Author name code: manso-sainz ADS astronomy entries on 2022-09-14 author:"Manso Sainz, Rafael" ------------------------------------------------------------------------ Title: Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE. The diverse ionization mechanisms acting in low-mass starbursts Authors: Cairós, L. M.; González-Pérez, J. N.; Weilbacher, P. M.; Manso Sainz, R. Bibcode: 2022A&A...664A.144C Altcode: 2022arXiv220602754C We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14 by means of integral field spectroscopic observations taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The large field of view of MUSE and its unprecedented sensitivity enable observations of the galaxy nebular emission up to large galactocentric distances, even in the important but very faint [O I] λ6300 diagnostic line. This allowed us to trace the ionized gas morphology and ionization structure of Haro 14 up to kiloparsec scales and, for the first time, to accurately investigate the excitation mechanism operating in the outskirts of a typical BCG. The intensity and diagnostic maps reveal at least two highly distinct components of ionized gas: the bright central regions, mostly made of individual clumps, and a faint component which extends up to kiloparsec scales and consists of widespread diffuse emission, well-delineated filamentary structures, and faint knots. Noteworthy are the two curvilinear filaments extending up to 2 and 2.3 kpc southwest, which likely trace the edges of supergiant expanding bubbles driven by galactic outflows. We find that while the central clumps in Haro 14 are H II-region complexes, the morphology and line ratios of the whole low-surface-brightness component are not compatible with star formation photoionization. In the spatially resolved emission-line-ratio diagnostic diagrams, spaxels above the maximum starburst line form the majority (∼75% and ∼50% in the diagnostic diagrams involving [O I] and [S II] respectively). Moreover, our findings suggest that more than one alternative mechanism is ionizing the outer galaxy regions. The properties of the diffuse component are consistent with ionization by diluted radiation and the large filaments and shells are most probably shocked areas at the edge of bubbles. The mechanism responsible for the ionization of the faint individual clumps observed in the galaxy periphery is more difficult to assess. These clumps could be the shocked debris of fragmented shells or regions where star formation is proceeding under extreme conditions.

Based on observations made with ESO Telescopes at Paranal Observatory under programme ID 60.A-9186(A). Title: Ultraviolet Spectropolarimetry: Investigating stellar magnetic field diagnostics Authors: Folsom, C. P.; Ignace, R.; Erba, C.; Casini, R.; del Pino Alemán, T.; Gayley, K.; Hobbs, K.; Manso Sainz, R.; Neiner, C.; Petit, V.; Shultz, M. E.; Wade, G. A. Bibcode: 2022arXiv220701865F Altcode: Magnetic fields are important for stellar photospheres and magnetospheres, influencing photospheric physics and sculpting stellar winds. Observations of stellar magnetic fields are typically made in the visible, although infrared observations are becoming common. Here we consider the possibility of directly detecting magnetic fields at ultraviolet (UV) wavelengths using high resolution spectropolarimetry, specifically considering the capabilities of the proposed Polstar mission. UV observations are particularly advantageous for studying wind resonance lines not available in the visible, but they can also provide many photospheric lines in hot stars. Detecting photospheric magnetic fields using the Zeeman effect and Least Squares Deconvolution is potentially more effective in the UV due to the much higher density of strong lines. We investigate detecting magnetic fields in the magnetosphere of a star using the Zeeman effect in wind lines, and find that this could be detectable at high S/N in an O or B star with a strong magnetic field. We consider detecting magnetic fields using the Hanle effect in linear polarization, which is complementary to the Zeeman effect, and could be more sensitive in photospheric lines of rapid rotators. The Hanle effect can also be used to infer circumstellar magnetism in winds. Detecting the Hanle effect requires UV observations, and a multi-line approach is key for inferring magnetic field properties. This demonstrates that high resolution spectropolarimetry in the UV, and the proposed Polstar mission, has the potential to greatly expand our ability to detect and characterize magnetic fields in and around hot stars. Title: Polarimetric characterization of segmented mirrors Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.; Collados, M. Bibcode: 2022ApOpt..61.4908P Altcode: 2022arXiv220514640P We study the impact of the loss of axial symmetry around the optical axis on the polarimetric properties of a telescope with segmented primary mirror when each segment is present in a different aging stage. The different oxidation stage of each segment as they are substituted in time leads to non-negligible crosstalk terms. This effect is wavelength dependent and it is mainly determined by the properties of the reflecting material. For an aluminum coating, the worst polarimetric behavior due to oxidation is found for the blue part of the visible. Contrarily, dust -- as modeled in this work -- does not significantly change the polarimetric behavior of the optical system . Depending on the telescope, there might be segment substitution sequences that strongly attenuate this instrumental