Search

Ground-based and satellite observations have revealed dust temperatures as low as ∼5−7 K in the centre of low-mass, pre-stellar cloud cores, where star formation takes place. However, external heating may rise the outer core temperatures up to ∼15−20 K. Such low temperatures at the centre of pre-stellar cores are a key factor to constrain the conditions that lead to the formation of gravitationally bound protostellar systems as was recently captured by highly-resolved Atacama large millimeter/submillimeter array observations. Here, we report consistent smoothed particle hydrodynamics collapse calculations of cold cores that demonstrate the formation of close protobinary systems via small-scale fragmentation of a gravitationally unstable protostellar disc. The results indicate that mean binary separations, of tens of astronomical units, are a consequence of disc fragmentation in cold pre-stellar cores. Cloud cores initially with temperatures ≤6 K and a low amplitude (a = 0.1), m = 2 density perturbation formed close protobinaries that were followed deep into the non-isothermal collapse for several orbital periods and appeared to survive as independent stellar entities. At temperatures ≥7 K disc fragmentation is no longer observed and the calculations terminate with the formation of a wide protobinary, which may occasionally be accompanied by small substellar objects emerging by fragmentation of the circumbinary disc. When the perturbation amplitude is raised to a = 0.25, disc fragmentation occurs again only in cores with initial temperatures ≤6 K. Therefore, increasing the perturbation amplitude does not necessarily imply that there will be disc fragmentation at higher core temperatures.

A sequence search method was developed for searching for regular frequency spacing in delta Scuti stars by visual inspection and algorithmic search. The sample contains 90 delta Scuti stars observed by CoRoT. An example is given to represent the visual inspection. The algorithm (SSA) is described in detail. The data treatment of the CoRoT light curves, the criteria for frequency filtering and the spacings derived by two methods (three approaches: VI, SSA and FT) are given for each target. Echelle diagrams are presented for 77 targets, for which at least one sequence of regular spacing was identified. Comparing the spacing and the shifts between pairs of echelle ridges revealed that at least one pair of echelle ridges is shifted to midway between the spacing for 22 stars. The estimated rotational frequencies compared to the shifts revealed rotationally split doublets, triplets and multiplets not only for single frequencies, but for the complete echelle ridges in 31 delta Scuti stars. Using several possible assumptions for the origin of the spacings, we derived the large separation ($\Delta\nu$), which are distributed along the mean density versus large separations relation derived from stellar models Suarez 2014., Comment: 25 pages, 16 figures, 9 tables. Accepted for publication in ApJS

The Praesepe cluster contains a number of δ Sct and γ Dor pulsators. Asteroseismology of cluster stars is simplified by the common distance, age and stellar abundances. Since asteroseismology requires a large number of known frequencies, the small pulsation amplitudes of these stars require space satellite campaigns. The present study utilizes photometric MOST satellite measurements in order to determine the pulsation frequencies of two evolved (EP Cnc, BT Cnc) and two main-sequence (BS Cnc, HD 73872) δ Sct stars in the Praesepe cluster. The frequency analysis of the 2008 and 2009 data detected up to 34 frequencies per star with most amplitudes in the submillimag range. In BS Cnc, two modes showed strong amplitude variability between 2008 and 2009. The frequencies ranged from 0.76 to 41.7 cd–1. After considering the different evolutionary states and mean stellar densities of these four stars, the differences and large ranges in frequency remain (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In 2009, the rapidly oscillating peculiar A-type (roAp) star 33 Lib was the target of an intense observing campaign, combining ground-based spectroscopy with space photometry obtained with the Microvariability and Oscillation of STars (MOST) satellite. We collected 780 spectra using the Echelle Spectro Polarimetric Device for the Observation of Stars (ESPaDOnS) spectrograph attached at the 3.6-m Canada–France–Hawaii Telescope and 374 spectra with the Fibre-fed Echelle Spectrograph attached at the 2.56-m Nordic Optical Telescope to perform time-resolved spectroscopy of 33 Lib. In addition, we used 111 Ultraviolet and Visual Echelle Spectrograph (UVES) spectra (2004) from the European Southern Observatory archive to check mode stability. Frequency analysis of the new radial velocity (RV) measurements confirms the previously reported frequency pattern (two frequencies and the first harmonic of the main one) and reveals an additional frequency at 1.991 mHz. The new frequency solution perfectly reproduces the RV variations from the 2004 and 2009 observational sets, providing strong support for p mode stability in this roAp star over at least 5 years.

