排序方式： 共有13条查询结果，搜索用时 15 毫秒
1.
T. Appourchaux K. Belkacem A.-M. Broomhall W. J. Chaplin D. O. Gough G. Houdek J. Provost F. Baudin P. Boumier Y. Elsworth R. A. García B. N. Andersen W. Finsterle C. Fröhlich A. Gabriel G. Grec A. Jiménez A. Kosovichev T. Sekii T. Toutain S. Turck-Chièze 《Astronomy and Astrophysics Review》2010,18(1-2):197-277
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. 相似文献
2.
M. Lazrek F. Baudin L. Bertello P. Boumier J. Charra D. Fierry-Fraillon E. Fossat A. H. Gabriel R. A. García B. Gelly C. Gouiffes G. Grec P. L. Pallé F. Pérez Hernández C. Régulo C. Renaud J.-M. Robillot T. Roca Cortés S. Turck-Chièze R. K. Ulrich 《Solar physics》1997,175(2):227-246
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. Here we present the results of the analysis of the first 8 months of data. Special emphasis is put into the frequency
determination of the p modes, as well as the splitting in the multiplets due to rotation. For both, we show that the improvement
in S/N level with respect to the ground-based networks and other experiments is essential in achieving a very low-degree frequency
table with small errors ∼ 2 parts in 10-5). On the other hand, the splitting found seems to favour a solar core which does not rotate slower than its surface. The
line widths do agree with theoretical expectations and other observations. 相似文献
3.
Initial results of round-the-clock observations of solar oscillations at the South Pole are briefly summarized by describing the Figures 1 to 4.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
4.
We experiment with a method of measuring the frequency of solar p modes, intended to extend the passband for the variations of the frequency spectrum as high as possible. So far this passband is limited to a fraction of μ Hz for the classical analysis based on numerical fits of a theoretical line profile to a power spectrum averaged over periods lasting at least several weeks. This limit for the present analysis can be shifted to the mHz range, corresponding to some of the “5 min” oscillations, but in this range we use a lower resolution which allows us to separate odd and even p modes. We show an example of the results for long term variations and apply this analysis to search for a modulation of the p‐mode frequency spectrum by asymptotic series of solar g modes. A faint signal is found in the analysis of 10 years of GOLF data. This very preliminary result possibly indicates the detection of a small number of g modes of degree l = 1. A tentative determination of an observational value of the parameter P0 follows. P0 is the scaling factor of the asymptotic series of g modes and is a key data for solar core physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
S. Turck-Chièze S. Basu A. S. Brun J. Christensen-Dalsgaard A. Eff-Darwich I. Lopes F. Pérez Hernández G. Berthomieu J. Provost R. K. Ulrich F. Baudin P. Boumier J. Charra A. H. Gabriel R. A. Garcia G. Grec C. Renaud J. M. Robillot T. Roca Cortés 《Solar physics》1997,175(2):247-265
After 8 months of nearly continuous measurements the GOLF instrument, aboard SOHO, has detected acoustic mode frequencies
of more than 100 modes, extending from 1.4 mHz to 4.9 mHz. In this paper, we compare these results with the best available
predictions coming from solar models. To verify the quality of the data, we examine the asymptotic seismic parameters; this
confirms the improvements achieved in solar models during the last decade.
Using the GOLF set of frequencies for l=0, 1, 2, 3 combined with the LOWL second year data set for l > 3 we then carry out
inversions to infer properties of the solar core.
This largely confirms the previous results down to around 0.1 R⊙, while there remain differences, even closer to the centre,
where the present study shows an extreme sensitivity of the inversion results to the values of the frequencies. We finally
consider physical processes which may influence directly or indirectly the solar core structure. 相似文献
6.
