Contributions méthodologiques à la conception de collecticiels:
Application aux réunions de planification coopérative du
satellite multi-instrument SOHO
Degré et Date: Thèse (PhD), Décembre 1996
Instituts: Université Toulouse I
Institut d'Astrophysique Spatiale,
Université Paris XI, Orsay, France
Co-Directeurs de Thèse: Prof. M.-F. Barthet
J.-C. Vial
Adresse actuelle: Institut Préparatoire aux Etudes d'Ingénieurs de Tunis, 2 rue Jawahar Lal Nehrou, 1000 Tunis, Tunisie
RESUME
Cette thèse s'inscrit dans le domaine de l'ingéniérie des systèmes multi-utilisateurs.
Notre recherche repose sur l'étude du travail coopératif et sur
l'introduction de solutions collecticielles capables d'assister les collectifs
dans leurs activités coopératives complexes.
Dans notre proposition, au niveau conceptuel, une situation coopérative
se caractérise par quatre variables fondamentales: l'objectif commun,
l'objet de la coopération, le résultat de celle-ci, et l'univers coopératif. La notion d'univers coopératif sert de base pour l'introduction d'une
notation semi-formelle et constitue également un fil
conducteur pour l'approche proposée pour la conception de collecticiels.
La méthodologie de conception proposée est incrémentale et participative.
Elle suit un cycle de vie en spirale englobant les étapes principales
suivantes: analyse des univers coopératifs, spécification de solutions
collecticielles, développement des solutions et leurs introductions au
collectif, évaluation des solutions proposées.
Outre la notation semi-formelle utile le long de ce cycle, et afin de tenir
compte de la coopération, nous proposons des méthodes spécifiques à
chaque étape.
En effet, pour l'étude de l'existant et de la coopération
nous précisons une approche orientée scénario.
Ensuite, nous basons la spécification sur la résolution de
dysfonctionnements détectés dans la coopération; nous proposons
également une nouvelle utilisation des diagrammes QOC
(``Question Option Criteria") pour l'aide à la
spécification de solutions collecticielles.
De plus, nous décrivons le développement rapide de prototypes et introduisons
les séances de simulation avec le collectif réel comme moyen d'introduction
progressive de solutions collecticielles. Enfin, nous soulignons la nécessité de disposer de situations de
référence pour l'évaluation de toute solution collecticielle. Des critères associés aux variables caractéristiques de la situation
coopérative à évaluer sont à considérer.
Sur le plan pratique, cette thèse traite une situation réelle où la
coopération est fondamentale entre les membres impliqués dans la
planification des opérations des instruments du satellite multi-instrument
SOHO (``SOlar and Heliospheric Observatory").
Les propositions précédentes sont appliquées dans ce cas,
allant de l'étude de la situation coopérative existante, de l'identification
de l'univers coopératif initial et des besoins du collectif, jusqu'à
la proposition d'une solution collecticielle assistée par un prototype d'éditeur
partage de planification; ce dernier étant développé à partir d'un
éditeur mono-utilisateur existant et utilisé par l'équipe SOHO."
Atmospheric Temperature Structure in the ROAp Stars
Degree and Date: MSc, December 1997
Institute: University of Cape Town
Thesis advisor: Prof. D.W. Kurtz
ABSTRACT
The rapidly oscillating Ap (roAp) stars are a sub-group of the chemically
peculiar stars of class 2 (CP2), which are characterised by peculiar spectra
and anomalously strong lines of Sr, Cr, Eu and other rare earth elements.
They have strong global dipole magnetic fields with effective strengths of
up to a few thousand gauss. Stars showing these phenomena cover the
spectral range B8p to F0 V-IV. About 20 years ago rapid non-radial pulsations were discovered in the
coolest members of the CP2 group, namely the roAp stars. These pulsations are
due to high over-tone, low degree p modes with periods between 5.6 and
15 minutes. Since then, studies of these rapid oscillations have revealed a
lot of information about these stars. The eigenfrequency spectra of roAp
stars can potentially reveal information such as their rotation periods,
rotational inclinations, magnetic geometries, internal magnetic field
strengths, radii, masses, luminosities and ages.
In 1990 Matthews et al. suggested a technique for determining empirically the T(T) relation for roAp stars. This technique involves comparing the pulsation amplitudes obtained from multi-colour photometry to the ones calculated from black-body pulsator models (assuming dipole mode pulsations). This comparison yielded limb-darkening coefficients which were used to determine T(T) in a way similar to what was done for the sun. Matthews et al. based their idea on the observed fact that pulsation amplitudes of roAp stars drop sharply with increasing wavelength. They thus explained this sharp decline of amplitude with wavelength in terms of the strongly wavelength-dependent limb-darkening.
The initial aim of this thesis was to investigate the technique proposed by Matthews et al., and to apply it to a number of roAp stars. However, when a linearised expression for the variation of the pulsation amplitude with wavelength, limb-darkening, inclination of the pulsation axis alpha, and deltaT/T0 (where deltaT is the polar pulsational temperature semi-amplitude and T0 is the atmospheric temperature) was derived, it was discovered that limb-darkening is too small an effect to account for the observed amplitudes. The result is based on the Wien approximation and uses the Planck function to represent intensity. Therefore limb-darkening cannot be measured from the amplitude vs wavelength data. This analysis and the results thereof are reported in this thesis. Numerical models based on realistic treatment of the intensity spectra (obtained from model atmospheres) are used to confirm and refine the analytical results.
