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With its imaged debris disk of dust, its evaporating exocomets, and an imaged giant planet, the young (~23 Myr) β Pictoris system is a unique proxy for detailed studies of planet formation processes as well as planet–disk interactions. Here, we study ten years of European Southern Observatory/High Accuracy Radial Velocity Planet Searcher (HARPS) high-resolution spectroscopic data of β Pictoris. After removing the radial velocity (RV) signals arising from the δ Scuti pulsations of the star, a ~1,200-d periodic signal remains, which, within our current knowledge, we can only attribute to a second planet in the system. The β Pic c mass is about nine times the mass of Jupiter; it orbits at ~2.7 au on an eccentric (e ~ 0.24) orbit. More RV data are needed to obtain more precise estimates of the properties of β Pic c. The current modelling of the planet’s properties and the dynamic of the whole system has to be reinvestigated in light of this detection. Radial velocity data of the young β Pictoris system acquired by HARPS and spanning 15 years show evidence of β Pic c, a gas giant of ~9 Jupiter masses orbiting on an eccentric orbit at ~2.4 au from the star, near the theoretical snowline. Both β Pic b and c, located close to the star, may have formed in situ by core accretion. more...

Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec$^{-2}$ in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric $67.1\pm4.2$ % of the time and veiled $21.8\pm2.0$ % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of $\sigma$ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general., Comment: 23 pages, 23 figures, A&A in press more...

We used the large photometric database of the ASTEP program, whose primary goal was to detect exoplanets in the southern hemisphere from Antarctica, to search for eclipsing binaries (EcBs) and variable stars. 673 EcBs and 1166 variable stars were detected, including 31 previously known stars. The resulting online catalogs give the identification, the classification, the period, and the depth or semi-amplitude of each star. Data and light curves for each object are available at http://astep-vo.oca.eu. more...

We present the analysis of the CoRoT star 105288363, a new Blazhko RR Lyrae star of type RRab (f0 = 1.7623 c/d), observed with the CoRoT space craft during the second long run in direction of the galactic center (LRc02, time base 145 d). The CoRoT data are characterized by an excellent time sampling and a low noise amplitude of 0.07 mmag in the 2-12 c/d range and allow us to study not only the fine details of the variability of the star but also long-term changes in the pulsation behaviour and the stability of the Blazhko cycle. We use, among other methods, standard Fourier analysis techniques and O-C diagrams to investigate the pulsational behavior of the Blazhko star 105288363. In addition to the frequency pattern expected for a Blazhko RR Lyrae star, we find an independent mode (f1 = 2.984 c/d) showing a f0/f1 ratio of 0.59 which is similar to that observed in other Blazhko RR Lyrae stars. The bump and hump phenomena are also analysed, with their variations over the Blazhko cycle. We carefully investigated the strong cycle-to-cycle changes in the Blazhko modulation (PB = 35.6 d), which seem to happen independently and partly diametrically in the amplitude and the phase modulation. Furthermore, the phasing between the two types of modulation is found to change during the course of the observations. more...

Context. HD 49434 is a bright (V = 5ṃ75) and multiperiodic γ Dor-type pulsator that has been selected for the asteroseismic core programme of the CoRoT satellite.Aims. An extensive and detailed study has been carried out to investigate the pulsational content of this object on the basis of the 136.9 d (331291 useful datapoints) time series collected by the CoRoT satellite during the long-run LRa01 (October 2007–March 2008).Methods. The frequency analysis was carried out using the recently available software package SigSpec and Period04.Results. The results confirm HD 49434 as a complex pulsator with a very dense pulsation spectrum. A total of 1686 significant peaks are formally detected, essentially in the region below 15 d-1 . No significant pulsation peaks are detected for frequencies higher than 30 d-1 . Solar-type oscillations are not detected in this star. The reliability of such a high number of detected peaks has been investigated on the basis of two independent methods. As a result, we propose a total of 840 frequencies that can be assumed to be intrinsic to the star. Conclusions. The CoRoT mission provides very high-quality light curves and datasets, which are excellent for asteroseismic studies of complex pulsating stars beacause they allow investigation of the frequency content down to amplitude levels of a few μ mag, unattainable with ground-based observations. In this way, hundreds of excited modes were detected in HD 49434. This is the first time that so many frequencies have been found in a γ Dor-type pulsator. more...

