Phil Charles Research Activities:

I've been involved with various aspects of X-ray astronomy since the 1970s, having done postdoctoral work at UC Berkeley before spending 20 years in the Astrophysics Department at Oxford. During that time, my research work has largely involved optical and X-ray observations of supernova remnants, active stellar coronae, cataclysmic variables, Be X-ray binaries and globular cluster X-ray sources. I was also Principal Investigator for the ISIS spectrograph on the 4.2m WHT on La Palma.

My current research projects are all in the field of Observational High Energy Astrophysics, with my group being divided between Oxford (Lee Homer, Katie McGowan, Liza van Zyl and Stephen Shih) and Southampton (Rob Hynes, Jeno Sokoloski and Diana Hannikainen). Here is a list of these projects with links to relevant papers/web pages:

1. Black-hole X-ray binaries (astro-ph/9806217)
The soft X-ray transients are low-mass X-ray binaries that contain a large fraction (~75%) of black-hole compact objects. We study both these and the related neutron-star systems with optical and IR photometry and spectroscopy which provides the best opportunities for accurate compact object mass determinations. X-ray, UV and optical work is also undertaken as Target of Opportunity over-rides during outbursts of these systems. This work is supported by PPARC and Leverhulme research grants.
2. Fast photometry of low-mass X-ray binaries (astro-ph/9909488 and 9803239)
The frame-transfer CCD on the SAAO telescopes is the only common-user device for fast photometry of faint objects. Combined with simultaneous RXTE and SAX observations these yield details of the X-ray/optical reprocessing in the accretion disc that surrounds the compact object.
3. Nature of the central X-ray source in M33 (astro-ph/9905085)
Our discovery of a 106d period in the luminous central X-ray source X-8 of our neighbour galaxy M33 is a potentially important link between galactic X-ray binaries and the central sources in AGN.
4. X-ray binaries in the LMC (astro-ph/0003236)
The proximity of the Large Magellanic Cloud makes it an ideal object for studying X-ray source populations. Furthermore its low extinction enables both soft X-ray and UV studies, which proved valuable for the "supersoft" sources. We have used the MACHO Project database to obtain long-term light-curves of supersoft sources (e.g. Southwell et al 1996ApJ...470.1065) and well-known LMC X-ray binaries.
5. IR spectroscopy and photometry of X-ray binaries
The high interstellar extinction in the galactic plane and towards the galactic centre makes it impossible to undertake optical studies of many of the brightest X-ray sources in our galaxy. We have therefore undertaken IR spectroscopy using the new generation of IR arrays on large telescopes (such as UKIRT). See e.g. Bandyopadhyay et al, 1997MNRAS.285..718B and 1999MNRAS.306..417B.
6. Globular cluster X-ray sources (astro-ph/9808323)
The globular clusters of our galaxy contain far more X-ray binaries (all low-mass X-ray binaries with neutron star compact objects) than expected for that number of stars, almost certainly due to exotic formation mechanisms in the extremely crowded central regions of these clusters.