References of "Morel, Thierry"
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See detailNitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
Morel, Thierry ULg; Hubrig, S.; Briquet, Maryline ULg

in Astronomy and Astrophysics (2008), 481

Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to ... [more ▼]

Evolutionary models for massive stars, accounting for rotational mixing effects, do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations, we present a detailed and fully-homogeneous, NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted, yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established, either from the occurrence of phase-locked UV wind line-profile variations, which can be ascribed to rotational modulation, or from theoretical modelling in the pulsating variables. The observational data presently available suggest a higher incidence of chemical peculiarities in stars with a (weak) detected magnetic field. This opens the possibility that magnetic phenomena are important in altering the photospheric abundances of early B dwarfs, even for surface field strengths at the one hundred Gauss level. However, further spectropolarimetric observations are needed to assess the validity of this hypothesis. [less ▲]

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See detailThe Chemical Composition of B-type Pulsators: Some Unexpected Results
Morel, Thierry ULg; Briquet, Maryline ULg; Aerts, C.

in Precision Spectroscopy in Astrophysics (2008)

We present a project aimed at self-consistently deriving the physical parameters and chemical composition of massive pulsators (β, Cephei stars, Slowly Pulsating B stars) based on high-resolution optical ... [more ▼]

We present a project aimed at self-consistently deriving the physical parameters and chemical composition of massive pulsators (β, Cephei stars, Slowly Pulsating B stars) based on high-resolution optical spectra. Such data will be essential for a proper theoretical interpretation of their oscillation spectrum, but may also contribute in a broader context to our understanding of mixing and diffusion processes in B-type stars. As an illustration, our first results reveal the existence of core-processed material at the surface of some slowly-rotating β, Cephei stars which is not predicted by current evolutionary models including rotation. [less ▲]

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See detailDeep Mixing in Slowly-rotating B Dwarfs: the Possible Role Played by Magnetic Fields
Morel, Thierry ULg

in Unsolved Problems in Stellar Physics: A Conference in Honor of Douglas Gough (2007, November 01)

Evolutionary models for massive stars which take into account rotational mixing effects do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. We present a ... [more ▼]

Evolutionary models for massive stars which take into account rotational mixing effects do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. We present a detailed and fully homogeneous non-LTE abundance analysis of a sample of largely unevolved B stars which points to the existence of a population of intrinsically slowly-rotating, yet nitrogen-rich objects contrary to theoretical expectations. These observations are discussed in relation to the boron content and the (weak) magnetic field detected in some targets. [less ▲]

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See detailReconciling Solar Interior Models and Helioseismological Data: Constraints on the Neon Content of the Sun from Nearby B Stars
Morel, Thierry ULg; Butler, Keith

in Unsolved Problems in Stellar Physics: A Conference in Honor of Douglas Gough (2007, November 01)

The recent downward revision of the solar CNO photospheric abundances now leads to severe inconsistencies between theoretical models for the Sun's internal structure and the results of helioseismology ... [more ▼]

The recent downward revision of the solar CNO photospheric abundances now leads to severe inconsistencies between theoretical models for the Sun's internal structure and the results of helioseismology. There have been claims that the solar Ne abundance may be underestimated and that an increase in this ill-defined quantity could alleviate (or even completely solve) this problem. To address the validity of this hypothesis, we present a fully homogeneous non-LTE abundance analysis of the optical Ne I/II lines in a sample of 18 nearby B-type stars. Our very preliminary results point towards a mean neon abundance slightly higher than the new solar value, but apparently insufficient by itself to restore the agreement between the solar models and the helioseismological constraints. [less ▲]

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See detailTowards an understanding of the Of ? p star HD 191612: optical spectroscopy
Howarth, Ian D.; Walborn, Nolan R.; Lennon, Danny J. et al

in Monthly Notices of the Royal Astronomical Society (2007), 381(2), 433-446

We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f ? pe-O8fp). The Balmer and He i lines show strongly variable emission which is highly reproducible on a well ... [more ▼]

