We have chosen the name of GYES, one of the mythological giants with one hundred arms,offspring of Gaia and Uranus, for our instrument study of a multifibre spectrograph forthe prime focus of the Canada-France-Hawaii Telescope. Such an instrument could provide anexcellent ground-based complement for the Gaia mission and a northern complement to theHERMES project on the AAT. The CFHT is well known for providing a stable prime focusenvironment, with a large field of view, which has hosted several imaging instruments, buthas never hosted a multifibre spectrograph. Building upon the experience gained at GÉPIwith FLAMES-Giraffe and X-Shooter, we are investigating the feasibility of a highmultiplex spectrograph (about 500 fibres) over a field of view one degree in diameter. Weare investigating an instrument with resolution in the range 15 000 to 30 000, whichshould provide accurate chemical abundances for stars down to 16th magnitude and radialvelocities, accurate to 1 km s-1 for fainter stars. The study is led byGÉPI-Observatoire de Paris with a contribution from Oxford for the study of thepositioner. The financing for the study comes from INSU CSAA and Observatoire de Paris.The conceptual study will be delivered to CFHT for review by October 1st 2010.

So as to prepare future observations of terrestrial extrasolar planets liable to shelter life, we attempt to detect the life on the Earth seen as a dot. We use the Moon Earthshine, in which any place reflects the totality of the enlightened part of Earth facing the Moon. Observing from OHP and from ESO, we detected terrestrial chlorophyll in the near infrared, the so-called Vegetation Red Edge, and this detection is larger when forests are present than when an ocean is mainly visible from the Moon. Only if observations are made from a high latitude location, and at some moments in the year, Earthshine can be observed during a large part of the day. During these long observing windows, different “landscapes" are facing the Moon. So the Earthshine corresponding to various parts of our Earth could be studied. Preliminary testing observations have been made at Concordia since the first winterover campaign and the LUCAS experiment has been set up.

We report 320 to 1020nm disk-averaged Earth reflectance spectra obtained from Moon's Earthshine observations with the EMMI spectrograph on the NTT at ESO La Silla (Chile). The spectral signatures of Earth atmosphere and ground vegetation are observed. A vegetation red-edge of up to 9% is observed on Europe and Africa and ${\approx}2%$ upon Pacific Ocean. The spectra also show that Earth is a blue planet when Rayleigh scattering dominates, or totally white when the cloud cover is large.

Classical Be stars – i.e. non-supergiants B stars with some emission – are very intriguing objects. They represent nearly 20% of B stars. Emission originates in a circumstellar envelope more or less concentrated around the equator, and whose origin is so far unexplained. Fast rotational velocity of Be stars does not attain break-up velocity and an additional process is needed to account for circumstellar region formation. Non-radial pulsations in Be stars were discovered for more than twenty years and asteroseismology is the only way to study the internal structure of these stars. It may also provide some clues to understand the “Be phenomenon”. The opportunity to observe Be stars during long times, without daily interruption, is specially important, considering non-radial pulsation periods of Be stars.

Omicron Andromedae is a multiple system composed of at least four components. The main component “A” is a variable Be star (B5II-III). The variations of this star are multiform: the circumstellar emission and absorption can vary drastically and can even disappear and reappear later, whereas changes in magnitude are also observed (see e.g. Sareyan et al., 1998). Rapid Spectroscopic and photometric variations are observed as well. As explained below, the rapid Spectroscopic variations of the Hα line observed in 1992 during a phase of moderate emission are very special (Briot et al., 2001). Then the emission of о And increased, so another program of observations of the Hα line was performed to investigate its rapid variations during different emission phases. We present here some preliminary results.

66 Oph has shown recurrent short-lived outbursts nicely detected from ground-based and space (Hipparcos) photometry.

Spectroscopic observations of He I 6678 and Hα lines were performed in June 1997 and June 1998. Search for short-term periodicities was done in He I 6678 line profiles as in equivalent width EW, radial velocity of the line centroid, and V and R components. At least two frequencies were present: ν = 4.0 c/d and ν = 2.2 c/d. The phase distribution of these frequencies over the line profile corresponds in the nrp frame to g-modes with ℓ ~ 3 − 4 and ℓ = 2 respectively.

The photoluminescence and Raman spectra of several Ga1−xAlxN layers (0 ≤ x ≤ 0.86) grown on sapphire substrates by metal-organic vapor phase epitaxy have been recorded at room temperature, under an excitation at 244 nm. Using the photoluminescence spectra, the variation of the band gap of these alloys can be followed only up to x = 0.5. From resonant Raman scattering, it can be deduced that the band gap energy of the solid solution for x very close to 0.7 corresponds to the incident photon energy (5.08 eV). This result is confirmed by a detailed comparison of the present work with previous experimental data on the A1(LO) phonon peak position, obtained under visible excitation.

Luminescence, induced absorption and degenerate four-wave mixing experiments are perform on GaN epilayers grown on a sapphire substrate by MOCVD.