A. H. Gabriel G. Grec J. Charra J. -M. Robillot T. Roca Cortés S. Turck-Chièze R. Bocchia P. Boumier M. Cantin E. Cespédes B. Cougrand J. Crétolle L. Damé M. Decaudin P. Delache N. Denis R. Duc H. Dzitko E. Fossat J. -J. Fourmond R. A. García D. Gough C. Grivel J. M. Herreros H. Lagardère J. -P. Moalic P. L. Pallé N. Pétrou M. Sanchez R. Ulrich H. B. van der Raay 《Solar physics》1995,162(1-2):61-99
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. 相似文献
7.
T. Toutain T. Appourchaux F. Baudin C. Fröhlich A. Gabriel P. Scherrer B. N. Andersen R. Bogart R. Bush W. Finsterle R. A. García G. Grec C. J. Henney J. T. Hoeksema A. Jiménez A. Kosovichev T. Roca Cortés S. Turck-Chièze R. Ulrich C. Wehrli 《Solar physics》1997,175(2):311-328
The three helioseismology instruments aboard SOHO observe solar p modes in velocity (GOLF and MDI) and in intensity (VIRGO
and MDI). Time series of two months duration are compared and confirm that the instruments indeed observe the same Sun to
a high degree of precision. Power spectra of 108 days are compared showing systematic differences between mode frequencies
measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighted
mean differences (V-I) are −0.1 μHz for l=0, and −0.16 μHz for l=1. The source of this systematic difference may be due to
an asymmetry effect that is stronger for modes seen in intensity. Wavelet analysis is also used to compare the shape of the
forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications
for structure inversions are discussed. 相似文献
8.
A. H. Gabriel J. Charra G. Grec J.-M. Robillot T. Roca Cortés S. Turck-Chièze R. Ulrich S. Basu F. Baudin L. Bertello P. Boumier M. Charra J. Christensen-Dalsgaard M. Decaudin H. Dzitko T. Foglizzo E. Fossat R. A. García J. M. Herreros M. Lazrek P. L. Pallé N. Pétrou C. Renaud C. Régulo 《Solar physics》1997,175(2):207-226
GOLF in-flight commissioning and calibration was carried out during the first four months, most of which represented the cruise
phase of SOHO towards its final L1 orbit. The initial performance of GOLF is shown to be within the design specification,
for the entire instrument as well as for the separate sub-systems. Malfunctioning of the polarising mechanisms after 3 to
4 months operation has led to the adoption of an unplanned operating sequence in which these mechanisms are no longer used.
This mode, which measures only the blue wing of the solar sodium lines, detracts little from the detection and frequency measurements
of global oscillations, but does make more difficult the absolute velocity calibration, which is currently of the order of
20%. Data continuity in the new mode is extremely high and the instrument is producing exceptionally noise-free p-mode spectra.
The data set is particularly well suited to the study of effects due to the excitation mechanism of the modes, leading to
temporal variations in their amplitudes. The g modes have not yet been detected in this limited data set. In the present mode
of operation, there are no indications of any degradation which would limit the use of GOLF for up to 6 years or more. 相似文献
9.
A. Baijumanov Sh. Ehgamberdiev E. Fossat G. Grec S. Ilyasov A. Kamaldinov Sh. Khalikov I. Khamitov J. F. Manigault G. Menshikov S. Raubaev T. Yuldashbaev 《Solar physics》1991,133(1):51-56
The second of the IRIS network instruments was commissioned in August 1988 at Kumbel mountain, located 75 km from Tashkent (U.S.S.R.). Atmospheric and operating conditions on Kumbel are discussed, as well as preliminary results derived from this station's global solar oscillation measurements. 相似文献
10.
In the framework of the IRIS programme, full-disk solar Doppler-shift measurements are made with an optical resonance sodium cell spectrophotometer, a new pattern of the instrument successfully used at the geographic South Pole 10 years ago. After many successive improvements, the IRIS version has now become a precise and reliable device, being limited only by the solar and/or by the atmospheric noise in all the frequency ranges of interest for the p-mode and the g-mode investigation. This instrument is described here in some detail, with the technical specification for each individual component being defined by comparison to the photon and the solar noise. 相似文献