Biographical Profile
Professor Nelson received his Ph.D. from Queen's University in 1984.
He subsequently held a postdoctoral fellowship at MIT
(Center for Space Research) that led to pioneering work on
the structure and evolution of a completely new class of substellar
objects known as Brown Dwarfs. From 1986-1988 he was a research fellow at CITA (Canadian Institute of
Theoretical Astrophysics). He joined the
department of physics at Bishop's as an Assistant Professor in 1988 and became a
full Professor in 1998. From 1996-1998 & 1999-2001, he served as Chair of the physics department.
Awards & Honours
Invited Review Speaker Aspen Conference on Binary Radio Pulsars (Jan. 2004)
Scientific Program Committee HPCS 2003
Canada Research Chair in Astrophysics (July 2002)
Paper presented at the 198th AAS Meeting selected for Press Release (June 2001)
Reinhardt Fellowship awarded by CITA (1999)
William & Nancy Turner (Chancellor's) Teaching Award (1996)
Interviewed on the CBC's Quirks & Quarks (1995)
Invited Contributor (News & Views) for Nature (1995)
Invited Review Speaker at NATO ASI on Baryonic Dark Matter (1989)
Teaching Interests
Statistical Methods for the Experimental Sciences (Physics 101)
Introduction to Astronomy (Physics 113)
Introductory Physics: Mechanics (Physics 191)
Advanced Mechanics (Physics 218)
Statistical & Thermal Physics (Physics 220)
Theoretical Topics (Physics 466)
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Research Activities
It is our understanding of the properties and evolution of stars that
gives us unique insights into the age, scale, and structure of the Universe. Most stars reside in "wide" binary systems
but some of the most important and exotic phenomena are observed in interacting binary systems.
They span the range from black-hole binaries to contact binaries. These systems are rich in physics (e.g.,
radiative hydrodynamics, thermonuclear runaways, the properties of dense matter) and can be used as a laboratory
in which we can test predictions from a diverse group of fields such as general relativity and high energy
physics. The primary focus of Professor Nelson's research is centered on the theory associated with the structure,
formation, and evolution of very-low to intermediate mass stars in close binary systems containing compact
stars — white dwarfs, neutron stars, and black holes.
The most important scientific objective is the
development of a self-consistent picture of the formation and evolution of interacting binary systems.
In particular, the goals are to:
(i) determine how each type of system forms and describe the specific evolutionary pathways
of systems associated with a certain population;
(ii) determine the salient theoretical properties of the
binaries at each stage in their evolution and compare these with the observed ones;
(iii) enumerate the probabilities associated with detecting the various types of "end-products" (remnants)
resulting from the evolution of these systems.
Although the theoretical picture is based on a combination
of population synthesis and stellar evolution techniques, its validity needs to be
tested rigorously. For example, the observed numbers and frequency distribution of the various types of
binaries can be compared with the theoretical predictions. Moreover, the properties of the various phenomena
associated with different phases of binary evolution (e.g., stable nuclear burning on the surface of
white dwarfs [as opposed to Novae], or the existence of a "period gap" in Cataclysmic Variables) can be
compared with what is seen
observationally. Thus comparison using observational results from a wide variety of
instruments such as the HST, Chandra, KECK, Gemini and SIRTF is essential.
Specific projects include:
determining the conditions that lead to quasi-steady nuclear burning on the
surfaces of accreting white dwarf stars. Fast-accreting white dwarfs may the progenitors of
Type Ia supernovae and thus it is mandatory that we determine whether there are
sufficient numbers of systems (e.g., SuperSoft X-ray Sources) to account for the observed frequency of
Type Ia SNe;
determining the (synthetic) orbital period distribution of recycled pulsars in the galactic disk
and trying to match the observed one. This type of analysis should allow us to comment on the
viability and applicability of such mechanisms as 'radioejection' and the propeller effect;
refining the accuracy of theoretical models describing the evolution of mass-losing stars
in low- and intermediate-mass binary systems and further exploring parameter space (e.g., metallicity
dependence and orbital angular momentum dissipation);
determining the cooling ages of low-mass He-degenerate dwarfs in binary millisecond pulsars (BMSPs)
and investigating the importance of hydrogen shell-flashes during the evolution of these objects. These
binaries are thought to contain two "independent" clocks and thus provide us with a unique opportunity to
confront our understanding of the rotational history of
pulsars (i.e., spin-down) with our models for the formation and cooling of the companions;
determining the relative probabilities of the evolutionary channels leading to the formation of
ultrashort-period binaries such as accreting millisecond pulsars. Three ultrashort-period accreting millisecond pulsars
have been discovered in the past two years and there is considerable debate as to their origin and
the reasons as to why we see them as X-ray pulsars; and,
carrying out population syntheses to analyze the expected count data for a comprehensive set of scenarios leading
to the formation of brown dwarfs and planetary-mass objects. This is particular timely given the recent launch of
the Spitzer Space Telescope (SST). The results of the deep imaging IR surveys will be combined with those
of other surveys (2MASS and DENIS) will result in statistically significant counts of substellar objects in the
solar neighborhood and in clusters.
