References of "Morel, Thierry"
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See detailThe gaia-ESO survey and massive stars
Blomme, R.; Fremat, Y.; Gosset, Eric ULg et al

in IAU Symposium 307 (2014)

As part of the Gaia-ESO Survey (GES), a number of clusters will be observed that were chosen speci cally for their massive-star content. We report on the procedures we followed to determine the stellar ... [more ▼]

As part of the Gaia-ESO Survey (GES), a number of clusters will be observed that were chosen speci cally for their massive-star content. We report on the procedures we followed to determine the stellar parameters from the massive-star spectra of this survey. We intercompare the results from the di erent techniques used by the nodes of our group to determine these parameters and discuss some of the problems encountered. We present preliminary results for NGC 6705, NGC 3293, and Trumpler 14. We study microturbulence in A-type stars, we use the repeat observation to investigate binarity, and we determine cluster membership from the radial velocity information. The large number of massive-star spectra obtained by the Gaia-ESO Survey will allow us to critically test stellar evolution modelling [less ▲]

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See detailNGC 3293 revisited by the Gaia-ESO Survey
Semaan, Thierry ULg; Morel, Thierry ULg; Gosset, Eric ULg et al

in IAU Symposium 307 (2014)

In the framework of the Gaia-ESO survey we have determined the fundamental parame- ters of a large number of B-type stars in the Galactic, young ope n cluster NGC 3293. The determination of the stellar ... [more ▼]

In the framework of the Gaia-ESO survey we have determined the fundamental parame- ters of a large number of B-type stars in the Galactic, young ope n cluster NGC 3293. The determination of the stellar parameters is based on medium- resolution spectra obtained with FLAMES/GIRAFFE at ESO-VLT. As a second step, we adopted the acc urate parameters to determine the chemical abundances of these hot stars. We pre sent a comparison of our results with those obtained by the ’VLT-FLAMES survey of massive sta rs’ (Evans et al. 2005). Our study increases the number of objects analysed and provides an extended view of this cluster. [less ▲]

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See detailAbundance study of two magnetic B-type stars in the Orion Nebula Cluster
Morel, Thierry ULg

in IAU Symposium 307 (2014)

We present the results of an abundance analysis of two magnetic B-type stars in the Orion Nebula Cluster that support the lack of a direct relationship between the existence of a magnetic field and a ... [more ▼]

We present the results of an abundance analysis of two magnetic B-type stars in the Orion Nebula Cluster that support the lack of a direct relationship between the existence of a magnetic field and a nitrogen excess in the photosphere. [less ▲]

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See detailThe B Fields in OB Stars (BOB) Survey
Morel, Thierry ULg; Castro, N.; Fossati, L. et al

in IAU Symposium (2014)

The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ... [more ▼]

The B fields in OB stars (BOB) survey is an ESO large programme collecting spectropolarimetric observations for a large number of early-type stars in order to study the occurrence rate, properties, and ultimately the origin of magnetic fields in massive stars. As of July 2014, a total of 98 objects were observed over 20 nights with FORS2 and HARPSpol. Our preliminary results indicate that the fraction of magnetic OB stars with an organised, detectable field is low. This conclusion, now independently reached by two different surveys, has profound implications for any theoretical model attempting to explain the field formation in these objects. We discuss in this contribution some important issues addressed by our observations (e.g., the lower bound of the field strength) and the discovery of some remarkable objects. [less ▲]

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See detailObservations of Red Giants in the Cluster NGC 6633 by the CoRoT Space Mission and the HARPS and SOPHIE Spectrometers
Barban, C.; Baudin, F.; Poretti, E. et al

in Astronomical Society of the Pacific Conference Series (2013, December 01)

The CoRoT space mission and the HARPS and SOPHIE ground-based spectrometers have observed red giants belonging to the open cluster NGC 6633. Solar-like oscillations are detected in the CoRoT data obtained ... [more ▼]

The CoRoT space mission and the HARPS and SOPHIE ground-based spectrometers have observed red giants belonging to the open cluster NGC 6633. Solar-like oscillations are detected in the CoRoT data obtained for four red giants. Spectroscopic data questions the cluster membership of one of these stars. The combination of these photometric and spectroscopic data will be a unique opportunity to estimate their global parameters as well as to probe their internal structure. [less ▲]