The linearised expression mentioned above suggests that an important factor that explains the sharp decline of amplitude with wavelength is the variation of the ratio deltaT/T0 with wavelength. Therefore, if the T(T) structure of a star is known a priori (from model atmospheres), the variation of deltaT with wavelength can be determined (provided non-adiabatic effects can be ignored). This new technique, together with the variation of opacity with wavelength in the atmospheres of roAp stars, is applied to HD 134214, HD 137949, HD 128898, HD 101065 and HR 3831 to determine deltaT cos alpha as a function of atmospheric depth. HR 3831 was observed at various rotation phases to investigate the effect of rotation on the derived deltaT cos alpha vs atmospheric depth relation. Preliminary results on this are included in the thesis.
Morphological and Surface Photometric Investigation of Some Galaxy Pairs
Containing UV-Excess Galaxies
Degree and Date: MSc, 1994
Institute: Egyptian National Research Institute of Astronomy and Geophysics
Thesis advisor: Prof. A.M.I. Osman
ABSTRACT
Morphological and photometric investigations of galaxies provide us with
important results useful in understanding their properties.
Active galaxies in particular have attracted a great deal of interest in
order to
understand their morphological and physical characteristics through
photometric and spectroscopic studies. The excess of ultraviolet radiation
is one of the forms of activity in active galaxies.
Most active galaxies tend to occur in pairs or groups that exhibit signs
of interaction between the components resulting in peculiarities in their
morphological structure and physical status. The majority of active galaxies
have been studied spectroscopically, but very few have been subjected to
morphological and photometric studies, especially in detail.
This thesis presents morphological and photometric studies of two galaxy pairs (NGC 833/835 and NGC 7770/7771) by means of the technique of photographic surface photometry. The emphasis of the study is on the state of interaction between the components of each pair through the peculiar features appearing in the isophotal maps as well as in the profiles. The colour distribution and the integrated colour have been studied for each component, taking into account that the blue colour together with unusual colour distribution are characteristics relevant to UV-excess galaxies.
Photometric analysis including isophotal contour maps, luminosity profiles and colour distribution along major and minor axes as well as position angle and ellipticity curves are obtained. Integration and decomposition of the luminosity profiles are also performed. The integrated photometric parameters are given as well. Many peculiar morphological features are noticed in both B and V contour maps of the pair NGC 833/835 as well as in the luminosity and position angle profiles of each component. These peculiar features are discussed and considered as a signature of interaction between the components of the pair. So we may conclude that the components of the pair are in a real state of interaction i.e., NGC 833/835 are a physical pair. A lower limit of the total orbital mass of the system is estimated to be Mt = 3.13 x 1011Msun, while the total mass-to-luminosity ratio is about 10.65 fsun.
The component NGC 833 has a red integrated colour ((B-V) =1.03) and a colour distribution which resembles that of the normal spirals. On the other hand, the component NGC 835 is of a blue colour ((B-V) =0.56) and has unusual colour distribution. This result, together with the colour index (U-B)=0.18 (RC3), confirms the classification of NGC 835 as an active galaxy with UV-excess.
We then discuss the pair NGC 7770/7771. The truncation of the luminosity profile along the side of interaction, the peculiar appearance of the ellipticity and position angle profiles are considered as strong evidence for the real state of interaction between the components of the pair. A lower limit of the total orbital mass of the system is found to be Mt = 1.36 x 1010Msun, and the total mass-to-luminosity ratio is about 0.63 fsun. Morphology of the nuclear region of the component NGC 7770 indicates that it has a complicated structure in the B band, while the V band shows a double nuclear structure. Photometric analysis of this component is given in detail.
Modélisation d'enveloppes d'étoiles Be à partir de données spectrophotométriques
Degré et Date: Thèse (PhD), Février 1998
Institut: DASGAL, Observatoire de Paris-Meudon & Institut d'Astrophysique de Paris, France
Co-Directeurs de Thèse: Dr. A.-M. Hubert & Dr. J. Zorec
Future adresse: 3-7 rue de l'Hôpital Dcheïra, Agadir, Maroc
RESUME
Dans une première partie nous étudions la variabilité à long terme de 49 étoiles Be (étoiles B avec raies d'émission) sélectionnées à partir de données spectrophotométriques réparties sur plus de cinquante ans [1].
Les observations sont interprétées en terme de corrélation avec les paramètres stellaires fondamentaux comme la rotation, la pression de radiation de l'étoile ou les caractéristiques géométriques de l'enveloppe (article soumis à Astron. Astrophys.).
La dernière partie de la thèse détaille les calculs de transfert de radiation dans une enveloppe circumstellaire. Les données spectrophotométriques sont alors étudiées en terme de paramètres physiques de l'enveloppe tels que l'expansion, l'opacité et la température d'excitation (article en préparation).
[1] Moujtahid, A., Zorec, J., Hubert, A.-M., Garcia, A., Burki, D.G., 1998, Long-term visual spectrophotometric behaviour of Be stars, Astron. Astrophys., in press