Density fluctuations in a torsional quiescent prominence were studied with Solar Optical Telescope on board of Hinode satellite. Continuous observations were made in Ca II H line from ~15:00 UT May 03, 2008; the observational duration was ~1 hr with a cadence time ~ 30s. The emission intensity along the prominence axis as functions of altitudes and time shows fluctuations in brightness with local peaks in Fourier power spectra, indicating the presence of periods and intervallic displacements to be 3 ~ 11 min and 2 ~ 7 Mm respectively and statistically significant peaks at 368 ± 63s & 620 ± 41 s, and 3.3 ± 0.6 Mm regime. The distance is the line of sight projection. These intensity disturbances may perhaps be caused by density fluctuations originated from compressional waves in which the possible origin could be the combinations of p-mode oscillations induced at the surface and twisting of the flux tube.

From radiation magnetohydrodynamic (RMHD) simulations we track the temporal evolution of a vertical magnetic flux sheet embedded in a two-dimensional non-stationary atmosphere that reaches all the way from the upper convection zone to the low chromosphere. Examining its temporal behavior near the interface between the convection zone and the photosphere, we describe the excitation of propagating longitudinal waves within the magnetic element as a result of convective motion in its surroundings.

In this paper, we investigate whether incorporating sunspot-groups classification information would further improve the performance of our previous logistic regression based solar flare forecasting method, which uses only line-of-sight photospheric magnetic parameters. A dataset containing 4913 samples from the year 2000 to 2005 is constructed, in which 2721 samples from the year 2000, 2002 and 2004 are used as a training set, and the remaining 2192 samples from the year 2001, 2003 and 2005 are used as a testing set. Experimental results show that sunspot-groups classification combined with total gradient on the strong gradient polarity neutral line achieve the highest forecasting accuracy and thus it testifies sunspot-groups classification does help in solar flare forecasting.

The Stellar Observations Network Group (SONG) is being developed as a network of 1-meter spectroscopic telescopes designed for and primarily dedicated to asteroseismology. It is patterned after the highly successful GONG project. The Danish prototype telescope will be installed in Tenerife in early 2011. Ultimately we hope to have as many as 8 identical nodes providing continuous high-resolution spectroscopic observations for targets anywhere in the sky. The primary scientific goals of SONG are asteroseismology and the search for Earth-mass exoplanets. The spectroscopic requirements for these programs push the limits of current technology, but the resulting spectrograph design will enable many secondary science programs with less stringent requirements. Doppler imaging of starspots can be accomplished using continuous observations over several stellar rotations using identical instrumentation at each node. It should be possible to observe the evolution of starspot morphology in real-time, for example. We discuss the design and status of the SONG project in general, and we describe how SONG could be used to probe short timescale changes in stellar surface structure.

We have carried out the B,V and R-band polarimetric and V-band photometric study of the star LO Peg. Our analysis reveal that LO Peg is highly polarized among the sun-like stars. The degree of polarization and polarization position angle are found to be rotationally modulated. The levels of polarization observed in LO Peg could be the result of scattering of an anisotropic stellar radiation field by an optically thin circumstellar envelope or scattering of the stellar radiation by prominence-like structures. The long term photometric observations of LO Peg indicate three independent groups of spots are present on the surface of LO Peg.

We present BV(RI)C photometric measurements of the dM4-type V374 Peg covering ~430 days. The star has a mass of ~0.28MSun, so it is supposed to be fully convective. Previous observations detected almost-rigid-body rotation and stable, axisymmetric poloidal magnetic field. Our photometric data agree well with this picture, one persistent active nest is found on the stellar surface. Nevertheless, the surface is not static: night-to-night variations and frequent flaring are observed. The flares seem to be concentrated on the brighter part of the surface. The short-time changes of the light curve could indicate emerging flux ropes in the same region, resembling to the active nests on the Sun. We have observed flaring and quiet states of V374 Peg changing on monthly timescale.

A simple nonlinear model is introduced here to describe the rotational evolution of main sequence cool (FGKM) stars. It is formulated only in terms of the ratio of a star's rotation period, P, to its convective turnover timescale, τ, and two dimensionless constants which are specified using solar- and open cluster data. The model explains the origin of the two sequences, C/fast and I/slow, of rotating stars observed in open cluster color-period diagrams, and describes their evolution from C-type to I-type through the rotational gap, g, separating them. It explains why intermediate-mass open cluster stars have the longest periods, while higher- and lower-mass cool stars have shorter periods. It provides an exact expression for the age of a rotating cool star in terms of P and τ, thereby generalizing gyrochronology. The possible range of initial periods is shown to contribute upto 128 Myr to the gyro age errors of solar mass field stars. A transformation to color-period space shows how this model explains some detailed features in the color-period diagrams of open clusters, including the shapes and widths of the sequences, and the observed number density of stars across these diagrams.

