Author name code: gough
ADS astronomy entries on 2022-09-14
author:"Gough, Douglas, O."
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Title: The Privileged Life of a Theoretical Observer
Authors: Gough, Douglas
Bibcode: 2022SoPh..297...95G
Altcode:
This is a summary of my scientific career, biased by my
personal view of events and unashamedly concentrating on those
aspects of some of the scientific developments to which I have
contributed. A selective unbiased alternative has been written by
Christensen-Dalsgaard and Thompson (A selective overview. In: Thompson,
M.J., Christensen-Dalsgaard, J. (Eds.) Stellar Astrophysical Fluid
Dynamics, Cambridge University Press, pp. 1 - 19, 2003), followed by
some further remarks by Christensen-Dalsgaard (Unsolved Problems in
Stellar Physics: A Conference in Honour of Douglas Gough, American
Institute of Physics Conference Series, 948, xii, 2007).
Title: Nigel Weiss (1936-2020)
Authors: Gough, Douglas O.; Proctor, Michael R. E.; Tobias, Steven M.
Bibcode: 2020A&G....61e5.11G
Altcode:
Nigel Weiss: astrophysicist, mathematician and former president of
the RAS
Title: Michael
Authors: Gough, Douglas
Bibcode: 2020ASSP...57...21G
Altcode:
I was very sorry that I could not attend the conference to help
celebrate Michael's life. I certainly would have come had I been able.
Title: What do we reliably know about how fast the Sun's core spins?
Authors: Scherrer, Philip H.; Gough, Douglas
Bibcode: 2019AAS...23430206S
Altcode:
Fossat et al. (2017) and Fossat & Schmider (2018) have attempted
to use solar p-mode frequency perturbations to detect rotational
splitting of g-modes. They claim that this approach detected the
Sun's core to be rotating about 3.8 times faster than the surrounding
radiative interior and the convection zone. We report an independent
study of the technique, the inconsistencies with the well-established
p-mode determinations of rotation, and with their assumption of which
g-modes might be sensed. Additionally we used both the same calibrated
80s SOHO/GOLF data used in the 2017 study and the then only publically
available GOLF 60s cadence data and verified the findings of Schunker et
al. (2018) that the g-mode detection was fragile: It vanished when the
GOLF data was sampled at the 60s vs 80s cadence and when the starting
point was shifted by 2 hours of the 15 years studied. We also applied
the same technique to all other available long duration low-degree data
collections including SOHO/MDI, SOHO/LOI, SDO/HMI, GONG, and BiSON and
found no evidence of the Fossat et al. (2017) reported signals. We note
that a second independent study by Appourchaux & Corbard (2019) came
to the same conclusions. Thus we doubt the validity of the 2017 findings
and conclude that there is no useful information about the rotation of
the solar core yet determined using these techniques (Scherrer &
Gough, 2019). References: Appourchaux, T., & Corbard, T. 2019,
Submitted to A&A, Fossat, E., Boumier, P., Corbard, T., et al. 2017,
A&A, 604, A40, Fossat, E., & Schmider, F. X. 2018, A&A,
612, L1, Scherrer, P. & Gough, D., Accepted by ApJ, 2019, Schunker,
H., Schou, J., Gaulme, P., & Gizon, L. 2018, SoPh, 293, 95
Title: A brief history of our perception of the solar tachocline
Authors: Gough, D.
Bibcode: 2019EAS....82..295G
Altcode:
I tell just part of the story of the quest to understand the dynamics
of the solar tachocline, from the point of view of my relationship
with my good friend Jean-Paul Zahn.
Title: A Critical Evaluation of Recent Claims Concerning Solar
Rotation
Authors: Scherrer, P. H.; Gough, D. O.
Bibcode: 2019ApJ...877...42S
Altcode: 2019arXiv190402820S
Fossat et al. recently reported detecting rotational splitting of
g-modes indirectly via the interaction with p-modes observed directly
by the Global Oscillations at Low Frequency (GOLF) instrument on
the Solar and Heliospheric Observatory (SOHO). They concluded that
the core of the Sun is rotating 3.8 ± 0.1 times faster than the
surrounding radiative envelope. This is startling, partly because
such rapid rotation almost contradicts direct inferences from the
p-mode rotational splitting inferred from the same data. Moreover,
the inferred amplitudes of the g-modes appear to exceed the upper
bound reported by Appourchaux et al. It is also suspect because the
theory of the procedure implies that the principal modes claimed to
have been measured should be undetectable. We point out that there are
other interpretations: one leads to a core rotation about twice as fast
as the surrounding envelope; another, to a core rotating more slowly
than the envelope. Here we also report on an independent assessment
of the Fossat et al. analysis by applying their procedure to different
representations of the GOLF data, expanding on Schunker et al. We also
analyze seismic data obtained from LOI and MDI (both also on SOHO),
from HMI (on SDO), and from the ground-based BiSON and GONG, and
we find the evidence reported by Fossat et al. not to be robust. We
also illustrate that merely fitting model spectra to observations,
which Fossat et al. do to support their g-mode detections, and as
Fossat & Schmider do for extracting additional g-mode splittings,
is not necessarily reliable. We are therefore led to doubt the claim.
Title: Anticipating the Sun's heavy-element abundance
Authors: Gough, D. O.
Bibcode: 2019MNRAS.485L.114G
Altcode: 2019MNRAS.tmpL..50G; 2019arXiv190400301G
Much of our understanding of the internal structure of the Sun derives
from so-called standard theoretical solar models. Unfortunately, none
of those models agrees completely with observations. The discrepancy
is commonly associated with chemical abundance, and has led to what
is now called the solar abundance problem, the resolution of which has
previously been out of sight. But now the Borexino Collaboration, which
recently announced measurements of the pp-chain solar neutrinos, are
optimistic that they will be able to measure the flux ΦCNO
of the neutrinos emitted by the relatively weak CNO cycle. Since C, N,
and O constitute the majority of the heavy elements, that measurement
will permit a crucial determination of the heavy-element abundance
Zc in the Sun's energy-generating core, thereby shedding
important light on the problem. To accomplish that determination,
a robust relation between Zc and ΦCNO will be
required. That relation is Z_c= 0.400 Φ _CNO, where ΦCNO
is in units of 1010 cm-2 s-1.
Title: On the hydrostatic stratification of the solar tachocline
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Knudstrup, E.
Bibcode: 2018MNRAS.477.3845C
Altcode: 2018MNRAS.tmp..730C; 2018arXiv180308675C
We present an attempt to reconcile the solar tachocline glitch, a thin
layer immediately beneath the convection zone in which the seismically
inferred sound speed in the Sun exceeds corresponding values in standard
solar models, with a degree of partial material mixing which we presume
to have resulted from a combination of convective overshoot, wave
transport, and tachocline circulation. We first summarize the effects
either of modifying in the models the opacity in the radiative interior
or of incorporating either slow or fast tachocline circulation. Neither
alone is successful. We then consider, without physical justification,
incomplete material redistribution immediately beneath the convection
zone which is slow enough not to disturb radiative equilibrium. It is
modelled simply as a diffusion process. We find that, in combination
with an appropriate opacity modification, it is possible to find a
density-dependent diffusion coefficient that removes the glitch almost
entirely, with a radiative envelope that is consistent with seismology.
Title: A fitting LEGACY - modelling Kepler's best stars
Authors: Aarslev, Magnus J.; Christensen-Dalsgaard, Jørgen; Lund,
Mikkel N.; Silva Aguirre, Victor; Gough, Douglas
Bibcode: 2017EPJWC.16003010A
Altcode:
The LEGACY sample represents the best solar-like stars observed in
the Kepler mission[5, 8]. The 66 stars in the sample are all on
the main sequence or only slightly more evolved. They each have
more than one year's observation data in short cadence, allowing
for precise extraction of individual frequencies. Here we present
model fits using a modified ASTFIT procedure employing two different
near-surface-effect corrections, one by Christensen-Dalsgaard[4] and
a newer correction proposed by Ball & Gizon[1]. We then compare
the results obtained using the different corrections. We find that
using the latter correction yields lower masses and significantly
lower χ2 values for a large part of the sample.
Title: Salvete
Authors: Gough, Douglas
Bibcode: 2017EPJWC.16000003G
Altcode:
This volume is a collection of original articles resulting from the
contributions presented at the international conference:
Title: Is the Sun a Magnet?
Authors: Gough, D. O.
Bibcode: 2017SoPh..292...70G
Altcode:
It has been argued (Gough and McIntyre in Nature394, 755, 1998) that
the only way for the radiative interior of the Sun to be rotating
uniformly in the face of the differentially rotating convection zone is
for it to be pervaded by a large-scale magnetic field, a field which is
responsible also for the thinness of the tachocline. It is most likely
that this field is the predominantly dipolar residual component of a
tangled primordial field that was present in the interstellar medium
from which the Sun condensed (Braithwaite and Spruit in Nature431, 819,
2004), and that advection by the meridional flow in the tachocline
has caused the dipole axis to be inclined from the axis of rotation
by about 60∘ (Gough in Geophys. Astrophys. Fluid Dyn.,
106, 429, 2012). It is suggested here that, notwithstanding its
turbulent passage through the convection zone, a vestige of that
field is transmitted by the solar wind to Earth, where it modulates
the geomagnetic field in a periodic way. The field variation reflects
the inner rotation of the Sun, and, unlike turbulent-dynamo-generated
fields, must maintain phase. I report here a new look at an earlier
analysis of the geomagnetic field by Svalgaard and Wilcox (Solar
Phys.41, 461, 1975), which reveals evidence for appropriate phase
coherence, thereby adding support to the tachocline theory.
Title: Some Glimpses from Helioseismology at the Dynamics of the
Deep Solar Interior
Authors: Gough, D. O.
Bibcode: 2017hdsi.book...21G
Altcode:
No abstract at ADS
Title: The Olsen Rotating Dipole, Revisited
Authors: Svalgaard, L.; Gough, D. O.; Scherrer, P. H.
Bibcode: 2016AGUFMSH31B2548S
Altcode:
Olsen (1948) and Wilcox & Gonzales (1971) reported evidence
of a solar equatorial magnetic dipole with a stable (synodic)
rotation period of 26 7/8 days maintaining its phase over 15 years
(1926-1941, Olsen) and possibly to 1968 as well (1963-1968, Wilcox &
Gonzales). Using a composite series of Interplanetary Magnetic Sector
Polarities covering the interval 1844-2016 (derived from geomagnetic
data before the space age and direct measurements during 1963-2016)
we find that 1) the response of geomagnetic activity to passage (at
Earth) of a sector boundary has been consistently the same in every
solar cycle from 9 through 24, thus validating the inferred times of
sector boudary passages over the past 173 years, and 2) the 'Olsen'
dipole can be traced back the 16 cycles to the year 1844, albeit
with a slightly different synodic rotation period of 26.86 days (431
nHz). Olsen ended his paper with "The persistence of a fixed period
during 15 years points to the possibility that the origin of the effect
is to be found in a layer on the Sun with a fixed rotation-period during
a long time" and Wilcox & Gonzales noted that "A rotating magnetic
dipole may be lurking within the sun". We compare the Olsen-period
with other evidence for rotation periods in the deep interior and for
the existence of a relic magnetic field.
Title: Some Glimpses from Helioseismology at the Dynamics of the
Deep Solar Interior
Authors: Gough, D. O.
Bibcode: 2015SSRv..196...15G
Altcode: 2015arXiv150504881G; 2015SSRv..tmp...32G
Helioseismology has taught us a great deal about the stratification
and kinematics of the solar interior, sufficient for us to embark upon
dynamical studies more detailed than have been possible before. The
most sophisticated studies to date have been the very impressive
numerical simulations of the convection zone, from which, especially
in recent years, a great deal has been learnt. Those simulations,
and the seismological evidence with which they are being confronted,
are reviewed elsewhere in this volume. Our understanding of the
global dynamics of the radiative interior of the Sun is in a much
more primitive state. Nevertheless, some progress has been made,
and seismological inference has provided us with evidence of more to
come. Some of that I summarize here, mentioning in passing hints that
are pointing the way to the future.
Title: Indications of R-mode Oscillations in SOHO/MDI Solar Radius
Measurements
Authors: Sturrock, P. A.; Bush, R.; Gough, D. O.; Scargle, J. D.
Bibcode: 2015ApJ...804...47S
Altcode: 2015arXiv150301039S
Analysis of solar radius measurements acquired by the Michelson Doppler
Imager on the Solar and Heliospheric Observatory spacecraft supports
previously reported evidence of solar internal r-mode oscillations
in Mt Wilson radius data and in 90Sr beta-decay data. The
frequencies of these oscillations are compatible with oscillations in
a putative inner tachocline that separates a slowly rotating core from
the radiative envelope.
Title: A personal view of the scientific career of Wojtek Dziembowski
(perceived by an admirer from abroad)
Authors: Gough, Douglas
Bibcode: 2014IAUS..301....3G
Altcode:
I present a personal view of Wojtek Dziembowski's scientific career,
derived mainly from my direct interactions with Wojtek. Necessarily
this presentation is biased towards the earlier days, partly because
we interacted more then, and partly because the presentation after
mine is by a local admirer who has been much more involved than I with
Wojtek's later work.
Title: Shocking Remarks on Stellar Pulsation
Authors: Gough, D. O.
Bibcode: 2013ASPC..479..355G
Altcode:
Smoothly varying sound waves steepen as they propagate, at a rate that
is an increasing function of the amplitude of the wave. If they are
not first absorbed or otherwise dissipated by diffusion, the waves
eventually shock. One might expect, therefore, that the steepening
process in the outwardly propagating component of a normal acoustic
pulsation mode in a star might permit the wave to escape more easily
into the atmosphere, thereby leaking energy in an amplitude-dependent
manner. Is this the process that limits low-amplitude intrinsically
overstable pulsations such as occur in roAp stars? Even if the waves
do not shock below the location of the acoustic cutoff associated
with the basic frequency of the wave, which is likely in low-amplitude
pulsators, the transmitted component might shock subsequently, heating
the atmosphere and perhaps even producing a chromosphere.
Title: A remark on the vertical transport of large-scale temperature
fluctuations by smaller-scale convection
Authors: Gough, D. O.
Bibcode: 2013EAS....63..255G
Altcode:
A simple mixing-length discussion of vertical diffusive transport of
a scalar by small-scale turbulent convection is presented, likening
it to the microscopic transport in a classical gas. If the scalar
is passive, the transport is governed by the well known telegraph
equation. Temperature, on the other hand, influences the dynamics of the
small-scale motion by modifying the buoyancy that drives the turbulent
eddies; it leads to a rather more complicated equation, which, for
relatively rapid variation reduces to the same wave equation as for
a passive scalar, with maximal propagation speed comparable with the
rms vertical eddy velocity; but in the slow diffusive limit it reduces,
for good reason, to the classical diffusion equation with a diffusivity
enhanced by a factor 3/2 over that pertaining to a passive scalar.
Title: Sylvie Vauclair
Authors: Gough, D.
Bibcode: 2013EAS....63....5G
Altcode:
Sylvie Vauclair is not only a superb scientist, an excellent musician,
a devoted mother, a passionate communicator of science to the public
and a Chevalier de la Légion d'honneur, but, most importantly,
a wonderful friend.
Title: Commentary on a putative magnetic field variation in the
solar convection zone
Authors: Gough, D. O.
Bibcode: 2013MNRAS.435.3148G
Altcode: 2013MNRAS.tmp.2186G
The implications of a component δoscν, oscillatory with
respect to frequency ν, of seismic frequency changes observed by
Libbrecht and Woodard during the rising phase of solar cycle 22, first
mooted by Goldreich, Murray, Willette and Kumar, and its relation to
a putative magnetic field, is discussed in relation to more detailed
analysis of data in a more limited frequency range obtained over the
subsequent cycle. The oscillatory component is associated with helium
ionization, and its temporal variation might be explained by a dilution
of the effect of the ionization-induced influence on an effective
adiabatic exponent of the stellar material by a relatively smooth
magnetic field whose intensity increases with surface activity. To
account for the magnitude of the variation in cycle 23 would require
the field strength to change by some 30 T. Moreover, the change in
δoscν in the high-frequency range that was analysed in
cycle 23 implies changes at lower frequency that are significantly
much greater than those observed by Libbrecht and Woodard in the
previous cycle.
Title: What Have We Learned from Helioseismology, What Have We Really
Learned, and What Do We Aspire to Learn?
Authors: Gough, Douglas
Bibcode: 2013SoPh..287....9G
Altcode: 2012arXiv1210.0820G; 2012SoPh..tmp..231G
Helioseismology has been widely acclaimed as having been a great
success: it appears to have answered nearly all the questions that
we originally asked, some with unexpectedly high precision. We
have learned how the sound speed and matter density vary throughout
almost all of the solar interior - something which not so very long
ago was generally considered to be impossible - we have learned how
the Sun rotates, and we have a beautiful picture, on a coffee cup,
of the thermal stratification of a sunspot, and also an indication
of the material flow around it. We have tried, with some success at
times, to apply our findings to issues of broader relevance: the test
of the General Theory of Relativity via planetary orbit precession
(now almost forgotten because the issue has convincingly been closed,
albeit no doubt temporarily) the solar neutrino problem, the manner
of the transport of energy from the centre to the surface of the Sun,
the mechanisms of angular-momentum redistribution, and the workings
of the solar dynamo. The first two were of general interest to the
broad scientific community beyond astronomy, and were, quite rightly,
principally responsible for our acclaimed success; the others are
still in a state of flux.
Title: On the magnetic field required for driving the observed
angular-velocity variations in the solar convection zone
Authors: Antia, H. M.; Chitre, S. M.; Gough, D. O.
Bibcode: 2013MNRAS.428..470A
Altcode: 2012MNRAS.tmp...41A; 2012arXiv1210.6606A
A putative temporally varying circulation-free magnetic-field
configuration is inferred in an equatorial segment of the solar
convection zone from the helioseismologically inferred angular-velocity
variation, assuming that the predominant dynamics is an angular
acceleration produced by the azimuthal Maxwell stress exerted by a field
whose surface values are consistent with photospheric line-of-sight
measurements.
Title: How Oblate Is the Sun?
Authors: Gough, Douglas
Bibcode: 2012Sci...337.1611G
Altcode:
No abstract at ADS
Title: Heliophysics Gleaned from Seismology
Authors: Gough, D. O.
Bibcode: 2012ASPC..462..429G
Altcode: 2012arXiv1210.1114G
Some of the principal heliophysical inferences that have been drawn
from, or refined by, seismology, and the manner in which those
inferences have been made, are very briefly described. Prominence is
given to the use of simple formulae, derived either from simple toy
models or from asymptotic approximations to more realistic situations,
for tailoring procedures to be used for analysing observations in such
a way as to answer specific questions about physics. It is emphasized
that precision is not accuracy, and that confusing the two can be
quite misleading.
Title: Pattern formation in rapidly oscillating peculiar A stars
Authors: Gough, Douglas
Bibcode: 2012GApFD.106..429G
Altcode:
Peculiar A stars harbour pairs of antipodal spots, detectable
in magnetic-field variation and chemical-abundance anomalies, and
which are inclined from the axis of rotation. Many of the stars are
observed to oscillate nonradially with frequencies of high-order
acoustic modes. The oscillations appear to be dipolar, with axes that
are almost always more-or-less aligned with the spots. It is known
theoretically that when the spots produce the dominating aspherical
influence on the dynamics of the oscillations, there is always an
oscillation eigenmode that is constrained to be aligned with the
spots, in accord with the observations. But under some circumstances
the spots may not have complete dynamical dominance, and Coriolis
precession can prevent a pure mode from remaining aligned. Yet, the
oscillations appear to be aligned. Here I investigate the proposal
that in such circumstances what is being observed is not a single
oscillation eigenmode, stationary with respect to the rotating star,
but an ensemble of precessing modes whose envelope is almost stationary,
and almost aligned with the spots. I present a one-dimensional toy
model of a slowly drifting (standing) acoustic mode in a medium with
thermal "spots", and show that under appropriate conditions stationary,
non-precessing, mode envelopes are possible.
Title: On Estimating Fluxes due to Small-Scale Turbulent Convection
in a Rotating Star
Authors: Gough, D. O.
Bibcode: 2012ISRAA2012E...2G
Altcode:
No abstract at ADS
Title: Towards a theory of rapidly oscillating Ap stars
Authors: Gough, Douglas
Bibcode: 2011arXiv1112.0863G
Altcode:
Peculiar A stars are so named because they exhibit abundance
peculiarities in their atmospheres. It is believed that these arise
as a result of differentiation of chemical species in large magnetic
spots in which convective mixing is inhibited: there might be just two
antipodal spots, whose axis is inclined to the axis of rotation. Many
of the Ap stars that are rotating slowly also pulsate, with periods
substantially shorter than the period of the fundamental radial
mode. The pulsations appear to be nonradial, but axisymmetric, with
their common axis usually aligned with the axis of the spots. In this
lecture I shall first discuss the magnetic suppression of convection in
the spots, and then I shall try to explain the pulsation phenomenon,
reviewing some of the suggestions that have been made to explain the
alignment and the excitation mechanism, and finally raising some issues
that need to be addressed.
Title: On the seismic age and heavy-element abundance of the Sun
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2011MNRAS.418.1217H
Altcode: 2011MNRAS.tmp.1623H; 2011arXiv1108.0802H
We estimate the main-sequence age and heavy-element abundance of the Sun
by means of an asteroseismic calibration of theoretical solar models
using only low-degree acoustic modes from the BiSON. The method can
therefore be applied also to other solar-type stars, such as those
observed by the NASA satellite Kepler and the planned ground-based
Danish-led Stellar Observations Network Group (SONG). The age, 4.60
± 0.04 Gyr, obtained with this new seismic method, is similar to,
although somewhat greater than, today's commonly adopted values, and
the surface heavy-element abundance by mass, Zs= 0.0142 ±
0.0005, lies between the values quoted recently by Asplund et al. and
by Caffau et al. We stress that our best-fitting model is not a seismic
model, but a theoretically evolved model of the Sun constructed with
'standard' physics and calibrated against helioseismic data.
Title: Nonlocal model for the turbulent fluxes due to thermal
convection in rectilinear shearing flow
Authors: Smolec, R.; Houdek, G.; Gough, D. O.
Bibcode: 2011arXiv1112.0014S
Altcode:
We revisit a phenomenological description of turbulent thermal
convection along the lines proposed by Gough (1977) in which eddies grow
solely by extracting energy from the unstably stratified mean state
and are subsequently destroyed by internal shear instability. This
work is part of an ongoing investigation for finding a procedure to
calculate the turbulent fluxes of heat and momentum in the presence
of a shearing background flow in stars.
Title: Stoked Dynamos: Magnetic Feeding of Dynamos and Nondynamos
Authors: Byington, Ben; Stone, Jen; Brummel, Nic; Gough, Douglas
Bibcode: 2011sdmi.confE..18B
Altcode:
Magnetic diffusion timescales in the sun are long enough that
dynamo mechanisms are not required to explain the mere presence of
a solar magnetic field. Rather, it is the large scale organization
and chaotically modulated oscillations that suggest dynamo
activity. However, one could ask what the effects of a fossil field
deep in the interior might have on the visible characteristics of
the system. In particular, could it be possible to save a failing
dynamo in the convective region, by leaking in small amounts of
fossil field from deep in the interior? If it were possible, could
one tell the difference between this system and a true dynamo? In
the present work, we examine the behavior of a number of non-dynamo
systems when they are ``stoked" through the addition of small amounts
of external field. Without stoking, these non-dynamo systems can share
many characteristics with dynamos, such as exponential growth in the
kinematic regime, yet ultimately fail to sustain magnetic field over
many diffusive timescales. For the first system examined (a kinematic
dynamo, but nonlinear non-dynamo), the stoking does not affect
the non-dynamo properties of the system, yet still sets up a basic
sustained equilibrium that may be hard to distinguish from a dynamo
for a distant observer, depending on the level of the stoking. Early
analysis has also been done on a second different type of system (an
essentially nonlinear failing dynamo) where stoking is more likely to
result in a system indistinguishable from a true dynamo.
Title: What have we learned, what have we really learned, and what
do we wish to learn?
Authors: Gough, Douglas
Bibcode: 2011sdmi.confE..40G
Altcode:
Helioseismology has been widely acclaimed to have been a great success:
it seems to have answered nearly all the questions that we originally
asked, some with unexpectedly high precision. So where are we going
now? It takes only a brief scrutiny of the equations describing
the structure and dynamical evolution of the Sun, together with
those governing the low-amplitude seismic modes of oscillation to
appreciate what can, at least in principle, be reliably inferred from
seismology. Anything further must depend on other criteria, such as
general physical argument, traditional astronomical observation, or even
prejudice. It is obligatory to be explicit about how such information
is used. Our subject has advanced to a new level of sophistication;
we are now trying to probe almost inaccessible aspects of the physics,
and the techniques for unravelling them are becoming more and more
intricate, beyond the point where most scientists wish to tread. There
must necessarily be increased trust, and it is our responsibility not
to betray it. The broader scientific community want simply to use our
results in their research; for that they must know their, and which
aspects of them can really be trusted. Much of the emphasis of SDO
seismology concerns the workings of the convection zone. We want to
know what controls the solar cycle, how magnetic field is amplified,
modulated and then suppressed, how sunspots are formed and destroyed -
and what determines their lifespan. We want to know the geometry of
at least the larger scales of convective motion, and how, beneath the
seen superficial layers of the Sun, the processes that control the total
radiative output are modulated. At least some of us want to understand
how all these matters influence our procedures for inferring the gross
properties of the Sun, and how they impinge on our broader ideas of the
evolution of the Sun in particular, and of stars in general. Addressing
such delicate issues with confidence may now seem an almost impossible
task for we who have lived through years of stumbling in the darkness,
finally emerging to bathe in the secure light illuminating the minute
arena of knowledge that we have been instrumental in uncovering. Now
it is incumbent on the young to proceed likewise: to grasp at the edge
perception with initially insecure data and ideas, fully appreciating
the uncertainty, of course; then moulding and strengthening them into
a new body of secure scientific knowledge.
Title: Closing Remarks
Authors: Gough, Douglas
Bibcode: 2011iasa.confE..44G
Altcode:
No abstract at ADS
Title: Modelling turbulent fluxes due to thermal convection in
rectilinear shearing flow
Authors: Smolec, Radoslaw; Houdek, Günter; Gough, Douglas
Bibcode: 2011IAUS..271..397S
Altcode: 2010arXiv1011.3813S
We revisit a phenomenological description of turbulent thermal
convection along the lines proposed originally by Gough (1965)
in which eddies grow solely by extracting energy from the unstably
stratified mean state and are subsequently destroyed by internal shear
instability. This work is part of an ongoing investigation for finding
a procedure to calculate the turbulent fluxes of heat and momentum in
the presence of a shearing background flow in stars.
Title: Variability in mode amplitudes in the rapidly oscillating Ap
star HR 1217
Authors: White, T. R.; Bedding, T. R.; Stello, D.; Kurtz, D. W.;
Cunha, M. S.; Gough, D. O.
Bibcode: 2011MNRAS.415.1638W
Altcode: 2011MNRAS.tmp..769W; 2011arXiv1105.3026W
HR 1217 is one of the best studied rapidly oscillating Ap stars
with eight known oscillation modes that are distorted by a strong,
global magnetic field. We have reanalysed the multisite observations
of HR 1217 taken in 1986 and 2000. We determined a weighting scheme
for the 1986 and 2000 data to minimize the noise level. A wavelet
analysis of the data has found that the modulation of the amplitude
due to rotation for all frequencies is, in general, consistent with
the expected modulation for modified ℓ= 1, 2 or 3 modes. Unexpected
variations in the rotational modulation are also seen, with variations
in the modulation profile, time of maximal pulsation and pulsational
energy in each mode. Interestingly, these changes take place on a short
time-scale, of the order of days. We consider potential explanations
for these behaviours.
Title: The Scientific Legacy of Fred Hoyle
Authors: Gough, Douglas
Bibcode: 2011slfh.book.....G
Altcode:
Introduction M. Rees; 1. Fred Hoyle's major work in the context of
astronomy and astrophysics today W. L. W. Sargent; 2. Sir Fred Hoyle
and the theory of the synthesis of the elements D. Arnett; 3. Fred
Hoyle: contributions to the theory of galaxy formation G. Efstathiou;
4. Highlights of Fred Hoyle's work on interstellar matter and star
formation P. M. Solomon; 5. Accretion H. Bondi; 6. From dust to life
C. Wickramasinghe; 7. Worlds without end or beginning J. D. Barrow;
8. Evolutionary cosmologies - then and now M. S. Longair; 9. Alternative
ideas in cosmology J. N. Narlikar; 10. Red Giants - then and now
J. Faulkner; 11. Modern alchemy: Fred Hoyle and element building by
neutron capture E. M. Burbidge; 12. Concluding remarks G. Burbidge.
Title: Some recent and future helioseismological inferences concerning
the solar convection zone
Authors: Gough, Douglas
Bibcode: 2011IAUS..271....3G
Altcode:
Several uncertain helioseismic findings of potential interest to Jüri
about the solar convection zone are briefly discussed, along with some
personal optimistic hopes for the future.
Title: Bridges between helioseismological and asteroseismological
inference
Authors: Gough, D. O.
Bibcode: 2011arXiv1107.5089G
Altcode:
Exactly eighty years ago, a very young Yehudi Menuhin was invited by
Bruno Walter to perform Beethoven's violin concerto with the Berlin
Philharmonic Orchestra. Walking through the streets of Berlin he
was unsure of his way, and asked a passer-by how he could get to the
Konzerthaus. The man looked at him, looked down at the violin case that
Yehudi was carrying, and said: `Practise, young man, practise'. It
was with such advice in their minds, I am sure, that Margarida and
Michael have asked me to try to build bridges between helioseismology
and asteroseismology. Asteroseismology is new and fresh, and the
young scientists who are entering the subject should be full of the
expectation of the delights of discovery of untrodden ground. Where
should they tread? They should be guided, perhaps, by our mature,
well practised, experiences with the Sun.
Title: History: Catching up with the Sun
Authors: Gough, Douglas
Bibcode: 2010Natur.468..504G
Altcode:
Douglas Gough enjoys a wide-ranging tour of the many influences of
our nearest star.
Title: Helioseismic Detection of Deep Meridional Flow
Authors: Gough, Douglas; Hindman, Bradley W.
Bibcode: 2010ApJ...714..960G
Altcode: 2009arXiv0911.2013G
Steady meridional flow does not make any first-order perturbations to
the frequencies of helioseismic normal modes. It does, however, Doppler
shift the local wavenumber, thereby distorting the eigenfunctions. For
high-degree modes, whose peaks in a power spectrum are blended into
continuous ridges, the effect of the distortion is to shift the
locations of those ridges. From this blended superposition of modes,
one can isolate oppositely directed wave components with the same
local horizontal wavenumber and measure a frequency difference which
can be safely used to infer the subsurface background flow. But such
a procedure fails for the components of the more deeply penetrating
low-degree modes that are not blended into ridges. Instead, one must
analyze the spatial distortions explicitly. With a simple toy model,
we illustrate a method by which that might be accomplished by measuring
the spatial variation of the oscillation phase. We estimate that by
using this procedure, it might be possible to infer meridional flow
deep in the solar convection zone.
Title: The quest for the solar g modes
Authors: Appourchaux, T.; Belkacem, K.; Broomhall, A. -M.; Chaplin,
W. J.; Gough, D. O.; Houdek, G.; Provost, J.; Baudin, F.; Boumier,
P.; Elsworth, Y.; García, R. A.; Andersen, B. N.; Finsterle, W.;
Fröhlich, C.; Gabriel, A.; Grec, G.; Jiménez, A.; Kosovichev, A.;
Sekii, T.; Toutain, T.; Turck-Chièze, S.
Bibcode: 2010A&ARv..18..197A
Altcode: 2010A&ARv.tmp....1A; 2009arXiv0910.0848A
Solar gravity modes (or g modes)—oscillations of the solar interior
on which buoyancy acts as the restoring force—have the potential
to provide unprecedented inference on the structure and dynamics of
the solar core, inference that is not possible with the well-observed
acoustic modes (or p modes). The relative high amplitude of the g-mode
eigenfunctions in the core and the evanesence of the modes in the
convection zone make the modes particularly sensitive to the physical
and dynamical conditions in the core. Owing to the existence of the
convection zone, the g modes have very low amplitudes at photospheric
levels, which makes the modes extremely hard to detect. In this article,
we review the current state of play regarding attempts to detect g
modes. We review the theory of g modes, including theoretical estimation
of the g-mode frequencies, amplitudes and damping rates. Then we go
on to discuss the techniques that have been used to try to detect g
modes. We review results in the literature, and finish by looking to
the future, and the potential advances that can be made—from both
data and data-analysis perspectives—to give unambiguous detections
of individual g modes. The review ends by concluding that, at the time
of writing, there is indeed a consensus amongst the authors that there
is currently no undisputed detection of solar g modes.
Title: Angular-Momentum Coupling Through the Tachocline
Authors: Gough, D. O.
Bibcode: 2010ASSP...19...68G
Altcode: 2009arXiv0905.4924G; 2010mcia.conf...68G
Astronomical observation of stellar rotation suggests that at least
the surface layers of the Sun have lost a substantial amount of
the angular momentum that they possessed at the beginning of the
main-sequence phase of evolution, and solar-wind observations indicate
that magnetic coupling is still draining angular momentum from the
Sun today. In addition, helioseismological analysis has shown that the
specific angular momentum at the top of the almost uniformly rotating
radiative interior is approximately (although not exactly) the same
as the spherically averaged value at the base of the (differentially
rotating) convection zone, suggesting that angular momentum is being
transported through the tachocline. The mechanism by which that
transport is taking place is not understood. Nor is there a consensus
of opinion. I review some of the suggestions that have been put forward,
biassing my discussion, no doubt, according to my own opinions.
Title: Vainu Bappu Memorial Lecture: What is a Sunspot?
Authors: Gough, D. O.
Bibcode: 2010ASSP...19...37G
Altcode: 2010mcia.conf...37G; 2009arXiv0909.5338G
Sunspots have been known in theWest since Galileo Galilei and Thomas
Harriot first used telescopes to observe the Sun nearly four centuries
ago; they have been known to the Chinese for more than 2,000 years. They
appear as relatively dark patches on the surface of the Sun, and are
caused by concentrations of magnetism, which impede the flow of heat
from deep inside the Sun up to its otherwise brilliant surface. The
spots are not permanent: the total number of spots on the Sun varies
cyclically in time, with a period of about 11 years, associated with
which there appear to be variations in our climate. When there are
many spots, it is more dangerous for spacecraft to operate. The cause
of the spots is not well understood; nor is it known for sure how
they die. Their structure beneath the surface of the Sun is in some
dispute, although much is known about their properties at the surface,
including an outward material flow, which was discovered by John
Evershed observing the Sun from Kodaikanal a 100 years ago. I shall
give you a glimpse of how we are striving to deepen our understanding
of these fascinating features, and some of the phenomena that appear
to be associated with them.