Context: We present the results of an extensive ground-based photometric and spectroscopic campaign on the gamma Dor CoRoT target HD49434. This campaign was preparatory to the CoRoT satellite observations, which took place from October 2007 to March 2008. Results: The frequency analysis clearly shows the presence of four frequencies in the 0.2-1.7 c/d interval, as well as six frequencies in the 5-12 c/d domain. The low frequencies are typical for gamma Dor variables while the high frequencies are common for delta Sct pulsators. We propose the frequency 2.666 c/d as a possible rotational frequency. All modes, for which an identification was possible, seem to be high-degree modes (3, 15 pages, 10 figures, 9 tables accepted for publication in Astronomy and Astrophysics more...

Context. We perform a new spectroscopy of RR Lyrae to gain an understanding of the Blazhko effect. The Blazhko effect is a periodic amplitude and/or phase modulation shown by some RR Lyrae stars. Aims. New high precision spectroscopic observations of RR Lyrae, the brightest Blazhko star, were obtained continuously over an entire Blazhko period (41 days), from June to August 2000. This data set allows for a detailed analysis. Methods. We used Fourier techniques to analyze the metallic absorption line–profile variations over the pulsation and the Blazhko cycle. Results. This data set shows a triplet frequency structure with a large asymmetry in the modulation amplitudes. The right sidepeak amplitudes are higher than those on the left, and there is a linear decrease of the amplitudes of both right and left modulation components. The new data reveal that there is a very narrow interval in the pulsation cycle, 20% of the pulsation period, in which the modulation shows intense variations. The interval occurs during the phase of the main shock passage across the atmosphere of RR Lyrae. We detected no evidence whatsoever of a quintuplet structure within a median 1 σ radial velocity uncertainty of 250 m/s. Our spectroscopic results make it more difficult to explain the Blazhko phenomenon with the current resonance models, which are the only theoretical models available that explain the Blazhko phenomenon, and give new insight for future Blazhko theoretical investigations. more...

We present high resolution spectroscopic observations of the γ Doradus star HD 195068. About 230 spectra were collected over 2 years. Time series analysis performed on radial velocity data shows a main peak at 1.61 d -1 , a frequency not yet detected in photometry. The Hipparcos photometric 1.25 d -1 frequency is easily recovered as is 1.30 d -1 while the third photometric frequency, 0.97 d -1 , is only marginally present. The good quality of our data, which includes 196 spectra collected over seven consecutive nights, shows that both the 1.61 d -1 and intermediate 1.27 d -1 (mixture of 1.25 and 1.30 d -1 ) frequencies are present in the line profile variations. Using the Fourier-Doppler Imaging (FDI) method, the variability associated with 1.61 d -1 can be successfully modeled by a non-radial pulsation mode $\ell=5\pm 1$, $|m|=4\pm 1$. For the intermediate frequency 1.27 d -1 we deduce $\ell=4\pm 1$, $|m|=3\pm 1$. Evidence that the star is not pulsating in the radial mode ($\ell=0$) rules out a previous classification as an RR Lyrae type star. We investigate the time variability of FDI power spectra concluding that the observed temporal variability of modes can be explained by a beating phenomenon between closely spaced frequencies of two non-radial modes. The distribution of the oscillation power within the line profile indicates that there is a significant tangential velocity component of oscillations characteristic of high radial order gravity modes which are predicted to be observed in γ Doradus type stars. more...

High resolution and high signal to noise ratio spectroscopic observations of the classical β Cephei star γ Peg were obtained between 1991 and 2005. The analysis of these data combined with previously published results shows that γ Peg is a spectroscopic binary with an orbital period of 370.5 d. We discovered three new frequencies in addition to the well-known 6.5897 d -1 (0.15175 d) one. That at 6.01 d -1 is a typical β Cephei frequency. The two others at 0.68 and 0.87 d -1 are similar to the high degree g -mode frequencies found in SPB stars. Thus, γ Peg is a hybrid β Cephei-SPB star. Its position in the HR diagram is compatible with such a status. In addition, a small increase of the main period has been detected between the 1995 and 2005 observations. more...

