References of "Morel, Thierry"
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See detailThe near-IR counterpart to the high-mass X-ray binary X1908+075
Morel, Thierry ULg; Grosdidier, Y.

in The Astronomer's Telegram (2004), 291

<html> We report the 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 ... [more ▼]

<html> We report the 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 (Wen et al. 2000, ApJ, 532, 1119; Levine et al. 2004, ApJ, submitted, astro-ph/0404428). The <em>Einstein</em> and <em>HEAO 1</em> satellites have localized this X-ray source with an uncertainty of about 50''. [less ▲]

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See detailThe Photospheric Abundances of Active Binaries: First Results
Morel, Thierry ULg; Micela, G.; Favata, F. et al

in Stars as Suns : Activity, Evolution and Planets (2004, January 01)

The coronal abundances of chromospherically active binaries have come under close scrutiny in recent years thanks to several X-ray satellites such as XMM or Chandra. Unfortunately a detailed analysis of ... [more ▼]

The coronal abundances of chromospherically active binaries have come under close scrutiny in recent years thanks to several X-ray satellites such as XMM or Chandra. Unfortunately a detailed analysis of the chemical fractionation processes that are possibly operating between the photosphere and the corona is plagued by the lack of reliable and accurate photospheric abundance determinations. In particular a detailed investigation of the photospheric metal content seems worthwhile in the light of several studies that have questioned the customary use of photometric indices as effective temperature indicators in active binaries. We shall present our ongoing effort to determine in a self-consistent way accurate physical parameters and photospheric abundances for a large number of systems and discuss the implications of our results on their abundance patterns and evolutionary status. Preliminary results suggest that these systems are not as iron-deficient as found in previous studies and indicate an overabundance of several key elements (e.g. Na Mg Al Ca) with respect to the solar pattern. [less ▲]

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See detailThe photospheric abundances of active binaries. II. Atmospheric parameters and abundance patterns for 6 single-lined RS CVn systems
Morel, Thierry ULg; Micela, G.; Favata, F. et al

in Astronomy and Astrophysics (2003), 412

Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been ... [more ▼]

Photospheric parameters and abundances are presented for a sample of single-lined chromospherically active binaries from a differential LTE analysis of high-resolution spectra. Abundances have been derived for 13 chemical species, including several key elements such as Li, Mg, and Ca. Two methods have been used. The effective temperatures, surface gravities and microturbulent velocities were first derived from a fully self-consistent analysis of the spectra, whereby the temperature is determined from the excitation equilibrium of the Fe I lines. The second approach relies on temperatures derived from the (B-V) colour index. These two methods give broadly consistent results for the stars in our sample, suggesting that the neutral iron lines are formed under conditions close to LTE. We discuss the reliability in the context of chromospherically active stars of various colour indices used as temperature indicators, and conclude that the (V-R) and (V-I) colours are likely to be significantly affected by activity processes. Irrespective of the method used, our results indicate that the X-ray active binaries studied are not as metal poor as previously claimed, but are at most mildly iron-depleted relative to the Sun (-0.41protect <~ [Fe/H]protect la +0.11). A significant overabundance of several chemical species is observed (e.g., the alpha -synthezised elements). These abundance patterns are discussed in relation to stellar activity. Based on observations collected at ESO (La Silla, Chile). 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/412/495 [less ▲]

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See detailLarge-Scale Structures in OB Supergiants: from an Inhomogeneous Surface to a Structured Wind
Morel, Thierry ULg; Marchenko, S. V.; Pati, A. K. et al

in Bulletin of the American Astronomical Society (2003, May 01)

In 2000-2001 we performed long-term spectroscopic monitoring of a sample of bright OB-supergiants aimed at establishing the incidence of co-rotating, large-scale wind structures. In the optical, this can ... [more ▼]

In 2000-2001 we performed long-term spectroscopic monitoring of a sample of bright OB-supergiants aimed at establishing the incidence of co-rotating, large-scale wind structures. In the optical, this can be achieved by detecting rotationally modulated variability in Hα . Practically all the surveyed stars show dramatic line-profile variations operating on a daily (and in some cases on a hourly) timescale. Here we discuss the case of HD 14134 (B3 Ia) where a periodic modulation seen in the optical continuum (stellar surface, P=12.825d) triggers spectacular variations in the Hα emission line (stellar wind). [less ▲]

