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Contains fulltext : 76072.pdf (Publisher’s version ) (Open Access) 5 p.

Contains fulltext : 111302.pdf (Author’s version preprint ) (Open Access) Contains fulltext : 111302.pdf (Publisher’s version ) (Closed access)

The aim of this work was to use a multi-approach technique to derive the most accurate values possible of the physical parameters of the ��Sct star HD174966. In addition, we searched for a periodic pattern in the frequency spectra with the goal of using it to determine the mean density of the star. First, we extracted the frequency content from the CoRoT light curve. Then, we derived the physical parameters of HD174966 and carried a mode identification out from the spectroscopic and photometric observations. We used this information to look for the models fulfilling all the conditions and discussed the inaccuracies of the method because of the rotation effects. In a final step, we searched for patterns in the frequency set using a Fourier transform, discussed its origin and studied the possibility of using the periodicity to obtain information about the physical parameters of the star. A total of 185 peaks were obtained from the Fourier analysis of the CoRoT light curve, being almost all reliable pulsating frequencies. From the spectroscopic observations, 18 oscillation modes were detected and identified, and the inclination angle ($62.5^{\circ}$$^{+7.5}_{-17.5}$) and the rotational velocity of the star (142 km/s) were estimated. From the multi-colour photometric observations, 3 frequencies were detected, which correspond to the main ones in the CoRoT light curve. We looked for periodicities within the 185 frequencies and found a periodic pattern ~64 ��Hz. Using the inclination angle, the rotational velocity and an Echelle diagram, showing a double comb outside the asymptotic regime, we concluded that the periodicity corresponds to a large separation structure. The periodic pattern allowed us to discriminate models from a grid, finding that the value of the mean density is achieved with a 6% uncertainty. So, the pattern could be used as a new observable for A-F type stars., 15 pages, 10 figures, 6 tables

We present a detailed spectroscopic study of 93 solar-type stars that are targets of the NASA/Kepler mission and provide detailed chemical composition of each target. We find that the overall metallicity is well-represented by Fe lines. Relative abundances of light elements (CNO) and alpha-elements are generally higher for low-metallicity stars. Our spectroscopic analysis benefits from the accurately measured surface gravity from the asteroseismic analysis of the Kepler light curves. The log g parameter is known to better than 0.03 dex and is held fixed in the analysis. We compare our Teff determination with a recent colour calibration of V-K (TYCHO V magnitude minus 2MASS Ks magnitude) and find very good agreement and a scatter of only 80 K, showing that for other nearby Kepler targets this index can be used. The asteroseismic log g values agree very well with the classical determination using Fe1-Fe2 balance, although we find a small systematic offset of 0.08 dex (asteroseismic log g values are lower). The abundance patterns of metals, alpha elements, and the light elements (CNO) show that a simple scaling by [Fe/H] is adequate to represent the metallicity of the stars, except for the stars with metallicity below -0.3, where alpha-enhancement becomes important. However, this is only important for a very small fraction of the Kepler sample. We therefore recommend that a simple scaling with [Fe/H] be employed in the asteroseismic analyses of large ensembles of solar-type stars., Comment: MNRAS, in press, 12 pages

