Multi-wavelength surveys of massive stars and their environments

Although massive stars (M>10M) are relatively rare, their significance for
astrophysics in general is enormous. They dominate the optical spectra of active
star-forming galaxies, both directly at optical-UV wavelengths, and indirectly at IR
and radio wavelengths (due to reprocessing by dust and gas). Ultimately, as
supernovae, and with the subsequent production of relativistic remnants (neutron
stars and black holes), they generate a substantial X-ray flux which dominates this
emission in normal galaxies. Massive-star winds and supernova eruptions provide
substantial inputs of mechanical energy and chemically enriched material into the
wider galactic environment, acting in concert in young, massive 'super star
clusters'.

Remarkably, many of the physical processes governing the evolution of massive stars are
still highly uncertain. Unlike solar-mass stars, the evolution of massive stars is
profoundly influenced by the amount of mass they lose throughout their lives, which is
currently uncertain at the order-of-magnitude level. The problems raised by this
dependency are illustrated by the diversity of core-collapse SNe and formation
of appropriate massive black hole binaries implied by the first gravitational wave
sources detected.

The objective of this research programme is to exploit high-sensitivity radio, mm and
sub-mm surveys of populations of massive stellar clusters in the Galaxy to advance our
understanding of fundamental physical processes in the evolution of massive stars;
these include mass-loss through clumped stellar winds, the incidence and role of
binarity, and the mechanical and chemical feedback from outflows. By focusing on
massive clusters we will also address the nebulae/ejecta/winds from these stars and how
they are being profoundly affected by the cluster in which they're embedded, and most
likely by the cluster wind. This in turn is highly significant to our understanding of
the environments into which supernovae explode.

The PhD project will be primarily based on spectroscopic (optical, UV) datsets, plus
the e-MERLIN COBRaS Legacy radio data (which is
being led from UCL), plus observations of massive clusters secured with ALMA and ATCA.
Our targets will include the Cyg OB2 association, the Westerlund 1 analogue to a
supercluster, Galactic Centre clusters and the Carina region. We seek to study the
mass-loss and environment of massive stars in all they key evolutionary phases,
including blue and red supergiants, yellow hypergiants, luminous blue variables and
Wolf-Rayet stars. We also have a major project approved using the MeerKAT facility,
which is a SKA precursor, to sample clusters in the Galactic plane. These datasets will
be combined to enable a very powerful multi-waveband analysis of massive stars, including
using the n-LTE synthesis code PoWR.