We present spectroscopic and photometric observations of the star HD 173977. It appears that the star is part of a double line binary system, with a period of 1.801 d, corresponding to twice the period of the photometric variations. Hence the star is an ellipsoidal variable. The system is probably synchronized. The physical parameters of both components were derived through two independant methods, one based on evolutionary tracks, the other being the result of the behaviour of light curves in a close binary system. After removing the ellipsoidal variations, 3 frequencies are detected in the photometric data: 8.56, 14.51 and 16.42 d -1 , while 2 additional frequencies are also possible: 10.96 and 12.11 d -1 . In accordance with its position in the HR diagram, the primary component of HD 173977 should be considered as a δ Scuti star and no longer as a γ Doradus star. In addition, HD 173844, used as a check star, is discovered variable with a 15.79 d -1 frequency and is classified as a δ Scuti star. more...

From new photometric observations ( UBVRI ), we present the characteristic features of the light variations of the evolved star HD 179821 (= SAO 124414 = IRAS 19114+0002). Our data, collected through 1999 and 2000, have been combined together with previous photometric measurements available in the literature. Thus, a long term V -light curve (gathering more than 10 years of observations for HD 179821) has been composed. We have analysed it with the Fourier transform method. Two main frequencies are present in the resulting power spectrum, reflecting a dominant bimodal pulsator behavior. A long term phenomenon is also found, but it is not possible to decide whether it is periodic. The Fourier analysis has also been applied on two other filters ( U and B ) and confirms the detected frequencies. On the basis of our period analysis, we discuss the nature of HD 179821: low-mass post-AGB star or high-mass star. more...

The study of RR Lyrae stars has recently been invigorated thanks to the long, uninterrupted, ultra-precise time series data provided by the Kepler and CoRoT space telescopes. We give a brief overview of the new observational findings concentrating on the connection between period doubling and the Blazhko modulation, and the omnipresence of additional periodicities in all RR Lyrae subtypes, except for non-modulated RRab stars. Recent theoretical results demonstrate that if more than two modes are present in a nonlinear dynamical system such as a high-amplitude RR Lyrae star, the outcome is often an extremely intricate dynamical state. Thus, based on these discoveries, an underlying picture of complex dynamical interactions between modes is emerging which sheds new light on the century-old Blazhko-phenomenon, as well. New directions of theoretical efforts, like multi-dimensional hydrodynamical simulations, future space photometric missions and detailed spectroscopic investigations will pave the way towards a more complete understanding of the atmospheric and pulsation dynamics of these enigmatic touchstone objects., Proceedings of the CoRoT Symposium 3 / Kepler KASC-7 joint meeting, Toulouse, July 2014. To be published by EPJ Web of Conferences more...

Aims. The Antarctica Search for Transiting Extrasolar Planets (ASTEP), an automatized 400 mm telescope located at Concordia station in Antarctica, monitored β Pictoris continuously to detect any variability linked to the transit of the Hill sphere of its planet β Pictoris b. The long observation sequence, from March to September 2017, combined with the quality and high level duty cycle of our data, enables us to detect and analyse the δ Scuti pulsations of the star.Methods. Time series photometric data were obtained using aperture photometry by telescope defocussing. The 66 418 data points were analysed using the software package Period04. We only selected frequencies with amplitudes that exceed four times the local noise level in the amplitude spectrum.Results. We detect 31 δ Scuti pulsation frequencies, 28 of which are new detections. All the frequencies detected are in the interval 34.76−75.68 d-1 . We also find that β Pictoris exhibits at least one pulsation mode that varies in amplitude over our monitoring duration of seven months. more...

New spectroscopic observations of the star 53 Psc are presented. A correlation technique has been used to derive the radial velocity curves with a high accuracy. Four frequencies have been detected in the radial velocity variations using four frequency analysis algorithms. Three frequencies (1.81, 1.22 and 1.57 cd 1 )a re typical SPB star frequencies, the last one being close to our detection threshold. They are associated to low amplitude velocities, of the order of 1{2 km s 1 . So we classify 53 Psc in the SPBs class in agreement with its position in the HR diagram. Line equivalent width and central depth variations are also observed. Two phenomena appear: rst, a smooth variation, present in all lines with a time scale of 10 days, could be related to the stellar rotation and a magnetic eld. Second, on two consecutive nights, a sudden and important increase (20%) of equivalent widths and central depths of H and He i lines could be due to an outburst similar to the ones present in some Be stars. The variation in the equivalent widths is mainly due to the increase of the central depth of the quoted lines. This suggests the existence of NLTE eects due to a hot low density plasma in the upper layers of the atmosphere of 53 Psc. An additional frequency is pointed out around 0.11 cd 1 . The best interpretation is more...