Title: Measuring Solar Abundances with Seismology
Authors: Mussack, K.; Gough, D.
Bibcode: 2009ASPC..416..203M
Altcode: 2008arXiv0810.2722M
The revision of the photospheric abundances proferred by Asplund
et al. (2005) has rendered opacity theory inconsistent with the
seismologically determined opacity through the Sun. This highlights the
need for a direct seismological measurement of solar abundances. Here
we describe the technique used to measure abundances with seismology,
examine our ability to detect differences between solar models using
this technique, and discuss its application in the Sun.
Title: Seismic signature of helium ionization in the Sun and stars
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2009arXiv0911.5044H
Altcode:
We present a summary of an asteroseismic signature of helium ionization
reported by Houdek & Gough (2007, 2008, 2009) for low-degree
p modes in solar-type stars, and illustrate its applications for
asteroseismic diagnoses.
Title: Further progress on solar age calibration
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2009CoAst.159...27H
Altcode: 2008arXiv0812.5044H
We recalibrate a standard solar model seismologically to estimate
the main-sequence age of the Sun. Our procedure differs from what
we have done in the past by removing from the observed frequencies
a crude representation of the effect of hydrogen ionization and the
superadiabatic convective boundary layer. Our preliminary result is
t_⊙=4.63±0.02 Gy.
Title: Progress report on solar age calibration
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2008IAUS..252..149H
Altcode:
We report on an ongoing investigation into a seismic calibration
of solar models designed for estimating the main-sequence age
and a measure of the chemical abundances of the Sun. Only modes
of low degree are employed, so that with appropriate modification
the procedure could be applied to other stars. We have found that,
as has been anticipated, a separation of the contributions to the
seismic frequencies arising from the relatively smooth, glitch-free,
background structure of the star and from glitches produced by helium
ionization and the abrupt gradient change at the base of the convection
zone renders the procedure more robust than earlier calibrations that
fitted only raw frequencies to glitch-free asymptotics. As in the past,
we use asymptotic analysis to design seismic signatures that are, to
the best of our ability, contaminated as little as possible by those
uncertain properties of the star that are not directly associated
with age and chemical composition. The calibration itself, however,
employs only numerically computed eigenfrequencies. It is based on
a linear perturbation from a reference model. Two reference models
have been used, one somewhat younger, the other somewhat older than
the Sun. The two calibrations, which use BiSON data, are more-or-less
consistent, and yield a main-sequence age t⊙ = 4.68 ±
0.02 Gy, coupled with a formal initial heavy-element abundance Z =
0.0169 ± 0.0005. The error analysis has not yet been completed,
so the estimated precision must be taken with a pinch of salt.
Title: AsteroFLAG — from the Sun to the stars
Authors: Chaplin, W. J.; Appourchaux, T.; Arentoft, T.; Ballot, J.;
Baudin, F.; Bazot, M.; Bedding, T. R.; Christensen-Dalsgaard, J.;
Creevey, O. L.; Duez, V.; Elsworth, Y.; Fletcher, S. T.; García,
R. A.; Gough, D. O.; Jiménez, A.; Jiménez-Reyes, S. J.; Houdek, G.;
Kjeldsen, H.; Lazrek, M.; Leibacher, J. W.; Monteiro, M. J. P. F. G.;
Neiner, C.; New, R.; Régulo, C.; Salabert, D.; Samadi, R.; Sekii,
T.; Sousa, S. G.; Toutain, T.; Turck-Chièze, S.
Bibcode: 2008JPhCS.118a2048C
Altcode:
We stand on the threshold of a critical expansion of asteroseismology
of Sun-like stars, the study of stellar interiors by observation
and analysis of their global acoustic modes of oscillation. The
Sun-like oscillations give a very rich spectrum allowing the internal
structure and dynamics to be probed down into the stellar cores to
very high precision. Asteroseismic observations of many stars will
allow multiple-point tests of crucial aspects of stellar evolution
and dynamo theory. The aims of the asteroFLAG collaboration are to
help the community to refine existing, and to develop new, methods
for analysis of the asteroseismic data on the Sun-like oscillators.
Title: Shock Waves and Line-Profile Variation in roAp Stars
Authors: Shibahashi, Hiromoto; Gough, Douglas; Kurtz, Donald W.;
Kambe, Eiji
Bibcode: 2008PASJ...60...63S
Altcode:
Line-profile variation of NdIII and PrIII spectrum lines of roAp stars
obtained with high spectral resolution and high time resolution seem
to be similar to those seen in rapidly rotating B-type line-profile
variables: features in the lines appear to move smoothly from blue to
red, but return to the blue discontinuously. It has been argued in the
past that such behaviour is in disagreement with the oblique-pulsator
interpretion of the photometric observations. We point out why
that argument is invalid. We propose that the properties of the
observed line-profile variation can in principle be explained as a
manifestation of a shocked wave train propagating upwards through an
acoustically thick layer high in the atmosphere, and demonstrate that
it is consistent with the underlying pulsation being an axisymmetric
low-degree, probably dipole oscillation more-or-less aligned with the
magnetic axis, in accord with the oblique-pulsator model.
Title: Temporal variations in the Sun's rotational kinetic energy
Authors: Antia, H. M.; Chitre, S. M.; Gough, D. O.
Bibcode: 2008A&A...477..657A
Altcode: 2007arXiv0711.0799A
Aims: We study the variation of the angular momentum and the
rotational kinetic energy of the Sun, and associated variations in the
gravitational multipole moments, on a timescale of the solar cycle.
Methods: These quantities are determined by inverting helioseismic
rotational splitting data obtained by the Global Oscillation Network
Group and by the Michelson Doppler Imager on the Solar and Heliospheric
Observatory.
Results: The temporal variation in angular momentum
and kinetic energy at high latitudes (>π/4) through the convection
zone is positively correlated with the level of solar activity,
whereas at low latitudes it is anticorrelated, except in the top 10%
by radius where both are correlated positively.
Conclusions: The
helioseismic data imply significant temporal variation in the angular
momentum and the rotational kinetic energy, and in the gravitational
multipole moments. The properties of that variation will help constrain
dynamical theories of the solar cycle.
Title: The Inconstant Sun
Authors: Antia, H. M.; Chitre, S. M.; Gough, D. O.
Bibcode: 2007AIPC..948..133A
Altcode:
We study temporal variation in the solar angular momentum, J,
rotational kinetic energy, T, and the rotational contribution to the
gravitational multipole moments J2k of the Sun, inferred
from helioseismic data from GONG and MDI over the last 11 years,
covering most of the cycle 23. We have found that the variations in
J and T at high latitudes (>45°) through the convection zone are
correlated positively with solar activity, while at low latitudes they
are correlated negatively, except for the top 10% of solar radius,
where the correlation is positive.
Title: On the Seismic Age of the Sun
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2007AIPC..948..219H
Altcode: 2007arXiv0710.0762H
We use low-degree acoustic modes obtained by the BiSON to estimate
the main-sequence age tsolar of the Sun. The calibration
is accomplished by linearizing the deviations from a standard solar
model the seismic frequencies of which are close to those of the
Sun. Formally, we obtain the preliminary value tsolar =
4.68+/-0.02 Gy, coupled with an initial heavy-element abundance Z =
0.0169+/-0.0005. The quoted standard errors, which are not independent,
are upper bounds implied under the assumption that the standard errors
in the observed frequencies are independent.
Title: Discussion on solar-like oscillators and γ Doradus stars
Authors: Gough, Douglas O.
Bibcode: 2007CoAst.150..155G
Altcode:
No abstract at ADS
Title: An elementary introduction to the JWKB approximation
Authors: Gough, D. O.
Bibcode: 2007AN....328..273G
Altcode: 2007astro.ph..2201G
Asymptotic expansion of the second-order linear ordinary differential
equation Ψ''+k2f(z)Ψ=0, in which the real
constant k is large and f=O(1), can be carried out in the manner
of Liouville and Green provided f does not vanish. If f does vanish,
however, at x_0 say, then Liouville-Green expansions can be carried out
either side of the turning point z = z_0, but it is then necessary to
ascertain how to connect them. This was first accomplished by Jeffreys,
by a comparison of the differential equation with Airy's equation. Soon
afterwards, the situation was found to arise in quantum mechanics,
and was discussed by Brillouin, Wentzel and Kramers, after whom the
method was initially named. It arises throughout classical physics
too, and is encountered frequently when studying waves propagating in
stars. This brief introduction is aimed at clarifying the principles
behind the method, and is illustrated by considering the resonant
acoustic-gravity oscillations (normal modes) of a spherical star.
Title: An asteroseismic signature of helium ionization
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2007MNRAS.375..861H
Altcode: 2006astro.ph.12030H; 2007MNRAS.tmp...10H
We investigate the influence of the ionization of helium on the
low-degree acoustic oscillation frequencies in model solar-type
stars. The signature in the oscillation frequencies characterizing
the ionization-induced depression of the first adiabatic exponent γ
is a superposition of two decaying periodic functions of frequency
ν, with `frequencies' that are approximately twice the acoustic
depths of the centres of the HeI and HeII ionization regions. That
variation is probably best exhibited in the second frequency
difference Δ2νn,l ≡ νn-1,l
- 2νn,l + νn+1,l. We show how an analytic
approximation to the variation of γ leads to a simple representation
of this oscillatory contribution to Δ2ν which can be used
to characterize the γ variation, our intention being to use it as a
seismic diagnostic of the helium abundance of the star. We emphasize
that the objective is to characterize γ, not merely to find a formula
for Δ2ν that reproduces the data.
Title: An introduction to the solar tachocline
Authors: Gough, Douglas
Bibcode: 2007sota.conf....3G
Altcode:
No abstract at ADS
Title: On seismic signatures of rapid variation
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2006ESASP.624E..88H
Altcode: 2006soho...18E..88H; 2006astro.ph.12025H
We present an improved model for an asteroseismic diagnostic contained
in the frequency spacing of low-degree acoustic modes. By modelling in
a realistic manner regions of rapid variation of dynamically relevant
quantities, which we call acoustic glitches, we can derive signatures of
the gross properties of those glitches. In particular, we are interested
in measuring properties that are related to the helium ionization zones
and to the rapid variation in the background state associated with the
lower boundary of the convective envelope. The formula for the seismic
diagnostic is tested against a sequence of theoretical models of the
Sun, and is compared with seismic diagnostics published previously by
Monteiro & Thompson (1998, 2005) and by Basu et al. (2004).
Title: The DynaMICS perspective
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
Bibcode: 2006ESASP.624E..24T
Altcode: 2006soho...18E..24T
No abstract at ADS
Title: The internal structure of the Sun inferred from g modes and
low-frequency p modes
Authors: Elsworth, Y. P.; Baudin, F.; Chaplin, W; Andersen, B;
Appourchaux, T.; Boumier, P.; Broomhall, A. -M.; Corbard, T.;
Finsterle, W.; Fröhlich, C.; Gabriel, A.; García, R. A.; Gough,
D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii,
T.; Toutain, T.; Turck-Chièze, S.
Bibcode: 2006ESASP.624E..22E
Altcode: 2006soho...18E..22E
The Phoebus group is an international collaboration of
helioseismologists, its aim being to detect low-frequency solar g
modes. Here, we report on recent work, including the development and
application of new techniques based on the detection of coincidences
in contemporaneous datasets and the asymptotic properties of the g-mode
frequencies. The length of the time series available to the community is
now more than ten years, and this has reduced significantly the upper
detection limits on the g-mode amplitudes. Furthermore, low-degree p
modes can now be detected clearly at frequencies below 1000 μHz.
Title: Scientific Objectives of the Novel Formation Flying Mission
Aspiics
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
Bibcode: 2006ESASP.617E.164L
Altcode: 2006soho...17E.164L
No abstract at ADS
Title: The EUV Variability Experiment (EVE) on the Solar Dynamics
Observatory (SDO): Science Plan and Instrument Overview
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
Bibcode: 2006ESASP.617E.165W
Altcode: 2006soho...17E.165W
No abstract at ADS
Title: Recent Progresses on g-Mode Search
Authors: Appourchaux, T.; Andersen, B.; Baudin, F.; Boumier, P.;
Broomhall, A. -M.; Chaplin, W.; Corbard, T.; Elsworth, Y.; Finsterle,
W.; Fröhlich, C.; Gabriel, A.; Garcia, R.; Gough, D. O.; Grec, G.;
Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.;
Turck-Chièze, S.
Bibcode: 2006ESASP.617E...2A
Altcode: 2006soho...17E...2A
No abstract at ADS
Title: The Dynamics Project
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
Bibcode: 2006ESASP.617E.162T
Altcode: 2006soho...17E.162T
No abstract at ADS
Title: Helioseismological Determination of the State of the Solar
Interior
Authors: Gough, D.
Bibcode: 2006ESASP.617E...1G
Altcode: 2006soho...17E...1G
No abstract at ADS
Title: Obituary: Norman Hodgson Baker Jr (1931 - 2005)
Authors: Dziembowski, Wojciech; Gautschy, Alfred; Gough, Douglas
Bibcode: 2006MmSAI..77...33D
Altcode:
No abstract at ADS
Title: On model predictions of the power spectral density of radial
solar p modes
Authors: Chaplin, W. J.; Houdek, G.; Elsworth, Y.; Gough, D. O.;
Isaak, G. R.; New, R.
Bibcode: 2005MNRAS.360..859C
Altcode: 2005MNRAS.tmp..510C
We investigate the frequency dependence of the power spectral density
of low-degree solar p modes by comparing measurements with the results
of a stochastic-excitation model. In the past it was common practice
to use the total power in such investigations. Using the maximum of
the power spectral density instead provides a direct comparison with
the measured mode heights in the observed power spectrum. This method
permits a more careful calibration of the adjustable parameters in the
excitation model, a model which we present here, for the first time,
in a format that precisely and unambiguously relates the amplitudes
of the modes of oscillation to the Reynolds stress in the equilibrium
model. We find that errors in the theory of the linear mode damping
rates, particularly at low frequency, have a dramatic impact on
the predictions of the mode heights in the spectral density, whereas
parameter changes in the stochastic excitation model, within a plausible
domain of parameter space, have a comparatively small effect.
Title: The Scientific Legacy of Fred Hoyle
Authors: Gough, Douglas
Bibcode: 2005slfh.book.....G
Altcode:
Introduction M. Rees; 1. Fred Hoyle's major work in the context of
astronomy and astrophysics today W. L. W. Sargent; 2. Sir Fred Hoyle
and the theory of the synthesis of the elements D. Arnett; 3. Fred
Hoyle: contributions to the theory of galaxy formation G. Efstathiou;
4. Highlights of Fred Hoyle's work on interstellar matter and star
formation P. M. Solomon; 5. Accretion H. Bondi; 6. From dust to life
C. Wickramasinghe; 7. Worlds without end or beginning J. D. Barrow;
8. Evolutionary cosmologies - then and now M. S. Longair; 9. Alternative
ideas in cosmology J. N. Narlikar; 10. Red Giants - then and now
J. Faulkner; 11. Modern alchemy: Fred Hoyle and element building by
neutron capture E. M. Burbidge; 12. Concluding remarks G. Burbidge.
Title: Helioseismic Ring Analyses of Artificial Data Computed for
Two-dimensional Shearing Flows
Authors: Hindman, Bradley W.; Gough, Douglas; Thompson, Michael J.;
Toomre, Juri
Bibcode: 2005ApJ...621..512H
Altcode:
The local helioseismological technique of ring analysis has been
crucial in the discovery of complex large-scale flows in the Sun's
near-surface shear layer. However, current implementations of
ring-analysis procedures assume that the flow field is horizontally
homogeneous over the analysis region. This assumption is certainly
incorrect, and in the present paper we assess the significance of this
approximation by analyzing artificial data sets computed from models of
horizontal shear flows. We consider the simple case of purely horizontal
and unidirectional flow that varies solely in the horizontal direction
orthogonal to the flow in a piecewise-constant manner. An ensemble
of plane waves is incident on the flow, and the scattered wave field
produced by the prescribed two-dimensional flow is computed to generate
an artificial helioseismic power spectrum. The artificial spectrum
is processed in a manner similar to standard ring analysis, and the
flow field that is thereby inferred is compared with the known imposed
flow. We find that the inferred flow velocity is essentially an average
of the true flow velocity over the region of the analysis, weighted by
the square of the spatial apodization function used in processing the
oscillation signal. Furthermore, the shape of a p-mode line profile
is determined by the distribution of speeds across the analysis region.
Title: On the detectability of a rotation-rate gradient in the
solar core
Authors: Chaplin, W. J.; Sekii, T.; Elsworth, Y.; Gough, D. O.
Bibcode: 2004MNRAS.355..535C
Altcode: 2004MNRAS.tmp..451C
We consider the problem of uncovering a possible gradient of rotation
in the solar core using seismic frequency splittings of low-degree
p-modes. The data are presumed to come from full-disc observations of
the Sun. In particular, we formulate an approach for determining the
diagnostic potential of a low-l splitting set to uncover, by inversion,
a difference in rotation between two target radii: one deep in the core,
the other in the mid-regions of the radiative zone. Our formulation
assumes the underlying rotation rate to be flat in the outer part
of the zone, but to vary linearly in the core (with the breakpoint
in behaviour located between the two target radii). Artificial data
are used to test the formulation, and to investigate the relative
importance at low l of deeply penetrating, high-order modes and
relatively shallow, low-order modes. Our results suggest that in
order to detect a significant difference between the rotation at r=
0.1R and 0.35R- with the input splitting data coming from a 10-yr
set of high-quality observations - that difference would need to be
a significant fraction of the rotation rate itself.
Title: How to interpret LPV in roAp stars
Authors: Shibahashi, H.; Kurtz, D. W.; Kambe, E.; Gough, D. O.
Bibcode: 2004IAUS..224..829S
Altcode:
Recent spectroscopic observations of roAp stars with high spectral
resolution and high time resolution show line profile variations (LPV)
which seem to be similar to those seen in rapidly rotating B-type
line-profile variables. At first glance these line profile variations
seem to be in disagreement with the mode identification based on the
photometric observations. We propose an interpretation according to
which the observed line profile variations are a manifestation of a
shock wave in the high atmosphere near the magnetic polar regions,
and show that the line profile variations can be still understood
in the framework of the oscillation mode being consistent with the
photometric observations.
Title: Equation-of-State and Phase-Transition in Models of Ordinary
Astrophysical Matter
Authors: Celebonovic, Vladan; Gough, Douglas; Däppen, Werner
Bibcode: 2004AIPC..731.....C
Altcode:
No abstract at ADS
Title: The power of helioseismology to address issues of fundamental
physics
Authors: Gough, Douglas
Bibcode: 2004AIPC..731..119G
Altcode:
I first argue that, so far as macroscopic dynamical processes
are concerned, to a high degree of accuracy the solar plasma, at
least beneath the photosphere, may be regarded as being electrically
neutral. I then turn to discuss, elaborating on Christensen-Dalsgaard's
excellent but brief introduction in these proceedings, some of those
aspects of helioseismology that are pertinent to determining those
properties of the Sun that are pertinent to studies of the equation
of state. I discuss one of the ways in which one can establish
a representation of the structure of the Sun that is consistent
with the helioseismic constraints, and I present some properties of
the outcome. Finally, I describe some minor conclusions concerning
opacity and the equation of state that can be drawn, mindful that in
the not-too-distant future more penetrating insight will be gained.
Title: The Effect of Helium Ionization on Stellar Eigenfrequencies
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2004ESASP.559..464H
Altcode: 2004soho...14..464H
We investigate the influence of the ionization of helium on the
low-degree acoustic oscillation frequencies in solar-type stars. The
signature in the oscillation frequencies that is produced by
the ionization of helium is approximated by two decaying periodic
functions with periods that are twice the acoustic depths of the
centres of the HeI and HeII ionization regions. We indicate how an
approximation to the variation of the first adiabatic exponent, γ,
leads to a simple representation of the oscillatory contribution to the
second frequency differences which can be used as a diagnostic of the
helium abundance of the star; and we show that our explicit inclusion
of the first ionization of helium, even though it is merged with the
ionization of hydrogen, provides a representation which is superior
to the corresponding representation that takes only HeII ionization
into account.
Title: Line profile variations in γ Equ: A puzzle
Authors: Shibahashi, Hiromoto; Kurtz, Don; Kambe, Eiji; Gough, Douglas
Bibcode: 2004ASPC..310..287S
Altcode: 2004IAUCo.193..287S; 2004vslg.conf..287S
Line profile variations in γ Equ show the classic blue-to-red traveling
bumps of m-modes resolved by rotation, and they have been identified
as l= 2 or 3, m = -l or -ll+1 by characterising the line shapes using
the moment method. The mode identifications cannot be correct, however,
since γ Equ is an extremely slowly rotating star (Prot >
70 yr). We propose an alternative interpretation, according to which
the observed line profile variations are a manifestation of a shock wave
in the high atmosphere near the magnetic polar regions; the oscillation
mode is then still consistent with the photometric observations.
Title: What we need to know about the Sun
Authors: Gough, Douglas
Bibcode: 2004IAUS..223..723G
Altcode: 2005IAUS..223..723G
No abstract at ADS
Title: Some remarks on solar neutrinos
Authors: Gough, D.
Bibcode: 2003Ap&SS.285..341G
Altcode:
In 1970 Fred Hoyle encouraged a study of solar neutrino production
which led to along-term investigation of the influence of what have
become known as `non-standard' processes (i.e. processes that are
not accounted for in the relatively naively constructed so-called
`standard' theoretical solar models). The outcome is a very much
sounder understanding of the structure and dynamics of the Sun,
which has yielded a knowledge of conditions in the energy-generating
core so precise that one can set quite tight reliable constraints on
neutrino-producing nuclear reactions, and thereby provide an important
contribution to the study of neutrino transitions.
Title: The seismic radius of the Sun, and structure inversions
Authors: Takata, M.; Gough, D. O.
Bibcode: 2003ESASP.517..397T
Altcode: 2003soho...12..397T
It is known (Schou et al., 1997; Antia, 1998) that the effective radius
of the Sun determined by f-mode frequencies is different by a few
hundredths per cent from the photospheric radius determined by direct
photometric measurement (Brown and Christensen-Dalsgaard 1998). It is
fair to say that we still do not fully comprehend the implications
of the difference, save that the two radii are rather different
quantities: the radius inferred from f-mode frequencies is determined
by the location of the maximum in the f-mode energy (Gough, 1993),
whereas the photospheric radius is determined by extrapolation to some
prescribed optical depth from a fiducial point in the limb-darkening
function using a theoretical solar model. Both depend in particular on
the structure of the upper superadiabatic convective boundary layer, the
physics of which is not well understood. In this report we attempt to
shed some light on the difference by determining a seismic radius from
p-mode frequencies; the outcome depends predominantly on the variation
of sound speed, and it is consistent with the f-mode value (Takata and
Gough 2001). By considering the mathematical structure of an inversion
process that does not explicitly distinguish f modes from p modes, we
offer an interpretation of the seismic radius. This interpretation has
led us to revise the method by which we carry out structure inversions.
Title: On the Effect of a Starspot on the Modes of Oscillation of
a Toy Ap Star Model
Authors: Montgomery, M. H.; Gough, D. O.
Bibcode: 2003aahd.conf..545M
Altcode:
No abstract at ADS
Title: On the Principal Asteroseismic Diagnostic Signatures
Authors: Gough, Douglas
Bibcode: 2003Ap&SS.284..165G
Altcode:
Many stellar model calibrations against seismic data will utilize
just the so-called large and small frequency separations. In this
report I explain in physical terms, based on resonance conditions for
constructive interference between simple waves, why those frequency
separations depend on the variation of sound speed through the star in
the manner in which they do. By so doing I hope to increase appreciation
of the nature of the stellar calibrations, and thereby provide a means
for assessing the credibility of the results.
Title: Some Remaining Open Questions and Directions for Future
Research
Authors: Gough, D.
Bibcode: 2003ASPC..305..389G
Altcode: 2003mfob.conf..389G
No abstract at ADS
Title: Modelling pulsation amplitudes of ξ Hydrae
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2002MNRAS.336L..65H
Altcode:
Amplitudes of stochastically excited oscillations of models of ξ Hydrae
(HR4450) are presented. The theoretical results are compared with the
recent measurements by an international group of astronomers announced
in the ESO press release 10/02. Using a stochastic excitation model
we find fair agreement between estimated velocity amplitudes and the
values quoted in the ESO press release.
Title: On the effect of error correlation on linear inversions
Authors: Gough, D. O.; Sekii, T.
Bibcode: 2002MNRAS.335..170G
Altcode:
We have examined the effect on linear helioseismic inversions of
correlations in data errors, taking an example from one-dimensional
rotational splitting inversion. Artificial data with correlated errors
were generated and then inverted with or without using the proper
covariance matrix. The effects of using incorrect covariance matrices,
on solutions as well as on trade-offs, are discussed. It is found
that improper account of the correlations can be deleterious to the
faithfulness of the inversions, and yields incorrect error estimates,
which under some circumstances can lead to misleading inferences.
Title: A search for solar g modes in the GOLF data
Authors: Gabriel, A. H.; Baudin, F.; Boumier, P.; García, R. A.;
Turck-Chièze, S.; Appourchaux, T.; Bertello, L.; Berthomieu, G.;
Charra, J.; Gough, D. O.; Pallé, P. L.; Provost, J.; Renaud, C.;
Robillot, J. -M.; Roca Cortés, T.; Thiery, S.; Ulrich, R. K.
Bibcode: 2002A&A...390.1119G
Altcode:
With over 5 years of GOLF data having some 90% continuity, a new
attempt has been made to search for possible solar g modes. Statistical
methods are used, based on the minimum of assumptions regarding the
solar physics; namely that mode line-widths are small compared with
the inverse of the observing time, and that modes are sought in the
frequency interval 150 to 400 mu Hz. A number of simulations are carried
out in order to understand the expected behaviour of a system consisting
principally of a solar noise continuum overlaid with some weak sharp
resonances. The method adopted is based on the FFT analysis of a time
series with zero-padding by a factor of 5. One prominent resonance at
284.666 mu Hz coincides with a previous tentative assignment as one
member of an n=1, l=1, p-mode multiplet. Components of two multiplets,
previously tentatively identified as possible g-mode candidates from
the GOLF data in 1998, continue to be found, although their statistical
significance is shown to be insufficient, within the present assumption
regarding the nature of the signal. An upper limit to the amplitude
of any g mode present is calculated using two different statistical
approaches, according to either the assumed absence (H0 hypothesis)
or the assumed presence (H1 hypothesis) of a signal. The former yields
a slightly lower limit of around 6 mm/s.
Title: How is solar activity influencing the structure of the Sun
Authors: Gough, D. O.
Bibcode: 2002ESASP.508..577G
Altcode: 2002soho...11..577G
To what extent does solar activity change the structure of the Sun? And
what is solar activity, for that matter? Some would say it is the
gamut of violent events seen in and above the upper atmosphere. If
that is all it is, then its effect on the Sun itself, that is the
region beneath the photosphere where almost all the matter resides,
must be utterly negligible. But if one includes the cause of these
violent events as part of the activity, then associated structure
changes in the Sun must be more profound.
Title: Helioseismology: some current issues concerning model
calibration
Authors: Gough, D. O.
Bibcode: 2002ESASP.485...65G
Altcode: 2002sshp.conf...65G
Aspects of helioseismic model calibration pertinent to
asteroseismological inference are reviewed, with a view to establishing
the uncertainties associated with some of the properties of the
structure of distant stars that can be inferred from the asteroseismic
data to be obtained by Eddington. It is shown that the seismic data
to be accrued by Eddington will raise our ability to diagnose the
structure of stars enormously, even though some previous estimates
of the errors in the derived stellar parameters appear likely to have
been somewhat optimistic, because the contribution from the imperfect
knowledge of the underlying physics was not accounted for.
Title: The solar interior
Authors: Gough, D. O.; Scherrer, P. H.
Bibcode: 2002css1.book.1035G
Altcode:
No abstract at ADS
Title: On the Hydrodynamics of Stellar Pulsation and Stability
(invited review)
Authors: Gough, D. O.
Bibcode: 2002ASPC..259...37G
Altcode: 2002rnpp.conf...37G; 2002IAUCo.185...37G
No abstract at ADS
Title: Reminiscences on Two Papers by Paul Ledoux
Authors: Gough, D. O.
Bibcode: 2002ASPC..259...12G
Altcode: 2002IAUCo.185...12G; 2002rnpp.conf...12G
No abstract at ADS
Title: Oscillations of α UMa and other red giants
Authors: Dziembowski, W. A.; Gough, D. O.; Houdek, G.; Sienkiewicz, R.
Bibcode: 2001MNRAS.328..601D
Altcode: 2001astro.ph..8337D
There is growing observational evidence that the variability of
red giants could be caused by self-excitation of global modes of
oscillation. The most recent evidence of such oscillations was reported
for αUMa by Buzasi et al. who analysed space photometric data from
the WIRE satellite. Little is understood concerning the oscillation
properties in red giants. In this paper we address the question as to
whether excited radial and non-radial modes can explain the observed
variability in red giants. In particular, we present the results of
numerical computations of oscillation properties of a model of αUMa
and of several models of a 2-Msolar star in the red giant
phase. The red giant stars that we have studied have two cavities that
can support oscillations: the inner core that supports gravity (g)
waves and the outer one that supports acoustic (p) waves. Most of the
modes in the p-mode frequency range are g modes confined in the core;
those modes with frequencies close to a corresponding characteristic
frequency of a p mode in the outer cavity are of mixed character and
have substantial amplitudes in the outer cavity. We have shown that
such modes of low degree, l=1 and 2, together with the radial (p)
modes, can be unstable. The linear growth rates of these non-radial
modes are similar to those of corresponding radial modes. In the model
of αUMa and in the 2-Msolar models in the lower regions of
the giant branch, high amplitudes in the p-mode cavity arise only for
modes with l=2. We have been unable to explain the observed oscillation
properties of αUMa, either in terms of mode instability or in terms of
stochastic excitation by turbulent convection. The modes with the lowest
frequencies, which exhibit the largest amplitudes and may correspond to
the first three radial modes, are computed to be unstable if all of the
effects of convection are neglected in the stability analyses. However,
if the Lagrangian perturbations of the turbulent fluxes (heat and
momentum) are taken into account in the pulsation calculation, only
modes with higher frequencies are found to be unstable. The observed
frequency dependence of amplitudes reported by Buzasi et al. does not
agree with what one expects from stochastic excitation. This mechanism
predicts an amplitude of the fundamental mode about two orders of
magnitude smaller than the amplitudes of modes with orders n>=5,
which is in stark disagreement with the observations.
Title: Changes in convective properties over the solar cycle: effect
on p-mode damping rates
Authors: Houdek, G.; Chaplin, W. J.; Appourchaux, T.;
Christensen-Dalsgaard, J.; Däppen, W.; Elsworth, Y.; Gough, D. O.;
Isaak, G. R.; New, R.; Rabello-Soares, M. C.
Bibcode: 2001MNRAS.327..483H
Altcode:
Measurements of both solar irradiance and p-mode oscillation
frequencies indicate that the structure of the Sun changes with
the solar cycle. Balmforth, Gough & Merryfield investigated the
effect of symmetrical thermal disturbances on the solar structure
and the resulting pulsation frequency changes. They concluded that
thermal perturbations alone cannot account for the variations in both
irradiance and p-mode frequencies, and that the presence of a magnetic
field affecting acoustical propagation is the most likely explanation
of the frequency change, in the manner suggested earlier by Gough &
Thompson and by Goldreich et al. Numerical simulations of Boussinesq
convection in a magnetic field have shown that at high Rayleigh number
the magnetic field can modify the preferred horizontal length scale
of the convective flow. Here, we investigate the effect of changing
the horizontal length scale of convective eddies on the linewidths
of the acoustic resonant mode peaks observed in helioseismic power
spectra. The turbulent fluxes in these model computations are obtained
from a time-dependent, non-local generalization of the mixing-length
formalism. The modelled variations are compared with p-mode linewidth
changes revealed by the analysis of helioseismic data collected by
the Birmingham Solar-Oscillations Network (BiSON); these low-degree
(low-l) observations cover the complete falling phase of solar activity
cycle 22. The results are also discussed in the light of observations
of solar-cycle variations of the horizontal size of granules and with
results from 2D simulations by Steffen of convective granules.
Title: On the dipolar f mode of stellar oscillation
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 2001MNRAS.326.1115C
Altcode:
The classification of adiabatic modes of non-radial stellar oscillation
was established by Cowling in 1941. In addition to acoustic and
gravity modes he identified an intermediate mode, which he labelled
the f mode, and which in simple stellar models has no radial node. The
motion of a dipolar f mode (of spherical-harmonic degree l=1) shifts
the centre of mass, and must have zero frequency. On the other hand,
if the perturbation to the gravitational potential is neglected (the
case considered by Cowling) the f mode has a frequency intermediate
between those of the gravity and acoustic modes; this is true of
modes of any degree (l>=1). Here we consider the properties of the
dipolar f mode, elucidating the origin of these differences through
continuous transformations between the various relevant cases; in
addition, we discuss the broader issues of the classification of modes
of non-radial oscillation.
Title: Solar Neutrino Emission Deduced from a Seismic Model
Authors: Turck-Chièze, S.; Couvidat, S.; Kosovichev, A. G.; Gabriel,
A. H.; Berthomieu, G.; Brun, A. S.; Christensen-Dalsgaard, J.; García,
R. A.; Gough, D. O.; Provost, J.; Roca-Cortes, T.; Roxburgh, I. W.;
Ulrich, R. K.
Bibcode: 2001ApJ...555L..69T
Altcode:
Three helioseismic instruments on the Solar and Heliospheric Observatory
have observed the Sun almost continuously since early 1996. This
has led to detailed study of the biases induced by the instruments
that measure intensity or Doppler velocity variation. Photospheric
turbulence hardly influences the tiny signature of conditions in the
energy-generating core in the low-order modes, which are therefore very
informative. We use sound-speed and density profiles inferred from GOLF
and MDI data including these modes, together with recent improvements
to stellar model computations, to build a spherically symmetric
seismically adjusted model in agreement with the observations. The
model is in hydrostatic and thermal balance and produces the present
observed luminosity. In constructing the model, we adopt the best
physics available, although we adjust some fundamental ingredients,
well within the commonly estimated errors, such as the p-p reaction
rate (+1%) and the heavy-element abundance (+3.5%); we also examine the
sensitivity of the density profile to the nuclear reaction rates. Then,
we deduce the corresponding emitted neutrino fluxes and consequently
demonstrate that it is unlikely that the deficit of the neutrino fluxes
measured on Earth can be explained by a spherically symmetric classical
model without neutrino flavor transitions. Finally, we discuss the
limitations of our results and future developments.
Title: Meeting contribution: Making a lens in the Sun
Authors: Gough, D. O.
Bibcode: 2001JBAA..111..166G
Altcode:
No abstract at ADS
Title: On the excitation mechanism in roAp stars
Authors: Balmforth, N. J.; Cunha, M. S.; Dolez, N.; Gough, D. O.;
Vauclair, S.
