A new seismic analysis of Alpha Centauri

Models of alpha Cen A & B have been computed using the masses determined by Pourbaix et al. (2002) and the data derived from the spectroscopic analysis of Neuforge and Magain (1997). The seismological data obtained by Bouchy and Carrier (2001, 2002) do help improve our knowledge of the evolutionary status of the system. All the constraints are satisfied with a model which gives an age of about 6 Gyr for the binary.Comment: to be published in Astronomy and Astrophysic

An asteroseismic study of the beta Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling

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.Comment: 16 pages, 11 figures, accepted in MNRA

First HARPSpol discoveries of magnetic fields in massive stars

In the framework of the Magnetism in Massive Stars (MiMeS) project, a HARPSpol Large Program at the 3.6m-ESO telescope has recently started to collect high-resolution spectropolarimetric data of a large number of Southern massive OB stars in the field of the Galaxy and in many young clusters and associations. In this Letter, we report on the first discoveries of magnetic fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and confirm the presence of a magnetic field at the surface of HD 105382 that was previously observed with a low spectral resolution device. The longitudinal magnetic field measurements are strongly varying for HD 130807 from $\sim$-100 G to $\sim$700 G. Those of HD 122451 and HD 105382 are less variable with values ranging from $\sim$-40 to -80 G, and from $\sim$-300 to -600 G, respectively. The discovery and confirmation of three new magnetic massive stars, including at least two He-weak stars, is an important contribution to one of the MiMeS objectives: the understanding of origin of magnetic fields in massive stars and their impacts on stellar structure and evolution.Comment: 4 pages, 2 figures, accepted for publication in A&A Lette

Rotation and Convective Core Overshoot in theta Ophiuchi

(abridged) Recent work on several beta Cephei stars has succeeded in constraining both their interior rotation profile and their convective core overshoot. In particular, a recent study focusing on theta$ Oph has shown that a convective core overshoot parameter of alpha = 0.44 is required to model the observed pulsation frequencies, significantly higher than for other stars of this type. We investigate the effects of rotation and overshoot in early type main sequence pulsators, and attempt to use the low order pulsation frequencies to constrain these parameters. This will be applied to a few test models and theta Oph. We use a 2D stellar evolution code and a 2D linear adiabatic pulsation code to calculate pulsation frequencies for 9.5 Msun models. We calculate low order p-modes for models with a range of rotation rates and convective core overshoot parameters. Using these models, we find that the convective core overshoot has a larger effect on the pulsation frequencies than the rotation, except in the most rapidly rotating models considered. When the differences in radii are accounted for by scaling the frequencies, the effects of rotation diminish, but are not entirely accounted for. We find that increasing the convective core overshoot decreases the large separation, while producing a slight increase in the small separations. We created a model frequency grid which spanned several rotation rates and convective core overshoot values. Using a modified chi^2 statistic, we are able to recover the rotation velocity and core overshoot for a few test models. Finally, we discuss the case of the beta Cephei star theta Oph. Using the observed frequencies and a fixed mass and metallicity, we find a lower overshoot than previously determined, with alpha = 0.28 +/- 0.05. Our determination of the rotation rate agrees well with both previous work and observations, around 30 km/s.Comment: 10 pages, 14 figures. Accepted for publication in A&A

Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field

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.Comment: 12 pages, 6 figures and 5 tables; accepted for publication in MNRAS on 2012 August 1

Dynamical Spot Evolution in HD 11753

Our recent studies of HD 11753, a late B-type star showing a HgMn peculiarity for the first time revealed the presence of a fast dynamical evolution of chemical spots on the surface of this chemically peculiar early-type star. These observations suggest a hitherto unknown physical process operating in stars with outer radiative envelopes. Furthermore, we have also discovered existence of magnetic fields on HgMn stars that were up to now considered non-magnetic. Here we will discuss the dynamical spot evolution in HD 11753 in detail, and also summarize our new results on the magnetic fields of the AR Aur binary system

Ground-based observations of the beta Cephei CoRoT main target HD 180642: abundance analysis and mode identification

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.Comment: Accepted for publication in Astronomy and Astrophysic

Detection of gravity modes in the massive binary V380 Cyg from Kepler spacebased photometry and high-resolution spectroscopy

We report the discovery of low-amplitude gravity-mode oscillations in the massive binary star V380 Cyg, from 180 d of Kepler custom-aperture space photometry and 5 months of high-resolution high signal-to-noise spectroscopy. The new data are of unprecedented quality and allowed to improve the orbital and fundamental parameters for this binary. The orbital solution was subtracted from the photometric data and led to the detection of periodic intrinsic variability with frequencies of which some are multiples of the orbital frequency and others are not. Spectral disentangling allowed the detection of line-profile variability in the primary. With our discovery of intrinsic variability interpreted as gravity mode oscillations, V380 Cyg becomes an important laboratory for future seismic tuning of the near-core physics in massive B-type stars.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS Letter

Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite

We aim to determine the fundamental parameters of a sample of B stars with apparent visual magnitudes below 8 in the field-of-view of the CoRoT space mission, from high-resolution spectroscopy. We developed an automatic procedure for the spectroscopic analysis of B-type stars with winds, based on an extensive grid of FASTWIND model atmospheres. We use the equivalent widths and/or the line profile shapes of continuum normalized hydrogen, helium and silicon line profiles to determine the fundamental properties of these stars in an automated way. After thorough tests, both on synthetic datasets and on very high-quality, high-resolution spectra of B stars for which we already had accurate values of their physical properties from alternative analyses, we applied our method to 66 B-type stars contained in the ground-based archive of the CoRoT space mission. We discuss the statistical properties of the sample and compare them with those predicted by evolutionary models of B stars. Our spectroscopic results provide a valuable starting point for any future seismic modelling of the stars, should they be observed by CoRoT.Comment: 31 pages (including 14 pages online material), 32 figure

KIC 4768731: a bright long-period roAp star in theKeplerfield

We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1. Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr