Abstract Booklet IAU SYMPOSIUM 305 Polarimetry: From the Sun to Stars and Stellar Environments Punta Leona, Costa Rica 30 November – 5 December 2014

Booklet IAU SYMPOSIUM 305 Polarimetry: From the Sun to Stars and Stellar Environments Punta Leona, Costa Rica 30 November – 5 December 2014 Abdel Hady, Ahmed The high energetic particles released during the decline phases of solar cycle 24 Poster B1 During the decline phases of the last five solar cycles, new peak has appeared releasing high energetic particles. During October 2003 (so-called Halloween storms), a sudden increase of the solar activity occurred during the decline phase which has bigger that that occurred during the main peak of that Solar cycle 23. The same situation was repeated again for the solar cycle 24, during its decline phase, giving a new peak during January 2014 and release high energetic particles, which was bigger than that occurred during the mean peak of cycle 24. This means that the solar cycles starting from the cycle 20 have two peaks, the second peak always producing higher energetic flares which affects the Earth’s magnetic field. The same situation happened in the cycles 21, and 22, but with lower release of energetic particle, compared with cycles 23 and 24. We will do descriptive studies of January 2014 events, according to data analysis, and compare the results. Alvarado-Gomez, Hussain, Grunhut The Coronal Structure of the Sun-Like Exoplanet-Host GJ 3021 Oral Session 8 GJ 3021 is a yellow-orange dwarf star of spectral type G8V, which in comparison to our Sun, has about 93% of its mass, 94% of its diameter, and 77% of its bolometric luminosity. It i also a confirmed exoplanethost, making it a very interesting target for understanding the coronal structure and circumstellar environment around it. Using a time-series of high-resolution spectro-polarimetric observations from HARPSpol, in combination with the Zeeman Doppler Imaging (ZDI) technique, we have successfully recovered the magnetic field distribution in the surface of the star. These surface field maps serve as initial inputs for the BATS-R-US 3D MHD code to model in detail the winds/outflows and the coronal structure around the star. We present the initial results and analysis of the simulations including the different coronal structures obtained for a given magnetic field distribution/rotation period and the mass/angular momentum loss rates predicted for this system. Amazo-Gomez Line variations profile of a solar analog star, the search Poster B 2 In the development of this work we use PolarBase and data base that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, with a spectral resolution of ≈65.000 in polarimetric mode or a higher resolving power of ≈76.000 when used for classical spectroscopy alone. During this work we analize extracted data of a solar analog star with hosting-planets from PolarBase, we studied the line profile, their periodicity and variations. Finally we analize the magnetic field and starspots correlations. We use Intensity spectra and simultaneous spectra in circular and linear polarization. Anan, Casini, Ichimoto Magnetic and electric fields inference in chromospheric jets using spectropolarimetric observations in HI Paschen lines Oral Session 8 The solar chromosphere is a collisional and partially ionized plasma, whose dynamics is governed by magnetic and electric fields. When the velocity of neutrals is different from that of ions, multi-fluid effects may affect the dissipation of high-frequency waves and the physics of reconnection, and possibly break the ideal MHD approximation. Neutral atoms that move across the magnetic field also experience an electric field. The ensuing Stark effect for H-like ions can be large enough to be detectable with modern spectropolarimetric instrumentation, and occurs at spatial and temporal scales accessible to existing solar telescopes. Electric fields can also have an effect on the atomic polarization of H-like ions via the alignment-to-orientation conversion mechanism, when the plasma is irradiated non-isotropically. We present full Stokes spectra observations of the Paschen series of hydrogen in chromospheric jets at the solar limb. We found no definitive evidence of the linear polarization produced by the Stark effect for a macroscopic electric field, nor a significant amount of atomic orientation. Hence we inverted the Stokes spectra taking into account only the effects of magnetic fields, including the Hanle effect and level-crossing interactions. We found that the observed signals are compatible with a magnetic field approximately aligned with the visible structure of the jets, and we derived upper limits for the electric field in the moving frame of the atoms. From this we estimated an upper limit to the velocity of hydrogen