We present the analysis of the time series observations of CoRoT\,102699796 obtained by the CoRoT satellite that show the presence of five independent oscillation frequencies in the range 3.6-5 c/d. Using spectra acquired with FLAMES@VLT, we derive the following stellar parameters: spectral type F1V, T$_{\rm eff}$=7000$\pm$200 K, log(g)=$3.8\pm0.4$, [M/H]=$-1.1\pm0.2$, $v$sin$i$=$50\pm5$ km/s, L/L$_{\odot}$=21$^{+21}_{-11}$. Thus, for the first time we report the existence of a metal poor, intermediate-mass PMS pulsating star. Ground-based and satellite data are used to derive the spectral energy distribution of CoRoT\,102699796 extending from the optical to mid-infrared wavelengths. The SED shows a significant IR excess at wavelengths greater than $\sim5 ��$. We conclude that CoRoT\,102699796 is a young Herbig Ae (F1Ve) star with a transitional disk, likely associated to the HII region [FT96]213.1-2.2. The pulsation frequencies have been interpreted in the light of the non-radial pulsation theory, using the LOSC code in conjunction with static and rotational evolutionary tracks. A minimization algorithm was used to find the best-fit model with M=1.84 M$_{\odot}$, T$_{\rm eff}$=6900 K which imply an isochronal age of t$\sim$2.5 Myr. This result is based on the interpretation of the detected frequencies as $g$-modes of low-moderate $n$-value. To our knowledge, this is the first time that such modes are identified in a intermediate-mass PMS pulsating star. Since CoRoT\,102699796 lies in the region of the HR diagram where the $��$ Sct and $��$ Dor instability strips intersect, we argue that the observed pulsation characteristics are intermediate between these classes of variables, i.e. CoRoT\,102699796 is likely the first PMS hybrid $��$ Dor-$��$ Sct pulsator ever studied., 13 pages, 7 figures. Accepted for publication in Monthly Notices of the RAS

Six O-type stars were observed continuously by the CoRoT satellite during a 34.3-day run. The unprecedented quality of the data allows us to detect even low-amplitude stellar pulsations in some of these stars (HD 46202 and the binaries HD 46149 and Plaskett's star). These cover both opacity-driven modes and solar-like stochastic oscillations, both of importance to the asteroseismological modelling of O stars. Additional effects can be seen in the CoRoT light curves, such as binarity and rotational modulation. Some of the hottest O-type stars (HD 46223, HD 46150 and HD 46966) are dominated by the presence of red-noise: we speculate that this is related to a sub-surface convection zone., Comment: 5 pages, 3 figures, conference paper. To be published in "Four decades of Research on Massive Stars", Astronomical Society of the Pacific. Eds. C. Robert, N. St-Louis and L. Drissen

The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the three medium class (M class) missions selected in 2010 for definition study in the framework of the ESA Cosmic Vision 2015-2025 program. The main scientific goals of PLATO are the i) discovery and study of extra-solar planetary systems, (including those hosting Earthlike planets in their habitable zone) by means of planetary transits detection from space and radial velocity follow-up from ground, and ii) the characterization of the hosting stars through seismic analysis, in order to determine with high accuracy planetary masses and ages. According to the study made by the PLATO Payload Consortium (PPLC) during the PLATO assessment phase, the scientific payload consists of 34 all refractive telescopes having small aperture (120 mm) and wide field of view (greater than 1000 degree2) observing over 0.5-1 micron wavelength band. The telescopes are mounted on a common optical bench and are divided in four families with an overlapping line-of-sight in order to maximize the science return. In this paper, we will describe the detailed design of the Telescope Optical Units (TOUs) focusing on the selected optical configuration and the expected performances.

Transiting planet systems offer an unique opportunity to observationally constrain proposed models of the interiors (radius, composition) and atmospheres (chemistry, dynamics) of extrasolar planets. The spectacular successes of ground-based transit surveys (more than 60 transiting systems known to-date) and the host of multi-wavelength, spectro-photometric follow-up studies, carried out in particular by HST and Spitzer, have paved the way to the next generation of transit search projects, which are currently ongoing (CoRoT, Kepler), or planned. The possibility of detecting and characterizing transiting Earth-sized planets in the habitable zone of their parent stars appears tantalizingly close. In this contribution we briefly review the power of the transit technique for characterization of extrasolar planets, summarize the state of the art of both ground-based and space-borne transit search programs, and illustrate how the science of planetary transits fits within the Blue Dots perspective., Comment: 9 pages, 3 figures, to be published in the proceedings (ASP Conf. Ser.) of the "Pathways Towards Habitable Planets" conference, held in Barcelona (14-18 Sep 2009)

We present an analysis of the ��-Scuti star object HD 174936 (ID 7613) observed by CoRoT during the first short run SRc01 (27 days). A total number of 422 frequencies we are 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 of around 52 \muHz. 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., 7 pages, 7 figures, 2 tables. Accepted for publication in A&A CoRoT Special Feature