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See detailHD 45314: a new γ Cassiopeiae analog among Oe stars
Rauw, Grégor ULg; Nazé, Yaël ULg; Spano, M. et al

in Astronomy and Astrophysics (2013), 555

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for ... [more ▼]

Context. Oe stars possibly form an extension to higher temperatures of the Be phenomenon, but it is still unclear whether these stars have disks. <BR /> Aims: X-ray spectra could provide hints for interactions of the star with a putative surrounding disk. <BR /> Methods: We obtained XMM-Newton observations of two Oe stars, HD 45314 and HD 60848. Spectra and light curves were extracted and analysed. Optical spectra were also obtained to support the X-ray observations. <BR /> Results: We find that both stars display very different X-ray properties. Whilst HD 60848 has an X-ray spectrum and emission level typical for its spectral type, HD 45314 displays a very hard X-ray emission, dominated by a thermal plasma with kT ~ 21 keV. Furthermore, HD 45314 displays count rate variations by a factor 2 on timescales of ~ 10[SUP]3[/SUP] s and a high log (L[SUB]X[/SUB]/L[SUB]bol[/SUB]) = -6.10 ± 0.03. <BR /> Conclusions: The X-ray properties of HD 45314 indicate that this star is a new member of the class of γ Cas analogs, the first one among the original category of Oe stars. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), and observations collected at the European Southern Observatory (La Silla, Chile) and the Observatoire de Haute Provence (France). [less ▲]

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See detailMassive Stars in the Gaia-ESO Survey
Blomme, Ronny; Fremat, Yves; Lobel, Alex et al

in Massive Stars: From alpha to Omega (2013, June 01)

The Gaia-ESO Survey (GES) is an ambitious project to study the formation and evolution of the Milky Way and its stellar populations. It is led by Gerry Gilmore and Sofia Randich and includes about 350 Co ... [more ▼]

The Gaia-ESO Survey (GES) is an ambitious project to study the formation and evolution of the Milky Way and its stellar populations. It is led by Gerry Gilmore and Sofia Randich and includes about 350 Co-Investigators. During 300 nights (spread over 5 years) of order 10^5 Giraffe spectra and 10^4 UVES spectra will be taken. As part of the survey, about 13 clusters will be observed that were chosen specifically for their massive-star content. We report on the preliminary analysis of GES data from two such clusters: NGC 3293 and NGC 6705. We determine stellar parameters for the B-type stars in NGC 3293 and compare the A-type stars population between the two clusters. We also use a repeat observation to study binarity and use the radial velocity information to study cluster membership in NGC 3293. We also list our plans for future observations, which include the Carina nebula region. [less ▲]

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See detailAn Observational Study of Mixing in Fast-Rotating Massive Stars: Description of the Method and Very First Results
Morel, Thierry ULg; Palate, Matthieu ULg; Rauw, Grégor ULg

in Massive Stars: From alpha to Omega (2013, June 01)

Collecting He and CNO abundances for a large sample of fast-rotating massive stars is crucial for addressing the efficiency of rotational mixing in these objects. This is becoming a pressing issue ... [more ▼]

Collecting He and CNO abundances for a large sample of fast-rotating massive stars is crucial for addressing the efficiency of rotational mixing in these objects. This is becoming a pressing issue following the recent recognition based on observations by the VLT-FLAMES Survey of massive stars that fast rotators can show no signs of deep mixing contrary to the predictions of models. We have embarked in a project aiming at determining the abundances of the key elements indicators of mixing in a sample of bright, Galactic OB dwarfs. We present here the method and the very first results for two of the fastest OB stars known vsin i = 400 km/s : HD 93521 and zeta Oph. [less ▲]

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See detailSolar-like oscillations in distant stars as seen by CoRoT : the special case of HD 42618, a solar sister
Barban, C.; Deheuvels, S.; Goupil, M. J. et al

in Journal of Physics: Conference Series (2013), 440

We report the observations of a main-sequence star, HD 42618 (T[SUB]eff[/SUB] = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its ... [more ▼]

