Mr. James Silvester BSc (Hons), MSc PhD Student / Research Assistant

Department of Physics

Certains des liens ci-dessous conduisent à un site d'une entité non assujettie à la Loi sur les langues officielles. L'information sur ce site est disponible dans la langue du site.

Stellar Astrophysics

About Me

I am currently finishing up my PhD (Queen's), which focuses on observational studies of magnetic and abundance structure in the atmospheres of A and B type stars. In particular I am performing Magnetic Doppler Imaging of a sample of Ap/Bp stars using data acquired with both the ESPaDOnS instrument at the Canada-France-Hawaii Telescope (CFHT), and the new NARVAL instrument at the Pic du Midi observatory.

I work under the supervision of Gregg Wade at RMC and David Hanes at Queen's, with assistance from Oleg Kochukhov working at the Uppsala Astronomical observatory (Sweden)

I also completed my MSc (Queen's) under the supervision of Gregg Wade and David Hanes, exploiting open clusters to explore the evolution and environmental dependence of chemical peculiarities and magnetic fields in Ap/Bp stars. For this project I used data obtained with the now-decomissioned MuSiCoS spectropolarimeter at Pic du Midi observatory. During the fall term of 2006 I was in tenure of an ESO Short-Term Studentship in Santiago, Chile.

During the academic year 2002-2003, I was on a 10 month student placement at the Pic du Midi Observatory in France, during which I observed extensively with the MuSiCoS spectropolarimeter.

I am a member of the Canadian Astronomical Society, and a former Fellow of the Royal Astronomical Society

Research: Magnetic Doppler Imaging of Ap Stars

My PhD project exploits the unique polarimetric capabilities of ESPaDOnS (CFHT, Hawaii) and NARVAL (TBL, France) to obtain high signal-to-noise ratio, high resolution, phase-resolved spectra of a selected sample of magnetic Ap stars in all 4 Stokes parameters. The resulting datasets will be used to construct detailed, assumption-free maps of the vector magnetic fields and chemical abundance structures in the photospheres of these stars using the technique known as Magnetic Doppler Imaging (MDI). Such maps represent a crucial step toward understanding the origin and evolution of magnetic fields in upper-main sequence stars, and for constraining the influence of these fields on the chemical separation and mixing processes (e.g. diffusion, convection, mass loss) in Ap stars.

Because different parts of the surface of a rotating star are moving with unequal velocities relative to the Earth, as a result of the Doppler effect spectral contributions of different surface regions are shifted in wavelength and surface structure is revealed spots revealed by distortions moving across line profiles as the star rotates. If we observe the star from all aspect angles, it becomes possible to construct a 2-D chemical or temperature map of the stellar surface. This technique combined with polarimetric data, allows the reconstruction of the vector magnetic map simultaneously and self-consistently with the distributions of chemical elements and temperature spots.

Prelimary magnetic field direction and intensity of 49 Cam, as recovered using the MDI technique and NARVAL Stokes IQUV spectropolarimetric data

This link leads to a site belonging to an entity not subject to the Official Languages Act. Information on this site is available in the language of the site.

Publications:

For list of publications, visit the NASA Astrophysics Data System.