Biography – Previous work

Since I started my research, my work has been oriented towards themes that always have the same common denominator: the detailed and in-depth study of the evolution of the chemical composition of stars over time. This study has repercussions in fields as varied as :

    • in-depth knowledge of stellar interiors
    • relationship with solar and stellar vibrations (helio- and asteroseismology)
    • constraints on particles (e.g. neutrino mass)
    • general evolution of the chemical composition of galaxies
    • constraints on the primordial universe and cosmology

The beginnings

I started working under the direction of Hubert Reeves in 1969 on the problem of nuclear reactions in stars. We were trying to understand why a small star called 3 centauri A had abnormal helium abundances. We didn’t find it, at least not within the framework of the theories we expected, but it still led to my graduate thesis, defended in January 1971, and to a 1972 Vauclair and Reeves paper (a graduate thesis at that time is about the same as a master’s degree today).

My next work consisted in a detailed study of the transport processes of chemical elements in stars and to show that they could account for a large number of observations, starting with the star 3 centauri A (Vauclair, Michaud and Charland 1974). I published during these years a series of papers that are considered as basic references on the subject, in particular with Georges Michaud, professor at the University of Montreal, Canada.the first and one of the best known of these papers is MCV2 (Michaud, Charland, Vauclair and Vauclair 1976), which laid the foundations for the theories of diffusion of elements in stars. Many other papers followed.

In 1973, I spent a winter in Moscow with my husband Gérard Vauclair, where I was an associate researcher at the Astronomical Council of the USSR Academy of Sciences. We were able to write an important scientific article with a young Russian astronomer, Alyosha Pamjatnikh, who is now a world-renowned researcher, astronomer at the Copernicus Institute in Warsaw, and whom we meet regularly during international symposiums. In this article, we showed the influence of helium diffusion on the internal structure of a star and the mixtures that occur there. At the same time I also showed the influence of a stellar wind on the amount of helium observed at the surface of stars.
In 1977-1978 we made a long stay in the United States. We went as a family, with a little boy of 4 years old and another one of 9 months old. I was first « Assistant Professor » at Stony Brook University, near New York, then « Research Associate » at Columbia University, in the center of New York. Finally, we spent a semester at the California Institute of Technology (Caltech), near Los Angeles. It was a very fruitful stay in terms of research and also life in general.

During this period, I showed that the diffusion of elements in a magnetic field could explain the silicon anomalies observed in some stars. Then, in collaboration with Professor Jessy Greenstein from Caltech and Gérard Vauclair, we studied the diffusion processes of elements in stars at the end of their life, the white dwarfs. We made predictions that were confirmed by many subsequent observations.

Many other examples could be described here, from this very fruitful time. In 1982, I published with G. Vauclair a review article in « Annual Review of Astronomy and Astrophysics » in which we reviewed all these works.

 

The years 1982-2002

In 1981, we left Paris and more precisely the Observatory of Paris-Meudon where I was doing my research and the University of Paris 7 where I was teaching, to settle in Toulouse. We participated in the creation of a new institute linked to the Pic du Midi, which was first called Observatoire du Pic du Midi et de Toulouse (OPMT) and which later became Observatoire Midi-Pyrénées (OMP). We were then a handful of researchers coming from Paris and Nice to build this new site in Toulouse, near the Paul Sabatier University and the CNES, in collaboration with the few astronomers who were already on site, either at the Pic du Midi (site now open to the public), or in the former observatory of Jolimont, which has now become a place of welcome for the public and the headquarters of the Air and Space Academy. For practical reasons, I was the first person to be physically installed in the new buildings, which had just been received. At present the OMP regroups 8 laboratories of sciences of the Universe, including my current laboratory, the Institut de Recherches en Astrophysique et Planétologie (IRAP), which represents a total of 900 researchers, research engineers, doctoral and post-doctoral students, and administrative staff.

During the twenty years from 1982 to 2002, I taught as a professor at the University Paul Sabatier to many students, whom I have the pleasure to see again from time to time, and I continued my research on the way chemical elements move inside stars over time. Indeed, due to their different masses and different atomic structure, the elements slowly fall towards the interior of the stars or are pushed outwards depending on the case. These motions have important repercussions on the structure and evolution of stars, with consequences for cosmology as well as for galaxies or, much closer to us, the relationship between the Sun and the Earth.

