To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Sharp variations of the structure of the star create a characteristic signal in its frequencies of oscillation (e.g. ). The zone of the second ionization of helium is such a localized feature of the structure whose properties depend mainly on the abundance of helium and the equation of state. Considering that such a signal should easily be detectable provided the frequencies are measured to rather better than 1μHz accuracy (the COROT project should measure oscillation frequencies with an accuracy of 0.1μHz), we present here a tool to study this aspect of stellar structure.
The edge of a convective region inside a star gives rise to a characteristic periodic signal in the frequencies of its global p-modes (e.g. , ), such that the frequencies ω are then essentially a smooth function of the mode order n plus a periodic component . Here the amplitude is , with A1 and A2 being values that depend weakly on frequency ω: A1 is always present in general, but A2 will be non-zero only if there is overshoot; is essentially the acoustical depth τ (i.e. the sound travel time) of the edge of the convection zone measured from the surface of the star; and Φ0 is a constant related to the phase of the eigenfunctions. To facilitate the comparison between different stars, we consider the amplitude evaluated at a fiducial frequency by defining . For the Sun, we chose as the reference frequency . If we take this value and scale it for other stars (using just a standard homology scaling for frequencies), we find .
Following the report of solar-like oscillations in the G0 V star η Boo (Kjeldsen et al. 1995), a first attempt to model the observed frequencies was made by Christensen-Dalsgaard et al. (1995). This attempt succeeded in reproducing the observed frequency separations Δv and δv02, although there remained a difference of ∼ 10 μHz between observed and computed frequencies. In those models, the near-surface region of the star was treated rather crudely: convection was described by means of a local mixing-length theory neglecting turbulent pressure, and the oscillations were assumed to be adiabatic. These approximations are likely to affect both Δv and absolute frequencies.
Email your librarian or administrator to recommend adding this to your organisation's collection.