Simulations of observations with the Optical Monitor of the X-ray Multi-Mirror Satellite

peer reviewedThis paper addresses the question of the observations to be performed with the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under several aspects. First, we discuss XMM-OM's photometric system and its colour transformations towards the standard U BV system. Second, we establish a set of procedures to determine the temperature and the amount of interstellar absorption affecting the observed stars. Last, we address the possibility of isolating quasars in multidimensional colour diagrams based on the XMM-OM filter set

Évidence d'une excitation préférentielle de N2 (A 3914 A) dans une aurore

Intensities of 5577 A[OI] and 3914 A (N+2 ;) emissions have been recorded during two rocket flights. A selection of the measurements effected with photometers axes parallel to a horizontal plane has shown a systematic variation of the ratio R(h) = I5577(h)/l3914(A). This ratio shows a minimum at the altitude of maximum ionisation. This result is compared with recent observations of ultra-violet emissions.Vreux Jean-Marie. Évidence d'une excitation préférentielle de N2 (A 3914 A) dans une aurore. In: Bulletin de la Classe des sciences, tome 57, 1971. pp. 655-668

Line profile variability in the spectrum of the O(f) supergiant HD 192639

We report the results of a medium-resolution spectroscopic investigation of the O(f) supergiant HD 192639. Particular attention is paid to the He {ii}\ lambda 4686 line. This line displays strong profile variability on time scales of a few days, changing from a P-Cygni profile with a double-peaked emission component to a pure blue-shifted emission line. It appears that the variability of most of the absorption lines present in our spectra is correlated to the deformation of the He {ii}\ lambda 4686 line and arises probably from a large scale structure in the low-velocity part of the stellar wind rather than from a photospheric phenomenon. We find that the time scale of the variability could be consistent with the estimated rotational period of HD 192639. Based on observations collected at the Observatoire de Haute Provence, France

Observations à faible dispersion du spectre de 25 étoiles de type Of entre 5850 Å et 8750 Å

Near infra-red spectrograms (5850 Å -8750 Å) of 25 Of type stars have been obtained between 1971 and 1973 at the Haute Provence Observatory. The main features observed in the spectral range are due to H I and He I. Hα is never observed in emission when He II λ 4686 is an absorption, the reverse is not true.Andrillat Yvette, Vreux Jean-Marie. Observations à faible dispersion du spectre de 25 étoiles de type Of entre 5850 Å et 8750 Å. In: Bulletin de la Classe des sciences, tome 60, 1974. pp. 430-435

Etude de la variabilité des étoiles de type Wolf-Rayet

Académie royale de Belgiqu

Sobolev type line profiles in case of wind density perturbations modulated by non radial pulsations

We have studied the modifications induced on the P Cygni line profiles of an outwards accelerating wind by density fluctuations modulated by non radial pulsations.Scuflaire Richard, Vreux Jean-Marie. Sobolev type line profiles in case of wind density perturbations modulated by non radial pulsations. In: Bulletin de la Classe des sciences, tome 72, 1986. pp. 525-543

The possible biperiodicity of WR 40

Strong arguments are presented in favor of the simultaneous presence of two periodicities in the variability of the Wolf-Rayet star WR 40. The frequencies are nu(A) = 0.16/d and nu(B) = 0.40/d. Some uncertainties remain concerning the choice of the actual one-year alias. On the basis of a detailed statistical analysis, reliable evidence that the variability related to nu(B) could be coherent is also presented: this points out nu(B) as a possible fundamental frequency linked to the 'core' of WR 40. No firm conclusion could be drawn about nu(A), suggesting that it could be a recurrent quasi-periodicity or a second order periodicity (e.g., a beat frequency). The two frequencies are sometimes hidden by the white noise, or slightly correlated, random process that constitutes the third component of the variability of WR 40