Bibcode: 2001MNRAS.323..362B
Altcode:
We investigate a model for the excitation of high-order oscillations
in roAp stars. In this model we assume that the strong concentration
of magnetic field about the magnetic poles is enough to suppress
convection. Thus the model considered is composed of two polar regions,
in which convection is presumed to be suppressed totally, and an
equatorial region, where the convection is unaffected. This model
is generated by building pairs of locally spherically symmetrical
equilibria to represent the polar and equatorial regions of the
star, which are patched together below the base of the convection
zone. Gravitational settling of heavy elements is taken into account
by choosing appropriate chemical composition profiles for both the
polar and equatorial regions. Our results indicate that the composite
model is unstable against axisymmetric non-radial high-order modes of
pulsation that are aligned with the magnetic poles. The oscillations
are excited by the κ mechanism acting principally in the hydrogen
ionization zones of the polar regions. The effect of the lateral
inhomogeneity on the second frequency differences is also investigated;
we find that the perturbation to them by the inhomogeneity is of the
same order as the second differences themselves, thereby hindering
potential attempts to use such differences to identify the degrees of
the modes in a straightforward way.
Title: Inhomogeneity in the solar core
Authors: Gough, D. O.
Bibcode: 2001SoPh..200..297G
Altcode:
In recent years, normal-mode helioseismology has shown that the
spherically averaged sound-speed distribution throughout the solar
interior is in remarkable agreement with suitable standard solar
models. This implies that any deviation of the theoretical models
from the Sun has only a very small influence on the oscillation
frequency spectrum (excluding the contributions from the uncertain
near-surface layers). Nevertheless, it is important to determine
whether the Sun really is very similar to a standard model, or whether
there are substantial differences. This is especially important of
the energy-generating core, particularly because it is likely to
be necessary to understand the conditions under which the nuclear
reactions are taking place in order to utilize neutrino detectors to
the full to measure the properties of neutrino transitions.
Title: Seismology of stellar envelopes: probing the outer layers of
a star through the scattering of acoustic waves
Authors: Lopes, Ilídio P.; Gough, Douglas
Bibcode: 2001MNRAS.322..473L
Altcode:
The outer layers of Sun-like stars are regions of rapid spatial
variation which modulate the p-mode frequencies by partially
reflecting the constituent acoustic waves. With the accuracy that
has been achieved by current solar observations, and that is expected
from imminent stellar observations, this modulation can be observed
from the spectra of the low-degree modes. We present a new and simple
theoretical calculation to determine the leading terms in an asymptotic
expansion of the outer phase of these modes, which is determined by
the structure of the surface layers of the star. Our procedure is to
compare the stellar envelope with a plane-parallel polytropic envelope,
which we regard as a smooth reference background state. Then we can
isolate a seismic signature of the acoustic phase and relate it to the
stratification of the outer layers of the convection zone. One can
thereby constrain theories of convection that are used to construct
the convection zones of the Sun and Sun-like stars. The accuracy of
the diagnostic is tested in the solar case by comparing the predicted
outer phase with an exact numerical calculation.
Title: Solar physics: Sizing up the Sun
Authors: Gough, Douglas
Bibcode: 2001Natur.410..313G
Altcode:
No abstract at ADS
Title: Solar Structure After Neutrinos and Helioseismology (CD-ROM
Directory: contribs/gough)
Authors: Gough, D. O.
Bibcode: 2001ASPC..223...83G
Altcode: 2001csss...11...83G
No abstract at ADS
Title: Comparison of phase inversion and time-distance analysis of
one-dimensional artificial seismic data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
Bibcode: 2001ESASP.464..207G
Altcode: 2001soho...10..207G
We have studied the application of a phase inversion technique (Gough,
Merryfield and Toomre 1991, 1993, 1998; Gough, Sekii and Toomre 1998,
2000) to stochastically excited damped oscillations in an inhomogeneous
one-dimensional loop, using artificial seismic data (Gough, Sekii and
Toomre 2000). It has been found that within a parameter range that might
be relevant to the solar case, strong damping can significantly degrade
inversions for the wave propagation speed. Here we analyse the same
artificial data by a time-distance technique, to compare how the two
techniques differ in their response to the presence of strong damping.
Title: The New Era in Helioseismology
Authors: Gough, D. O.
Bibcode: 2001IAUS..203....3G
Altcode:
The end of the millennium marks the beginning of the third phase
of helioseismology. The first phase was the establishment of the
initial astronomical inferences, such as estimates of the depth of the
solar convection zone and the protosolar helium abundance obtained
by comparing the seismic properties of theoretical solar models
with the first wave of helioseismic data acquired using instruments
that had not been designed for the purpose. The second phase was the
determination of the spherically symmetric component of the hydrostatic
stratification throughout most of the solar interior, and the angular
velocity, using inverse methods to analyse the frequencies of normal
modes estimated from data obtained most recently from purpose-built
networks of ground-based observatories and from space. We have reached
the point beyond which further pursuit of the now-well-tried methods
to improve the inferences will be apparently slow. The next era will
be characterized by painstaking attention to detail, to extract a new
level of precision necessary to isolate subtle properties of the Sun
for asking more sophisticated questions. We are already seeing the
normal-mode representation of helioseismic waves being complemented
by other representations that may be more suitable for investigating
inhomogeneity and time variability particularly of the Sun's surface
layers. The outcome will enable us to address more accurately issues
concerning global dynamics, the equation of state and the chemical
composition, and also the properties of convection and the seat of
solar activity.
Title: Towards a Generalization of a Mixing-length Model for
Nonradially Pulsating Stars: Convection in a Shear
Authors: Houdek, G.; Gough, D. O.
Bibcode: 2001IAUS..203..115H
Altcode:
Convection models based on the mixing-length approach still represent
the main method for computing the turbulent fluxes in stars with
convectively unstable layers. In such layers the pulsationally stability
of the star is affected not only by the radiative heat flux but also by
both the modulation of the convective heat flux and by direct mechanical
coupling of the pulsation with the convective motion via the Reynolds
stresses. Time-dependent formulations of the mixing-length approach
for radial pulsation have been proposed for example, by Unno (1967)
and Gough (1977). Using Gough's model Balmforth (1992) reported good
agreement between theoretical damping rates of radial p modes of a
solar model and observed linewidths. In this contribution we discuss a
generalization of Gough's time-dependent mixing-length formulation for
nonradial pulsation. The pulsation is described by a time-dependent mean
flow. The lateral component of this mean flow represents a shearing
motion in the linearized fluctuation equations. The shearing motion
stretches the convective elements and generates off-diagonal terms
in the Reynolds stress tensor. In this description another parameter,
additional to the mixing-length parameter, is introduced representing
the angle between the lateral components of the mean flow and of the
wave vector characterizing the convective element.
Title: The influence of uncertainties in the Sun's radius on
inversions for the solar structure
Authors: Takata, M.; Gough, D. O.
Bibcode: 2001ESASP.464..543T
Altcode: 2001soho...10..543T
It is customary when carrying out inversions of global p-mode
frequencies to assume that the radius Rsolar of the Sun
is known. This can introduce systematic error, in part because the
structure of the Sun between the region of acoustic propagation and
the visible atmosphere is neither well known nor readily accessible
seismologically, and in part because there is significant uncertainty
in the direct measurements of the Sun's radius itself. We demonstrate
how the influence of this error might be identified, and how it
might be eliminated from structural inversions. Moreover, the solar
radius itself is constrained only by the p-mode frequencies. Using
the SOHO/MDI frequency data, we estimate that R = 695.69+/-0.14 Mm,
which is consistent with the value determined by the f-mode frequencies
(Schou et al. 1997). We believe that our result is not so sensitive
to the uncertainties in the subsurface structure of the Sun because
their effects on the inversions are more or less removed by taking
account of the surface term.
Title: Mixing-length analysis of Rayleigh-Bénard convection in the
presence of a shear
Authors: Gough, D. O.; Houdek, G.
Bibcode: 2001ESASP.464..637G
Altcode: 2001soho...10..637G
According to linearized perturbation theory, an externally implied
low-amplitude horizontal plane Couette shear distorts the streamlines
of convective cells. This augments the eddy vorticity. Within the
framework of the mixing-length formalism in which turbulent convective
eddies grow according to linearized theory and are subsequently broken
up by internal shear instability, there is a consequent reduction in
the mean amplitude of the eddy motion, and a corresponding reduction
in the heat flux. In its simplest form, the generalization of the
formalism requires the introduction of no new parameters. Consequently,
the reduction in the heat flux predicted can be compared with experiment
to provide an additional calibration of the formalism.
Title: Dependence on azimuthal order of the amplitudes of low-degree
p modes
Authors: Fröhlich, C.; Appourchaux, T.; Gough, D. O.
Bibcode: 2001ESASP.464..629F
Altcode: 2001soho...10..629F
The m-dependence of the amplitudes of the multiplets of low-degree p
modes contains information about the latitudinal distribution of the
power in the excitation of the oscillations. We present estimates of
those amplitudes from 4 years of VIRGO/LOI observations. Variation of
the excitation with magnetic activity is studied.
Title: The opacity mechanism in roAp stars
Authors: Cunha, Margarida S.; Gough, Douglas
Bibcode: 2001ESASP.464..419C
Altcode: 2001soho...10..419C
In the present paper we present the first results of work whose
main goal is to understand the details of the process of high-order
mode excitation in roAp stars. Motivated by the work by Balmforth et
al. (1999, 2000), according to which convection might be suppressed in
the polar regions of roAp stars, we show that in a radiative region
the excitation of high-order pulsations takes place in the region of
hydrogen ionization, and is the direct consequence of the abrupt change
in the opacity derivative κT = (∂lnκ/∂lnT)ρ
in these layers.
Title: Lessons Learned From Solar Oscillations
Authors: Gough, D. O.
Bibcode: 2001ASPC..245...31G
Altcode: 2001aats.conf...31G
No abstract at ADS
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
Toutain, T.
Bibcode: 2001ESASP.464..467A
Altcode: 2001soho...10..467A
We review the recent developments in determining the upper limits to
g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
address how this limit can be improved by way of new helioseismic
instruments and/or new collaborations, hopefully providing in the not
too distant future unambiguous g-mode detection.
Title: Magnetic perturbations to the acoustic modes of roAp stars
Authors: Cunha, Margarida S.; Gough, Douglas
Bibcode: 2000MNRAS.319.1020C
Altcode:
We study the effect of a large-scale surface magnetic field on the
non-radial acoustic modes of roAp stars. Special attention is given to
the use of a variational principle which is used for determining the
shifts in the frequencies with relative ease, enabling us to avoid
having to calculate the perturbed eigenfunctions. With knowledge of
the frequency shifts we then estimate the eigenfunctions in a simpler,
albeit approximate way. The results indicate frequency shifts of the
order of few μHz, which depend on the order, degree and azimuthal order
of the mode. The loss of energy through Alfvén waves is also estimated
from the imaginary parts of the frequency shifts. The results indicate
that the loss is particularly high near specific frequencies. This
might indicate the presence of a selection effect, which could make
some modes more likely to be excited than others. However, our results
do not explain why the modes observed appear always to be aligned
with the axis of the magnetic field. Finally, the estimated perturbed
eigenfunctions contain strong components of spherical harmonics that
differ from those of the original unperturbed modes.
Title: On measuring low-degree p-mode frequency splitting with
full-disc integrated data
Authors: Appourchaux, T.; Chang, H. -Y.; Gough, D. O.; Sekii, T.
Bibcode: 2000MNRAS.319..365A
Altcode:
The standard method of measuring rotational splitting from solar
full-disc oscillation data, based on maximum-likelihood fitting of
multi-Lorentzian profiles to oscillation power spectra, systematically
overestimates the splitting. One of the reasons is that the maximum
likelihood estimators (MLE) become unbiased only asymptotically as
the number of data tends to infinity; for a finite data set they
are often biased, inducing a systematic error. In this paper we
assess by Monte Carlo simulations the amount of systematic error
in the splitting measurement, using artificially generated power
spectra. The simulations are carried out for multiplets of degree
S(t) = ΣkSk(t), l=1, 2 and 3 with various
signal-to-noise ratios, linewidths and observing times. We address
the possible use of non-MLE estimators that could provide a smaller
or negligible systematic error. The implication for asteroseismology
is also discussed.
Title: Seismology of the solar envelope: sound-speed gradient in
the convection zone and its diagnosis of the equation of state
Authors: Baturin, V. A.; Däppen, W.; Gough, D. O.; Vorontsov, S. V.
Bibcode: 2000MNRAS.316...71B
Altcode:
We report the results of an asymptotic inversion of solar oscillation
data for the gradient of the sound speed in the convection zone. This
gradient reveals details of the non-ideal Coulomb interactions between
particles, including pressure ionization. A simplified physical model
is used to track down the effect of various physical assumptions in
the sound-speed derivative. The model contains a calibration for the
size of the H and He atoms and the He+ ion. We find that,
for the pressure-ionization regions of hydrogen and helium, such a
model matches the data better than any of the currently available
parameter-free theories.
Title: Phase inversion of one-dimensional artificial seismic data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
Bibcode: 2000SoPh..195....1G
Altcode:
Oscillations of an inhomogeneous one-dimensional loop have been
simulated for the purpose of examining the effect of excitation and
damping on the sound-speed inversion based on phase analysis. It has
been demonstrated that the procedure is robust against the realization
noise arising from frequent, stochastic excitation of weakly damped
waves, but that strong damping can spoil the inversion.
Title: Observational Upper Limits to Low-Degree Solar g-Modes
Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.;
Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema,
J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.;
Sekii, T.; Toutain, T.
Bibcode: 2000ApJ...538..401A
Altcode:
Observations made by the Michelson Doppler Imager (MDI) and Variability
of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and
Heliospheric Observatory (SOHO) and by the ground-based Birmingham
Solar Oscillations Network (BiSON) and Global Oscillations Network
Group (GONG) have been used in a concerted effort to search for solar
gravity oscillations. All spectra are dominated by solar noise in the
frequency region from 100 to 1000 μHz, where g-modes are expected to be
found. Several methods have been used in an effort to extract any g-mode
signal present. These include (1) the correlation of data-both full-disk
and imaged (with different spatial-mask properties)-collected over
different time intervals from the same instrument, (2) the correlation
of near-contemporaneous data from different instruments, and (3) the
extraction-through the application of complex filtering techniques-of
the coherent part of data collected at different heights in the solar
atmosphere. The detection limit is set by the loss of coherence
caused by the temporal evolution and the motion (e.g., rotation)
of superficial structures. Although we cannot identify any g-mode
signature, we have nevertheless set a firm upper limit to the amplitudes
of the modes: at 200 μHz, they are below 10 mm s-1 in
velocity, and below 0.5 parts per million in intensity. The velocity
limit corresponds very approximately to a peak-to-peak vertical
displacement of δR/Rsolar=2.3×10-8 at the
solar surface. These levels which are much lower than prior claims,
are consistent with theoretical predictions.
Title: Towards Understanding Solar Convection and Activity -
(Invited Review)
Authors: Gough, Douglas
Bibcode: 2000SoPh..192....3G
Altcode:
The dynamics of the large-scale eddies which advect angular momentum
through the convection zone is controlled in a significant way by the
boundary conditions, which, if they are not modelled adequately, do
not lead to a distribution of angular velocity that is consistent with
observation. The transition boundary layer separating the convection
zone from the radiative interior is thought to play a critical role in
controlling the magnetic field in the convection zone, and is probably
not wholly irrelevant to understanding the cycle of solar activity.
Title: News from the Solar Interior
Authors: Gough, D.
Bibcode: 2000Sci...287.2434G
Altcode:
No abstract at ADS
Title: Free energy of a screened ion pair
Authors: Brüggen, M.; Gough, D. O.
Bibcode: 2000JMP....41..260B
Altcode: 2000JMPS...41..260B
We calculate the effect of weak electrostatic screening of ions in a
plasma. The original calculation by Salpeter is based on a linearization
of the Poisson-Boltzmann equation for the screened electrostatic
potential. This approximation is valid where the potential is small,
but is formally invalid in the vicinity of the ions where the solutions
for the potential and the associated charge distribution diverge. In
reality, quantum exclusion must prevent the divergence of the charge
density of the screening cloud. Nevertheless, in the limit in which
screening is weak, Salpeter's value for the total screening energy is
essentially correct. Here we extend Salpeter's calculation to account
approximately for both quantum-mechanical exclusion in the vicinity
of the ions, using what we call the Poisson-Boltzmann-Fermi-Dirac
approximation, and the polarization of the screening cloud. By matching
the solution onto an expression for the two-center Poisson-Boltzmann
charge distribution far from the ions we are able to construct a
consistent solution over all space. We obtain the first-order term in
the expansion of that solution, from which we calculate the free-energy
associated with the screened ion pair.
Title: Excitation Mechanism in roAp Stars
Authors: Balmforth, N. J.; Cunha, M. S.; Dolez, N.; Gough, D. O.;
Vauclair, S.
Bibcode: 2000ASPC..203..453B
Altcode: 2000ilss.conf..453B; 2000IAUCo.176..453B
In the present work we develop a theoretical model for roAp stars
characterized by the suppression of convection around the magnetic
poles. When calculating the growth rates of acoustic oscillations in
models of this type we find that most models whose positions in the
HR diagram coincide with that of the observed roAp stars are unstable
against high-order pulsations.
Title: The Effect of the Solar Cycle on the Resonant Coupling of
g Modes
Authors: Jordinson, C.; Gough, D. O.
Bibcode: 2000ASPC..203..390J
Altcode: 2000ilss.conf..390J; 2000IAUCo.176..390J
We consider the effect of the solar cycle on g-mode parametric
resonance, and hence on the limiting amplitude of the overstable solar
g1(l=1) mode. We find no change in the expected limiting
amplitude from that found by Dziembowski (1983), who ignored cycle
variations.
Title: Some Remarks on Stellar Pulsation
Authors: Gough, D.
Bibcode: 2000ASPC..203..529G
Altcode: 2000IAUCo.176..529G; 2000ilss.conf..529G
I wondered at first why I had been asked to perform the task of
commenting on the scientific discussion of this meeting, until a member
of the Scientific Organising Committee pointed out to me that I have not
published a serious paper on the subject of the colloquium in his memory
(I am not sure whether this is more a statement of the seriousness
of my publications, of my publication frequency or of the duration of
Jørgen's memory); however, I am presumably considered to be unbiased
by recent advances. Nevertheless, the time allotted (for the oral
address) and the corresponding space (in these published proceedings)
are inadequate for a complete and balanced review -- in any case, that
is hardly either desirable or necessary, since the discussions are all
still fresh in our minds -- and therefore I have been freed to comment
personally on some selected issues that have captured my interest.
Title: Amplitudes of stochastically excited oscillations in
main-sequence stars
Authors: Houdek, G.; Balmforth, N. J.; Christensen-Dalsgaard, J.;
Gough, D. O.
Bibcode: 1999A&A...351..582H
Altcode: 1999astro.ph..9107H
We present estimates of the amplitudes of intrinsically stable
stochastically excited radial oscillations in stars near the
main sequence. The amplitudes are determined by the balance
between acoustical energy generation by turbulent convection (the
Lighthill mechanism) and linear damping. Convection is treated with
a time-dependent, nonlocal, mixing-length model, which includes both
convective heat flux and turbulent pressure in both the equilibrium
model and the pulsations. Velocity and luminosity amplitudes are
computed for stars with masses between 0.9 M_sun and 2.0 M_sun in the
vicinity of the main sequence, for various metallicities and convection
parameters. As in previous studies, the amplitudes are found to increase
with stellar mass, and therefore with luminosity. Amongst those stars
that are pulsationally stable, the largest amplitudes are predicted
for a 1.6 M_sun model of spectral type F2; the values are approximately
15 times larger than those measured in the Sun.
Title: Prospects for Measuring Differential Rotation in White Dwarfs
through Asteroseismology
Authors: Kawaler, Steven D.; Sekii, Takashi; Gough, Douglas
Bibcode: 1999ApJ...516..349K
Altcode: 1998astro.ph.11286K
We examine the potential of asteroseismology for exploring the internal
rotation of white dwarf stars. Data from global observing campaigns
have revealed a wealth of frequencies, some of which show the signature
of rotational splitting. Tools developed for helioseismology to use
many solar p-mode frequencies for inversion of the rotation rate with
depth are adapted to the case of more limited numbers of modes of
low degree. We find that the small number of available modes in white
dwarfs, coupled with the similarity between the rotational-splitting
kernels of the modes, renders direct inversion unstable. Accordingly,
we adopt what we consider to be plausible functional forms for the
differential rotation profile; this is sufficiently restrictive to
enable us to carry out a useful calibration. We show examples of this
technique for PG 1159 stars and pulsating DB white dwarfs. Published
frequency splittings for white dwarfs are currently not accurate
enough for meaningful inversions; reanalysis of existing data can
provide splittings of sufficient accuracy when the frequencies of
individual peaks are extracted via least-squares fitting or multipeak
decompositions. We find that, when mode trapping is evident in the
period spacing of g modes, the measured splittings can constrain dΩ/dr.
Title: Calibration of the Thickness of the Solar Tachocline
Authors: Elliott, J. R.; Gough, D. O.
Bibcode: 1999ApJ...516..475E
Altcode:
Material circulation in the solar tachocline mixes the tachocline
material with the convection zone, which causes the sound speed in
and immediately beneath the tachocline to exceed what one would expect
from current standard solar models. Calibration against a helioseismic
determination of the sound speed from SOI/MDI data of a sequence of
solar models having mixed layers of different thicknesses yields a value
of 0.019 Rsolar for the mean tachocline thickness Δ, with a
formal standard error of about 5%. This value for Δ is somewhat smaller
than previous estimates based on measuring shear in the seismically
inferred angular velocity, and it has important implications concerning
our understanding of the magnetohydrodynamics of the tachocline.
Title: Helioseismology and solar neutrinos
Authors: Gough, D. O.
Bibcode: 1999NuPhS..77...81G
Altcode:
The manner by which helioseismic data are obtained and analysed to
diagnose the interior structure and rotation of the Sun is briefly
described. The principal results of the analysis pertinent to solar
neutrino production are presented; they have constrained standard
theoretical models of the Sun in such a way as to prevent them from
explaining the neutrino flux measurements without recourse to neutrino
transitions. However, standard solar models do not represent the entire
class of plausible models, and indeed they suffer the deficiency of
being unstable. Models in which the products of the nuclear reactions
are redistributed in the core may represent the Sun more closely,
and should at least be considered and tested further in the process
of developing a reliable model of the neutrino source.
Title: Turbulent Convection beyond Mixing-Length Models
Authors: Houdek, G.; Gough, D. O.
Bibcode: 1999ASPC..173..237H
Altcode: 1999sstt.conf..237H
No abstract at ADS
Title: On the Location of the Instability Strip
Authors: Houdek, G.; Balmforth, N. J.; Christensen-Dalsgaard, J.;
Gough, D. O.
Bibcode: 1999ASPC..173..317H
Altcode: 1999sstt.conf..317H
No abstract at ADS
Title: Understanding Solar Convection and Activity
Authors: Gough, Douglas
Bibcode: 1999soho....9E..32G
Altcode:
The dynamics of the large-scale eddies which advect angular momentum
through the convection zone is controlled in a significant way by the
boundary conditions, which, if they are not modelled adequately, do
not lead to a distribution of angular velocity that is consistent with
observation. The transition boundary layer separating the convection
zone from the radiative interior is thought to play a critical role in
controlling the magnetic field in the convection zone, and is probably
not wholly irrelevant to understanding the cycle of solar activity.
Title: Solar Convection and the Activity Cycle
Authors: Houdek, G.; Gough, D. O.
Bibcode: 1999soho....9E..65H
Altcode:
Measurements of both solar irradiance and p-mode oscillation
frequencies indicate that the structure of the sun changes with the
solar cycle. Balmforth, Gough & Merryfield (1996) investigated
the effect of symmetrical thermal disturbances on the solar structure
and the resulting pulsation frequency changes using a time-dependent,
local mixing-length formulation for computing the stratification of the
convection zone. In this contribution we follow the work by Balmforth
et al. and model the disturbances by introducing a time-dependent
inhomogeneous term in the linearized equations governing the structural
changes of the star about the undisturbed state. The perturbations of
the turbulent fluxes are obtained from a nonlocal generalization (Gough
1976) of the time-dependent mixing-length formulation. We investigate
the effect of changing the horizontal length scale of convective eddies
on p-mode properties, in particular on the linewidths of the spectral
peaks in the acoustical power spectrum. The results are discussed in
the light of observations of solar-cycle variations of the horizontal
size of granules and with results from 2-D simulations by Steffen
(1987) of convective granules.
Title: Phase Inversion of One-Dimensional Artificial Seismic Data
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
Bibcode: 1999soho....9E..30G
Altcode:
It has been pointed out (Sekii 1997; Gough, Sekii & Toomre 1998,
1999) that the application of the phase inversion technique (Gough,
Merryfield & Toomre 1991, 1993, 1998) to the solar high-degree
sectoral data, for detecting the background inhomogeneity in the
solar equatorial region, may be facing difficulty arising from the
presence of excitation and damping. We have studied the implication of
the effects of these, using a simple model of stochastically excited
damped oscillations of a one-dimensional loop. The results of phase
inversions for various cases will be presented and various strategies
to overcome the difficulty will be discussed.
Title: Simulation of Wave Fields to Assess the Sensitivity of
Ring-Diagram Analyses to Shearing Flows
Authors: Hindman, B. W.; Gough, D. O.; Haber, D. A.; Thompson, M. J.;
Toomre, J.
Bibcode: 1999soho....9E..64H
Altcode:
Ring-diagram analyses of acoustic-wave distortion by flows map
horizontal motions within the solar convection beneath the localized
regions where the observations are taken. To leading order, the
flow field responsible for the advection of waves is taken to be
horizontally uniform across the region. Current ring-diagram analyses
are only carried out to this order, although in reality the flow
is likely to vary across the local patch of the Sun. It is crucial
for the interpretation of the results of ring-diagram analyses that
the effects of shearing flows be assessed. Furthermore, the present
analyses ignore any influence on the ring parameters of flows exterior
to the region being studied. We present a progress report on the
forward calculation of the modification of ring parameters produced
by spatially varying flow fields. We examine effects of flow fields
both inside and outside the region of observation. Additionally,
we assess the influence of the non-uniform flow on the maps of the
velocity field obtained by inverting the ring-parameter data. The
effect of the inhomogeneous flow can be studied as a scattering
problem. We have developed Green functions connecting an underlying
inhomogeneous horizontal flow to the scattered wave field that results
when an incident plane wave encounters the flow. By considering an
ensemble of such incident waves, ring parameters can be inferred from
the wave field. One application is to analyze artificial data sets,
computed from models that contain horizontal shear flows. The scattered
wave field produced by a prescribed 3-D shearing flow is computed,
and the original and scattered wave fields are combined to generate an
artificial helioseismic data set. The artificial data so produced should
then be passed through a ring-diagram analysis and the deduced velocity
field compared to the known imposed flow. Another application is to
compute 3-D kernels relating the ring parameters to the underlying flow:
these will in the future permit 3-D inversions for the flows within
the solar convection zone, using mosaics of many ring-diagram samplings.
Title: Inversion for the internal structure and rotation of the Sun
and other sun-like stars
Authors: Gough, D. O.
Bibcode: 1998mons.proc...33G
Altcode:
Asteroseismic data of the kind accessible to MONS add enormously to
the observational information that we can gather about stars. Even
simple calibrations of theoretical stellar models based on elementary
combinations of oscillation frequencies enable us to refine our
knowledge of the interior structure of a star substantially. More
sophisticated analyses permit us to proceed further, and to address
specific questions that are pertinent to our more general understanding
of the structure and evolution of stars.
Title: Helioseismic Studies of Differential Rotation in the Solar
Envelope by the Solar Oscillations Investigation Using the Michelson
Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
Bibcode: 1998ApJ...505..390S
Altcode:
The splitting of the frequencies of the global resonant acoustic modes
of the Sun by large-scale flows and rotation permits study of the
variation of angular velocity Ω with both radius and latitude within
the turbulent convection zone and the deeper radiative interior. The
nearly uninterrupted Doppler imaging observations, provided by the
Solar Oscillations Investigation (SOI) using the Michelson Doppler
Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
positioned at the L1 Lagrangian point in continuous sunlight,
yield oscillation power spectra with very high signal-to-noise ratios
that allow frequency splittings to be determined with exceptional
accuracy. This paper reports on joint helioseismic analyses of
solar rotation in the convection zone and in the outer part of the
radiative core. Inversions have been obtained for a medium-l mode set
(involving modes of angular degree l extending to about 250) obtained
from the first 144 day interval of SOI-MDI observations in 1996. Drawing
inferences about the solar internal rotation from the splitting data
is a subtle process. By applying more than one inversion technique
to the data, we get some indication of what are the more robust
and less robust features of our inversion solutions. Here we have
used seven different inversion methods. To test the reliability and
sensitivity of these methods, we have performed a set of controlled
experiments utilizing artificial data. This gives us some confidence
in the inferences we can draw from the real solar data. The inversions
of SOI-MDI data have confirmed that the decrease of Ω with latitude
seen at the surface extends with little radial variation through much
of the convection zone, at the base of which is an adjustment layer,
called the tachocline, leading to nearly uniform rotation deeper
in the radiative interior. A prominent rotational shearing layer in
which Ω increases just below the surface is discernible at low to
mid latitudes. Using the new data, we have also been able to study the
solar rotation closer to the poles than has been achieved in previous
investigations. The data have revealed that the angular velocity
is distinctly lower at high latitudes than the values previously
extrapolated from measurements at lower latitudes based on surface
Doppler observations and helioseismology. Furthermore, we have found
some evidence near latitudes of 75° of a submerged polar jet which
is rotating more rapidly than its immediate surroundings. Superposed
on the relatively smooth latitudinal variation in Ω are alternating
zonal bands of slightly faster and slower rotation, each extending
some 10° to 15° in latitude. These relatively weak banded flows
have been followed by inversion to a depth of about 5% of the solar
radius and appear to coincide with the evolving pattern of ``torsional
oscillations'' reported from earlier surface Doppler studies.
Title: Inevitability of a magnetic field in the Sun's radiative
interior
Authors: Gough, D. O.; McIntyre, M. E.
Bibcode: 1998Natur.394..755G
Altcode:
The gas in the convective outer layers of the Sun rotates faster at the
equator than in the polar regions, yet deeper inside (in the radiative
zone) the gas rotates almost uniformly. There is a thin transition
layer between these zones, called the tachocline. This structure has
been measured seismologically, but no purely fluid-dynamical mechanism
can explain its existence. Here we argue that a self-consistent model
requires a large-scale magnetic field in the Sun's interior, as well
as consideration of the Coriolis effects in the convection zone and
in the tachocline. Turbulent stresses in the convection zone induce
(through Coriolis effects) a meridional circulation, causing the gas
from the convection zone to burrow downwards, thereby generating the
horizontal and vertical shear that characterizes the tachocline. The
interior magnetic field stops the burrowing, and confines the shear,
as demanded by the observed structure of the tachocline. We outline a
dynamical theory of the flow, from which we estimate a field strength
of about 10-4 tesla just beneath the tachocline. An
important test of this picture, after numerical refinement, will be
quantitative consistency between the predicted and observed interior
angular velocities.
Title: On the Power Distribution of Solar p MODES
Authors: Chang, H. -Y.; Gough, D. O.
Bibcode: 1998SoPh..181..251C
Altcode:
We present a simple idealized model of stochastically forced solar
oscillations, and compare the distribution function of energy, averaged
over 12-hour intervals, with that of low-degree solar modes. We find
that the simulated energy distribution is similar to the observations,
except at extremely high energy.
Title: Phase Inversion: Inferring Solar Subphotospheric Flow and
Other Asphericity from the Distortion of Acoustic Waves
Authors: Gough, Douglas; Merryfield, William J.; Toomre, Juri
Bibcode: 1998ApJ...501..882G
Altcode:
A method is proposed for analyzing an almost monochromatic train of
waves propagating in a single direction in an inhomogenous medium that
is not otherwise changing in time. An effective phase is defined in
terms of the Hilbert transform of the wave function, which is related,
via the JWKB approximation, to the spatial variation of the background
state against which the wave is propagating. The contaminating effect
of interference between the truly monochromatic components of the train
is eliminated using its propagation properties. Measurement errors,
provided they are uncorrelated, are manifest as rapidly varying noise;
although that noise can dominate the raw phase-processed signal, it can
largely be removed by low-pass filtering. The intended purpose of the
analysis is to determine the distortion of solar oscillations induced by
horizontal structural variation and material flow. It should be possible
to apply the method directly to sectoral modes. The horizontal phase
distortion provides a measure of longitudinally averaged properties
of the Sun in the vicinity of the equator, averaged also in radius
down to the depth to which the modes penetrate. By combining such
averages from different modes, the two-dimensional variation can be
inferred by standard inversion techniques. After taking due account
of horizontal refraction, it should be possible to apply the technique
also to locally sectoral modes that propagate obliquely to the equator
and thereby build a network of lateral averages at each radius, from
which the full three-dimensional structure of the Sun can, in principle,
be determined as an inverse Radon transform.
Title: On the Composition of the Solar Interior Rapporteur Paper I
Authors: Gough, Douglas
Bibcode: 1998SSRv...85..141G
Altcode:
Standard solar models, although they are free from the influence of
much of the fluid motion that is bound to be present in the Sun, have
been shown by helioseismology to represent the spherically averaged
structure of the Sun amazingly well. This state of affairs has come
about after painstaking refinements by a great many people of the
pertinent microphysics, including that which controls the equation
of state, the opacity, the nuclear reaction rates and the diffusion
that inhibits gravitational segregation of chemical elements. It has
instilled confidence in the modellers in being able to predict the
composition of the solar interior. But there are consequences of the
flow, related particularly to redistribution of chemical species, that
can be difficult to identify observationally, yet which may degrade
any inferences we might make. Their potential presence must at least
be acknowledged by anyone who tries to asses the reliability of the
models. This report summarizes the discussions in the preceding pages
of this volume of the current theoretical and observational status of
the subject, pointing to many of the caveats that have been raised,
and attempting at the same time to put them into a seemingly coherent
discourse in the context of our present understanding of the workings
of the solar interior.
Title: The Sun is not severely deficient in heavy elements
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1998Obs...118...25C
Altcode:
No abstract at ADS
Title: Helioseismic Determination of the Solar Tachocline Thickness
Authors: Elliott, J. R.; Gough, D. O.; Sekii, T.
Bibcode: 1998ESASP.418..763E
Altcode: 1998soho....6..763E
Inversions of rotational splitting data reveal the existence of a
shear layer at the base of the convection zone, which is known as the
tachocline. The angular velocity in the convection zone varies with
latitude, whereas the angular velocity in the outer layers of the
radiative envelope is more nearly uniform. The differential rotation
of the convection zone is no doubt driven by anisotropic Reynolds
stresses associated with the turbulent convection. It is likely
that the radiative envelope is held rigid by a large-scale magnetic
field. The transition between the two is too sharp to be resolved
by the seismic splitting data. However, it must necessarily support
an Ekman circulation (Spiegel & Zahn, 1992), which advects heavy
elements that have settled under gravity back into the convection zone,
causing an abrupt discontinuity in chemical composition at the base of
the tachocline, thereby modifying the hydrostatic stratification. We
have calibrated theoretical solar models incorporating the tachocline
mixing against the latest seismic data from SOI/MDI, from which we have
obtained a value for the tachocline thickness which is substantially
more precise than the formal resolving power of the seismic data.
