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Research Developments in 2002
Flynn has led the DARKSTAR project, ``Space Based Studies of Dark
Matter'', which is funded under the
ANTARES program of the Academy of
Finland and TEKES. DARKSTAR acheived its first year of operation in
2002 and continues until early 2004. The entire year 2002 was spent by
Flynn on sabbatical leave (supported by the Academy of Finland ) at the Astrophysics and Supercomputing
Centre at Swinburne University
of Technology in Melbourne, Australia. Most of the time was spent
analysing dwarf stars measured by the the
European Space Agency 's Hipparcos satellite.
These studies have lead to two spin-off results and are presently being
utilised to constrain the amount of visible matter in the Galaxy's
``normal'' (i.e. stellar halo), for comparison with studies which seek
to constrain the luminosity of the ``dark halo''. The second spin-off
was that we have developed a rather precise (indirect) means to measure
the cosmic production of Helium since the Big Bang. This and other
research
is described below.
Dark Matter as black holes
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Jyrki Hänninen
completed a numerical study of the orbits of stars in the disk of the
Galaxy by masive black holes (dark matter) and giant moleclar clouds,
for comparison with data also obtained from the Hipparcos satellite. We
conclude that black holes remain a possible but
unlikely source of disk heating. We are presently extending these
simulations to the rest of the Galactic disk, not just the region near
the Sun. We intend combining our code with the Galaxy formation models
being developed
at Swinburne by Fenner and Gibson. The figure shows the Galactic disk,
seen edge-on, and surrounded by massive balck
holes.
MOVIE (in gif
format).
The simulation shows stars (shown in green) in the disk being heated by
black holes (shown in red) as they orbit in a Galactic potential.
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Dark Matter as white dwarfs
Janne Holopainen
is nearing compeletion of his masters thesis. He studied white dwarfs
as dark matter candidates, utilising recent space and ground based
data. We concluded that claims in the literature that (part of) the
dark matter has been found in the form of ancient white dwarfs are
premature. The dark matter might be in this form, but there is little
direct evidence for it yet.
The diagram shows good comparison between a large proper motion survey
and one of our simulations.
Ongoing work on K dwarf stars
Eira Kotoneva completed her Ph.D. thesis in January 2002. She
computed the chemical composition of a large uniform set of K dwarf
stars in the European Space Agency's Hipparcos satellite. The sample
allows a very precise measurement to be made of the distribution of
``heavy'' elements (i.e. elements heavier than Helium) in a
representative sample of stars near the Sun. This is a major constraint
on models of the evolution of galaxies, and can be used inderectly to
constrain the density of matter (dark or otherwise) near the Sun.
Eira Kotoneva has
also used archival Hipparcos data to demonstrate a simple and elegant
relation between the stellar position in the lower main sequence (stars
less massive than the Sun) and metallicity. The relationship we have
uncovered is really remarkably tight -- so clear and with such little
scatter, that it leads to metallicities for stars which are as accurate
as doing detailed spectroscopic work. The relationship is predicted by
stellar theory, but never empirically demonstrated.
The technique leads to a new, independent distance estimator,
and very useful because it can be applied to existing Hubble Space Telescope
data. We are now applying the method to Hubble data, with a view to
constraining the density of dwarf stars in the Galactic halo, now with
very mich more accurate distance measurements than all work previously.
This is a useful quantity for comparison with studies of the dark
matter content of the Galactic halo in low mass stars.
Distances to galaxies in the extended local group
Rami Rekola
has
obtained observations of dwarf elliptical and irregular galaxies of the
extended local group using the NOT
. Distances to the galaxies are being determined via the surface
brightness fluctuation method (with Helmut Jerjen, Mount Stromlo Observatory ).
Cepheid based distances for IC 342, a large, starburst spiral galaxy,
are being determined, using observations with the NOT over a long baseline (5 years).
Planetary nebulae are being used for a distance determination to NGC
253 (using imaging data from the ESO 3.6 meter). Mass determinations
for a small set of low surface brightness disk galaxies (with a view to
determining their dark matter content) are also underway. This is part
of a longer term program to assemble reliable masses and distances for
the extended local group galaxies with a view to simulating their
dynamics.
Personnel Movements in 2002
Flynn
was
at the Astrophysics and
Supercomputing Centre , at the
Swinburne University of Technology , in
Melbourne, Australia for a sabbatical year (2002) and was appointed an Academy of Finland Senior Researcher
for the period 2002-2007.
Eira Kotoneva has
accepted a post-doc position at York
University in Toronto, Canada, for 2003-2004. Rami
Rekola spent three months during 2002 at the Nordic Optical Telescope acting as
Support Astronomer.
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