity variations, we determine or constrain the mode degree, $\ell$, for all pulsational frequencies. Including the effects of rotation, we show that the dominant frequency, $ν_1$, is most likely a pure $\ell=1$ mode and the low frequency, $ν_A$, is a dipole retrograde mode. We construct a set of seismic models which fit two pulsational frequencies corresponding to the modes $\ell= 0,$ p$_1$ and $\ell= 1,$ g$_1$ and reproduce also the c…
$ν$ Eridani is a well known multiperiodic $β$ Cephei pulsator which exhibits also the SPB (Slowly Pulsating B-type stars) type modes. Recent frequency analysis of the BRITE photometry of $α$ Lupi showed that the star is also a hybrid $β$ Cep/SPB pulsator, in which both high and low frequencies were detected. We construct complex seismic models in order to account for the observed frequency range, the values of the frequencies themselves and the non-adiabatic parameter $f$ for the dominant mode. Our studies suggest, that significant modifications of the opacity profile at the temperature range …
Since the early nineties it is accepted that the excitation mechanism of B-type pulsators on the main sequence is due to the opacity peak in the iron-group elements at $T\approx 200,000$ K. The Fe content plays then a major role in the excitation of $β$ Cep and SPB pulsations. While theoretical non-adiabatic computations predict no $β$ Cep pulsators and only a small number of SPBs for low metallicity environments such as that of the Magellanic Clouds (MCs), recent variability surveys of B stars in the SMC have reported the detection of a significant number of SPB and $β$ Cep candidates. Since …
We used Johnson UBV photometric CCD observations to identify pulsating and other variable stars in the young open cluster NGC 6231. The multi-color information was used to classify pulsating variables, perform frequency analysis, and - where possible - to compare observed to theoretical amplitude ratios for mode identification. The data reduction was performed with standard IRAF tools. Differential light curves have been obtained by identifying a set of suitable comparison stars and the frequency analysis was then conducted on the basis of Fourier methods. Our classification of pulsating stars…
We present the results of a spectroscopic multisite campaign for the beta Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with 8 different telescopes in a time span of 11 months. In addition we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the SPB-like g-mode with frequency 0.3428 1/d reported before is detected in our spectroscopy. We identify the four main modes as (l1,m1) = (1,…
We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid Beta Cep/SPB pulsator Gamma Peg. Frequency analyses reveal the presence of six g modes of high radial order together with eight low-order Beta Cep oscillations in both data sets. Mode identification shows that all pulsations have spherical degrees l = 0 - 2. An 8.5 solar mass model reproduces the observed pulsation frequencies; all theoretically predicted modes are detected. We suggest, contrary to previous authors, that Gamma Peg is a single star; the claimed orbital variations are due to …
We carried out a multi-colour time-series photometric study of six stars claimed as "hybrid" p and g mode pulsators in the literature. Gamma Peg was confirmed to show short-period oscillations of the Beta Cep type and simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars. From the measured amplitude ratios in the Stromgren uvy passbands, the stronger of the two short period pulsation modes was identified as radial; the second is l=1. Three of the four SPB-type modes are most likely l=1 or 2. Comparison with theoretical model calculations suggests that Gamma Peg is eithe…
We present the results of complex seismic modelling of the Slowly Pulsating B-type star HD74560. The star pulsates in five frequencies detected in photometric observations. For all these frequencies, we identify the mode degree, $\ell$. For two of them, found also in spectroscopic data, we are able to derived the empirical values of the complex nonadiabatic parameter $f$. We test effects of chemical composition and opacity data. Our results show that the properties of seismic models of SPB stars differ significantly from those of the more massive $β$ Cephei stars.
Asteroseismology offers the possibility of probing stellar interiors and testing evolutionary and seismic models. Precise photometry and spectroscopy obtained during multi-site campaigns on young open clusters allows discovering rich samples of pulsating stars and using them in a simultaneous seismic modelling called ensemble asteroseismology. The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, perfor…
We study the energetic aspects of hybrid pressure-gravity modes pulsations. The case of hybrid beta Cephei-SPB pulsators is considered with special attention. In addition to the already known sensitivity of the driving mechanism to the heavy elements mixture (mainly the iron abundance), we show that the characteristics of the propagation and evanescent regions play also a major role, determining the extension of the stable gap in the frequency domain between the unstable low order pressure and high order gravity modes. Finally, we consider the case of hybrid delta Sct-gamma Dor pulsators.
We propose to observe with Kepler an age sequence of nearby uncrowded open clusters. The current Kepler field contains very few (only 4) somewhat distant and/or old clusters. Nearby open clusters are already well characterized from ground- and many space-based observations. Our proposal focuses on mid and upper main-sequence variables (main sequence and pre-main sequence gamma Dor or delta Scuti stars, SPB/beta Cep stars, Cepheids, or yellow supergiants), having periods of hours to days accessible by longer cadence observations. Asteroseismology for these objects to date is limited by the numb…
Massive stars are important for the chemical enrichment of the universe. Since internal mixing processes influence their lives, it is very important to place constraints on the corresponding physical parameters, such as core overshooting and the internal rotation profile, so as to calibrate their stellar structure and evolution models. Although asteroseismology has been shown to be able to deliver the most precise constraints so far, the number of detailed seismic studies delivering quantitative results is limited. Our goal is to extend this limited sample with an in-depth case study and provi…
We analyse time-series observations from the BRITE-Constellation of the well known $β$ Cephei type star $θ$ Ophiuchi. Seven previously known frequencies were confirmed and nineteen new frequency peaks were detected. In particular, high-order g modes, typical for the SPB (Slowly Pulsating B-type star) pulsators, are uncovered. These low-frequency modes are also obtained from the 7-year SMEI light curve. If g modes are associated with the primary component of $θ$ Oph, then our discovery allows, as in the case of other hybrid pulsators, to infer more comprehensive information on the internal stru…
Context: OB stars are important in the chemistry and evolution of the Universe, but the sample of targets well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models. Our study extends this sample with two spectroscopic binary systems. AIMS. Our goal is to provide orbital solutions, fundamental parameters and abundances from disentangled high-resolution high signal-to-noise spectra, as well as to analyse and interpret the variations in the Kepler light curve of these carefully selected targets. This way we continue our e…
