   The LMC transition star R 84 and the core of the LH 39 OB association.; ; Rauw, Grégor  et alin Astronomy and Astrophysics (1997), 326 On the basis of sub-arcsecond imaging obtained at the ESO NTT with SUSI and the ESO ADONIS adaptive optics system at the 3.6m telescope, we resolve and study the core components of the LMC OB association ... [more ▼] On the basis of sub-arcsecond imaging obtained at the ESO NTT with SUSI and the ESO ADONIS adaptive optics system at the 3.6m telescope, we resolve and study the core components of the LMC OB association LH 39. The central star of the association, the rare transition object R 84, is also investigated using CASPEC echelle spectroscopy at the ESO 3.6m telescope. A new, powerful image restoration code that conserves the fluxes allows us to obtain the magnitudes and colors of the components. We bring out some 30 stars in a ~16"x16" area centered on R 84. At a resolution of 0.19"(FWHM), the closest components to R 84 are shown to be stars #21 and #7 lying at 1.1"NW and 1.7"NW respectively of the transition star. The former is possibly a blue star of V=16.7mag and the latter with its V=17.5mag is the reddest star of the field, after R 84. Star #7 turns out to be too faint to correspond to the red M2 supergiant previously reported to contaminate the spectrum of R 84. If the late-type spectrum is due to a line-of-sight supergiant with a luminosity comparable to R 84, it should lie closer than 0.12" to R 84. The transition star shows spectral variability between 1982 and 1991. We also note some slight radial velocity variations of the Of emission lines over timescales of several years. Furthermore, we derive the spectral types of two of the brightest stars of the cluster, using long slit spectra obtained at the NTT telescope equipped with EMMI, and discuss the apparent absence of O type stars in this association. [less ▲] Detailed reference viewed: 18 (3 ULg) The puzzling Luminous Blue Variable-like object HD 5980 in the Small Magellanic Cloud.; Rauw, Grégor ; et alin Astronomy and Astrophysics (1997), 322 We have observed the exceptional SMC star HD 5980 during several runs from 1989 to 1995 at ESO La Silla. CASPEC at the 3.6m telescope and EMMI in echelle and long slit modes at NTT were used for ... [more ▼] We have observed the exceptional SMC star HD 5980 during several runs from 1989 to 1995 at ESO La Silla. CASPEC at the 3.6m telescope and EMMI in echelle and long slit modes at NTT were used for spectroscopy. Sub-arcsecond images were obtained using SUSI at NTT and also an adaptive optics system at the 3.6m telescope. In all our spectra taken before 1994 September HD 5980 shows a spectral type of WN6. The 1994 September spectra were taken shortly after the maximum of the visual light-curve of the LBV-like phenomenon (Bateson & Jones, 1993PVSS...19...50B) and about one month before the observations of Barba et al. (1995ApJ...446L..23B). Near maximum visual brightness, HD 5980 displays a WN11-like spectrum with the HeI lines and the Balmer lines Hdelta and Hgamma showing well-developed PCyg profiles. The sub-arcsecond images (0.17" FWHM), through the near infrared bands J, H, and K, obtained in 1993 and 1996, show no stellar components down to 6.7 mag fainter than HD 5980 in K at a separation of 1.0" and the 3sigma level. For a separation of 0.3" this upper bound is 4.1mag fainter than HD 5980. The observed behavior of this object raises serious problems for our comprehension of the LBV phenomenon in the conventional scenarios of massive star evolution. The present observations cover a crucial period in the evolution of HD 5980 and will therefore be helpful for better understanding this peculiar object especially during its outburst as well as the evolution of W-R stars in general. [less ▲] Detailed reference viewed: 127 (0 ULg)The WN 11-like Spectrum of HD 5980 during the early Stages of the 1994 Eruption; Rauw, Grégor ; in Luminous Blue Variables: Massive Stars in Transition (1997) Not Available Detailed reference viewed: 4 (0 ULg)The very massive star HDE269676 and its components; Hutsemekers, Damien in Astronomy and Astrophysics (1991), 244 It is shown that one of the most luminous stars of the LMC, HDE269676, is in fact a massive star cluster. On the basis of observations with the ESO New Technology Telescope (NTT) the main components of ... [more ▼] It is shown that one of the most luminous stars of the LMC, HDE269676, is in fact a massive star cluster. On the basis of observations with the ESO New Technology Telescope (NTT) the main components of the cluster are classified and it is shown that there are several O type stars in HDE269676 instead of the one or two previously known. This is interesting for the initial mass function in the LMC and implies that