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Register a new userMultisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field
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We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic beta Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign (Handler et al. 2012) and known in the literature. Using the photometric constraints on the degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for the mass (M in [8.2,9.6] M_o) and central hydrogen abundance (X_c in [0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and n_3=-2, and to derive an equatorial rotation velocity v_eq in [71,75] km s^{-1}. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (alpha_ov in [0,0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic beta Cep star theta Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.
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We report a multisite photometric campaign for the Beta Cep stars V2052 Oph and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l=4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o <beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l=3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent, light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are briefly discussed.
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, 1), (l2,m2) = (0, 0), (l3,m3) = (1, 0) and (l4,m4) = (2, 1) for f1 = 5.178964 1/d, f2 = 5.334224 1/d, f3 = 5.066316 1/d and f4 = 5.490133 1/d, respectively. Our seismic modelling shows that f2 is likely the radial first overtone and that the core overshooting parameter alpha_ov is lower than 0.4 local pressure scale heights.
Results of mode identification and seismic modelling of the $beta$ 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, $ u_1$, is most likely a pure $ell=1$ mode and the low frequency, $ u_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 complex amplitude of the bolometric flux variations, $f$, for both frequencies simultaneously. Some of these seismic models reproduce also the frequency $ u_A$, as a mode $ell= 1,$ g$_{13}$ or g$_{14}$, and its empirical values of $f$. Moreover, it was possible to find a model fitting the six 12 Lac frequencies (the first five and $ u_A$), only if the rotational splitting was calculated for a velocity of $V_{rm rot}approx 75$ km/s. In the next step, we check the effects of model atmospheres, opacity data, chemical mixture and opacity enhancement. Our results show that the OP tables are preferred and an increase of opacities in the $Z-$bump spoils the concordance of the empirical and theoretical values of $f$.
Recent BRITE-Constellation space photometry of the slowly rotating, magnetic $beta$ Cep pulsator $xi^1$ CMa permits a new analysis of its pulsation properties. Analysis of the two-colour BRITE data reveals the well-known single pulsation period of $0.209$ d, along with its first and second harmonics. A similar analysis of SMEI and TESS observations yields compatible results, with the higher precision TESS observations also revealing several low-amplitude modes with frequencies below 5 d$^{-1}$; some of these are likely $g$ modes. The phase lag between photometric and radial velocity maxima - equal to 0.334 cycles - is significantly larger than the typical value of $1/4$ observed in other large-amplitude $beta$ Cep stars. The phase lag, as well as the strong dependence of phase of maximum light on wavelength, can be reconciled with seismic models only if the dominant mode is the fundamental radial mode. We employ all published photometric and radial velocity measurements, spanning over a century, to evaluate the stability of the pulsation period. The $O-C$ diagram exhibits a clear parabolic shape consistent with a mean rate of period change $dot P=0.34pm 0.02$ s/cen. The residuals from the best-fit parabola exhibit scatter that is substantially larger than the uncertainties. In particular, dense sampling obtained during the past $sim$20 years suggests more complex and rapid period variations. Those data cannot be coherently phased with the mean rate of period change, and instead require $dot Psim0.9$ s/cen. We examine the potential contributions of binarity, stellar evolution, and stellar rotation and magnetism to understand the apparent period evolution.
We present a comprehensive seismic study of the three pulsating stars of $beta$ Cep/SPB type: $ u$ Eridani, 12 Lacertae and $gamma$ 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.
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