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Accurate photometric CoRoT space observations of a secondary seismological target, HD 174884, led to the discovery that this star is an astrophysically important double-lined eclipsing spectroscopic binary in an eccentric orbit ($e\sim0.3$), unusual for its short 3$\fd$65705 orbital period. The high eccentricity, coupled with the orientation of the binary orbit in space, explains the very unusual observed light curve with strongly unequal primary and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT “seismo” passband. Without the high accuracy of the CoRoT photometry, the secondary eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up program provided 45 high dispersion spectra. The analysis of the CoRoT light curve was performed with an adapted version of PHOEBE that supports CoRoT passbands. The final solution was obtained by a simultaneous fitting of the light and the radial velocity curves. Individual star spectra were obtained by spectrum disentangling. The uncertainties of the fit were achieved by bootstrap resampling and the solution uniqueness was tested by heuristic scanning. The results provide a consistent picture of the system composed of two late B stars. The Fourier analysis of the light curve fit residuals yields two components, with orbital frequency multiples and an amplitude of ~0.1 mmag, which are tentatively interpreted as tidally induced pulsations. An extensive comparison with theoretical models is carried out by means of the Levenberg-Marquardt minimization technique, and the discrepancy between the models and the derived parameters is discussed. The best fitting models yield a young system age of 125 million years which is consistent with the eccentric orbit and synchronous component rotation at periastron.

Context. Solar-like oscillations have now been observed in several stars, thanks to ground-based spectroscopic observations and space-borne photometry. CoRoT, which has been in orbit since December 2006, has observed the star HD49933 twice. The oscillation spectrum of this star has proven difficult to interpret.

Aims. We report the discovery of very shallow ($\Delta F/F \approx 3.4\times 10^{-4}$), periodic dips in the light curve of an active $V = 11.7$G9V star observed by the CoRoT  satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion.

Context. The origin of the short-term variability in Be stars remains a matter of controversy. Pulsations and rotational modulation are the components of the favored hypothesis.

We present an analysis of the δ-Scuti star HD 174936(ID 7613) observed by CoRoT during the first short run SRc01 (27 days). A total number of 422 frequencies were extracted from the light curve using standard prewhitening techniques. This number of frequencies was obtained by considering a spectral significance limit of sig = 10 using the software package SigSpec. Our analysis of the oscillation frequency spectrum reveals a spacing periodicity around 52 μHz. Although modes considered here are not in the asymptotic regime, a comparison with stellar models confirms that this signature may stem from a quasi-periodic pattern similar to the so-called large separation in solar-like stars.

Context. We present spectroscopic ground-based observations of the early Be star HD 49330 obtained simultaneously with the CoRoT-LRA1 run just before the burst observed in the CoRoT data.

Context. The presence of pulsations in late-type Be stars is still a matter of controversy. It constitutes an important issue to establish the relationship between non-radial pulsations and the mass-loss mechanism in Be stars.

Context. HD 181231is a B5IVe star, which has been observed with the CoRoT satellite during ~5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry.

Context. We present the CoRoT light curve of the $\beta\,$Cep star HD 180642, assembled during the first long run of the space mission, as well as archival single-band photometry.

Context. The CoRoT short runs give us the opportunity to observe a large variety of late-type stars through their solar-like oscillations. We report observations of the star HD 175726 that lasted for 27 days during the first short run of the mission. The time series reveals a high-activity signal and the power spectrum presents an excess due to solar-like oscillations with a low signal-to-noise ratio.

Context. The estimate of solar-like oscillation properties, such as their frequencies, amplitudes and lifetimes, is challenging because of their low amplitudes and will benefit from long and uninterrupted observing runs. The space telescope CoRoT allows us to obtain high-performance photometric data over a long and quasi continuous period. Among its main targets are stars for which we expect solar-like oscillations.

Context.

Context. The CoRoT satellite searches for planets by applying the transit method, monitoring up to 12 000 stars in the galactic plane for 150 days in each observing run. This search is contaminated by a large fraction of false positives, caused by different eclipsing binary configurations that might be confused with a transiting planet.

Context. Be stars undergo outbursts producing a circumstellar disk from the ejected material. The beating of non-radial pulsations has been put forward as a possible mechanism of ejection.

