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Register a new userAsteroseismology of the Beta Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification
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We report a multisite photometric campaign for the Beta Cephei star 12 Lacertae. 750 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with 9 telescopes during 190 nights. Our frequency analysis results in the detection of 23 sinusoidal signals in the light curves. Eleven of those correspond to independent pulsation modes, and the remainder are combination frequencies. We find some slow aperiodic variability such as that seemingly present in several Beta Cephei stars. We perform mode identification from our colour photometry, derive the spherical degree l for the five strongest modes unambiguously and provide constraints on l for the weaker modes. We find a mixture of modes of 0 <= l <= 4. In particular, we prove that the previously suspected rotationally split triplet within the modes of 12 Lac consists of modes of different l; their equal frequency splitting must thus be accidental. One of the periodic signals we detected in the light curves is argued to be a linearly stable mode excited to visible amplitude by nonlinear mode coupling via a 2:1 resonance. We also find a low-frequency signal in the light variations whose physical nature is unclear; it could be a parent or daughter mode resonantly coupled. The remaining combination frequencies are consistent with simple light-curve distortions. The range of excited pulsation frequencies of 12 Lac may be sufficiently large that it cannot be reproduced by standard models. We suspect that the star has a larger metal abundance in the pulsational driving zone, a hypothesis also capable of explaining the presence of Beta Cephei stars in the LMC.
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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 $f$.
The known beta Cephei star HD 180642 was observed by the CoRoT satellite in 2007. From the very high-precision light curve, its pulsation frequency spectrum could be derived for the first time (Degroote and collaborators). In this paper, we obtain additional constraints for forthcoming asteroseismic modeling of the target. Our results are based on both extensive ground-based multicolour photometry and high-resolution spectroscopy. We determine T_eff = 24 500+-1000 K and log g = 3.45+-0.15 dex from spectroscopy. The derived chemical abundances are consistent with those for B stars in the solar neighbourhood, except for a mild nitrogen excess. A metallicity Z = 0.0099+-0.0016 is obtained. Three modes are detected in photometry. The degree l is unambiguously identified for two of them: l = 0 and l = 3 for the frequencies 5.48694 1/d and 0.30818 1/d, respectively. The radial mode is non-linear and highly dominant with an amplitude in the U-filter about 15 times larger than the strongest of the other modes. For the third frequency of 7.36673 1/d found in photometry, two possibilities remain: l = 0 or 3. In the radial velocities, the dominant radial mode presents a so-called stillstand but no clear evidence of the existence of shocks is observed. Four low-amplitude modes are found in spectroscopy and one of them, with frequency 8.4079 1/d, is identified as (l,m)=(3,2). Based on this mode identification, we finally deduce an equatorial rotational velocity of 38+-15 km/s.
We present the mode identification of frequencies found in spectroscopic observations of the Gamma Doradus star HD135825. Four frequencies were successfully identified: 1.3150 +/- 0.0003 1/d; 0.2902 +/- 0.0004 1/d; 1.4045 +/- 0.0005 1/d; and 1.8829 +/- 0.0005 1/d. These correspond to (l, m) modes of (1,1), (2,-2), (4,0) and (1,1) respectively. Additional frequencies were found but they were below the signal-to-noise limit of the Fourier spectrum and not suitable for mode identification. The rotational axis inclination and vsini of the star were determined to be 87 degrees (nearly edge-on) and 39.7 km/s (moderate for Gamma Doradus stars) respectively. A simultaneous fit of these four modes to the line profile variations in the data gives a reduced chi square of 12.7. We confirm, based on the frequencies found, that HD135825 is a bona fide Gamma Doradus star.
The prototype star for the {gamma} Doradus class of pulsating variables was studied em- ploying photometric and spectroscopic observations to determine the frequencies and modes of pulsation. The four frequencies found were self-consistent between the obser- vation types and almost identical to those found in previous studies (1.3641 d-1 ,1.8783 d-1 , 1.4742 d-1 and 1.3209 d-1). Three of the frequencies are classified as l, m = (1, 1) pulsations and the other is ambiguous between l = 2 modes. Two frequencies are shown to be stable over twenty years since their first identification. The agreement in ground-based work makes this star an excellent calibrator for the upcoming TESS observations and a standard for continued asteroseismic modelling.
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