ESA Science & Technology - Publication Archive
Document reference: CDF-175(C)
This document is the assessment study report for GaiaNIR (Gaia Near Infra-Red), which was one of the proposals received in response to the 2016 Call for New Science Ideas in ESA's Science Programme. Three mission concepts were selected as a result of this call, and GaiaNIR was one of them.
The GaiaNIR proposal encompasses:
- Enlarging the astrometric achievement of Gaia to the astronomical sources which are only visible in Near Infra-Red
- Maintaining the accuracy of the Gaia optical reference frame
- Improving the star parallax and proper motion accuracy by revisiting the astronomical sources a number of years after Gaia.
This document was updated on 8 June 2018, with minor edits made to page 249 according to the final version of the document. The concerned lines are indicated by a blue band on the side of that page.
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.
[Remainder of abstract truncated due to character limitations]