Title: Calibrating the Upper Convective Boundary Layer of the Sun
using MDI/SOI Data
Authors: Lopes, I.; Gough, D.
Bibcode: 1998ESASP.418..485L
Altcode: 1998soho....6..485L
No abstract at ADS
Title: Some Comments on Phase Inversions
Authors: Gough, D. O.; Sekii, T.; Toomre, J.
Bibcode: 1998ESASP.418..789G
Altcode: 1998soho....6..789G
The method of phase inversion have been proposed and tested for simple
cases by Gough, Merryfield and Toomre(1991,1993,1998) for detection of
inhomogeneity in media by observing wave propagation. We discuss some of
the difficulties that are encountered with the procedure in practice,
and what might be done to overcome them in transferring the technique
to the solar case, such as in the study of horizontal inhomogeneity in
the solar cavity along the equator using the MDI sectoral-mode data. A
complication seems to arise, aside from observational problems, from
the fact that the waves are not only scattered by inhomogeneity, but
are also excited and damped, as is observed in the broadening of the
ridges in the k-ω diagram.
Title: On the Composition of the Solar Interior
Authors: Gough, D.
Bibcode: 1998sce..conf..141G
Altcode:
No abstract at ADS
Title: On the Influence of Unaccounted Error Correlations of Linear
Inversions
Authors: Gough, D. O.; Sekii, T.
Bibcode: 1998ESASP.418..787G
Altcode: 1998soho....6..787G
Continuing our previous study (Gough 1996, also see Kosovichev et
al. 1995) on the effects of correlated errors on linear inversions,
we investigate how the optimally localized averaging method and the
regularized least-square fitting method, both of which are `optimal'
in different ways, respond differently to the use of wrong covariance
matrices in one-dimensional rotation inversions. Our results demonstrate
how important it is to exercise care in estimating error correlations
when trying to extract mode frequencies from helioseismic data.
Title: On Solar Frequency Changes
Authors: Cunha, M. S.; Brüggen, M.; Gough, D. O.
Bibcode: 1998ESASP.418..905C
Altcode: 1998soho....6..905C; 1998astro.ph..7123C
The structure of the surface layers of the Sun is changed by the
magnetic activity. This, in turn, affects the boundary of the acoustic
cavity, consequently changing the propagation times and frequencies
of resonant modes of oscillation. Currently available observations
are compared to ascertain whether or not it is plausible that the
frequency changes are produced predominantly by sunspots.
Title: LOI/SOHO constraints on oblique rotation of the solar core
Authors: Gizon, L.; Appourchaux, T.; Gough, D. O.
Bibcode: 1998IAUS..185...37G
Altcode:
The Sun is usually assumed to rotate about a single axis, tilted with
respect to the ecliptic normal by an angle of 7.25 degrees. Although
we have an excellent knowledge of the direction of the rotation axis of
the photospheric layers, we cannot exclude a priori that the direction
of the rotation axis could vary as a function of radius. We have tried
to check whether the assumption of rotation about a unique axis is
consistent with helioseismic data. We report on an attempt to measure
the directions of the pulsation axes of several low-degree modes of
oscillation in the LOI/SOHO Fourier spectra.
Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes
Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.;
Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.;
Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T.
Bibcode: 1998ESASP.418...95A
Altcode: 1998soho....6...95A
The amplitudes of solar p-modes decrease steeply with decreasing
radial order below about 17. The background solar signal (solar noise)
in general increases steadily with decreasing frequency. For the
irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this
combination makes it difficult to detect low degree modes below about
1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the
ground based BISON network is significantly lower in this region than
in intensity measurements. This allows low degree modes to be observed
close to 1 mHz. We present results of detection and charaterization
of the lowest order observable p-modes both in velocity and intensity
measurements. Where applicable the properties of the modes observed
with the two methods are compared.
Title: On the Effect of Acoustical Radiation on Convection in
Solar-type Stars
Authors: Houdek, G.; Gough, D. O.
Bibcode: 1998ESASP.418..479H
Altcode: 1998soho....6..479H
Essentially all the theories used today for computing the stratification
of convection zones in stellar models assume the anelastic approximation
to the fluid equations. In this approximation the time derivative
in the density fluctuation in the continuity equation is neglected,
which is equivalent to filtering-out high-frequency phenomena such as
sound waves. This approximation is certainly not valid in the upper
layers of the convective domain in solar-type stars and red giants,
where the convective velocities of the turbulent elements may become
comparable with the local sound speed in the background fluid. Through
the generation of sound waves (Lighthill mechanism), kinetic energy
from the turbulent motion will be converted into acoustic radiation and
thus reduce the efficacy with which the motion might otherwise have
released potential energy originating from the buoyancy forces. In
this contribution we investigate the effect of acoustical radiation
upon the retardation of the convective velocities in solar-type stars
with masses of (1.0 -- 1.9) Modot. The turbulent fluxes
(heat and momentum) are obtained from a nonlocal generalization of
the mixing-length theory. The acoustic flux is assumed to be generated
by the fluctuating Reynolds stress (quadrupole emission) and is thus
proportional to the eighth power of the convective velocities. Through
the inclusion of the acoustic flux in the equilibrium model, the
turbulent Mach number for a 1.6 Modot ZAMS star is found
to be reduced by about 10%.
Title: Rotation and Zonal Flows in the Solar Envelope from the
SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
T.; Title, A. M.; Thompson, M. J.; Toomre, J.
Bibcode: 1997AAS...191.7310S
Altcode: 1997BAAS...29.1322S
We report on the latest inferences concerning solar differential
rotation that have been drawn from the helioseismic data that are now
available from the Solar Oscillations Investigation (SOI) using the
Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
(SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
Lagrangian point L_1, in order to obtain continuous Doppler-imaged
observations of the sun with high spatial fidelity. Doppler velocity,
intensity and magnetic field images are recorded, based on modulations
of the 676.8 nm Ni I solar absorption line. The high spatial resolution
of MDI thereby permits the study of many millions of global resonant
modes of solar oscillation. Determination and subsequent inversion
of the frequencies of these modes, including the degeneracy-splitting
by the rotation of the sun, enables us to infer how the sun's angular
velocity varies throughout much of the interior. The current MDI data
are providing substantial refinements to the helioseismic deductions
that can be made about differential rotation both within the convection
zone and in its transition to the radiative interior. The shearing
layer evident in the angular velocity Omega just below the solar
surface is becoming better defined, as is the adjustment layer or
tachocline near the base of the convection zone. The MDI data are also
revealing a prominent decrease in Omega at high latitudes from the
rotation rate expressed by a simple three-term expansion in latitude
that was originally deduced from surface Doppler measurements. Further,
there are indications that a submerged polar vortex involving somewhat
faster Omega than its surroundings exists at about 75(deg) in latitudes.
Title: On Electrostatic Screening of Ions in Astrophysical Plasmas
Authors: Brüggen, M.; Gough, D. O.
Bibcode: 1997ApJ...488..867B
Altcode: 1997astro.ph..2102B
There has been some controversy over the expression for the so-called
interaction energy associated with screening of charged particles
in a plasma. Even in the relatively simple case of weak screening,
first discussed in the context of astrophysical plasmas by Salpeter,
there is disagreement. In particular, Shaviv and Shaviv have recently
claimed that by not considering explicitly the complete screening cloud
in his calculation, Salpeter obtained a result for the interaction
energy between two nuclei separated by a distance r that in the limit r
--> 0 is only 2/3 the correct value. It appears that this claim has
arisen from a fundamental misconception concerning the dynamics of the
interaction. We rectify this misconception, and show that Salpeter's
formula is indeed correct.
Title: Obituaries: Roger John Tayler
Authors: Gough, Douglas
Bibcode: 1997PhT....50i..98G
Altcode:
No abstract at ADS
Title: Solar physics: Gravity waves with a new spin
Authors: Gough, Douglas
Bibcode: 1997Natur.388..324G
Altcode:
No abstract at ADS
Title: Essay review The Sun as seen by a stellar physicist
Authors: Gough, D. O.
Bibcode: 1997ConPh..38..431G
Altcode:
Available from http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0010-7514&volume=38&issue=6&spage=431
Title: Structure and Rotation of the Solar Interior: Initial Results
from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
Milford, P. N.
Bibcode: 1997SoPh..170...43K
Altcode:
The medium-l program of the Michelson Doppler Imager instrument on board
SOHO provides continuous observations of oscillation modes of angular
degree, l, from 0 to ∽ 300. The data for the program are partly
processed on board because only about 3% of MDI observations can be
transmitted continuously to the ground. The on-board data processing,
the main component of which is Gaussian-weighted binning, has been
optimized to reduce the negative influence of spatial aliasing of the
high-degree oscillation modes. The data processing is completed in a
data analysis pipeline at the SOI Stanford Support Center to determine
the mean multiplet frequencies and splitting coefficients. The initial
results show that the noise in the medium-l oscillation power spectrum
is substantially lower than in ground-based measurements. This enables
us to detect lower amplitude modes and, thus, to extend the range of
measured mode frequencies. This is important for inferring the Sun's
internal structure and rotation. The MDI observations also reveal the
asymmetry of oscillation spectral lines. The line asymmetries agree
with the theory of mode excitation by acoustic sources localized in the
upper convective boundary layer. The sound-speed profile inferred from
the mean frequencies gives evidence for a sharp variation at the edge
of the energy-generating core. The results also confirm the previous
finding by the GONG (Gough et al., 1996) that, in a thin layer just
beneath the convection zone, helium appears to be less abundant than
predicted by theory. Inverting the multiplet frequency splittings from
MDI, we detect significant rotational shear in this thin layer. This
layer is likely to be the place where the solar dynamo operates. In
order to understand how the Sun works, it is extremely important to
observe the evolution of this transition layer throughout the 11-year
activity cycle.
Title: Structure inversions with the VIRGO data
Authors: Appourchaux, Th.; Sekii, Takashi; Gough, Douglas; Lee, Umin;
Wehrli, Christoph; Virgo Team
Bibcode: 1997IAUS..181..159A
Altcode:
No abstract at ADS
Title: Sounding solar and stellar interiors: Conclusion and prospects
Authors: Gough, D.
Bibcode: 1997IAUS..181..397G
Altcode:
No abstract at ADS
Title: Internal structure and rotation of the Sun: First results
from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
C. J.; Zayer, I.; Milford, P. N.
Bibcode: 1997IAUS..181..203K
Altcode:
No abstract at ADS
Title: First results from VIRGO on SoHO
Authors: Frohlich, C.; Andersen, B. N.; Appourchaux, T.; Berthomieu,
G.; Crommelynck, D. A.; Domingo, V.; Fichot, A.; Finsterle, W.;
Gómez, M. F.; Gough, D.; Jiménez, A.; Leifsen, T.; Lombaerts, M.;
Pap, J. M.; Provost, J.; Roca Cortés, T.; Romero, J.; Roth, H. -J.;
Sekii, T.; Telljohann, U.; Toutain, T.; Wehrli, C.
Bibcode: 1997IAUS..181...67F
Altcode:
No abstract at ADS
Title: First Results from VIRGO, the Experiment for Helioseismology
and Solar Irradiance Monitoring on SOHO
Authors: Fröhlich, Claus; Andersen, Bo N.; Appourchaux, Thierry;
Berthomieu, Gabrielle; Crommelynck, Dominique A.; Domingo, Vicente;
Fichot, Alain; Finsterle, Wolfgang; Gómez, Maria F.; Gough, Douglas;
Jiménez, Antonio; Leifsen, Torben; Lombaerts, Marc; Pap, Judit M.;
Provost, Janine; Roca Cortés, Teodoro; Romero, José; Roth, Hansjörg;
Sekii, Takashi; Telljohann, Udo; Toutain, Thierry; Wehrli, Christoph
Bibcode: 1997SoPh..170....1F
Altcode:
First results from the VIRGO experiment (Variability of solar IRradiance
and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and
Heliospheric Observatory) are reported. The observations started
mid-January 1996 for the radiometers and sunphotometers and near the
end of March for the luminosity oscillation imager. The performance of
all the instruments is very good, and the time series of the first 4-6
months are evaluated in terms of solar irradiance variability, solar
background noise characteristics and p-mode oscillations. The solar
irradiance is modulated by the passage of active regions across the
disk, but not all of the modulation is straightforwardly explained in
terms of sunspot flux blocking and facular enhancement. Helioseismic
inversions of the observed p-mode frequencies are more-or-less in
agreement with the latest standard solar models. The comparison of
VIRGO results with earlier ones shows evidence that magnetic activity
plays a significant role in the dynamics of the oscillations beyond
its modulation of the resonant frequencies. Moreover, by comparing
the amplitudes of different components ofp -mode multiplets, each of
which are influenced differently by spatial inhomogeneity, we have
found that activity enhances excitation.
Title: The seismic structure of the Sun from GONG
Authors: Anderson, E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre,
S. M.; Christensen-Dalsgaard, J.; Eff-Darwich, A.; Elliott, J. R.;
Giles, P. M.; Gough, D. O.; Guzik, J. A.; Harvey, J. W.; Hill,
F.; Leibacher, J. W.; Kosovichev, A. G.; Monteiro, M. J. P. F. G.;
Richard, O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.;
Toomre, J.; Vauclair, S.; Vorontsov, S. V.
Bibcode: 1997IAUS..181..151A
Altcode:
No abstract at ADS
Title: Astereoasteroseismology
Authors: Gough, D. O.
Bibcode: 1996Obs...116..313G
Altcode:
No abstract at ADS
Title: Perspectives in Helioseismology
Authors: Gough, D. O.; Leibacher, J. W.; Scherrer, P. H.; Toomre, J.
Bibcode: 1996Sci...272.1281G
Altcode:
Helioseismology is probing the interior structure and dynamics of
the sun with ever-increasing precision, providing a well-calibrated
laboratory in which physical processes can be studied under conditions
that are unattainable on Earth. Nearly 10 million resonant modes
of oscillation are observable in the solar atmosphere, and their
frequencies need to be known with great accuracy in order to gauge the
sun's interior. The advent of nearly continuous imaged observations
from the complementary ground-based Global Oscillation Network Group
(GONG) observatories and the space-based Solar and Heliospheric
Observatory instruments augurs a new era of discovery. The flow of
early results from GONG resolves some issues and raises a number of
theoretical questions whose answers are required for understanding
how a seemingly ordinary star actually operates.
Title: The Current State of Solar Modeling
Authors: Christensen-Dalsgaard, J.; Dappen, W.; Ajukov, S. V.;
Anderson, E. R.; Antia, H. M.; Basu, S.; Baturin, V. A.; Berthomieu,
G.; Chaboyer, B.; Chitre, S. M.; Cox, A. N.; Demarque, P.; Donatowicz,
J.; Dziembowski, W. A.; Gabriel, M.; Gough, D. O.; Guenther, D. B.;
Guzik, J. A.; Harvey, J. W.; Hill, F.; Houdek, G.; Iglesias, C. A.;
Kosovichev, A. G.; Leibacher, J. W.; Morel, P.; Proffitt, C. R.;
Provost, J.; Reiter, J.; Rhodes, E. J., Jr.; Rogers, F. J.; Roxburgh,
I. W.; Thompson, M. J.; Ulrich, R. K.
Bibcode: 1996Sci...272.1286C
Altcode:
Data from the Global Oscillation Network Group (GONG) project and
other helioseismic experiments provide a test for models of stellar
interiors and for the thermodynamic and radiative properties, on which
the models depend, of matter under the extreme conditions found in the
sun. Current models are in agreement with the helioseismic inferences,
which suggests, for example, that the disagreement between the predicted
and observed fluxes of neutrinos from the sun is not caused by errors in
the models. However, the GONG data reveal subtle errors in the models,
such as an excess in sound speed just beneath the convection zone. These
discrepancies indicate effects that have so far not been correctly
accounted for; for example, it is plausible that the sound-speed
differences reflect weak mixing in stellar interiors, of potential
importance to the overall evolution of stars and ultimately to estimates
of the age of the galaxy based on stellar evolution calculations.
Title: The Seismic Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toomre, J.; Anderson,
E.; Antia, H. M.; Basu, S.; Chaboyer, B.; Chitre, S. M.;
Christensen-Dalsgaard, J.; Dziembowski, W. A.; Eff-Darwich, A.;
Elliott, J. R.; Giles, P. M.; Goode, P. R.; Guzik, J. A.; Harvey,
J. W.; Hill, F.; Leibacher, J. W.; Monteiro, M. J. P. F. G.; Richard,
O.; Sekii, T.; Shibahashi, H.; Takata, M.; Thompson, M. J.; Vauclair,
S.; Vorontsov, S. V.
Bibcode: 1996Sci...272.1296G
Altcode:
Global Oscillation Network Group data reveal that the internal
structure of the sun can be well represented by a calibrated standard
model. However, immediately beneath the convection zone and at the
edge of the energy-generating core, the sound-speed variation is
somewhat smoother in the sun than it is in the model. This could be a
consequence of chemical inhomogeneity that is too severe in the model,
perhaps owing to inaccurate modeling of gravitational settling or to
neglected macroscopic motion that may be present in the sun. Accurate
knowledge of the sun's structure enables inferences to be made about
the physics that controls the sun; for example, through the opacity,
the equation of state, or wave motion. Those inferences can then be
used elsewhere in astrophysics.
Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
Bibcode: 1996Sci...272.1300T
Altcode:
Splitting of the sun's global oscillation frequencies by large-scale
flows can be used to investigate how rotation varies with radius
and latitude within the solar interior. The nearly uninterrupted
observations by the Global Oscillation Network Group (GONG) yield
oscillation power spectra with high duty cycles and high signal-to-noise
ratios. Frequency splittings derived from GONG observations confirm
that the variation of rotation rate with latitude seen at the surface
carries through much of the convection zone, at the base of which is
an adjustment layer leading to latitudinally independent rotation at
greater depths. A distinctive shear layer just below the surface is
discernible at low to mid-latitudes.
Title: The Internal Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; GONG Structure Inversions
Team
Bibcode: 1996AAS...188.5303G
Altcode: 1996BAAS...28..903G
The principal first inferences that have been drawn from the GONG data
concerning the internal structure of the Sun will be reported. After
explaining briefly the procedures by which the inferences have been
drawn, deviations of the spherically averaged structure of the Sun
from that of standard solar models will be presented. Those deviations
occur predominantly near the base of the convection zone, and perhaps
in the energy-generating core. There is also evidence for a deviation
from spherical symmetry, principally near the surface. The possible
physical implications of our findings will be discussed.
Title: Inferring Spatial Variation of Solar Properties from
Helioseismic Data
Authors: Gough, D. O.; Sekii, T.; Stark, P. B.
Bibcode: 1996ApJ...459..779G
Altcode:
A common method to infer that solar properties vary with position is
to compare linear estimates of averages of those properties centered
at different locations. If some of the confidence intervals for the
averages do not overlap, one concludes that the property varies. In
order for this conclusion to be statistically valid, the lengths of
the intervals must be adjusted to obtain the correct "simultaneous
coverage probability." We illustrate the notion of simultaneous coverage
probability using coin tossing as an example. We present four methods
for adjusting the lengths of confidence intervals for linear estimates,
and a complementary approach to infer changes based on constructing
a linear estimator that is directly sensitive to changes. The first
method for constructing simultaneous confidence intervals is based
on Bonferroni's inequality, and applies generally to confidence
intervals for any set of parameters, from dependent or independent
observations. The second method is based on a 2 measure of fit to the
data, which allows one to compute s1multaneous confidence intervals for
any number of linear functionals of the model. The third method uses a
^{2 }distribution in the space of estimates, which yields "Scheffe'"
confidence intervals for the functionals. The fourth method, which
produces the shortest confidence intervals, uses the infinity-norm
in the space of estimates to construct "maximum-modulus" confidence
intervals. We apply the four methods to search for radial changes in
averages of solar angular velocity, using data from Big Bear Solar
Observatory (BBSO) averaged for the 4 yr 1986, 1988-1990. Finally,
we apply the new differencing estimator to the BBSO data, finding
strong evidence that the average solar angular velocity is lower near
the poles than near the equator over a range of depths, as is observed
at the surface as well.
Title: STARS - Seismic Telescope for Astrophysical Research from
Space. Report on the phase A study.
Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen,
S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortés, T.; Roxburgh,
I. W.; Sterken, C.; Volonté, S.
Bibcode: 1996star.book.....B
Altcode:
STARS is an asteroseismology mission, which, through the acquisition of
very accurate light curves, will detect oscillations in a wide variety
of stars. This will allow, for the first time, the internal structure
of stars of different age, composition and spectral type, to be studied
directly, bringing the spectacular successes of helioseismology within
reach for a large number of other stars spreading over most of the
Hertzsprung-Russell diagram, including solar-type stars in open
clusters. The results of the phase A study are presented in this report.
Title: Structural changes to the Sun through the solar cycle
Authors: Balmforth, N. J.; Gough, D. O.; Merryfield, W. J.
Bibcode: 1996MNRAS.278..437B
Altcode:
Measurements of both solar irradiance and 5-min oscillation frequencies
indicate that the structure of the Sun changes with the solar cycle. We
report calculations addressing how global changes in the stratification
of a star are induced by an internal thermal disturbance, and how
this in turn affects the characteristic pulsation frequencies. The
results indicate that deeply seated perturbations of the stratification
invariably lead to relatively large radius changes over the cycle,
contrary to observation. Moreover, the structural changes resulting
from such perturbations predict oscillation frequency changes that do
not reproduce the observed dependence on mode frequency. Therefore a
magnetic layer at the base of the solar convection zone, for example,
cannot be directly responsible for the dominant contribution to the
observed structural changes. Disturbances near the surface of the
Sun, on the other hand, lead to pulsation frequency changes which do
reproduce observations. However, the luminosity is then predicted to
decrease from solar minimum to maximum, by an amount that is about
45 times the increase observed. Thus purely thermal changes in the
superficial layers of the Sun also fail to account for the observed
structural variations.
Title: The Success Story of the Transfer and Development of Methods
from Geophysics to Helioseismology
Authors: Gough, Douglas
Bibcode: 1996imie.conf....1G
Altcode:
No abstract at ADS
Title: STARS: Seismic Telescope for Astrophysical Research from Space
Authors: Badiali, M.; Catala, C.; Favata, F.; Fridlund, M.; Frandsen,
S.; Gough, D. O.; Hoyng, P.; Pace, O.; Roca-Cortes, T.; Roxburgh,
I. W.; Sterken, C.; Volonte, A.
Bibcode: 1996ESADS...4....1B
Altcode:
No abstract at ADS
Title: Testing solar models: the inverse problem.
Authors: Gough, D.
Bibcode: 1996stsu.conf..141G
Altcode:
The following topics were dealt with: the idea of inversion; on
model-calibration; direct asymptotic inversions; formulating linear
helioseismic inverse problems; on 'solving' linearized inverse
problems in one dimension; linearized two-dimensional inversions;
towards realism.
Title: VIRGO: Experiment for Helioseismology and Solar Irradiance
Monitoring
Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli,
Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente;
Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost,
Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier,
André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema,
Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés,
Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C.
Bibcode: 1995SoPh..162..101F
Altcode:
The scientific objective of the VIRGO experiment (Variability of solar
IRradiance and Gravity Oscillations) is to determine the characteristics
of pressure and internal gravity oscillations by observing irradiance
and radiance variations, to measure the solar total and spectral
irradiance and to quantify their variability over periods of days to
the duration of the mission. With these data helioseismological methods
can be used to probe the solar interior. Certain characteristics of
convection and its interaction with magnetic fields, related to, for
example, activity, will be studied from the results of the irradiance
monitoring and from the comparison of amplitudes and phases of the
oscillations as manifest in brightness from VIRGO, in velocity from
GOLF, and in both velocity and continuum intensity from SOI/MDI. The
VIRGO experiment contains two different active-cavity radiometers for
monitoring the solar `constant', two three-channel sunphotometers (SPM)
for the measurement of the spectral irradiance at 402, 500 and 862 nm,
and a low-resolution imager (LOI) with 12 pixels, for the measurement
of the radiance distribution over the solar disk at 500 um. In this
paper the scientific objectives of VIRGO are presented, the instruments
and the data acquisition and control system are described in detail,
and their measured performance is given.
Title: Global Oscillations at Low Frequency from the SOHO Mission
(GOLF)
Authors: Gabriel, A. H.; Grec, G.; Charra, J.; Robillot, J. -M.; Roca
Cortés, T.; Turck-Chièze, S.; Bocchia, R.; Boumier, P.; Cantin, M.;
Cespédes, E.; Cougrand, B.; Crétolle, J.; Damé, L.; Decaudin, M.;
Delache, P.; Denis, N.; Duc, R.; Dzitko, H.; Fossat, E.; Fourmond,
J. -J.; García, R. A.; Gough, D.; Grivel, C.; Herreros, J. M.;
Lagardère, H.; Moalic, J. -P.; Pallé, P. L.; Pétrou, N.; Sanchez,
M.; Ulrich, R.; van der Raay, H. B.
Bibcode: 1995SoPh..162...61G
Altcode:
The GOLF experiment on the SOHO mission aims to study the internal
structure of the sun by measuring the spectrum of global oscillations in
the frequency range 10−7 to 10−2 Hz. Bothp
andg mode oscillations will be investigated, with the emphasis on
the low order long period waves which penetrate the solar core. The
instrument employs an extension to space of the proven ground-based
technique for measuring the mean line-of-sight velocity of the viewed
solar surface. By avoiding the atmospheric disturbances experienced
from the ground, and choosing a non-eclipsing orbit, GOLF aims to
improve the instrumental sensitivity limit by an order of magnitude
to 1 mm s−1 over 20 days for frequencies higher than
2.10−4 Hz. A sodium vapour resonance cell is used in
a longitudinal magnetic field to sample the two wings of the solar
absorption line. The addition of a small modulating field component
enables the slope of the wings to be measured. This provides not only
an internal calibration of the instrument sensitivity, but also offers a
further possibility to recognise, and correct for, the solar background
signal produced by the effects of solar magnetically active regions. The
use of an additional rotating polariser enables measurement of the
mean solar line-of-sight magnetic field, as a secondary objective.
Title: Slow rotation of the Sun's interior
Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller,
B. A.; New, R.; Wheeler, S. J.; Gough, D. O.
Bibcode: 1995Natur.376..669E
Altcode:
THE rotation of the Sun is not that of a rigid body; at its surface,
the gas near the poles has a lower angular velocity than that near
the equator1. This latitudinal variation persists to
the base of the convection zone, below which the angular velocity
becomes approximately uniform2,3. Any variations
of angular velocity at much greater depths are, however, poorly
constrained4-10. Observations of solar oscillation modes
have been used to probe density variations in the Sun; rotational
splitting of degenerate modes, although difficult to resolve, provides
important constraints on the dynamical structure11. Here we
report observations of rotationally split modes made over a three-year
period with the Birmingham Solar Oscillations Network. Our results
indicate that there is a substantial region inside the Sun that is
rotating more slowly than the surface. This situation seems likely
to be transient—the minimum-energy state would have all the deeper
regions rotating with the same angular velocity—and is at variance
with our current ideas about the rotational evolution of main-sequence
stars12. We have no solution to the dynamical problem
this poses.
Title: Waves in the wind
Authors: Gough, Douglas
Bibcode: 1995Natur.376..120G
Altcode:
No abstract at ADS
Title: On Frequency Determination and Temporal Data Sampling
Authors: Chang, H. -Y.; Gough, D.; Sekii, T.
Bibcode: 1995ESASP.376b.175C
Altcode: 1995soho....2..175C; 1995help.confP.175C
The authors have further developed the procedure described by Chang
and Gough (1995) in GONG94 to analyse low-degree helioseismic time
series. An idealized model was used to construct artifical data
representing a superposition of undamped oscillations in a cavity which
is varying slowly with time in an unknown manner. The procedure involves
matching a model of the data to the actual data by minimizing a measure
of misfit. This requires a multidimensional parameter search which,
if a generic procedure such as the simplex algorithm used for GONG94
is employed, is computationally expensive. The authors have developed
an efficient scheme tailored explicitly to the problem in hand, which
uses a combination of an approximate factorization of the parameter
space with an alternation of a jumping algorithm between local minima
and Newton-Ralphson iteration.
Title: Is There a Seismic Signature of the Sun's Magnetic Field?
Authors: Zweibel, E. G.; Gough, D.
Bibcode: 1995ESASP.376b..73Z
Altcode: 1995soho....2...73Z; 1995help.confP..73Z
Both weak magnetic fields and latitudinally dependent acoustic
perturbations remove the degeneracy with respect to the azimuthal
quantum number m of acoustic modes of an otherwise spherically
symmetrical solar model. In the case of acoustic perturbations,
the degeneracy is removed because the range of latitude in which a
mode propagates depends on m, and therefore modes of like principal
order n and degree l sample the aspherical (scalar) sound-speed
distribution differently. In the magnetic case too, the removal of the
degeneracy is caused by the same geometrical effect, and it is also
influenced by the anisotropy of the Lorentz forces. Given any set of
frequency splittings arising from a perturbation to the equilibrium
configuration, it is possible to invert them to solve for a purely
acoustic perturbation that might have produced them. In particular,
if those splittings were actually produced by a magnetic field, there
is thus an acoustic perturbation that mimics the field. The authors
use asymptotic analysis to show that the frequency splittings cannot
be unambiguously attributed to the direct effect of a magnetic field.
Title: Analysis of Helioseismic Wave Fields to Examine Horizontal
Structures
Authors: Julien, K. A.; Gough, D. O.; Toomre, J.
Bibcode: 1995ESASP.376b.155J
Altcode: 1995help.confP.155J; 1995soho....2..155J
Presents and evaluates a preliminary inversion procedure for carrying
out a local area analysis on simulated oscillation data to deduce
two-dimensional subsurface structures in the horizontal, representative
of thermal variations, potentially as function of depth.
Title: Observational Constraints on the Internal Solar Angular
Velocity
Authors: Sekii, T.; Genovese, C. R.; Gough, D. O.; Stark, P. B.
Bibcode: 1995ESASP.376b.279S
Altcode: 1995help.confP.279S; 1995soho....2..279S
No abstract at ADS
Title: An Attempt to Measure Latitudinal Variation of the Depth of
the Convection Zone
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1995ESASP.376b..47G
Altcode: 1995help.confP..47G; 1995soho....2...47G
The location of the base of the convection zone coincides with the
sharp variation of the slope of the relative difference in the quantity
u = p/ρ between the Sun and a solar model, provided that the zone
of adiabatic convection is deeper in the model than in the Sun. The
authors have determined the difference δu/u as a function of radius at
various latitudes between the Sun and a spherically symmetrical solar
model by inverting the BBSO data (Libbrecht and Woodard, 1993). The
results offer evidence that the convection zone may be somewhat deeper
at the equator than it is at the poles. The variation of the depth,
however, does not exceed 0.2 Rsun.
Title: On the Elimination of the Influence of Uncertain Surface
Layers on Inversions of the Structure and Rotation of the Sun
Authors: Gough, D. O.
Bibcode: 1995ESASP.376b..49G
Altcode: 1995help.confP..49G; 1995soho....2...49G
Uncertainties in the structure of the superficial layers of the Sun,
and additionally in the physics of the oscillations in those layers,
can lead to substantial uncertainties in the oscillation eigenfunctions
and the associated eigenfrequencies. However, the functional form of
the errors that may arise is sufficiently restricted that the errors
in the eigenfunctions in all but the uncertain outer layers can be
corrected. Consequently, the influence of those uncertainties can
essentially be confined to remain within the outer layers, permitting
subsequent execution of the usual inversion procedures to determine
conditions deep in the interior. As a byproduct, information about the
outer convective boundary layer is also obtained. This paper outlines
the broad principles behind the elimination procedure in the context
of inversion of free-oscillation frequencies.
Title: Local-Area Analysis of High-Degree Solar Oscillations: New
Ring-Fitting Procedures
Authors: Haber, D. A.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1995ESASP.376b.141H
Altcode: 1995help.confP.141H; 1995soho....2..141H
Local-area analysis of five-minute solar oscillations using ring
diagrams to determine subphotospheric velocity flows is on the brink
of becoming an important tool in understanding convective zone
dynamics. One of the main problems up to this point has been the
large computational burden of fitting the rings. The authors present a
faster method for carrying out the ring fits using data obtained with
the High-l Helioseismometer at Kitt Peak. The authors first eliminate
serious sources of noise, then use a perturbation approach to fit the
azimuthally averaged spectrum. The parameters so determined are held
constant while fitting the entire ring diagram.
Title: Time-Series Analysis of Oscillations with Gaps
Authors: Chang, H. -Y.; Gough, D.
Bibcode: 1995ESASP.376b.179C
Altcode: 1995help.confP.179C; 1995soho....2..179C
It is almost impossible to avoid temporal gaps in solar oscillation
data from ground-based observations. Even though there exist general
deconvolution algorithms designed to suppress noise due to gaps,
techniques that take little or no account of the physics responsible for
the data must necessarily fail when the duty cycle is low. The authors
demonstrate a simple but effective method to remove the deleterious
effects of the gaps by fitting the temporal signal to a model produced
by the superposition of many modes, rather than using its power
spectrum. This technique uses the fact that the unknown component to the
wandering of the amplitude and phases of the constituent oscillators
arising from the temporal variation of the cavity in which they are
confined are related to each other in a known way. The technique can
be used to determine the natural frequencies of modes more precisely,
and also to reproduce an underlying frequency modulation function.
Title: Seismology of the solar envelope: measuring the acoustic
phase shift generated in the outer layers
Authors: Gough, D. O.; Vorontsov, S. V.
Bibcode: 1995MNRAS.273..573G
Altcode:
Partial reflection of acoustic waves by regions of rapid spatial
variation modulates the solar p-mode frequencies, in a manner that
is often described in terms of an acoustic phase alpha. At low
degree, alpha is a function of frequency alone. At higher degrees,
the inclination of the acoustic ray paths from the normal to the
reflecting layers becomes significant, and gives rise to a degree
dependence. With the current accuracy of frequency measurements,
this phenomenon is significant for all the p modes trapped in the
convection zone. We describe a technique capable of separating the
degree-dependent component from the leading term alpha_0(omega). We
determine the leading-order contribution to the degree dependence
of alpha from the solar p-mode frequencies reported by Libbrecht,
Woodard & Kaufman, and compare the results with direct computations
from a solar model based on the formalism described by Brodsky &
Vorontsov. The dominant contribution comes from the second helium
ionization zone, and can be used as a new source of information relevant
to the helioseismic calibration of the equation of state of the solar
plasma and to the determination of the solar helium abundance.
