Bibcode
Fossat, E.; Boumier, P.; Corbard, T.; Provost, J.; Salabert, D.; Schmider, F. X.; Gabriel, A. H.; Grec, G.; Renaud, C.; Robillot, J. M.; Roca-Cortés, T.; Turck-Chièze, S.; Ulrich, R. K.; Lazrek, M.
Bibliographical reference
Astronomy and Astrophysics, Volume 604, id.A40, 17 pp.
Advertised on:
8
2017
Journal
Citations
76
Refereed citations
66
Description
Context. Over the past 40 years, helioseismology has been enormously
successful in the study of the solar interior. A shortcoming has been
the lack of a convincing detection of the solar g modes, which are
oscillations driven by gravity and are hidden in the deepest part of the
solar body - its hydrogen-burning core. The detection of g modes is
expected to dramatically improve our ability to model this core, the
rotational characteristics of which have, until now, remained unknown.
Aims: We present the identification of very low frequency g modes
in the asymptotic regime and two important parameters that have long
been waited for: the core rotation rate, and the asymptotic equidistant
period spacing of these g modes. Methods: The GOLF instrument on
board the SOHO space observatory has provided two decades of full-disk
helioseismic data. The search for g modes in GOLF measurements has been
extremely difficult because of solar and instrumental noise. In the
present study, the p modes of the GOLF signal are analyzed differently:
we search for possible collective frequency modulations that are
produced by periodic changes in the deep solar structure. Such
modulations provide access to only very low frequency g modes, thus
allowing statistical methods to take advantage of their asymptotic
properties. Results: For oscillatory periods in the range between
9 and nearly 48 h, almost 100 g modes of spherical harmonic degree 1 and
more than 100 g modes of degree 2 are predicted. They are not observed
individually, but when combined, they unambiguously provide their
asymptotic period equidistance and rotational splittings, in excellent
agreement with the requirements of the asymptotic approximations. When
the period equidistance has been measured, all of the individual
frequencies of each mode can be determined. Previously, p-mode
helioseismology allowed the g-mode period equidistance parameter
P0 to be bracketed inside a narrow range, between
approximately 34 and 35 min. Here, P0 is measured to be 34
min 01 s, with a 1 s uncertainty. The previously unknown g-mode
splittings have now been measured from a non-synodic reference with very
high accuracy, and they imply a mean weighted rotation of 1277 ±
10 nHz (9-day period) of their kernels, resulting in a rapid rotation
frequency of 1644 ± 23 nHz (period of one week) of the solar core
itself, which is a factor 3.8 ± 0.1 faster than the rotation of
the radiative envelope. Conclusions: The g modes are known to be
the keys to a better understanding of the structure and dynamics of the
solar core. Their detection with these precise parameters will certainly
stimulate a new era of research in this field.
Related projects
Helio and Astero-Seismology and Exoplanets Search
The principal objectives of this project are: 1) to study the structure and dynamics of the solar interior, 2) to extend this study to other stars, 3) to search for extrasolar planets using photometric methods (primarily by transits of their host stars) and their characterization (using radial velocity information) and 4) the study of the planetary
Savita
Mathur