Hintze Centre for Astrophysical Surveys

Abstract:

The optical backscatter of the 4W CW laser used to produce a mesospheric sodium-layer laser guide star for the MPE adaptive optics system (ALFA) has been observed from a neighbouring 2.2 m telescope. The observations, taken at the Max Planck Observatory in Calar-Alto (Spain), in August 1998, had two aims: study the Na plume (altitude and profile variations) and the Rayleigh cone to achieve Rayleigh scattering measurements. In the framework of the network, 'Laser Guide Star for 8m class telescopes', a program of the European Commission, ESO, MPE and NUI, Galway are collaborating on studying the light pollution due to the MPE ALFA laser. The light pollution of the observatory is due to Rayleigh and Mie scattering, including water scattering, of the laser beam in the low atmosphere. With the increase of Laser Guide Star Adaptive Optics system use, there is a need for a laser management policy. In order to optimise observing time, it is important to evaluate exactly when to stop the LGS, as the line of sight of one telescope gets near the laser beam, and as a function of other telescope observing programme. In this perspective, not only the single and multiple Rayleigh scattering by atmospheric molecules but also Mie scattering by aerosols has to be taken into account. Modeling of these phenomena needs an experimental calibration in realistic circumstances, and precise measurements of single and multiple light scattering in the surroundings of the beam at various altitudes. We report here on the result of such experiments.

Abstract:

We present near TR spectra (0.8-2.5 μm) of the two candidate B[e]/X-ray binary systems CI Cam/XTE J0421+560 and HD34921/1H 0521+37. The spectra of both systems show evidence for a more complex circumstellar environment than those seen in classical Be/X-ray binaries. Strong H I and He I emission is seen, confirming the presence of a dense circumstellar wind; O I, Fe II and [Fe II] emission in CI Cam points to recombination of this wind. He II emission, presumably due to excitation by the compact companion is observed in CI Cam. Finally, emission is seen from Na I and CO, which implies regions of the circumstellar environment with much lower excitation temperatures and higher densities, shielded from direct stellar radiation. Both systems show evidence for continuum emission from circumstellar dust. Neither of these two features has previously been observed in any other classical Be/X-ray binary system. Adopting the classification criteria of Lamers et al. (1998) we suggest identifications of unclB[e] and sgB[e] for HD34921 and CI Cam respectively, making them the first High Mass X-ray Binaries with primaries showing the B[e] phenomenon known.

Abstract:

Half hour exposures using the ESO VLT/FORS1 combination at Parañal in Chile have allowed us to obtain spectra for three B supergiants in the dwarf irregular galaxy NGC 6822. The spectra have been analysed using non-LTE techniques and temperatures, gravities, helium content and abundances have been obtained. Overall the metallicity of NGC 6822 is found to lie between that of the LMC and of the SMC, in agreement with previous observations of H II regions and in contrast to the earlier findings of Massey et al. (1995). The analysis of Hα yields estimates of the mass-loss rates and wind momenta. These results demonstrate that significantly longer exposures with the same instruments will allow us to perform quantitative spectroscopy of blue supergiants in galaxies far beyond the Local Group.