We initiated long-term optical interferometry monitoring of the diameters of unstable yellow hypergiants (YHG) with the goal of detecting both the long-term evolution of their radius and shorter term formation related to large mass-loss events. We observed HR5171 A with AMBER/VLTI. We also examined archival photometric data in the visual and near-IR spanning more than 60 years, as well as sparse spectroscopic data. HR5171A exhibits a complex appearance. Our AMBER data reveal a surprisingly large star for a YHG R*=1315+/-260Rsun\ (~6.1AU) at the distance of 3.6+/-0.5kpc. The source is surrounded by an extended nebulosity, and these data also show a large level of asymmetry in the brightness distribution of the system, which we attribute to a newly discovered companion star located in front of the primary star. The companion's signature is also detected in the visual photometry, which indicates an orbital period of Porb=1304+/-6d. Modeling the light curve with the NIGHTFALL program provides clear evidence that the system is a contact or possibly over-contact eclipsing binary. A total current system mass of 39^{+40}_{-22} solar mass and a high mass ratio q>10 is inferred for the system. The low-mass companion of HR5171 A is very close to the primary star that is embedded within its dense wind. Tight constraints on the inclination and vsini of the primary are lacking, which prevents us from determining its influence precisely on the mass-loss phenomenon, but the system is probably experiencing a wind Roche-Lobe overflow. Depending on the amount of angular momentum that can be transferred to the stellar envelope, HR5171 A may become a fast-rotating B[e]/Luminous Blue Variable (LBV)/Wolf-Rayet star. In any case, HR5171 A highlights the possible importance of binaries for interpreting the unstable YHGs and for massive star evolution in general., Accepted in Astronomy & Astrophysics (Jan 2014) more...

High-resolution spectroscopy of pulsating stars is a powerful tool to study the dynamical structure of their atmosphere. Lines asymmetry is used to derive the center-of-mass velocity of the star, while a direct measurement of the atmospheric velocity gradient helps determine the projection factor used in the Baade-Wesselink method of distance determination. We aim at deriving the center-of-mass velocity and the projection factor of the beta-Cephei star alpha-Lup. We present HARPS high spectral resolution observations of alpha-Lup. We calculate the first-moment radial velocities and fit the spectral line profiles by a bi-Gaussian to derive line asymmetries. Correlations between the gamma-velocity and the gamma-asymmetry (defined as the average values of the radial velocity and line asymmetry curves respectively) are used to derive the center-of-mass velocity of the star. By combining our spectroscopic determination of the atmospheric velocity gradient with a hydrodynamical modelof the photosphere of the star, we derive a semi-theoretical projection factor for alpha Lup. We find a center-of-mass velocity of Vgamma = 7.9 +/- 0.6 km/s and that the velocity gradient in the atmosphere of alpha Lup isnull. We apply to alpha Lup the usual decomposition of the projection factor into three parts, p = p0 fgrad fog (originally developed for Cepheids), and derive a projection factor of p = 1.43 +/-0.01. By comparing our results with previous HARPS observations of classical Cepheids, we also point out a linear relation between the atmospheric velocity gradient and the amplitude of the radial velocity curve. Moreover, we observe a phase shift (Van Hoof effect), whereas alpha Lup has no velocity gradient., 10 pages, 9 figures more...

The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars. We propose three main groups to describe the observed variety in pulsating A-F type stars: gamma Dor, delta Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much larger fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the gamma Dor and delta Sct range, also between 5 and 10 c/d, which is a challenge for the current models. We find indications for the existence of delta Sct and gamma Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the delta Sct and gamma Dor instability strips, and beyond. Non-variable stars seem to exist within the instability strips. The location of gamma Dor and delta Sct classes in the (Teff,logg)-diagram has been extended. We investigate two newly constructed variables 'efficiency' and 'energy' as a means to explore the relation between gamma Dor and delta Sct stars. Our results suggest a revision of the current observational instability strips, and imply an investigation of other pulsation mechanisms to supplement the kappa mechanism and convective blocking effect to drive hybrid pulsations., Accepted for publication in Astronomy and Astrophysics (language edited version). 70 pages, 4 tables, 13 figures. The tables can be found as an appendix to the paper. The quality of the figures has been downgraded compared to the original more...

