Abstracts
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"Magnetic Fields on Young Stars and Their Role in Accretion and Disk Locking"
Stellar magnetic fields, including a strong dipole component, are believed
to play a critical role in the early evolution of newly formed, low mass
stars (T Tauri stars) and their circumstellar accretion disks. It is
currently believed that the stellar magnetic field truncates the accretion
disk several stellar radii above the star. This action forces accreting
material to flow along the field lines and accrete onto the star
preferentially at high stellar latitudes. It is also thought that the
stellar rotation rate becomes locked to the Keplerian velocity at the radius
where the disk is truncated. While less certain, many of these ideas are
also believed to occur in intermediate mass youg stars (the Herbig Ae/Be
stars) as well. High energy emissions resulting from magnetic activity may
also play a role in setting the ionization balance in the disk which is
important in both the action of the magneto-rotational instability and
determining the thermal and chemical equilibrium of the disk. I will review
recent efforts to measure the magnetic field properties of young stars,
focussing on how the observations compare with the theoretical expectations.
A picture is emerging indicating that quite strong fields do indeed cover
essentially the entire surface of T Tauri stars; however, it is not yet
clear how strong the dipole component of these stars generally is. The
situtation for Herbig Ae/Be stars is less clear. I will also discuss how
the observations compare to predictions from models of field generation
in these young stars. |
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"Towards an Understanding of the Inner Regions of Protoplanetary Disks"
The inner regions of protoplanetary disks are thought to be the most
active regions for planet formation and thus potentially hold the key
to understanding the formation of solar systems like our own. Direct
spatial imaging is mainly limited to dust observations, which can
reveal signs of evolution such as central holes. However,
spectroscopic studies can probe gas within regions that are
inaccessible to imaging and trace the dominant mass component. CO is a
excellent tracer of the gas being both abundant and easily observable.
We have used the CRIRES spectrograph on the ESO VLT to obtain high
resolution spectra (R~100,000, v=3 km/s) of the 4.7 micron CO v=1-0
fundamental emission band for a large sample (~100) young stars in
various stages of evolution from embedded protostars to transition
disks, where dust clearing has begun. The emission shows a variety of
line profiles indicating complex structure in the inner few AU.
Detailed knowledge of dust and gas in the inner regions of disks is a
key component needed to determine the evolutionary process of how
circumstellar disks transform into planetary systems. |
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"Structure and Evolution of Exoplanets: from Super-Earths to Super-Jupiters"
The number of exoplanets newly discovered increases rapidly with time,
providing new and sometime puzzling informations about their formation and
their structure. In this talk, I will examine our present understanding of
the internal structure and evolution of exoplanets.The detection of
transiting planets around their parent star allow the determination of
their mass and radius, and thus of their mean density. Such valuable
information indicates that a significant fraction of these planets are
enriched in heavy elements (ice, rocks), as observed in the giant planets
of our Solar System. The treatment of heavy materials in planetary interior
and the resulting uncertainties on the mass-radius relationship will be
discussed. I will also address the case of short-period, strongly irradiated
planets and review the different mechanisms, including tidal dissipation,
which have been suggested to explain their anomalously large radii. |
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