Observations of magnetic fields of stars at the pre-main sequence phase can provide important new insights into the complex physics of the late stages of star formation. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organised, and therefore most amenable to direct study. Recent circularly-polarised spectroscopic observations of pre-main sequence Herbig Ae/Be stars have revealed the presence of organised magnetic fields in the photospheres of a small fraction of these objects. To date, 9 magnetic HAeBe stars have been detected, and those detections confirmed by repeated observations. The morphology and variability of their Stokes V signatures indicates that their magnetic fields have important dipole components of kG strength, and that the dipole is stable on timescales ofat least years. These magnetic stars exhibit a large range of stellar mass, from about 2-13 solar masses, and diverse rotational properties, with vsini from a few km/s to 200 km/s. Most magnetic HAeBe stars show approximately solar abundances; they clearly do not generally exhibit the strong and systematic peculiarities of the magnetic main sequence A and B type stars (the Ap/Bp stars). The observed fractional bulk incidence of magnetic HAeBe stars is about 7%, a value compatible with the incidence of magnetic intermediate-mass stars on the main sequence. This low incidence is at odds with formation scenarios generally involving magnetically-mediated accretion. The similarily between the magnetic properties of the pre-main sequence and main sequence intermediate-mass stars appears compatible with the hypothesis of a fossil origin of magnetism in these objects., Comment: 13 pages, 7 figs, proceedings of "Astronomical Polarimetry 2008: From small to large telescopes" (invited presentation)

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. Aims. Ground-based spectroscopic observations of the early Be star HD 49330 obtained during the precursor phase and just before the start of an outburst allow us to disantangle stellar and circumstellar contributions and identify modes of stellar pulsations in this rapidly rotating star. Methods. Time series analysis (TSA) is performed on photospheric line profiles of He i and Si iii by means of the least squares method. Results. We find two main frequencies f1 = 11.86 c d^−1 and f2 = 16.89 c d^−1 which can be associated with high order p-mode pulsations. We also detect a frequency f3 = 1.51 c d^−1 which can be associated with a low order g-mode. Moreover we show that the stellar line profile variability changed over the spectroscopic run. These results are in agreement with the results of the CoRoT data analysis, as shown in Huat et al. (2009). Conclusions. Our study of mid- and short-term spect roscopic variability allows the identification of p- and g- modes in HD 49330. It also allows us to display changes in the line profile variability before the start of an outburst. This brings new constraints for the seimic modelling of this star.

Context. HD 181231 is a B5IVe star, which has been observed with the CoRoT satellite during ∼5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry. Aims. By analysing these data, we aim to detect and characterize as many pulsation frequencies as possible, to search for the presence of beating effects possibly at the origin of the Be phenomenon. Our results will also pr ovide a basis for seismic modelling. Methods. The fundamental parameters of the star are determined from spectral fitting and from the study of the circumstellar emission. The CoRoT photometric data and ground-based spectroscopy are analysed using several Fourier Techniques: CLEAN-NG,PASPER,and TISAFT, as well as a time-frequency technique. A search for a magnetic field is performed by applying the LSD technique to the spectropolarimetric data. Results. We find that HD 181231 is a B5IVe star seen with an inclination of ∼45 degrees. No magnetic field is detected in its photo-sphere. We detect at least 10 independent significant frequencies of variations among the 54 detected frequencies, interpreted in termsof non-radial pulsation modes and rotation. Two longer-term variations are also detected: one at ∼14 days resulting from a beating effect between the two main frequencies of short-term variations, the other at ∼116 days due either to a beating of frequencies or to a zonal pulsation mode. Conclusions. Our analysis of the CoRoT light curve and ground-based spectroscopic data of HD 181231 has led to the determination of the fundamental and pulsational parameters of the star, including beating effects. This will allow a precise seismic modelling of this star.

Contains fulltext : 75637.pdf (Publisher’s version ) (Open Access) 13 p.