atoms across the magnetic field, which is far below the bulk velocity of the plasma measured by the Doppler shift. We thus concluded that the hydrogen plasma neutral must be highly frozen to the magnetic field in these plasma structures. Anche, Anupama, Sen, Reddy, Sankarasubramanian, Sivarani, Sengupta, Skidmore, Ramprakash, Pandey, Atwood Analytical Modelling of Thirty Meter Telescope Polarization Poster Session A 1 The Thirty Meter Telescope (TMT) is an advanced, wide eld (20 arcmin), altitude-azimuth telescope. The primary mirror is segmented, consisting of 492, 1.44-meter hexagonal segments. The telescope will have adaptive optics capability at rst light,together with two instruments in the near-infrared region: Infrared imaging spectrograph (IRIS) an instrument with parallel imaging and integral eld spectroscopy and Infrared multi slit spectrometer (IRMS) an imaging, multi-slit instrument. A seeing limited, wide-eld, multi-object optical imaging spectrograph (MOBIE) will also be available at rst light. Studies of many types of astrophysical processes or objects utilize the information conveyed in the polarization properties of the light from the sources. Polarimetric observations are technically dificult to carry out but the scientic information that can be obtained is very rich. Polarimetric capabilities are now routinely provided at all major observatories and their use is growing over time. A polarimetric science capability is an important capability that the TMT will be called upon to support. The instrument development program will provide a means to respond to the needs of the community. However the telescope itself and the AO system should be able to support polarimetric instruments. Towards this, it is important to estimate the polarimetric budget of the telescope optics. An analytical model to estimate the polarimetric properties of the telescope optics is built on ray tracing from the primary till the tertiary (Nasmyth) focus. The instrumental polarization introduced after re ection from each mirror is estimated using this model. The Mueller Matrices are generated for each reecting surface, which are compared with the respective Mueller Matrices generated using the Zemax optical design software. The estimation is done for all instrument congurations on the Nasmyth platform i.e, dierent orientations of the tertiary mirror and also for dierent zenith angles. The wavelength range considered is 300-5000 nm. The eld of view considered in this study is 10 arcmin. In this study, the primary is considered as a 30m diameter monolithic, hyperboloid mirror. A baseline Gemini coating is assumed for the telescope optics. The study indicates that the instrumental polarization of the telescope optics is higher below 400nm. The study also indicates a change in the instrumental polarization with the eld angle. Asensio Ramos New generation Stokes inversion codes Oral Session 5 Our instruments are currently able to easily carry out two-dimensional spectropolarimetric observations of the solar surface. The interpretation of these observations has usually been achieved in a pixel-by-pixel manner. In this talk I will present our efforts to improve over current inversion codes and present what we consider the next generation 2D and 3D inversion codes. Baes, Stalevski, Camps, Fritz, Popovic Radiative transfer simulations of multiphase AGN tori: thermal emission and polarization Poster Session B3 The unification model of active galactic nuclei postulates an accreting supermassive black hole as the central engine, surrounded by a putative dusty torus. This dust absorbs the incoming radiation, re-emits it in the infrared and obscures our view of the central region at certain inclinations. We present new radiative transfer simulations of AGNs, in which the torus is modelled as a 3D multiphase sponge-like medium. We show that these new models can explain the observed spectral energy distribution of AGNs over the entire infrared domain, including the observed silicate feature strength and the level of near-infrared continuum. We also show the first polarisation simulations of our new models, and compare the difference between the polarisation signature of clumpy and smooth models. Bagnulo, Cellino, Sterzik Linear spectro-polarimetry: a new tool for the physical characterization of asteroids Oral Session 9 The surfaces of atmosphere-less objects of our solar system are traditionally probed via reflectivity measurements and/or broadband linear polarimetry. Little attention has been paid so far to the wavelength dependence of the linear polarization of the scattered light. We have decided to explore the potential of spectro-polarimetry as a remote sensing tool for asteroids in addition to traditional reflectivity measurements, and carried out a