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See detailLarge-scale Wind Structures in OB Supergiants: a Search for Rotationally Modulated Halpha variability
Morel, Thierry ULg; Marchenko, S. V.; Pati, A. K. et al

in Bulletin of the Astronomical Society of India (2003), 31

We present preliminary results of a long-term spectroscopic monitoring of a sample of bright OB-supergiants aimed at establishing the incidence of co-rotating, large-scale wind structures by detecting ... [more ▼]

We present preliminary results of a long-term spectroscopic monitoring of a sample of bright OB-supergiants aimed at establishing the incidence of co-rotating, large-scale wind structures by detecting rotationally modulated variability in H. Dramatic line-profile variations operating on a daily (and in some cases on a hourly) timescale are observed. A detailed period analysis has been so far carried out for 2 stars, and revealed in both cases the existence of cyclical H variations consistent with rotational modulation. In the case of HD 14134, the same periodicity is found in the contemporaneous light curve. [less ▲]

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See detailInfrared colours of star-forming galaxies and a flux calibration of ISOCAM ELAIS catalogues
Vaisanen, Petri; Morel, Thierry ULg

in Exploiting the ISO Data Archive. Infrared Astronomy in the Internet Age (2003, February 01)

We present J and K-band near-infrared photometry of a sample of ISOCAM sources detected by the European Large Area ISO-Survey (ELAIS). All of the high-reliability LW2 (6.7 μm) sources and 80 per cent of ... [more ▼]

We present J and K-band near-infrared photometry of a sample of ISOCAM sources detected by the European Large Area ISO-Survey (ELAIS). All of the high-reliability LW2 (6.7 μm) sources and 80 per cent of the LW3 (15 μm) sources are identified in the near-IR survey reaching K â 17.5 mag. The near- to mid-IR flux ratios can effectively be used to separate stars from galaxies in mid-IR surveys: at 6.7 μm, 80 per cent of the identified ELAIS objects are stars while at 15 μm 80 per cent are galaxies. The stars are then used to perform an accurate new calibration of the ELAIS ISOCAM data at both 6.7 and 15 μm: we adopt values of 1.23 and 1.05 ADU/gain/s/mJy for the LW2 and LW3 filters, respectively. The ISOCAM ELAIS survey is found to mostly detect strongly star-forming late-type galaxies. We show that near to mid-IR colour-colour diagrams can be used to further classify galaxies, as well as study star-formation. In a [15/2.2] vs. [6.7/2.2] plot the Hubble type of a galaxy can be roughly estimated from its position along the diagonal ([6.7/15] = 1) and the star-forming efficiency from a galaxys departure from the diagonal (eg. [6.7/15] <1). The ELAIS galaxies yield an average mid-IR flux ratio LW2/LW3 =0.67 ± 0.27. We discuss this [6.7/15] ratio as a star formation tracer using ISO and IRAS data of a local comparison sample. The [2.2/15] ratio is also found to be a good indicator of activity level in galaxies and conclude that the drop in the [6.7/15] ratio seen in strongly star-forming galaxies is a result of both an increase of 15 μm emission and an apparent depletion of 6.7 μm emission. [less ▲]

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See detailNear- and mid-infrared colours of star-forming galaxies in European Large Area ISO Survey fields
Vaisanen, Petri; Morel, Thierry ULg; Rowan-Robinson, M. et al

in Monthly Notices of the Royal Astronomical Society (2002), 337

We present J- and K-band near-infrared (near-IR) photometry of a sample of mid-infrared (mid-IR) sources detected by the Infrared Space Observatory (ISO) as part of the European Large Area ISO Survey ... [more ▼]