Context. The F8 star HD 181906 (effective temperature ${\sim}6300$K) was observed for 156 days by the CoRoT satellite during the first long run in the direction of the galactic centre. Analysis of the data reveals a spectrum of solar-like acoustic oscillations. However, the faintness of the target (mv= 7.65) means the signal-to-noise (S/N) in the acoustic modes is quite low, and this low S/N leads to complications in the analysis.

Context. CoRoT light curves have an unprecedented photometric quality, having simultaneously a high signal-to-noise ratio, a long time span and a nearly continuous duty-cycle.

Context. We present an analysis of the observations of HD 51106 and HD 50747 by the satellite CoRoT, obtained during its initial run, and of the spectroscopic preparatory observations.

Aims. We observe the nearby, weakly-active single giant, Pollux, in order to directly study and infer the nature of its magnetic field.

Context. To understand the origin of stellar activity in pre-main-sequence Herbig Ae/Be stars and to get a deeper insight into the interior of these enigmatic stars, the pulsational instability strip of Palla and Marconi is investigated. In this article we present a first discovery of non radial pulsations in the Herbig Ae spectroscopic binary star RS Cha.

Context. Recent spectropolarimetric observations of Herbig Ae/Be stars have yielded new arguments in favour of a fossil origin for the magnetic fields of intermediate mass stars.

Context.With a Jupiter-mass planet orbiting at a distance of only 0.031 AU, the active K2 dwarf HD 189733 is a potential candidate in which to study the magnetospheric interactions of a cool star with its recently-discovered close-orbiting giant planet.

Context.In a recent work, we tried to obtain a calibration of the two components of the pre-main sequence binary system RS Cha by means of theoretical stellar models. We found that the only way to reproduce the observational parameters of RS Cha with standard stellar models is to decrease the initial abundances of carbon and nitrogen derived from the GN93 solar mixture of heavy elements by a few tenths of dex.

Context.The calibration of binary systems with accurately known masses and/or radii provides powerful tools to test stellar structure and evolution theory and to determine the age and helium content of stars. We study the eclipsing double-lined spectroscopic binary system RS Cha, for which we have accurate observations of the parameters of both stars (masses, radii, luminosities, effective temperatures and metallicity).

Context.The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum.

We present new spectroscopic observations of the pre-main sequence eclipsing spectroscopic binary RS Cha. A sample of 174 spectra were obtained with the GIRAFFE spectrograph at the SAAO at 32 000 resolution. The radial velocity curves derived from these spectra were combined with previous observations spanning a period of about 30 years to correct the ephemeris of the system, and the result indicates that the orbital period is not constant.
Residuals of the binary radial velocity curve for both components with amplitudes up to a few km s-1and periods on the order of 1 h are clearly seen in our data, which we interpret as the signatures of delta-Scuti type pulsations.
We revisited the masses of both components and determined the surface metallicity Zof both components of the RS Cha system by fitting synthetic spectra to observed spectra in a set of selected spectral regions. The synthetic spectra are calculated with the SYNTH code using stellar atmosphere models computed with the Kurucz ATLAS 9 code, along with a list of lines obtained from the VALD database. A selection of the best spectra and the most relevant spectral regions allowed us to determine $Z = 0.028 \pm 0.005$. We also derived new values of $v\sin i$: $64 \pm 6$km s-1and $70 \pm 6$km s-1for the primary and the secondary star, respectively. Finally, we observationally confirm that the RS Cha system is a synchronized and circularized system.

We report the discovery, using FORS1 at the ESO-VLT and ESPaDOnS at the CFHT, of magnetic fields in the young A-type stars HD 101412, V380 Ori and HD 72106A. Two of these stars (HD 101412 and V380 Ori) are pre-main sequence Herbig Ae/Be (HAeBe) stars, while one (HD 72106A) is physically associated with a HAeBe star. Remarkably, evidence of surface abundance spots is detected in the spectra of HD 72106A. The magnetic fields of these objects display intensities of order 1 kG at the photospheric level, are ordered on global scales, and appear in approximately 10% of the stars studied. Based on these properties, the detected stars may well represent pre-main sequence progenitors of the magnetic Ap/Bp stars. The low masses inferred for these objects (2.6, 2.8 and 2.4 $M_\odot$) represent additional contradictions to the hypothesis of Hubrig et al. (2000, ApJ, 539, 352), who claim that magnetic fields appear in intermediate-mass stars only after 30% of their main sequence evolution is complete. Finally, we fail to confirm claims by Hubrig et al. (2004, A&A, 428, L1) of magnetic fields in the Herbig Ae star HD 139614.

