Showing results 221 to 240 of 245
  Interstellar Bubbles in Two Young H II RegionsNazé, Yaël  ; ; et alin Astronomical Journal (The) (2001), 122 Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for ... [more ▼] Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for wind-blown bubbles around main-sequence O stars, we have obtained high-resolution Hubble Space Telescope WFPC2 images and high-dispersion echelle spectra of two pristine H II regions, N11B and N180B, in the Large Magellanic Cloud. These H II regions are ionized by OB associations that still contain O3 stars, suggesting that the H II regions are young and have not hosted any supernova explosions. Our observations show that wind-blown bubbles in these H II regions can be detected kinematically, but not morphologically, because their expansion velocities are comparable to or only slightly higher than the isothermal sound velocity in the H II regions. Bubbles are detected around concentrations of massive stars, individual O stars, and even an evolved red supergiant (a fossil bubble). Comparisons between the observed bubble dynamics and model predictions show a large discrepancy (1-2 orders of magnitude) between the stellar wind luminosity derived from bubble observations and models and that derived from observations of stellar winds. The number and distribution of bubbles in N11B differ from those in N180B, which can be explained by the difference in the richness of stellar content between these two H II regions. Most of the bubbles observed in N11B and N180B show a blister structure, indicating that the stars were formed on the surfaces of dense clouds. Numerous small dust clouds, similar to Bok globules or elephant trunks, are detected in these H II regions, and at least one of them hosts on-going star formation. [less ▲] Detailed reference viewed: 26 (0 ULg)What is the real nature of HD 108?Nazé, Yaël ; Vreux, Jean-Marie ; Rauw, Grégor in Astronomy and Astrophysics (2001), 372 Since the beginning of the past century, the nature of HD 108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to ... [more ▼] Since the beginning of the past century, the nature of HD 108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to changes in the stellar wind of a single star. In this article, we analyse a 30 year campaign of spectroscopic observations of this star with special emphasis on the last 15 years during which photographic plates have been replaced by CCD detectors. Our investigation of the radial velocities of HD 108 yields no significant short- or long-term period and does not confirm the published periodicities either. Though the radial velocity of HD 108 appears clearly variable, the variations cannot be explained by the orbital motion in a spectroscopic binary. However, our data reveal spectacular changes in the H I Balmer lines and some He I profiles over the years. These lines continuously evolved from P Cygni profiles to ``pure'' absorption lines. A similar behaviour has already been observed in the past, suggesting that these changes are recurrent. HD 108 seems to share several characteristics of Oe stars and we discuss different hypotheses for the origin of the observed long-term variations. As we are now in a transition period, a continuous monitoring of HD 108 should be considered for the next few years. Based on observations collected at the Observatoire de Haute-Provence (France). [less ▲] Detailed reference viewed: 11 (1 ULg)Astronomers Meet in Isfahan; Nazé, Yaël Article for general public (2001) Not Available Detailed reference viewed: 12 (0 ULg)Un certain regard (2): la sagesse orientaleNazé, Yaël Article for general public (2001) Detailed reference viewed: 2 (0 ULg) The strange case of the massive binary HD 149404Rauw, Grégor ; Nazé, Yaël ; et alin Astronomy and Astrophysics (2001), 368 We report the analysis of an extensive set of high-resolution spectroscopic observations of the massive binary system HD 149404. We compare different techniques to measure the radial velocities of the ... [more ▼] We report the analysis of an extensive set of high-resolution spectroscopic observations of the massive binary system HD 149404. We compare different techniques to measure the radial velocities of the heavily blended absorption lines and we derive a new orbital solution. The absorption lines display strong variability that slightly affects the orbital solution and the determination of the spectral types of the components of the binary. We find that the primary is probably of spectral type O7.5 I(f), while the secondary is most likely an ON9.7 I supergiant. The secondary seems to be the most evolved component of the system and its current evolutionary status could best be explained if the system has undergone a Roche lobe overflow episode during the past. The secondary could actually still be rather close to filling its critical volume and this could lead to an enhanced mass loss of the secondary. The spectrum of HD 149404 displays many emission lines some of which show phase-locked line profile variations. In particular, the Halpha line displays a double-peaked morphology at orbital phases near conjunction. We investigate the radial velocity behaviour of the emission lines and we find that some of them must be formed in an interaction region. We propose a simple model where some of the optical emission lines arise in a heavily bended shock region. Based on observations collected at the European Southern Observatory (La Silla, Chile) and at the Cerro Tololo Inter-American Observatory (CTIO). [less ▲] Detailed reference viewed: 31 (2 ULg)Un certain regard (1): des pierres levées vers le CielNazé, Yaël Article for general public (2001) Detailed reference viewed: 2 (0 ULg)Des planètes par milliers ...Nazé, Yaël Article for general public (2000) Detailed reference viewed: 5 (0 ULg)Voyage au pays de Darius et des ayattolahsNazé, Yaël ; Article for general public (2000) Detailed reference viewed: 16 (0 ULg)Un télescope de 100 kilomètres de diamètreNazé, Yaël Article for general public (2000) Detailed reference viewed: 1 (0 ULg)Des miroirs... liquides!Nazé, Yaël Article for general public (2000) Not Available Detailed reference viewed: 4 (2 ULg)PSF modeling of the XMM flight mirror modulesStockman, Yvan ; Houbrechts, Yvette ; Nazé, Yaël et alin Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (1999, October 01) In the frame of XMM testing, all the mirror modules have been illuminated by a vertical EUV collimated beam a the Centre Spatial de Liege. A mirror module consists in 58 co- focal and co-axial Wolter I ... [more ▼] In the frame of XMM testing, all the mirror modules have been illuminated by a vertical EUV collimated beam a the Centre Spatial de Liege. A mirror module consists in 58 co- focal and co-axial Wolter I mirrors. Up to now the images obtained at CSL have been used to assess the Mirror Module optical performances in a flight representative configuration, and also to verify the impact of the thermal environmental and vibration test on the optical performance. Due to the highly complex design of the Mirror Modules, simulating XMM images in details is very difficult. The Point Spread Function of some of the mirror modules presents slight asymmetry. In the facility design study, it has been demonstrated that the diffraction impact at 58.4 nm is negligible with respect to the half energy width mirror module specification. Presently all the mirror modules are better than 165 arcsec. This paper presents first the diffraction contribution on the image. In a second step a point spread function is built by using the metrological mirror shell data. EUV images are then analyzed to evaluate the impact of the mirror interface structure integration process on the PSF. An analytical model of the measured EUV pSF is developed. The modelization technique is applied to simulate in-orbit image. Finally the different modelizations are evaluated and compared. [less ▲] Detailed reference viewed: 38 (5 ULg)Petite mythologie astronomique (3): la LuneNazé, Yaël Article for general public (1998) Detailed reference viewed: 5 (0 ULg)Petite mythologie astronomique (2): le SoleilNazé, Yaël Article for general public (1998) Detailed reference viewed: 5 (0 ULg)Echo des nocturnesNazé, Yaël ; Article for general public (1998) Detailed reference viewed: 2 (0 ULg)Petite mythologie astronomique (1): le cielNazé, Yaël Article for general public (1998) Detailed reference viewed: 3 (1 ULg) |
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