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.

We report the discovery of CoRoT 102980178 (R.A.= 06:50:12.10, Dec.= -02:41:21.8, J2000) an Algol-type eclipsing binary system with a pulsating component (oEA). It was identified using a publicly available 55 day long monochromatic lightcurve from the CoRoT initial run dataset (exoplanet field). Eleven consecutive 1.26m deep total primary and the equal number of 0.25m deep secondary eclipses (at phase 0.50) were observed. The following light elements for the primary eclipse were derived: HJD_MinI= 2454139.0680 + 5.0548d x E. The lightcurve modeling leads to a semidetached configuration with the photometric mass ratio q=0.2 and orbital inclination i=85 deg. The out-of-eclipse lightcurve shows ellipsoidal variability and positive O'Connell effect as well as clear 0.01m pulsations with the dominating frequency of 2.75 c/d. The pulsations disappear during the primary eclipses, which indicates the primary (more massive) component to be the pulsating star. Careful frequency analysis reveals the second independent pulsation frequency of 0.21 c/d and numerous combinations of these frequencies with the binary orbital frequency and its harmonics. On the basis of the CoRoT lightcurve and ground based multicolor photometry, we favor classification of the pulsating component as a gamma Doradus type variable, however, classification as an SPB star cannot be excluded., Comment: 16 pages, 7 figures, 3 tables, accepted to Communications in Asteroseismology

Context. Photometric time series obtained from space are one of the best ways to study pulsations in pre-main sequence (PMS) stars, especially as the corresponding amplitudes are at the millimagnitude level or below. We present high-precision time-series photometry of stars in the field of NGC 2264 obtained with the MOST (Microvariability & Oscillations of STars) satellite. Aims. A search for pulsating A and F type members of NGC 2264 with ultra-precise MOST photometry was conducted. Methods. 68 stars in the field of NGC 2264 were observed simultaneously with the MOST satellite, 34 of which were previously identified as potential targets to search for PMS pulsation. The routines SigSpec and Period04 were used for the frequency analysis. Results. We discovered pulsation in 4 potential A and F type PMS members of NGC 2264 with frequencies between 2.7 h and 23 min. For one of the PMS pulsators identified with MOST after the first days of observation, simultaneous ground-based Stromgren photometry was obtained with the OSN 0.9 m telescope and confirms the highest frequency identified in the MOST photometry. 26 stars with other (i.e., hotter and cooler) spectral types show clear variability: SPB and γ Doradus pulsation, red giant oscillations, eclipsing binaries and variability caused by rotational modulation.

A Data Reduction pipeline for MOST Guide Star data is presented together with the results obtained for two observing runs in 2004 (i.e. κ Ceti 2004 and HR 1217 2004 runs) containing four and seven Guide Stars respectively. Among these Guide Stars, four are clearly variable with only one known before the MOST observations: the long period variable HD24338 (M2III). The data reduction relies on the decorrelation technique employed by Reegen et al. (2006) for their data reduction pipeline of MOST Fabry targets. The main difference is that the MOST Guide Star data include no background information. A coarse on-board background subtraction is performed, but leaves considerable residual stray light in the data, which is subject to a more sophisticated reduction 1Based on data from the MOST (Microvariability & Oscillation of STars) satellite, a Canadian Space Agency mission jointly operated by Dynacon, Inc., the University of Toronto Institute of Aerospace Studies, and the University of British Columbia, with assistance from the University of Vienna, Austria. M.Hareter, P. Reegen, R.Kuschnig, et al. 49 technique. Since at least four stars are observed simultaneously, common features of the light curves can be recognized and removed. Among different data reduction methods, the decorrelation technique is more versatile and often has better results than differential photometry or data smoothing. Individual Objects: HD 20884, HD20790, HD 24338, HD24217