spectro-polarimetric survey of asteroids -to our best knolwedge, the first of its kind. We have observed a sample of asteroids of different albedo and taxonomic classes, as well as a few regions at the limb of the Moon. We show that objects exhibiting similar reflectivity spectra may display totally different polarized spectra, and we suggest that both intensity and polarized spectra should be used for asteroid classification. We found that the variation of linear polarization with wavelength is correlated with the albedo, and we found that in some cases the Umov law is violated, that is, in contrast to what is expected from simple physical considerations, the fraction of linear polarization and the reflectivity may be correlated positively. We conclude that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectivity and polarization spectra. Bagnulo, Fossati, Landstreet, Kochukov The importance of non-photon noise in astronomical spectro-polarimetry Poster A2 Stellar spectro-polarimetry has become extremely popular during the last decade, and has led to major advances in the studies of stellar magnetic fields. Many important discoveries have been obtained thanks to ultra-precise measurements of very small polarimetric signals, which require very stable instruments and special observing strategies. The so called “beam-swapping technique” is a well-known polarimetric technique capable of suppressing many spurious signals due to various instrumental effects. However, when one is interested in ultra-high signal-to-noise ratio measurements, observers start to hit various limitations introduced by the instrument, by the atmosphere, and even by the software for data-reduction. These limitations cannot be overcome by the observing strategies, and sources of errors other than photonnoise must be taken into account. Here we will show in detail the advantages of the beam-swapping technique, and then we will discuss the impact of small instrument and atmospheric instabilities or datareduction inaccuracies, and how these issues offer an explanation for the origin of the apparently significant observed polarisation signals produced by effects other than those intrinsic to the observed target. We will consider the case of sharp spectral lines observed with the Cassegrain-mounted instrument FORS of the ESO Very Large Telescope, and we will discuss how simple quality-check controls may help to distinguish between spurious signals and exciting discoveries. Bagnulo, Sterzik, Cellino, Azua Is there life in our solar system? Poster B4 Linear broad-band polarimetry is used to characterize the objects of our solar system, and has been proposed as a diagnostic tool for the atmospheres of exo-solar planets. Homochirality, which characterizes life as we know, induces circular polarization in the diffuse reflectance spectra of biotic material, hence it has been suggested that circular polarimetry may be used as a remote sensing tool for the search of extraterrestrial life. Using astronomical instrumentation, we have decided to explore the potential of both linear and circular spectro-polarimetry as a diagnostic tool for remote sensing of biotic material. We have used the calibration unit of the EFOSC2 instrument of the La Silla Observatory and obtained low resolution circular and linear spectro-polarimetric measurements of a number inorganic and organic materials. Here we present linear and circular polarization signatures from chlorophyll-a pigment response around 680 nm and other pigments like carotinoids and phycocyanins. We then compare our "laboratory data" with linear and circular spectro-polarimetric observations of various asteroids, of the Moon, and of Earthshine obtained with instruments very similar to that one used for our laboratory samples. Baur, Petrak, Schubert, Phipps New Optics for Astronomical Polarimetry Oral Session 4 A variety of new polarization optics can be employed for polarimetry and for polarization control. Many are enabled by new materials including polymers and liquid crystals. We survey these and other relatively newdevices and components available commercially that open new possibilities for astronomers. Bellot Rubio, Gosic The magnetic flux history of supergranular cells in the photosphere of the Sun Oral Session 1 Convection is an important process in the atmospheres of late-type stars. In the Sun, for example, supergranular cells provide an intimate connection between plasma flows and magnetic fields. They are surrounded by the magnetic network and their interior is home to myriad of weak internetwork magnetic patches that continually appear and disappear. However, the magnetism of solar supergranular cells is poorly understood, due to the absence of sufficiently sensitive polarimetric observations. In this work we use deep