Steven Parsons

My research involves a group of systems known as post common envelope binaries (PCEBs). These systems were originally composed of two stars relatively close to one another (periods of between 10-1000 days). When the more massive star runs out of nuclear fuel it will expand and its material will spill over onto the other star. The result of this is that the two stars end up orbiting within an envelope of material, the so-called common envelope phase.

The frictonal forces within this envelope cause the two stars to spiral in towards one another and results in the envelope of material being thrown off into space. Whats left is the core of the more massive star (which will become a white dwarf) and the lower mass main-sequence star, a PCEB.

A small group of PCEBs are aligned such that, as viewed from Earth, they show deep eclipses as the dimmer, but larger, main-sequence star passes in front of the brighter white dwarf. Eclipsing systems offer a chance to determine extremely precise masses and radii of the two stars independantly of any models and with very few assumptions. Therefore these systems are valuable tools for testing mass-radius relations for both white dwarfs and low mass stars.

Eclipses also offer us a chance to detect any period variations in these systems. These variations could be signs of angular momentum loss in the system which will eventually drive the two stars closer together and initiate mass transfer from the main-sequence star on to the surface of the white dwarf. Alternately, these period variations may be the result of an unseen companion to the binary. The accuracy of eclipse timings mean that this method can probe down to planetary masses offering us a chance to detect planets in some of the most extreme locations in the Galaxy. See for example the planets we recently discovered in orbit around the PCEB NN Ser.

I'm also interested in close double white dwarf binaries and we identified the second ever eclipsing double white dwarf binary. These binaries will slowly spiral towards one another and either merge together or potentially explode as a supernova.

If you are trying to reduce X-Shooter spectra then this presentation might come in handy

Published papers:

The chemical diversity of exo-terrestrial planetary debris around white dwarfs

Gänsicke B. T., Koester D., Farihi J.,Girven J. M., Parsons S. G., Breedt E., 2012, MNRAS, in press, arXiv:1205.0167

Gaseous Material Orbiting the Polluted, Dusty White Dwarf HE1349-2305

Melis C., Dufour P., Farihi J., Bochanski J., Burgasser A. J., Parsons S. G., Gänsicke B. T., Koester D., Swift B. J., 2012, ApJ, 751L, 4

The evolutionary state of short period magnetic white dwarf binaries

Breedt E., Gänsicke B. T., Girven J. M., Drake A. J., Copperwheat C. M., Parsons S. G., Marsh T. R., 2012, MNRAS, in press, arXiv:1203.4711

A Spitzer Space Telescope Study of the Debris Disks around four SDSS White Dwarfs

Brinkworth C. S., Gänsicke B. T., Girven J. M., Hoard D. W., Marsh T. R., Parsons S. G., Koester D., 2012, ApJ, 750, 86

A radial velocity study of CTCVJ1300-3052

Savoury C. D. J., Littlefair S. P., Marsh T. R., Dhillon V. S., Parsons S. G., Copperwheat C. M., Steeghs D., 2012, MNRAS, 422, 469

A J-band detection of the donor star in the dwarf nova OY Carinae, and an optical detection of its `iron curtain'

Copperwheat C. M., Marsh T. R., Parsons S. G., Hickman R., Steeghs D., Breedt E., Dhillon V. S., Littlefair S. P., Savoury C., 2012, MNRAS, 421, 149

A precision study of two eclipsing white dwarf plus M dwarf binaries

Parsons S. G., Marsh T. R., Gänsicke B. T., Rebassa-Mansergas A., Dhillon V. S., Littlefair S. P., Copperwheat C. M., Hickman R. D. G., Burleigh M. R., Kerry P., Koester D., Nebot Gómez-Morán A., Pyrzas S., Savoury C. D. J., Schreiber M. R., Schmidtobreick L., Schwope A. D., Steele P. R., Tappert C., 2012, MNRAS, 420, 1365

Post Common Envelope Binaries from SDSS. XV: Accurate stellar parameters for a cool 0.4-solar mass white dwarf and a 0.16-solar mass M-dwarf in a 3 hour eclipsing binary

Pyrzas S., Gänsicke B. T., Brady S., Parsons S. G., Marsh T. R., Koester D., Breedt E., Copperwheat C. M., Nebot Gomez-Moran A., Rebassa-Mansergas A., Schreiber M. R., Zorotovic M., 2012, MNRAS, 419, 817

The shortest period detached white dwarf + main-sequence binary

Parsons S. G., Marsh T. R., Gänsicke B. T., Dhillon V. S., Copperwheat C. M., Littlefair S. P., Pyrzas S., Drake A. J., Koester D., Schreiber M. R., Rebassa-Mansergas A., 2012, MNRAS, 419, 304

Cataclysmic Variables below the Period Gap: Mass Determinations of 14 Eclipsing Systems

Savoury C. D. J., Littlefair S. P., Dhillon V. S., Marsh T. R., Gänsicke B. T., Copperwheat C. M., Kerry P., Hickman R. D. G., Parsons S. G., 2011, MNRAS, 415, 2025

A Deeply Eclipsing Detached Double Helium White Dwarf Binary

Parsons S. G., Marsh T. R., Gänsicke B. T., Drake A. J., Koester D., 2011, ApJ, 735L, 30

A stellar prominence in the white dwarf/red dwarf binary QS Vir: evidence for a detached system

Parsons S. G., Marsh T. R., Gänsicke B. T., Tappert C., 2011, MNRAS, 412, 2563

Two planets orbiting the recently formed post-common envelope binary NN Serpentis

Beuermann K., Hessman F. V., Dreizler S., Marsh T. R., Parsons S. G., Winget D. E., Miller G. F., Schreiber M. R., Kley W., Dhillon V. S., Littlefair S. P., Copperwheat C. M., Hermes J. J., 2010, A&A, 521L, 60

Orbital period variations in eclipsing post-common-envelope binaries

Parsons S. G., Marsh T. R., Copperwheat C. M., Dhillon V. S., Littlefair S. P., Hickman R. D. G., Maxted P. F. L., Gänsicke B. T., Unda-Sanzana E., Colque J. P., Barraza N., Sanchez N., Monard L. A. G., 2010, MNRAS, 407, 2362

The Mass of the White Dwarf in GW Libra

van Spaandonk L., Steeghs D., Marsh T. R., Parsons S. G., 2010, ApJ, 715L, 109

Precise mass and radius values for the white dwarf and low mass M dwarf in the pre-cataclysmic binary NN Serpentis

Parsons S. G., Marsh T. R., Copperwheat C. M., Dhillon V. S., Littlefair S. P., Gänsicke B. T., Hickman R. D. G., 2010, MNRAS, 402, 2591