We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f ? pe-O8fp). The Balmer and He i lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. He ii absorptions and metal lines (including many selective emission lines but excluding He ii lambda 4686 angstrom emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P-orb = 1542 d, e = 0.45. We conduct a model-atmosphere analysis of the spectrum, and find that the system is consistent with a similar to O8 giant with a similar to B1 main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying 'clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint. [less ▲]

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See detailAn abundance analysis of slowly pulsating B stars
Briquet, Maryline ULg; Morel, Thierry ULg

in Communications in Asteroseismology (2007), 150

We present the methodology and the first results of a study aimed to determine in a self-consistent way the physical parameters T_{eff} and log g as well as NLTE abundances of the majority of all ... [more ▼]

We present the methodology and the first results of a study aimed to determine in a self-consistent way the physical parameters T_{eff} and log g as well as NLTE abundances of the majority of all confirmed slowly pulsating B stars (hereafter SPBs). [less ▲]

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See detailNitrogen excess in slowly-rotating beta Cephei stars: deep mixing or diffusion?
Morel, Thierry ULg; Butler, K.; Aerts, C. et al

in Communications in Asteroseismology (2007), 150

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of ... [more ▼]

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of nitrogen-enriched material at their surface. Although the origin of this nitrogen excess remains unclear, an overabundance preferentially occurring in stars with a detected magnetic field seems to emerge at this stage. Full details can be found in Morel et al. (2006). [less ▲]

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See detailAn abundance study of the B-type targets for the asteroseismology programme of the CoRoT mission
Morel, Thierry ULg; Aerts, C.

in Communications in Asteroseismology (2007), 150

We present the very first results of a project aimed at deriving the detailed chemical composition of the B-type stars in the eyes of CoRoT, focusing here on the two primary targets HD 170580 and HD ... [more ▼]

We present the very first results of a project aimed at deriving the detailed chemical composition of the B-type stars in the eyes of CoRoT, focusing here on the two primary targets HD 170580 and HD 180642. [less ▲]

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See detailThe early-type close binary CV Velorum revisited
Yakut, K.; Aerts, C.; Morel, Thierry ULg

in Astronomy and Astrophysics (2007), 467

Aims:Our goal was to improve the fundamental parameters of the massive close double-lined eclipsing B2.5V+B2.5V binary CV Velorum. <BR />Methods: We gathered new high-resolution échelle spectroscopy on ... [more ▼]

Aims:Our goal was to improve the fundamental parameters of the massive close double-lined eclipsing B2.5V+B2.5V binary CV Velorum. <BR />Methods: We gathered new high-resolution échelle spectroscopy on 13 almost consecutive nights covering two orbits. We computed a simultaneous solution to all the available high-quality radial-velocity and light data with the latest version of the Wilson-Deviney code. <BR />Results: We obtained the following values for the physical parameters: M[SUB]1[/SUB] = 6.066(74)~M_ȯ, M[SUB]2[/SUB] = 5.972(70)~M_ȯ, R[SUB]1[/SUB] = 4.126(24)~R_ȯ, R[SUB]2[/SUB] = 3.908(27)~R_ȯ, log L[SUB]1[/SUB] = 3.20(5)~L_ȯ, and log L[SUB]2[/SUB] = 3.14(5)~L_ȯ. The quoted errors contain a realistic estimate of systematic uncertainties mainly stemming from the effective temperature estimation. We derived abundances for both components and found them to be compatible with those of B stars in the solar neighbourhood. We discovered low-amplitude periodic line-profile variations with the orbital frequency for both components. Their interpretation requires new data with a longer time span. The primary rotates subsynchronously while the secondary's v sin i and radius are compatible with synchronous rotation. We provide an update of the empirical mass-luminosity relation for main-sequence B stars which can be used for statistical predictions of masses or luminosities. Based on spectroscopic observations gathered with the CORALIE spectrograph mounted on the 1.2 m Euler telescope at La Silla, Chile. [less ▲]

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See detailAn asteroseismic study of the β cephei star θ ophiuchi : constraints on global stellar parameters and core overshooting
Briquet, Maryline ULg; Morel, Thierry ULg; Thoul, Anne ULg et al

in Monthly Notices of the Royal Astronomical Society (2007), 381(4), 1482-1488

We present a seismic study of the beta Cephei star theta Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split l = 1 triplet and three components of a rotationally ... [more ▼]