The star CoRoT102781750 reveals a puzzle, showing a very complex and altering variation in different `CoRoT colours'. We established without doubt that more than a single star was situated within the CoRoT mask. Using a search for periodicity as a tool, our aim is to disentangle the composite light curve and identify the type of sources behind the variability. Both flux and magnitude light curves were used. Conversion was applied after a jump- and trend-filtering algorithm. We applied different types of period-finding techniques including MuFrAn and Period04. The amplitude and phase peculiarities obtained from the independent analysis of CoRoT r, g, and b colours and ground-based follow-up photometric observations ruled out the possibility of either a background monoperiodic or a Blazhko type RR Lyrae star being in the mask. The main target, an active star, shows at least two spotted areas that reveal a $P_rot = 8.8$ hours $(f_0 = 2.735$ c d$^{-1})$ mean rotation period. The evolution of the active regions helped to derive a period change of $dP/dt = 1.6\cdot 10^{-6}$ (18 s over the run) and a differential rotation of $\alpha = \Delta\Omega/\Omega = 0.0074$. The $0\fm 015$ linear decrease and a local $0\fm 005$ increase in the dominant period's amplitude are interpreted as a decay of the old spotted region and an appearance of a new one, respectively. A star that is detected only in the CoRoT b domain shows a $f_1 = 7.172$ c d$^{-1}$ pulsation connected to a $14\fd 83$ periodicity via an equidistant triplet structure. The best explanation for our observation is a $\beta$ Cep star with a corotating dust disk., Comment: 12 pages, 10 figures, abstract truncated. (For better availability.) more...

High-precision interferometric measurements of pulsating stars help to characterize their close environment. In 1974, a close companion was discovered around the pulsating star beta Cep using the speckle interferometry technique and features at the limit of resolution (20 milli-arcsecond or mas) of the instrument were mentioned that may be due to circumstellar material. Beta Cep has a magnetic field that might be responsible for a spherical shell or ring-like structure around the star as described by the MHD models. Using the visible recombiner VEGA installed on the CHARA long-baseline interferometer at Mt. Wilson, we aim to determine the angular diameter of beta Cep and resolve its close environment with a spatial resolution up to 1 mas level. Medium spectral resolution (R=6000) observations of beta Cep were secured with the VEGA instrument over the years 2008 and 2009. These observations were performed with the S1S2 (30m) and W1W2 (100m) baselines of the array. We investigated several models to reproduce our observations. A large-scale structure of a few mas is clearly detected around the star with a typical flux relative contribution of 0.23 +- 0.02. Our best model is a co-rotational geometrical thin ring around the star as predicted by magnetically-confined wind shock models. The ring inner diameter is 8.2 +- 0.8 mas and the width is 0.6 +- 0.7 mas. The orientation of the rotation axis on the plane of the sky is PA = 60 +- 1 deg, while the best fit of the mean angular diameter of beta Cep gives UD[V] = 0.22 +- 0.05 mas. Our data are compatible with the predicted position of the close companion of beta Cep. These results bring additional constraints on the fundamental parameters and on the future MHD and asteroseismological models of the star., Comment: Paper accepted for publication in A&A (in press) more...

International audience; Context. The CoRoT - Convection Rotation and planetary Transits - space mission is a great opportunity for monitoring stars with excellent time-sampling and unprecedented photometric precision for up to 150 days. As an important benefit, high-quality RR Lyrae light curves are obtained with a quasi-uninterrupted coverage over several pulsation and Blazhko cycles. Aims: The Blazhko effect in RR Lyrae stars is an unsolved problem of astrophysics. We used the high-precision space data to contribute more precise knowledge to explain the possible physical processes behind the phenomenon. Methods: We applied different period-finding techniques including Period04, MuFrAn, PDM and SigSpec. Amplitude and phase modulation were investigated by an analytical function method as well as with the traditional O-C diagrams. Results: The Blazhko modulation frequency is directly detected in the spectrum, as well as its first and second harmonics. It shows the non-linear nature of the Blazhko modulation. Besides the triplets, further higher-order modulation side peaks appear around the pulsation frequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet structures. Additional frequencies, not belonging to the classical multiplet structures, are detected, as well as their linear combinations with the fundamental radial mode. We interpret these additional terms as non-radial modes. During the five consecutive Blazhko cycles, there is a shift of the maximum phase around 0.011 pulsation phase which is likely the consequence of a long term modulation. more...