We combine photometric data from field stars, plus over a dozen open clusters and associations, to explore how the maximum photometric amplitude (Amax) and the distribution of amplitudes varies with stellar properties. We find a complex variation of Amax with inverse Rossby number Ro−1, which nevertheless can be modeled well with a simple model including an increase in Amax with rotation for low Ro−1, and a maximum level. Amax may then be further affected by differential rotation and a decline at the highest Ro−1. The distribution of Aspot below Amax varies with Ro−1 : it peaks at low Aspot with a long tail towards Amax for low Ro−1, but is more uniformly distributed at higher Ro−1. We investigate further dependences of the Aspot distributions on stellar properties, and speculate on the source of these variations.

We have undertaken an observational program to photometrically monitor several transiting planet host stars. The Rabus et al. result for TrES-1 showed the dramatic effects star spots can have on transit photometry. We will investigate the effects of spots on transit light curves and estimates of planetary radii. The observed spot patterns will be used to derive the rotational periods of our sample. Our sample includes several of the newly discovered transiting ESPs from the SuperWASP, HAT, TrES, and Kepler projects.

We studied 16 sunspots with different sizes and shapes using the observations with the Hinode Solar Optical Telescope. The ratio of G-band and CaII H images reveal rich structures both within the umbra and penumbra of most spots. The striking features are the compact blob at the foot point of the umbra side of the penumbral fibrils with disk center-limb side asymmetry. In this paper, we present properties of these features using the spectropolarimetry and images in G-band, CaII and blue filters. We discuss the results using the contemporary models of the sunspots.

A laboratory plasma experiment has been constructed to simulate the eruption of arched magnetic flux ropes (AMFRs e.g., coronal loops, solar prominences) in an ambient magnetized plasma. The laboratory AMFR is produced using an annular hot LaB6 cathode and an annular anode in a vacuum chamber which has additional electrodes to produce the ambient magnetized plasma. Two laser beams strike movable carbon targets placed behind the annular electrodes to generate controlled plasma flows from the AMFR footpoints that drives the AMFR eruption. The experiment operates with a 0.5 Hz repetition rate and is highly reproducible. Thus, time evolution of the AMFR is recorded in three-dimensions with high spatio-temporal resolutions using movable diagnostic probes. Experimental results demonstrate outward expansion of the AMFR, release of its plasma to the background, and excitation of fast magnetosonic waves during the eruption.

Microwave emissions from sunspots are circularly polarized in the sense of rotation (right or left) determined by the polarity (north or south) of coronal magnetic fields. However, they may convert into unpolarized emissions under certain conditions of magnetic field and electron density in the corona, and this phenomenon of depolarization could be used to derive those parameters. We propose another diagnostic use of microwave depolarization based on the fact that an observed depolarization strip actually represents the coronal magnetic polarity inversion line (PIL) at the heights of effective mode coupling, and its location itself carries information on the distribution of magnetic polarity in the corona. To demonstrate this diagnostic utility we generate a set of magnetic field models for a complex active region with the observed line-of-sight magnetic fields but varying current density distribution and compare them with the 4.9 GHz polarization map obtained with the Very Large Array (VLA). The field extrapolation predicts very different locations of the depolarization strip in the corona depending on the amount of electric currents assumed to exist in the photosphere. Such high sensitivity of microwave depolarization to the coronal magnetic field can therefore be useful for validating electric current density maps inferred from vector magnetic fields observed in the photosphere.

We investigate the combined effects of thermal conduction, compressive viscosity and optically thin radiative losses on the period ratio, P1/2P2, (P1 is the period of the fundamental mode and P2 is the period of its first harmonic) of a slow mode propagating one dimensionally. We obtain the dispersion relation and solve it to study the influence of non-ideal effects on the period ratio. The dependence of period ratio on thermal conductivity, compressive viscosity and radiative losses has been shown graphically. It is found that the effect of thermal conduction on the period ratio is negligible while compressive viscosity and radiation have sufficient effects for small loops and large loops respectively.

Most solar eruptions occur above strong photospheric magnetic polarity inversion lines (PILs). What overlays a PIL is unknown, however, and this has led to a debate over the existence of sheared magnetic arcades vs. helical magnetic flux ropes. We argue that this debate may be of little meaning: numerous small-scale magnetic reconnections, constantly triggered in the PIL area, can lead to effective transformation of mutual to self magnetic helicity (i.e. twist and writhe) that, ultimately, may force the magnetic structure above PILs to erupt to be relieved from its excess helicity. This is preliminary report of work currently in progress.