magnetograms acquired with the Hinode Narrowband Filter Imager to study the magnetic flux budget and evolution of supergranules. We determine the flux appearance and disappearance rates in individual supergranular cells over periods of up to 38 hours, covering a large fraction of their lifetimes. We find that flux appears in the cell interiors at a remarkably constant rate of 40 Mx cm^-2 day^{-1} over the entire solar surface, with little temporal variations. Most elements show up as unipolar patches, but bipolar emergence is sometimes observed. The primary mechanism of flux removal from the cell interiors is transfer of internetwork flux to the network. Actually, the internetwork turns out to be the main source of flux for the network. This implies a change of paradigm, as ephemeral regions were previously thought to supply the bulk of the network flux. Magnetic flux is removed from the cells faster than it appears in the supergranules, by a factor of approximately 2.2. This is a result of the tendency of internetwork elements to gain flux upon appearance on the solar surface. Such a flux increase may indicate that elements form by coalescence of background flux that is too weak to be detected until it concentrates by some mechanism, or that the magnetic field lines become more vertical with time. Distinguishing between the two possibilities is important, since in the first case no new flux is brought to the surface and the actual amount of flux emerging in supergranular cells may be much smaller than currently thought. Bhasari, Anusha, Nagendra, Uitenbroek Effect of cross-redistribution on the resonance scattering polarization of O {\sc i} line at 1302 \AA\ Oral Session 5 In this paper we present the results of our recent study of scattering polarization in the resonance line of neutral Oxygen at 1302 \AA\. In particular we study the effect of cross-redistribution (XRD) on the fractional scattering polarization in this line using two-dimensional radiative transfer in a composite atmosphere constructed using a two-dimensional magneto-hydrodynamical snapshot in the photosphere and columns of the one-dimensional FALC atmosphere in the chromosphere. We compare the scattering polarization profiles computed using ordinary partial frequency redistribution and XRD scattering mechanisms. We find that to reproduce the amplitude and shape of scattering polarization signals of the O {\sc i} line at 1302 \AA\, multi-dimensional radiative transfer including XRD effects becomes important. Bermúdez Bustamante, Iñiguez-Garin, Bermúdez, Hiriart, Castro-Chacon, Colorado, García, Guisa, Herrera, Martínez, Nuñez-Alfonoso, Ochoa, Valdez, Ramire Polima-2: A dual-beam imaging polarimeter for the San Pedro Martir National Observatory Poster Session A3 We present the design, construction and calibration of a new Dual-Beam Imaging Polarimeter (polima-2) to measure optical linear polarization of point sources in U, B, V, R, I and H-alpha bands. The instrument is mounted to the 0.84m telescope of the San Pedro Martir National Astronomical Observatory in Mexico. This dual-beam polarimeter is capable to measure two orthogonal polarization states simultaneously. The measurements are unsensitive to atmospheric extinction effects or seeing. Polima-2 is capable to measure percentages of linear polarization for astronomical sources of V~10.8 mag with a precision of 0.03%. Bhasari, Anusha, K. N. Nagendra, Uitenbroek Effect of cross-redistribution on the resonance scattering polarization of O {\sc i} line at 1302 \AA\ Oral Session 5 In this paper we present the results of our recent study of scattering polarization in the resonance line of neutral Oxygen at 1302 \AA\. In particular we study the effect of cross-redistribution (XRD) on the fractional scattering polarization in this line using two-dimensional radiative transfer in a composite atmosphere constructed using a two-dimensional magneto-hydrodynamical snapshot in the photosphere and columns of the one-dimensional FALC atmosphere in the chromosphere. We compare the scattering polarization profiles computed using ordinary partial frequency redistribution and XRD scattering mechanisms. We find that to reproduce the amplitude and shape of scattering polarization signals of the O {\sc i} line at 1302 \AA\, multi-dimensional radiative transfer including XRD effects becomes important. Bianda, A ZIMPOL polarimeter system installed at GREGOR in Tenerife, first results Oral Session 4 High resolution polarimetric measurements of solar structures, from the blue atmospheric cut off up to about 900 nm, are possible with ZIMPOL. This polarimeter was initially designed and built at ETH, and it is nowpermanently installed and used at IRSOL, where it is maintained and further developed in collaboration with SUPSI. A ZIMPOL system is foreseen