We found evidence for radial p-modes and nonradial mixed modes in the oscilla-tion spectrum of the K giant HD20884 based on 20.6 days of nearly continuoushigh-precisionphotometryobtainedbytheCanadianmicrosatelliteMOST 1 .Os-cillation frequencies range from 5-31µHz (periods of about 2.3d - 9hr) withluminosity amplitudes between about 300 and 950 ppm and mode lifetimes ex-ceeding 10 days are indicated. The mode identifications are based on searchesof a large grid of models for a best fit to the frequencies and temperature ofHD20884. The latter is better constrained now by spectroscopy obtained atthe David Dunlap Observatory as part of this work. Individual Objects: HD20884, HD20790, κ 1 Ceti, ǫOph, ξHya, HD146490 Introduction Our understanding of the Sun’s structure has been revolutionised over the last threedecades by helioseismology. This technique allows investigations of the solar interiorby observing p-modes at the stellar surface. Observing sun-like oscillations in otherstars was hampered for a long time by the extremely small pulsation amplitudes. Forstars cooler and more luminous than the Sun, the expected amplitudes are greater andshould be more easily observable. However, the larger radii of red giants extend theirpulsation periods from ∼5 minutes in the Sun to a range of several hours to severaldays. This again complicates groundbased detections and frequency identifications,especially due to daily aliasing.As ultra-precise rapid photometry from space and high-precision radial velocitymeasurements from the ground became available, detections of stochastically drivenoscillations were reported for several giants (see Bouchy & Carrier 2003 for a review).Examples include the G9.5 giant ǫOph, based on radial velocities from the CORALIEand ELODIE spectrographs (De Ridder et al. 2006) and Fabry Imaging photometryfromtheMOSTsatellite(Barbanetal. 2007), andtheG7giantξHya, basedonradialvelocity measurements with the CORALIE spectrograph (Frandsen et al. 2002), orthe K2.5 giant star GSC09137-03505 where Kallinger et al. (2005) found oscillations,based on Fine Guidance Sensor photometry by the Hubble Space Telescope.If pulsating red giants do indeed have radial and observable nonradial modes withrelatively long lifetimes, then these modes will enable to constrain the deep interiorof red giant stars, as well as set limits to the excitation mechanisms. But recentinvestigations (e.g., Barban et al. 2007 or Stello et al. 2006 ) suggest that only radialmodes with very short lifetimes (< 3 days) should be observable in red giants. Onthe other hand, Kallinger et al. (2008b) report strong evidence for the existence ofradial and nonradial modes in ǫOph (with lifetimes longer than 10 days) based on

Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red-giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red-giants targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help for ensemble asteroseismology., Accepted 03/05/2015

The 131 days long, high-precision light curves observed in the CoRoT exo-field during LRa01 were investigated for γ Dor and δ Sct-γ Dor hybrid stars. In total 418 γ Dor and 274 δ Sct-γ Dor hybrid candidates were identified. For a fraction of these candidates spectra are available obtained at the Anglo-Australian Observatory. Effective temperatures and surface gravity were derived by fitting synthetic spectra of three Balmer lines, i.e. Hα, Hβ, and Hγ, as well as of the Ca K line at 3933 °A. The bona fide γ Dor and hybrid stars were plotted in an Teff- log g diagram that shows the expected concentration of γ Dor stars at the cool border of the δ Sct strip. In contrast, the hybrids fill the whole δ Sct instability strip without a noticeable concentration. Remarkably, the fraction of constant stars, with no signal above 3 times the noise level, is smallest in the same temperature regime (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Pulsating stars in binary systems are ideal laboratories to test stellar evolution and pulsation theory, since a direct, model-independent determination of component masses is possible. The high-precision CoRoT photometry allows a detailed view of the frequency content of pulsating stars, enabling detection of patterns in their distribution. The object HD 51844 is such a case showing periastron brightening instead of eclipses. We present a comprehensive study of the HD 51844 system, where we derive physical parameters of both components, the pulsation content and frequency patterns. Additionally, we obtain the orbital elements, including masses, and the chemical composition of the stars. Time series analysis using standard tools was mployed to extract the pulsation frequencies. Photospheric abundances of 21 chemical elements were derived by means of spectrum synthesis. We derived orbital elements both by fitting the observed radial velocities and the light curves, and we did asteroseismic modelling as well. We found that HD 51844 is a double lined spectroscopic binary. The determined abundances are consistent with delta Delphini classification. We determined the orbital period (33.498 +- 0.002 d), the eccentricity (0.484 +- 0.020), the mass ratio (0.988 +- 0.02), and the masses to 2.0 +- 0.2 M_sun for both components. Only one component showed pulsation. Two p modes (f_22 and f_36) and one g mode (f_orb) may be tidally excited. Among the 115 frequencies, we detected triplets due to the frequency modulation, frequency differences connected to the orbital period, and unexpected resonances (3:2, 3:5, and 3:4), which is a new discovery for a delta Scuti star., 15 pages, 11 figures, accepted for publication in A&A