We present J- and K-band near-infrared (near-IR) photometry of a sample of mid-infrared (mid-IR) sources detected by the Infrared Space Observatory (ISO) as part of the European Large Area ISO Survey (ELAIS) and study their classification and star-forming properties. We have used the Preliminary ELAIS Catalogue for the 6.7-μm (LW2) and 15-μm (LW3) fluxes. All of the high-reliability LW2 sources and 80 per cent of the LW3 sources are identified in the near-IR survey reaching K~ 17.5 mag. The near-IR/mid-IR flux ratios can effectively be used to separate stars from galaxies in mid-IR surveys. The stars detected in our survey region are used to derive a new accurate calibration for the ELAIS ISOCAM data in both the LW2 and LW3 filters. We show that near- to mid-IR colour-colour diagrams can be used to classify galaxies further, as well as to study star formation. The ELAIS ISOCAM survey is found mostly to detect strongly star-forming late-type galaxies, possibly starburst-powered galaxies, and it also picks out obscured active galactic nuclei. The ELAIS galaxies yield an average mid-IR flux ratio LW2/LW3 = 0.67 +/- 0.27. We discuss the f[SUB]ν[/SUB](6.7 μ m)/f[SUB]ν[/SUB](15 μ m) ratio as a star formation tracer using ISO and IRAS data of a local comparison sample. We find that the f[SUB]ν[/SUB](2.2 μ m)/f[SUB]ν[/SUB](15 μ m) ratio is also a good indicator of activity level in galaxies and conclude that the drop in the f[SUB]ν[/SUB](6.7 μ m)/f[SUB]ν[/SUB](15 μ m) ratio seen in strongly star-forming galaxies is a result of both an increase of 15-μm emission and an apparent depletion of 6.7-μm emission. Near-IR together with the mid-IR data make it possible to estimate the relative amount of interstellar matter in the galaxies. [less ▲]

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See detailThe Quadruple Wolf-Rayet System GP Cephei: Spectral Types, Masses, Mass-Loss Rate, and Colliding Winds
Demers, H.; Moffat, A. F. J.; Marchenko, S. V. et al

in Astrophysical Journal (2002), 577

We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is ... [more ▼]

We have reevaluated the orbital elements for each pair of the quadruple (W-R+O) + (O+O) stellar system GP Cep and propose new spectral types WN6o/WCE + O3-6, B0: I + B1: V-III. It is shown that there is only one Wolf-Rayet (W-R) star in GP Cep, contrary to a previous claim. A rate of change P=1.3+/-0.2 s yr[SUP]-1[/SUP] is determined for the W-R+O pair, which leads to a new period of 6.6887 days and to a W-R mass-loss rate of (0.8-3.0)à 10[SUP]-5[/SUP] M[SUB]solar[/SUB] yr[SUP]-1[/SUP]. Masses for this pair are estimated to be M[SUB]W-R[/SUB]>~6 M[SUB]solar[/SUB] and M[SUB]O[/SUB]>~21 M[SUB]solar[/SUB]. The effects of wind-wind collision in the W-R+O pair are studied. It is shown that even after allowing for dilution by the OB components of the quadruple system, these effects are not as strong as in the binary V444 Cygni (WN5+O6, P=4.212 days). In GP Cep, the phase-dependent, relatively weak excess emission does not originate in the arms of the bow shock cone. Rather, it emerges from the extra heated portion of the W-R wind facing the hot O companion. The trailing bow shock arm is clearly seen, however, as an enhanced He I absorption component near quadrature at phase ~0.73. An anomalous blueshifted He I absorption is present at phase ~0.9, as is also seen in V444 Cyg, in the WC8+O9 I/O8 III binary γ Velorum and in the LBV-cotype binary R81 (B2.5 Iab:e). A 3.5 day orbit for the eclipsing B star pair is confirmed. [less ▲]

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See detailNear-infrared [Fe II] emission from supernova remnants and the supernova rate of starburst galaxies
Morel, Thierry ULg; Doyon, R.; St-Louis, N.

in Monthly Notices of the Royal Astronomical Society (2002), 329

In an effort better to calibrate the supernova rate of starburst galaxies as determined from near-infrared [FeII] features, we report on a [FeII] λ1.644μm line-imaging survey of a sample of 42 optically ... [more ▼]