We report the observations of a main-sequence star, HD 42618 (T[SUB]eff[/SUB] = 5765 K, G3V) by the space telescope CoRoT. This is the closest star to the Sun ever observed by CoRoT in term of its fundamental parameters. Using a preliminary version of CoRoT light curves of HD 42618, p modes are detected around 3.2 mHz associated to l = 0, 1 and 2 modes with a large spacing of 142 μHz. Various methods are then used to derive the mass and radius of this star (scaling relations from solar values as well as comparison between theoretical and observationnal frequencies) giving values in the range of (0.80 - 1.02)M[SUB]solar[/SUB] and (0.91 - 1.01)R[SUB]solar[/SUB]. A preliminary analysis of l = 0 and 1 modes allows us also to study the amount of penetrative convection at the base of the convective envelope. [less ▲]

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See detailAbundance study of the two solar-analogue CoRoT targets HD 42618 and HD 43587 from HARPS spectroscopy
Morel, Thierry ULg; Rainer, M.; Poretti, E. et al

in Astronomy and Astrophysics (2013), 552

We present a detailed abundance study based on spectroscopic data obtained with HARPS of two solar-analogue main targets for the asteroseismology programme of the CoRoT satellite: HD 42618 and HD 43587 ... [more ▼]

We present a detailed abundance study based on spectroscopic data obtained with HARPS of two solar-analogue main targets for the asteroseismology programme of the CoRoT satellite: HD 42618 and HD 43587. The atmospheric parameters and chemical composition are accurately determined through a fully differential analysis with respect to the Sun observed with the same instrumental set-up. Several sources of systematic errors largely cancel out with this approach, which allows us to narrow down the 1-σ error bars to typically 20 K in effective temperature, 0.04 dex in surface gravity, and less than 0.05 dex in the elemental abundances. Although HD 42618 fulfils many requirements for being classified as a solar twin, its slight deficiency in metals and its possibly younger age indicate that, strictly speaking, it does not belong to this class of objects. On the other hand, HD 43587 is slightly more massive and evolved. In addition, marked differences are found in the amount of lithium present in the photospheres of these two stars, which might reveal different mixing properties in their interiors. These results will put tight constraints on the forthcoming theoretical modelling of their solar-like oscillations and contribute to increase our knowledge of the fundamental parameters and internal structure of stars similar to our Sun. Based on observations collected at the La Silla Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6-m telescope, under programme LP185.D-0056.Tables 1 and 2 are available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailDifferential population studies using asteroseismology: Solar-like oscillating giants in CoRoT fields LRc01 and LRa01
Miglio, A.; Chiappini, C.; Morel, Thierry ULg et al

in European Physical Journal Web of Conferences (2013, March 01)

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric ... [more ▼]

Solar-like oscillating giants observed by the space-borne satellites CoRoT and Kepler can be used as key tracers of stellar populations in the Milky Way. When combined with additional photometric/spectroscopic constraints, the pulsation spectra of solar-like oscillating giant stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which can be used as proxies for the ages of these evolved stars. In this contribution we provide supplementary material to the comparison we presented in Miglio et al. (2013) between populations of giants observed by CoRoT in the fields designated LRc01 and LRa01. [less ▲]

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See detailAn abundance study of the red giants in the seismology fields of the CoRoT satellite
Morel, Thierry ULg; Miglio, A.; Lagarde, N. et al

in European Physical Journal Web of Conferences (2013, March 01)

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. The optical spectra obtained for 19 targets have been ... [more ▼]

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. The optical spectra obtained for 19 targets have been used to accurately estimate their fundamental parameters and chemical composition. The extent of internal mixing is also investigated through the abundances of Li, CNO and Na (as well as [SUP]12[/SUP]C/[SUP]13[/SUP]C in a few cases). [less ▲]

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See detailHigh-precision CoRoT space photometry and fundamental parameter determination of the B2.5V star HD 48977
Thoul, Anne ULg; Degroote, Pieter; Catala, Claude et al

in Astronomy and Astrophysics (2013), 551

We present the CoRoT light curve of the bright B2.5V star HD 48977 observed during a short run of the mission in 2008, as well as a high-resolution spectrum gathered with the HERMES spectrograph at the ... [more ▼]

