Modeling Repeatedly Flaring δ\delta Sunspots

Active regions (AR) appearing on the surface of the Sun are classified into $\alpha$, $\beta$, $\gamma$, and $\delta$ by the rules of the Mount Wilson Observatory, California on the basis of their topological complexity. Amongst these, the $\delta$-sunspots are known to be super-active and produce the most X-ray flares. Here, we present results from a simulation of the Sun by mimicking the upper layers and the corona, but starting at a more primitive stage than any earlier treatment. We find that this initial state consisting of only a thin sub-photospheric magnetic sheet breaks into multiple flux-tubes which evolve into a colliding-merging system of spots of opposite polarity upon surface emergence, similar to those often seen on the Sun. The simulation goes on to produce many exotic $\delta$-sunspot associated phenomena: repeated flaring in the range of typical solar flare energy release and ejective helical flux ropes with embedded cool-dense plasma filaments resembling solar coronal mass ejections.Comment: Minor changes consistent with Phys Rev Lett versio

What do global p-modes tell us about banana cells?

We have calculated the effects of giant convection cells also know as sectoral rolls or banana cells, on p-mode splitting coefficients. We use the technique of quasi-degenerate perturbation theory formulated by Lavely & Ritzwoller in order to estimate the frequency shifts. A possible way of detecting giant cells is to look for even splitting coefficients of 'nearly degenerate' modes in the observational data since these modes have the largest shifts. We find that banana cells having an azimuthal wave number of 16 and maximum vertical velocity of 180 m/s cannot be ruled out from GONG data for even splitting coefficients.Comment: 7 pages 2 figures. To appear in Journal of Physics: Conference Series (JPCS) for GONG 2010 - SoHO 24: A new era of seismology of the Sun and solar-like star

The Origin of Helicity in Solar Active Regions

We present calculations of helicity based on our solar dynamo model and show that the results are consistent with observational data.Comment: To appear in the Proceedings of IAU Symposium 22

Why does the Sun's torsional oscillation begin before the sunspot cycle?

Although the Sun's torsional oscillation is believed to be driven by the Lorentz force associated with the sunspot cycle, this oscillation begins 2--3 yr before the sunspot cycle. We provide a theoretical explanation of this with the help of a solar dynamo model having a meridional circulation penetrating slightly below the bottom of the convection zone, because only in such dynamo models the strong toroidal field forms a few years before the sunspot cycle and at a higher latitude.Comment: 4 pages 3 figures. Unfortunately there were some errors in the figures which appeared in PRL. We are putting the corrected figures here. The text is the same as the text in PRL. An erratum is being sent to PRL pointing out the errors in the figures. We would like to thank Bidya Binay Karak for assistance in preparing the corrected figure

Possibility of higher dimensional anisotropic compact star

We have provided here a new class of interior solutions for anisotropic stars admitting conformal motion in higher dimensional noncommutative spacetime. The Einstein fields equations are solved by choosing a particular density distribution function of Lorentzian type \cite{Nozari} under noncommutative geometry. Several cases with dimensions $4D$ and higher, e.g. $5D$, $6D$ and $11D$ have been discussed separately. An overall observation is that the model parameters, such as density, radial pressure, transverse pressure, anisotropy all are well behaved and represent a compact star with radius $4.17$ km. However, emphasis has been given on the acceptability of the model from physical point of view. As a consequence it is observed that higher dimensions, i.e. beyond $4D$ spacetime, exhibit several interesting yet bizarre features which are not at all untenable for a compact stellar model of strange quark type and thus dictates a possibility of its extra dimensional existence.Comment: 21 pages, 6 figures, 1 table, Substantial modification in the whole manuscript, Accepted in Eur. Phys. J.

How do f-mode frequencies change with solar radius?

We test the relation between relative f-mode frequency variation (δ ν/ν) and Lagrangian perturbation in the solar radius (δ r/r) obtained by Dziembowski and Goode using several pairs of solar models and show that it does not hold true for any of the model pairs we have used. We attempt to derive a better approximation for the kernel linking the relative frequency changes and the solar radius variation in the subsurface layers

A theoretical model of torsional oscillations from a flux transport dynamo model

Assuming that the torsional oscillation is driven by the Lorentz force of the magnetic field associated with the sunspot cycle, we use a flux transport dynamo to model it and explain its initiation at a high latitude before the beginning of the sunspot cycle.Comment: 3 pages, 2 figures. proceedings of IAU symposium 273, Physics of Sun and star spots, Ventura, California 22-26 August 201