To assist the efforts of various international collaborations working on problems related to interacting
binary evolution we have developed the Bishop's University
Interacting Binary Evolution Server that
will allow scientists to download specific evolutionary tracks from an archive of data (and, in addition, request
completely new evolutionary results).
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Team Members/Active Collaborations
- Sylvain Turcotte [Bishop's]: The Bishop's group has become affiliated with the ASCI consortium and will be using the FLASH code to simulate
nova-related phenomena on hydrodynamic timescales. The physics of chemical diffusion is also being incorporated in an interacting
binary code to investigate the properties of hydrogen shell flashes that occur in some binary millisecond pulsar systems.
- Ernest Dubeau [Bishop's]: Current investigations are focused on the origin of Red Stragglers in globular clusters. This work is
also related to a model being devised to explain the 'period gap' in the orbital period distribution of (wide) low-mass binary pulsars.
- Michel Barrette [U. Sherbrooke/Bishop's] has been working in conjunction with the CCS team (under the direction of Alain Veilleux) to build and
expand a Beowulf type cluster (Elix2) using the OSCAR software suite. The cluster has
been constructed in collaboration with André-Marie
Tremblay at the University of Sherbrooke.
- Saul Rappapport [MIT]: Population synthesis techniques
are being used to determine the formation probabilities of ultracompact binaries (e.g., accreting
millisecond pulsars) according to the TAMS-NS scenario. A simplified stellar evolution code ("FastCode")
is currently being tested and its purpose is to allow population syntheses to be carried out more efficiently.
The evolutionary pathways leading to the formation of neon-enriched degenerate donors in ultracompact X-ray binaries
is also being investigated (in conjunction with graduate student Adrienne Juett).
- Chris Deloye & Lars Bildsten [UCSB]: The thermal properties of hydrogen-depleted and pure-helium dwarfs
in ultracompact binaries are being studied in order to gain more insight into the evolution of AM CVn-type systems.
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Research Infrastructure
The infrastructure for the CFI funded
project entitled Cluster Computing Environment for Research in Theoretical Astrophysics and Other
Sciences at Bishop's University consists of two major components:
(2) The creation of a high-performance computing (HPC)
environment that allows researchers working in the area of theoretical astrophysics to
develop computer simulations that will give us a better understanding of the
properties and evolution of interacting and exploding stars (such as supernovae).
The main servers (SunBlade 2000s) were manufactured by Sun Microsystems and have been completely
installed and configured. These computers can communicate with other computers both on and off campus
using a Gigabit ethernet connection. To fully utilize this bandwidth capability, a Gigabit
"blade" was purchased collaboratively using funds from this project and Bishop's University.
Thus all computer users at Bishop's (e.g., professors, researchers, and students) can benefit from
a superior level of service. Another innovative aspect of this project was the installation
of videoconferencing tools that give researchers the ability
to communicate more easily with colleagues outside of the University.
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Selected Publications
"Formation and Evolution of Binary Millisecond Pulsars with Helium White Dwarf Companions", NELSON, L.A.
Binary Radio Pulsars, in press. (2004) [PDF file]
"Evolutionary Properties of Low-Mass, Degenerate Dwarfs in Binaries
Containing Compact Companions", NELSON, L.A., Dubeau, E. & MacCannell, K.
Astrophysical Journal, in press. (2004) [PDF file]
"On the Properties of Galactic Novae and Their Orbital Period Distribution", NELSON, L.A., MacCannell, K. & Dubeau, E.
Astrophysical Journal, 602, 938. (2004) [PDF file]
"Theoretical Considerations on the Properties of Accreting Millisecond Pulsars", NELSON, L.A. & Rappaport, S.
Astrophysical Journal, 598, 431. (2003) [PDF file]
"An Exploration of the Paradigm for the 2-3 Hour Period Gap in
Cataclysmic Variables", Howell, S.B., NELSON, L.A. & Rappaport, S.
Astrophysical Journal, 550, 897. (2001) [PDF file]
"On the Theoretical Orbital Period Distribution of Galactic Novae", NELSON, L.A., MacCannell, K. & Dubeau, E.
Bulletin of the American Astronomical Society, 33, 803. (2001) [Press Release]
"On the Companions of Binary Millisecond Pulsars", NELSON, L.A. & Davis, A.
New Astronomy Reviews, 44, 99. (2000)
"Luminous Supersoft X-Ray Sources as Type Ia Progenitors", Di Stefano, R., NELSON, L.A., Lee, W., Wood, T. & Rappaport, S.
