possible ph.d. projects
project 1: the outcomes of stellar collisions and near misses in
globular clusters
The dense cores of globular clusters are fantastic stellar
crash test laboratories. Direct physical collisions between cluster members
are believed to produce the so-called blue straggler stars that are
seen in essentially all globular clusters. Near misses are thought to
produce a large number
of close binaries that can then actually drive the dynamical evolution of
their host clusters. The goal of this project will be to first find
and then study these outcomes of stellar collisions and near misses in globular
clusters. this may involve analyses of chandra, hst and ground-based
infrared/adaptive optics observations.
The pictures shown above illustrate one promising way of finding blue
stragglers and close binaries in globular clusters. Both images are of
the same field in
the central regions of the globular cluster 47 Tuc, and both were
obtained with the Hubble Space Telescope. However, the left image was
taken through a u-band filter (centered around 336 nm), whereas the
right one was taken through a far-ultraviolet filter (centerered
around 170 nm). The dramatic difference in the appearance of these
images arises because the vast majority of "normal" stars that crowd
the u-band frame are too red to show up in the far-UV image. However,
blue stragglers and close binaries are much hotter than normal stars
and are therefore particularly prominent in the far-UV.
project 2: the late evolution of cataclysmic binaries
Cataclysmic variables (CVs) are interacting binary systems in which a
white dwarf siphons material off a companion star. During the early
part of a CVs evolution, the mass donor is an ordinary main sequence
star, and the mass exchange causes the CV evolve from long to short
orbital periods. However, gigayears of mass transfer will eventually
whittle the mass donor down to a brown dwarf. At this stage, the
orbital period of a CV should start to increase again. Thus there is a
well-defined period minimum through which all CVs are expected to
pass. However, even though 70% of CVs are theoretically
predicted to have evolved through the period minimum already, only
a handful of potential "period bouncers" are actually known. The goal
of this project will be to study these candidates in order to
determine which, if any, are period bouncers. This will involve the
use of both HST and ground-based observations.
The project will also look at the extraordinarily luminous
recurrent nova T Pyx. This short-period CV is unlikely to be a period
bouncer itself, but may represent an evolutionary pathway that
explains the conspicous absence of period bouncers. The picture
shown above is an HST
image of T Pyx, which reveals the intricate, clumpy structure of the
nebula around the system. This nebula is thought to have been ejected
during one or more of T Pyx's nova eruptions.
Interested? Then send an email to me
(christian@astro.soton.ac.uk)
go to my home page
go to astronomy group home page
go to school of physics and astronomy home page
go to southampton university home page
