SAUL RAPPAPORT, Professor
of Physics
Research Interests
Professor Rappaport's current research interests
are centered on theoretical studies of the formation, evolution,
and population synthesis of binary systems containing collapsed
stars—white dwarfs, neutron stars, and black holes. Recent
focus has been on the development of a number of comprehensive population
synthesis codes to study the following types of binary systems:
(i) cataclysmic variables and supersoft X-ray
sources with white dwarf accretors;
(ii) low- and intermediate mass X-ray binaries
with neutron star accretors;
(iii) recycled binary millisecond pulsars,
and
(iv) planetary nebulae which form in interacting
binaries.
The formation and evolution of binaries in
categories (i), (ii) and (iii) above in globular clusters are significantly
different than in the galactic plane due to the possibility of exchange
collisions in clusters; both types of scenarios are being investigated.
For planetary nebulae formed in interacting binary systems, the
wind of the asymptotic giant branch star may be shaped by either
the binary companion or a possible collimated fast outflow from
the companion. These are being studied with smooth particle hydrodynamic
simulations.
Such population synthesis calculations yield
theoretical distributions of the properties of the systems of interest,
including the masses of the compact object and its companion, the
orbital period, and the mass transfer rate at the current epoch.
By comparing the theoretical distributions to the observational
results obtained by X-ray, optical, and radio astronomers, one can
hope to learn about the validity of the various input parameters
utilized in the calculations. For example, the assumptions about
stellar birth rates, orbital period distribution, and mass ratios
of primordial binaries can be tested. Moreover, the method of handling
the common envelope phase of the binary evolution (likely involved
in the production of most collapsed stars in binary systems), and
the distribution of 'kick' velocities imparted to the neutron star
during its birth in a supernova explosion, are also testable.
The observational side of Prof. Rappaport's
research emphasizes studies of X-ray pulsars. These involve precise
determinations of orbital parameters, orbital decay rates, apsidal
motion, and the constituent masses, including the neutron stars.
His group is particularly interested in what implications the observational
results have for binary star evolution. Recent work includes the
first determination of the orbit of the neutron star in the well-known
classical Be-star system X Per. The combination of the wide orbital
separation (about 2 AU) and the small orbital eccentricity (0.11)
has significant implications for the 'kick' velocities imparted
to neutron stars at their birth. This discovery bolsters previous
claims by some researchers that the natal kick distribution is bimodal,
with a substantial fraction of neutron stars receiving at most a
small kick.
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Biographical Sketch
Professor Rappaport joined the MIT Department of Physics as an
Assistant Professor in 1969 and became a full Professor in 1981.
From 1993-95, he was Head of the Astrophysics Division.
He received his A.B. from Temple University (1963) and his Ph.D.
from MIT in 1968.
[top] Selected Publications
"A New Technique for Calculations of
Binary Stellar Evolution, with Application to Magnetic Braking,"
RAPPAPORT S, VERBUNT F, JOSS PC, ASTROPHYSICAL JOURNAL 275
(2): 713-731 1983.
"On the Evolutionary Status of Bright,
Low-Mass X-ray Sources," WEBBINK RF, RAPPAPORT S, SAVONIJE
GJ, ASTROPHYSICAL JOURNAL 270 (2): 678-693 1983.
"The Evolution of Highly Compact Binary
Stellar-Systems," RAPPAPORT S, JOSS PC, WEBBINK RF, ASTROPHYSICAL
JOURNAL 254 (2): 616-640 1982.
"Accreting White-Dwarf Models for CAL-83,
CAL-87 and Other Ultrasoft X-ray Sources in the LMC," VANDENHEUVEL
EPJ, BHATTACHARYA D, NOMOTO K, RAPPAPORT SA, ASTRONOMY AND ASTROPHYSICS
262 (1): 97-105 AUG 1992.
"Formation and Evolution of Luminous
Supersoft X-ray Sources," RAPPAPORT S, DISTEFANO R, SMITH JD,
ASTROPHYSICAL JOURNAL 426 (2): 692-703 Part 1 MAY 10 1994.
"The Rings Around the Egg Nebula,"
Harpaz A, Rappaport S, Soker N, ASTROPHYSICAL JOURNAL 487
(2): 809-817 Part 1 OCT 1 1997.
"Collisions of Free-floating Planets
with Evolved Stars in Globular Clusters," Soker N, Rappaport
S, Fregeau J, ASTROPHYSICAL JOURNAL 563 (1): L87-L90 Part
2 DEC 10 2001.
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