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.Aims.We present our analysis of CoRoT data of the B8IIIe star HD 175869 observed during the first short run in the center direction (SRC1).Methods.We review both the instrumental effects visible in the CoRoT light curve and the analysis methods used by the CoRoT Be team. We applied these methods to the CoRoT light curve of the star HD 175869. A search for line-profile variations in the spectroscopic data was also performed. We also searched for a magnetic field, by applying the LSD technique to spectropolarimetric data.Results.The light curve exhibits low-amplitude variations of the order of 300 μ mag with a double wave shape. A frequency within the range determined for the rotational frequency and 6 of its harmonics are detected. The main frequency and its first harmonic exhibit amplitude variations of a few days. Other significant frequencies of low-amplitude from 25 to a few μmag are also found. The analysis of line profiles from ground-based spectrosc opic data does not detect an y variation. In addition, no Zeeman signature was found.Conclusions.Inhomogeneities caused by stellar activity in or just above the photosphere are proposed to produce the photometric variability detected by CoRoT in the Be star HD 175869. The hypothesis that non-radial pulsations are the origin of these variations cannot be excluded.

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. Our goal is to analyse the detailed behaviour present in the light curve and interpret it in terms of excited mode frequencies. After describing the noise properties in detail, we use various time series analysis and fitting techniques to model the CoRoT light curve, for various physical assumptions. We apply statistical goodness-of-fit criteria that allow us to select the most appropriate physical model fit to the data. We conclude that the light curve model based on nonlinear resonant frequency and phase locking provides the best representation of the data. The interpretation of the residuals is dependent on the chosen physical model used to prewhiten the data. Our observational results constitute a fruitful starting point for detailed seismic stellar modelling of this large-amplitude and evolved Beta Cep star., Comment: 13 pages, 12 figures, accepted for publication in A&A, 27 may 2009

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution., Comment: 12 pages, 16 figures

The origin of the magnetic fields of the chemically peculiar main sequence Ap/Bp stars is still matter of intense debate. The recent discoveries of magnetic fields in Herbig Ae/Be stars using high resolution data obtained with the spectropolarimeter ESPaDOnS at CFHT provide a strong argument in favour of the fossil field hypothesis. Using a simple oblique rotator model of a centered dipole, we fit the Stokes V LSD profiles of two of these magnetic HAeBe stars, HD 200775 and V380 Ori, as well as their variations on timescales from days to months. We find that in both cases the dipole hypothesis is acceptable and we determine the rotation period, the angle between rotation and magnetic axes and the intensity of the magnetic field at pole., Comment: 5 pages, 4 figures. Proceeding of the 2006 conference of the Special Astrophysical Observatory of the Russian Academy of Sciences

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). Aims: We have calculated several sets of stellar models for the components of the RS Cha system, with the aim of reproducing simultaneously the available observational constraints and to estimate the age and initial helium abundance of the system. Methods: Using the CESAM stellar evolution code, we model both components starting from the initial mass and metallicity and adjusting the input parameters and physics in order to satisfy the observational constraints. Results: We find that the observations cannot be reproduced if we assume that the abundance ratios are solar but they are satisfied if carbon and nitrogen are depleted in the RS Cha system with respect to the Sun. This is in accordance with the abundances observed in other young stars. The RS Cha system is in an evolutionary stage at the end of the PMS phase where models are not strongly sensitive to various physical uncertainties. However we show that the oscillations of these two stars, which have been detected, would be able to discriminate between different options in the physical description of this evolutionary phase., Comment: 9 pages, 10 figures, accepted by Astronomy & Astrophysics

One of the goals of the ground-based support program for the COROT and MONS/RØMER satellite 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 COROT main targets using the semi-automatic software VWA. For two additional COROT targets 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 VWA software. 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 (ν sin i < 15 km s-1). For most of the stars we find good agreement with the parameters found from line depth ratios, Hα lines, Strömgren indices, previous spectroscopic studies, and also log g determined from the HIPPARCOS parallaxes. For the fast rotators (v sin i > 60 km s-1) it is not possible to constrain the atmospheric parameters.