We present the CoRoT light curve of the bright B2.5V star HD 48977 observed during a short run of the mission in 2008, as well as a high-resolution spectrum gathered with the HERMES spectrograph at the Mercator telescope. We use several time series analysis tools to explore the nature of the variations present in the light curve. We perform a detailed analysis of the spectrum of the star to determine its fundamental parameters and its element abundances. We find a large number of high-order g-modes, and one rotationally induced frequency. We find stable low-amplitude frequencies in the p-mode regime as well. We conclude that HD 48977 is a new Slowly Pulsating B star with fundamental parameters found to be Teff = 20000 $\pm$ 1000 K and log(g)=4.2 $/pm$ 0.1. The element abundances are similar to those found for other B stars in the solar neighbourhood. HD 48977 was observed during a short run of the CoRoT satellite implying that the frequency precision is insufficient to perform asteroseismic modelling of the star. Nevertheless, we show that a longer time series of this star would be promising for such modelling. Our present study contributes to a detailed mapping of the instability strips of B stars in view of the dominance of g-mode pulsations in the star, several of which occur in the gravito-inertial regime. [less ▲]

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See detailGalactic archaeology: mapping and dating stellar populations with asteroseismology of red-giant stars
Miglio, A.; Chiappini, C.; Morel, Thierry ULg et al

in Monthly Notices of the Royal Astronomical Society (2013), 429

Our understanding of how the Galaxy was formed and evolves is severely hampered by the lack of precise constraints on basic stellar properties such as distances, masses and ages. Here, we show that solar ... [more ▼]

Our understanding of how the Galaxy was formed and evolves is severely hampered by the lack of precise constraints on basic stellar properties such as distances, masses and ages. Here, we show that solar-like pulsating red giants represent a well-populated class of accurate distance indicators, spanning a large age range, which can be used to map and date the Galactic disc in the regions probed by observations made by the CoRoT and Kepler space telescopes. When combined with photometric constraints, the pulsation spectra of such evolved stars not only reveal their radii, and hence distances, but also provide well-constrained estimates of their masses, which are reliable proxies for the ages of the stars. As a first application, we consider red giants observed by CoRoT in two different parts of the Milky Way, and determine precise distances for ˜2000 stars spread across nearly 15 000 pc of the Galactic disc, exploring regions which are a long way from the solar neighbourhood. We find significant differences in the mass distributions of these two samples which, by comparison with predictions of synthetic models of the Milky Way, we interpret as mainly due to the vertical gradient in the distribution of stellar masses (hence ages) in the disc. In the future, the availability of spectroscopic constraints for this sample of stars will not only improve the age determination, but also provide crucial constraints on age-velocity and age-metallicity relations at different Galactocentric radii and heights from the plane. [less ▲]

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See detailCoRoT Observations of O Stars: Diverse Origins of Variability
Blomme, R.; Briquet, Maryline ULg; Degroote, P. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

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 ... [more ▼]

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 modeling 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. [less ▲]

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See detailAre Magnetic OB Stars More Prone to Mixing? Still an Unsettled Issue
Morel, Thierry ULg

in Astronomical Society of the Pacific Conference Series (2013, January 01)

We review our knowledge of the mixing properties of magnetic OB stars and discuss whether the observational data presently available support, as predicted by some theoretical models, the idea that ... [more ▼]

We review our knowledge of the mixing properties of magnetic OB stars and discuss whether the observational data presently available support, as predicted by some theoretical models, the idea that magnetic phenomena favour the transport of chemical elements. A (likely statistical) relationship between enhanced mixing and the existence of a field has been emerging over the last few years. As discussed in this contribution, however, a clear answer to this question is presently hampered by the lack of large and well-defined samples of magnetic and non-magnetic stars. [less ▲]

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See detailGAUFRE: a tool for an automated determination of atmospheric parameters from spectroscopy
Valentini, Marica ULg; Morel, Thierry ULg; Miglio, Andrea et al

in 40th Liege International Astrophysical Colloquium 'Ageing low-mass stars: from red giants to white dwarfs' (2013, January 01)

We present an automated tool for measuring atmospheric parameters (T_eff, log(g), [Fe/H]) for F-G-K dwarf and giant stars. The tool, called GAUFRE, is written in C++ and composed of several routines ... [more ▼]