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate their fundamental parameters and the abundances of 16 chemical species in a self-consistent manner. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general abundance trends as a function of the metallicity observed in stars of the Galactic disk. After an allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN cycle. A contamination by NeNa-cycled material in the most massive stars is also discussed. With the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low- and intermediate-mass stars., Accepted for publication in A&A, 25 pages, 13 colour figures (revised version after language editing)

The star HD 51844 was observed in CoRoT LRa02 as a Seismo target which turned out to be an SB2 system. The 117 days long light curve revealed delta Scuti pulsation in the range of 6 to 15 d^{-1} where four frequencies have amplitudes larger than 1.4 mmag and a rich frequency spectrum with amplitudes lower than 0.6 mmag. Additionally, the light curve exhibits a brightening event recurring every 33.5 days with a maximum of 3 mmag and a duration of about 5 days. Thus, this star can be considered as a heartbeat candidate. The radial velocities from spectroscopy confirmed an eccentric binary system with nearly identical masses and physical parameters. The brightening event of the light curve coincides with the maximum radial velocity separation showing that the brightening is in fact caused by tidal distortion and/or reflected light. One component displays large line profile variations, while the other does not show significant variation. The frequency analysis revealed a quintuplet structure of the four highest-amplitude frequencies, which is due to the orbital motion of the pulsating star., Comment: 4 pages, 3 figures, To appear in Proceedings of IAU Syposium 301, Precision Asteroseismology, August 2013, Wroclaw, Poland

A sequence search method was developed to search regular frequency spacing in delta Scuti stars by visual inspection and algorithmic search. We searched for sequences of quasi-equally spaced frequencies, containing at least four members per sequence, in 90 delta Scuti stars observed by CoRoT. We found an unexpectedly large number of independent series of regular frequency spacing in 77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We introduce the sequence search method presenting the sequences and echelle diagram of CoRoT 102675756 and the structure of the algorithmic search. Four sequences (echelle ridges) were found in the 5-21 d^{-1} region, where the pairs of the sequences are shifted (between 0.5-0.59 d^{-1}) by twice the value of the estimated rotational splitting frequency (0.269 d^{-1}). The general conclusions for the whole sample are also presented in this paper. The statistics of the spacings derived by the sequence search method, by FT and that of the shifts are also compared. In many stars, more than one almost equally valid spacing appeared. The model frequencies of FG Vir and their rotationally split components were used to reveal a possible explanation that one spacing is the large separation, while the other is a sum of the large separation and the rotational frequency. In CoRoT 102675756, the two spacings (2.249 and 1.977 d^{-1}) agree better with the sum of a possible 1.710 d^{-1} large separation and two or one times, respectively, the value of the rotational frequency., 12 pages, 10 figures, accepted for publication in ApJ

