My main field of
expertise is asteroseismology, determining the interior structures of
stars by modeling their pulsational eigenmode spectra. I am observationally
oriented and a good part of my work so far consisted of worldwide multisite
observing projects, although my focus now rapidly shifts towards observations
from space. In addition, I have also assisted leading theorists in modeling.
Previous
results
Within these avenues
of research, I was able to obtain the first seismic distance measurement
to a Delta Scuti star (1997,
MNRAS 286, 303). I also systematically studied variable central
stars of young Planetary Nebulae for the first time and was able to
show that they constitute a new class of variable stars (the ZZ Leporis
stars) that I postulated and defined (1998, PhD thesis,
University of Vienna). I participated in the definition of the Gamma
Doradus stars, then a new class of pulsating
star (1999,
PASP 111, 840) and was able to lay out their instability region
in the HR diagram for the first time (1999,
MNRAS 309, L19). As this instability region overlaps with that of
the Delta Scuti stars, I suspected the presence, and made the discovery
of, the first member of two classes of pulsating star (2002,
MNRAS 333, 251), whose in-depth study represents the best evidence
for tidal excitation of stellar pulsations so far (2002,
MNRAS 333, 262). I provided additional examples of stars that show
two different sets of pulsational mode spectra (2004,
MNRAS 347, 454; 2006,
MNRAS 365, 327; 2009,
MNRAS 398, 1339), and I organized a study revealing the first star
with two separate mode spectra sufficiently rich for detailed interior
structure modeling (2009,
ApJ 698, L56). I occasionally work on pulsating white dwarf stars,
where I was able to provide measurements allowing a determination of
the 12C(α,γ)16O nuclear reaction rate
(2002,
MNRAS 335, 698). My recent efforts concentrated on the massive Beta
Cephei stars, which led to the first detailed picture of such an object's
interior, implying significant changes to present models of stellar
structure (concerning angular momentum transport, convective core size
and interior chemical composition) are needed (2004,
MNRAS 350, 1022).
Present scientific
efforts
Asteroseismic space
missions are now delivering photometric measurements of unprecedented
accuracy, up to two orders of magnitude better than possible from the
ground. This allows the detection of enormous numbers of stellar pulsation
modes to be used for interior structure modeling. The highest-profile
mission in this regard is NASA's
Kepler satellite that also has an asteroseismology program. I am
head of Kepler's working group of Beta
Cephei stars and actively participate in the working groups on Delta
Scuti stars, Gamma Doradus stars, compact oscillators (Kepler is the
only asteroseismology mission capable of investigating these stars for
many years to come) and Cepheids. Kepler has the potential to reveal
solar-like oscillations in kappa-driven main sequence, and it is my
intention to study such "hybrid" pulsators with these data,
taking advantage of the different oscillation spectra to sound the stars
in very detail. Along those lines, my PhD student Victoria Antoci is
searching for solar-like oscillators among Delta Scuti stars via a high-precision
radial velocity study. A detection of solar-like oscillations in these
stars is expected to bring new insights into the physics of convection
and Delta Scuti pulsators.
The Austrian-Canadian
BRITE
mission (due to launch in spring 2011) is of high interest for me as
it will naturally mostly observe hot stars which is my present work
focus. Ground-based support observations of the mission's bright targets,
as well of the fainter Kepler targets, are expected to be a major focus
of my future work. In addition, I am involved in the ground-based DARC
(the previous Whole
Earth Telescope) network as a member of the advisory board and I
participate in the Danish-led SONG
(to study solar-like oscillations in bright stars with the radial velocity
technique) network.
The Beta
Cephei stars are tomorrow's supernovae. Knowing their interior structure
before the explosion will lead to an improved understanding of the enrichment
of the interstellar medium, and thus how galaxies evolve chemically.
With asteroseismic studies of Beta Cephei stars we will be able to calibrate
stellar evolutionary models on the main sequence, which can then be
extrapolated to the pre-supernova stage. As they are young objects,
Beta Cephei stars often occur in open clusters and associations. This
allows cross-comparison of seismic results for a population of objects
with a similar evolutionary history and understanding the extent of
the Beta Cephei phenomenon, also using the space observations mentioned
before (theory predicts such stars at temperatures and luminosities
where no oscillations were observed so far).
Although I provided
a description of the ZZ Leporis stars, it is
not clear what physical mechanism causes their variability (pulsation
or variable mass loss). Consequently, more ZZ Leporis stars must be
found and some should be studied extensively, by means of both ground-based
optical photometry and spectroscopy and space-based photometry and ultraviolet
spectroscopy. I successfully proposed one of these objects for the Kepler
mission.