We present an automated tool for measuring atmospheric parameters (T_eff, log(g), [Fe/H]) for F-G-K dwarf and giant stars. The tool, called GAUFRE, is written in C++ and composed of several routines: GAUFRE-RV measures radial velocity from spectra via cross-correlation against a synthetic template, GAUFRE-EW measures atmospheric parameters through the classic line-by-line technique and GAUFRE-CHI2 performs a chi^2 fitting to a library of synthetic spectra. A set of F-G-K stars extensively studied in the literature were used as a benchmark for the program: their high signal-to-noise and high resolution spectra were analysed by using GAUFRE and results were compared with those present in literature. The tool is also implemented in order to perform the spectral analysis after fixing the surface gravity (log(g)) to the accurate value provided by asteroseismology. A set of CoRoT stars, belonging to LRc01 and LRa01 fields was used for first testing the performances and the behaviour of the program when using the seismic log(g). [less ▲]

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See detail2009: A Colliding-Wind Odyssey
Fahed, R.; Moffat, A. F. J.; Zorec, J. et al

in Astronomical Society of the Pacific Conference Series (2013, January 01)

We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which ... [more ▼]

We present the results from two optical spectroscopic campaigns on colliding-wind binaries (CWB) which both occurred in 2009. The first one was on WR 140 (WC7pd + O5.5fc), the archetype of CWB, which experienced periastron passage of its highly elliptical 8-year orbit in January. The WR 140 campaign consisted of a unique and constructive collaboration between amateur and professional astronomers and took place at half a dozen locations, including Teide Observatory, Observatoire de Haute Provence, Dominion Astrophysical Observatory, Observatoire du Mont-Mégantic and at several small private observatories. The second campaign was on a selection of 5 short-period WR + O binaries not yet studied for colliding-wind effects: WR 12 (WN8h), WR 21 (WN5o + O7 V), WR 30 (WC6 + O7.5 V), WR 31 (WN4o + O8), and WR 47 (WN6o + O5). The campaign took place at Leoncito Observatory, Argentina, during 1 month. We provide updated values of most of these systems for the orbital parameters, new estimates for the WR and O star masses and new constraints on the mass-loss rates and colliding wind geometry. [less ▲]

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See detailMultisite spectroscopic seismic study of the β Cep star V2052 Ophiuchi: inhibition of mixing by its magnetic field
Briquet, Maryline ULg; Neiner, C.; Aerts, C. et al

in Monthly Notices of the Royal Astronomical Society (2012), 427

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is ... [more ▼]

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d-1) and by rotational modulation (P_rot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03 d-1 and f3 = 6.823 08 d-1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees ℓ of the pulsation modes, we show that both f_2 and f_3 are prograde modes with (ℓ, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6] M_sun) and central hydrogen abundance (X_c ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n1 = 1, n2 = -3 and n3 = -2, and to derive an equatorial rotation velocity v_eq ∈ [71, 75] km s-1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (α_ov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior. [less ▲]

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See detailThe nature of the high Galactic latitude O-star HD 93521: new results from X-ray and optical spectroscopy
Rauw, Grégor ULg; Morel, Thierry ULg; Palate, Matthieu ULg

in Astronomy and Astrophysics (2012), 546

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations ... [more ▼]

Context. Owing to its unusual location and its isolation, the nature of the high Galactic latitude O9.5 Vp object HD 93521 is still uncertain. <BR /> Aims: We have collected X-ray and optical observations to characterize the star and its surroundings. <BR /> Methods: X-ray images and spectra are analysed to search for traces of a recent star formation event around HD 93521 and to search for the signature of a possible compact companion. Optical echelle spectra are analysed with plane-parallel model atmosphere codes, assuming either a spherical star or a gravity darkened rotationally flattened star, to infer the effective temperature and surface gravity, and to derive the He, C, N and O abundances of HD 93521. <BR /> Results: The X-ray images reveal no traces of a population of young low-mass stars coeval with HD 93521. The X-ray spectrum of HD 93521 is consistent with a normal late O-type star although with subsolar metallicity. No trace of a compact companion is found in the X-ray data. In the optical spectrum, He and N are found to be overabundant, in line with the effect of rotational mixing in this very fast rotator, whilst C and O are subsolar. A critical comparison with the properties of subdwarf OB stars, indicates that, despite some apparent similarities, HD 93521 does not belong to this category. <BR /> Conclusions: Despite some ambiguities on the runaway status of the star, the most likely explanation is that HD 93521 is a Population I massive O-type star that was ejected from the Galactic plane either through dynamical interactions or a result of a supernova event in a binary system. Based on observations collected at the Observatoire de Haute Provence (France) and with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA).Hα images are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A77</A> [less ▲]

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