My Research Interests
My main research field is asteroseismology of pre-main sequence (PMS) stars.
I am using data obtained from ground with telescopes located, e.g., in
Chile, South Africa and Texas (USA) and from space with the satellites MOST and CoRoT.
I am also involved in the first Austrian space mission, BRITE-Constellation.
In the following I will give short descriptions on the above mentioned topics
What is asteroseismology?
Similar to seismology on the Earth - where we use the sound waves
produced by earthquakes to learn about the interior of the Earth -
asteroseismology allows us to probe the inner structures of stars. It
is the only method that enables us to look inside stars.
What are pre-main sequence stars and why are they interesting?
Stars in their earliest evolutionary phases that have just emerged from
their birth cloud and evolve towards the zero-age main sequence (i.e.
the moment where hydrogen burning starts in the cores) are called
pre-main sequence stars. The nuclear energy that is needed during this
stage of stellar evolution is produced by gravitational contraction and
later on by burning of deuterium. PMS stars are frequently still
embedded in remnants of their birth environment, i.e. they are often
surrounded by circumstellar disks.
The
Figure shows a beautiful example of a young star which is surrounded by
a dense circumstellar disk and shows pulsations. HD 142666 is a
so-called Herbig Ae star that was observed twice using the MOST
satellite (see below). The observations in the first season lasted ~12
days (top panel), in the second season HD 142666 data for ~38 days were
obtained (middle panel). The irregular variability of ~1 magnitude can
clearly be seen. The pulsations occur at the millimagnitude level - a
zoom into the light curve is given in the lowest panel. For more
information see the paper entitled "MOST photometry of the enigmatic
PMS pulsator HD 142666" (Zwintz et al. 2009, A&A 494, 1031).
The MOST satellite
MOST (Microvariability and Oscillations of STars) is a highly successful Canadian micro-satellite mission.
On June 30, 2003, MOST was launched from Plesetzk, Russia, aboard a
ROCKOT launcher into a polar, sun-synchronous orbit. Hence, it can
observe stars located in its Continuous Viewing Zone (ranging from
-19° to +36° in declination) for up to 7 weeks without
interruption. The satellite was designed to perform seismology of
Sun-like and magnetic stars, to study microvariability in Wolf-Rayet
winds and to investigate exoplanetary systems. The suitcase-sized
(dimensions are about 60 x 60 x 24 cm) microsatellite bus with only 60
kg mass houses a 15 cm Maksutov telescope. The image of the primary
target is detected on a frame transfer CCD over one of 36 microlenses,
while additional stars located close to the main target are observed
directly (i.e. without microlenses).
MOST already has exceeded by far its nominal lifetime of one year, is
now in its eighth year of operation and is expected to work up to three
more years. Meanwhile it became possible to observe targets outside of
the Continuous Viewing Zone taking into account a lower duty cycle, but
bringing targets aiming at other science within reach of the satellite.
MOST has also successfully observed stars that have not been primary
subjects of the project, such as Be (e.g. Walker et al. 2005b) and beta
Cephei stars, K giants and even stellar clusters with ground-breaking
results. MOST also contributed significantly to the investigation of
PMS pulsators with dedicated observations of pulsating Herbig Ae field
stars and of the young cluster NGC 2264 where three new pulsating PMS
cluster members could be discovered (Zwintz et al. 2009, A&A 502,
239).
One of the three ground stations that provide communication with MOST is located (see picture) on the roof of the Institute of Astronomy in Vienna.
The other two ground stations are in Vancouver and Toronto (Canada).
The CoRoT satellite
CoRoT is the third of the petites-missions of the french space agency
CNES (Centre National d'Études spatiales). It was launched on
December 27, 2007 by a Soyuz rocket from Baikonur into a polar orbit.
The picture shows CoRoT before launch in the Alcatel laboratories.
The CoRoT telescope is an all reflecting system with 27 cm diameter of clear aperture.
The CoRoT mission is primarily devoted to understand the physical
processes that determine the internal structures of stars
and to detect and observe extrasolar planets.
More information can be found unter http://corot.oamp.fr.
The BRITE-Constellation nanosatellites
The BRITE-Constellation mission currently consists of the first two Austrian (nano)satellites named UniBRITE and BRITE-Austria, two Polish and two Canadian nanosatellites. The 20x20x20 cm cube satellites will be operated together in close collaboration between the scientific teams from Austria, Canada and Poland.
The scientific goal of this nanosatellite mission is high precision photometry in two colours of the brightest stars in the sky (V < 4 mag) and with reduced accuracy also for fainter stars (down to V ~ 7 mag) for studying their brightness variations.
The two Austrian satellites are currently assembled and will be launched in the middle of 2011. The picture below shows one of the satellites in the clean room.
Since 2009 I am member of the BRITE-Constellation International Advisory Team (BIAST).
More information on this mission can be found under http://www.brite-constellation.at.