In an effort better to calibrate the supernova rate of starburst galaxies as determined from near-infrared [FeII] features, we report on a [FeII] λ1.644μm line-imaging survey of a sample of 42 optically selected supernova remnants (SNRs) in M33. A wide range of [FeII] luminosities are observed within our sample (from less than 6 to 695L[SUB]solar[/SUB]). Our data suggest that the bright [FeII] SNRs are entering the radiative phase and that the density of the local interstellar medium (ISM) largely controls the amount of [FeII] emission. We derive the following relation between the [FeII] λ1.644μm line luminosity of radiative SNRs and the electronic density of the post-shock gas, n[SUB]e[/SUB]: L[SUB][FeII][/SUB] (L[SUB]solar[/SUB])~1.1n[SUB]e[/SUB] (cm[SUP]-3[/SUP]). We also find a correlation in our data between L[SUB][FeII][/SUB] and the metallicity of the shock-heated gas, but the physical interpretation of this result remains inconclusive, as our data also show a correlation between the metallicity and n[SUB]e[/SUB]. The dramatically higher level of [FeII] emission from SNRs in the central regions of starburst galaxies is most likely due to their dense environments, although metallicity effects might also be important. The typical [FeII]-emitting lifetime of a SNR in the central regions of starburst galaxies is found to be of the order of 10[SUP]4[/SUP]yr. On the basis of these results, we provide a new empirical relation allowing the determination of the current supernova rate of starburst galaxies from their integrated near-infrared [FeII] luminosity. [less ▲]

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See detailThe European Large Area ISO Survey - VI. Discovery of a new hyperluminous infrared galaxy
Morel, Thierry ULg; Efstathiou, A.; Serjeant, S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 327

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is ... [more ▼]

We report the discovery of the first hyperluminous infrared galaxy (HyLIG) in the course of the European Large Area ISO Survey (ELAIS). This object has been detected by ISO at 6.7, 15 and 90μm, and is found to be a broad-line, radio-quiet quasar at a redshift [formmu4]z=1.099. From a detailed multicomponent model fit of the spectral energy distribution, we derive a total IR luminosity L[SUB]IR[/SUB] [formmu5](1-1000μm)~1.0à 10[SUP]13[/SUP]h65-2L[SUB]solar[/SUB] [formmu6](q[SUB]0[/SUB]=0.5), and discuss the possible existence of a starburst contributing to the far-IR output. Observations to date present no evidence for lens magnification. This galaxy is one of the very few HyLIGs with a X-ray detection. On the basis of its soft X-ray properties, we suggest that this broad-line object may be the face-on analogue of narrow-line, Seyfert-like HyLIGs. [less ▲]

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See detailOptical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205
Morrell, N. I.; Barbá, R. H.; Niemela, V. S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 326

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii ... [more ▼]

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the Heii lambda4686Å (primary component) and Hei lambda4471Å (secondary component) absorption lines yield semi-amplitudes of 133+/-2 and 314+/-2kms[SUP]-1[/SUP] for each binary component, resulting in minimum masses of 31 and 13M[SUB]solar[/SUB] (q=0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a `normal' mass of 22-25M[SUB]solar[/SUB] we would derive for the primary O3V a mass of `only' 52-60M[SUB]solar[/SUB] and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185+/-16yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed. [less ▲]

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See detailMid-FIR Properties of ELAIS Sources
Marquez, I.; Masegosa, J.; Morel, Thierry ULg et al

in The Promise of the Herschel Space Observatory (2001, July 01)

We present the properties of all the galaxies detected by ISO at 7, 15 and 90 microns in ELAIS northern fields. The spectral energy distribution (SED) of those 20 galaxies with IRAS detections can ... [more ▼]

We present the properties of all the galaxies detected by ISO at 7, 15 and 90 microns in ELAIS northern fields. The spectral energy distribution (SED) of those 20 galaxies with IRAS detections can generally be well fitted by a predominant cirrus component plus a modest starburst contribution. Follow-up spectroscopy has shown that all the objects are emission-line galaxies but without a very intense star formation event. Most of the galaxies analyzed by means of optical R band photometry result to host an important exponential disk component, in good agreement with the SED IR modelling. We note that galaxies with morphological signs of perturbations seem to show slightly higher f[SUB]15[/SUB]/f[SUB]6.7[/SUB] ratios, indicating that star formation could be more important in them. One of the objects is a broad-line, radio-quiet quasar at z=1.099; its spectral energy distribution indicates that it is a hyperluminous infrared galaxy (HLIG), the first HLIG detected in the ELAIS areas. [less ▲]