Title: Constrained Estimates of Low-Degree Mode Frequencies and the
Determination of the Interior Structure of the Sun
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
Bibcode: 1995SoPh..157....1G
Altcode:
Low-degreep-modes penetrate to the solar centre and provide direct
information about the core. However, the high observational accuracy
that is required to resolve the details of the structure of the core
is difficult to achieve because the oscillation power spectrum is
significantly distorted by stochastic forcing of the oscillations,
which appears as multiplicative noise. Here, an attempt is reported to
reduce uncertainties of spectral parameter estimation by incorporating
constraints imposed by smooth behaviour of some of the parameters
(e.g., linewidths, background noise, rotational splitting) over a
group of lines. Instead of estimating these parameters independently
for each line, we determine them as smooth functions of frequency. It
is expected that this procedure gives more accurate estimates of the
average frequencies of any multiplet in the power spectrum, to which
we have applied no constraints. We give some examples of the procedure
for whole-disk measurements by the IPHIR space experiment. It is shown
that the additional constraints do not result in significant changes
in the frequency estimates, except for one mode whose peak in the power
spectrum has the lowest signal-to-noise ratio. However, the uncertainty
in the frequency of that mode does not influence substantially the
results of the structure inversion in the core. Inversions of the IPHIR
datasets are compared with corresponding inversions of data from the
Birmingham Solar Oscillation Network (BISON). The IPHIR data indicate
a sharp increase towards the centre of the deviation of the squared
sound speed of the sun from that of a standard solar model, whereas the
BISON data show a decrease. The difference between the IPHIR and BISON
inversions is significant, preventing any definite conclusion about
the deviation of the structure of the solar core from that of the model.
Title: STARS: A Proposal for a Dedicated Space Mission to Study
Stellar Structure and Evolution
Authors: Fridlund, M.; Gough, D. O.; Jones, A.; Appourchaux, T.;
Badiali, M.; Catala, C.; Frandsen, S.; Grec, G.; Roca Cortes, T.;
Schrijver, K.
Bibcode: 1995ASPC...76..416F
Altcode: 1995gong.conf..416F
No abstract at ADS
Title: Inversion for Background Inhomogeneity from Phase Distortion
of Two-Dimensional Wave Fields
Authors: Julien, K.; Gough, D.; Toomre, J.
Bibcode: 1995ASPC...76..196J
Altcode: 1995gong.conf..196J
No abstract at ADS
Title: Testing the Statistical Significance of the Asymmetries of
p-Mode Line Profiles: Application to the IPHIR Data
Authors: Appourchaux, T.; Toutain, T.; Gough, D. O.; Kosovichev, A.
Bibcode: 1995ASPC...76..314A
Altcode: 1995gong.conf..314A
No abstract at ADS
Title: High-Frequency Oscillations of a Polytropic Layer
Authors: Rast, M. P.; Gough, D. O.
Bibcode: 1995ASPC...76..322R
Altcode: 1995gong.conf..322R
No abstract at ADS
Title: Prospects for Asteroseismic Inference
Authors: Gough, D. O.
Bibcode: 1995ASPC...76..551G
Altcode: 1995gong.conf..551G
No abstract at ADS
Title: Constraints on Oblique Rotation of the Solar Core from
Low-Degree Modes
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
Bibcode: 1995ASPC...76...55G
Altcode: 1995gong.conf...55G
No abstract at ADS
Title: Asymptotic Signatures of Jovian Discontinuities
Authors: Gough, D. O.; Sekii, T.
Bibcode: 1995ASPC...76..374G
Altcode: 1995gong.conf..374G
No abstract at ADS
Title: Working Group 9 - Interior Structure and Inversions
Authors: Kosovichev, A. G.; Basu, S.; Christensen-Dalsgaard, J.;
Eff-Darwich, A.; Gough, D. O.; Iglesias, C. A.; Pérez-Hernández,
F.; Rogers, F.; Sekii, T.; Shibahashi, H.
Bibcode: 1995ESASP.376a.211K
Altcode: 1995heli.conf..211K
No abstract at ADS
Title: Inversions of BBSO Rotational Splitting Data
Authors: Sekii, T.; Gough, D. O.; Kosovichev, A. G.
Bibcode: 1995ASPC...76...59S
Altcode: 1995gong.conf...59S
No abstract at ADS
Title: Frequencies of Low-Degree Modes and the Structure of the
Solar Core
Authors: Gough, D. O.; Kosovichev, A. G.; Toutain, T.
Bibcode: 1995ASPC...76..176G
Altcode: 1995gong.conf..176G
No abstract at ADS
Title: Asymptotic Modal Inertia
Authors: Gough, D. O.
Bibcode: 1995ASPC...76..330G
Altcode: 1995gong.conf..330G
No abstract at ADS
Title: The Future of Helioseismology
Authors: Gough, D. O.
Bibcode: 1995ESASP.376a.181G
Altcode: 1995heli.conf..181G; 1995soho....1..181G
Describes some of the inferences that will be made from the helioseismic
data that will be obtained from SOHO and GONG. Data-processing
techniques and inversion procedures are reviewed.
Title: A Narrative Computer Programme for Solar Evolution
Authors: Gough, D. O.; Novotny, E.
Bibcode: 1995LIACo..32..369G
Altcode: 1995sews.book..369G
No abstract at ADS
Title: Rotational Splitting of Low-Degree Solar P Modes
Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller,
B. A.; Wheeler, S. J.; New, R.; Gough, D. O.
Bibcode: 1995ASPC...76...43E
Altcode: 1995gong.conf...43E
No abstract at ADS
Title: Seismic Effects of North-South Asymmetry of Sun's Rotation
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1995ASPC...76...63G
Altcode: 1995gong.conf...63G
No abstract at ADS
Title: On Measuring Solar Frequency Variation
Authors: Chang, H. -Y.; Gough, D. O.
Bibcode: 1995ASPC...76..512C
Altcode: 1995gong.conf..512C
No abstract at ADS
Title: Solar Oscillation Ring Diagrams: Benefits of Great Circle
Remapping
Authors: Haber, D.; Toomre, J.; Hill, F.; Gough, D.
Bibcode: 1995ASPC...76..272H
Altcode: 1995gong.conf..272H
No abstract at ADS
Title: Helioseismology: A Window into the Sun
Authors: Gough, Douglas
Bibcode: 1994AAS...185.3901G
Altcode: 1994BAAS...26.1369G
The sun is vibrating in many modes simultaneously. By listening to
the tones one can try to recognise its structure, just as one can
recognise from its sound a particular musical instrument in a symphony
orchestra. The importance to astrophysics is that it is possible to use
the information to test the theory of the structure and evolution of
stars, and to calibrate theoretical models of the sun. Once we know the
internal state of the sun, we have at our disposal a valuable laboratory
in which we can carry out physical measurements under conditions that
cannot be achieved on Earth. Already, such measurements have caused
a revision in calculations of atomic radiative transitions in dense
plasmas, which has resolved several long-standing problems in stellar
astrophysics. The measurements have also put tight constraints on the
structure of the energy generating core, and have thereby eliminated
many of the suggestions that have been offered to resolve the solar
neutrino problem. Moreover, they have provided us for the first time
direct and somewhat surprising information about the internal rotation,
which has caused us to rethink our ideas about the evolution of the
angular momentum and about the generation of the Sun's magnetic field.
Title: Seismic Consequence of the Shoemaker-Levy Impact
Authors: Gough, D. O.
Bibcode: 1994MNRAS.269L..17G
Altcode:
Comet Shoemaker-Levy 9 is about to collide with Jupiter. The impacts
will be on the far side. However, seismic disturbances induced by
momentum transfer will propagate through the planet to cause waves
on the near-side surface, which will begin to concentrate near the
antipodes about 1.9 h after each impact. Unfortunately, the amplitudes
of the waves are likely to be insufficient to provide an observable
diagnostic of the internal structure of the planet. Key words: waves
- comets: individual: Shoemaker-Levy 9 - planets and satellites:
individual: Jupiter.
Title: A Model of Crustal Conductive Structure In the Canadian
Cordillera
Authors: Majorowicz, Jacek A.; Gough, D. Ian
Bibcode: 1994GeoJI.117..301M
Altcode:
No abstract at ADS
Title: On scintillation obfuscation
Authors: Badiali, M.; Catala, C.; Fossat, E.; Fransden, S.; Gough,
D. O.; Rocca-Cortes, T.; Schrijver, K.
Bibcode: 1994Obs...114...53B
Altcode:
No abstract at ADS
Title: The Solar f-Mode as an Interfacial Mode at the
Chromosphere-Corona Transition
Authors: Rosenthal, C. S.; Gough, D. O.
Bibcode: 1994ApJ...423..488R
Altcode:
Observations of the solar f-mode at intermediate and high spherical
harmonic degree show substantial departures from the dispersion relation
expected for a pure surface gravity oscillation. We suggest that the
waves are reflected by the high density gradient in the region of the
chromosphere-corona transition and are therefore characterized better
as interfacial modes localized near the transition. An analytical
calculation, for a simple model in which the transition is treated as
a discontinuity, shows that such modes have a dispersion relation with
the correct qualitative features to explain the observations. However,
quantitative agreement is not possible for reasonable parameter
values. We next consider a more general atmospheric structure with
a continuous stratification for which asymptotic frequency estimates
are obtained. These are compared with direct numerical solutions of
the differential equations. The frequencies are found to give a much
closer quantitative agreement with the observations. We suggest that
f-mode seismology might be used to obtain direct information about
the average structure of the solar atmosphere and transition region.
Title: Seismology of the Sun and Stars
Authors: Gough, D. O.
Bibcode: 1994ASSL..187..187G
Altcode: 1994fsgb.book..187G
No abstract at ADS
Title: Internal Rotation of the Sun
Authors: Duvall, T. L., Jr.; Dziembowski, W.; Goode, P. R.; Gough,
D. O.; Harvey, J. W.; Leibacher, J. W.
Bibcode: 1994snft.book..414D
Altcode:
No abstract at ADS
Title: Towards a helioseismic calibration of the equation of state
in the solar convective envelope
Authors: Vorontsov, S. V.; Baturin, V. A.; Dappen, W.; Gough, D. O.
Bibcode: 1994esa..conf..545V
Altcode: 1994IAUCo.147..545V
No abstract at ADS
Title: IRIS VI
Authors: Gough, D. O.; Roxburgh, I. W.
Bibcode: 1994iris.conf.....G
Altcode:
No abstract at ADS
Title: The Depth of the Solar Convection Zone
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
Bibcode: 1994snft.book..427C
Altcode:
No abstract at ADS
Title: Seismology of the Sun
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Toomre, J.
Bibcode: 1994snft.book..418C
Altcode:
No abstract at ADS
Title: What can we Learn from Oscillation Studies about Irradiance
and Radius Changes?
Authors: Gough, D.
Bibcode: 1994svsp.coll..252G
Altcode: 1994IAUCo.143P.252G
No abstract at ADS
Title: The Influence of Low-Degree P-Mode Frequencies on the
Determination of the Structure of the Solar Interior
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1993MNRAS.264..522G
Altcode:
Accurate measurements of the frequencies of low-degree acoustic
oscillations provide valuable information about the structure of the
solar core. We determine the radial resolution that can be achieved by
direct inversions of frequency data sets recently obtained by various
observers to find the hydrostatic parameters density, sound speed and
a parameter of convective stability. The outcome of those inversions
indicates that the outer part of the radiative zone of the Sun is
similar to that of a solar model that takes account of helium settling
against microscopic diffusion. From the two data sets with lowest
estimated errors (those by Toutain & Fröhlich and Anguera Gubau
et al.) there is some evidence for an error in the modelling of the
energy-generating core, which could be accounted for by local material
redistribution in the core. Another data set by Elsworth et al.,
however, is almost compatible with the core of the theoretical model.
Title: Are the 1986--1988 Changes in Solar Free-Oscillation Frequency
Splitting Significant?
Authors: Gough, Douglas; Stark, Philip B.
Bibcode: 1993ApJ...415..376G
Altcode:
The solar normal-mode splitting coefficients deduced from Big
Bear Solar Observatory (BBSO) data differ between 1986 and 1988;
inversions for equatorial rotation are slower at depth and faster near
the surface in 1988 than in 1986. The significance of the change has
been disputed. The data sets overlap for five splitting coefficients
(a(j))super 5j = 1 associated with 710 multiplets. On
the assumption that rotation rate varies smoothly with radius, both
data sets are satisfied by the same rotation model at all colatitudes
except near 30-40 deg and near 70 deg (and at their southern hemisphere
reflections 140-150 deg and 110 deg). The evidence for equatorial
change is weak. Nonparametric tests show a significant offset in the
magnitudes of a(1), a(2), and a(4), and of linear combinations sensitive
to rotation at colatitudes of 60-80 deg (and 120 deg). Nonparametric
tests show significant radial trends in the changes to a(2), a(4),
and (less significantly) a(5). There is strong anticorrelation between
a(2) and a(4), a(1) and a(3), and a(3) and a(5), suggesting that the
estimates are not independent. Individual coefficients a(j) show more
evidence for change than do 'physical' linear combinations, adding
weight to this hypothesis. Some of the changes in splitting might be
related to solar activity, which changed most near colatitude 70 deg
from 1986 to 1988.
Title: Prisma - the First Space Mission to See Inside the Stars
Authors: Appourchaux, T.; Gough, D. O.; Catala, C.; Frandsen, S.;
Frohlich, C.; Hoyng, P.; Jones, A.; Lemaire, P.; Tondello, G.; Weiss,
W. W.
Bibcode: 1993ASPC...42..411A
Altcode: 1993gong.conf..411A
No abstract at ADS
Title: Seismic evidence of modulation of the structure and angular
velocity of the Sun associated with the solar cycle
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
Woodard, M. F.
Bibcode: 1993ASPC...40...93G
Altcode: 1993IAUCo.137...93G; 1993ist..proc...93G
No abstract at ADS
Title: On the Influence of Treatment of Heavy Elements in the Equation
of State on the Resulting Values of the Adiabatic Exponent
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Rhodes,
E. J., Jr.
Bibcode: 1993ASPC...40..304D
Altcode: 1993ist..proc..304D
No abstract at ADS
Title: The High-Frequency P-Mode Spectrum
Authors: Milford, P. N.; Scherrer, P. H.; Frank, Z.; Kosovichev,
A. G.; Gough, D. O.
Bibcode: 1993ASPC...42...97M
Altcode: 1993gong.conf...97M
No abstract at ADS
Title: Inversion for Background Inhomogeneity from Phase Distortions
of One-Dimensional Wave Trains
Authors: Gough, D. O.; Merryfield, W. J.; Toomre, J.
Bibcode: 1993ASPC...42..257G
Altcode: 1993gong.conf..257G
No abstract at ADS
Title: When is an F-Mode not an F-Mode
Authors: Rosenthal, C. S.; Gough, D. O.
Bibcode: 1993ASPC...42..185R
Altcode: 1993gong.conf..185R
No abstract at ADS
Title: The Form of the Angular Velocity in the Solar Convection Zone
Authors: Gough, D. O.; Kosovichev, A. G.; Sekii, T.; Libbrecht, K. G.;
Woodard, M. F.
Bibcode: 1993ASPC...42..213G
Altcode: 1993gong.conf..213G
No abstract at ADS
Title: On the Determination of the Temporal Properties of Free
Oscillators
Authors: Chang, H. Y.; Gough, D. O.
Bibcode: 1993ASPC...42..457C
Altcode: 1993gong.conf..457C
No abstract at ADS
Title: Linear adiabatic stellar pulsation.
Authors: Gough, D. O.
Bibcode: 1993afd..conf..399G
Altcode:
Contents: 1. Introduction. 2. The equilibrium state. 3. Linearized
equations. 4. Radial pulsations. 5. Nonradial oscillations
about a spherically symmetric state. 6. Inversion of asymptotic
formulae. 7. Perturbation theory. 8. Asymptotic representation by
locally plane waves. 9. Concluding remarks.
Title: on the Detection of Convective Overshoot
Authors: Gough, D. O.; Sekii, T.
Bibcode: 1993ASPC...42..177G
Altcode: 1993gong.conf..177G
No abstract at ADS
Title: Initial asteroseismic inversions
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1993ASPC...40..541G
Altcode: 1993IAUCo.137..541G; 1993ist..proc..541G
No abstract at ADS
Title: On the asteroseismic calibration of solar-type stars
Authors: Gough, D. O.; Novotny, E.
Bibcode: 1993ASPC...40..550G
Altcode: 1993ist..proc..550G; 1993IAUCo.137..550G
No abstract at ADS
Title: Impact of Observations on Prejudice and Input Physics
Authors: Gough, D. O.
Bibcode: 1993ASPC...40..767G
Altcode: 1993IAUCo.137..767G; 1993ist..proc..767G
No abstract at ADS
Title: Seismic Analysis of Stellar P-Mode Spectra
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1993ASPC...42..351G
Altcode: 1993gong.conf..351G
No abstract at ADS
Title: The Significance of Changes in Solar Free-Oscillation Splitting
from 1986-1990
Authors: Gough, D.; Stark, P. B.
Bibcode: 1993ASPC...42..221G
Altcode: 1993gong.conf..221G
No abstract at ADS
Title: PRISMA: Probing Stars from Core to Corona
Authors: Appourchaux, T.; Catala, C.; Catalano, S.; Fransden, S.;
Fröhlich, C.; Gough, D. O.; Hoyng, P.; Jones, A.; Lemaire, P.;
Tondello, G.; Weiss, W.
Bibcode: 1993ASSL..183..505A
Altcode: 1993pssc.symp..505A
No abstract at ADS
Title: It is possible to determine whether a star is rotating about
a unique axis?
Authors: Gough, D. O.; Kosovichev, A. G.
Bibcode: 1993ASPC...40..566G
Altcode: 1993IAUCo.137..566G; 1993ist..proc..566G
No abstract at ADS
Title: A procedure for two-dimensional asymptotic rotational-splitting
inversion
Authors: Sekii, T.; Gough, D. O.
Bibcode: 1993ASPC...40..569S
Altcode: 1993IAUCo.137..569S; 1993ist..proc..569S
No abstract at ADS
Title: Asteroseismic Calibration of Stellar Clusters
Authors: Gough, D. O.; Novotny, E.
Bibcode: 1993ASPC...42..355G
Altcode: 1993gong.conf..355G
No abstract at ADS
Title: PRISMA: a new space mission for stellar physics.
Authors: Appourchaux, T.; Gough, D.; Hyoyng, P.; Catala, C.; Frandsen,
S.; Froehlich, C.; Jones, A.; Lemaire, P.; Tondello, G.; Weiss, W. W.
Bibcode: 1993ASPC...40..812A
Altcode: 1993ist..proc..812A; 1993IAUCo.137..812A
This paper mainly focuses on the scientific objectives that can be
achieved with a new space mission of the European Space Agency -
PRISMA (Probing Rotation and Interior of Stars: Microvariability
and Activity). The scientific objectives can be classified into
three areas of interest: (1) Stellar structure and evolution. (2)
Stellar atmospheres and magnetic fields. (3) Stellar dynamics and
stellar dynamos.
Title: Electromagnetic images of regional structure in the southern
Canadian Cordillera
Authors: Jones, Alan G.; Gough, D. I.; Kurtz, Ron D.; Delaurier,
Jon M.; Boerner, David E.; Craven, James A.; Ellis, Rob G.; McNeice,
Gary W.
Bibcode: 1992GeoRL..19.2373J
Altcode:
As part of Lithoprobe's Southern Cordilleran transect investigations,
magnetotelluric (MT) soundings were made at 160 sites providing
unprecedented coverage from the Rockies to the west coast. Striking
lateral variation, which spatially correlates with the morphogeological
belt boundaries, is apparent at periods sensing the lower crust
(≈10 s). For the Rockies, MT phases are around 35°, indicative
of a moderately resistive (100's - 1000's Ω·m) North American
Basement. Foreland belt phases are transitional and increase from
60° in the east to 70° in the west. Omineca and Coast belt phases
are high (75°), implying a conductive (10-30 Ω·m) lower crust,
whereas Intermontane belt phases are more than 10° lower (equivalent
to ≈150 Ω·m). The regional variation in conductivity correlates to
first order with surface heat flow changes along the profile and is also
correlative with coincident seismic reflection sections in some aspects.
Title: Sources of uncertainty in direct seismological measurements
of the solar helium abundance
Authors: Kosovichev, A. G.; Christensen-Dalsgaard, J.; Daeppen, W.;
Dziembowski, W. A.; Gough, D. O.; Thompson, M. J.
Bibcode: 1992MNRAS.259..536K
Altcode:
The methods by which Dappen et al. (1988, 1990, 1991) and Dziembowski
et al. (1990, 1991, 1992) recently obtained discrepant estimates of
the helium abundance in the solar convection zone are compared. The
aim of the investigation reported in this paper is to identify the
main source of the discrepancy. Using as proxy data eigenfrequencies
of a set of modes of a theoretical solar model, computed with the
same physics as were the frequencies of a reference model with which
these data are compared, the two methods yield similar results. Thus
we ascertain that the principal source of the discrepancy is not in
the inversions themselves, which yield essentially a measure of the
variation of the adiabatic exponent gamma of the material in the He II
ionization zone. Instead it is in the approximations adopted in the
treatment of heavy elements in the equation of state used to relate
the variation of gamma to chemical composition. We obtain acceptably
consistent results when inverting solar data by two methods using the
same equation of state. We attempt to identify the likely residual
sources of uncertainty.
Title: On the rate of destruction of lithium in late-type
main-sequence stars
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
Bibcode: 1992A&A...264..518C
Altcode:
It it shown that the rate of destruction of lithium by nuclear reactions
in the outer mixed layers of late-type main-sequence stars depends on
both the depth of the region where mixing occurs and the stratification
within it. The mixed region includes and probably extends beneath the
base of the convection zone. As the star evolves on the main sequence,
the properties of the convection zone vary in a simple manner. If
the mixed layer behaves similarly, then the mean destruction rate
can easily be related to the present local value evaluated at the
base of the mixed layer. In the case of the sun, it is found that if
mixing is rapid compared with the nuclear destruction rate, then the
mean destruction rate is approximately equal to one-half the present
local value.
Title: Localized Excitation of Solar Oscillations
Authors: Goode, Philip R.; Gough, Douglas; Kosovichev, Aleksandr G.
Bibcode: 1992ApJ...387..707G
Altcode:
Solar oscillation data are well described in terms of waves produced
by isolated expansive events occurring less than 200 km below the base
of the photosphere. The events last about 5 minutes.
Title: The role of helioseismology in neutrino physics.
Authors: Gough, D. O.
Bibcode: 1992pnap.conf...25G
Altcode:
The author discusses what we know about the internal structure of
the sun, based on a combination of observation and plausible physical
reasoning.
Title: Electromagnetic exploration for fluids in the Earth's crust
Authors: Gough, D. Ian
Bibcode: 1992ESRv...32....3G
Altcode:
Electromagnetic geophysical techniques yield information on the spatial
distribution of electrical conductivity, a parameter sensitive to
fluids in the rocks. The paper describes electromagnetic techniques of
use through the Earth's crust, including magnetovariation (MV) arrays,
magnetotelluric (MT) sounding and DC resistivity sounding. Field studies
using these techniques lead to a discussion of various causes of high
crustal conductivity, including aqueous fluids, silicate partial melt
and films of graphite or magnetite on grain surfaces. Water in the
crust is proposed as the preferred cause of high conductivity in the
juvenile crust of tectonically active regions, in particular where
the anomalous conductivity is correlated with high heat flow and other
geophysical and geological parameters.
Title: Helium inhomogeneities in main-sequence magnetic stars.
Authors: Vauclair, S.; Dolez, N.; Gough, D. O.
Bibcode: 1991A&A...252..618V
Altcode:
Helium abundance variations are computed in models of main-sequence
magnetic stars with masses in the range 1.6-5 solar mass (Teff =
8,000-19,000 K). To represent a predominantly dipolar magnetic field,
regions in the stars are schematically designated either polar, with
vertical magnetic fields, or equatorial, with horizontal fields. A
stellar wind is supposed to exist at the magnetic poles. The mass-loss
rate is varied as a free parameter in the computations. Under these
conditions, helium is underabundant at the magnetic equators, while it
can accumulate at the poles in the region of the first ionization of
helium. The accumulation occurs if the mass-loss rate is of the order
of that caused by the solar wind. The helium peak is visible in the
atmospheres of the hottest stars, which can account for the observed
He-rich stars. It lies below the photosphere and should not be visible
in the coolest stars; but it can help to excite the pulsations of
rapidly oscillating Ap stars by the Kappa mechanism.
Title: The Depth of the Solar Convection Zone
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Thompson, M. J.
Bibcode: 1991ApJ...378..413C
Altcode:
The transition of the temperature gradient between being subadiabatic
and adiabatic at the base of the solar convection zone gives rise to
a clear signature in the sound speed. Helioseismic measurements of the
sound speed therefore permit a determination of the location of the base
of the convection zone. Two techniques were tested by applying them
to artifical data, obtained by adding simulated noise to frequencies
computed from two different solar models. The determinations appear to
be relatively insensitive to uncertainties of the physics of the solar
interior. From an analysis of observed frequencies of solar oscillation
it is concluded that the depth of the solar convection zone is (0.287 +
or - 0.003) solar radii.
Title: The Sun and Space Exploration
Authors: Gough, D.; Garriott, O.
Bibcode: 1991BAAS...23.1039G
Altcode:
No abstract at ADS
Title: Simulation of Effects of Atmospheric Seeing on the Observation
of High-Degree Solar Oscillations
Authors: Hill, Frank; Gough, Douglas; Merryfield, William J.;
Toomre, Juri
Bibcode: 1991ApJ...369..237H
Altcode:
Numerical simulations of the effects of atmospheric seeing distortions
on observations of solar oscillations of intermediate and high degree
are performed. The simulations involve a representation of about 100
p-modes of oscillation, with degrees l = 50-150 (intermediate-degree)
and 150-450 (high-degree), formed from the complement of a sexated mode
set. These modes are superposed on a steady large-scale convective
background, and projected onto the plane of the sky. Image motion is
modeled by displacement maps generated from two-dimensional turbulence
power spectra; the maps are scaled so that the rms amplitude of the
displacements has values of 2-5 arcsec. The distorted velocity field is
then Fourier analyzed to produce simulated (l, nu) power diagrams, where
nu is the temporal cyclic frequency. The results show that power in the
mode ridges is diminished as atmospheric seeing worsens, particularly
at high degrees. Redistribution of power produces an apparent decrease
in the frequencies of the oscillations as measured by the centroids
of the ridges in the power spectra. It is found that time-averaging
the observations is quite effective in reducing the noise.
Title: Crustal structures from MT soundings in the Canadian Cordillera
Authors: Majorowicz, J. A.; Gough, D. Ian
Bibcode: 1991E&PSL.102..444M
Altcode:
Magnetotelluric soundings have been made across the Intermontane and
Omineca tectonic belts of the Canadian Cordillera between latitudes 51.5
and 53.5°N. The frequency range, 0.016 to 130 Hz, gives penetration
into the middle crust. In this part of the Cordillera the upper crust
has very low resistivities, ranging from 3 to 300 ohm m, compared with
continental shields and stable platforms. The most resistive rocks
(100-300 ohm m) rise to the surface as the Coast Plutonic Complex is
approached, and we identify them with confidence as granodiorites and
similar plutonic rocks (hereafter "plutonics"). Phase pseudosections
and resistivity-depth sections are used to infer that these plutonics
continue northeastward from the Coast Plutonic Complex, across more
than half of the width of the Intermontane Belt, with a sharp edge well
located in the phase pseudosections. The Miocene basalts have extremely
low resistivities (3-30 ohm m) and form a sheet 0-2 km thick covering
the plutonics. The very low resistivities in all rocks are probably
caused by saline hot water in connected spaces, with low fracture
density giving relatively high resistivities in the plutonic rocks,
and much greater fracture densities giving extremely low resistivities
in the volcanics. This is consistent with the lower mechanical strength
of basalt as against granodiorite; the volcanics may have accommodated
most of the post-Miocene extension of the upper crust. Off the edge of
the plutonic rocks beneath the basalts, very low resistivities extend
at least into the middle crust; this deep extension of the highly
conductive rock may mark the feeder channel of the Miocene basalt to the
surface. Three resistivity-depth sections show a fall of resistivity
with depth, to values of 10 ohm m or even less, at a depth of only 8
km. Heat flow is high in the region, and the temperature at 8 km may
be as high as 350°C. The increase in conductivity may be due in part
to the temperature effect on NaCl solutions, and in part to release
of water from hydrated minerals. All crustal features disclosed in
this work support the hypothesis advanced earlier, that the interior
Canadian Cordillera lie above an elongated upflow in the mantle inland
from the currently active subduction.
Title: Nonlinear Behavior of Solar Gravity Modes Driven by 3He in
the Core. II. Numerical Simulations
Authors: Merryfield, William J.; Toomre, Juri; Gough, Douglas
Bibcode: 1991ApJ...367..658M
Altcode:
The nonlinear behavior of gravity-mode oscillations driven by
He-3-destroying reactions in the solar core has been examined
by numerically integrating equations describing a very simplified
model. The results of a previous bifurcation analysis, which suggest
that such oscillations are unlikely to attain amplitudes sufficient
to trigger core convection, are verified. These results are extended
to models whose nuclear reaction rates and thermal stratification
represent the core somewhat more accurately. Nonlinear processes give
rise to a preference for the oscillations to develop as standing waves
rather than traveling waves, thus breaking the degeneracy between
these two types of motion which exists in linearized theory. Study
of the large-amplitude behavior of the oscillations is hindered by a
tendency for the model to become thermally unstable.
Title: On the Analysis of Physical Wave Trains
Authors: Gough, D. O.; Merryfield, W. J.; Toomre, J.
Bibcode: 1991LNP...388..265G
Altcode: 1991ctsm.conf..265G
When a wave train whose constituent frequencies and wave numbers are
unresolved by observation propagates through an inhomogeneous medium,
beating between the components can contaminate deductions one might
naively draw about the inhomogeneous background. This is a severe
problem to anyone confronted with analysing helioseismic data with
a view to determining the structure of giant convective cells. We
propose a procedure for analysing wave trains, based on approximating
a packet as a single representative pure wave. We present some
preliminary results of analysing artificial data. For simplicity, we
have deliberately excluded some of the effects of wave interference,
which must be faced by any means of analysis. Therefore we do not
claim to have found a complete procedure for analysing real data.
Title: Challenges to Theories of the Structure of Moderate-Mass Stars
Authors: Gough, Douglas; Toomre, Juri
Bibcode: 1991LNP...388.....G
Altcode: 1991ctsm.conf.....G
No abstract at ADS
Title: Pulsations of Arcturus
Authors: Balmforth, N. J.; Gough, D. O.; Tout, C. A.
Bibcode: 1991LNP...388..381B
Altcode: 1991ctsm.conf..381B
No abstract at ADS
Title: Seismic constraints on the solar neutrino problem.
Authors: Gough, D. O.
Bibcode: 1991NYASA.647..199G
Altcode: 1991tsra.symp..199G
Contents: 1. Introduction. 2. Standard solar models and the reactions
of the pp chain. 3. The solar neutrino problem. 4. Helioseismic
inversion. 5. Results of the inversion. 6. Modified standard models,
and WIMP accretion. 7. Macroscopic motion in the core. 8. Conclusion.
Title: The Vibrational Stability of the Sun
Authors: Balmforth, N. J.; Gough, D. O.
Bibcode: 1991LNP...388..221B
Altcode: 1991ctsm.conf..221B
No abstract at ADS
Title: The inversion problem.
Authors: Gough, D. O.; Thompson, M. J.
Bibcode: 1991sia..book..519G
Altcode:
The authors discuss some fundamental problems associated with inverting
helioseismic data to infer properties of the solar interior, and
review various methods used to invert frequencies of normal modes of
oscillation. After discussing linear methods, the authors present and
compare different asymptotic methods that have been used to infer the
internal solar sound speed. They also discuss numerical inversions
for solar structure, and address the issue of inverting for more than
one function. Methods of inverting for the nonspherically symmetric
structure of the Sun are presented.
Title: Program at ITP: Helioseismology — Probing the interior of
a star
Authors: Gough, Douglas; Toomre, Juri
Bibcode: 1991LNP...388....1G
Altcode: 1991ctsm.conf....1G
The research program in helioseismology carried out at the Institute
for Theoretical Physics (ITP) at the University of California, Santa
Barbara during the six-month interval from January to June 1990
involved 61 scientists of diverse disciplines: theorists, observers
and instrumentalists in physics, astrophysics and geophysics. The main
topics of research and joint discussion included mode excitation and
decay, the internal structure of the sun and its sensitivity to the
physics of the equation of state and opacity, seismological inverse
procedures, and solar rotation and convection-zone dynamics.
Title: Challenges to theories of the structure of moderate-mass stars
Authors: Gough, Douglas; Tomre, Juri
Bibcode: 1991ctts.conf.....G
Altcode: 1991QB539.I5C47....
No abstract at ADS
Title: Internal Solar Rotation
Authors: Gough, D. O.
Bibcode: 1991ASIC..340..271G
Altcode: 1991amey.conf..271G
No abstract at ADS
Title: Seismic observations of the solar interior.
Authors: Gough, Douglas; Toomre, Juri
Bibcode: 1991ARA&A..29..627G
Altcode:
Contents: 1. Introduction. 2. Solar evolution. 3. Properties of
modes. 4. Observational principles. 5. Inversion of data. 6. Inference
of hydrostatic structure. 7. The neutrino problem. 8. Rotation and
other subsurface flows. 9. Mode excitation and decay. 10. Solar cycle
variations. 11. Asteroseismology.
Title: A New Inversion for the Hydrostatic Stratification of the Sun
Authors: Däppen, W.; Gough, D. O.; Kosovichev, A. G.; Thompson, M. J.
Bibcode: 1991LNP...388..111D
Altcode: 1991ctsm.conf..111D
Inversions for the spherically symmetric component of the hydrostatic
stratification of the Sun are presented. These employ the Backus-Gilbert
optimally localized averaging procedure applied to oscillation multiplet
frequencies in the range 1.5 - 3 mHz of modes with 4 l 140 determined
by Libbrecht et al. (1990) from observations carried out in 1986. We
also obtain an estimate of the helium abundance in the solar convective
envelope.
Title: Effluent Stellar Pulsation
Authors: Balmforth, N. J.; Gough, D. O.
Bibcode: 1990ApJ...362..256B
Altcode:
Near-discontinuities in the density of a star, such as that encountered
in the transition between a chromosphere and a corona, reflect acoustic
waves and thereby partially contain them within the star. These
reflections help to establish a resonant acoustic cavity with discrete
characteristic frequencies, even for modes with frequencies above the
acoustic cutoff frequency. Reflection is not complete, however, and
energy propagates away from the star, contributing to the decay of the
mode. Nevertheless, for coronae with temperatures of order 10 to the
6th K, the contribution that such decay is likely to make to the line
width in a power spectrum of the oscillations is substantially less
than the frequency separation between modes of adjacent order and like
degree. Therefore, in that case, characteristic acoustic frequencies
exist. A physical discussion of the phenomena is presented, and is
illustrated by a simple analytical model. The results are compared
with numerical stability calculations of high-order radial modes of
a model of the sun.