Delta Sct - gamma Dor hybrids pulsate simultaneously in p- and g-modes, which carry information on the structure of the envelope as well as to the core. Hence they are key objects for investigating A and F type stars with asteroseismic techniques. An important requirement for seismic modeling are small errors in temperature, gravity and chemical composition. Furthermore, we want to investigate the existence of an abundance indicator typical for hybrids, something that is well established for the roAp stars. Previous to the present investigation, the abundance pattern of only one hybrid and another hybrid candidate has been published. We obtained high-resolution spectra of HD 114839 and BD +18 4914 using the SOPHIE spectrograph of the Observatoire de Haute-Provence and the HARPS spectrograph at ESO La Silla. For each star we determined fundamental parameters and photospheric abundances of 16 chemical elements by comparing synthetic spectra with the observations. We compare our results to that of seven delta Sct and nine gamma Dor stars. For the evolved BD +18 4914 we found an abundance pattern typical for an Am star, but could not confirm this peculiarity for the less evolved star HD 114839, which is classified in the literature as uncertain Am star. Our result supports the concept of evolved Am stars being unstable. With our investigation we nearly doubled the number of spectroscopically analyzed delta Sct - gamma Dor hybrid stars, but did not yet succeed in identifying a spectroscopic signature for this group of pulsating stars. A statistically significant spectroscopic investigation of delta Sct - gamma Dor hybrid stars still is missing, but would be rewarding considering the asteroseismological potential of this group., 20 pages, 8 figures, accepted for publication in APJ

Using the CoRoT space based photometry of the O-type binary HD46149, stellar atmospheric effects related to rotation can be separated from pulsations, because they leave distinct signatures in the light curve. This offers the possibility of characterising and exploiting any pulsations seismologically. Combining high-quality space based photometry, multi-wavelength photometry, spectroscopy and constraints imposed by binarity and cluster membership, the detected pulsations in HD46149 are analyzed and compared with those for a grid of stellar evolutionary models in a proof-of-concept approach. We present evidence of solar-like oscillations in a massive O-type star, and show that the observed frequency range and spacings are compatible with theoretical predictions. Thus, we unlock and confirm the strong potential of this seismically unexplored region in the HR diagram., Comment: 11 pages, 12 figures, accepted for publication in A&A

The more massive counterparts of T Tauri stars, Herbig Ae/Be stars, are known to vary in a complex way with no variability mechanism clearly identified. We attempt to characterize the optical variability of HD~37806 (MWC 120) on time scales ranging between minutes and several years. A continuous, one-minute resolution, 21 day-long sequence of MOST (Microvariability & Oscillations of STars) satellite observations has been analyzed using wavelet, scalegram and dispersion analysis tools. The MOST data have been augmented by sparse observations over 9 seasons from ASAS (All Sky Automated Survey), by previously non-analyzed ESO (European Southern Observatory) data partly covering 3 seasons and by archival measurements dating back half a century ago. Mutually superimposed flares or accretion instabilities grow in size from about 0.0003 of the mean flux on a time scale of minutes to a peak-to-peak range of, Comment: Accepted for publication by Astron. & Astroph. 8 pages, 9 figures. For some reason Fig.5 incorrectly shows in arXiv: Contours OK, gray scale not

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

The beta Cephei star GSC 06272‐01557 is the only of its class discovered by the MOST satellite so far. Analyses of a 30 days long data set have already revealed 9 frequencies. Recent measurements of the Stromgren indices attribute a Teff around 24500 K and a log g of 3.9, which places the star in the middle of the β Cephei instability strip. Recently observed multicolor photometric ground based data will enable us to identify the modes of pulsation.

Theoretical predictions of solar‐like oscillations in cool Delta Scuti stars motivated us to organize a spectroscopic observing campaign of the metal‐rich star Rho Puppis. High precision radial velocity measurements obtained in 2008 through an iodine cell attached to UCLES at the Anglo Australian Telescope (extracted with the code iSONG) as well as high resolution spectra observed with CORALIE at the Swiss 1.2−m Leonard Euler telescope, are the basis material for detecting the solar‐like pulsation. Furthermore we have 30 days of photometry observed with the MOST satellite, which led to the detection of at least two additional frequencies attributed to nonradial modes. Further intrinsic signals cannot be excluded. In this poster paper we present preliminary results.