To explain the origin of Herbig Ae/Be stars activity, it has been recently proposed that strong mass-losses trigger rotational instabilities in the envelope of fast rotating stars. The kinetic energy transferred to turbulent motions would then be the energy source of the active phenomena observed in the outer atmosphere of Herbig Ae/Be stars (Vigneron et al. 1990; Lignieres et al. 1996). In this paper, we present a one-dimensional model of angular momentum transport which allows to estimate the degree of differential rotation induced by mass-loss. Gradients of angular velocity are very close to - 2 \Omega / R (\Omega being the surface rotation rate and R the stellar radius). For strong mass-loss, this process occurs in a short time scale as compared to other processes of angular momentum transport. Application of existing stability criteria indicates that rotational instabilities should develop for fast rotating star. Thus, in fast rotating stars with strong winds, shear instabilities are expected to develop and to generate subphotospheric turbulent motions. Albeit very simple, this model gives strong support to the assumption made by Vigneron et al. 1990 and Lignieres et al. 1996., Comment: 7 pages, 5 figures, submitted to Astronomy and Astrophysics

Contains fulltext : 91637.pdf (Author’s version preprint ) (Open Access)

International audience

We are investigating the magnetic characteristics of pre-main sequence Herbig Ae/Be stars, with the aim of (1) understanding the origin and evolution of magnetism in intermediate-mass stars, and (2) exploring the influence of magnetic fields on accretion, rotation and mass-loss at the early stages of evolution of A, B and O stars. We have begun by conducting 2 large surveys of Herbig Ae/Be stars, searching for direct evidence of photospheric magnetic fields via the longitudinal Zeeman effect. From observations obtained using FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, we report the confirmed detection of magnetic fields in 4 pre-main sequence A- and B-type stars, and the apparent (but as yet unconfirmed) detection of fields in 2 other such stars. We do not confirm the detection of magnetic fields in several stars reported by other authors to be magnetic: HD 139614, HD 144432 or HD 31649. One of the most evolved stars in the detected sample, HD 72106A, shows clear evidence of strong photospheric chemical peculiarity, whereas many of the other (less evolved) stars do not. The magnetic fields that we detect appear to have surface intensities of order 1 kG, seem to be structured on global scales, and appear in about 10% of the stars studied. Based on these properties, these magnetic stars appear to be pre-main sequence progenitors of the magnetic Ap/Bp stars., v2: Include comment regarding publication source To appear in the proceedings of "Solar Polarisation 4", held in Boulder, USA, Sept. 2005

We lack a reliable scenario for the formation and evolution of stars and their planetary systems, involving key factors such as magnetic fields and turbulence. We present the case for a mission concept that will clarify these problems and give us a global view of the evolution of combined star and planetary systems. This will be achieved by simultaneously addressing the search for planetary transits in front of a large number of stars, including many nearby stars, the study of their internal structure and evolution via asteroseismology, and that of their magnetic activity, via UV monitoring.

Recently, strong, globally-ordered magnetic fields have been detected in some Herbig Ae and Be (HAeBe) stars, suggesting a possible evolutionary connection to main sequence magnetic chemically peculiar Ap and Bp stars. We have undertaken a detailed study of the binary system HD 72106, which contains a B9 magnetic primary and a HAeBe secondary, using the ESPaDOnS spectropolarimeter mounted on the CFHT. A careful analysis of the very young primary reveals that it has an approximately dipolar magnetic field geometry, strong chemical peculiarities, and strong surface chemical abundance inhomogeneities. Thus the primary is very similar to an Ap/Bp star despite having completed less then 1.5% of its main sequence life, and possibly still being on the pre-main sequence. In contrast, a similar analysis of the secondary reveals solar chemical abundances and no magnetic field., Proceedings of the CP#AP Workshop held in Vienna in September 2007

