Moving Dipolar Features in an Emerging Flux Region

Solar Physics - On 25 January, 2000, we observed active region NOAA&;nbsp;8844 with the Flare Genesis Experiment (FGE), a balloon-borne observatory with an 80-cm solar telescope. FGE was...     

On the possibility of nucleosynthesis in any matter-antimatter symmetric cosmology

In any matter-antimatter symmetric cosmology the primeval nucleosynthesis imposes a typical size of a region of matter (antimatter) much larger than the diffusion length of neutrons. Observational results on the abundances of cosmic deuterium and helium are used to evaluate how large it has to be. As a result we find that a minimal sizeL ₁～1.5×10⁸ cm at the temperatureT=1 MeV is compatible with the standard abundances of primeval helium and deuterium.     

Solar-interplanetary modeling: 3-D solar wind solutions in prescribed non-radial magnetic field geometries

A model is presented which describes the 3-dimensional non-radial solar wind expansion between the Sun and the Earth in a specified magnetic field configuration subject to synoptically observed plasma properties at the coronal base. In this paper, the field is taken to be potential in the inner corona based upon the Mt. Wilson magnetograph observations and radial beyond a certain chosen surface. For plasma boundary conditions at the Sun, we use deconvoluted density profiles obtained from synopticK-coronameter brightness observations. The temperature is taken to be 2 × 10⁶ K at the base of closed field lines and 1.6 x 10⁶K at the base of open field lines. For a sample calculation, we employ data taken during the period of the 12 November 1966 eclipse. Although qualitative agreement with observations at 1 AU is obtained, important discrepancies emerge which are not apparent from spherically symmetric models or those models which do not incorporate actual observations in the lower corona. These discrepancies appear to be due to two primary difficulties - the rapid geometric divergence of the open field lines in the inner corona as well as the breakdown in the validity of the Spitzer heat conduction formula even closer to the Sun than predicted by radial flow models. These two effects combine to produce conductively dominated solutions and lower velocities, densities, and field strengths at the Earth than those observed. The traditional difficulty in solar wind theory in that unrealistically small densities must be assumed at the coronal base in order to obtain observed densities at 1 AU is more than compensated for here by the rapid divergence of field lines in the inner corona. For these base conditions, the value ofβ(ratio of gas pressure to magnetic pressure) is shown to be significantly greater than one over most of the lower corona - suggesting that, for the coronal boundary conditions used here, the use of a potential or force-free magnetic field configuration may not be justified. The calculations of this paper point to the directions where future research on solar-interplanetary modelling should receive priority:

1. better models for the coronal magnetic field structure
2. improved understanding of the thermal conductivity relevant for the solar wind plasma.

     

About the prominence heating mechanisms during its eruptive phase

Recent EUV observations reveal that the `image' of the prominence overlaying coronal emission sometimes suddenly changes from absorption of EUV radiation to emission during the eruptive phase. This change reveals fast heating of the plasma within the prominence. We propose a kinetic mechanism of heating the fluid particles that transforms magnetic energy of the pre-eruptive magnetic configuration stored in the filament electric current into heat through collision processes of counteracting flows. The shape of the flux that the filament is made of should include upward concave segments to provide the counter flows within the erupting prominence. A typical twisted flux rope easily meets this requirement. Gas dynamic calculations are offered in addition to permit a quantitative evaluation of the relevant parameters and their time variations.     

Instantaneous Phase and Amplitude Correlation in the Solar Cycle

In the present study we address the issue of discerning between deterministic and stochastic paradigms in order to understand the behavior of the solar cycle. To this end we show the degree of correlation between the instantaneous amplitude and frequency in the sunspot number time series by the use of the Gabor analytic signal. We compare this correlation with those arising from two theoretical models: (a) the Barnes model of widespread use in the literature and (b) a spatial truncation of the MHD equations. We show that comparisons between the correlation observed in the sunspot time series with those arising from theoretical models can be used to refute one of the models.     

Discovery of the 'missing' mode in HR 1217 by the Whole Earth Telescope

HR 1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals  1.5×33.3 μHz)  to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multisite photometric campaign on the rapidly oscillating Ap star HR 1217 using the 'Whole Earth Telescope'. While a complete analysis of the data will appear in a later paper, one outstanding result from this run is the discovery of a newly detected frequency in the pulsation spectrum of this star, at the frequency predicted by Cunha.