Title: Astrophysical Sun
Authors: Gough, D. O.
Bibcode: 1990Natur.347..346G
Altcode: 1990Natur.347..346F
No abstract at ADS
Title: Mixing-Length Theory and the Excitation of Solar Acoustic
Oscillations
Authors: Balmforth, N. J.; Gough, D. O.
Bibcode: 1990SoPh..128..161B
Altcode: 1990IAUCo.121P.161B
The stability of radial solar acoustic oscillations is studied
using a time-dependent formulation of mixing-length theory. Though
the radiation field is treated somewhat simplistically with the
Eddington approximation, and we appreciate that any coupling of the
pulsation to the radiation field is important, for the lower frequency
radial modes that have been computed this should not produce too
serious an error. Instead, we have concentrated upon treating the
coupling with convection as accurately as is currently possible with
generalized mixing-length theory in order to learn something about
its pertinence. Our principal conclusion is that, according to this
theory, solar radial acoustic oscillations are expected to be stable
and generated by turbulence. Moreover, the theory predicts changes in
mode frequency that may, in part, explain the discrepancy between solar
observations and the adiabatic pulsation frequencies of theoretical
models. We also compute the amplitudes of the modes using a theory
of stochastic excitation. These are in good agreement with observed
power spectra.
Title: Sensitivity of Solar Eigenfrequencies to the Age of the Sun
Authors: Gough, D. O.; Novotny, E.
Bibcode: 1990SoPh..128..143G
Altcode: 1990IAUCo.121P.143G
The increasing central concentration of the Sun with age modifies
the acoustic eigenfrequencies. In particular, the frequency separation
dl=3(2l+3)−1«vn,l−vn−1,l+2»
for modes with l + 1/2 ≪ n decreases as nuclear reactions augment
the molecular-weight gradient in the energy-generating core. If,
for example, the Sun were older than is generally believed, one
might therefore expect dl to be smaller than current
theoretical predictions. On the other hand, to ensure that the
luminosity is consistent with observations, the presumed initial
hydrogen abundance would need to be enhanced, thereby reducing the
resultant molecular-weight gradient. Thus there is some degree of
cancellation of the two major factors that determine dl.
Title: Shaky clues to solar activity
Authors: Gough, Douglas
Bibcode: 1990Natur.345..768G
Altcode:
No abstract at ADS
Title: On Possible Origins of Relatively Short-Term Variations in
the Solar Structure
Authors: Gough, D. O.
Bibcode: 1990RSPTA.330..627G
Altcode:
The general large-scale redistribution of magnetic field over the
solar cycle is possible associated with an overall variation of thermal
structure of the convection zone, which modulates not only the total
luminosity but also the latitudinal distribution of radiative flux,
thereby modifying the irradiance of the Earth. Whether the cause of
this variation lies within the convection zone or is more deeply seated
is still an open question.
Title: Nonlinear Behavior of Solar Gravity Modes Driven by 3He in
the Core. I. Bifurcation Analysis
Authors: Merryfield, William J.; Toomre, Juri; Gough, Douglas
Bibcode: 1990ApJ...353..678M
Altcode:
The nonlinear development of solar gravity modes driven by He-3 burning
in the solar core is investigated by means of an idealized dynamical
model. Possible outcomes that have been suggested in the literature
include the triggering of subcritical direct convection, leading to
core mixing, and the saturation of the excitation processes, leading
to sustained finite-amplitude oscillations. The present simple model
suggests that the latter is the more likely. The limiting amplitude
of the oscillations is estimated, ignoring possible resonances with
other gravity modes, to be of order 10 km/s at the solar surface. Such
oscillations would be easily observable. That large-amplitude gravity
modes have not been observed suggests either that these modes are not
unstable in the present era or that they are limited to much smaller
amplitudes by resonant coupling.
Title: The effect of rotation and a buried magnetic field on stellar
oscillations
Authors: Gough, D. O.; Thompson, M. J.
Bibcode: 1990MNRAS.242...25G
Altcode:
A perturbation method is presented for calculating the frequency
modification of stellar oscillations caused by rotation and internal
magnetic field. A short-wavelength asymptotic analysis derived from
ray theory is also presented. The effects on high-order solar acoustic
modes of various hypothetical angular velocity and magnetic field
configurations are investigated using both methods of calculation. The
asymptotic formulas provide a good estimate for the frequency splitting
of five-minute modes when the field and the rotation vary sufficiently
smoothly. On the other hand, a localized magnetic field, for example at
the base of the convection zone, produces a characteristic oscillatory
perturbation to the eigenfrequencies.
Title: On possible origins of relatively short-term variations in
the solar structure.
Authors: Gough, D. O.
Bibcode: 1990ecvs.conf..627G
Altcode:
The general large-scale redistribution of magnetic field over the
solar cycle is possibly associated with an overall variation of thermal
structure of the convection zone, which modulates not only the total
luminosity but also the latitudinal distribution of radiative flux,
thereby modifying the irradiance of the Earth. Whether the cause of
this variation lies within the convection zone or is more deeply seated
is still an open question.
Title: Open Questions
Authors: Gough, Douglas O.
Bibcode: 1990ASSL..159..451G
Altcode: 1990IAUCo.121..451G; 1990insu.conf..451G
No abstract at ADS
Title: Comments on Helioseismic Inference
Authors: Gough, D. O.
Bibcode: 1990LNP...367..283G
Altcode: 1990LNP...367..281G; 1990psss.conf..283G
Helioseismic inference can be made within a wide spectrum of
sophistication, from arguments based on the results of very simple
and highly idealized model problems which depend on specific limited
aspects of the data to a variety of formal numerical inversions of
all the data that are available. The idealized problems are relatively
simple to analyze, and provide a tool for making immediate qualitative
and sometimes even quantitative estimates of certain aspects of
the structure of the sun. If well chosen, they are likely to add
substantially to our understanding of the situation; indeed, they can
be an extremely useful guide to designing the more formal techniques
which, though numerically more precise, are frequently also more
opaque. Therefore it is often prudent to utilize methods throughout
the entire spectrum. In this lecture a selection of the techniques
for making immediate inferences will be discussed, and illustrated
with examples of topical interest.
Title: The Internal Structure of Late Type Main-Sequence Stars
Authors: Gough, D. O.
Bibcode: 1990arpf.symp...13G
Altcode: 1990arpf.conf...13G
Homology scaling laws for main-sequence stars are derived, and used to
estimate how late-type stars evolve during their core hydrogen-burning
phase. Though not exactly representative of realistic stellar models,
the scaling laws do provide a useful method of making estimates
of small perturbations either to the initial conditions or to the
physics used in the so-called standard theory of stellar evolution. In
particular, evolution with varying gravitational constant and varying
mass are considered explicitly. The scaling laws are used to determine
how gross observable parameters such as luminosity neutrino flux or
acoustic oscillation frequencies depend on the mass, composition and
age of the star. By inverting the relations it is shown that with the
precision of the best measurements of luminosity, effective temperature
and the heavy-element to hydrogen abundance ratio, supplemented with
a knowledge of the principle parameters characterizing the high-order
acoustic oscillation spectrum, theoretical models could be calibrated to
determine mass and age to within about 20 percent. No useful information
about the helium abundance can be obtained in this way.
Title: Pulsations of Model Mira Variables
Authors: Balmforth, N. J.; Gough, D. O.; Merryfield, W. J.
Bibcode: 1990fmpn.coll...85B
Altcode:
The objective of the study was to investigate how the properties
of the linear acoustic modes of model Mira variables are affected by
convection. The approach used is based on the generalized time-dependent
formulation of the mixing-length theory of Gough (1977). The formulation
makes it possible to include the turbulent pressure, which is quite
significant in these stars. Results of the linear stability analysis
are summarized.
Title: Using Helioseismic Data to Probe the Hydrogen Abundance in
the Solar Core
Authors: Gough, D. O.; Kosovichev, Alexander G.
Bibcode: 1990ASSL..159..327G
Altcode: 1990IAUCo.121..327G; 1990insu.conf..327G
No abstract at ADS
Title: Inferring the Sun's Internal Angular Velocity from Observed
p-Mode Frequency Splittings
Authors: Brown, Timothy M.; Christensen-Dalsgaard, Jorgen; Dziembowski,
Wojciech A.; Goode, Philip; Gough, Douglas O.; Morrow, Cherilynn A.
Bibcode: 1989ApJ...343..526B
Altcode:
The sun's internal solar velocity Omega is studied as a function of
latitude and radius using the solar oscillation data of Brown and
Morrow (1987). An attempt is made to separate robust inferences about
the sun from artifacts of the analysis. It is found that a latitudinal
variation of Omega similar to that observed at the solar surface exists
throughout the sun's convection zone and that the variation of Omega
with latitude persists to some extent even beneath the convection zone.
Title: Seismology of Solar Oscillation Line Widths
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Libbrecht, K. G.
Bibcode: 1989ApJ...341L.103C
Altcode:
Recent measurements of line widths of solar p-modes are compared with
damping rates computed under several different assumptions. There
is reasonable agreement with a calculation taking some account of
perturbations in the convective fluxes induced by the oscillations,
whereas calculations neglecting these flux perturbations are further
from the observations. This opens up the prospect of using observations
of solar oscillations to test theories of time-dependent convection. The
results should be of importance to studies of other types of pulsating
stars.
Title: Differential asymptotic sound-speed inversions
Authors: Christensen-Dalsgaard, J.; Thompson, M. J.; Gough, D. O.
Bibcode: 1989MNRAS.238..481C
Altcode:
An asymptotic method for determining the internal solar sound speed
from the differences between observed p-mode frequencies and those
of a standard reference solar model is presented. In order to test
the method, it has been applied to the frequency differences between
pairs of solar models, where in each case one takes the part of the
reference model and the other the role of the sun. The results of
these numerical experiments indicate that by using this simple method
one may in principle be able to determine the sound speed from the
energy-generating core to the helium ionization zone.
Title: Estimation of the magnetic fields of current channels in
magnetovariational data
Authors: Wang, Xi-Shuo; Samson, J. C.; Gough, D. I.
Bibcode: 1989GeoJI..96..381W
Altcode:
No abstract at ADS
Title: Rotational Enhancement of Doppler Measurements of Solar and
Stellar Hexadecapole Oscillations
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1989SoPh..119....5C
Altcode:
Rotational enhancement of the sensitivity of whole-disk Doppler
observations of solar oscillations may permit the measurement of
five-minute modes with l = 4. We estimate from superposed power spectra
of artificial solar data that there might be identifiable power lying
above the noise in the data acquired by Pallé et al. (1986), which
could provide confirmation of the rotational splitting measured by
Duvall and Harvey (1984).
Title: Magnetometer array studies, earth structure, and tectonic
processes.
Authors: Gough, D. Ian
Bibcode: 1989RvGeo..27..141G
Altcode:
This review presents results from magnetovariation fields recorded
by two-dimensional arrays of magnetometers. The emphasis is on
the conductive structures mapped and studied and their tectonic
implications.
Title: Scattering and multiple scattering of acoustic waves in a
stratified medium.
Authors: Rosenthal, C. S.; Gough, Douglas O.
Bibcode: 1988ESASP.286..457R
Altcode: 1988ssls.rept..457R
Bogdan and Zweibel have studied the effect on wave propagation of
scattering from an ensemble of vertical magnetic flux tubes in a
stratified atmosphere, using the WKB approximation. The authors analyse
the effect of an ensemble of general axisymmetric scatterers on acoustic
waves in a stratified atmosphere, without using the WKB approximation,
and obtain a dispersion relation valid for small filling factors. The
properties of this dispersion relation are studied for scattering
from density inhomogeneities in a two-layer model atmosphere. It is
found that increased strafication tends to decrease the frequency
perturbation induced by a population of cylindrical inhomogeneities.
Title: Book Review: The internal solar angular velocity. / Reidel,
1987
Authors: Gough, D. O.
Bibcode: 1988Obs...108..235G
Altcode:
No abstract at ADS
Title: Deep roots of solar cycles
Authors: Gough, Douglas
Bibcode: 1988Natur.336..618G
Altcode:
Recent gains made in understanding the inner structure of the sun
through the use of helioseismology are reviewed. The remeasurement of
two coefficients that describe the acoustical properties of the sun
which depend on its departure from spherical symmetry is discussed. The
origin of the acoustical asphericity and its relation to the magnetic
cycle is addressed. The effects of asphericity on solar luminosity
and on solar oscillations are considered.
Title: Obituary - Severny, Andrei 1913-1987
Authors: Gough, D.
Bibcode: 1988QJRAS..29..584G
Altcode:
No abstract at ADS
Title: Determination of the solar internal sound speed by means of
a differential asymptotic inversion.
Authors: Christensen-Dalsgaard, J.; Gough, Douglas O.; Thompson, M. J.
Bibcode: 1988ESASP.286..493C
Altcode: 1988ssls.rept..493C
The authors present a simple asymptotic inversion method for
obtaining an estimate of the difference in internal sound speed from
differences between five-minute p-mode oscillation frequencies. Thus,
given a known model and a set of frequencies of a model of unknown
structure, or of the Sun, the internal sound speed of the latter can be
estimated. Numerical experiments with error-free frequencies indicate
that this method can provide an estimate of the sound speed, from the
energy-generating core to the helium ionization zone, with smaller
fractional error than any previously published results. The authors
have applied the method to real solar data, and find that the solar
sound speed is indeed broadly as determined by an earlier investigation
at those depths for which the earlier inversion should be reliable.
Title: An attempt to understand the stanford p-mode data.
Authors: Gough, Douglas O.; Kosovichev, A. G.
Bibcode: 1988ESASP.286..195G
Altcode: 1988ssls.rept..195G
The p-mode frequencies reported by Henning and Scherred (1986),
showing anomalous behavior at degree 5 and frequencies below 2
mHz were investigated. No plausible solar model is consistent with
them. A density inversion including the low-degree 5 min data of
Jimenez et al. (1988) implies that the density of the solar core
is 10 percent greater than it is in the standard solar model 1 of
Christensen-Dalsgaard (1982). Although that result is in keeping with
previous suggestions either that the Sun has a greater evolutionary
age than is usually supposed or that there is a cloud of weakly
interacting massive particles in the solar core and its environs,
the behavior of the sound speed in the core is not consistent with
either hypothesis. Both the inferred sound-speed variation, and a
secondary inversion for hydrogen abundance (relying on an assumption of
thermal balance), provide evidence for material redistribution in the
energy-generating core. A sound-speed inversion for the entire radiative
interior, using also frequencies of low and intermediate degree compiled
by Duvall et al. (1988), confirms the earlier finding that the sound
speed in the Sun exceeds that of a standard solar model by up to 1
percent in a region extending 30 percent of the solar radius and centred
at r = 0.4R. That is consistent with, though does not necessarily
imply, that the opacity in the outer layers of the radiative interior
at temperatures of up to 4 million K is underestimated by 20 percent.
Title: Towards an independent calibration of the mixing-length theory.
Authors: Tooth, P. D.; Gough, Douglas O.
Bibcode: 1988ESASP.286..463T
Altcode: 1988ssls.rept..463T
The standard astrophysical mixing-length theory of turbulent convection,
and modifications thereof, are calibrated with laboratory experimental
data over a range of Rayleigh numbers and Prandtl numbers. Both
local and nonlocal theories are considered, and an analysis made of
the effects on the calibration of different degrees of small-scale
turbulence, eddy decay-probability and presumed nonlocalization (both
symmetrical and asymmetrical). It is found that while the local theory
does adequately describe some of the features of laboratory convection
(though it would predict a mixing-length parameter of at least 2.4),
its qualitative agreement is poor. Nonlocal theories with this parameter
around 1.8 - 2.0 give a much better agreement with experiment over
the whole range of experimental Rayleigh and Prandtl numbers. The
authors conclude that both local and nonlocal mixing-length theories
can be adjusted to give apparently accurate descriptions of turbulent
laboratory convection in the ranges 104 ≤ Rayleigh
number ≤ 108 and 10-2 ≤ Prandtl number ≤
102, but that the nonlocal theory provides a more physically
realistic description of the flow.
Title: Nonlinear studies of solar gravity modes driven by nuclear
burning of the 3He in the core.
Authors: Merryfield, W. J.; Toomre, J.; Gough, Douglas O.
Bibcode: 1988ESASP.286...21M
Altcode: 1988ssls.rept...21M
The finite-amplitude behavior of gravity-mode oscillations driven
within the deep interior of the sun has been studied by means of a
simple idealized model. Such g modes may be self-excited by their
ability to extract energy from the nuclear burning of 3He
in the core. Both a nonlinear bifurcation analysis and numerical
simulations of the behavior of this instability suggest that the
growth of 3He-driven oscillations is likely be limited to
an amplitude which is insufficient to induce convective instability
in the core, a process which has been proposed as a mechanism for core
mixing. The numerical results also indicate that if the oscillations are
linarly unstable then the degeneracy in linear theory between standing
and travelling g modes is broken by nonlinear effects. The oscillations
thus develop into a left- or right-travelling wave rather than a
standing wave or other superposition of horizontally propagating waves.
Title: On radiative and convective influences on stellar pulsational
stability.
Authors: Balmforth, N. J.; Gough, Douglas O.
Bibcode: 1988ESASP.286...47B
Altcode: 1988ssls.rept...47B
Recent theoretical investigations have shown that there is a delicate
balance between instability and stability mechanisms in certain
stars when physical influences, such as convection and radiative
transfer, are considered in a finer detail than in a typical pulsation
computation. Baker and Gough (1979) and Xiong (1980) demonstrated the
susceptibility of pulsations to stabilization towards the red edge of
the RR Lyrae and Cepheid instability strips by a convection-pulsation
coupling. Moreover, Christensen-Dalsgaard and Frandsen (1983) have
illustrated the stabilizing effect of radiative transfer when it is
included consistently in the calculation of a solar model. Here the
authors extend the calculations of Baker and Gough to Cepheids and
the sun.
Title: Stellar disharmony.
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Perez Hernandez, F.
Bibcode: 1988MNRAS.235..875C
Altcode:
Frequency differences between high-order p-modes of two stellar models,
both with the mass and luminosity of the sun, are compared with results
of asymptotic theory. The computed relative differences are closely
approximated by averages of the relative sound-speed differences,
weighted by the local sound travel-time, over the regions where the
modes are trapped.
Title: On taking observers seriously.
Authors: Gough, Douglas
Bibcode: 1988ESASP.286..679G
Altcode: 1988ssls.rept..679G
The lastest measurements of the even component of degeneracy
splitting of five-minute oscillations announced at this symposium add
substantially to the evidence for temporal variations in the solar
acoustic asphericity that are correlated with the solar cycle. The
asphericity appears to extend from the photosphere, through the
convection zone, into the radiative interior. It may exist even in
the core of the sun, but there is yet no sound direct evidence for
that. The next observations will be carried out well into the new cycle,
and are therefore likely to clarify the situation significantly.
Title: Further progress on the helium abundance determination.
Authors: Daeppen, W.; Gough, Douglas O.; Thompson, M. J.
Bibcode: 1988ESASP.286..505D
Altcode: 1988ssls.rept..505D
The authors report on further progress in attempting to determine the
helium abundance in the solar convection zone by analysing the position
and shape of the "helium hump" in a thermodynamic quantity Θ which
can be inferred from the sound speed in the vicinity of the He II
ionization zone. At present they are estimating the sound speed from
frequencies of high-degree oscillations by a differential asymptotic
technique. The helium abundance Y is then determined by fitting the hump
inferred to one obtained by interpolation in a grid of theoretical model
envelopes. They have tested the procedure by carrying out a double-blind
experiment on artificial data, and have found that accurate knowledge
of the equation of state is essential for a useful determination. The
authors have also carried out the procedure on real solar data, but
they judge that the frequencies are at present too poorly determined
to enable us to obtain a reliable estimate of Y in the sun.
Title: Andrei Borisovich Severny (11 May 1913 - 4 April 1987).
Authors: Gough, D.
Bibcode: 1988QJRAS..29..581G
Altcode: 1988QJRAS..29..581.
No abstract at ADS
Title: Local effects of a major flare on solar five-minute
oscillations.
Authors: Haber, D. A.; Toomre, J.; Hill, Frank; Gough, Douglas O.
Bibcode: 1988ESASP.286..301H
Altcode: 1988ssls.rept..301H
Doppler velocity images of the full Sun were obtained both during and
after a major white-light flare. These velocities were interpolated onto
a cylindrical coordinate system centered on the flare and decomposed
into radially propagating waves defined by Hankel functions. For
a similar analysis of quiet Sun regions the authors find fairly
comparable power in incoming and outgoing waves irrespective of the
presence of the flare. However, for the flaring region, there is 14%
greater power in incoming as opposed to outgoing waves when there
is no flare, but 5% greater power in outgoing than in incoming waves
during the flare. This result suggests that the flare may have excited
outgoing waves which counteracted the more usual absorption of incoming
acoustic waves by sunspots.
Title: Prediction of solar oscillation frequencies
Authors: Gough, D. O.
Bibcode: 1988Natur.336..720G
Altcode:
No abstract at ADS
Title: Modelling the variation of solar p-mode frequencies.
Authors: Daeppen, W.; Gough, Douglas O.; Turck-Chieze, S.
Bibcode: 1988ESASP.286..511D
Altcode: 1988ssls.rept..511D
The authors present a Green's function technique to study long-term
variations of the Sun (with characteristic time scales from one month
to millions of years). The method is the combination of two previous
analyses carried out independently by Gough and by Däppen. Their study
has been motivated by the recent observational progress on solar p-mode
frequency variations.
Title: SOI: The Solar Oscillations Imager on SOHO
Authors: Scherrer, P. H.; Hoeksema, J. T.; Bogart, R. S.; Walker,
A. B. C., Jr.; Title, A. M.; Tarbell, T. D.; Wolfson, C. J.; Brown,
T. M., Jr.; Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1988sohi.rept...25S
Altcode:
The Solar Oscillations Imager (SOI) program for SOHO (solar and
heliospheric observatory) is described. It will consist of a Michelson
Doppler Imager (MDI) instrument, a facility providing data reduction
and analysis capability, and a coordinated set of investigations
designed to address a set of science objectives. The MDI is designed
to take advantage of the anticipated SOHO telemetry by organizing
the observations into four observation programs: structure (at all
times), dynamics (two months per year), campaign (eight hours per day,
ten months per year), and magnetic fields (few minutes per day). The
MDI will measure line-of-sight velocity by Doppler shift, transverse
velocity by local correlation tracking, line and continuum intensity,
and line-of-sight magnetic fields with both 4 and 1.4 arc-second
resolution (2 and 0.7 arc-sec pixels respectively).
Title: Book-Review - the Internal Solar Angular Velocity - Theory
Observations and Relationship to Solar Magnetic Fields
Authors: Durney, B. R.; Sofia, S.; Gough, D.
Bibcode: 1988JBAA...98..261D
Altcode:
No abstract at ADS
Title: Helium Diffusion in Rapidly Oscillating Ap-Stars
Authors: Dolez, N.; Gough, D. O.; Vauclair, S.
Bibcode: 1988IAUS..123..291D
Altcode:
Suppression of convection near the poles of magnetic A stars and
inhibition of winds near the equator influence chemical composition
gradients resulting from diffusion, leading to appreciable horizontal
variation in the equilibrium configurations of the stars. The authors
conjecture that it is this variation which is responsible for the
apparent alignment of non-radial pulsations with the magnetic axes of
the stars, and also for a possible previous misidentification of the
modes. It is suggested that nonadiabatic excitation can be sufficient
to overcome energy leakage into the atmosphere.
Title: Do Solar Models with Weakly Interacting Massive Particles
Reproduce the Stanford Seismic Data
Authors: Ellis, A. N.; Gough, D. O.
Bibcode: 1988IAUS..123..111E
Altcode:
The discrepancy between theoretical eigenfrequencies of standard solar
models and the frequencies of solar modes of degree between 2 and 5
measured at Stanford is degree-independent for cyclic frequencies above
about 2 mHz. Below that frequency the discrepancy for dotriacontapole
modes diverges from that of the modes of lower degree. The differences
between eigenfrequencies of a simple solar model containing a cloud
of weakly interacting particles in its core and of one without do not
reproduce this behaviour.
Title: Book-Review - Seismology of the Sun and the Distant Stars
Authors: Gough, D. O.
Bibcode: 1988ApL&C..26..374G
Altcode: 1988ApL....26..374G
No abstract at ADS
Title: Solar Equatorial Rotation Rate Inferred from Inversion of
Frequency Splitting of High-Degree Modes
Authors: Hill, F.; Gough, D. O.; Toomre, J.; Haber, D. A.
Bibcode: 1988IAUS..123...45H
Altcode:
The equatorial rotation rate has been inferred as a function of depth
through the outer 16 Mm of the Sun from observations of high-degree
five-minute oscillations. The results imply that the solar rotation
rate increases with depth by 0.023 μHz reaching a maximum at about
2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.
Title: On the Excitation of Solar 5-MINUTE Oscillations
Authors: Antia, H. M.; Chitre, S. M.; Gough, D. O.
Bibcode: 1988IAUS..123..371A
Altcode:
A simple prescription for the dynamics of convection perturbed by
stellar pulsation is used in an estimation of the growth rates of solar
five-minute modes. Convection appears to enhance the excitation of
the modes, and the maximum in the growth rate versus frequency found
previously when oscillatory convective perturbations were ignored is
still present.
Title: Theory of solar variation
Authors: Gough, D. O.
Bibcode: 1988stre.conf...90G
Altcode:
No abstract at ADS
Title: On the Implications of the Symmetric Component of the
Frequency Splitting
Authors: Gough, D. O.; Thompson, M. J.
Bibcode: 1988IAUS..123..175G
Altcode:
The component of the frequency splitting of solar five-minute
oscillations observed by Duvall, Harvey and Pomerantz that is even
in azimuthal degree measures latitudinal and depth variations in the
structure of the sun. The authors indicate how the data hint that there
is a shallow perturbation, possibly associated with a magnetic field,
that is concentrated at low latitudes.
Title: Magnetic Perturbations to Stellar Oscillation Eigenfrequencies
Authors: Gough, D. O.; Thompson, M. J.
Bibcode: 1988IAUS..123..155G
Altcode:
Magnetic fields contribute to the splitting of the degeneracy of modes
of like order and degree. The splitting is estimated for some simple
hypothetical toroidal magnetic field configurations in the sun, and
the results are compared with previous asymptotic estimates. Splitting
by a field confined to a thin layer at the base of the convection zone
is found not to agree with recent measurements.
Title: Magnetotelluric Soundings In the Canadian Rocky Mountains
Authors: Hutton, V. R. S.; Gough, D. I.; Dawes, G. J. K.; Travassos, J.
Bibcode: 1987GeoJ...90..245H
Altcode: 1987GeoJI..90..245H
No abstract at ADS
Title: Seismological measurement of stellar ages
Authors: Gough, Douglas
Bibcode: 1987Natur.326..257G
Altcode:
Accurate measurements of stellar acoustic oscillation frequencies, which
are likely to be obtained in the coming years, will provide important
new data enabling us to diagnose the internal structure of stars. The
ages of main-sequence stars are likely to be determined to a higher
precision than has been possible in the past and much more accurate
estimates of the total heavy-element abundances should be possible.
Title: Models of conductive structure under the Canadian Cordillera
Authors: Ingham, M. R.; Gough, D. I.; Parkinson, W. D.
Bibcode: 1987GeoJ...88..477I
Altcode: 1987GeoJI..88..477I
No abstract at ADS
Title: Stress Near the Surface of the Earth
Authors: Gough, D. I.; Gough, W. I.
Bibcode: 1987AREPS..15..545G
Altcode:
No abstract at ADS
Title: Book-Review - Seismology of the Sun and the Distant Stars
Authors: Gough, D. O.
Bibcode: 1986S&T....72..479G
Altcode:
No abstract at ADS
Title: Local Response of the Five-Minute Oscillations to a Major
Solar Flare
Authors: Haber, D. A.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1986BAAS...18Q1011H
Altcode:
No abstract at ADS
Title: Book-Review - Seismology of the Sun and the Distant Stars
Authors: Gough, D. O.; Hoyng, P.
Bibcode: 1986SSRv...44..401G
Altcode:
No abstract at ADS
Title: Weakly interacting massive particles and solar oscillations
Authors: Faulkner, J.; Gough, D. O.; Vahia, M. N.
Bibcode: 1986Natur.321..226F
Altcode:
If the Sun were to contain even a minute mass fraction of
weakly interacting massive particles (WIMPs), there could be
a significant influence on its central thermal structure. In
particular, a relative concentration as small as ~10-11
by number may lower the central temperature sufficiently to bring
the predicted electron neutrino detection rate into agreement with
observation1-6. Helioseismology7,8 provides
a means for an independent test of the validity of this and other
proposed resolutions of the solar neutrino problem. Theoretically,
it is the low-degree g modes that are most sensitive to conditions in
the core, the only region where substantial deviations from so-called
standard solar models occur. Indeed, solar models with WIMPs have a
g-mode period spacing that is markedly different from that of other
solar models. Therefore g-mode observations hold the promise of a
sensitive test, although unfortunately their current interpretation
is fraught with difficulties. The best test currently available
involves instead the frequency separation of low-degree p modes with
like (n+½l) (where n and l are respectively the order and degree of
the mode). Standard solar models produce p-mode separations somewhat
larger than those observed. Conventional attempts to resolve the solar
neutrino problem9,10 make the situation worse; in some cases,
grossly so. We show that, in contrast, a relevant WIMP model predicts
p-mode separations that are reduced by ~10% this is consistent with
the observations.
Title: Solar physics: What causes the solar cycle?
Authors: Gough, Douglas
Bibcode: 1986Natur.319..263G
Altcode:
No abstract at ADS
Title: Progress report on helium abundance determination.
Authors: Dappen, W.; Gough, D. O.
Bibcode: 1986ASIC..169..275D
Altcode: 1986ssds.proc..275D
Intermediate results from a programme to determine the helium
abundance of the solar convection zone are presented. The method uses
the influence of helium ionization on the local sound speed, which
can be gauged from inversions of solar oscillation frequencies. The
resolution of the principal diagnostic function by the data justifies
optimism for an abundance determination in a future step.
Title: Solar and solar-like oscillations: theory.
Authors: Gough, D. O.
Bibcode: 1986HiA.....7..283G
Altcode:
Solar five-minute oscillations provide a means of testing theoretical
models of the sun. By judiciously combining data from low-degree
modes, properties of the central and surface regions of the sun can be
inferred separately. In principle, it should be possible to draw similar
inferences from other stars, once adequate data are available. Recent
solar rotational splitting data imply that in the equatorial regions
much of the radiative envelope of the sun is rotating more slowly than
the photosphere.
Title: EBK Quantization of Stellar Waves
Authors: Gough, D. O.
Bibcode: 1986hmps.conf..117G
Altcode:
An asymptotic approximation to linear adiabatic oscillations of a
spherically symmetrical star is discussed. On the whole, the resulting
formulae are not new, and can be obtained by other methods, but it is
hoped that the discussion elucidates a potentially important technique
which can also be applied to stars whose symmetry has been broken. For
the simple symmetrical case considered here, the results are found to
be in satisfactory agreement with results obtained previously.
Title: Asymptotic sound-speed inversions.
Authors: Gough, D. O.
Bibcode: 1986ASIC..169..125G
Altcode: 1986ssds.proc..125G
An asymptotic analysis of stellar p modes in the short-wavelength
limit is summarized. The formula can be used as a means of estimating
the sound speed in the solar interior from a knowledge of identified
eigenfrequencies. The accuracy of the procedure is discussed, and it
is shown how the results can be used to measure properties such as
the location of the base of the convection zone.
Title: Seismology of the Sun and the distant stars. Proceedings
of a NATO Advanced Research Workshop, held at Cambridge, UK, 17 -
21 June 1985.
Authors: Gough, Douglas O.
Bibcode: 1986ASIC..169.....G
Altcode: 1986ssds.proc.....G
The conference presents papers on the properties of solar oscillations,
the theoretical aspects of helio- and asteroseismology, observations
of low-degree p-mode oscillations in 1984, and the detection of global
convective wave flows on the sun. Other topics include asymptotics and
quantum chaos in stellar oscillations, measuring the sun's internal
rotation using solar p-mode oscillations, and umbral oscillations as a
sunspot diagnostic. Consideration is also given to magnetic torques and
differential rotation, long-period variations in the solar diameter,
and the K 769.9-nm line profile.
Title: Inverting Helioseismic Data
Authors: Gough, D.
Bibcode: 1985SoPh..100...65G
Altcode:
Methods by which the observed frequencies of solar oscillations can be,
and in some cases have been used to infer the internal structure of the
Sun are discussed. Attention is confined to so-called inverse methods
that identify and extract the information that is actually contained in
the data. Because only a finite quantity of data can ever be acquired,
the functions describing the interior stratification of the Sun can
never be established completely without the acceptance of certain
assumptions. Nevertheless, the assumptions that are required are simple
to understand, and the results do not depend on the complicated and
uncertain theory of stellar evolution which has traditionally been used
to construct solar models. First results of the inversions have given
us an estimate of the sound speed and the angular velocity throughout
much of the solar interior. These estimates have already stimulated
speculation which hopefully will encourage further theoretical and
observational research that will improve our understanding of the Sun.
Title: Seismology of the Sun
Authors: Christensen-Dalsgaard, J.; Gough, D.; Toomre, J.
Bibcode: 1985Sci...229..923C
Altcode:
Oscillations of the sun make it possible to probe the inside of a
star. The frequencies of the oscillations have already provided measures
of the sound speed and the rate of rotation throughout much of the solar
interior. These quantities are important for understanding the dynamics
of the magnetic cycle and have a bearing on testing general relativity
by planetary precession. The oscillation frequencies yield a helium
abundance that is consistent with cosmology, but they reinforce the
severity of the neutrino problem. They should soon provide an important
standard by which to calibrate the theory of stellar evolution.
Title: Internal Structure of the Sun
Authors: Frohlich, C.; Gough, D.
Bibcode: 1985ESASP.235..241F
Altcode: 1985fmsh.work..241F
No abstract at ADS
Title: Theory of Solar Oscillations
Authors: Gough, D. O.
Bibcode: 1985ESASP.235..183G
Altcode: 1985shpp.rept..183G; 1985fmsh.work..183G
This paper reviews some of the most recent analyses of
helioseismological data, and discusses briefly some theoretical issues
they raise. The properties of resonant modes of oscillation are briefly
reviewed, for the purpose of subsequently understanding what aspects of
the solar structure can be measured from their frequencies. A recent
determination of the variation of sound speed through much of the
interior of the sun is then described. The measurement reveals the
presence of macroscopic motion in the solar core.
Title: Speed of sound in the solar interior
Authors: Christensen-Dalsgaard, J.; Duvall, T. L., Jr.; Gough, D. O.;
Harvey, J. W.; Rhodes, E. J., Jr.
