Colloquium @ Division of Physics, Hokkaido University

A Colloquium @ Division of Physics, Hokkaido University Colloquium 2001 2000 1999 1998 1997

Colloquium 2001

以下のように物理コロキュウムが予定されています。皆さん奮って御参加下さい。

Upper bounds on the mass of the axion from white dwarf asteroseismology
(白色矮星の星震からのアクシオンの質量上限)

Dr. Enrique Garcia-Berro
(Professor at Universitat Politecnica deCatalunya)

2002年2月14日（木曜日）16:00-
物理学専攻大学院講義室（2-211）にて

要旨：White dwarfs are well studied objects. The relative simplicity of theirphysics allows to obtain very detailed models which can be ultimately compared with their observed properties. Among white dwarfs there is a specific class of stars, known as ZZ-Ceti objects, which have a hydrogen-rich envelope and show periodic variations in their light curves. G117-B15A belongs to this particular set of stars. The luminosity variations have been successfully explained as due to $g$-mode pulsations. G117-B15A has been recently claimed to be the most stable optical clock ever found, being the rate of change of its 215.2 s period very small: $\dot{P}= (2.3 \pm 1.4) \times 10^{-15} {\rm s\, s}^{-1}$, with a stability comparable to that of the most stable millisecond pulsars. The rate of change of the period is closely related to its cooling timescale, which can be accurately computed. In this paper we study the pulsational properties of G117-B15A and we use the observed rate of change of the period to impose constraints on the axion emissivity and, thus, to obtain a preliminary upper bound to the mass of the axion. This upper bound turns out to be $4\cos^{2}{\beta}\; {\rm meV}$ at the 95\% confidence level. Although there are still several observational and theoretical uncertainties, we conclude that G117-B15A is a very promising stellar object to set up constraints on particle physics.

物理コロキウム世話人:
　　　　北　孝文 (x 2687) <kita@phys.sci.hokudai.ac.jp>
　　　　末廣一彦(x 2686) <suehiro@particle.sci.hokudai.ac.jp>