A field star, HD 61199 (V ~ 8), simultaneously observed with Procyon by the MOST (Microvariability & Oscillations of STars) satellite in continuous runs of 34, 17, and 34 days in 2004, 2005, and 2007, was found to pulsate in 11 frequencies in the delta Scuti range with amplitudes from 1.7 down to 0.09 mmag. The photometry also showed variations with a period of about four days. To investigate the nature of the longer period, 45 days of time-resolved spectroscopy was obtained at the Thueringer Landessternwarte Tautenburg in 2004. The radial velocity measurements indicate that HD 61199 is a triple system. A delta Scuti pulsator with a rich eigenspectrum in a multiple system is promising for asteroseismology. Our objectives were to identify which of the stars in the system is the delta Scuti variable and to obtain the orbital elements of the system and the fundamental parameters of the individual components, which are constrained by the pulsation frequencies of the delta Scuti star. Classical Fourier techniques and least-squares multi-sinusoidal fits were applied to the MOST photometry to identify the pulsation frequencies. The groundbased spectroscopy was analysed with least-squares-deconvolution (LSD) techniques, and the orbital elements derived with the KOREL and ORBITX routines. Asteroseismic models were also generated. The photometric and spectroscopic data are compatible with a triple system consisting of a close binary with an orbital period of 3.57 days and a delta Scuti companion (HD 61199,A) as the most luminous component. The delta Scuti star is a rapid rotator with about vsin i = 130 km/s and an upper mass limit of about 2.1 Msun. For the close binary components, we find they are of nearly equal mass, with lower mass limits of about 0.7 Msun., Comment: 11 pages, 14 figures, accepted by A&A

Context: We present 31.2 days of nearly continuous MOST photometry of the roAp star 10Aql. Aims:The goal was to provide an unambiguous frequency identification for this little studied star, as well as to discuss the detected frequencies in the context of magnetic models and analyze the influence of the magnetic field on the pulsation. Methods: Using traditional Fourier analysis techniques on three independent data reductions, intrinsic frequencies for the star are identified. Theoretical non-adiabatic axisymmetric modes influenced by a magnetic field having polar field strengths Bp = 0-5kG were computed to compare the observations to theory. Results: The high-precision data allow us to identify three definite intrinsic pulsation frequencies and two other candidate frequencies with low S/N. Considering the observed spacings, only one (50.95microHz) is consistent with the main sequence nature of roAp stars. The comparison with theoretical models yields a best fit for a 1.95Msun model having solar metallicity, suppressed envelope convection, and homogenous helium abundance. Furthermore, our analysis confirms the suspected slow rotation of the star and sets new lower limits to the rotation period (Prot>1 month) and inclination (i>30\pm10deg.). Conclusions:The observed frequency spectrum is not rich enough to unambiguously identify a model. On the other hand, the models hardly represent roAp stars in detail due to the approximations needed to describe the interactions of the magnetic field with stellar structure and pulsation. Consequently, errors in the model frequencies needed for the fitting procedure can only be estimated. Nevertheless, it is encouraging that models which suppress convection and include solar metallicity, in agreement with current concepts of roAp stars, fit the observations best., accepted by A&A

HD 144277 was previously discovered by MOST space photometry to be a young and hot delta Scuti star showing regular groups of pulsation frequencies. The first asteroseismic models required lower than solar metallicity to fit the observed frequency range based on a purely photometric analysis. High-resolution, high S/N spectroscopic data obtained with the HARPS spectrograph were used to determine the fundamental parameters and chemical abundances of HD 144277. These values were put into context alongside the results from asteroseismic models. The effective temperature, Teff, of HD 144277 was determined as 8640(+300)(-100) K, log g is 4.14 +/- 0.15 and the projected rotational velocity, vsini, is 62.0 +/- 2.0 km/s. As the vsini value is significantly larger than previously assumed, we refined the first asteroseimic model accordingly. The overall metallicity Z was determined to be 0.011 where the light elements He, C, O, Na, and S show solar chemical composition, but the heavier elements are significantly underabundant. In addition, the radius of HD 144277 was determined to be 1.55 +/- 0.65 Rsun from spectral energy distribution fitting, based on photometric data taken from the literature. From the spectroscopic observations, we could confirm our previous assumption from asteroseismic models that HD 144277 has less than solar metallicity. The fundamental parameters derived from asteroseismology, Teff, log g, L/Lsun and R\Rsun, agree within one sigma to the values found from spectroscopic analysis. As the vsini value is significantly higher than assumed in the first analysis, near-degeneracies and rotational mode coupling were taken into account in the new models. These suggest that HD 144277 has an equatorial rotational velocity of about 80 km/s and is seen equator-on. The observed frequencies are identified as prograde modes., 7 pages, 8 figures, Astronomy & Astrophysics in press