We measure the nonlinear behavior of the luminescence spectra near the excitonic resonance, by using an excitation at 4.026 eV from an excimer laser. At low intensities of excitation, spectra show a saturation of the I2 line due to the finite donor density in the sample. Higher intensities of excitation induce collision processes between photo-created quasi-particles.

Using a dye laser as a pump beam, we measure the induced variation of absorption of a probe beam as a function of the intensity and of the wavelength of the excitation. With increasing intensities of the pump beam, transmission spectra show a red-shift of the absorption edge and of the excitonic resonance.

Pulsed degenerate four-wave mixing experiments were performed using the third harmonic of a picosecond Nd-YAG laser at 3.492 eV. A characteristic time constant of 16 ps has been measured, which is independent of the temperature, spacing of the interference fringe and of the intensity of the pump beams.

Omicron Andromedae is a multiple system of at least four stars: a B ↔Be star (component A), a spectroscopic binary (components B1–B2) and a close companion (component a). According to several studies (see Hill et al. 1988, 1989):

1. - the distance between A and the B1–B2 system decreased from 0.39″ in 1975 to 0.25″ in 1987 (McAlister and Hartkopf 1988)

2. - the few previous speckle measurements of component a have shown the possibility of a 3.7 years orbit around A, according to the 1975 to 1984 observations (mean distance 0.05″). The calculations with this 3.7 yr orbit lead to the prediction of a maximum distance of 0.77″ at 1992.738, i.e. at the end of september 1992, with a North-South orientation.

It is very important for the understanding of the Be phenomenon, and particularly for locating a possible Be phase in the evolutionary track of B stars, to accurately determine the proportion of Be stars among all B stars. This type of study was already made several times in the past. Results obtained generally show a maximum Be frequency around spectral type B2 then a decrease towards late spectral types. Actually Be stars do not have the same characteristics as “normal” B stars and we have to take this into account in the determination of the ratio : number of Be stars / number of B stars. We use the Bright Star Catalogue (Hoffleit & Jaschek 1982) and the Supplement to the Bright Star Catalogue (Hoffleit, Saladyga & Wlasuk 1983) containing stars V= 7.10 and brighter. This study needed to be made separately for the different spectral types because:

- Physical parameters of B stars are very different from B0 to B9;

- Emission characteristics of Be stars vary very much, with a decrease from B0e to B9e.

We successively consider three effects which can influence the frequency of Be stars:

- The over-luminosity of Be stars as compared with B stars;

- Spectral type changes during constant mass evolution;

- Spectral type changes due to the fast rotation of Be stars.

We present here a preliminary report on the analysis of simultaneous photometric and spectroscopic observations of the Be star α Eri, taken during 1992 at the Laboratório Nacional de Astrofísica. α Eri (Archenar, HR472, HD10144, B3–4 III-IV) is the brightest Be star in the sky. It shows activity cycles in a time scale of a few years. Balona et al. (1987) presented a comprehensive study of the star based on photometric and spectroscopic observations. They found a periodicity of 1.26 days in both radial velocity and light variations and argued that a spotted star rotating at this period is the simplest working model that explains the observations.

It is well known that the intrinsic colors of Be stars are not the same as those of “normal” B stars and they are often redder. So interstellar absorption of Be stars determined from photometric indices may be overestimated. In order to avoid this, a method often used to determine the interstellar absorption of Be stars is based on the ultraviolet interstellar absorption bump at 2200 Å (Dorschner 1975; Nandy et al. 1975, 1976). However some peculiar Be stars exist whose circumstellar matter contributes to the 2200 Å bump (Savage et al. 1978). The aim of this work is to test the deredenning method from the 2200 Å bump for “classical” Be stars, in determining the interstellar absorption in the region of the Be star, using the surrounding normal stars.

One of the greatest difficulties in interpreting the continuous spectrum of Be stars is to separate the effects of interstellar reddening from the effects due to the presence of the envelope. This difficulty has been avoided in the two types of correlations considered here. In the first one, parameters not affected by interstellar reddening are used (the Balmer jump and the Balmer decrement). In the second one, the parameters used can be affected by the interstellar extinction but comparisons are made only between values which correspond to the same (but variable) Be star, at different epochs, with different amounts of emission.

A method free of interstellar reddening of comparing the energy distributions in the far-UV of Be/Shell stars to those of normal B stars is presented. The deviations of Be/Shell stars from the sequences of normal stars are correlated with other physical parameters observed in these stars. The largest UV color differences to the sequences of normal stars are found for those Be/Shell stars having the largest IR color excesses.

We searched for the general properties of the Be stars with Paschen emission lines. First, we obtained a relation between the infrared excess of the Be stars and the presence of emission in the Paschen lines. Until now, these emission excesses could be related to no physical characteristics of classical Be stars. Then, the measures of Paschen decrements of 12 stars whose spectral types range from B0e to B5e allowed us to check several theoretical calculations about the formation of emission lines in the envelopes of Be stars. Thus we can see the prominent part played by the electronic collisions in the Sobolev theory. Indeed, only with calculations taking the electronic collisions into account, can we obtain theoretical values agreeing with both measured Paschen and Balmer decrements for the hottest stars of our sample. However, no theoretical values agree with the observed decrements for the cooler stars.