A 10-night asteroseismic observation programme has been conducted in January 2004 with the spectrometer harpsat the ES0 3.6-m telescope. The selected target, the 6th magnitude F5V star HD 49933, was chosen among the prime candidates of corot, the European space mission dedicated to characterize stellar oscillations mode with high precision photometry measurements. This star shows important line profiles variations, indicating a surprisingly high activity with respect to its low rotation rate. However, with the help of tools developed for disentangling the signatures of activity and oscillations, we are able to observe its oscillation spectrum in the frequency range [1.2, 2.2 mHz]. We measure the large separation ($88.7\pm0.4$μHz) and the maximum amplitude (around $0.4 \pm 0.1$m s-1rms), respectively in agreement and marginal agreement with the predicted values.

We present an analysis of the FUSEspectra of HD 163296, a young isolated Herbig Ae star. The spectra in the far UV spectral range are dominated by strong emission lines of $\ion{C}{iii}$and $\ion{O}{vi}$, which exhibit broad and complex asymmetric profiles with wings extending over more than 1000 km s-1. The $\ion{H}{i}$Ly αand the $\ion{C}{iii}$emission profiles show evidence for an outflow with a terminal velocity of 270 km s-1. We also identified several narrower emission lines due to fluorescent decays in $\ion{Fe}{ii}$. Using an HST/STIS archive spectrum, we checked that the $\ion{H}{i}$Ly αline, which has a clear type III P Cygni emission profile, is broad enough to provide the photons required to photo-excite the $\ion{Fe}{ii}$upper levels. As previously explored for the well-known Herbig Ae star AB Aur, most of the spectral features including the fluorescent lines are consistent with the presence of a chromosphere above the photosphere. However, the over-ionized species cannot be produced in this region alone and we discuss two alternative mechanisms to explain such spectral signatures: magnetospheric accretion and a magnetically confined wind. Both interpretations involve a large-scale magnetic field whose detection is now a challenge for the new generation of spectropolarimeters such as ESPaDOnS.

We present the results of multisite observations spanning two years of the pre-main-sequence Herbig Ae star HD 104237. The star was observed in high resolution spectroscopy (R≥35 000) for a total of 157.3 h of effective exposure time, over 42 nights, corresponding to a data base of 1888 individual echelle spectra. We confirm that the HD 104237 system includes a spectroscopic binary, whose primary component HD 104237 A is pulsating. The resulting high quality radial velocity curve allows us to detect for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star. Five different modes are detected with very high confidence, with frequencies ranging between 28.5 and 35.6 d-1, typical of δScuti pulsations; an additional 3 frequencies have been extracted from the data, but with a lower level of confidence. The pattern of frequencies indicates that at least some of the detected modes are non-radial. The precise orbit determination and the measurement of the double line spectroscopic binary observed around periastron enabled us to determine a mass ratio of 1.29 ±0.02 between the primary and the secondary; based on the primary mass of 2.2 ±0.1 $M_\odot$we conclude that the spectroscopic secondary HD 104237 b should have a mass of 1.7 ±0.1 $M_\odot$and lie outside the pre-main sequence instability strip towards later spectral types. A search for pulsations in the radial velocity curve of the much weaker secondary component was not conclusive at this stage. The location of the primary in the HR diagram and its position with respect to recent pre-main sequence evolutionary tracks and isochrones implies a location of the secondary indicative of spectral type K3.

One of the goals of the ground-based support program for the corotand mons/rømersatellite missions is to characterize suitable target stars for the part of the missions dedicated to asteroseismology. We present the detailed abundance analysis of nine of the potential corotmain targets using the semi-automatic software vwa. For two additional corottargets we could not perform the analysis due to the high rotational velocity of these stars. For five stars with low rotational velocity we have also performed abundance analysis by a classical equivalent width method in order to test the reliability of the vwasoftware. The agreement between the different methods is good. We find that it is necessary to measure abundances extracted from each line relative to the abundances found from a spectrum of the Sun in order to remove systematic errors. We have constrained the global atmospheric parameters Teff, $\log g$, and [Fe/H] to within $70{-}100$K, $0.1{-}0.2$dex, and 0.1 dex for five stars which are slow rotators ($v\sin i < 15 {\rm km\,s}^{-1}$). For most of the stars we find good agreement with the parameters found from line depth ratios, H αlines, Strömgren indices, previous spectroscopic studies, and also $\log g$determined from the hipparcosparallaxes. For the fast rotators ($v\sin i > 60 {\rm km\,s}^{-1}$) it is not possible to constrain the atmospheric parameters.