We present a seismic study of the beta Cephei star theta Ophiuchi. Our analysis is based on the observation of one radial mode, one rotationally split l = 1 triplet and three components of a rotationally split l = 2 quintuplet for which the m values were well identified by spectroscopy. We identify the radial mode as fundamental, the triplet as p(1) and the quintuplet as g(1). Our non-local thermodynamic equilibrium abundance analysis results in a metallicity and CNO abundances in full agreement with the most recent updated solar values. With X epsilon [0.71, 0.7211] and Z epsilon [0.009, 0.015], and using the Asplund et al. mixture but with a Ne abundance about 0.3 dex larger, the matching of the three independent modes enables us to deduce constrained ranges for the mass (M = 8.2 +/- 0.3 M circle dot) and central hydrogen abundance (X-c = 0.38 +/- 0.02) of theta Oph and to prove the occurrence of core overshooting (alpha(ov) = 0.44 +/- 0.07). We also derive an equatorial rotation velocity of 29 +/- 7 km s(-1). Moreover, we show that the observed non-equidistance of the l = 1 triplet can be reproduced by the second-order effects of rotation. Finally, we show that the observed rotational splitting of two modes cannot rule out a rigid rotation model. [less ▲]

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See detailGRB 070920A: deep optical observations at the NOT.
Jaunsen, A. O.; Gorosabel, J.; Fynbo, J. P. U. et al

in GRB Coordinates Network (2007), 6921

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See detailAbundance analysis of prime B-type targets for asteroseismology. I. Nitrogen excess in slowly-rotating beta Cephei stars
Morel, Thierry ULg; Butler, K.; Aerts, C. et al

in Astronomy and Astrophysics (2006), 457

Seismic modelling of the β Cephei stars promises major advances in our understanding of the physics of early B-type stars on (or close to) the main sequence. However, a precise knowledge of their ... [more ▼]

Seismic modelling of the β Cephei stars promises major advances in our understanding of the physics of early B-type stars on (or close to) the main sequence. However, a precise knowledge of their physical parameters and metallicity is a prerequisite for correct mode identification and inferences regarding their internal structure. Here we present the results of a detailed NLTE abundance study of nine prime targets for theoretical modelling: <ASTROBJ>γ Peg</ASTROBJ>, <ASTROBJ>δ Cet</ASTROBJ>, <ASTROBJ>ν Eri</ASTROBJ>, <ASTROBJ>β CMa</ASTROBJ>, <ASTROBJ>ξ1 CMa</ASTROBJ>, <ASTROBJ>V836 Cen</ASTROBJ>, <ASTROBJ>V2052 Oph</ASTROBJ>, <ASTROBJ>β Cep</ASTROBJ> and DD (12) Lac (hereafter <ASTROBJ>12 Lac</ASTROBJ>). The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our curve-of-growth abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, Ω R, from seismic or line-profile variation studies: <ASTROBJ>β Cep</ASTROBJ> (Ω R ~ 26 km s[SUP]-1[/SUP]), <ASTROBJ>V2052 Oph</ASTROBJ> (Ω R ~ 56 km s[SUP]-1[/SUP]), <ASTROBJ>δ Cet</ASTROBJ> (Ω R < 28 km s[SUP]-1[/SUP]) and <ASTROBJ>ξ1 CMa</ASTROBJ> (Ω R sin i ⪠10 km s[SUP]-1[/SUP]). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in β Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied β Cephei stars compared to non-pulsating B-type stars of similar characteristics. [less ▲]

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See detailPhotospheric Abundance Peculiarities in RS CVn Binaries
Morel, Thierry ULg; Micela, Giuseppina; Favata, Fabio

in Astrophysics & Space Science (2006), 304

We discuss the results of a LTE abundance study of 14 single-lined RS CVn binaries. Increasingly peculiar abundance ratios are observed for the cooler and more active stars in this sample (this is best ... [more ▼]

We discuss the results of a LTE abundance study of 14 single-lined RS CVn binaries. Increasingly peculiar abundance ratios are observed for the cooler and more active stars in this sample (this is best illustrated in the case of oxygen). This may arise from the existence of large spot groups, departures from LTE much larger than anticipated and/or inadequacies in the Kurucz model atmospheres for these objects. [less ▲]

