UCL Hot-Star Group: Research Interests
Massive stars play a dominant role in the ecology of their parent galaxies since their stellar winds inject a great deal of material and energy into their environment. In particular, our research effort is directed towards modelling of O-, B-type, and Wolf-Rayet stars, with a view to understanding their atmospheres and winds, and thereby to constrain their evolution. These stars occupy the top-left corner of the Hertzsprung-Russell diagram, and are the most massive stars known.
PowerPoint poster on Hot Star Winds (adapted from Stan Owocki's original)
Current studies include:
Mass-loss from
stellar winds. Hot stars
lose mass via stellar winds, at a rate of a several millionths of
a solar mass per year (about an earth mass per year). Over their
lifetimes (several million years) this has a dramatic effect on
their evolution, such that mass is `peeled' away from the surface
of stars, the inner regions, which may contain products of nuclear
burning, are exposed. The abundances of helium, carbon, nitrogen,
and oxygen are sensitive indicators of processed material.
Variability. We are studying variability in
the outflows from massive O, B and Wolf-Rayet stars using UV, optical,
IR and radio observations.
Stellar-wind geometry through spectropolarimetry.
If a star has an asymmetric outflow, then continuum photons formed
inside electron-scattering optical depth unity will be polarized.
Typically, emission lines are formed at larger radii, undergo less
electron-scattering, and so are less polarized. The resulting depolarization
through emission lines is a diagnostic of the geometry of the outflows.
Non-radial pulsations
and other types of photospheric velocity field.
Helioseismology can provide a direct probe of the interior structure
of stars. We are analysing the characteristics of non-radial
pulsations in the atmospheres of early-type stars, and how these
pulsations interact with the stars' rotation and mass loss.
Luminous Blue Variables represent rare, poorly understood
unstable stars which are losing a great deal of enriched material in a dense,
slow stellar wind. We have recently analysed HST observations of an LBV
in a galaxy 10,000,000 light years away that is currently undergoing a rare
giant eruption in which one Earth mass of material is being ejected every
day!
Ring nebulae are formed when the powerful
winds of massive stars interacts with its circumstellar material,
and allows the recent evolutionary history of massive stars to be
investigated. We also study the formation of circumstellar dust
in Luminous Blue Variables and WR stars.
Starburst galaxies represent galaxies in which
recent star formation has occured - clusters of massive stars are born
in Starbursts when galaxies collide. We use UV/optical/IR observations
to improve our understanding of the Starburst phenomenon.
Winds from Cataclysmic Variables. Close, interacting
binary systems often have as one member a white dwarf with a
surrounding accretion disk. These stars, and their disks, show
stellar winds which have much physics in common with `normal'
hot stars. Also, some
central stars of Planetary Nebulae with O-type
and Wolf-Rayet spectral types can be analysed in a similar way to
massive stars even though their evolutionary history is completely
different.
A list of publications in these areas is available here.
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