This confirmation of an advanced physical theory has proved that processes long considered as secondary are in fact fundamental. We now know that they are involved in all stars, to varying degrees. It was therefore necessary to study them in the most precise way possible. My work has focused on the further development of the theory and modeling of the diffusion of atoms in stars and I have started, with several collaborators and research students, to study in detail the processes that compete with these diffusion phenomena.

The most cited paper of this period is known as « V88 » (Vauclair 1988), in which I proposed for the first time that the observed abundance of lithium in stars, young and old, could be explained in a coherent way by the transport phenomena of this element in the stellar interiors. Many works were then published on this subject. They have a cosmological importance because lithium is one of the very rare elements to have been partially formed in the Big Bang.

In 1996, calculations made with Olivier Richard, then a PhD student, in collaboration with Corinne Charbonnel, from Toulouse and Geneva, and Wojtek Dziembowski, from the Copernicus Institute in Warsaw, allowed us to develop one of the best models of the Sun existing then in the international community. The corresponding article is the most cited of my entire list of publications.

In collaboration with J.D. Landstreet, from the University of Western Ontario, Canada, we have been able to show indirectly the existence of stellar winds in some stars, by examining the consequences on the abundances of some chemical elements.

In collaboration with Douglas O. Gough (Institute of Astronomy, Cambridge, England), then Margarida Cunha (Astronomy Center of the University of Porto, Portugal) we studied the pulsating magnetic stars. I also led, with several students, works on the subject of the abundance of lithium in stars. Our studies of this element have given valuable information about the Universe as a whole.

 

Work done since 2002

My election as a senior member of the Institut universitaire de France in October 2002 allowed me to devote even more time to research, while keeping teaching responsibilities as well as collective responsibilities.

At the same time, the field of stellar physics has entered a new dimension thanks to asteroseismology, or the study of internal oscillations of stars. Indeed, stars vibrate like resonance boxes of musical instruments. The repercussions of these internal sound waves lead to surface vibrations that can be detected with appropriate instruments. For the first time, the international community has succeeded in developing technologies (on the ground or in space) allowing to probe the interior of stars and to test with precision the physics introduced in the models. In the course of my work, I have been especially interested in seismic testing of stars and in the search for variations in their chemical composition.

Moreover, for the last fifteen years, planets have been discovered around stars other than the Sun: the « exoplanets ». Several hundred are now known. The instruments used to detect these exoplanets are the same as those used to detect stellar vibrations.

Thus, since 2002, I have started an in-depth study of the repercussions of an internal variation of chemical composition on the oscillation frequencies of stars, and particularly in connection with the studies of the formation processes of planetary systems. It is a question of studying, in the precise way offered by the new techniques of asteroseismology, the central stars of planetary systems and to compare them to stars which do not have planets detected.

In June 2004, I observed the oscillations of the mu star Arae, from Chile, with my thesis student Michaël Bazot. The results obtained were spectacular, and we proved the importance and the potentiality of this type of studies. Moreover, we had the chance to discover thanks to these observations the smallest exoplanet known at the time, of 14 Earth masses. This discovery, later confirmed by our colleagues of the Geneva observatory, was the subject of press releases at the national and international level and « made the headlines » of several newspapers and magazines during the summer of 2004.

This work was continued with other students, Matthieu Castro, Marion Laymand, Mélanie Soriano, Maria-Eliana Escobar. Other central stars of planetary systems have been particularly studied. One of them is called iota Hor. The seismic study of this star, observed in the southern hemisphere, proved that it was actually formed with the stars of the Hyades cluster, itself observed in the northern hemisphere, and then escaped. The consequences are important for several sub-disciplines, in particular the dynamics of the Galaxy. These results have also been the subject of press releases, and articles have appeared in the international press with the theme « the birthplace of a star revealed by its music ».
I « retired » from Paul Sabatier University in October 2012 and became « professor emeritus », which means that I continue my research work in my laboratory, the IRAP. I currently have a PhD student, co-directed with Olivier Richard, now a member of the Laboratoire Univers et Particules de Montpellier (LUPM). The fact that I no longer give university courses leaves me more time to devote to the general public, to give conferences and to write books.