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See detailX1908+075: A Late O-Type Supergiant with a Neutron Star Companion
Morel, Thierry ULg; Grosdidier, Yves

in Astrophysics & Space Science (2006), 304

X1908 + 075 is a highly-absorbed Galactic X-ray source likely made up of a pulsar accreting wind material from a massive companion. We have used near-IR photometric data complemented by follow-up ... [more ▼]

X1908 + 075 is a highly-absorbed Galactic X-ray source likely made up of a pulsar accreting wind material from a massive companion. We have used near-IR photometric data complemented by follow-up spectroscopy to identify the likely counterpart to this X-ray source and to assign a spectral type O7.5 9.5 If to the primary. Further details can be found in Morel and Grosdidier (2005). [less ▲]

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See detailA Comparison of Methods for Photospheric Abundance Determinations in K-Type Stars
Affer, L.; Micela, G.; Morel, Thierry ULg et al

in Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites, ESO ASTROPHYSICS SYMPOSIA. ISBN 978-3-540-34135-2. Springer-Verlag, 2006, p. 31 (2006)

We have performed a detailed abundance analysis of six inactive K-type stars using high-resolution optical spectra. We have used three different techniques and compared the results obtained in order to ... [more ▼]

We have performed a detailed abundance analysis of six inactive K-type stars using high-resolution optical spectra. We have used three different techniques and compared the results obtained in order to establish their respective merits and faults. The two spectroscopic methods give consistent results suggesting that non- LTE effects are small, whereas the â mixedâ spectroscopic-photometric method leads to photospheric parameters and abundances systematically lower than those obtained with the other two. We have also determined the starsâ positions in H-R diagrams and made a comparison between the gravities derived from the ionization equilibrium of the iron lines and from the evolutionary tracks: the agreement is reasonably good. [less ▲]

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See detailSome Concerns About the Reliability of LTE Abundance Analyses in Cool, Active Stars
Morel, Thierry ULg; Micela, G.; Favata, F.

in Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites, ESO ASTROPHYSICS SYMPOSIA. ISBN 978-3-540-34135-2. Springer-Verlag, 2006, p. 64 (2006)

We discuss recent observational evidence illustrating the current limitations plaguing classical LTE abundance analyses of cool (T [SUB]eff[/SUB] < 5500 K), chromospherically active stars. Although ... [more ▼]

We discuss recent observational evidence illustrating the current limitations plaguing classical LTE abundance analyses of cool (T [SUB]eff[/SUB] < 5500 K), chromospherically active stars. Although significant progress on this issue can be evidently expected from a more realistic atmospheric modelling and treatment of NLTE line formation, a homogeneous abundance study of a large sample of inactive K-type stars may also prove valuable in disentangling temperature and activity effects. [less ▲]

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See detailSpectroscopic determination of photospheric parameters and chemical abundances of 6 K-type stars
Affer, L.; Micela, G.; Morel, Thierry ULg et al

in Astronomy and Astrophysics (2005), 433

High resolution, high -S/N- ratio optical spectra have been obtained for a sample of 6 K-type dwarf and subgiant stars, and have been analysed with three different LTE methods in order to derive detailed ... [more ▼]

