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Dear All,

The Department of Physics invites you to a colloquium on "Extreme Supersoft Sources and their links to HMXBs"

Abstract: V Sge is a peculiar, highly luminous long-period (12.3h) cataclysmic variable that displays a supersoft emitting component (SSS) when in the faint phase of its V~10-13 range of variability.  It appears to be undergoing extremely heavy accretion from its more massive secondary, almost certainly at, or above, an Eddington-limited rate, indicating that it is in a very rare, short-lived phase of its binary evolution, placing it firmly in the SSS-DD channel for eventually detonating as a SNIa.  Its complex and highly variable set of optical emission features, from Balmer and HeII up to high ionisation emission lines, including strong fluorescence features, have made it a target of detailed spectroscopic studies going back 60 years. It is the brightest galactic SSS, yet we only have poor constraints on the donor properties.  We have obtained VLT X-Shooter spectra of V Sge as a function of orbital phase, revealing multiple components in both high and low ionisation lines which have allowed us to track V Sge's principal emitting regions, one of which is a circumbinary ring.  I will compare V Sge and related systems with another remarkable Be+WD system in the LMC, which has been shown to be the first (and so far, only) BeX SSS with a He star donor.  This work is revealing more about the long-sought Be-WD systems, with implications for the properties of the Be equatorial ("excretion") disc, which are a feature of many HMXBs.

About the Speaker: Prof. Philip Allan Charles is an Emeritus Professor of Astronomy in the Department of Physics and Astronomy at the University of Southampton, and a Visiting Professor at the University of Oxford. Prior, he was Head of the Department of Physics & Astronomy at the University of Southampton and held a Visiting Professor appointment at the University of Cape Town (UCT). He was Director of the South African Astronomical Observatory (SAAO) from 2004-2011.  Previously he was Head of the Astronomy Group at the Isaac Newton Group (ING), La Palma (1987-1992), and Head of Astrophysics at the University of Oxford (1994-1999).

​Prof. Charles research interest lies in High- and low-mass X-ray binaries; properties of neutron stars and black holes; cataclysmic variables​ and dwarf novae; time-domain astrophysics; optical instrumentation (PI/co-PI for ISIS on WHT 4.2m​ and FRODOSPEC on Liverpool Telescope).

We look forward to your active participation.