Bibcode: 1985Natur.315..378C
Altcode:
Frequencies of solar 5-min oscillations can be used to determine
directly the sound speed of the solar interior. The determination
described here does not depend on a solar model, but relies only on a
simple asymptotic description of the oscillations in terms of trapped
acoustic waves.
Title: Changes in Subsurface Horizontal Velocities Inferred from
Observations of High Degree 5-Minute Solar Oscillations
Authors: Hill, F.; Toomre, J.; Gough, D. O.
Bibcode: 1985BAAS...17..643H
Altcode:
No abstract at ADS
Title: Stellar structure: Beginnings of asteroseismology
Authors: Gough, Douglas
Bibcode: 1985Natur.314...14G
Altcode:
No abstract at ADS
Title: Recent Advances in Helioseismology
Authors: Gough, D.
Bibcode: 1985spit.conf..137G
Altcode:
No abstract at ADS
Title: Rotational inversion from global solar oscillations.
Authors: Christensen-Dalsgaard, J.; Gough, D.
Bibcode: 1984sses.nasa...79C
Altcode: 1984sss..conf...79C
The authors investigate the degree to which various sets of solar
oscillations can resolve the solar internal rotation. Genuine
observations were simulated by the following procedure: First an
artificial angular velocity was invented by one of the authors,
and from it the rotational splitting of a set of normal modes
was calculated; to that was added some random noise. The result was
treated as artificial data by the other author, acting as an observer,
who attempted to recover the rotation law by using the Backus-Gilbert
optimal averaging procedure. The observer knew neither the original
rotation law nor the amount of noise that had been added. Finally his
conclusion was compared with the actual artificial angular velocity.
Title: Solar inverse theory.
Authors: Gough, D.
Bibcode: 1984sses.nasa...49G
Altcode: 1984sss..conf...49G
Helioseismological inversion, as with the inversion of any other data,
is divided into three phases. The first is the solution of the so-called
forward problem: namely, the calculation of the eigenfrequencies of a
theoretical equilibrium state. The second is an attempt to understand
the results, either empirically by determining how those frequencies
vary as chosen parameters defining the equilibrium model are varied, or
analytically from asymptotic expansions in limiting cases of high order
or degree. The third phase is to pose and solve an inverse problem,
which seeks to find a plausible equilibrium model of the Sun whose
eigenfrequencies are consistent with observation. The three phases
are briefly discussed in this review, and the third, which is not
yet widely used in helioseismology, is illustrated with some selected
inversions of artificial solar data.
Title: Sensitivity of inferred subphotospheric velocity field to
mode selection, analysis technique and noise.
Authors: Hill, F.; Gough, D.; Toomre, J.
Bibcode: 1984sses.nasa...95H
Altcode: 1984sss..conf...95H
The horizontal velocity immediately below the photosphere can be
inferred from observations of high-degree solar oscillations by an
optimal-averaging inversion technique. The authors investigate the
sensitivity of the results to various details of both the inversion
and the determination of the frequencies. The results are shown to be
quite stable to the choice of most parameters, suggesting that this
procedure produces reliable estimates of the subsurface velocity.
Title: Implications of observed frequencies of solar p modes.
Authors: Christensen-Dalsgaard, J.; Gough, D.
Bibcode: 1984sses.nasa..199C
Altcode: 1984sss..conf..199C
The authors present a preliminary comparison of the observed frequencies
of 5-min modes reported by Duvall & Harvey in these proceedings with
theoretical frequencies for a traditional solar model. The differences
between observations and theory can be understood qualitatively in
terms of two separate sources of error in the frequency calculation,
one near the solar surface and the other at the base of the convection
zone. There is no indication of errors in the deep interior of the
model.
Title: On the Rotation of the Sun
Authors: Gough, D. O.
Bibcode: 1984RSPTA.313...27G
Altcode: 1984RSLPT.313...27G
An asymptotic method is developed to estimate the rotational splitting
of sectoral five-minute solar oscillations. Integral formulae are
obtained which can be inverted to yield the variation with depth of
the Sun's angular velocity near the equatorial plane. The result is a
functional of smoothed data, and does not rely on a detailed theoretical
model of the Sun. The method has been tested with artificial data
(computed from a theoretical solar model) of a kind similar to some real
solar data obtained recently by Duvall & Harvey (Nature, Lond. 310,
19 (1984)). The results are encouraging, for they reproduce at least
the broadest feature of the somewhat arbitrary angular velocity with
which the theoretical model was endowed. When applied to the real
data, the method yields a result similar to that derived by Duvall et
al. (Nature, Lond. 310, 22 (1984)) by another procedure.
Title: The Early Solar System and the Rotation of the Sun: Discussion
Authors: Zinnecker, H.; Gold, T.; McCrea, W. H.; Tayler, R. J.;
Woolfson, M. M.; Gough, D. O.
Bibcode: 1984RSPTA.313...43Z
Altcode:
No abstract at ADS
Title: Mantle upflow under North America and plate dynamics
Authors: Gough, D. I.
Bibcode: 1984Natur.311..428G
Altcode:
In the development of plate dynamics there are two fundamental
questions. First, do the plates slide over a passive asthenosphere,
or are they driven by a convecting upper mantle? Second, are all
ocean ridges passive, pull-apart plate margins, or do some lie above
upcurrents in the mantle and in that sense become active margins? The
combination of stress orientations in the crust of North America with
other geophysical and geological information favours an active mantle
interpretation, both for the North American plate and for the mantle
upflow which lay beneath the East Pacific Rise in Tertiary times and
which now lies beneath the western United States.
Title: Internal rotation of the Sun
Authors: Duvall, T. L., Jr.; Dziembowski, W. A.; Goode, P. R.; Gough,
D. O.; Harvey, J. W.; Leibacher, J. W.
Bibcode: 1984Natur.310...22D
Altcode:
The frequency difference between prograde and retrograde sectoral
solar oscillations is analysed to determine the rotation rate of
the solar interior, assuming no latitudinal dependence. Much of the
solar interior rotates slightly less rapidly than the surface, while
the innermost part apparently rotates more rapidly. The resulting
solar gravitational quadrupole moment is J2 = (1.7+/-0.4)
× 10-7 and provides a negligible contribution to current
planetary tests of Einstein's theory of general relativity.
Title: On the identification of normal modes of oscillation from
observations of the solar periphery
Authors: Gough, D. O.; Latour, J.
Bibcode: 1984AExpr...1....9G
Altcode:
The decomposition of solar oscillations into their constituent
normal modes requires a knowledge of both the spatial and temporal
variation of the perturbation to the sun's surface. The task can
be especially difficult when only limited spatial information is
available. Observations of the limb-darkening function, for example, are
probably sensitive to too large a number of modes to permit most of the
modes to be identified in a power spectrum of measurements at only a few
points on the limb, unless the results are combined with other data. In
this paper a procedure is considered by which the contributions from
quite small groups of modes to spatially well resolved data obtained
at any instant can be extracted from the remaining modes. Combining
these results with frequency information then permits the modes to
be identified, at least if their frequencies are low enough to ensure
that modes of high degree do not contribute substantially to the signal.
Title: Attempt to measure the solar subsurface velocity
Authors: Hill, F.; Gough, D.; Toomre, J.
Bibcode: 1984MmSAI..55..153H
Altcode:
Five-minute oscillation modes are advected by horizontal velocities
below the solar surface, and thus can be used as probes of rotation
and large-scale convective flows. Results of inverse theory applied
to observations of high-degree modes carried out on six separate days
reveal variations in horizontal velocities with depth from day to day
that may be the result of giant convection cells, through noise in
the data makes this interpretation somewhat tentative.
Title: Influence of rotation and magnetic fields on stellar
oscillation eigenfrequencies
Authors: Gough, D. O.; Taylor, P. P.
Bibcode: 1984MmSAI..55..215G
Altcode:
A formalism to calculate rotational and magnetic splitting of otherwise
degenerate high-order oscillation p modes of low degree is outlined. For
the purposes of illustration, attention is restricted to axisymmetric
toroidal magnetic fields, with axes of symmetry that are permitted to
be different from the rotation axis. It is found that advection is
the most important contributor to rotational splitting; in general,
magnetic perturbations add to the complexity of the frequency spectrum
when the oscillations are viewed from an inertial frame. The effect
of a field whose axis lies close to the sun's equatorial plane is
briefly considered. It is found that such a field is not able to split
five-minute dipole modes into observable triplets.
Title: On the identification of normal modes of oscillation from
observations of the solar periphery
Authors: Gough, D. D.; Latour, J.
Bibcode: 1984MmSAI..55..227G
Altcode: 1984STIN...8429844G
The decomposition of solar oscillations into their constituent normal
modes requires a knowledge of both the spatial and temporal variation of
the perturbation to the Sun's surface. The task is especially difficult
when only limited spatial information is available. Observations of the
limb darkening function, for example, are probably sensitive to too
large a number of modes to permit most of the modes to be identified
in a power spectrum of measurements at only a few points on the
limb, unless the results are combined with other data. A procedure
was considered by which the contributions from quite small groups
of modes to spatially well resolved data obtained at any instant
can be extracted from the remaining modes. Combining these results
with frequency information then permits the modes to be identified,
at least if their frequencies are low enough to ensure that modes of
high degree do not contribute substantially to the signal.
Title: Simulation of Effects of Atmospheric Seeing on Observations
of Solar Five-Minute Oscillations
Authors: Merryfield, W. J.; Toomre, J.; Hill, F.; Gough, D. O.
Bibcode: 1984BAAS...16..532M
Altcode:
No abstract at ADS
Title: Horizontal Velocities in the Solar Convection Zone Inferred
from High Degree 5-Minute Oscillations
Authors: Hill, F.; Toomre, J.; Gough, D. O.
Bibcode: 1984BAAS...16R.451H
Altcode: 1984BAAS...16..451H
No abstract at ADS
Title: Geminga and the 160-min solar oscillation
Authors: Fabian, A. C.; Gough, D. O.
Bibcode: 1984Natur.308..160F
Altcode:
The idea that solar oscillations might have been stimulated by
gravitational radiation from a nearby binary system1,2 has
recently been explored by Delache and co-workers3,4. They
have announced that the γ-ray source CG195+4, known as Geminga, varies
in intensity with a period of 159.96min (ref. 3), and therefore has a
frequency just (1 yr)-1 greater than the 160.01-min solar
oscillation5-7. From this coincidence they have inferred a
gravitational connection between the two oscillations. We show here
that if the generally accepted ideas of gravitational radiation are
correct, the 160-min solar oscillation could not have been driven to
its observed amplitude by any binary system of stellar mass. Only if
there were a sustained resonance between the incident radiation and a
solar mode of oscillation could there be any chance of an observable
response. However, gravitational radiation causes the binary system
to spin up, prohibiting it from remaining in resonance with a 160-min
mode for long enough to have a perceptible effect It is just possible
that 5-min oscillations in the Sun could be excited to an observable
amplitude by a binary system having an orbital period of ~10 min at
1,000 AU.
Title: Helioseismology: Oscillations as a Diagnostic of the Solar
Interior
Authors: Deubner, Franz-Ludwig; Gough, Douglas
Bibcode: 1984ARA&A..22..593D
Altcode:
Contents: (1) Introduction. (2) Resonant cavities in the
Sun. (3) Observational methods. (4) High-degree modes: Solar
structure. Subphotospheric velocities. (5) Low-degree modes: High-order
p modes. Gravity modes. Solar structure. (6) Five-minute modes of
intermediate degree. (7) Limb observations. (8) Problems for the
immediate future. Appendix: Classification of stellar oscillations.
Title: On the Determination of the Helium Abundance of the Solar
Convection Zone
Authors: Dappen, W.; Gough, D. O.
Bibcode: 1984LIACo..25..264D
Altcode: 1984tpss.conf..264D; 1984trss.conf..264D
No abstract at ADS
Title: Helioseismology
Authors: Gough, D. O.
Bibcode: 1984IScRv...9..240G
Altcode:
No abstract at ADS
Title: Immediate and long-term prospects for helioseismology
Authors: Gough, D. O.
Bibcode: 1984AdSpR...4h..85G
Altcode: 1984AdSpR...4...85G
Recent extensive measurements of frequencies of free oscillation of the
Sun have permitted a first direct estimate of the variation of sound
speed and angular velocity throughout the Sun. The results hint that
the answers to some tantalizing questions concerning the Sun's interior
structure and its history are almost within grasp. Optimists like
myself believe that in a few years a worldwide network of ground-based
observing stations will give us important clues. However, it may be
necessary to make observations from space before we can be sure of
the answers.
Title: Towards a solar model
Authors: Gough, D. O.
Bibcode: 1984MmSAI..55...13G
Altcode:
The physics of the most important solar-oscillation modes is reviewed
on the basis of published observations, and the constraints placed on
models of solar structure by the oscillation data are examined. Topics
discussed include the low-order high-degree acoustic modes and their
implications for convection-zone structure, low-degree 5-min p-modes,
and rotational splitting. Diagrams and spectra are provided, and a ray
theory for an isothermal spherical cavity is presented in an appendix.
Title: Helioseismology: Oscillations as a probe of the Sun's interior
Authors: Gough, Douglas
Bibcode: 1983Natur.304..689G
Altcode:
No abstract at ADS
Title: An upper bound to the periods of radial pulsation of the sun
Authors: Christensen-Dalsgaard, J.; Cooper, A. J.; Gough, D. O.
Bibcode: 1983MNRAS.203..165C
Altcode:
The nature of the 160 min oscillation of the sun is investigated. It
is shown that the periods of linear adiabatic radial pulsation of any
stably stratified star with given mass M and radius R, and constant
adiabatic exponent gamma, are bounded above by the period of the
fundamental radial mode of the adiabatically stratified model. If M and
R have the solar values, it is determined that the greatest period is
101.5 min. While this analysis does not generalize to the case when
gamma is permitted to vary in a realistic way, it is argued that in
that case the period of the adiabatically stratified model is likely
to be a good estimate of the upper bound. This period is shown to be
weakly dependent on composition, with its greatest value being 101.9
min when the heavy-element abundance is taken to be 2%.
Title: Solar atmospheric temperature inhomogeneities induce a 13-day
oscillation in full-disk Doppler measurements
Authors: Edmunds, M. G.; Gough, D. O.
Bibcode: 1983Natur.302..810E
Altcode:
Claverie et al.1 have reported a 13-day oscillation in
full-disk solar spectrum-line shifts, which they claim to be evidence
for rapid rotation of the Sun's core. We point out here that the passage
of active regions across the disk could be responsible for oscillations
of this kind. Variations in line shifts and in irradiance are expected
with frequencies comparable to both the photospheric rotation rate
and to higher harmonics. For line-shift oscillations the power in the
second harmonic is substantially greater than it is for irradiance
variations. Therefore a prominent 13-day component is not surprising,
especially as we know that the second harmonic is strong in the sunspot
distribution2. We estimate the amplitude, period and phase
that would be expected to have been found in line-shift data, obtaining
results comparable with those of Claverie et al.1. We
suggest that the 13-day oscillation is a direct consequence of the
inhomogeneity of the solar surface. Our analysis complements and
extends a recent study by Durrant and Schröter3.
Title: A magnetovariational study of a geothermal anomaly
Authors: Ingham, M. R.; Bingham, D. K.; Gough, D. I.
Bibcode: 1983GeoJ...72..597I
Altcode: 1983GeoJI..72..597I
No abstract at ADS
Title: Solar structure: A bridge in a gap in solar oscillations
Authors: Gough, Douglas
Bibcode: 1983Natur.302...18G
Altcode:
No abstract at ADS
Title: The protosolar helium abundance
Authors: Gough, D. O.
Bibcode: 1983prhe.work..117G
Altcode:
The theory of stellar evolution applied to the sun cannot alone
determine the solar helium abundance. Only if the neutrino flux is
taken into account can a formal calibration be carried out. But
that procedure appears to give the wrong result. An astronomical
argument for calibrating mixing-length theory, using a measure
of chromospheric activity in lower main-sequence stars, suggests
that the protosolar abundance by mass is about 0.25. More direct
measurements, using five-minute high-degree oscillation frequencies to
measure conditions in the upper regions of the convection zone, and
five-minute low-degree oscillations to probe the radiative interior,
corroborate this finding. A recent unpublished report of quadrupole
g-mode frequencies is also consistent. It is difficult to assess the
uncertainty in the estimated abundance, because there are systematic
unexplained discrepancies between theory and observation. However,
the spread in the various determinations, excluding that involving
the neutrino flux, is less than 10 percent of the mean value.
Title: Detection of solar five-minute oscillations of low degree
Authors: Scherrer, Philip H.; Wilcox, John M.; Christensen-Dalsgaard,
J.; Gough, D. O.
Bibcode: 1983SoPh...82...75S
Altcode: 1983IAUCo..66...75S
Solar five-minute oscillations of degree l = 3, 4, and 5 have been
observed at Stanford, in the Doppler shift of the Fe 5124 line. The
frequencies and amplitudes are in broad agreement with previous
observations of modes with l ≤ 3, though we note that there are some
systematic discrepancies between the results of different observers.
Title: Our First Inferences from Helioseismology
Authors: Gough, D. O.
Bibcode: 1983PhB....34..502G
Altcode:
No abstract at ADS
Title: Temporal solar variations.
Authors: Gough, D. O.
Bibcode: 1983ESAJ....7..325G
Altcode:
Temporal variations of the sun on time scales ranging from about 5
min to 10 to the 10th yr are discussed. Attention is restricted to
only the inner 99.999999996 percent by mass of the sun. Variations on
the longest time scales relate to the overall evolution of the sun,
and are predicted from the theory of stellar structure. Any evidence
that can be gathered to confirm such variations is therefore pertinent
not only to the sun, but to stars in general.
Title: On the Detection of Subphotospheric Convective Velocities
and Temperature Fluctuations
Authors: Gough, D. O.; Toomre, J.
Bibcode: 1983SoPh...82..401G
Altcode: 1983IAUCo..66..401G
A procedure is outlined for estimating the influence of large-scale
convective eddies on the wave patterns of five-minute oscillations
of high degree. The method is applied to adiabatic oscillations, with
frequency ω and wave number k, of a plane-parallel polytropic layer
upon which is imposed a low-amplitude convective flow. The distortion to
the k - ω relation has two constituents: one depends on the horizontal
component of the convective velocity and has a sign which depends on
the sign of ω/k; the other depends on temperature fluctuations and
is independent of the sign of ω/k. The magnitude of the distortion
is just at the limit of present observational sensitivity. Thus there
is reasonable hope that it will be possible to reveal some aspects of
the large-scale flow in the solar convection zone.
Title: Foreword
Authors: Gough, D. O.
Bibcode: 1983SoPh...82....7G
Altcode: 1983IAUCo..66....7G
No abstract at ADS
Title: On the influence of nonlinearities on the eigenfrequencies
of five-minute oscillations of the Sun
Authors: Belvedere, G.; Gough, D.; Paterno, L.
Bibcode: 1983SoPh...82..343B
Altcode: 1983IAUCo..66..343B
Fitting the results of linear normal-mode analysis of the solar
five-minute oscillations to the observed k - ω diagram selects a
class of models of the Sun's envelope. It is a property of all the
models in this class that their convection zones are too deep to
permit substantial transmission of internal g modes of degree 20 or
more. This is in apparent conflict with Hill and Caudell's (1979)
claim to have detected such modes in the photosphere.
Title: Problems of solar and stellar oscillations; Proceedings of the
Sixty-sixth Colloquium, Nauchny, Ukrainian SSR, September 1-5, 1981
Authors: Gough, D. O.
Bibcode: 1983SoPh...82.....G
Altcode: 1983IAUCo..66.....G
The present conference on solar and stellar oscillations discusses the
structure of the solar oscillations with near-160 min period (together
with their velocity and brightness manifestations), solar oscillation
observations, oscillation modes of the sun in the 10 min-2 hour period
range, the superposed epoch method for the analysis of solar radiation
data, wave motion spectral-spatial analysis, solar oscillation radiative
transfer, and a novel method for determining the He abundance of the
solar atmosphere. Also considered are the study of internal solar
structure by means of its oscillations, adiabatic oscillations of
solar models, a solar oblique magnetic rotator, resonant coupling
between solar gravity modes, the seismology of sunspot atmospheres,
solar convection, power spectrum variability in the solar five-minute
oscillations, torsional solar oscillations, and atmospheric internal
gravity waves.
Title: Time-dependent solutions of multimode convection equations
Authors: Toomre, J.; Gough, D. O.; Spiegel, E. A.
Bibcode: 1982JFM...125...99T
Altcode:
Truncated modal equations are used to study the time evolution of
thermal convection. In the Boussinesq approximation these nonlinear
equations are obtained by expanding the fluctuating velocity and
temperature fields in a finite set of planforms of the horizontal
coordinates. Numerical studies dealing with two or three modes with
triad interactions are discussed. Rich time dependence was found
in these cases: periodic and aperiodic solutions can be obtained,
along with various steady solutions. Three-mode solutions reproduce
the qualitative appearance of spoke-pattern convection as observed in
experiments at high Prandtl numbers. Though the values of the periods of
the time-dependent solutions do not agree with those of the experiments,
their variation with Rayleigh number compares favorably. Except at
the highest Rayleigh number considered (10,000,000), the theoretical
Nusselt numbers agree well with experiment.
Title: Single-mode theory of diffusive layers in thermohaline
convection
Authors: Gough, D. O.; Toomre, J.
Bibcode: 1982JFM...125...75G
Altcode:
A two-layer configuration of thermohaline convection is studied,
with the principal aim of explaining the observed independence of
the buoyancy-flux ratio on the stability parameter when the latter is
large. Temperature is destabilizing and salinity is stabilizing, so
diffusive interfaces separate the convecting layers. The convection is
treated in the single-mode approximation, with a prescribed horizontal
planform and wavenumber. Surveys of numerical solutions are presented
for a selection of Rayleigh numbers R, stability parameters lambda
and horizontal wavenumbers. The solutions yield a buoyancy flux
ratio chi that is insensitive to lambda, in accord with laboratory
experiments. However chi increases with increasing R, in contradiction
to laboratory observations.
Title: Solar Five-Minute Oscillations, Subsurface Velocities and
Inverse Theory
Authors: Gough, D. O.; Hill, F.; Toomre, J.
Bibcode: 1982BAAS...14..938G
Altcode:
No abstract at ADS
Title: Internal rotation and gravitational quadrupole moment of
the Sun
Authors: Gough, D. O.
Bibcode: 1982Natur.298..334G
Altcode:
The internal angular velocity of the Sun is estimated from observations
of apparent rotational splitting of low-order low-degree global
oscillations detected in fluctuations in the limb-darkening function. A
sidereal rotation of 3 µHz is inferred for the deep interior; this is
more than six times greater than the equatorial rotation frequency of
the photosphere. The inferred angular velocity distribution does not
vary strongly with latitude, and yields a gravitational quadrupole
moment J2~=3.6×10-6. When combined with the
results of planetary radar observations to determine (2-β+2γ)/3,
a combination of Eddington-Robertson post-newtonian parameters which
in general relativity is unity, a value of about 0.994 (+/-0.012)
is thus obtained.
Title: Evidence for an oblique magnetic solar rotator
Authors: Gough, D. O.
Bibcode: 1982Natur.298..350G
Altcode:
The observation by Claverie et al.1. of fine structure in the
peaks in the power spectrum of low-degree 5-min solar oscillations has
been interpreted as being a result of rotational splitting. Claverie
et al.1 claim that their measurements imply that an
appropriately weighted average Ωmacr of the interior angular velocity
Ω(r) of the Sun is about twice the value of Ω at the surface. At
first sight their claim looks doubtful, because all 2l + 1 components
of the set of modes of degree l appear in the spectrum, whereas only
l + 1 of them should be detectable. However, Isaak2 has
recently speculated that the additional components are produced by
an intense rotating magnetic core, such as had been postulated by
Dicke3,4 to account for the 12.2-day periodic component
in the Princeton oblateness data5-9. Isaak2
pointed out that the mean period 2π/Ω~=15 days of the solar interior
that was inferred from the Birmingham data1 is consistent
with a central core rotating with the 12.2-day period and an outer
envelope rotating with the photosphere. Moreover, his rough estimate
of a few megagauss for the r.m.s. magnetic field that is required to
support his conjecture is within about a factor 10 of that required
by Dicke3. Thence he concluded that the Birmingham
data1 provide the first clear empirical evidence for an
intense internal solar magnetic field. Here I examine this evidence
in more detail, and show that the conclusion is premature. If the
magnetic core does exist, the 5-min oscillations provide no clear
evidence that it is rotating rapidly. Furthermore, unless one accepts
a contrived magnetic-field configuration, an explanation for the 2l +
1 components of the multiplets is still lacking.
Title: Observation of additional low-degree 5-min modes of solar
oscillation
Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.;
Gough, D.
Bibcode: 1982Natur.297..312S
Altcode: 1982STIN...8315246S
By measuring the difference between the shifts in the Fe 5,124
spectrum line from light integrated from a central circular portion
of the solar disk and from an annular portion exterior to it,
we have detected high-order solar oscillations with degrees l
= 3, 4 and 5. The frequencies of the octupole modes agree well
with the values obtained from whole-disk measurements at the South
Pole1. A least-squares fit of the observed frequencies to
values interpolated between and extrapolated from the predictions
of a sequence of solar models with different chemical compositions
selects two models. One of these is almost identical to that obtained
by a previous fit15 of modes with l<=2, and has a helium
abundance somewhat greater than 25% by mass.
Title: Detection of solar five minute oscillations of low degree
Authors: Scherrer, P. H.; Wilcox, J. M.; Christensen-Dalsgaard, J.;
Gough, D. O.
Bibcode: 1982STIN...8317445S
Altcode:
Solar five-minute oscillations of degree small = 3, 4 and 5 have been
observed at the Stanford Solar Observatory, in the Doppler shift of the
Fe5124 line. The frequencies and amplitudes are in broad agreement with
previous observations of modes with small less than or 3, though we
note that there are some systematic discrepancies between the results
of different observers.
Title: On the interpretation of five-minute oscillations in solar
spectrum line shifts.
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1982MNRAS.198..141C
Altcode:
It is suggested that p modes in the sun are on average excited to a
surface amplitude which is solely a function of frequency, except
in the case of modes of the highest degree. Observational data in
the 2-4 mHz range seem to be consistent with this hypothesis. The
sharp-line component first reported by Claverie et al (1979) in the
power spectra of whole-disc measurements is due to a near coincidence
of the eigenfrequencies of modes of low degree, which are the modes
to which such measurements are most sensitive. Previously, similar
observations did not isolate the sharp-line component, in part, because
although the amplitudes of the motion observed were consistent with
the stated hypothesis, the observing intervals were too short. The
amplitudes of the higher-degree modes responsible for the five-minute
oscillations reported by Leighton. Noyes and Simon (1962) are also
essentially in accord with the hypothesis presented.
Title: A review of: "A perspective of physics, vol. 3"
Authors: Gough, D. O.
Bibcode: 1982GApFD..19..155G
Altcode:
Edited by Sir Harrie Massey. Gordon and Breach, New York, London,
Paris, 1979. 354 pp. ($35.50 (ISBN 0 677 15970 6))
Title: Diagnostics of the Solar Interior
Authors: Gough, D. O.
Bibcode: 1982EuNew..13....3G
Altcode:
No abstract at ADS
Title: On the Problem of Interpreting Rapidly Oscillating Ap-Stars
Authors: Dolez, N.; Gough, D. O.
Bibcode: 1982pccv.conf..248D
Altcode:
No abstract at ADS
Title: A Review of the Theory of Solar Oscillations and its
Implications Concerning the Internal Structure of the Sun
Authors: Gough, D. O.
Bibcode: 1982pccv.conf..117G
Altcode:
No abstract at ADS
Title: Comparison of observed solar whole-disk oscillation frequencies
with the predictions of a sequence of solar models
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1981A&A...104..173C
Altcode:
It is noted that solar models computed under a consistent set of
assumptions, and calibrated to the present luminosity and radius,
usually depend on one or more parameters. A one-parameter sequence of
models is considered here, each model being labeled by its initial
heavy-element abundance Z. Given Z, the helium abundance Y and
the mixing length used in the convection formulas are fixed by the
calibration. An additional constraint is required to determine Z. Use
is made here of the whole-disk five-minute oscillation data as a guide.
Title: On the seat of the solar cycle
Authors: Gough, D.
Bibcode: 1981NASCP2191..185G
Altcode: 1981vsc..conf..185G
A discussion of some of the issues raised in connection with the seat
of the solar cycle are presented. Is the cycle controlled by a strictly
periodic oscillator that operates in the core, or is it a turbulent
dynamo confined to the convection zone and possibly a thin boundary
layer beneath it? Sunspot statistics are discussed, with a view to
ascertaining the length of the memory of the cycle, without drawing a
definitive conclusion. Also discussed are some of the processes that
might bring about variations delta L and delta R in the luminosity
and the radius of the photosphere. It appears that the ratio W =
delta lnR/delta lnL increases with the depth of the disturbance that
produces the variations, so that imminent observations might determine
whether or not the principal dynamical processes are confined to only
the outer layers of the Sun.
Title: Solar Interior Structure and Luminosity Variations
Authors: Gough, D. O.
Bibcode: 1981SoPh...74...21G
Altcode:
The assumptions of standard solar evolution theory are mentioned
briefly, and the principle conclusions drawn from them are
described. The result is a rationalization of the present luminosity and
radius of the Sun. Because there is some uncertainty about the interior
composition of the Sun, a range of models is apparently acceptable.
Title: Problems with solar oscillations
Authors: Gough, Douglas
Bibcode: 1981Natur.293..703G
Altcode:
No abstract at ADS
Title: Inferences from Solar Oscillations
Authors: Gough, D.
Bibcode: 1981IrAJ...15..116G
Altcode:
No abstract at ADS
Title: A new measure of the solar rotation
Authors: Gough, D. O.
Bibcode: 1981MNRAS.196..731G
Altcode:
It is suggested that the fluctuations in the Princeton solar oblateness
data, recently reanalyzed by Dicke, may result from rotational splitting
of non-axisymmetrical oscillations. If this hypothesis is correct,
the splitting frequency provides an integral measure of the internal
rotation of the sun. Upper and lower bounds to the solar gravitational
quadrupole moment are computed under the assumption that a single mode
of oscillation predominates. The results depend on the nature of that
mode: if it is a p mode the upper bound may be greater than the direct
estimates obtained from the value of the oblateness of the solar image;
but if it is a g mode, the upper bound is considerably lower than the
value Dicke and Goldenberg have claimed.
Title: On the Frequencies of the Solar 5 min Oscillations of High
Degree
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1981BAAS...13..859C
Altcode:
No abstract at ADS
Title: Problems of solar and stellar oscillations
Authors: Gough, D. O.
Bibcode: 1981psso.conf.....G
Altcode:
No abstract at ADS
Title: Is the Sun helium-deficient?
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1980Natur.288..544C
Altcode:
The recent observations ofsolar 5-min oscillations of low degree agree
approximately with the predictions of a standard solar model with
normal abundances of helium and heavy elements. Much of the apparent
discrepancy noticed when the observations werefirst announced was
a result of having neglected the influence of the Sun 's atmosphere
in the normal mode analysis of the theoretical models. Our standard
solar models are not in perfect agreement with observation, but it
seems that major modifications will not be necessary to remove the
remaining small discrepancies.
Title: Climate and variability in the solar constant
Authors: Gough, Douglas
Bibcode: 1980Natur.288..639G
Altcode:
No abstract at ADS
Title: Conductive structures in southernmost Africa: a magnetometer
array study
Authors: Beer, J. O.; Gough, D. I.
Bibcode: 1980GeoJ...63..479B
Altcode: 1980GeoJI..63..479B
No abstract at ADS
Title: Implications of the whole-disk Doppler observations of the sun
Authors: Christensen-Dalsgaard, J.; Gough, D.
Bibcode: 1980LNP...125..184C
Altcode: 1980nnsp.work..184C
The recent discovery by Claverie et al. (1980) of distinct,
approximately evenly spaced peaks in the power spectra of whole disk
solar Doppler measurements is interpreted with respect to implications
about the structure of the solar interior. It is inferred that
those observations imply a lower sound speed, appropriately averaged
throughout the interior, and probably a lower mean temperature than
predicted by standard solar models.
Title: Perturbations in gravitational potential associated with
solar oscillations
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1980LNP...125..369C
Altcode: 1980nnsp.work..369C
The relation between the amplitudes of the gravitational potential
perturbation and the displacement eigenfunctions of adiabatic
oscillations of a solar model is discussed, and numerical results are
tabulated for a selection of modes of low degree. In particular, a solar
quadrupole oscillation with period 160 min and rms surface velocity
of 1 m/sec would induce a perturbation in the external gravitational
potential with an oscillating quadrupole moment of amplitude about
one-third that of the static moment that would be produced by a uniform
interior rotation of the sun with angular velocity comparable with that
observed on the surface. It is concluded that quadrupole oscillations
might be detectable gravitationally.
Title: Introduction to Nonradial and Nonlinear Stellar Pulsation
Authors: Gough, D.
Bibcode: 1980LNP...125....1G
Altcode: 1980nnsp.work....1G
No abstract at ADS
Title: How deep is the solar convection zone
Authors: Christensen-Dalsgaard, J.; Dziembowski, W.; Gough, D.
Bibcode: 1980LNP...125..313C
Altcode: 1980nnsp.work..313C
The interpretation by Hill and Caudell (1979) of some of their solar
oscillation data as being due to g modes of degree greater than 20 seems
to imply that the solar convection zone is much shallower than that in
standard solar models, probably representing only a few percent of the
radius. It is here attempted to match the observed periods in models
of this nature; the rather complicated spectrum of oscillations in
such models can be understood in terms of the asymptotic behavior of
modes of large degree. Possible excitation mechanisms for the modes
are briefly discussed.
Title: Theoretical Prediction of Eigen Frequencies of the Solar Five
Minute Oscillation
Authors: Berthomieu, G.; Cooper, A. J.; Gough, D. O.; Osaki, Y.;
Provost, J.; Rocca, A.
Bibcode: 1980jfss.conf...32B
Altcode:
No abstract at ADS
Title: Sensitivity of five minute eigenfrequencies to the structure
of the sun
Authors: Berthomieu, G.; Provost, J.; Rocca, A.; Cooper, A. J.; Gough,
D. O.; Osaki, Y.
Bibcode: 1980LNP...125..307B
Altcode: 1980nnsp.work..307B
The dependence of theoretical eigenfrequencies of five minute
oscillation modes on the parameters that determine model solar
envelopes has been investigated. It was found that the p mode
frequencies are quite strongly correlated with the depth of the
convection zone. Comparison of theory with observation suggests that
the solar convection zone is about 200,000 km deep.
Title: Some theoretical remarks on solar oscillations
Authors: Gough, D.
