Atoms in Astrophysics

366 Pages·1983·6.171 MB·English

by  P. G. Burke, W. Eissner (auth.), P. G. Burke, W. B. Eissner, D. G. Hummer, I. C. Percival (eds.)

ATOMS IN
ASTROPHYSICS
PHYSICS OF ATOMS AND MOLECULES
Series Editors:
P. G. Burke, The Queen's University of Belfast, Northern Ireland
H. Kleinpoppen, Institute of Atomic Physics, University of Stirling, Scotland
Editorial Advisory Board:
R. B. Bernstein (New York, U.S.A.) C. J. Joachain (Brussels, Belgium)
J. C. Cohen-Tannoudji (Paris, France) W. E. Lamb, Jr. (Tucson, U.S.A.)
R. W. Crompton (Canberra, Australia) P.-O. Liiwdin (Gainesville, U.S.A.)
J. N. Dodd (Dunedin, New Zealand) H. O. Lutz (Bielefeld, Germany)
G. F. Drukarev (Leningrad, U.S.S.R.) M. R. C. McDowell (London, u.K.)
W. Hanle (Giessen, Germany) K. Takayanagi (Tokyo, Japan)
1979:
ATOM-MOLECULE COLLISION THEORY: A Guide for the Experimentalist
Edited by Richard B. Bernstein
1980:
COHERENCE AND CORRELATION IN ATOMIC COLLISIONS
Edited by H. Kleinpoppen and J. F. Williams
VARIATIONAL METHODS IN ELECTRON-ATOM SCATTERING THEORY
R. K. Nesbet
1981 :
DENSITY MATRIX THEORY AND APPLICATIONS
Karl Blum
INNER-SHELL AND X-RAY PHYSICS OF ATOMS AND SOLIDS
Edited by Derek J. Fabian, Hans Kleinpoppen, and Lewis M. Watson
1982:
INTRODUCTION TO THE THEORY OF LASER-ATOM INTERACTIONS
Marvin H. Mittleman
1983:
ATOMS IN ASTROPHYSICS
Edited by P. G. Burke, W. B. Eissner, D. G. Hummer, and I. C. Percival
1983:
ELECTRON - ATOM AND ELECTRON - MOLECULE COLLISIONS
Edited by Juergen Hinze
1983:
PROGRESS IN ATOMIC SPECTROSCOPY, Part C
Edited by H. J. Beyer and Hans Kleinpoppen
A Continuation Order Plan is available for this series. A continuation order will bring delivery of
each new volume immediately upon publication. Volumes are billed only upon actual shipment.
For further information please contact the publisher.
ATOMS IN
ASTROPHYSICS
Edited by
P. G. BURKE
The Queen's University of Belfast
Belfast, Northern Ireland
W B. EISSNER
Science and Engineering Research Council
Daresbury, England
D. G. HUMMER
Joint Institutefor Laboratory Astrophysics
University of Colorado
Boulder, Colorado
and
I. C. PERCIVAL
University of London
London, England
PLENUM PRESS • NEW YORK AND LONDON
Library of Congress Cataloging in Publication Data
Main entry under title:
Atoms in astrophysics.
(Physics of atoms and molecules)
Includes bibliographical references and index.
1. Astrophysics. 2. Atoms. 3. Seaton, M. J. 1. Burke, P. G. II. Series
QB463.A86 1983 523.01'97 82-22517
ISBN -13: 978-1-4613-3538-2 e-ISBN -13 :978-1-4613-3536-8
DOl: 10.1007/978-1-4613-3536-8
© 1983 Plenum Press, New York
Softcover reprint of the hardcover 1st edition 1983
A Division of Plenum Publishing Corporation
233 Spring Street, New York, N. Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form
or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise,
without written permission from the Publisher
CONTRIBUTORS
D. R. BATES. Department of Applied Mathematics and Theoretical Physics, The
Queen's University of Belfast, Belfast BT7 INN, Northern Ireland
P. G. BURKE. Department of Applied Mathematics and Theoretical Physics, The
Queen's University of Belfast, Belfast BT7 INN, Northern Ireland
A. DALGARNO • Harvard-Smithsonian Center for Astrophysics, Cambridge, Mas
sachusetts 02138
JACQUES DUBAU • Observatoire de Paris-Meudon, 92190 Meudon, France
W. ElSSNER • Daresbury Laboratory, Science and Engineering Research Council,
Daresbury, Warrington WA4 4AD, England
D. R. FLOWER • Department of Physics, University of Durham, Durham DH1
3LE, England
DAVID L. MOORES • University College London, Gower Street, London WCI
E6BT, England
D. W. NORCROSS. Joint Institute for Laboratory Astrophysics, University of
Colorado and National Bureau of Standards, Boulder, Colorado 80309
H. NUSSBAUMER • Institute of Astronomy, ETH Zentrum, CH 3092 Zurich,
Switzerland
G. PEACH • Department of Physics and Astronomy, University College London,
Gower Street, London WCI E6BT, England
IAN PERCIVAL. Department of Applied Mathematics, Queen Mary College, Uni
versity of London, Mile End Road, London EI 4NS, England
HANNELORE E. SARAPH • University College London, Gower Street, London
WCI E6BT, England
P. J. STOREY. Department of Physics and Astronomy, University College London,
Gower Street, London WCI E6BT, England
HENRI VAN REGEMORTER • Observatoire de Paris-Meudon, 92190 Meudon,
France

PREFACE
It is hard to appreciate but nevertheless true that Michael John Seaton,
known internationally for the enthusiasm and skill with which he pursues
his research in atomic physics and astrophysics, will be sixty years old on
the 16th of January 1983. To mark this occasion some of his colleagues and
former students have prepared this volume. It contains articles that de
scribe some of the topics that have attracted his attention since he first
started his research work at University College London so many years ago.