to be permanently installed at GREGOR in Tenerife. The first installation campaign was performed in 2013, while an observing campaign is foreseen in October 2014. In this talk, we present the first observations carried out by combining the high polarimetric sensitivity of ZIMPOL with the high spatial and spectral resolution of GREGOR. Observations at GREGOR are expected to complement IRSOL observations where high spatial resolution is required to explore the physical conditions of small solar structures, as well as the physical processes taking place therein. Examples of elusive polarimetric signatures to highlight this point will be shown. ZIMPOL at GREGOR will also be used for exploring the behavior of high resolution polarimeters on large aperture telescopes. Blazère, Petit, Lignières, Aurière, Böhm Ultra-weak magnetic fields and atmospheric dynamics of Am stars: beta UMa and theta Leo Oral Session 7 An extremely weak circularly-polarized signature was recently detected in the spectral lines of the prototypical Am star Sirius A (Petit et al. 2011). With a prominent positive lobe, the shape of the phaseaveraged Stokes V line profile was atypical of stellar Zeeman signatures, casting doubts on its magnetic origin. We report here on ultra-deep spectropolarimetric observations of two more bright Am stars: beta Uma and theta Leo. Stokes V line signatures are detected in both objects, with a shape and amplitude similar to the one observed on Sirius A. We demonstrate that the amplitude of the Stokes V line profiles depend on various line parameters (Lande factor, wavelength, depth) as expected from a Zeeman signature, confirming that sub-Gauss magnetic fields are likely present in a large fraction of Am stars. We suggest that the strong asymmetry of the polarized signatures, systematically observed so far in Am stars and never reported in strongly magnetic Ap stars, bears unique information about the structure and dynamics of the thin surface convective shell of Am stars. Bommier The multiline observations of the THEMIS telescope reveal the effect of the solar surface anisotropy on the magnetic field Oral Session 1 The THEMIS telescope was designed in order to perform depth probing of the solar surface magnetic field, by means of multiline observations. The observations are spectropolarimetric ones, in order to infer the magnetic field vector. Magnetic inversion is performed on the observations, but the result is ambiguous, because two field vectors symmetrical with respect to the line-of-sight have the same polarimetric signature. Trying to solve this ambiguity by minimizing divB from observations in two lines formed at different heights, namely Fe I 6301.5 and 6302.5, also observed by HINODE/SOT/SP, we encountered the following problem. The observations have revealed a decrease of the vertical magnetic flux along height in sunspot umbræ and penumbræ, which is not compensated for by an increase of the horizontal magnetic flux. Turning to the literature, we found 15 references confirming the fact, and no reference invalidating it. We show that the lack of spatial resolution, horizontal as well as vertical, cannot be responsible for this difference. This is confirmed by numerical tests about unresolved magnetic structures. We propose to explain the fact by a plasma effect, the Debye shielding, made anisotropic by the strong stratification, which is present as at any star surface. The strong stratification introduces an "aspect ratio" between horizontal and vertical typical lengths. When this aspect ratio is applied to the observed divB, this quantity becomes null again, and the ambiguity resolution becomes operational. This theoretical proposal about how the surface strong stratification affects the surface magnetic field via the Debye shielding, is available in the Open Access paper by V. Bommier at http://www.hindawi.com/journals/physri/2013/195403/ . Bommier Theoretical polarization spectrum of Na I D1 & D2 near the solar limb Poster A4 We present an application to the Na I D1 & D2 scattering polarization spectrum, of our new code XTAT for multilevel-multiline polarized radiative transfer with PRD. This code is based on the new theory including both coherent (Rayleigh) and resonant scatterings, presented in Bommier (1997a,b). Raman scattering was added later on (Bommier, 1999, SPW2). In this theory, which is straightly derived from the Schr\”odinger equation for the atomic density matrix, the radiative line broadening appears as a nonMarkovian process of atom-photon interaction? The collisional broadening is included. The Rayleigh (Raman) scattering appears as an additional term in the emissivity from the 4th order of the atom-photon interaction perturbation development. The development is pursued and finally summed up, leading to a