Bibcode: 1980LNP...125..273G
Altcode: 1980nnsp.work..273G
The properties of the linear modes of oscillation of a nonrotating
nonmagnetic star, with particular reference to the sun, are briefly
described. The most likely mechanisms by which they might be excited are
reviewed, and it is concluded that stochastic excitation by turbulence
is probably the dominant mechanism that drives the solar five minute
oscillations. Phase coherence of one of the components of the SCLERA
diameter data is illustrated, and the new five minute oscillations in
the Birmingham whole-disk Doppler data are discussed. Finally some of
the problems raised by conflicting evidence concerning the structure
of the sun are aired, but not resolved.
Title: The pre-main-sequence evolution of the sun
Authors: Gough, D.
Bibcode: 1980asfr.symp..533G
Altcode:
The phase of solar evolution after the dynamical collapse is
considered. The physics of the Kelvin-Helmholtz phase of gravitational
collapse is described, attention being given to the early stages of the
star when it was completely convective. It is noted that subsequently,
a radiative core developed and evolution was controlled by the rate
at which heat can diffuse through it by radiative transfer. Since the
study of the Kelvin-Helmholtz contraction alone does not give enough
information regarding the state of the sun when it first settled down
to approximate hydrostatic equilibrium, other stars are studied, and
information on the sun is obtained by analogy. Many young solar-type
stars, such as the T Tauri stars, are not in the completely convective
Hayashi (1961) phase; hence it is proposed that the sun was completely
mixed soon after its formation, which has some bearing on the sun's
chemical structure. It is suggested that the surface of the sun was
very nonuniform compared with the photosphere of today. The simple
solar evolution model presented gives a good guide to the general way
in which the sun contracted to the main sequence.
Title: Pulsations of model RR Lyrae stars.
Authors: Baker, N. H.; Gough, D. O.
Bibcode: 1979ApJ...234..232B
Altcode:
Radial pulsations of models of RR Lyrae stars are studied in
linearized nonadiabatic theory. Convection in the hydrogen and helium
ionization zones is treated by use of a time-dependent generalization
of mixing-length theory. In a series of models of constant mass,
luminosity, and composition, effective temperature is varied as a
parameter. It is found, in agreement with previous work, that models
in the instability strip are pulsationally unstable. Cooler models,
however, are stabilized by the convention. Very cool models with deep
convective envelopes are nearly neutrally stable to pulsation.
Title: Northeast-southwest compressive stress in Alberta evidence
from oil wells
Authors: Bell, J. S.; Gough, D. I.
Bibcode: 1979E&PSL..45..475B
Altcode:
The introduction of the four-arm dipmeter well-logging tool has
permitted hole asymmetry to be recognised and hole ellipticity to be
measured and oriented. Many wells in Alberta, western Canada, have
been shown to exhibit depth ranges over which they are non-circular
as a result of caving of their walls. These break-outs occur so as to
elongate the holes in a northwest-southeast direction. This direction
of elongation is consistent between the break-outs in a given well,
and between wells distributed over an area of more than 3 × 10
5 km 2. Asymmetric hole elongation occurs in
siltstones, sandstones, limestones, dolomites and one shale formation,
and through the stratigraphic column from Devonian to Cretaceous. It
is unrelated to dip of the strata. The hypothesis is advanced that
the break-outs are caused by concentration of stress at the walls of
the wells, in a stress field with large, unequal horizontal principal
stresses, the larger oriented NE-SW. It is shown that a normal stress
field (with the largest principal stress, σ 1, vertical)
is unlikely to produce large enough horizontal stresses to produce the
break-outs. Consequently our hypothesis requires σ 1 to be
horizontal and oriented NE-SW. The vertical principal stress could be
either σ 2 (strike-slip stress field) or σ 3
(thrust stress field). The orientation of σ 1 at right
angles to the Rocky Mountains fold axes suggests the possibility that
the stress field responsible for the thrust faulting in the mountains
is still present. A strike-slip stress field is also possible. The most
prominent system of surface joints outcropping in Alberta, shown by
Babcock to have sets oriented NE-SW and NW-SE, could have been formed
in the proposed stress field. Direct measurements of the stress tensor
at two or three points, if they verified this interpretation, would
combine with the oil well break-outs to demonstrate a remarkably uniform
stress field over a substantial part of the North American plate. The
stresses in the Alberta crust here proposed may be related to tractions
now acting on the edges and underside of the North American plate,
including those producing postglacial uplift of Hudson's Bay; or may
be residual stresses from past tectonic events such as the Laramide
compression of the Rocky Mountains.
Title: Nonradial and nonlinear stellar pulsation
Authors: Gough, Douglas
Bibcode: 1979Natur.278..685G
Altcode:
No abstract at ADS
Title: Dirty solar models.
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Morgan, J. G.
Bibcode: 1979A&A....73..121C
Altcode:
Solar models with low initial heavy-element abundances, Zzero
= 0.004 and 0.001, are evolved from the zero-age main sequence on the
assumption that their surfaces are contaminated by interstellar material
accreted at such a rate as to increase Z uniformly to a value of 0.02
now. The models have thin convective envelopes and low neutrino fluxes,
as do uncontaminated models with low Z. Oscillation periods of several
modes of low degree are presented for these two models and for a model
with Z = 0.02 throughout. They are found to differ sufficiently from
model to model for an observational test to be possible, once the
degree of the modes observed can be identified.
Title: Erratum: "Dirty solar models" [Astron. Astrophys., Vol. 79,
p. 121 - 128 (1979)].
Authors: Christensen-Dalsgaard, J.; Gough, D. O.; Morgan, J. G.
Bibcode: 1979A&A....79..260C
Altcode:
No abstract at ADS
Title: A polar magnetic substorm observed in the evening sector with
a two-dimensional magnetometer array.
Authors: Gough, D. I.; Bannister, J. R.
Bibcode: 1978GeoJ...55..435G
Altcode: 1978GeoJI..55..435G
No abstract at ADS
Title: New data from solar oscillations
Authors: Gough, Douglas
Bibcode: 1978Natur.274..739G
Altcode:
No abstract at ADS
Title: A study of two polar magnetic substorms with a two-dimensional
magnetometer array.
Authors: Bannister, J. R.; Gough, D. I.
Bibcode: 1978GeoJ...53....1B
Altcode: 1978GeoJI..53....1B
A two-dimensional array of 23 three-component magnetometers located
beneath the auroral oval in western Canada provided information on the
three-dimensional magnetospheric-ionospheric currents that resulted
in the polar magnetic substorms of September 7 and 18, 1974. Current
density distributions were modeled at six representative epochs of
the substorms through use of Oldenburg's (1976) inverse method. The
principal ionospheric current was westward, though significant eastward
current was also noted north of the westward electrojet. Bends in the
ionospheric current segments toward the northwest appeared to follow
the auroral oval in some cases, though in other instances they may
have been associated with the Harang discontinuity.
Title: The Significance of Solar Oscillations
Authors: Gough, D.
Bibcode: 1978pfsl.conf...81G
Altcode: 1978ESPM....2...81G
No abstract at ADS
Title: Development of a polar magnetic substorm: a two-dimensional
magnetometer array study.
Authors: Bannister, J. R.; Gough, D. I.
Bibcode: 1977GeoJ...51...75B
Altcode: 1977GeoJI..51...75B
No abstract at ADS
Title: Magnetic anisotropy and fabric of redbeds of the Great Slave
Supergroup of Canada
Authors: Gough, D. I.; And, Aziz-Ur-Rahman; Evans, M. E.
Bibcode: 1977GeoJ...50..685G
Altcode: 1977GeoJI..50..685G
No abstract at ADS
Title: Mixing-length theory for pulsating stars.
Authors: Gough, D. O.
Bibcode: 1977ApJ...214..196G
Altcode:
The mixing length theory of convection is generalized for use
in the envelopes of nonrotating, radially pulsating stars by the
methods proposed by Gough (1965) and Unno (1967). The essential
differences between the physical assumptions made in the two
approaches are explained. The detailed formulas required for a linear
pulsational-stability analysis of a static star are derived.
Title: The geoid and single-cell mantle convection
Authors: Gough, D. I.
Bibcode: 1977E&PSL..34..360G
Altcode:
The geoid shows an antisymmetric departure from the spheroid of best
fit. A single zero-elevation contour divides its surface into nearly
equal strips in one of which the elevation is everywhere positive and in
the other everywhere negative. These two areas are interleaved roughly
like the strips covering a tennis ball. This pattern may indicate
global single-cell convection in the mantle. It is argued that on this
convection hypothesis, the upcurrents underlie the low-geoid strip,
although the opposite view could be supported. No simple relation
is to be expected between the proposed whole-mantle convection and
plate motions, because other constraints act on plates and because the
asthenosphere will partially decouple the whole-mantle motions from
the lithosphere. However, the proposed whole-mantle convective system
is consistent with rapid northwestward motion of the Pacific plate,
with fast spreading of the East Pacific Rise and with slow spreading
of the North Atlantic Ridge. Seismological velocity anomalies in the
mantle, while highly relevant to whole-mantle convection, do not at
present decide for or against the hypothesis here advanced.
Title: Random Remarks on Solar Hydrodynamics
Authors: Gough, D.
Bibcode: 1977ebhs.coll....3G
Altcode: 1977IAUCo..36....3G
No abstract at ADS
Title: Theoretical Predictions of Variations in the Solar Output
Authors: Gough, D. O.
Bibcode: 1977soiv.conf..451G
Altcode:
No abstract at ADS
Title: The current state of stellar mixing-length theory
Authors: Gough, D.
Bibcode: 1977LNP....71...15G
Altcode: 1977IAUCo..38...15G; 1977stco.coll...15G; 1977psc..conf...15G
The physical model, assumptions, uncertainties, and degree of contact
with reality involved in mixing-length theory as applied to stellar
convection are reviewed. Attention is given to the ideas behind
mixing-length theories, equations of motion, local mixing-length
formalisms for a stationary envelope, the assumed structure of the
convective flow, and the dynamics of convective eddies. A specific
mixing-length model is considered in which the flow is represented by
a conglomerate of cells or eddies that form, grow, and subsequently
break up. The growth of convective eddies is examined along with
the eddy convection rate, initial conditions, an eddy-annihilation
hypothesis, and turbulent fluxes. The choice of a mixing length and
the calibration of the heat-flux formula are discussed, Reynolds
stress is analyzed, and transport of heat and momentum by small-scale
turbulence is incorporated into the dynamics. Additional refinements
and generalizations are described.
Title: Stellar convection
Authors: Gough, D. O.
Bibcode: 1977LNP....71..349G
Altcode: 1977stco.coll..349G; 1977psc..conf..349G; 1977IAUCo..38..349G
Ways in which stellar convection is usually modeled are discussed. An
ice-water experiment that can model some aspects of penetration and
overshooting is described. Salient features of 33 different attempts at
modeling stellar convection and overshoot are noted. Attention is also
given to previous studies of subcritical convection, effects of rotation
and magnetic fields on convective motion, and time-dependent convection.
Title: On taking mixing-length theory seriously
Authors: Gough, D. O.; Spiegel, E. A.
Bibcode: 1977LNP....71...57G
Altcode: 1977IAUCo..38...57G; 1977psc..conf...57G; 1977stco.coll...57G
A clarification of mixing-length theory is recommended, and the
determination of the equations of motion of quasi-particles is
discussed. The treatment makes use of a specific model which considers
the star to be composed of a background fluid through which discrete
well-defined parcels of fluid move. These parcels may be thought of
as quasi-particles whose number density is sufficiently high so that
they constitute a second fluid permeating the background fluid. The
convective model is a two-fluid model analogous to a composite model
of radiation and matter except that the quasi-particle fluid is more
complicated than the photon gas. Two approaches to the equations of
motion are examined - one in which the quasi-particles are treated
as idealizations of buoyant thermals, and the other in which the
solution of the differential equations is sought and then applied in
conjunction with hypotheses about the distribution of initial conditions
of quasi-particles to compute heat flow.
Title: Numerical solutions of single-mode convection equations
Authors: Toomre, J.; Gough, D. O.; Spiegel, E. A.
Bibcode: 1977JFM....79....1T
Altcode:
In the Boussinesq approximation, single-mode equations describing
thermal convection are constructed by expanding the fluctuating velocity
and temperature fields in a complete set of functions (or planforms)
of the horizontal coordinates and retaining just one term. Numerical
solutions of the single-mode equations are investigated, chief
consideration being given to hexagonal planforms. Extensive surveys of
steady solutions are presented for various Rayleigh numbers, Prandtl
numbers, and horizontal wavenumbers. The dependences on Rayleigh number
and Prandtl number at very large Rayleigh number are in satisfactory
agreement with the results of asymptotic expansions.
Title: Seiches in supergranules
Authors: Gough, D. O.; Pringle, J. E.; Spiegel, E. A.
Bibcode: 1976Natur.264..424G
Altcode:
THE recent report by Hill, Stebbins and Brown1 of
oscillations of an apparent solar radius has stirred a mild
controversy2. In particular, the failure of Grec and
Fossat3 to detect Doppler variations with similar periods
in solar spectral lines provides striking contrast with the results of
Hill et al. Both sets of observations have been carefully performed and
thoughtfully analysed and, if one accepts both sets of results at face
value, the problem of reconciling the two must be confronted. Here
we consider seiches in supergranules as a possible cause of the
discrepancy.
Title: The calibration of stellar convection theories.
Authors: Gough, D. O.; Weiss, N. O.
Bibcode: 1976MNRAS.176..589G
Altcode:
Any formula used to calculate the temperature gradient in a stellar
convection zone must be calibrated, for example, by evolving
1-solar-mass stellar models to fit the present age, luminosity, and
effective temperature of the sun. When this procedure is followed
for various convection theories, including those of Opik (1950)
and Boehm-Vitense (1958), the corresponding models become almost
indistinguishable. In particular, they predict the same depth, around
150,000 km, for the solar convective zone.
Title: Talk on Solar Oscillation Theory
Authors: Gough, D. O.
Bibcode: 1976Obs....96..133G
Altcode:
No abstract at ADS
Title: Convective Instability in a Compressible Atmosphere. II
Authors: Gough, D. O.; Moore, D. R.; Spiegel, E. A.; Weiss, N. O.
Bibcode: 1976ApJ...206..536G
Altcode:
The onset of steady convection in polytropic atmosphere with constant
viscosity is studied numencally. Subject headings: convection :
atmospheres
Title: Theory of Solar Oscillations
Authors: Gough, D. O.
Bibcode: 1976IAUTB..16..245G
Altcode: 1976IAUT...16B.245G
No abstract at ADS
Title: Stellar constitution (Constitution des étoiles).
Authors: Mestel, L.; Tinsley, B. M.; Ostriker, J. P.; Gough, D. O.;
Arnett, W. D.; Pines, D.
Bibcode: 1976IAUTA..16b.161M
Altcode:
No abstract at ADS
Title: Towards a heliological inverse problem
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1976Natur.259...89C
Altcode:
Theoretical periods of normal modes of vibration of the Sun are compared
with the observed periods of oscillation of the solar surface. It is
inferred from the comparison that it may soon be possible to use solar
oscillations to measure aspects of the internal structure of the Sun.
Title: Stellar Convection
Authors: Gough, D. O.
Bibcode: 1976IAUTA..16..169G
Altcode: 1976IAUT...16A.169G
No abstract at ADS
Title: The shivering sun opens its heart.
Authors: Gough, D.
Bibcode: 1976NewSc..70..590G
Altcode:
No abstract at ADS
Title: The North American Central Plains Conductivity Anomaly
Authors: Alabi, A. O.; Camfield, P. A.; Gough, D. I.
Bibcode: 1975GeoJ...43..815A
Altcode: 1975GeoJI..43..815A
No abstract at ADS
Title: Convection in Pulsating Stars
Authors: Baker, N. H.; Gough, D. O.; Stellingwerf, R. F.
Bibcode: 1975BAAS....7Q.504B
Altcode:
No abstract at ADS
Title: Preface
Authors: Gough, D. I.; Jones, F. W.
Bibcode: 1975PEPI...10D...3G
Altcode:
No abstract at ADS
Title: Anomalies in Daily Variation Magnetic Fields and Structure
Under North-western United States and South-western Canada
Authors: Camfield, P. A.; Gough, D. I.
Bibcode: 1975GeoJ...41..193C
Altcode: 1975GeoJI..41..193C
No abstract at ADS
Title: Modal equations for cellular convection
Authors: Gough, D. O.; Spiegel, E. A.; Toomre, J.
Bibcode: 1975JFM....68..695G
Altcode:
We expand the fluctuating flow variables of Boussinesq convection in
the planform functions of linear theory. Our proposal is to consider a
drastic truncation of this expansion as a possible useful approximation
scheme for studying cellular convection. With just one term included,
we obtain a fairly simple set of equations which reproduces some of the
qualitative properties of cellular convection and whose steady-state
form has already been derived by Roberts (1966). This set of 'modal
equations' is analyzed at slightly supercritical and at very high
Rayleigh numbers. In the latter regime the Nusselt number varies
with Rayleigh number just as in the mean-field approximation with one
horizontal scale when the boundaries are rigid. However, the Nusselt
number now depends also on the Prandtl number in a way that seems
compatible with experiment. The chief difficulty with the approach is
the absence of a deductive scheme for deciding which planforms should
be retained in the truncated expansion.
Title: Highly stretched meshes as functionals of solutions
Authors: Gough, D. O.; Spiegel, E. A.; Toomre, J.
Bibcode: 1975LNP....35..191G
Altcode:
No abstract at ADS
Title: Nonadiabatic nonradial oscillations of a solar model
Authors: Christensen-Dalsgaard, J.; Gough, D. O.
Bibcode: 1975MSRSL...8..309C
Altcode: 1975phs..conf..309C
The stability of a solar model on the main sequence to linearized
nonadiabatic nonradial oscillations has been studied. In the inner 99.9
per cent b.y. radius the eigenfunctions were barely distinguishable
from those of the adiabatic approximation. The integrated effect of
this region is to stabilize the oscillations at zero age, but after
a time of order .1 b.y. the destabilizing effect of the 3He (3He, 2p)
4He reactions exceeds the damping. However, there is much more severe
damping in a nonadiabatic shell beneath the photosphere about 300 km
thick, which dominates the entire effect from the rest of the star
interior to this shell.
Title: The stability of a solar model to non-radial oscillations.
Authors: Christensen-Dalsgaard, J.; Dilke, F. W. W.; Gough, D. O.
Bibcode: 1974MNRAS.169..429C
Altcode:
The stability of a solar model to low-order gravity modes has been
investigated in quasi-adiabatic approximation, neglecting any direct
effects of convection on the oscillations. The zero age main sequence
model was found to be stable, but after about 200 m.y. the g1
(l = I) mode became unstable. The dominant destabilization comes
from the dependence of the pp chain reaction rate on the abundances
of He-3 and H when nuclear equilibrium is disturbed, and is felt
once a sufficient He-3 inhomogeneity is established in the energy
generating core.
Title: A Magnetometer Array Study in Southern Australia
Authors: Gough, D. I.; McElhinny, M. W.; Lilley, F. E. M.
Bibcode: 1974GeoJ...36..345G
Altcode: 1974GeoJI..36..345G
No abstract at ADS
Title: A Magnetometer Array Study in Southern Africa
Authors: Gough, D. I.; Beer, J. H.; Zijl, J. S. V.
Bibcode: 1973GeoJ...34..421G
Altcode: 1973GeoJI..34..421G
No abstract at ADS
Title: The geophysical significance of geomagnetic variation anomalies
Authors: Gough, D. I.
Bibcode: 1973PEPI....7..379G
Altcode:
Analytic procedures in classical geomagnetic deep sounding and
in two-dimensional magnetometer array studies are outlined. Three
types of magnetic variation anomaly are considered, and anomalies of
one geographical area. Continental-edge anomalies remain somewhat
ambiguous as to the contribution of structure in the upper mantle;
the geophysical significance in geothermal terms is understood, if the
effect exists. Subduction-zone anomalies in the Peruvian Andes and in
central Japan are considered in relation to the ascent of an andesitic
melt fraction from the lithosphere slab, a process which accounts
also for uplift and support of the mountains. In western North America
anomalies are closely related to heat flow and indicate complex tectonic
activity with considerable fine structure in general agreement with
seismological parameters. The Basin and Range Province has a highly
conductive upper mantle and still higher conductivities are found
under the Wasatch fault belt and under the southern Rockies. Under the
northern Rockies the evidence is for only a thin conductive layer in the
upper mantle and in general for much lower heating than in mid-latitudes
of the United States. Crustal anomalies are discussed in relation to
the current concentration effect. It is suggested that some of them may
mark metamorphic belts in crystalline basement rocks. This association
has been demonstrated for the North American Central Plains anomaly.
Title: The Solar Spoon
Authors: Dilke, F. W. W.; Gough, D. O.
Bibcode: 1972Natur.240..262D
Altcode:
Overstability causes the Sun's core to mix every few hundred million
years. This induces geological ice ages and temporarily depresses the
solar neutrino flux.
Title: Conductive Structures in the North-western United States and
South-west Canada
Authors: Porath, H.; Gough, D. I.; Camfield, P. A.
Bibcode: 1971GeoJ...23..387P
Altcode: 1971GeoJI..23..387P
No abstract at ADS
Title: Mantle Conductive Structures in the Western United States
from Magnetometer Array Studies
Authors: Porath, H.; Gough, D. I.
Bibcode: 1971GeoJ...22..261P
Altcode: 1971GeoJI..22..261P
No abstract at ADS
Title: Magnetometer Array Studies in the North-Western United States
and South-Western Canada
Authors: Camfield, P. A.; Gough, D. I.; Porath, H.
Bibcode: 1971GeoJ...22..201C
Altcode: 1971GeoJI..22..201C
No abstract at ADS
Title: Load-induced Earthquakes at Lake Kariba?II
Authors: Gough, D. I.; Gough, W. I.
Bibcode: 1970GeoJ...21...79G
Altcode: 1970GeoJI..21...79G
No abstract at ADS
Title: Stress and Deflection in the Lithosphere near Lake Kariba?I
Authors: Gough, D. I.; Gough, W. I.
Bibcode: 1970GeoJ...21...65G
Altcode: 1970GeoJI..21...65G
No abstract at ADS
Title: Separation of Magnetic Variation Fields and Conductive
Structures in the Western United States
Authors: Porath, H.; Oldenburg, D. W.; Gough, D. I.
Bibcode: 1970GeoJ...19..237P
Altcode: 1970GeoJI..19..237P
No abstract at ADS
Title: Geomagnetic Deep Sounding and Upper Mantle Structure in the
Western United States
Authors: Reitzel, J. S.; Porath, H.; Gough, D. I.; Anderson, C. W.
Bibcode: 1970GeoJ...19..213R
Altcode: 1970GeoJI..19..213R
No abstract at ADS
Title: Intermediate Scale Lunar Roughness
Authors: Bastin, J. A.; Gough, D. O.
Bibcode: 1969Icar...11..289B
Altcode: 1970Icar...11..289B
A model surface consisting of parallel troughs has been examined in
order to assess the importance of roughness in accounting for the
properties of lunar thermal radiation. Insolation, emission from
the surface, reabsorption of emitted radiation, and conduction are
all considered. Brightness temperatures both in the midinfrared and
microwave region are computed for eclipse and lunation conditions, not
only as a function of lunar phase, lattitude, longitude, and direction
of observation, but also for a variety of trough dimensions. All
those features of the observed thermal radiation which cannot be
accounted for on the basis of a plane homogeneous model are listed
and the extent to which they can be accounted for by the proposed
model is considered. In particular, a model for which the width and
height of the raised portions are both equal to a quarter of the trough
interval gives good agreement with the directional effects observed for
lunar daytime radiation in the 10-14 μ wavelength band. In addition
a number of other anomalies, including some already accounted for in
the literature by other causes, receive more or less good explanations
on the basis of roughness.
Title: Magnetic Anomalies and Tectonics of the Cayman Trough
Authors: Gough, D. I.; Heirtzler, J. R.
Bibcode: 1969GeoJ...18...33G
Altcode: 1969GeoJI..18...33G
No abstract at ADS
Title: The Anelastic Approximation for Thermal Convection.
Authors: Gough, D. O.
Bibcode: 1969JAtS...26..448G
Altcode:
A formal scale analysis of the equations of motion in a plane parallel
atmosphere is made, assuming conditions to be such that relative
fluctuations in density and temperature are small. It is found that an
energetically consistent set of approximate equations can be derived
which preclude the existence of acoustic motions. Such equations can be
used to describe subsonic convection or internal gravity waves. Under
certain conditions the analysis can be generalized to include vertical
pulsations of the atmosphere.
Title: Vorticity expulsion by turbulence: astrophysical implications
of an Alka-Seltzer experiment
Authors: Gough, D. O.; Lynden-Bell, D.
Bibcode: 1968JFM....32..437G
Altcode:
No abstract at ADS
Title: Convection in Pulsating Stars: Time-Dependent Mixing-Length
Theory in the One-Zone Model.
Authors: Gough, D. O.
Bibcode: 1967AJ.....72S.799G
Altcode:
By considering in detail the motions of convective elements, Vitense's
mixing-length theory of turbulent convection has been reformulated so
that it can be used in stellar envelopes whose ensemble mean properties
are time dependent. To determine in which regions of the H-R diagram
radially pulsating stars lie, it is usual to perform a linear stability
analysis of static models. The time dependence of the perturbations is
exponential; the equation of motion of the convective elements can then
be integrated analytically, and explicit expressions for the variations
in convective heat flux and turbulent pressure can be obtained. To
gain insight into how convection can affect the stability of a star,
the revised mixing-length theory has been applied to Baker's one-zone
model [Stellar Evolut*on (Plenum Press, Xew York, 1966), p. 333J to
estimate how the convection varies as the star pulsates. In general,
the convective heat flux increases as the star compresses and so exerts
a stabilizing influence. Furthermore, because the variations in the
convective velocities are not in phase with the pulsation, the turbulent
pressure can do work on, or be worked on by the star, and so influence
the growth or decay of the pulsations. When the characteristic time
scale of the convection is very much greater than the pulsation period,
the effect is stabilizing, but when the convection time scale is short,
the converse is true. Although no definite conclusions concerning the
stability of a star can be drawn from the one-zone model, it does seem
likely that convection tends to stabilize stars at the right-hand edge
of the Cepheid instability strip, bringing theoretical predictions
into closer agreement with the observations, and also provides an
important destabilizing mechanism in the long-period variables. This
work was supported by the Science Research Council, while the author
was in receipt of a Research Studentship, and by the Xational Science
Foundation under Grant GP-4859.
Title: Convection in Pulsating Stars: Quasi-Adiabatic Cepheid Models.
Authors: Baker, N. H.; Gough, D. O.
Bibcode: 1967AJ.....72Q.784B
Altcode: 1967AJ.....72..784B
The time-dependent mixing-length theory described in the previous
abstract has been applied, in the quasi-adiabatic approximation, to a
series of models of ~ Cephei stars of 7Mo previously studied by Baker
and Kippenhahn (Astrophys. J. 142, 868,1965). The hottest models of
this series have negligible surface convection zones, but the coolest
models have deep convection zones that include the low-lying hydrogen
and helium ionization regions. On the basis of the quasi-adiabatic
approximation, which is not valid near the surface of our stellar
envelopes, we tentatively conclude that the increasing importance of
convection in stars of lower effective temperature is responsible for
the return to stability at the cool edge of the Cepheid strip. This
work has been supported by the National Science Foundation under Grant
GP-5568 (N.H.B) and Grant GP-4859 (D.O.G.).
Title: Convection in astrophysics
Authors: Gough, Douglas Owen
Bibcode: 1966PhDT.......109G
Altcode:
No abstract at ADS
Title: The influence of a magnetic field on Schwarzschild's criterion
for convective instability in an ideally conducting fluid
Authors: Gough, D. O.; Tayler, R. J.
Bibcode: 1966MNRAS.133...85G
Altcode:
The influence of a magnetic field on the onset of adiabatic thermal
convection in a compressible ideally conducting fluid is studied. In
the absence of a magnetic field Schwarzschild's criterion for the
onset of convection is a purely local criterion; a magnetic field
connects fluid at different levels and a local criterion which is
necessary and sufficient for stability against convection can no
longer be obtained. However, it is shown that, for certain simple
magnetic field configurations which do not introduce hydromagnetic
instabilities, there are simple local criteria which are sufficient
for the stability of the system. It is pointed out that, in a fluid of
finite electrical resistivity, a magnetic field cannot be expected to
lead to complete stabilization of convective motions. In such a case,
if the sufficient condition is satisfied, there should probably be a
substantial reduction in the growth rate of the instability and in the
energy carried by fully developed convection. One of the sufficient
conditions for stability is applied to a sunspot model recently
constructed by Chitre and it is found that it is satisfied throughout
most of the model. Although the theory is not general enough to apply
to this case, it is suggestive that a high degree of suppression of
convection by a magnetic field should occur in such a spot.
Title: On the Periods of Pulsating Stars.
Authors: Gough, D. O.; Ostriker, J. P.; Stobie, R. S.
Bibcode: 1965ApJ...142.1649G
Altcode:
No abstract at ADS
Title: The Paleomagnetism of the Shawa Ijolite
Authors: Gough, D. I.; Brock, A.
Bibcode: 1964JGR....69.2489G
Altcode:
Oriented cores have been drilled at seven sites in ijolite exposures of
the Shawa carbonatite complex, Southern Rhodesia. The ijolite has been
dated at 209±16 m.y. from Rb → Sr decay. The directions of natural
remanent magnetization are not consistent between sites. The ijolite
proved difficult to treat by partial demagnetization in alternating
fields, as instability of the direction of remanent magnetization tended
to develop with demagnetizing fields only slightly larger than those
required to remove isothermal magnetizations. Nevertheless, consistent
directions of remanent magnetization were secured from five of the
seven sites, after alternating-field treatment. On the assumption of
a geocentric dipole field, the mean south magnetic pole position is
64.2°S, 85.6°E, with radius of 95 per cent confidence 14.1°. This is
in excellent agreement with other Mesozoic pole positions from Africa.
Title: The Paleomagnetism of the Ring Complexes at Marangudzi and
the Mateke Hills
Authors: Gough, D. I.; Brock, A.; Jones, D. L.; Opdyke, N. D.
Bibcode: 1964JGR....69.2499G
Altcode:
Oriented rock cores have been drilled at nineteen sites in four
intrusive ring complexes in the Nuanetsi igneous province of
southeastern Southern Rhodesia. At Marangudzi eleven sites were
distributed among nine rock types; the aim was to investigate
the relation between rock type and remanent magnetization. Six of
these sites, and one from another complex, gave no paleomagnetic
results. At ten sites stable components of remanent magnetization,
which remained after partial demagnetization in alternating fields,
gave closely grouped directions approximately reversed with respect to
the present geomagnetic field. These directions are considered to be
those of thermoremanent magnetizations acquired when the rocks were
intruded. The mean north paleomagnetic pole position from these ten
sites is 60.9°S, 86.2°E, and A95 = 6.5°. Samples from
Marangudzi have been dated from K-Ar decay at close to 190 m.y., and
it is probable that the other complexes are of approximately the same
age. Two sites in different complexes are normally magnetized, which
suggests that the geomagnetic field changed sense from reversed to
normal near the close of the intrusive episode. Evidence is presented
which shows that relative movement between Africa and the pole was
small during the Mesozoic era.
Title: A Spinner Magnetometer
Authors: Gough, D. I.
Bibcode: 1964JGR....69.2455G
Altcode:
A spinner type rock remanent magnetometer is described. The instrument
measures specimens having moments from 2 × 10-6 emu upward,
and measures moments from 10-5 emu with precisions of 1° in
direction and 5 per cent in magnitude. The lower limit for measurement
corresponds to an intensity of magnetization of 5 × 10-8
emu cm-3 for the largest size of specimen which can be
accommodated. A discussion is given of the factors which limit the
sensitivity of a spinner magnetometer. Annulment of the geomagnetic
field at the rotor is shown to be desirable when rocks having low
remanence and high susceptibility are to be measured.
Title: The Significance of Paleomagnetic Results from Africa
Authors: Gough, D. I.; Opdyke, N. D.; McElhinny, M. W.
Bibcode: 1964JGR....69.2509G
Altcode:
Paleomagnetic results from Africa are critically reviewed and
polar-wander curves are presented for the early Precambrian and for
the interval from the Permian to the present. The data are shown to be
consistent with the hypothesis that the dispersion of the geomagnetic
field with respect to an axial geocentric dipole field was similar to
its present dispersion both in the early Precambrian and in Mesozoic
times. Strong evidence is presented that relative movement between
Africa and the pole was slight during the Mesozoic. Similar evidence
exists for Australia. Mesozoic paleomagnetic poles from the four
southern continents are shown to form widely separated groups. Polar
wander alone cannot account for both the divergence of the poles and the
stability of the Mesozoic paleomagnetic poles relative to Africa and
Australia. The results can be reconciled, however, by the supposition
that relative movement has occurred between the southern continents
since the Mesozoic. A Mesozoic reconstruction of Gondwanaland and
also a tentative reconstruction for the Permian are proposed. These
are based on the most reliable paleomagnetic results available.
Title: The Palaeomagnetism of the Lupata Alkaline Volcanics
Authors: Gough, D. I.; Opdyke, N. D.
Bibcode: 1963GeoJ....7..457G
Altcode: 1963GeoJI...7..457G
No abstract at ADS
Title: The Palaeomagnetism of the Great Dyke of Southern Rhodesia
Authors: McElhinny, M. W.; Gough, D. I.
Bibcode: 1963GeoJ....7..287M
Altcode: 1963GeoJI...7..287M
No abstract at ADS
Title: Isostatic anomalies and crustal structure in the Southern Cape
Authors: Hales, A. L.; Gough, D. I.
Bibcode: 1961GeoJ....5..263H
Altcode: 1961GeoJI...5..263H
No abstract at ADS
Title: Isostatic Anomalies and Crustal Structure in the Southern Cape
Authors: Hales, A. L.; Gough, D. I.
Bibcode: 1960GeoJ....3..225H
Altcode: 1960GeoJI...3..225H
No abstract at ADS
Title: Gravity Anomalies and Crustal Structure in South Africa
Authors: Hales, A. L.; Gough, D. I.
Bibcode: 1959GeoJ....2..324H
Altcode: 1959GeoJI...2..324H
No abstract at ADS
Title: a Study of the Palaeomagnetism of the Pilansberg Dykes
Authors: Gough, D. I.; Hales, A. L.
Bibcode: 1956GeoJ....7..196G
Altcode: 1956GeoJI...7..196G
No abstract at ADS
Title: Measurements of gravity in Southern Africa
Authors: Hales, A. L.; Gough, D. I.
Bibcode: 1950mgsa.book.....H
Altcode: 1950QB335.H34......
No abstract at ADS
Title: Blackett's Fundamental Theory of the Earth's Magnetic Field
Authors: Hales, A. L.; Gough, D. I.
Bibcode: 1947Natur.160..746H
Altcode:
SOON after the publication of Prof. P. M. S. Blackett's
paper1, Dr. E. C. Bullard suggested to us that
it should be possible to test Blackett's theory against other
theories by measurements of the magnetic field of the earth in the
mines of the Witwaters-rand. By courtesy of the management of the
Blyvooruitzicht G.M. Co., we made a series of underground observations
on Blyvooruitzicht mine.