We present here preliminary results concerning 32 stars identified as main gamma Doradus candidates by the COROT Variable Classifier (CVC) among the 4 first fields of the exoplanet CCDs., To appear in "Stellar Pulsation: Challenges for Theory and Observation", AIP more...

The bump, a manifestation of a shock wave on the descending branch or around minimum, is a very remarkable feature of certain monoperiodic RR Lyrae stars. Excellent theoretical identification, as one of the three shock waves, is given by Fokin et al. [5]. The CoRoT Space telescope supports us with incredibly high precision datasets. They allow us to carry out investigations that have never been possible before. Using a 152‐day long CoRoT dataset we are able to divide it not only into shorter subsets (check for short‐term variability) but into segments according to the remarkable features of the light curve.EN2_STAR_MON_0101370131 is a monoperiodic, non‐Blazhko CoRoT RR Lyrae star of the first long run with a very definite bump on the lower part of the descending branch. The light curve is nicely fitted by the pulsation period and its 33 harmonics. The harmonics are highly needed to describe the descending branch. A definite question was addressed to the dataset: can we connect certain harmonics to the spe... more...

We present a method, based on the phase coherence, which is efficient to estimate the reliability of the large number of frequencies found in CoRoT stars.

PAIX (Photometer AntarctIca eXtinction) is an extended programme monitoring the Blazhko circumpolar stars from one of the highest Antarctica plateau, Dome C (3300 m), using a multi‐color photometer attached at the focus of a 40 cm Ritchey‐Chretien telescope installed during the polar summer 2006. Several high quality RRLyrae light curves are obtained with a quasi‐uninterrupted time coverage over several pulsation and Blazhko cycles. Here, we present the first time series photometry from Dome C obtained on S Ara and during the 2007 polar night, from June to August 2007. Our results show that S Arae is “bona fide” a Blazhko star with strong nonlinearity and triplet structure. New phenomenological descriptions of the light curve variation are reported giving new insight for future Blazhko theoretical investigations and a unique opportunity to cope with the hydrodynamical challenge in connection with the radial pulsation. We conclude that high‐precision CCD photometry with exceptional time coverage can be undertaken at Dome C in order to successfully gain an understanding of the Blazhko effect. more...

In this paper we report on new RR Lyrae stars discovered in the first long run fields (LRc01 and LRa01) of the CoRoT mission. CoRoT frequency analysis of the high quality light curve with an unprecedented photometric accuracy and uninterrupted coverage over long period (∼150 days) are shown. The CoRoT results reveal four of the seven stars affected with the Blazhko effect and showing a very high fraction of the Blazhko stars ever obtained. The CoRoT RRLyrae stars show pulsation periods strongly nonlinear and complex multiplet structures, such as the triplet, quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet frequency structures. Additional frequencies are detected as well with a linear combination with the fundamental radial mode, showing a strong evidence for direct detections of nonradial pulsations. We put into evidence new classes of RR Lyrae stars showing the Blazhko double mode RR Lyrae stars (fundamental and second overtone), nonradial and radial (multimodes) pu... more...

A hydrodynamical model is generated for the high-amplitude β Cephei star BW Vulpeculae, and the spectral line profiles are calculated for different pulsational phases. The pulsational characteristics and line profiles are compared with recent observational data obtained during seven consecutive nights in August 2000. We found a generally good agreement in the basic photometric and spectral parameters. Two strong shock waves appear during one period, and the "stillstand" is due to the gas dynamics between the passages of these shocks. Note that this good agreement suppose a metallicity Z = 0.03, while a metallicity Z = 0.02 does not lead to the correct amplitudes and shapes of the curves. more...

