J. Sánchez Almeida

Physical Properties of the Solar Magnetic Photosphere under the MISMA Hypothesis. II. Network and Internetwork Fields at the Disk Center

This paper is the second in a series that models photospheric magnetic structures in terms of atmo- spheres having optically thin —uctuations of magnetic —eld and thermodynamic state (the MISMA hypothesis). We apply an inversion procedure to the polarization of Fe I j6301.5 and Fe I j6302.5 observed in network and internetwork regions with the Advanced Stokes Polarimeter. Some 5200 inde- pendent spectra, comprising mildly asymmetric to very abnormal Stokes pro—les, were reproduced by a single type of model atmosphere. It has three components, two that are magnetized and one that is not. A large fraction among the —eld strengths we measure are in the kG regime, but simulations suggest that the polarization of the observed Fe I lines weakens below detectable levels for —elds substantially smaller than the observed ones. Synthesis of Stokes pro—les of the IR Fe I j15648.5 line in MISMAs reveals the opposite behavior, i.e., an increase of polarization for sub-kG —elds. The highly transparent MISMAs inferred from observations are signi—cantly brighter in the continuum than an unmagnetized atmosphere. The mass of the magnetic structures tends to be at rest, although a minor fraction undergoes strong down—ows. Down—ows are also present in the nonmagnetic environment. A signi—cant number of —tted Stokes pro—les require opposite magnetic polarities within the same resolution element. The occurrence of mixed polarities increases with weakening degree of polarization, such that 25% of the weakest signals require mixed polarity. The weak polarization signals account for most of the total (unsigned) magnetic —ux of the observed region. By extrapolation, this indicates that a signi—cant fraction of photospheric magnetic —ux remains undetected. The MISMA framework provides a uni—ed and physically consistent scenario for interpretation of quiet Sun magnetism. Moreover, it is the only one available at present that is able to —t the abnormal Stokes pro—les as revealed by the new generation of sensitive Stokes polari- meters. Subject headings: line: pro—lesmethods: data analysispolarizationradiative transfer ¨ Sun: atmosphereSun: magnetic —elds

Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample: a publicly available Bayesian automated classification

We present an automated morphological classification in 4 types (E, S0, Sab, Scd) of ∼700 000 galaxies from the SDSS DR7 spectroscopic sample based on support vector machines. The main new property of the classification is that we associate a probability to each galaxy of being in the four morphological classes instead of assigning a single class. The classification is therefore better adapted to nature where we expect a continuous transition between different morphological types. The algorithm is trained with a visual classification and then compared to several independent visual classifications including the Galaxy Zoo first-release catalog. We find a very good correlation between the automated classification and classical visual ones. The compiled catalog is intended for

CONVECTIVELY DRIVEN VORTEX FLOWS IN THE SUN

We have discovered small whirlpools in the Sun, with a size similar to the terrestrial hurricanes (. 0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral in their way to be engulfed by a downdraft. Our disk center observations show 0.9×10 −2 vortexes per Mm 2 , with a lifetime of the order of 5 min, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs. Subject headings: convection – Sun: photosphere – Sun: granulation

Observation and interpretation of the asymmetric Stokes Q, U, and V line profiles in sunspots

We present a first approach to systematic characterization and interpretation of observed asymmetries of Stokes profiles as a function of spatial position within sunspots. Spatial maps of the full Stokes profiles of Fe I 6302.5 A gathered in large sunspots using the HAO Stokes II instrument reveal asymmetries that vary systematically across large sunspots observed during 1980. We use the inversion technique by Landolfi to extract the velocity gradients along the line of sight (LOS) which give rise to these asymmetries. The gradients derived from full Stokes profiles are in agreement with previous characterizations of the Evershed flow derived from Stokes I profiles alone (i.e., a flow increasing with depth in the atmosphere). By coupling this semiempirical gradient of velocity with a magnetic field inclination varying along the LOS, the synthesized profiles are able to mimic basic observed features of the broad-band circular polarization present in our data and observed previously by others. This characterization has magnetic field lines which become progressively more horizontal with depth in the penumbra.

Quiet-Sun Magnetic Fields at High Spatial Resolution

We present spectropolarimetric observations of internetwork magnetic fields at the solar disk center. A Fabry-Perot spectrometer was used to scan the two Fe I lines at 6301.5 and 6302.5 A. High spatial resolution (05) magnetograms were obtained after speckle reconstruction. The patches with magnetic fields above noise cover approximately 45% of the observed area. Such large coverage renders a mean unsigned magnetic flux density of some 20 G (or 20 Mx cm-2), which exceeds all previous measurements. Magnetic signals occur predominantly in intergranular spaces. The systematic difference between the flux densities measured in the two iron lines leads to the conclusion that, typically, we detect structures with intrinsic field strengths larger than 1 kG occupying only 2% of the surface.

