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Astrophysics
research topics: Observational
astronomy applied to stellar physics -
Cepheids:
Innovative application of
diffferent observation techniques to the study of Cepheids:
interferometry
(VLTI), high resolution spectroscopy (HARPS), imaging,... Discovery in
2005 of
circumstellar envelopes around four Cepheids (VLTI/VINCI, MIDI and
CHARA/FLUOR). Study of the light echoes and distance measurement of RS
Pup in
2007 (NTT/EMMI). VISIR observations of the envelopes around a sample of
12
nearby Cepheids in 2008 (work in progress). - Main
sequence stars: First
combination of
constraints from interferometry, photometry, asteroseismology,
spectroscopy for
the modeling of nearby dwarf and subgiant stars (alpha Cen,
Procyon,
Sirius,...). Interferometric study of the limb darkening of a Cen B
(VLTI/VINCI).
Micro-arcsec differential astrometry with NACO and high-resolution
spectroscopy
with HARPS of the multiple system d Velorum
(work in
progress). -
Fast-rotating stars:
Measurement of the
spectacular flattening of the nearby Be
star Achernar in 2003 (VLTI/VINCI). Similar measurements obtained on
Altair and
Vega (2006). Discovery of the stellar wind of Achernar in 2007, and of
its 5th
magnitude close-in companion (separation 0.3") in 2007 using
the VLT/VISIR
instrument in diffraction-limited regime. Identification of the nature
of this
companion in 2008 (A2V star) using NACO imaging and long-slit
spectroscopy
(contrast 30, separation 150 mas). ESO accepted programs for 2009 with
NACO
(cube and SAM imaging). Instrumentation
for long-baseline interferometry: -
2007-present:
in charge of the scientific data reduction software of GRAVITY, one of
the
second generation VLTI instruments, aimed at ultra-high accuracy
astrometry of
the Galactic Center. -
2006-present:
member of the science team of VEGA (visible interferometric instrument). -
2001-2004:
reponsible at ESO of the successful VINCI instrument of the VLTI. Teaching
activities: ~90
h/yr Fourier
optics and coherence, Master 1, Obs.
de Paris, Instrumentation module (18 h/yr) Methodology
course high angular resolution,
Master 2 Research, Obs. de Paris (8 h/yr) Post-Master
course Proposals for large
telescopes (15 h/yr) Remote
teaching Astronomy and Celestial
Mechanics, Obs. De Paris (22 h/yr) Pedagogical
projets with school pupils (2
projects in 2006-2007, 1 project in 2007-2008) Supervision
of students: 2008-2011:
supervisor of the Ph.D. Thesis of
Alexandre Gallenne, together with Antoine Mérand on the
subject of the
characterization of Cepheid envelopes. 2005-2008:
supervision of three Master 2
students, two Master 1 students, and one L3 student Administrative
and scientific reponsibilities: - since
2007: elected member of the french Conseil National des
Astronomes et
Physiciens (CNAP), the institution
in charge of the recruitement and career management
of french astronomers. - since
2007: member
of the scientific council of the JMMC (center for
long-baseline interferometry). - since
2007: co-responsible of the
FP7/OPTICON programme ÒEnhancing the scientific output of
Interferometry with
Denis Mourard and Françoise Delplancke. -
2005-2007: expert adviser for the ESO OPC
in panel D (stars), for four periods. -
referee for A&A, ApJ, PASP,... expert
adviser for the European Research Council (ERC). "Application of interferometry to the study of Cepheids and dwarf stars", Manuscript (in french): http://tel.archives-ouvertes.fr/tel-00258916/en/ Responsible
at
ESO, first as PhD student then as fellow of the construction and
operation of
the highly successful VINCI
instrument
of the VLTI. Lead author of the data reduction software of this
instrument.