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See detailSpectroscopic Properties of New IR Galaxies Detected in the European Large Area ISO Survey
Cabrera-Guerra, F.; Perez-Fournon, I.; Gonzalez-Solares, E. A. et al

in The Promise of the Herschel Space Observatory (2001, July 01)

We present preliminary results of multi-object spectroscopy of new mid-, and far-infrared selected galaxies detected in the European Large Area ISO Survey (ELAIS). The data have been obtained with the ... [more ▼]

We present preliminary results of multi-object spectroscopy of new mid-, and far-infrared selected galaxies detected in the European Large Area ISO Survey (ELAIS). The data have been obtained with the fibre spectrographs WYFFOS at the William Herschel Telescope (Observatorio del Roque de los Muchachos, ORM, Canary Islands) and Hydra at the WIYN Telescope (Kitt Peak Observatory, Arizona). The sample includes ISO sources detected at 7, 15 and 90 microns and radio sources from our deep VLA survey in the ELAIS areas. [less ▲]

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See detailThe European Large Area ISO Survey - IV. The preliminary 90-microns luminosity function
Serjeant, S.; Efstathiou, A.; Oliver, S. et al

in Monthly Notices of the Royal Astronomical Society (2001), 322

We present the luminosity function of 90-μm-selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities are in the range 10[SUP]9[/SUP]< h 65 -2L/L[SUB]solar ... [more ▼]

We present the luminosity function of 90-μm-selected galaxies from the European Large Area ISO Survey (ELAIS), extending to z=0.3. Their luminosities are in the range 10[SUP]9[/SUP]< h 65 -2L/L[SUB]solar[/SUB]<10[SUP]12[/SUP], i.e. non-ultraluminous. From our sample of 37 reliably detected galaxies in the ELAIS S1 region from the Efstathiou et al. S[SUB]90[/SUB]>=100mJy data base, we have found optical, 15-μm or 1.4-GHz identifications for 24 (65 per cent). We have obtained 2dF and UK Schmidt FLAIR spectroscopy of 89 per cent of identifications to rigid multivariate flux limits. We construct a luminosity function assuming that (i) our spectroscopic subset is an unbiased sparse sample, and (ii) there are no galaxies that would not be represented in our spectroscopic sample at any redshift. We argue that we can be confident of both assumptions. We find that the luminosity function is well described by the local 100-μm luminosity function of Rowan-Robinson, Helou & Walker. Assuming this local normalization, we derive luminosity evolution of (1+z)[SUP]2.45+/-0.85[/SUP] (95 per cent confidence). We argue that star formation dominates the bolometric luminosities of these galaxies, and we derive comoving star formation rates in broad agreement with the Flores et al. and Rowan-Robinson et al. mid-infrared-based estimates. [less ▲]

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See detailA Near-IR [Fe II] line imaging survey of supernova remnants in M33
Morel, Thierry ULg; Doyon, R.; St-Louis, N.

in Proceedings 232. WE-Heraeus Seminar (2000, December 01)

We report on the first near-IR [Fe II] line imaging survey of extragalactic SNRs. Observations of a sample of 42 objects drawn from an optically-selected catalogue of SNRs in M33 provide evidence for a ... [more ▼]

We report on the first near-IR [Fe II] line imaging survey of extragalactic SNRs. Observations of a sample of 42 objects drawn from an optically-selected catalogue of SNRs in M33 provide evidence for a wide range in the [Fe II]λ 1.644 micron luminosities. This can be understood as being primarily due to variations in the chemical abundances and density of the local ISM, although shock conditions may also play a significant role. We briefly discuss how these results may be used to better calibrate the supernova rate of star-forming galaxies. [less ▲]

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See detailThe European Large Area ISO Survey - I. Goals, definition and observations
Oliver, Seb; Rowan-Robinson, Michael; Alexander, D. M. et al

in Monthly Notices of the Royal Astronomical Society (2000), 316

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT ... [more ▼]