We present the first Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of HD 76534, a Herbig Be star. Here we focus on the analysis of the H2absorption lines which allow to quantify the gaseous content along the line of sight. This analysis evidences large amounts of cold and warm H2toward the star. We demonstrate that the H2is bound to HD 76534 and we argue that it is likely distributed in a circumstellar envelope. In addition, the present study gives clues for the existence of common properties for the circumstellar H2of Herbig Ae/Be stars.

By pursuing the goal to find new variables in the COROT field–of–view we characterised a sample of stars located in the lower part of the instability strip. Our sample is composed of stars belonging to the disk population in the solar neighbourhood. We found that 23% of the stars display multiperiodic light variability up to a few mmag in amplitude, i.e., easily detectable on a single night of photometry. $uvby\beta$photometry fixed most of the variables in the middle of the instability strip and high–resolution spectroscopy established that they have $v\sin i >100$km s-1. An analysis of the Rodriguez & Breger ([CITE]) sample (δSct stars in the whole Galaxy) shows slightly different features, i.e., most δSct stars have a 0.05–mag redder $(b-y)_0$index and lower $v\sin i$values. Additional investigation in the open cluster NGC 6633 confirms the same incidence of variability, i.e., around 20%. The wide variety of pulsational behaviours of δSct stars (including unusual objects such as a variable beyond the blue edge or a rapidly rotating high–amplitude pulsator) makes them very powerful asteroseismic tools to be used by COROT. Being quite common among bright stars, δSct stars are suitable targets for optical observations from space.

We present simultaneous and continuous observations of the Hα, Hβ, He iD3, Na iD1,D2doublet and the Ca iiH & K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of $2\fd8$. Two large optical flares were observed, both showing an increase in the emission of Hα, Ca iiH & K, Hβand He iD3and a strong filling-in of the Na iD1, D2doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Hαand He iD3in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5 V star was in front. A possible periodicity in the X-ray flare-like events was also found.

One of the goals of the ground-based support program for the COROT and MONS/Rømer satellite missions is to select and characterise suitable target stars for the part of the missions dedicated to asteroseismology. While the global atmospheric parameters may be determined with good accuracy from the Strömgren indices, careful abundance analysis must be made for the proposed main targets. This is a time consuming process considering the long list of primary and secondary targets. We have therefore developed new software called vwafor this task. The vwaautomatically selects the least blended lines from the atomic line database vald, and consequently adjusts the abundance in order to find the best match between the calculated and observed spectra. The variability of HD 49434 was discovered as part of COROT ground-based support observations. Here we present a detailed abundance analysis of HD 49434 using vwa. For most elements we find abundances somewhat below the Solar values, in particular we find [Fe/H] $= -0.13 \pm 0.14$. We also present the results from the study of the variability that is seen in spectroscopic and photometric time series observations. From the characteristics of the variation seen in photometry and in the line profiles we propose that HD 49434 is a variable star of the γDoradus type.

ωOri(HD 37490, HR 1934) is a Be star known to have presented variations. In order to investigate the nature and origin of its short-term and mid-term variability, a study is performed of several spectral lines (Hα, Hδ, $\ion{He}{i}$4471, 4713, 4921, 5876, 6678, $\ion{C}{ii}$4267, 6578, 6583, $\ion{Mg}{ii}$4481, $\ion{Si}{iii}$4553 and $\ion{Si}{ii}$6347), based on 249 high signal-to-noise high-resolution spectra taken with 8 telescopes over 22 consecutive nights during the MuSiCoS (Multi SIte COntinuous Spectroscopy) campaign in November-December 1998. The stellar parameters are revisited and the projected rotational velocity ($v\sin i = 179$km s-1) is redetermined using several methods. With the MuSiCoS 98 dataset, a time series analysis of line-profile variations (LPVs) is performed using the Restricted Local Cleanest (RLC) algorithm and a least squares method. The behaviour of the velocity of the centroid of the lines, the equivalent widths and the apparent vsinifor several lines, as well as Violet and Red components of photospheric lines affected by emission (red $\ion{He}{i}$lines, $\ion{Si}{ii}$6347, $\ion{C}{ii}$6578, 6583) are analyzed. The non-radial pulsation (NRP) model is examined using phase diagrams and the Fourier-Doppler Imaging (FDI) method. The LPVs are consistent with a NRP mode with $l = 2$or 3, $|m| = 2$with frequency 1.03 c d-1. It is shown that an emission line outburst occurred in the middle of the campaign. Two scenarios are proposed to explain the behaviour of a dense cloud, temporarily orbiting around the star with a frequency 0.46 c d-1, in relation to the outburst.

