On the relation between penumbral intensity and flow filaments

Schlichenmaier, R.; Rubio, L. R. Bellot; Tritschler, A.

doi:10.1002/asna.200410394

Cited by 22 publications

(23 citation statements)

References 16 publications

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“…The curves depicted in Fig. 14 reveal that larger continuum intensities are associated with larger LOS velocities, i.e., the Evershed flow is more intense in the brighter structures, at least in the inner center-side penumbra. This agrees with the conclusions of Bello González et al (2005) and Schlichenmaier et al (2005).…”

Section: Do We See Individual Flow Channels?supporting

confidence: 94%

Two-dimensional spectroscopy of a sunspot

Rubio

Schlichenmaier

Tritschler

2006

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We investigate the thermal and kinematic configuration of a sunspot penumbra using high spectral and spatial resolution intensity profiles of the non-magnetic Fe i 557.6 nm line. The data set was acquired with the 2D solar spectrometer TESOS. The profiles are inverted using a one-component model atmosphere with gradients of the physical quantities. From this inversion we obtain the stratification with depth of temperature, line-of-sight velocity, and microturbulence across the penumbra. Our results suggest that the physical mechanism(s) responsible for the penumbral filaments operate preferentially in the lower photosphere. The spot, located at an heliocentric angle of 23• , exhibits larger continuum intensities in the center-side penumbra as compared with the limb side, which translates into an average temperature difference of 100−150 K at log τ 500 = 0. We investigate the nature of the bright ring that appears in the inner penumbra when sunspots are observed in the wing of spectral lines. It is suggested that the bright ring does not reflect a temperature enhancement in the mid photospheric layers. The line-of-sight velocities retrieved from the inversion are used to determine the flow geometry at different heights in the photosphere. Both the flow speed and flow angle increase with optical depth and radial distance. Downflows are detected in the mid and outer penumbra, but only in deep layers (log τ 500 ≥ −1.4). We demonstrate that the velocity stratifications retrieved from the inversion are consistent with the idea of penumbral flux tubes channeling the Evershed flow. Finally, we show that larger Evershed flows are associated with brighter continuum intensities in the inner center-side penumbra. Dark structures, however, are also associated with significant Evershed flows. This leads us to suggest that the bright and dark filaments seen at 0. 5 resolution are not individual flow channels, but a collection of them. Our analysis highlights the importance of very high spatial resolution spectroscopic and spectropolarimetric measurements for a better understanding of sunspot penumbrae.

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Section: Do We See Individual Flow Channels?supporting

confidence: 94%

Two-dimensional spectroscopy of a sunspot

Rubio

Schlichenmaier

Tritschler

2006

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“…These properties can change with radial distance. For example, Schlichenmaier et al (2005) suggested that flow filaments link bright and dark continuum features at different radial distances. Since ECs move along intra-spines (i.e., flow filaments), we may expect them to be associated with locally bright features in the inner penumbra.…”

Section: Comparison Of Line Parameters In Ecs and Intra-spinesmentioning

confidence: 99%

Temporal evolution of the Evershed flow in sunspots

Solana¹,

Rubio²,

Beck

et al. 2007

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Context. The magnetic and kinematic properties of the photospheric Evershed flow are relatively well known, but not completely understood. The evolution of the flow with time, which is mainly due to the appearance of velocity packets called Evershed clouds (ECs), may provide information to further constrain its origin. Aims. We undertake a detailed analysis of the evolution of the Evershed flow by studying the properties of ECs. In this first paper we determine the sizes, proper motions, location in the penumbra, and frequency of appearance of ECs, as well as their typical Doppler velocities, linear and circular polarization signals, Stokes V area asymmetries, and continuum intensities. Methods. High-cadence, high-resolution, full vector spectropolarimetric measurements in visible and infrared lines are used to characterize the EC phenomenon through a simple line-parameter analysis. Results. ECs appear in the mid penumbra and propagate outward along filaments having large linear polarization signals and enhanced Evershed flows. The frequency of appearance of ECs varies between 15 and 40 min in different filaments. ECs exhibit the largest Doppler velocities and linear-to-circular polarization ratios of the whole penumbra. In addition, lines formed deeper in the atmosphere show larger Doppler velocities, much in the same way as the "quiescent" Evershed flow. According to our observations, ECs can be classified in two groups: type I ECs, which vanish in the outer penumbra, and type II ECs, which cross the outer penumbral boundary and enter the sunspot moat. Most of the observed ECs belong to type I. On average, type II ECs can be detected as velocity structures outside of the spot for only about 14 min. Their proper motions in the moat are significantly reduced with respect to the ones they had in the penumbra.

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“…As mentioned in the introduction, the Evershed flow is observed to be directed along the more inclined intra-spines, which coincide with dark filaments in the outer penumbra and bright filaments in the inner penumbra Schlichenmaier et al 2005;Bellot Rubio et al 2006;Ichimoto et al 2007). Since dark material usually means cooler and therefore more neutral plasma, the conjecture is that neutral iron lines mainly form in dark filaments (those harboring Evershed flow in the outer penumbra) and ionized iron lines form in the hotter and brighter filaments with stronger and more vertical fields.…”

Section: Discussion Of the Results And Uncertaintiesmentioning

confidence: 62%

“…The relation between the brightness of penumbral filaments and the Evershed flow is not straightforward. There are indications that the more horizontal component of intraspines coincides with dark filaments in the outer penumbra and with bright ones in the inner penumbra (Schlichenmaier et al 2005;Bellot Rubio et al 2006;Ichimoto et al 2007). Up-and downflows are superimposed on the radial outflow and produce a difference in the velocity inclination angle between the bright and dark features depending on the radial distance in the penumbra .…”

Section: Introductionmentioning

confidence: 97%

Evershed flow observed in neutral and singly ionized iron lines

Khomenko

Collados

Shchukina

et al. 2015

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The amplitudes of the Evershed flow are measured using pairs of carefully selected Fe i and Fe ii spectral lines that are close in wavelength and registered simultaneously. A sunspot belonging to the NOAA 11582 group was scanned using the spectrograph of the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). Velocities were extracted from intensity profiles using the λ-meter technique. The formation heights of the observed spectral lines were calculated using semi-empirical models of a bright and dark penumbral filament taking into account the sunspot location at the limb. Our objective is to compare azimuthally averaged amplitudes of the Evershed flow extracted from neutral and ion lines. We find measurable differences in the radial component of the flow. All five pairs of lines show the same tendency; the flow measured from the Fe i lines has an amplitude that is a few hundred m s −1 larger than that of the Fe ii lines. This tendency is preserved at all photospheric heights and radial distances in the penumbra. We discuss the possible origin of this effect.

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On the relation between penumbral intensity and flow filaments

Cited by 22 publications

References 16 publications

Two-dimensional spectroscopy of a sunspot

Two-dimensional spectroscopy of a sunspot

Temporal evolution of the Evershed flow in sunspots

Evershed flow observed in neutral and singly ionized iron lines

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