Magnetic Properties of Photospheric Regions with Very Low Magnetic Flux

The magnetic properties of the quiet Sun are investigated using a novel inversion code, FATIMA, based on the Principal Component Analysis of the observed Stokes profiles. The stability and relatively low noise sensitivity of this inversion procedure allows for the systematic inversion of large data sets with a very weak polarization signal. Its application to quiet-Sun observations of network and internetwork regions reveals that a significant fraction of the quiet-Sun contains kilogauss fields (usually with very small filling factors) and confirms that the pixels with weak polarization account for most of the magnetic flux. Mixed polarities in the resolution element are also found to occur more likely as the polarization weakens.

Inter-network magnetic fields observed with sub-arcsec resolution

We analyze a time sequence of Inter-Network (IN) magnetograms observed at the solar disk center. Speckle recon- struction techniques provide a good spatial resolution (0: 00 5c uto frequency) yet maintaining a fair sensitivity (some 20 G). Patches with signal above noise cover 60% of the observed area, most of which corresponds to intergranular lanes. The large surface covered by signal renders a mean unsigned magnetic flux density between 17 G and 21 G (1 G 1M x cm 2 ). The dierence depends on the spectral line used to generate the magnetograms (Fei6302.5 A or Fei6301.5 A). Such systematic dierence can be understood if the magnetic structures producing the polarization have intrinsic field strengths exceeding 1 kG, and consequently, occupying only a very small fraction of the surface (some 2%). We observe both, magnetic signals changing in time scales smaller than 1 min, and a persistent pattern lasting longer than the duration of the sequence (17 min). The pattern resembles a network with a spatial scale between 5 and 10 arcsec, which we identify as the mesogranulation. The strong depen- dence of the polarization signals on spatial resolution and sensitivity suggests that much quiet Sun magnetic flux still remains undetected.

The Distribution of Quiet Sun Magnetic Field Strengths from 0 to 1800 G

The quiet-Sun photospheric plasma has a variety of magnetic field strengths going from zero to 1800 G. The empirical characterization of these field strengths requires a probability density function (PDF), i.e., a function P(B) describing the fraction of quiet Sun occupied by each field strength B. We show how to combine magnetic field strength measurements based on the Zeeman effect and the Hanle effect to estimate an unbiased P(B). The application of the method to real observations renders a set of possible PDFs, which outline the general characteristics of the quiet-Sun magnetic fields. Their most probable field strength differs from zero. The magnetic energy density is a significant fraction of the kinetic energy of the granular motions at the base of the photosphere (larger than 15% or larger than 2 × 103 ergs cm-3). The unsigned flux density (or mean magnetic field strength) has to be between 130 and 190 G. A significant part of the unsigned flux (between 10% and 50%) and of the magnetic energy (between 45% and 85%) are provided by the field strengths larger than 500 G, which, however, occupy only a small fraction of the surface (between 1% and 10%). The fraction of kG fields in the quiet Sun is even smaller, but they are important for a number of reasons. The kG fields still trace a significant fraction of the total magnetic energy, they reach the high photosphere, and they appear in unpolarized light images. The quiet-Sun photosphere has far more unsigned magnetic flux and magnetic energy than the active regions and the network combined.

Physical Properties of the Solar Magnetic Photosphere under the MISMA Hypothesis. I. Description of the Inversion Procedure

The paper describes an automatic inversion code to recover microstructured magnetic atmospheres (MISMAs) by fitting Stokes profiles. These solar model atmospheres incorporate small-scale fluctuations of the magnetic field vector, the velocity, the temperature, etc., which seems to be an intrinsic property of the magnetic photosphere. The model MISMAs considered for inversion have several distinct components. Each one of them is made of slender flux tubes, so that the whole vertical stratification of the MISMA is reconstructed from a finite set of parameters. The inversion code has been thoroughly tested using both synthetic and real observations. In particular, it successfully reproduces line profiles and model atmospheres corresponding to the quiet Sun and plage regions. As a by-product, we introduce a new error estimate for nonlinear least-squares minimizations.

SUNRISE/IMaX Observations of Convectively Driven Vortex Flows in the Sun

We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE telescope. By visual inspection of time series, we find some 3.1 ? 10?3 vortices Mm?2 minute?1, which is a factor of ~1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9?minutes, with a standard deviation of 3.2?minutes. In addition, we find several events appearing at the same locations along the duration of the time series (31.6?minutes). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are 6 ? 10?3 s?1, which corresponds to a period of rotation of some 35?minutes. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation.