Seismology of the Sun and the Distant Stars

472 Pages·1986·17.2 MB·English

by  Juri Toomre (auth.), D. O. Gough (eds.)

Seismology of the Sun
and the Distant Stars
NATO ASI Series
Advanced Science Institutes Series
A series presenting the results of activities sponsored by the NATO Science Committee,
which aims at the dissemination of advanced scientific and technological knowledge,
with a view to strengthening links between scientific communities.
The series is published by an international board of publishers in conjunction with the
NATO Scientific Affairs Division
A Life Sciences Plenum Publishing Corporation
B Physics London and New York
C Mathematical D. Reidel Publishing Company
and Physical Sciences Dordrecht, Boston, Lancaster and Tokyo
D Behavioural and Social Sciences Martinus Nijhoff Publishers
E Engineering and The Hague, Boston and Lancaster
Materials Sciences
F Computer and Systems Sciences Springer-Verlag
G Ecological Sciences Berlin, Heidelberg, New York and Tokyo
Series C: Mathematical and Physical Sciences Vol. 169
Seismology of the Sun
and the Distant Stars
edited by
D. O. Gough
Institute of Astronomy and Department of Applied Mathematics
and Theoretical Physics, University of Cambridge,
Cambridge, UK
D. Reidel Publishing Company
Dordrecht / Boston / Lancaster / Tokyo
Published in cooperation with NATO Scientific Affairs Division
Proceedings of the NATO Advanced Research Workshop on
Seismology of the Sun and the Distant Stars
Cambridge, U.K.
June 17-21,1985
Library of Congress Cataloging in Publication Data
NATO Advanced Research Workshop on Seismology of the Sun and the Distant Stars (1985:
Cambridge, Cambridgeshire)
Seismology of the sun and the distant stars.
(NATO ASI series. Series C, Mathematical and physical sciences; vol. 169)
"Proceedings of the NATO Advanced Research Workshop on Seismology of the Sun
and the Distant Stars, Cambridge, U.K., June 17-21, 1985"-T.p. verso.
"Published in cooperation with NATO Scientific Affairs Division."
Includes index.
1. Sun-Congresses. 2. Stars-Congresses. 3. Seismology-Congresses. I. Gough,
D. O. II. North Atlantic Treaty Organization. Scientific Affairs Division. III. Title.
IV. Series: NATO ASI series.
Series C, Mathematical and physical sciences; vol. 169.
QB520.N36 1985 551:2'2'09994 85-31186
ISBN-13: 978-94-010-8547-2 e-ISBN-13: 978-94-009-4608-8
001: 10.1007/978-94-009-4608-8
Published by D. Reidel Publishing Company
P.O. Box 17,3300 AA Dordrecht, Holland
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All Rights Reserved
© 1986 by D. Reidel Publishing Company, Dordrecht, Holland.
Softcover reprint of the hardcover 1s t edition 1986
No part of the material protected by this copyright notice may be reproduced or utilized
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TABLE OF CONTENTS
Preface ix
List of participants X1
Properties of solar oscillations
J. Toomre 1
Theoretical aspects of helio- and asteroseismology
J. Christensen-Dalsgaard 23
Observations of low-degree p-mode oscillations in 1984
H.M. Henning and P.H. Scherrer 55
Another reason to search for solar g-modes and new limits
from solar ellipticity measurements
J .R. Kuhn 63
Phase studies of solar 5 m1n oscillations
S. Frandsen 73
Observations of gravity waves in the solar atmosphere
F.-L. Deubner 81
Is there an anisotropy of p-modes?