Pulsational properties of 1.8 $M_{\odot }$stellar models covering the latest stages of contraction toward the main sequence up to early hydrogen burning phases are investigated by means of linear nonadiabatic analyses. Results confirm that pre-main sequence stars (pms) which cross the classical instability strip on their way toward the main sequence are pulsationally unstable with respect to the classical opacity mechanisms. For both pms and main sequence types of models in the lower part of the instability strip, the unstable frequency range is found to be roughly the same. Some non-radial unstable modes are very sensitive to the deep internal structure of the star. It is shown that discrimination between pms and main sequence stages is possible using differences in their oscillation frequency distributions in the low frequency range.

A reanalysis of photometric data for the bright, southern Herbig Ae star HR 5999 obtained by Praderie et al. ([CITE]) at ESO in 1985 shows δScuti pulsation with the same period, 4.812 d-1, and semi-amplitude, 6 mmag, found by Kurtz & Marang ([CITE]) in data obtained from SAAO in 1994. HR 5999 is, therefore, a potential candidate to test Breger & Pamyatnykh's ([CITE]) predictions of evolutionary period changes 10 to 100 times faster in pre-main sequence δScuti stars than in post-main sequence stars. We argue that the low frequency, low amplitude $\alpha^2$CVn variability of HR 6000 with a period near 2 d, and its long-term variability are no hindrance to using it as a comparison star for study of the δScuti variability of HR 5999. With a separation of 44 arcsec between HR 5999 and HR 6000, and similar brightnesses for the two stars, we urge the use of small telescopes with CCD photometers to obtain the long-term data necessary for the study of period change. We point out that this can be done under less-than-ideal photometric conditions and urban lighting with CCD photometers on small telescopes which are widely available at small observatories, at universities and at the home observatories of serious amateur astronomers.

Context. We present an analysis of the observations of HD?51106 and HD?50747 by the satellite CoRoT, obtained during its initial run, and of the spectroscopic preparatory observations.Aims. We complete an analysis of the light curve, extract the main frequencies observed, and discuss some preliminary interpretations about the stars.Methods. We used standard Fourier transform and pre-whitening methods to extract information about the periodicities of the stars.Results. HD 51106 is an ellipsoidal binary, the light curve of which can be completely explained by the tidal deformation of the star and smaller secondary effects. HD?50747 is a triple system containing a variable star, which exhibits many modes of oscillation with periods in the range of a few hours. On the basis of this period range and the analysis of the physical parameters of the star, we conclude that HD?50747 is a ?-Doradus star.

Context. Aims. This work presents the results obtained by CoRoT on HD?50844, the only ? Sct star observed in the CoRoT initial run (57.6?d). The aim of these CoRoT observations was to investigate and characterize for the first time the pulsational behaviour of a ? Sct star, when observed at a level of precision and with a much better duty cycle than from the ground.Methods. The 140?016 datapoints were analysed using independent approaches (SigSpec software and different iterative sine-wave fittings) and several checks performed (splitting of the timeseries in different subsets, investigation of the residual light curves and spectra). A level of 10-5?mag was reached in the amplitude spectra of the CoRoT timeseries. The space monitoring was complemented by ground-based high-resolution spectroscopy, which allowed the mode identification of 30?terms. Results. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0?30?d-1. All the cross-checks confirmed this new result. The initial guess that ? Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high-degree modes (up to ?=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground-based observations indicate that HD?50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term (f1=6.92?d-1) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data.?Conclusions.