Experience of 300 nights at Paranal (VLTI commissioning and scientific
observations), and more than 150 nights at other interferometric
facilities
(CHARA, PTI, IOTA). "Optical interferometry with the VLT – Application to the study of Cepheids", with High Honors, Manuscrit (in french): http://tel.archives-ouvertes.fr/tel-00258928/en/
- Master
in
Mechanical and Structural
Engineering (1995-96),
Paris 6 University, with Honors - Engineer
in
Electro-Mechanics
(1993-96), Ecole Spéciale des Travaux Publics du
Bâtiment et de l'Industrie (Paris), head
of the list |
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Habilitation à Diriger des Recherches:
Application
of
interferometry to the study of Cepheids and dwarf stars Defended
on 11 July 2007 at Institut d'Astrophysique de Paris Manuscript
(in french): http://tel.archives-ouvertes.fr/tel-00258916/en/ Jury: G.
Rousset (President), A. Barrau (Referee), A. Chelli (Referee), P.
Léna (Referee), D.
Bersier, P. Fouqué, D. Mourard, F. Thévenin Optical interferometry is a powerful technique for the study of stars in exquisite details, by enabling the spatial resolution of their disks. I present three applications of this technique to the study of different types of stars: Cepheids, main sequence stars, and fast rotators. Cepheids are a famous class of supergiants that are widely used as standard candles for distance measurements, through the period-luminosity (P-L) relations. Interferometry allows to apply a refined version of the Baade--Wesselink method to estimate the distance to nearby Cepheids, and therefore calibrate the P--L relations. While this method is promising and potentially very precise, several points in its application are critical, in particular the projection factor. Main sequence stars are by far the most numerous stellar class in the universe, as all stars spend the majority of their life as dwarfs. I have applied interferometry to a broad range of main sequence stars, from the very low mass {Proxima} to hot stars. In particular, I have realized the first combination of interferometric and asteroseismic constraints for the modeling of stars (the two components of Alpha Centauri, as well as other stars). In a third part, I describe the recent results that we have obtained on fast rotating stars. Due to the very strong centrifugal force at the equator, the photosphere of these stars is strongly distorted. Interferometry allows to observe these deformations, and I describe our observations of three bright, fast rotating stars: Altair (Alpha Aql), Achernar (Alpha Eri) and Vega (Alpha Lyr). PhD Thesis: Optical
interferometry with the VLT – Application to the study of
Cepheids Defended
on 14 November 2001 at the Observatoire de Paris, in Meudon,
with High Honors Manuscript
(in french): http://tel.archives-ouvertes.fr/tel-00258928/en/ Advisors: P.
Léna
(Paris 7 Univ.), V. Coudé du Foresto (Obs.
de Paris) and A. Glindemann (ESO) Jury: D.
Rouan (President), D. Mourard (Referee), S. T. Ridgway (Referee),
P. Léna, A.
Glindemann, V. Coudé du Foresto Installed at the heart of the Very Large Telescope Interferometer (VLTI, located on top of the Cerro Paranal, in northern Chile), the VINCI instrument allows to combine coherently the infrared light coming from two separate telescopes. Therefore, it opens an access to very high angular resolution observations of the sky (down to a few milliarcseconds). Many important astrophysical questions will be adressed by this instrumen t: the physics of stars, protoplanetary disks and extrasolar planets, among other programs. My thesis work on the VINCI instrument has covered its conception, in particular the functionnal definition of its software system, its installation on top of the Cerro Paranal and its first scientific observations. In the first part of this document, I describe the principles of the beam combination with VINCI and its performances both in the laboratory and in real observational conditions. In a second part, I describe the application of long-baseline optical interferometry to the study of the Cepheid variable stars. These pulsating supergiants play a fundamental role in the measurement of distances in the Universe, since it has been established that their photometric variation period it linked to their intrinsic luminosity through the famous period-luminosity relationship. The calibration of this relation requires that the distance to a number of nearby Cepheids is measured directly, unfortunately, these distances are currently poorly known, even to the closest Cepheids. The very high angular resolution allowed by VINCI and the VLTI will soon enable the refined study of the pulsation of the nearby Cepheids. By combining simultaneous observations of the radial velocity of their photosphere with angular diameter measurements, it will be possible to estimate directly their distance. The goal of this program: the calibration of the period-luminosity relationship with a precision better than 0,01 mag, a factor ten better than our current knowledge. In addition to this fundamental program, I decribe also the possibilities offered by VINCI for the study of the main sequence dwarfs, in particular solar-type stars (with an application to the binary star Aplha Centauri A and B), and I briefly discuss the case of the extrasolar giant planets.
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