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6th ESO/OHP Summer School in Astrophysical Observations
M.-P. Véron, and G. Meylan

Résumé en français

The 6th ESO/OHP Summer School was hosted again at the Observatoire de Haute-Provence (OHP) from 15 to 25 July 1998. The school, held only every second years, selects 18 of Europe's most promising young doctoral students in astronomy. Courses of lectures, observations, and analysis form the intellectual menu which is aimed at teaching the process of extracting astrophysically digestible results from the photons harvested at the telescopes, such as the ESO VLT, whose four telescopes will become available to the community in turn during the next few years.

The OHP is exceptionally well equipped to provide all the required ingredients of success for the school. The four main telescopes, reserved for the students, have state-of-the-art instruments and detectors. The observatory, in its beautiful site, is ideally placed to provide a proper mix of clear skies and other facilities, all contributing to the ambience which insures that the various items on the menu form a coherent whole and inspire the students, their tutors, and all around to pursue the tasks at hand with vigour and enthusiasm.

The basic programme for the school was unchanged from previous years. Students were formed into groups of three, and each group was assisted by a tutor. The tutors helped the students prepare observing programmes for both imaging and spectroscopy. The telescopes and instruments setups were prepared carefully according to the requiremnts of the programmes. The observations were performed and data analysed.

Figure 1: The official group photo (High-resolution version JPEG 220 kb) is taken during the break of the talk by H.-J. Röser. From left to right in the first row: M. Billères, J. Dias, M. Van den Bergh, A. Shaker, B. Wolff, I. Burud, M. Scodeggio. Second row: H.-J. Röser, T. Böhm, G. Meylan, M.-P. Véron, G. Jasniewicz, C. Boisson, L. Vannier, N. Przybilla, R. Kotak, A. Gonçalves. Third row: J. Kahanpää, R. Ibata, G. Marino, P. Woudt, G. Bergond, J. Vink, P. Kervella, S. Wolf, A. Zappelli, B. Parodi, Y. Momany. (See also the picture taken on the first day)

The tutors this years were Rodrigo Ibata, Marco Scodeggio, and Patrick Woudt from ESO (Garching), Torsten Böhm from Observatoire Midi-Pyrénées (Toulouse), Catherine Boisson from Observatoire de Paris (Meudon), and Gérard Jasniewicz from Université de Montpellier. There is no doubt that the success of the school is very much a result of their efforts; this was confirmed to us by the students themselves.

R. Ibata led G. Bergond, I. Burud, and J. Vink in a determination of the velocity ellipsoid in the solar neighbourhood. The most direct way to accomplish this is to measure radial velocities to high precision from high resolution spectra they obtained at the 1.52-m telescope with the Aurelie spectrometer. From broad-band (BVRI) images of the same stars obtained at the 1.20-m telescope, they derived their extinction-corrected absolute magnitudes, addressing the issue of whether the observed dispersion in the Hipparcos main sequence is intrinsic or simply due to the effects of reddening.

M. Scodeggio led J. Dias, R. Kotak, and B. Wolff in a study of scaling relations of early-type galaxies, such as the Faber-Jackson and the Fundamental-Plane relations. Such relations involve determinations of a scale radius and a corresponding surface brightness they obtained from images of the sample galaxies acquired at the 1.20-m telescope; the required velocity dispersion determinations were deduced from their spectroscopic data obtained with the CARELEC spectrometer at the 1.93-m telescope.

P. Woudt led N. Przybilla, M. Van den Berg, and A. Zappeli in a study of an accurate determination of the galactic foreground extinction. The 1.93-m telescope with CARELEC was used to obtain spectra roughly centred on the redshifted Mg b lines, i.e., at about 5200 - 5300 Å, providing a reddening index calibrated with Lick standard stars. Images in B and R bands were acquired with the 1.20-m telescope. An empirical relation between the Mg2 spectral index and the (B-R)0 colour of elliptical galaxies was used to determine the reddening of the sample galaxies.

Under the guidance of T. Böhm, J. Kahanpää, P. Kervella, and Y. Momany studied the activity of Herbig Ae/Be stars. According to standard theory of stellar evolution, these stars are not supposed to possess outer convection zones, but rather convective cores surrounded by radiative sub-photospheric envelopes. However observations unveiled spectral variations in such stars, with strong stellar winds. These students used Aurelie spectra from the 1.52-m telescope to monitor possible spectral variability of ``active'' lines, which are good indicator for the presence of a magnetically structured stellar atmosphere. Images, acquired with the 1.20-m telescope, of Herbig Ae/Be stars in young open stellar clusters provided powerful constraints on early phases of stellar evolution.

C. Boisson led M. Billères, G. Marino, and S. Wolf in a study of the properties of the host galaxies of AGNs, since the relationship of a Seyfert nucleus to its host galaxy remains an important unanswered question. They used spectroscopy, acquired with CARELEC at the 1.93-m telescope, for a sample of AGNs selected to cover the various classes of active galaxies as well as different environments. Broad-band images obtained with the 0.80-m telescope allowed the study of the morphological features of these galaxies.

Under the guidance of G. Jasniewicz, B. Parodi, A. Shaker, and L. Vannier studied a few post-AGB stars, objects which suffer some of the violent and final phases of stellar evolution, such as the He-shell flash. From high-resolution spectra obtained at the 1.52-m telescope with Aurelie, they focused on the C2 molecular bands, the absorption components of the Na I D, and stellar emission lines. Broad-band (UBV) images of the same stars obtained at the 0.80-m telescope allowed estimates of the color of the central objects and of the surrounding faint nebulae.

The other major ingredient in the school was a series of invited lectures on topics related to observations, instrumentation, detectors, and data reduction. H.-J. Röser gave a comprehensive overview on imaging and photometry, with careful emphasis on how to avoid all clasical pitfalls during observations as well as data reduction. D. Baade presented an equally useful presentation on low- and high-resolution spectroscopy. M. Dennefeld described optical and IR detectors, emphasizing their physical processes and limitations, with present and future VLT instruments in perspective. P. Magain presented in a very clear way the subtilities and difficulties of deconvolution techniques applied to the process of data reduction. F. Rigaut gave a stimulating presentation of active and adaptive optics, the former technique beeing a must for the VLT meniscus monolithic 8.2-m mirrors, the later allowing to forecast major technological improvements in the near future.

On the final day, each group of students presented a summary of their results. Although the analysis techniques had, for the most part, just been learned, all groups presented interesting and in some cases potentially publishable results. This is no small achievement considering that most of them were entirely new to the scientific subject, the observing process, and the data analysis.

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