F.-L. Deubner 83
Influence of spatial filtering on possible anisotropies
in solar oscillations
F. Hill, D.A. Haber, J. Toomre and L.H. November 85
The detection of global convective wave flows on the sun
P.H. Scherrer, R. Bogart, J.T. Hoeksema and H. Yoshimura 93
First evidence of a large-scale circulation in the
solar convection zone
E. Ribes and P. Mein 103
Solar Doppler shifts: sources of continuous spectra
T.L. Duvall Jr. and J.W. Harvey 105
Comments on techniques for spectral deconvolution
P.H. Scherrer 117
vi TABLE OF CONTENTS
Sound speed in the interior of solar models
1. W. Roxburgh 121
Asymptotic sound-speed inversions
D.O. Gough 125
Asymptotics and quantum chaos in stellar oscillations
J. Perdang 141
An improved asymptotic formula for solar gravity-mode
periods
A.N. Ellis 173
Solar g modes: a method to find the depth of the convective
envelope
M. Gabriel 177
The influence of convection theory uncertainties on the
deduction of the speed of sound in the solar interior
R.K. Ulrich 187
Measuring the sun's internal rotation using solar p-mode
oscillations
T.M. Brown 199
Rotational splitting of £= 1 p modes
H.B. van der Raay, P.L. Palle and T. Roca Cortez 215
Linewidth and rotational splitting of low degree modes
in the 5 minute region
G.R. Isaak 223
Solar core rotation: a down to earth view
P. Connes 229
The internal rotation of the sun
P.R. Goode 237
On the solar rotation
M. Gabriel and F. Nemry 243
The internal rotation of the sun
1. W. Roxburgh 249
Magnetic torques and differential rotation
N.O. Weiss 253
Internal rotation of the sun as a consequence of
instabilities in the radiative interior
W.A. Dziembowski, L. Paterno and R. Ventura 257
TA SLE OF CONTENTS vii
Fl· nl. te amp l'l tu de 1"l mlt 0 f t h e 3H e l. nstab 1' ll' ty
I. W. Roxburgh 265
Is the existence of a strong magnetic field in the sun's
core plausible?
W.A. Dziembowski, L. Paterno and R. Ventura 271
Progress report on helium abundance determination
W. D~ppen and D.O. Gough 275
On wave reflection or absorption at hydromagnetic
critical levels
L.M.B.C. Campos and J.C.G.C. Leitao 281
On umbral oscillations as a sunspot diagnostic
L.M.B.C. Campos 293
Change of solar oscillation eigenfrequencies with the
solar cycle
M.F. Woodard and R.W. Noyes 303
Long period variations in the solar diameter
P. Delache 305
The 1984 solar oscillation program of the Mt. Wilson
60-foot tower
E.J. Rhodes Jr, A. Cacciani, S. Tomczyk and R.K. Ulrich 309
The K 769.9 nm line profile
H.B. van der Raay, P.L. Palle and T. Roca Cortes 333
Ground based measurements of global solar intensity
oscillations
B.N. Andersen 339
A liquid crystal modulator
D.G. Eccles, Y. Elsworth, H.B. van der Raay, P.L. Palle
and T. Roca Cortes 343
A Fabry-Perot based stellar seismometer
H.R. Butcher and T.R. Hicks 347
Applications of the magneto-optical filter to stellar
pulsation measurements
E.J. Rhodes Jr, A. Cacciani and S. Tomczyk 359
A new Fabry-Perot radial velocity spectrometer
K.A.R.B. Pietraszewski, N.K. Reay and J. Ring 377
Interferometric stellar oscillation spectrometry
K.A.R.B. PJietraszewski, J. Ring and A.K. Forrest 391
viii TA BLE OF CONTENTS
Absolute astronomical accelerometry
P. Connes 403
Evidence for p-modes on Alpha Centauri and Procyon
E. Fossat, B. Gelly and G. Grec 405
A review of the rapidly oscillating Ap stars
D.W. Kurtz 417
Asterseismology for certain Ap stars
W. Dziembowski and P.R. Goode 441
Nonradial modes in line-profile variable stars
Y. Osaki 453
Observational properties of nonradial oscillations in
early-type stars and their possible effect on mass loss:
the example of s Puppis (04 If)
D. Baade 465
Southern ZZ Ceti stars
D. O'Donoghue 467
How well do we know stellar parameters?
S. Frandsen 473
Index 477
PREFACE
The history of modern helioseismology is only ten years old. In 1975
F-L Deubner separated for the first time the spatial and temporal pro
perties of the solar five-minute oscillations, and was thus able to
measure the dispersion relation for high-degree acoustic modes (p modes).
The diagnostic value of these observations was appreciated immediately.
Indeed, by comparing the observed relation with computations that had
already been carried out by R.K. Ulrich, and subsequently by H. Ando and
Y. Osaki, it was recognised that contemporary solar models that had been
constructed with the low observed neutrino flux in mind were too hot in
their outer layers. Moreover, their convection zones were too shallow.
Since that time the observations have improved. There is now good reason
to suppose that a sufficiently careful analysis will lead to a direct
determination of the helium abundance in the solar convection zone,
especially when foreseeable further improvements in the observations
have been achieved. The data will also provide useful diagnostics of
the uncertain equation of state of partially ionized plasmas, and they
might also enable us to measure the large-scale structure of the convec
tive flow.
