Publications of Thierry Morel
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See detailA comprehensive variability study of the enigmatic WN8 stars - Final results
Marchenko, S. V.; Moffat, A. F. J.; Eversberg, T. et al

in Monthly Notices of the Royal Astronomical Society (1998), 294

As a conclusion of our all-sky variability survey of the 'enigmatic' variable WN8 stars, we have carried out coordinated multisite photometric and spectroscopic observations of WN8 stars in 1989 and 1994 ... [more ▼]

As a conclusion of our all-sky variability survey of the 'enigmatic' variable WN8 stars, we have carried out coordinated multisite photometric and spectroscopic observations of WN8 stars in 1989 and 1994-1995. We confirm the leading role of the stellar core in restructuring the whole wind. This emerges as a statistical trend: the higher the level of the continuum (i.e., core) light variations, the higher the variability of the P Cygni edges of the optical emission lines. However, the form of the correlation between the light and profile variations is generally different for each individual star. The high level of activity of WN8 stars may be supported/induced by pulsational instability. [less ▲]

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See detailConfirmation of a 2.3-DAY Periodicity in the Wolf-Rayet Star WR 134: a Twin of EZ Cma?
Morel, Thierry ULiege; Marchenko, S. V.; Eenens, P. R. J. et al

in Cyclical Variability in Stellar Winds (1998)

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See detailOptical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind
Morel, Thierry ULiege; St-Louis, Nicole; Marchenko, Sergey V

in Astrophysical Journal (1997), 489

In the paper "Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind" by Thierry Morel, Nicole St-Louis, and Sergey V. Marchenko (ApJ, 482, 470 [1997]), there ... [more ▼]

In the paper "Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind" by Thierry Morel, Nicole St-Louis, and Sergey V. Marchenko (ApJ, 482, 470 [1997]), there are several errors that should be corrected. In the legends to Figures 3 and 6 and on page 483, 55% should read 99%. The revised version of Figure 12 given here replaces Figure 12 in the paper. [less ▲]

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See detailOptical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind
Morel, Thierry ULiege; St-Louis, Nicole; Marchenko, Sergey V

in Astrophysical Journal (1997), 482

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also ... [more ▼]

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also monitored EZ CMa using narrowband photometry. The light curve was found to be remarkably stable when folded with the P=3.77 day period, and it had a peak-to-valley amplitude of 0.1 mag. The P Cygni absorption components of He I lambda 3889 and He I lambda 5876 display a similar global pattern of variability as was found for the simultaneously acquired UV profiles. The strengthening of the P Cygni absorption component of these transitions is associated with the maximum of the continuum flux. Conversely, the absorption trough of N V lambda 4604 gradually disappears as the star brightens. Although the emission parts of the lines are variable at different levels, they all show the same pattern of variability, which consists of phase-dependent shifts of extra emission components superposed on the profiles. A strong correlation is found between the continuum-light level and the equivalent width of most transitions. The line skewness and the full-width at half-maximum show a daily recurrence timescale, reflecting the light curve changes. We have addressed in a rigorous statistical way the significance of the variations by calculating the "temporal variance spectrum." For any given line, we found enhanced variability at some velocities, although the whole profile displays a statistically significant level of variability. Arguments against a compact companion as the cause of the observed periodic variability are presented. Instead, our observations strongly support the suggestion in the IUE Mega analysis that the atypical level of variability results from the rotation of a structured wind. We propose that the wind variability of EZ CMa is triggered by photospheric activity, or that the wind is controlled by a large-scale magnetic field. [less ▲]

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See detailThe "photosphere-wind connection" in Wolf-Rayet stars: simultaneous photometry and spectroscopy of EZ CMa
Morel, Thierry ULiege; St-Louis, N.; Marchenko, S. V.

in Liege International Astrophysical Colloquia (1996)

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See detailThe all-variable WN8 stars : the stellar core as driver
Marchenko, S.; Moffat, A.; Eversberg, T. et al

in Liege International Astrophysical Colloquia (1996)

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See detailStudy of Transmitted Light Through Neptune's Atmosphere
Dobrijevic, M.; Morel, Thierry ULiege; Parisot, J. P. et al

in Bulletin of the American Astronomical Society (1993, June 01)

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