Seaton's association with University College London has now
stretched over a period of some 37 years, first as an undergraduate student,
then as a research student, and then, successively, as Assistant Lecturer,
Lecturer, Reader, and Professor. Seaton arrived at University College
London in 1946 to become an undergraduate in the Physics Department,
having just left the Royal Air Force in which he had served as a navigator
in the Pathfinder Force of Bomber Command. There are a number of
stories of how his skill with instruments and the precision of his calcula
tions, later to be so evident in his research, saved his crew from enemy
action, and on one occasion, on a flight through the Alps, from a collision
with Mount Blanc that at the time was shrouded in clouds. Only when the
clouds suddenly lifted to reveal the mountain in all its glory close by, did
the crew have cause to be grateful that, as many of the readers of this book
will be well aware, a Seaton calculation is carried out as if his life depended
on it.
The period immediately after the Second World War marked the start
of a new era, both for atomic physics and astrophysics at University
College London, and for the influnce that UCL was to have internationally
in these fields. Having worked on the Manhattan Project, H. S. W. Massey
had just returned to his appointment as Goldsmid Professor of Applied
Mathematics, and he was joined in the Department of Mathematics by a
number of colleagues, including D. R. Bates, R. L. F. Boyd, R. A.
Buckingham, E. H. S. Burhop, J. C. Gunn and J. B. Hasted. A. Dalgarno,
B. L. Moiseiwitsch, E. A. Power and A. L. Stewart were among the students
who joined this group soon afterwards.
Seaton graduated with a first-class honors degree in Physics in 1948,
and started his research under the direction of Bates in the Mathematics
Department. Bates, of course, took his role as supervisor very seriously, and
Vll
V111 PREFACE
on one occasion gave a formal series of lectures that only one student,
Seaton, attended. This clearly provides a strong argument against the
present overwhelming emphasis that is put upon staff-student ratios and
the undesirability of small classes. Between 1949 and 1951, during the
course of the work for his Ph.D. thesis on Quantal Calculations of Certain
Reaction Rates with Applications to Astrophysical and Geophysical Problems,
Seaton published six papers, and significantly these were equally distrib
uted between Monthly Notices of the Royal Astronomical Society and physics
journals. The theme of this thesis was to become the basis of his subsequent
scientific work.
In October 1950 Massey moved to the Physics Department to take up
his new appointment as Quain Professor of Physics. He was accompanied
by Bates, Buckingham, and Burhop who became Readers in Physics,
L. Castillejo and Seaton who became Assistant Lecturers, Boyd and Hasted
who were appointed to ICI Fellowships, and Dalgarno and Moiseiwitsch
who were then completing their Ph.D. research. At about this time, Seaton
started his classic paper on The Hartree-Fock Equations for Continuous
States with Applications to Electron Excitation of the Gound State Configura
tion Terms of OJ. How this work laid the foundation for the later develop
ments is shown in the review on Low-Energy Electron Collisions with
Complex Atoms and Ions by two co-editors of this book, P. G. Burke who
owes his introduction to atomic collision physics to Seaton in 1956 and
W. Eissner whom Seaton introduced in 1967 to methods for complex atoms
feasible with the advent of the new generation of computers. In addition, in
his chapter on Forbidden Atomic Lines in Auroral Spectra, Bates discusses
the important influence this paper has had on certain astrophysical prob
lems.
In 1957, together with I. C. Percival, another co-editor of this book,
Seaton gave the first rigorous discussion of the partial wave theory of
electron-hydrogen collisions, and in collaboration with Castillejo, also
discussed the theory of the long-range interactions between electrons and
hydrogen atoms. Seaton's longstanding interest in this topic is highlighted
in the chapter on Long-Range Interactions in Atoms and Diatomic Molecules
by G. Peach. In 1958, Percival and Seaton published the first general
algebraic formulation of the problem of the polarization of line radiation
by electron impact, and this paper now forms the basis for the interpreta
tion of electron-photon coincidence experiments.