Low-degree solar p modes were first recognised by G.R. Isaak and
his colleagues in 1979 from whole-disk observations. Many of them pene
trate to the centre of the sun, and therefore sense conditions in the
energy-generating core. A long continuous interval of observation per
mitted G. Grec, E. Fossat and M.A. Pomerantz to isolate and identify the
degrees of the modes, and somewhat different observations by P.H. Scherre~
the late J.M. Wilcox and their colleagues extended the data to higher
degrees. From a comparison of the observed frequencies with the eigen
frequencies of solar models constructed from stellar evolution theory, it
appeared that the theory of the chemical evolution of the core was roughly
correct: at least,a substantial dilution of the reaction products"had not
been affected by mixing with the hydrogen-rich environment. Moreover, it
was possible to estimate the primordial solar helium abundance, which is
of considerable cosmological interest.
More recently, spatially resolved measurements by T. Duvall and
J.W. Harvey have yielded frequencies of p modes of both low and inter
mediate degree. These have permitted the computation of the sound speed
throughout much of the solar interior. By bridging the gap between the
low and the high degree, the observations indisputably established the
orders of the low-degree modes whose frequencies were known already from
the observations with little or no spatial resolution. Rotational split
ting of sectoral modes yielded the angular velocity in the vicinity of
the equatorial plane, suggesting a value for the sun's gravitational
quadrupole moment J? that is consistent with the analyses of planetary
orbits and General Relativity. T.M. Brown, at the workshop, presented
data that permits the determination of the sun's angular velocity away
ix
x PREFACE
from the equatorial plane, which essentially confirms the previous
estimate of J2.
Low-degree modes have been observed using detectors with no spatial
resolution. Consequently, in principle the methods can be used for
other stars. Of special interest are the stars that pulsate in many
modes simultaneously, for these are the most likely to provide fruitful
diagnostic information. Several attempts have already been made, and in
the last years data have been collected that are enabling us to confront
the predictions of stellar structure theory. For example, D. Kurtz and
J. Seeman have reported six modes of oscillation of the Ap star HD 24712
which have raised some interesting questions whose answers are not
immediately obvious in the light of current thinking. Also E. Fossat
and his collaborators and R. Noyes and his collaborators have found
evidence for asymptotically spaced high-order p-mode frequencies in the
more solar-like stars a Centauri A and E Eridani, whose spacing provides
estimates of the sound travel time from the centre to the surface of the
star. The value for a Centarui A appears to be inconsistent with what
one would have deduced from previous astronomical analyses. In addition,
very interesting data have been obtained from B stars and ZZ Ceti stars.
These pioneering investigations have assured us that our hopes for
studying the seismology of the distant stars might be realised.
The workshop gathered theorists and observers who are actively
working on helioseismology together with some observers who have a know
ledge of techniques that can be used for measuring low-amplitude stellar
oscillations. Its purpose was twofold. First, it was to provide an
opportunity for helioseismologists to discuss their latest researches on
the sun, and to plan future coherent programmes of research. Hopefully
the discussion would heighten the stellar astronomers' awareness of the
considerable diagnostic power of seismic observations. The second purpose
was to stimulate programmes to search for stars that support a spectrum
of oscillations, with a view to carrying out subsequent systematic
observations on those that promise to yield useful results.
The timeliness of the meeting is evident. The experience of the
helioseismologists is now sufficiently mature that an effective fertili
zation of astronomers could lead to a new powerful method for studying
the structures of stars in the solar neighbourhood. Moreover, the few
recent seismological results that have been obtained from stars other
than the sun indicate that available instrumental sensitivity is probably
adequate for the task.
The workshop appeared to achieve its immediate objectives, though
these proceedings record only the lesser part of the activities:- the
formal presentations which concentrate on what has already been attained.
I am extremely grateful for the help I received from my scientific
colleagues on the Organising Committee: Harvey Butcher, J~rgen
Christensen-Dalsgaard, Jack Harvey and Jliri Toomre, and for the practical
support from Jean Burris, Margaret Harding, Michael Ingham, Sally Roberts
and Norah Tate.
On behalf of all the participants, I thank the Director of the
Scientific Affairs Division of NATO, and the Institute of Astronomy in
the University of Cambridge, for granting financial support for a
fruitful Advanced Research Workshop.
Douglas Gough
October, 1985