non-perturbative final result. In this formalism, the use of redistribution functions is avoided. The formalism has now been complemented for multilevel-multiline atom modeling, including lower level alignment. The role of the collisions as balancing coherent and resonant scatterings is fully taken into account. A code XTAT, based on this formalism, has been recently developed. We present numerical results about the modeling of the scattering polarization profile of Na I D1 & D2 formed near the solar limb. The solution of the radiative transfer (1D) is of the lambda-iteration type, but the statistical equilibrium equations for the atomic density matrix are resolved at each depth and for each atomic velocity class. Ng acceleration is applied. Carciofi, Faes High Precision Polarimetry of Magnetic Massive Stars Oral Session 7 Some massive stars possess quite strong magnetic fields (larger than several kilogauss) that trap the wind material in a magnetosphere. Spectroscopic and photometric observations of these structures were successfully modeled with the Rigidly Rotating Magnetosphere model of Townsend et al. (2005). Recently, such structure was detected and studied for the first time in polarized light for the helium-strong star $\sigma$ Orionis E. The observed rotational modulation of the linear polarization was found to be quite small (between 0.03 and 0.07%), while the position angle varied by about 50 degrees. The polarimetric data presented a challenge for the Rigidly Rotating Magnetosphere model that failed at reproducing both the polarimetric and the photometric data simultaneously. This result suggests that the model, at least in its current formalism, cannot predict the correct distribution of material throughout the magnetosphere. In this contribution I will outline the main results obtained for sigma Ori E, and report on new observations made for two other stars: HR5907 and HR7355. Carlin Ramirez Chromospheric diagnosis with forward-scattering Hanle effect in hydrodynamical models Oral Session 3 The synthesis of polarization signals produced by scattering processes in Hanle regime offers an exceptional way of diagnosing the weak magnetic fields of the quiet Sun and the chromosphere through the detailed description of the atomic system, the solar atmosphere and the matter-radiation interaction. However, due to technical, physical and historical reasons the resolution of the corresponding radiative transfer problem has been typically limited to near-limb line of sights and semi-empirical models with no macroscopic velocities. This contribution breaks that trend by presenting several novel approaches and results. We summarize the several effects that solar dynamics has on the generation of scattering polarization signals and explain why solar dynamics is crucial for modeling the polarization signals produced by Hanle effect in chromospheric spectral lines. We also show the first scattering polarization maps that have ever been calculated as well as the most interesting conclusions derived from their analysis. Furthermore, special emphasis will be put in the forward-scattering geometry as a new and more precise way of doing chromospheric Hanle diagnosis. Our arguments converge in the physical interest of combining all the ingredients to model the linear polarization of the 4227 A line. We will show the great diagnostic capability and exciting challenge that means to consistently explain the whole spectral polarization profile of such line in realistic chromospheric models. Casini Theoretical Tools for Spectro-Polarimetry Oral Session 3 The understanding of solar magnetism and of the Sun's short-term variability lies at the foundation of any predictive capability of Space Weather. The measurement of the solar magnetic field represents the necessary observational basis for such endeavor. As we cannot (yet) probe directly the Sun's magnetic field by means of in-situ measurements, we must rely on the remote sensing of the solar atmosphere's physical properties. In particular, the polarization state of the solar spectrum carries the signature of symmetry breaking processes that occur in the solar atmosphere, such as the interaction of the ambient electromagnetic field with the emitting gas, and the excitation of the latter by non-isotropic radiation and colliding particles. A reliable modeling of the Sun's polarized spectrum is needed to interpret observations, to develop new plasma diagnostics, and also to set realistic science requirements for new polarimetric instrumentation. Such modeling is rooted in the fundamental description of the interaction of radiation with matter based on quantum electrodynamics. In this talk, I will give an overview of the theoretical tools that are needed for the modeling of the Sun's polarized spectrum.