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6deg[SUP]2[/SUP] being covered at 6.7μm and 1deg[SUP]2[/SUP] at 175μm. This paper discusses the goals of the project and the techniques employed in its construction, as well as presenting details of the observations carried out, the data from which are now in the public domain. We outline the ELAIS `preliminary analysis' which led to the detection of over 1000 sources from the 15 and 90-μm surveys (the majority selected at 15μm with a flux limit of ~3mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISOCAM and ISOPHOT. We detail how the ELAIS survey complements other ISO surveys in terms of depth and areal coverage, and show that the extensive multi-wavelength coverage of the ELAIS fields resulting from our concerted and on-going follow-up programme has made these regions amongst the best studied areas of their size in the entire sky, and, therefore, natural targets for future surveys. This paper accompanies the release of extremely reliable subsets of the `preliminary analysis' products. Subsequent papers in this series will give further details of our data reduction techniques, reliability and completeness estimates and present the 15- and 90-μm number counts from the `preliminary analysis', while a further series of papers will discuss in detail the results from the ELAIS `final analysis', as well as from the follow-up programme. [less ▲]

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See detailOn the nature of the spectral and photometric periodic variability of apparently single Wolf-Rayet stars
Morel, Thierry ULg

in The Observatory (1999), 119

Not Available

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See detailAn investigation of the large-scale variability of the apparently single Wolf-Rayet star WR 1
Morel, Thierry ULg; Georgiev, L. N.; Grosdidier, Y. et al

in Astronomy and Astrophysics (1999), 349

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with ... [more ▼]

In recent years, much studies have focused on determining the origin of the large-scale line-profile and/or photometric patterns of variability displayed by some apparently single Wolf-Rayet stars, with the existence of an unseen (collapsed?) companion or of spatially extended wind structures as potential candidates. We present observations of <ASTROBJ>WR 1</ASTROBJ> which highlight the unusual character of the variations in this object. Our narrowband photometric observations reveal a gradual increase of the stellar continuum flux amounting to Delta v ~ 0.09 mag followed by a decline on about the same timescale (3-4 days). Only marginal evidence for variability is found during the 11 following nights. Strong, daily line-profile variations are also observed but they cannot be easily linked to the photometric variations. Similarly to the continuum flux variations, coherent time-dependent changes are observed in 1996 in the centroid, equivalent width, and skewness of He Ii lambda 4686. Despite the generally coherent nature of the variations, we do not find evidence in our data for the periods claimed in previous studies. While the issue of a cyclical pattern of variability in <ASTROBJ>WR 1</ASTROBJ> is still controversial, it is clear that this object might constitute in the future a cornerstone for our understanding of the mechanisms leading to the formation of largely anisotropic outflows in Wolf-Rayet stars. [less ▲]

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See detailA 2.3 Day Periodic Variability in the Apparently Single Wolf-Rayet Star WR 134: Collapsed Companion or Rotational Modulation?
Morel, Thierry ULg; Marchenko, Sergey V; Eenens, Philippe R J et al

in Astrophysical Journal (1999), 518

The apparently single WN 6 type star WR 134 (HD 191765) is distinguished among the Wolf-Rayet star population by its strong, presumably cyclical (P~2.3 day) spectral variations. A true periodicity-which ... [more ▼]

The apparently single WN 6 type star WR 134 (HD 191765) is distinguished among the Wolf-Rayet star population by its strong, presumably cyclical (P~2.3 day) spectral variations. A true periodicity-which is still very much debated-would render WR 134 a prime candidate for harboring either a collapsed companion or a rotating, large-scale, inhomogeneous outflow. We have carried out an intensive campaign of spectroscopic and photometric monitoring of WR 134 from 1989 to 1997 in an attempt to reveal the true nature of this object. This unprecedentedly large data set allows us to confirm unambiguously the existence of a coherent 2.25+/-0.05 day periodicity in the line-profile changes of He II lambda4686, although the global pattern of variability is different from one epoch to another. This period is only marginally detected in the photometric data set. Assuming the 2.25 day periodic variability to be induced by orbital motion of a collapsed companion, we develop a simple model that aims to investigate (1) the effect of this strongly ionizing, accreting companion on the Wolf-Rayet wind structure, and (2) the expected emergent X-ray luminosity. We argue that the predicted and observed X-ray fluxes can only be matched if the accretion on the collapsed star is significantly inhibited. Additionally, we performed simulations of line-profile variations caused by the orbital revolution of a localized, strongly ionized wind cavity surrounding the X-ray source. A reasonable fit is achieved between the observed and modeled phase-dependent line profiles of He II lambda4686. However, the derived size of the photoionized zone substantially exceeds our expectations, given the observed low-level X-ray flux. Alternatively, we explore rotational modulation of a persistent, largely anisotropic outflow as the origin of the observed cyclical variability. Although qualitative, this hypothesis leads to greater consistency with the observations. [less ▲]