the number of O type stars in the LMC is generally underestimated. The most massive star of the system being about a factor three less luminous than previously estimated is a super-giant O5f with a zero age main sequence mass of about 80 solar. [less ▲] Detailed reference viewed: 9 (2 ULg)The most massive star of the largest H II region in the Small Magellanic Cloud; Hutsemekers, Damien in Astronomy and Astrophysics (1991), 243 It is shown that the brightest star in the most important H II region of the Small Magellanic Cloud (SMC) is a multiple system. The zero-age main sequence mass of this star drops significantly from the ... [more ▼] It is shown that the brightest star in the most important H II region of the Small Magellanic Cloud (SMC) is a multiple system. The zero-age main sequence mass of this star drops significantly from the previously estimated value of 130 or 110 solar masses to less than 85 solar masses, while its present mass falls from 113 to 58 solar masses, both due to multiplicity and extinction correction. This is another piece of evidence against the existence of stars more massive than about 100 solar masses in the SMC. It is also shown that the present mass of one of the two known O3 stars in the SMC is significantly smaller than presently believed. [less ▲] Detailed reference viewed: 10 (1 ULg)Two more very massive stars resolved; ; Magain, Pierre in Astronomy and Astrophysics (1989), 222 New evidence against the existence of very massive stars in the Magellanic Clouds is presented. Using high resolution CCD images and appropriate image restoration methods, it is shown that Sk 157 and Sk ... [more ▼] New evidence against the existence of very massive stars in the Magellanic Clouds is presented. Using high resolution CCD images and appropriate image restoration methods, it is shown that Sk 157 and Sk-69 deg 253, lying in the SMC and LMC, respectively, are not single, very massive, but multiple systems. Thus, two of the most massive stars in existence, with the estimated masses of about 85 solar masses and greater than 120 solar masses vanish from astronomy. The results presented here have important implications for star formation models and the extragalactic distance scale. [less ▲] Detailed reference viewed: 15 (1 ULg)New evidence against the existence of very massive stars; ; Magain, Pierre in Astronomy and Astrophysics (1988), 201 The most luminous stars are our first probes for exploring the stellar content of distant galaxies. They have also been used as standard candles for extragalactic distance determinations. The authors show ... [more ▼] The most luminous stars are our first probes for exploring the stellar content of distant galaxies. They have also been used as standard candles for extragalactic distance determinations. The authors show that Sk -66°41, one of the brightest stars in the Large Magellanic Cloud (LMC), is a multiple system consisting of at least six components. This result has important consequences for the understanding of star formation mechanisms, especially the upper limit to stellar masses. Moreover, when primary distance indicators are not available, care should be taken in using the brightest blue stars. The derived distances, depending on the number of cluster members, can easily be underestimated by more than a factor 2, leading to larger values for the Hubble constant. [less ▲] Detailed reference viewed: 7 (2 ULg)The SMC compact blob N 81 - A detailed multi-wavelength investigation; ; Magain, Pierre in Astronomy and Astrophysics (1988), 195 The physical characteristics of the compact Small Magellanic Cloud (SMC) H II region N 81 are investigated using several observational techniques with various telescopes at ESO, namely CCD, Image ... [more ▼] The physical characteristics of the compact Small Magellanic Cloud (SMC) H II region N 81 are investigated using several observational techniques with various telescopes at ESO, namely CCD, Image Dissector Scanner, and Reticon high, medium, and low resolution spectroscopy in the 3700-10,000 A range; CCD imaging; and UBVRI and JHK photometry. Compared to the SMC blobs N 88 A and the LMC N 160 A 1, N 81 was found to be neither dense nor reddened. It is suggested that the nebula N 81 is excited by one star of about 60 solar masses, the absolute visual magnitude of which was derived to be equal to -5.1. The high-resolution profile of N 81 at H-beta was decomposed into its various components, with the most probable three-dimensional turbulent velocity in N 81 estimated to be about 3 km/s. The chemical abundances of He, O, N, Ne, S, and Ar were computed and compared with the mean values available for the SMC. [less ▲] Detailed reference viewed: 15 (0 ULg) |
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