International audience; We present the first results of a 2-year high-resolution spectroscopy campaign of 59 candidate $\gamma$ Doradus stars which were mainly discovered from the HIPPARCOS astrometric mission. More than 60% of the stars present line profile variations which can be interpreted as due to pulsation related to $\gamma$ Doradus stars. For all stars we also derived the projected rotation velocity (up to more than 200 km s -1). The amplitude ratios $2K/\Delta m$ for the main HIPPARCOS frequency are in the range 35-96 km s -1 mag -1. About 50% of the candidates are possible members of binary systems, with 20 stars being confirmed $\gamma$ Doradus. At least 6 stars present composite spectra, and in all but one case (for which only one spectrum could be obtained), the narrow component shows line profile variations, pointing towards an uncomfortable situation if this narrow component originates from a shell surrounding the star. This paper is the first of a series concerning mode identification using both photometric and spectroscopic methods for the confirmed $\gamma$ Doradus stars of the present sample. more...

We search for signs of period doubling in CoRoT RR Lyrae stars. The occurrence of this dynamical effect in modulated RR Lyrae stars might help us to gain more information about the mysterious Blazhko effect. The temporal variability of the additional frequencies in representatives of all subtypes of RR Lyrae stars is also investigated. We pre-process CoRoT light curves by applying trend and jump correction and outlier removal. Standard Fourier technique is used to analyze the frequency content of our targets and follow the time dependent phenomena. The most comprehensive collection of CoRoT RR Lyrae stars, including new discoveries is presented and analyzed. We found alternating maxima and in some cases half-integer frequencies in four CoRoT Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This reinforces that period doubling is an important ingredient to understand the Blazhko effect - a premise we derived previously from the Kepler RR Lyrae sample. As expected, period doubling is detectable only for short time intervals in most modulated RRab stars. Our results show that the temporal variability of the additional frequencies in all RR Lyrae sub-types is ubiquitous. The ephemeral nature and the highly variable amplitude of these variations suggest a complex underlying dynamics of and an intricate interplay between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence of additional modes in all types of RR Lyrae - except in non-modulated RRab stars - implies that asteroseismology of these objects should be feasible in the near future (Abridged)., Comment: 20 pages, 13 figures, accepted for publication in A&A more...

The presence of g- and p-modes allows testing stellar models from the core to the envelope. Moreover, binarity in an eclipsing system constrains the physical parameters of the pulsating star. CoRot ID 100866999 is a relatively large-amplitude hybrid gDor - dSct star with two clearly distinct frequency domains. The large number of detected frequencies allows a detailed study of the interaction between them. In addition, we can derive the fundamental parameters of both components from the study of the eclipsing light curve. After removing the eclipsing phases, we analyzed the data with the Period04 package up to S/N=4. The light curve was then prewhitened with these oscillation frequencies to derive the fundamental parameters of the two components. The eclipsing light curve analysis results in a (1.8+1.1)\,Mo system, both components being main sequence stars. We detect 124 frequencies related to luminosity variations of the primary. They are present in two well-separated domains: 89 frequencies in the interval [0.30;3.64]/d and 35 in the interval [14.57; 33.96]/d. There are 22 gDor frequencies separated by a constant period interval Delta P = 0.03493 d. These frequencies correspond to a series of g-modes of degree ell=1 with successive radial orders k. We identify 21 linear combinations between the first nine gDor frequencies. The dSct domain is dominated by a large-amplitude frequency F=16.9803 /d. The eight first gDor frequencies f_i are present with much lower amplitude in the delta Scuti domain as F +/- f_i. These interactions between g- and p-modes confirm the phenomenon we detected in another CoRoT star. The amplitude and the phase of the main frequency F shows a double-wave modulation along the orbital phase, giving rise to series of combination frequencies. Such combination frequencies are also detected, with lower amplitude, for the first gDor modes. more...