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See detailSur la nature de la variabilite spectrale et photometrique periodique d'etoiles Wolf-Rayet apparemment isolees
Morel, Thierry ULg

Doctoral thesis (1999)

Il est depuis longtemps suspecté que les étoiles Wolf-Rayet apparemment isolées présentant des variations périodiques dans le profil de leurs raies spectrales, en photométrie ou en polarimétrie ... [more ▼]

Il est depuis longtemps suspecté que les étoiles Wolf-Rayet apparemment isolées présentant des variations périodiques dans le profil de leurs raies spectrales, en photométrie ou en polarimétrie sont associées à un compagnon dégénéré (étoile à neutron ou trou noir), et constituent ainsi une phase évolutive dont l'existence, bien que prédite par les modèles évolutifs des systèmes binaires massifs rapprochés, n'a pas encore été catégoriquement confirmée observationnellement. Cependant, de récentes études ayant trait à la variabilité spectrale des étoiles OB laissent émettre quelques doutes quant à la pertinence de ce modèle, en démontrant que des vents largement asphériques peuvent se développer dans les étoiles de type précoce. Le scénario alternatif serait donc de considérer que la variabilité périodique observée n'est pas due à la présence d'un compagnon dégénéré affectant la structure à grande échelle du vent de l'étoile Wolf-Rayet, mais est au contraire induite par la modulation par rotation d'un vent nettement anisotropique. Cet ouvrage présente les résultats d'un vaste programme d'observations spectroscopiques et photométriques (généralement simultanées) se proposant de lever l'ambiguïté sur la nature précise des étoiles Wolf-Rayet apparemment isolées dont la périodicité des variations est. soit depuis longtemps établie (WR 6), soit suspectée (WR 1, WR 134, WR 136). Notre étude a permis de confirmer l'existence d'une périodicité de 2.3 jours pour l'étoile WR 134. En outre, nous présentons des arguments mettant en doute l'éventuelle association de WR 6 et WR 134 avec un compagnon dégénéré. Alternativement, nous proposons que la variabilité périodique observée serait plutôt induite, à l'instar de nombreuses étoiles OB, par la rotation de structures azimutalement étendues dans le vent. Ce modèle est plus à même d'appréhender certains aspects de la variabilité, notamment la nature globalement différente du patron de variabilité selon l'époque d'observation, le caractère périodique des variations présentées par les raies spectrales formées à proximité du coeur stellaire, ou encore la causalité des variations affectant les parties internes et externesdu vent. Cette assertion est également supportée par la déficience de rayons-X observée dans le contexte d'une accrétion du vent stellaire par un objet dégénéré. La similitude des variations spectrales de l'étoile WR 1 avec celles des étoiles précitées laisse présumer qu'une variabilité de nature cyclique pourrait éventuellement être révélée dans un proche avenir. Dans ce cas de figure, nos données semblent imposer une limite inférieure de 5 jours pour une quelconque périodicité. Le cas échéant, ces structures à grande échelle dans le vent des étoiles WR 6 et WR 134 doivent probablement leur formation à une activité photosphérique dont la nature précise reste à déterminer. L'existence de pulsations radiales ou non radiales du noyau, ou de structures magnétiques (``photosphériques'' ou plus vraisemblablement d'origine fossile) pourrait néanmoins être à l'origine de ce phénomène. [less ▲]

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