High resolution, high -S/N- ratio optical spectra have been obtained for a sample of 6 K-type dwarf and subgiant stars, and have been analysed with three different LTE methods in order to derive detailed photospheric parameters and abundances and to compare the characteristics of analysis techniques. The results have been compared with the aim of determining the most robust method to perform complete spectroscopic analyses of K-type stars, and in this perspective the present work must be considered as a pilot study. In this context we have determined the abundance ratios with respect to iron of several elements. In the first method the photospheric parameters (T_eff, log g, and ξ) and metal abundances are derived using measured equivalent widths and Kurucz LTE model atmospheres as input for the MOOG software code. The analysis proceeds in an iterative way, and relies on the excitation equilibrium of the ion{Fe}{i} lines for determining the effective temperature and microturbulence, and on the ionization equilibrium of the ion{Fe}{i} and ion{Fe}{ii} lines for determining the surface gravity and the metallicity. The second method follows a similar approach, but discards the ion{Fe}{i} low excitation potential transitions (which are potentially affected by non-LTE effects) from the initial line list, and relies on the B-V colour index to determine the temperature. The third method relies on the detailed fitting of the 6162 à ion{Ca}{i} line to derive the surface gravity, using the same restricted line list as the second method. Methods 1 and 3 give consistent results for the program stars; in particular the comparison between the results obtained shows that the ion{Fe}{i} low-excitation potential transitions do not appear significantly affected by non-LTE effects (at least for the subgiant stars), as suggested by the good agreement of the atmospheric parameters and chemical abundances derived. The second method leads to systematically lower T_eff and log g values with respect to the first one, and a similar trend is shown by the chemical abundances (with the exception of the oxygen abundance). These differences, apart from residual non-LTE effects, may be a consequence of the colour-T_eff scale used. The α-elements have abundance ratios consistent with the solar values for all the program stars, as expected for â normalâ disk stars. The first method appears to be the most reliable one, as it is self-consistent, it always leads to convergent solutions and the results obtained are in good agreement with previous determinations in the literature. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roche de los Muchachos of the Instituto de Astrofisica de Canarias. Table 6 is only available in electronic form at http://www.edpsciences.org [less ▲]

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See detailPhotospheric abundance peculiarities in chromospherically active stars
Morel, Thierry ULg; Micela, G.; Favata, F.

in 13th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun (2005, March 01)

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See detailNear-infrared identification of the counterpart to X1908+075: a new OB-supergiant X-ray binary
Morel, Thierry ULg; Grosdidier, Y.

in Monthly Notices of the Royal Astronomical Society (2005), 356

We report the near-infrared (near-IR) identification of the likely counterpart to X1908+075, a highly absorbed Galactic X-ray source recently suspected to belong to the rare class of OB supergiant-neutron ... [more ▼]

We report the near-infrared (near-IR) identification of the likely counterpart to X1908+075, a highly absorbed Galactic X-ray source recently suspected to belong to the rare class of OB supergiant-neutron star binary systems. Our JHK[SUB]s[/SUB]-band imaging of the field reveals the existence within the X-ray error boxes of a near-IR source consistent with an early-type star lying at d~ 7 kpc and suffering A[SUB]V[/SUB]~ 16 mag of extinction, the latter value being in good agreement with the hydrogen column density derived from modelling of the X-ray spectrum. Our follow-up, near-IR spectroscopic observations confirm the nature of this candidate and lead to a late O-type supergiant classification, thereby supporting the identification of a new Galactic OB-supergiant X-ray binary. [less ▲]

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See detailThe photospheric abundances of active binaries. III. Abundance peculiarities at high activity levels
Morel, Thierry ULg; Micela, G.; Favata, F. et al

in Astronomy and Astrophysics (2004), 426

We report the determination from high-resolution spectra of the atmospheric parameters and abundances of 13 chemical species (among which lithium) in 8 single-lined active binaries. These data are ... [more ▼]

We report the determination from high-resolution spectra of the atmospheric parameters and abundances of 13 chemical species (among which lithium) in 8 single-lined active binaries. These data are combined with our previous results for 6 other RS CVn systems to examine a possible relationship between the photospheric abundance patterns and the stellar activity level. The stars analyzed are generally found to exhibit peculiar abundance ratios compared to inactive, Galactic disk stars of similar metallicities. We argue that this behaviour is unlikely to be an artefact of errors in the determination of the atmospheric parameters or non-standard mixing processes along the red giant branch, but diagnoses instead the combined action of various physical processes related to activity. The most promising candidates are cool spot groups covering a very substantial fraction of the stellar photosphere or NLTE effects arising from nonthermal excitation. However, we cannot exclude the possibility that more general shortcomings in our understanding of K-type stars (e.g. inadequacies in the atmospheric models) also play a significant role. Lastly, we call attention to the unreliability of the (V-R) and (V-I) colour indices as temperature indicators in chromospherically active stars. Based on observations collected at the European Southern Observatory, Chile (Proposals 64.L-0249 and 071.D-0260). Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/1007 [less ▲]

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