Author name code: cabrera-solana ADS astronomy entries on 2022-09-14 author:"Cabrera Solana, Daniel" ------------------------------------------------------------------------ Title: Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Borrero, J. M.; Del Toro Iniesta, J. C. Bibcode: 2008A&A...477..273C Altcode: 2007arXiv0709.1601C Context: Evershed clouds (ECs) represent the most conspicuous variation of the Evershed flow in sunspot penumbrae.
Aims: We determine the physical properties of ECs from high spatial and temporal resolution spectropolarimetric measurements. This information is used to investigate the nature of the EC phenomenon.
Methods: The Stokes profiles of four visible and three infrared spectral lines are subject to inversions based on simple one-component models as well as more sophisticated realizations of penumbral flux tubes embedded in a static ambient field (uncombed models).
Results: According to the one-component inversions, the EC phenomenon can be understood as a perturbation of the magnetic and dynamic configuration of the penumbral filaments along which the ECs move. The uncombed inversions, on the other hand, suggest that ECs are the result of enhancements in the visibility of penumbral flux tubes. We conjecture that these enhancements are caused by a perturbation of the thermodynamic properties of the tubes, rather than by changes in the vector magnetic field. This mechanism is investigated performing numerical experiments of thick penumbral tubes in mechanical equilibrium with a background field.
Conclusions: While the one-component inversions confirm many of the properties indicated by a simple line parameter analysis (Paper I of this series), we give more credit to the results of the uncombed inversions because they take into account, at least in an approximate manner, the fine structure of the penumbra.

Appendix A is only available in electronic form at http://www.aanda.org Title: Temporal evolution of the Evershed flow in sunspots. I. Observational characterization of Evershed clouds Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2007A&A...475.1067C Altcode: 2007arXiv0707.2629C 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.

Appendices A and B are only available in electronic form at http://www.aanda.org Title: Temporal evolution of the Evershed flow and its magnetic properties Authors: Cabrera Solana, Daniel Bibcode: 2007PhDT........27C Altcode: No abstract at ADS Title: Inversion of Visible and IR Stokes Profiles in Sunspots Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2006ASPC..358...25C Altcode: We present an analysis of simultaneous observations of a sunspot in two different spectral ranges (630 nm and 1565 nm). The dataset was acquired with the POlarimetric LIttrow Spectrograph (POLIS) and the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT) of Observatorio del Teide. Inversions of both sets of lines are carried out to retrieve physical quantities such as temperature and magnetic fields. We find that: a) the differences between the atmospheric parameters inferred from the two ranges are small, demonstrating that inversion techniques provide unique results; b) there is a cross-talk between temperature and stray light for visible lines; c) a more realistic treatment of the stray light contamination is required. Making use of both visible and infrared lines we obtain < dB/dz >=-2.3±0.6 G km-1 and < dγ/dz >=-0.019±0.015 deg km-1 in the umbra. Finally, we show how simultaneous spectro-polarimetric observations of the Sun in visible and infrared wavelengths improve the diagnostic capabilities of a single spectral range alone. Title: Evershed Clouds as Precursors of Moving Magnetic Features around Sunspots Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; Beck, C.; del Toro Iniesta, J. C. Bibcode: 2006ApJ...649L..41C Altcode: 2006astro.ph..9108C The relation between the Evershed flow and moving magnetic features (MMFs) is studied using high-cadence, simultaneous spectropolarimetric measurements of a sunspot in visible (630.2 nm) and near-infrared (1565 nm) lines. Doppler velocities, magnetograms, and total linear polarization maps are calculated from the observed Stokes profiles. We follow the temporal evolution of two Evershed clouds that move radially outward along the same penumbral filament. Eventually, the clouds cross the visible border of the spot and enter the moat region, where they become MMFs. The flux patch farther from the sunspot has the same polarity of the spot, while the MMF closer to it has opposite polarity and exhibits abnormal circular polarization profiles. Our results provide strong evidence that at least some MMFs are the continuation of the penumbral Evershed flow into the moat. This, in turn, suggests that MMFs are magnetically connected to sunspots. Title: Sensitivity of spectral lines to temperature, velocity, and magnetic field Authors: Cabrera Solana, D.; Bellot Rubio, L. R.; del Toro Iniesta, J. C. Bibcode: 2005A&A...439..687C Altcode: We present an analytical and numerical study of the sensitivity of weak solar photospheric lines to temperature, velocity, and magnetic fields. Our investigation is based on the concept of response functions (Landi degl'Innocenti & Landi degl'Innocenti 1977; Ruiz Cobo & del Toro Iniesta 1994). Lines commonly used in solar spectropolarimetry, like Fe I 630.25 nm in the visible and Fe I 1564.85 nm in the infrared, are examined in detail as emerging from reference quiet Sun and sunspot models. We develop a simple phenomenological model capable of describing the response of any given line to these atmospheric parameters. We find that: (a) the sensitivity of the lines to velocity and magnetic fields increases with the sharpness of the intensity and circular polarization profiles; (b) the sensitivity to temperature is determined mainly by the variation of the source function with temperature, which is smaller at longer wavelengths; and (c) lines quoted to be insensitive to temperature, like Fe I 1564.85 nm and Fe I 557.61 nm, exhibit larger changes in equivalent width than lines presumed to have higher sensitivities to T, such as Fe I 630.25 nm. The relations provided by our model are universal and can be used to decide which line is better suited to measuring a given atmospheric parameter. The results of this study are of practical interest for the design of new instruments and for better exploitation of existing ones.