Presiding: H P Warren, Naval Research Laboratory; K D Leka, Colorado Research Associates Division, NorthWest Research Associates
Statistical Study of Rapid Penumbral Decay Associated with Flares
We present results of statistical study of rapid penumbral decay associated with flares. In total, we investigated 402 events from 05/09/98 to 07/17/04, including 40 X-class, 173 M-class and 189 C-class flares. We show strong evidence that penumbral segments decayed rapidly and permanently right after many flares. The rapid changes, which can be identified in the time profiles of white-light(WL) mean intensity are permanent, not transient, thus are not due to flare emissions. Our study shows that penumbral decay is more likely to be detected when associated with large solar flares. The larger the flare magnitude, the stronger the penumbral decay is. For X-class flares, almost 50% events show distinct decay. But for M- and C-class flares, this percentage drops to 16% and 10%, respectively. For all the events that clear decay can be observed, we find that the locations of penumbral decay are associated with flare emissions and are connected by prominent TRACE post-flare loops. To explain these observations, we propose a reconnection picture in that the penumbral fields change from a highly inclined to a more vertical configuration, leading to penumbral decay.
The 1564.6nm CN Line in Sunspots
The line strength of CN absorption has been observed to vary with the continuum intensity within sunspots, and the Doppler shift of the CN line at 1564.6nm has been shown to reveal fast Evershed flows in the penumbra. We examine several sunspots observed from 2002-2005 using intensity spectroscopy and spectropolarimetry to determine the line strength, plasma flow velocity, and the local magnetic field configuration as functions of position in these sunspots.
Elemental Abundances in a Sunspot Plume Observed With SERTS
We present an EUV spectrum of a sunspot plume obtained with the SERTS sounding rocket experiment. The spectrum contains emission lines from various ionization stages of elements with a low (less than 10 eV) first ionization potential (low FIP: Al, Ca, Fe, Mg, Ni, Si) and a high FIP (C, He, Ne, O). The plume appears much brighter than its surroundings in lines formed at log T around 5.6, i.e., lines of high-FIP Ne VI and low-FIP Mg VI. Based upon the differential emission measure (DEM) derived from all of the lines available, we are able to compare the abundances of low-FIP and high-FIP elements in the plume. Results indicate whether plume plasma abundances are photospheric or coronal.
Photospheric and Chromospheric structure of Sunspots using IBIS.
We use the Interferometric BIdimensional Spectrometer (IBIS) of the INAF/Arcetri Astrophysical Observatory and installed at the National Solar Observatory's (NSO) Dunn Solar Telescope, to understand the structure of sunspots. Using the spectral lines FeI 6301.5Å, FeII 7224.4Å and CaII 8542.6Å, we examine the spectroscopic variation of sunspot penumbral and umbral structures about the heights of formation of these lines. Simultaneous white-light imaging data helps us to register and track the images. We map the spatio-temporal variation of Doppler signatures in these spectral lines, from the photosphere to the chromosphere, and discuss the implication of these variations for sunspot models. These high resolution observations were acquired on 2004 July 30-31, on a sunspot NOAA 10654, using the higher order NSO adaptive optics system.
Moving Magnetic Features Inside the Penumbra of NOAO 10008
Over 30 years of observations and theories comprise the study of moving magnetic features (MMFs). MMFs, which often occur in opposite polarity pairs, migrate radially outward through the sunspot moat at speeds of about 1 km~s-1. A sequence of sixteen scans of the active region NOAO 10008 were taken using the NSO-CSUN IR camera at the NSO McMath-Pierce Solar Telescope on 24 June 2002 17:38-21:59. Using the Fe I absorption line at 1564.8nm, magnetogram images and maps of the magnetic field vector were produced, revealing magnetic features within the penumbra that appear to move radially outward at similar velocities and azimuth angles as those of MMFs in the moat. We use polar time slice images to measure the radial velocities of both types of features. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program.
Understanding the Mechanism of the Penumbra and the Curled Light Bridge
We analyzed the mechanisms of the penumbra and the curled light bridge by utilizing the SIR (Stokes Inversion based on Response functions) inversion program. The magnetic field strength, LOS (line of sight) velocity, and inclination were the main focus of both stratifications. The research on the penumbra was to compare the data with the siphon flow model and interchange convection model. From analyzing the data, pertaining to the penumbra, we concluded both models gave a logical representation of the penumbral mechanism. The light bridge system was under investigation for comparison to the cluster model. There is no definite answer, however with our data collection we concluded the cluster model gave a good theory on the mechanism of the light bridge.
Representation of Sun Spots with Shapelets
Shapelets are complete set of orthonormal functions that can be used to represent most images. These functions are Gauss-Hermite polynomials and are the eigenfunctions of the 2D harmonic oscillator. They were first used in image processing to study the shape of galaxies. Shapelets have properties that allow one to compute quantities such as chirality, shear and asymmetry in images. We use these functions to represent magnetograms of sunspots, allowing us to calculate a large set of descriptive quantities including those previously mentioned. These quantities are then correlated with the current classification schemes used to type sunspots.
Flow filaments linking bright and dark filaments in a sunspot penumbra
We present two-dimensional spectroscopic sunspot observations of high spatial (≈ 0.5 arcsec) and high spectral resolution (λ/Δλ = 250000). The observations were taken with the Telecentric Solar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope on Tenerife. We examine a single scan taken in the popular non-magnetic neutral iron line at 557.6 nm and concentrate our analysis on the unsettled issue of the relation between the Evershed flow and the intensity structure in a sunspot penumbra. At the end of the 20th century, observers concluded that the highest flow velocities are connected to the dark filaments which harbour more horizontal magnetic fields than the bright filaments. Based on a correlation analysis we find that the correlation between flows and intensity varies from the inner to the outer penumbra, from the center-side to the limb-side penumbra, and depends on the length of the trace used to perform the correlation. The line-of-sight velocity maps reveal that the Evershed flow on the center-side penumbra appears highly organised in narrow flow filaments, while the flows in the red-shifted limb-side penumbra do not show a filamentary fine-structure. A high correlation between flow speed and intensity is only observed over small spatial scales, i.e. considering short traces cutting individual features. The correlation is positive in the inner centre and limb-side penumbra, and tends to be negative in the outer penumbra. Our results imply that the Evershed flow is present in bright and dark filaments. In individual cases we find that flow filaments connect bright and dark filaments supporting the moving tube model for the penumbral fine structure.