The satellite CoRoT (Convection, Rotation, and planetary Transits) has provided high-quality data for almost six years. We show here the asteroseismic analysis and modeling of HD169392A, which belongs to a binary system weakly gravitationally bound as the distance between the two components is of 4250 AU. The main component, HD169392A, is a G0IV star with a magnitude of 7.50 while the second component is a G0V-G2IV star with a magnitude of 8.98. This analysis focuses on the main component, as the secondary one is too faint to measure any seismic parameters. A complete modeling has been possible thanks to the complementary spectroscopic observations from HARPS, providing Teff=5985+/-60K, log g=3.96+/-0.07, and [Fe/H]=- 0.04+/-0.10., 6 pages, 1 figure. Proceedings of the Fujihara seminar held in Hakone (Japan) in November 2012

International audience

We present the preliminary results of a frequency and line-profile analysis of the CoRoT gamma Dor candidate HD171834. The data consist of 149 days of CoRoT light curves and a ground-based dataset of more than 1400 high-resolution spectra, obtained with six different instruments. Low-amplitude frequencies between 0 and 5 c/d, dominated by a frequency near 0.96 c/d and several of its harmonics, are detected. These findings suggest that HD171834 is not a mere gamma Dor pulsator and that stellar activity plays an important role in its variable behaviour. Based on CoRoT space data and on ground-based observations with ESO Telescopes at the La Silla Observatory under the ESO Large Programmes ESO LP 178.D-0361 and ESO LP 182.D-0356 (FEROS/2.2m and HARPS/3.6m), and data collected with FOCES/2.2m at the Centro Astronomico Hispano Aleman at Calar Alto, SOPHIE/1.93m at Observatoire de Haute Provence, FIES/NOT at Observatorio del Roque de los Muchachos, and HERCULES/1.0m at Mount John University Observatory., 4 pages, 4 figures, 1 table. Proceedings of the HELAS IV Conference, Lanzarote, February 2010

International audience; We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution.

Today, one of the greatest challenges concerning the Ap/Bp stars is to understand the origin of their slow rotation and their magnetic fields. The favoured hypothesis for the latter is the fossil field, which implies that the magnetic fields subsist throughout the different evolutionary phases, and in particular during the pre-main sequence phase. The existence of magnetic fields at the pre-main sequence phase is also required to explain the slow rotation of Ap/Bp stars. However, until recently, essentially no information was available about the magnetic properties of intermediate-mass pre-main sequence stars, the so-called Herbig Ae/Be stars. The new high-resolution spectropolarimeter ESPaDOnS, installed in 2005 at the Canada-France-Hawaii telescope, provided the capability necessary to perform surveys of the Herbig Ae/Be stars in order to investigate their magnetism and rotation. These investigations have resulted in the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars, ranging in mass from 2 to nearly 15 solar masses. In this contribution I will present the results of our survey, as well as their implications for the origin and evolution of the magnetic fields and rotation., Comment: Proceedings of the CP#AP Workshop held in Vienna in September 2007

Among the main sequence intermediate mass A and B stars, around 5% host large-scale organized magnetic fields. Most of these stars are very slow rotators compared to their non-magnetic counterparts, and show photospheric abundance anomalies. They are referred to as the Ap/Bp stars. One of the greatest challenges, today is to understand the origin of their magnetic field and their slow rotation. The favoured hypothesis is a fossil origin of the magnetic field, in which the magnetic fields of Ap/Bp stars are relics of those which existed in the parental molecular clouds during the formation. This implies that the magnetic field must survive all the initial phases of the stellar evolution and especially the pre-main sequence (PMS) phase. This is consistent with the general belief that magnetic braking occurs during the PMS phase, which sheds angular momentum and slows the rotation of these stars. In this context, we proceeded with a survey of a sample of around 50 PMS Herbig Ae/Be stars, using the new spectropolarimeter ESPaDOnS at the CFHT, in order to study the magnetic field and the rotation velocity of these stars. This talk reviews the results of our survey, as well as their consequences for the origin of the magnetic fields and the evolution of the rotation of intermediate mass stars during the PMS phase., 6 pages. To appear in the proceedings of "SF2A-2007: Semaine de l'Astrophysique Francaise", 2007, Grenoble, France (J. Bouvier, A. Chalabaev, C. Charbonnel eds)