Until the early 1960's the detailed calculation of wave functions for
complex atomic systems was still a very tedious and formidable task, even
for the electron-hydrogen system, and theoreticians could not hope to
provide astrophysicists with the large amounts of atomic data that they
required. Simpler methods were explored, and Seaton applied the semiclas-
PREFACE lX
sical impact parameter method to the excitation of allowed transitions
between states of high principal quantum number. Percival's chapter on
Collisions between Charged Particles and Highly Excited Atoms links up with
this early work.
Seaton took a leave of absence from VCL for the academic year
1954-5 and went to France as Charge de Recherche at the Institut
d' Astrophysique in Paris. This visit marked the start not only of his long
association with H. van Regemorter, but also of the close collaboration that
has subsequently developed between University College and the Ob
servatoire de Paris at Meudon. More recently, this collaboration has been
extended to include the Observatoire de Nice. The chapter by J. Dubau
and H. van Regemorter on Electron-Ion Processes in Hot Plasmas repre
sents one area that has been strongly influenced by this association. In
recognition of his contributions to atomic physics and astrophysics, Seaton
was awarded the degree of Docteur honoris causa by the Observatoire de
Paris in 1976.
Also in 1954, Seaton realized that the quantum defect theory provided
a powerful tool for the interpretation and production of atomic data, and
his first publication on this subject appeared in Comptes Rendus in 1955.
The enormous developments in this field are described in this book by
D. L. Moores and H. E. Saraph in their chapter on Applications of Quantum
Defect Theory.
Finally, during this period, Seaton carried out the work that estab
lished the importance of proton collisions with atomic ions in laboratory
and astrophysical plasmas. These processes are discussed by Dalgarno in
the chapter on Proton Impact Excitation of Positive Ions.
In 1961 Seaton visited the University of Colorado at Boulder. At this
time the Joint Institute for Laboratory Astrophyics was being established,
and in 1964 Seaton was appointed a Fellow-Adjoint of the Institute in
recognition of his contribution to its scientific activities. A very active
collaboration between UCL and JILA in both atomic physics and astro
physics followed. Three former postgraduate students of Seaton's are now
staff members of JILA, and five others have visited Boulder on postdoc
toral or visiting fellowships. One of these students, D. G. Hummer, another
co-editor, began his career in astrophysics with Seaton in 1959, and during
the period 1961-4, published several papers with him on the structure of
planetary nebulae. Although for many years Hummer has been a senior
member of JILA, he continues to be a regular and welcome visitor to UCL.
In the 1960's Seaton also became interested in the properties of the
central stars of planetary nebulae, and in a joint paper with the late R. J.
Harman, managed for the first time to obtain a well-defined track for these
objects on the Hertzsprung-Russell diagram. They showed that these
x PREFACE
exceptionally hot stars in fact represented a natural stage in stellar evolu
tion. In his chapter on Planetary Nebulae D. R. Flower reviews the present
state of our knowledge of these astrophysical plasmas.
Seaton became well-known as one of the few people who understood
both the detailed methods for the calculation of atomic data, and the
requirements for these data in astrophysics. He strove to teach astrophysi
cists about the calculation of atomic data and he encouraged the atomic
physicists to produce accurate data of direct relevance to astrophysical
problems. In fact, it was a problem in the interpretation of processes in the
solar corona, pointed out to Seaton in a letter from A. Unsold, that led to
the discovery in 1964, by his former student and colleague A. Burgess, of
the importance of dielectronic recombination. In the book published in
honor of Bates' 60th birthday, Seaton and P. J. Storey devote a chapter to
the complex processes involved. He also became very keen to make
astronomical observations himself. He made a pact with the astronomer
D. E. Osterbrock that they would swap jobs for a year. Osterbrock would
come to UCL to calculate atomic data and he would spend a year carrying
out observations. Osterbrock fulfilled his pledge in 1968, but it was not
until 1978 that Seaton started to make observations with the International
Ultraviolet Explorer. Such was his enthusiasm, that between 1978 and 1981
he collaborated on ten papers that combined observations of novae and
nebulae with interpretative theory. During much of this period he also had
the honor to be president of the Royal Astronomical Society, and was
deeply involved in the Society's affairs.
In the late 1960's he decided to exploit the new generation of comput
ers that were then becoming available to obtain accurate data on atomic
structure and on atomic collisions that could be used with confidence in
astrophysics. Typically, he became completely immersed in the use of this
new technology, doing a lot of programming himself and developing new
computational methods. As a result, a package of programs was developed
at University College that is now widely used throughout the world. Some
of these programs are described in the chapter by H. Nussbaumer and P. J.
Storey on The University College Computer Package for the Calculation of
A.tomic Data: Aspects of Development and Application. Other aspects of the
programs for electron-atom collisions are described by D. W. Norcross in
his chapter on Numerical Methods for Asymptotic Solutions of Scattering
Equations.
In 1968 Seaton played a major role in setting up and supporting the
international journal Computer Physics Communications, both as an Advi
sory Editor and as an active contributor of programs. He was also involved
in launching the Journal of Physics series in 1968; he was the first Honorary