8,891 research outputs found
Rotation of the solar convection zone from helioseismology
Helioseismology has provided very detailed inferences about rotation of the
solar interior. Within the convection zone the rotation rate roughly shares the
latitudinal variation seen in the surface differential rotation. The transition
to the nearly uniformly rotating radiative interior takes place in a narrow
tachocline, which is likely important to the operation of the solar magnetic
cycle.The convection-zone rotation displays zonal flows, regions of slightly
more rapid and slow rotation, extending over much of the depth of the
convection zone and converging towards the equator as the solar cycle
progresses. In addition, there is some evidence for a quasi-periodic variation
in rotation, with a period of around 1.3 yr, at the equator near the bottom of
the convection zone.Comment: 12 pages, 8 figures. To appear in Proc. IAU Symposium 239: Convection
in Astrophysics,eds F. Kupka, I. W. Roxburgh & K. L. Chan, Cambridge
University Pres
On the choice of parameters in solar structure inversion
The observed solar p-mode frequencies provide a powerful diagnostic of the
internal structure of the Sun and permit us to test in considerable detail the
physics used in the theory of stellar structure. Amongst the most commonly used
techniques for inverting such helioseismic data are two implementations of the
optimally localized averages (OLA) method, namely the Subtractive Optimally
Localized Averages (SOLA) and Multiplicative Optimally Localized Averages
(MOLA). Both are controlled by a number of parameters, the proper choice of
which is very important for a reliable inference of the solar internal
structure. Here we make a detailed analysis of the influence of each parameter
on the solution and indicate how to arrive at an optimal set of parameters for
a given data set.Comment: 14 pages, 15 figures. Accepted for publication on MNRA
Open issues in stellar modelling
An important goal of helio- and asteroseismology is to improve the modelling
of stellar evolution. Here I provide a brief discussion of some of the
uncertain issues in stellar modelling, of possible relevance to asteroseismic
inferences.Comment: Proc. HELAS Workshop on `New insights into the Sun', eds M. S. Cunha
and M. J. Thompson (invited talk
The Sun as a fundamental calibrator of stellar evolution
The Sun is unique amongst stars in having a precisely determined age which
does not depend on the modelling of stellar evolution. Furthermore, other
global properties of the Sun are known to much higher accuracy than for any
other star. Also, helioseismology has provided detailed determination of the
solar internal structure and rotation. As a result, the Sun plays a central
role in the development and test of stellar modelling. Here I discuss solar
modelling and its application to tests of asteroseismic techniques for stellar
age determination.Comment: To appear in Proc. IAU Symposium 258, The Ages of Stars, eds E. E.
Mamajek, D. R. Soderblom & R. F. G. Wyse, IAU and Cambridge University Pres
Stellar model fits and inversions
The recent asteroseismic data from the CoRoT and Kepler missions have
provided an entirely new basis for investigating stellar properties. This has
led to a rapid development in techniques for analysing such data, although it
is probably fair to say that we are still far from having the tools required
for the full use of the potential of the observations. Here I provide a brief
overview of some of the issues related to the interpretation of asteroseismic
data.Comment: Proc. ESF Conference : "The Modern Era of Helio- and
Asteroseismology", Obergurgl, 20 - 25 May, 2012. To appear in Astron. Nach.
Guest editor: Markus Rot
Correcting stellar oscillation frequencies for near-surface effects
In helioseismology, there is a well-known offset between observed and
computed oscillation frequencies. This offset is known to arise from improper
modeling of the near-surface layers of the Sun, and a similar effect must occur
for models of other stars. Such an effect impedes progress in asteroseismology,
which involves comparing observed oscillation frequencies with those calculated
from theoretical models. Here, we use data for the Sun to derive an empirical
correction for the near-surface offset, which we then apply three other stars
(alpha Cen A, alpha Cen B and beta Hyi). The method appears to give good
results, in particular providing an accurate estimate of the mean density of
each star.Comment: accepted for publication in ApJ Letter
Yersinia ruckeri challenge on rainbow trout fed different diet types
A challenge for sustainable rainbow trout production is an increasing use of plant sources in fish feed due to shortage of marine protein and oil sources. Diets with high plant content are known to cause enteritis and injury to the intestine, which will affect the absorption of nutrients, affecting the overall health status and welfare of the fish. The result is a higher risk of disease following exposure to pathogenic microorganisms. The aim of this study was to elucidate how different feed types with varying amounts of marine versus organic plant protein and oil sources affected the survival of rainbow trout in connection with an infection. Enteric redmouth disease caused by Yersinia ruckeri is an economically important disease which causes problems in rainbow trout. Experimental infections (intraperitoneal injection of 150-200 g fish fed the different diets over a two month period) were done and mortalities in the different diet groups were recorded. Two weeks post challenge the mortalities in the different groups were between 50 and 89 %. The mortalities were lowest in the group fed the diet where half of the fish oil was replaced by organic plant oil. Unfortunately, the results were blurred due to a natural infection with Y. ruckeri that had occurred in the diet groups two months prior to the experimental infection (mortalities between 2 and 9 % in the different groups), and the half fish oil half plant oil group had had the highest cumulative mortality percentage in connection with this natural infection
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