CoRoT ID 105733033 is an excellent example of hybrid pulsators as it shows g- and p-modes with almost similar amplitudes in two clearly distinct frequency domains. Classical Fourier analysis allows the dectection of frequencies with an amplitude as small as 0.1 mmag up to 50c/d. The frequency spectrum of CoRoT ID 105733033 clearly consists of two distinct ranges, which are typical of gamma Doradus and delta Scuti pulsation. Focus was placed on the identification of linear combinations and frequencies due to the coupling between gamma Doradus and delta Scuti modes. We detect 198 gamma Doradus type frequencies in the range [0.25;4]c/d, of which 180 are not combination frequencies, and 24 of them are separated by a constant period-interval Delta P=0.03074d. According to the asymptotic theory, these 24 frequencies correspond to a series of g-modes of the same ell-degree and different radial orders n. We also detect 246 delta Scuti type frequencies in the range [10.1;63.4]c/d. The dominant frequency F=12.6759c/d was identified as the fundamental radial mode. Our most noteworthy result is that all the main gamma Doradus frequencies f_i are also detected in the delta Scuti domain as F +- f_i with four times smaller amplitudes. Once these frequencies were removed, only 59 can be considered as individual delta Scuti frequencies. A coupling between g- and p-modes is proposed to be a tool for detecting g-modes in the Sun, but this coupling has never yet been observed. Our present study may be valuable input to theoretical studies, addressing the mutual influence of g- and p-mode cavities and the deviation from classical theory. Furthermore, we identify a sequence of g-modes belonging to the same ell but with consecutive orders n. more...

α Lup (HR 5469) is a multiperiodic beta Cep star. According to Shobbrook (1979) and Lampers & Goossens (1982) the main period (P=0.25985 day) corresponding to the radial mode is constant. The amplitude of the secondary period, attributed to a non radial mode, is so small that it does not affect the determination of maximum dates. more...

ζ Cas (HR 153, mv=3.66, vsini=18 kms-1) was classified as a 53 Per variable by Smith (1980). He detected variations in the profile of the 4552 A Si III line with a period of 0.9 day. The radial velocity and the luminosity were observed to be constant by Abt & Levy (1978) and by Jerzykiewicz (1993) respectively. more...

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1. more...

Context. In the context of long and continuous time-series photometry and after the MOST, CoRoT, KEPLER space missions and large geographic longitude ground-based networks, a new method is offered by the polar location helping to cope with the problem associated with the Earth’s day-night cycle. Aims. We present the first long time -series photometry from Dome Charlie in the heart of Antarctica and analyze ∼4400 photometric measurements of RR Lyrae star S Arae obtained in July and August 2007. Methods. The 40-cm telescope and Photometer AntarctIca eXtinction named PAIX were used for long photometric measurements with high time resolution and a duty cycle of 65%. The Fourier technique was used for the frequency analysis. New high-precision spectroscopic observations of S Arae were also collected using HARPS over one pulsation cycle of S Arae. Results. We confirm the known radial fundamental period of 0.452 day. The high order of its harmonics shows the nonlinear nature of the radial mode. The Blazhko modulation is directly detected in the spectrum and shows a value around 48 d. Together with the Blazhko frequency we also detected triplet structure components up to 15th order showing a nonlinear behavior of the Blazhko modulation. Thus, we conclude that S Arae is a bona fide Blazhko star. The data reveal that there are irregular changes in the S Arae atmosphere during the Blazhko cycle. A residual scatter phenomenon is detected and is more intense where the nonlinear effects are strongest. Therefore, the connection between temporal hydrodynamic phenomena and such modulation has to be taken into account in Blazhko models. Conclusions. High-precision CCD photometry with a very good time resolution can be undertaken at Dome Charlie in Antarctica, and it helps to complete astrophysical measurement time-series. more...

ζ Cas (HR 153, mv=3.66, vsini=18 kms-1) was classified as a 53 Per variable by Smith (1980). He detected variations in the profile of the 4552 Å Si III line with a period of 0.9 day. The radial velocity and the luminosity were observed to be constant by Abt & Levy (1978) and by Jerzykiewicz (1993) respectively. more...

α Lup (HR 5469) is a multiperiodic beta Cep star. According to Shobbrook (1979) and Lampers & Goossens (1982) the main period (P=0.25985 day) corresponding to the radial mode is constant. The amplitude of the secondary period, attributed to a non radial mode, is so small that it does not affect the determination of maximum dates. more...

β Cru (HR 4853) is a multiperiodic β Cep star. The main period has been found constant between 1958 and 1973 by Cuypers (1982). In order to extend the basis of the ephemeris, we computed two values of radial velocity maxima from individual measurements published by Campbell & Moore (1928) and Sahade & Albarracin (1952). In lack of simultaneous spectroscopic and photometric observations, we used an arbitrary value equal to 0.25 period for the phase lag. more...