Professor of Physics


  Research Activities


  Research Infrastructure

  Student Involvement


  Related Links

  Interacting Binary Evolution Server

Email: lnelson@ubishops.ca

Phone: (819) 822-9600x2372

Fax: (819) 822-9661

Office: Johnson Room 2

Research Interests

  • Interacting Binary Stars

  • Type Ia Supernovae

  • Millisecond Pulsars

  • Brown Dwarfs & Dark Matter

  • 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)


    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).


    Team Members/Active Collaborations


    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:

    (1) A Beowulf cluster that allows researchers to carry out multi-scalar (and in some cases parallel) numerical simulations.  This technologically innovative cluster is being built in conjunction with the Centre de calcul scientifique (CCS) at the Université de Sherbrooke and with the collaboration of Prof. André-Marie Tremblay.  The cluster (Elix2) now consists of about 200 nodes each powered by an Intel Pentium 4 CPU (~2.4GHz). Because this cluster has been assembled from generic-source components, it is an extremely cost-effective solution for researchers requiring intensive, large-scale numerical computations.  It has already been heavily used by international collaborators of researchers at both Bishop's and the U. de Sherbrooke.

    (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.


    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)


    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


    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


    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.

    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



    Professor Lorne A. Nelson
    Bishop's University
    Department of Physics
    Johnson Building Room 2
    2600 College Street
    Sherbrooke, QC Canada
    J1M 0C8
    Phone: (819)822-9600x2372
    Fax: (819)822-9661


    Last Modified on January 26th, 2004
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