The high accuracy of space data increased the number of the periodicities determined for pulsating variable stars, but the mode identification is still a critical point in the non-asymptotic regime. We use regularities in frequency spacings for identifying the pulsation modes of the recently discovered delta Sct star ID 102749568. In addition to analysing CoRoT light curves (15252 datapoints spanning 131 days), we obtained and analysed both spectroscopic and extended multi-colour photometric data. We applied standard tools (MUFRAN, Period04, SigSpec, and FAMIAS) for time-series analysis. A satisfactory light-curve fit was obtaining by means of 52 independent modes and 15 combination terms. The frequency spacing revealed distinct peaks around large (25.55-31.43 microHz), intermediate (9.80, 7.66 microHz), and low (2.35 microHz) separations. We directly identified 9 modes, and the l and n values of other three modes were extrapolated. The combined application of spectroscopy, multi-colour photometry, and modelling yielded the precise physical parameters and confirmed the observational mode identification. The large separation constrained the log g and related quantities. The dominant mode is the radial first overtone., Comment: 13 pages, 8 figures, accepted for publication in A&A

Context. OB stars are important building blocks of the Universe, but we have only a limited sample of them well understood enough from an asteroseismological point of view to provide feedback on the current evolutionary models. Our study adds one special case to this sample, with more observational constraints than for most of these stars. Aims. Our goal is to analyse and interpret the pulsational behaviour of the B3 IV star HD 43317 using the CoRoT light curve along with the ground-based spectroscopy gathered by the Harps instrument. This way we continue our efforts to map the Beta Cep and SPB instability strips. Methods. We used different techniques to reveal the abundances and fundamental stellar parameters from the newly-obtained high-resolution spectra. We used various time-series analysis tools to explore the nature of variations present in the light curve. We calculated the moments and used the pixel-by-pixel method to look for line profile variations in the high-resolution spectra. Results. We find that HD 43317 is a single fast rotator (v_rot ~ 50% v_crit) and hybrid SPB/Beta Cep-type pulsator with Solar metal abundances. We interpret the variations in photometry and spectroscopy as a result of rotational modulation connected to surface inhomogeneities, combined with the presence of both g and p mode pulsations. We detect a series of ten consecutive frequencies with an almost constant period spacing of 6339 s as well as a second shorter sequence consisting of seven frequencies with a spacing of 6380 s. The dominant frequencies fall in the regime of gravito-inertial modes., Accepted for publication in Astronomy and Astrophysics on 21/03/2012, 13 pages, 10 figures, 6 tables

OB stars are important constituents for the ecology of the Universe, and there are only a few studies on their pulsational properties detailed enough to provide important feedback on current evolutionary models. Our goal is to analyse and interpret the behaviour present in the CoRoT light curve of the B0.5 IV star HD 51756 observed during the second long run of the space mission, and to determine the fundamental stellar parameters from ground-based spectroscopy gathered with the CORALIE and HARPS instruments after checking for signs of variability and binarity, thus making a step further in mapping the top of the Beta Cep instability strip. We compare the newly obtained high-resolution spectra with synthetic spectra of late O-type and early B-type stars computed on a grid of stellar parameters. We match the results with evolutionary tracks to estimate stellar parameters. We use various time series analysis tools to explore the nature of the variations present in the light curve. Additional calculations are carried out based on distance and historical position measurements of the components to impose constraints on the binary orbit. We find that HD 51756 is a wide binary with both a slow (v sin i \approx 28 km s^-1) and a fast (v sin i \approx 170 km s^-1) early-B rotator whose atmospheric parameters are similar (T_eff \approx 30000 K and log g \approx 3.75). We are unable to detect pulsation in any of the components, and we interpret the harmonic structure in the frequency spectrum as sign of rotational modulation, which is compatible with the observed and deduced stellar parameters of both components. The non-detection of pulsation modes provides a feedback on the theoretical treatment, given that non-adiabatic computations applied to appropriate stellar models predict the excitation of both pressure and gravity modes for the fundamental parameters of this star., Accepted for publication in Astronomy and Astrophysics on 14/01/2011, 11 pages, 9 figures, 4 tables