Thermonuclear Supernovae, 147. (1996)
"On the Numbers and Properties of Close-Binary Supersoft Sources", Di Stefano, R. & NELSON, L.A.
Supersoft X-Ray Sources, 472, 3. (1996)
"On the Detectability of Brown Dwarfs: Predictions and Uncertainties", NELSON, L.A., Dubeau, E. & MacCannell, K.
Astrophysical Journal, 404, 723. (1993).
"On the Li and Be Tests for Brown Dwarfs", NELSON, L.A., Rappaport, S. & Chiang, E.
Astrophysical Journal, 413, 9. (1993)
"Theoretical Models of Low Mass Stars and Brown Dwarfs I. The Lower Main Sequence", Dorman, B., NELSON, L.A., & Chau, W.Y.
Astrophysical Journal, 342, 1003. (1989)
"The Evolutionary Status of 4U 1820-30", Rappaport, S., NELSON, L.A., Ma, C. & Joss, P.
Astrophysical Journal, 322, 842. (1987)
"The Evolution of Very Low-Mass Stars", NELSON, L.A., Rappaport, S. & Joss, P.
Astrophysical Journal, 311, 226. (1986)
"On the Nature of the Companion to Van Biesbroeck 8", NELSON, L.A., Rappaport, S. & Joss, P. Nature, 316, 42. (1985)
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Related Links
Bishop's University
Interacting Binary Evolution Server
A data
server giving scientists the ability to retrieve archival evolutionary tracks of low-mass
interacting binaries containing compact objects and to
request the computation of new tracks.
Bishop's University Binary Evolution Animations
A variety of high- and low-resolution animations showing the evolution of
interacting binaries that leads to the formation of a binary millisecond pulsar
or ultrashort-period accreting millisecond pulsars.
Research Affiliations and Other Relevant Sites
MIT Center for Space
Research
CITA
Center for
Computations in Science (CCS)
UCSB Astrophysics
Northwestern Astrophysics
The Planetary Science
Institute
Space Telescope Science Institute
Chandra X-Ray Center
Rossi X-Ray Timing Explorer
Canadian Astronomical Society
Spitzer Space Telescope
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Where are They (Former Students) Now?
The following is an abbreviated list of former students and their current positions/accomplishments.
They were either thesis students or worked as summer (undergraduate) research assistants.
| STUDENT'S
NAME |
TITLE OF PROJECT/
DISSERTATION TITLE |
PRESENT POSITION |
| Jonathan Benjamin |
Investigation of the Conditions for Steady Nuclear
Burning on the Surface of White Dwarfs |
MSc student (PGS A)
going to UBC |
| Rene Bilodeau |
Convective Mixing in Brown Dwarfs |
PhD (McMaster U.); PDF at
Berkeley ALS |
| Kirk Buckley |
Stellar Modelling and Numerical Visualizations |
PhD (UBC); NSERC PDF |
| Chris Burns |
Brown Dwarf Detectability |
PhD (Toronto); Asst.
Prof. (Swarthmore U.) |
| Aaron Davis |
A Study on the Cooling of Degenerate Helium
White Dwarfs in Recycled Pulsars |
MSc (Dalhousie); PhD in progress
(RMIT) |
| Ernest Dubeau |
The Evolution of Interacting Binaries Containing
Evolved Companions |
Research Assistant
(Bishop's U.) |
| Scott Kirkwood |
Population III Brown Dwarfs |
MSc (Queen's U.); Software Engineer
|
| William Lee |
Moments of Inertia of Giant and Subgiant Stars |
MEng (U. Waterloo); CAE
Engineer |
| Drew MacCannell |
Simulation of Nova Explosions and the Orbital
Period Distribution of Galactic Novae |
PhD Student (UCSD) |
| Grainne Masterson |
Sensitivity Analysis of Stellar Models to Radiative
Opacities |
MD Student (McMaster
U.) |
| Sean Mooney |
An Investigation of Binary Millisecond Pulsars
using Population Synthesis Techniques |
Numerical Simulations
Analyst (CAE) |
| Marie-Paule
Portelance |
Close Binary SuperSoft X-Ray Sources |
MSc; PhD in progress (U.
Western Ontario) |
| Jamie Lee Ramsey |
Refinements to the Cooling of Helium Degenerate
Dwarfs |
MSc (U. Ottawa) |
| Trevor Wood |
On the Age of the Pleiades Using the Lithium Test |
PhD (Boston U.); GE
Corporate Engineer |
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Coordinates
Professor Lorne A. Nelson
Bishop's University
Department of Physics
Johnson Building Room 2
2600 College Street
Sherbrooke, QC Canada
J1M 0C8
lnelson@ubishops.ca
Phone: (819)822-9600x2372
Fax: (819)822-9661
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Last Modified on January 26th, 2004
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