polarization. Title: MUSE observations of the blue compact dwarf galaxy Haro 14. Data analysis and first results on morphology and stellar populations Authors: Cairós, L. M.; González-Pérez, J. N.; Weilbacher, P. M.; Manso Sainz, R. Bibcode: 2021A&A...654A.142C Altcode: 2021arXiv210809107C Investigations of blue compact galaxies (BCGs) are essential to advancing our understanding of galaxy formation and evolution. BCGs are low-luminosity, low-metallicity, gas-rich objects that form stars at extremely high rates, meaning they are good analogs to the high-redshift star-forming galaxy population. Being low-mass starburst systems, they also constitute excellent laboratories in which to investigate the star formation process and the interplay between massive stars and their surroundings. This work presents results from integral field spectroscopic observations of the BCG Haro 14 taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope in wide-field adaptive optics mode. The large MUSE field of view (1'×1'; = 3.8 × 3.8 kpc2 at the adopted distance of 13 Mpc) enables simultaneous observations of the central starburst and the low-surface-brightness host galaxy, which is a huge improvement with respect to previous integral field spectroscopy of BCGs. From these data we built galaxy maps in continuum and in the brightest emission lines. We also generated synthetic broad-band images in the VRI bands, from which we produced color index maps and surface brightness profiles. We detected numerous clumps spread throughout the galaxy, both in continuum and in emission lines, and produced a catalog with their position, size, and photometry. This analysis allowed us to study the morphology and stellar populations of Haro 14 in detail. The stellar distribution shows a pronounced asymmetry; the intensity peak in continuum is not centered with respect to the underlying stellar host but is displaced by about 500 pc southwest. At the position of the continuum peak we find a bright stellar cluster that with Mv = −12.18 appears as a strong super stellar cluster candidate. We also find a highly asymmetric, blue, but nonionizing stellar component that occupies almost the whole eastern part of the galaxy. We conclude that there are at least three different stellar populations in Haro 14: the current starburst of about 6 Myr; an intermediate-age component of between ten and several hundred million years; and a red and regular host of several gigayears. The pronounced lopsidedness in the continuum and also in the color maps, and the presence of numerous stellar clusters, are consistent with a scenario of mergers or interactions acting in Haro 14.

Based on observations made with ESO Telescopes at Paranal Observatory under programme ID 60.A-9186(A). Title: Solar Disk Center Shows Scattering Polarization in the Sr I 4607 Å Line Authors: Zeuner, Franziska; Manso Sainz, Rafael; Feller, Alex; van Noort, Michiel; Solanki, Sami K.; Iglesias, Francisco A.; Reardon, Kevin; Martínez Pillet, Valentín Bibcode: 2020ApJ...893L..44Z Altcode: 2020arXiv200403679Z Magnetic fields in turbulent, convective high-β plasma naturally develop highly tangled and complex topologies - the solar photosphere being the paradigmatic example. These fields are mostly undetectable by standard diagnostic techniques with finite spatio-temporal resolution due to cancellations of Zeeman polarization signals. Observations of resonance scattering polarization have been considered to overcome these problems. But up to now, observations of scattering polarization lack the necessary combination of high sensitivity and high spatial resolution in order to directly infer the turbulent magnetic structure at the resolution limit of solar telescopes. Here, we report the detection of clear spatial structuring of scattering polarization in a magnetically quiet solar region at disk center in the Sr I 4607 Å spectral line on granular scales, confirming theoretical expectations. We find that the linear polarization presents a strong spatial correlation with the local quadrupole of the radiation field. The result indicates that polarization survives the dynamic and turbulent magnetic environment of the middle photosphere and is thereby usable for spatially resolved Hanle observations. This is an important step toward the long-sought goal of directly observing turbulent solar magnetic fields at the resolution limit and investigating their spatial structure. Title: The Magnetic Sensitivity of the Resonance and Subordinate Lines of Mg II in the Solar Chromosphere Authors: del Pino Alemán, T.; Trujillo Bueno, J.; Casini, R.; Manso Sainz, R. Bibcode: 2020ApJ...891...91D Altcode: 2020arXiv200409176D We carry out a theoretical study of the polarization of the solar Mg II h-k doublet (including its extended wings) and the subordinate ultraviolet (UV) triplet around 280 nm. These lines are of great diagnostic interest, as they encode information on the physical properties of the solar atmosphere from the upper photosphere to the chromosphere-corona transition region. We base our study on radiative transfer calculations of spectral line polarization in one-dimensional models of quiet and plage regions of the solar atmosphere. Our calculations take into account the combined action of atomic polarization, quantum level interference, frequency redistribution, and magnetic fields of arbitrary strength. In particular, we study the sensitivity of the emergent Stokes profiles to changes in the magnetic field through the Zeeman and Hanle effects. We also study the impact of the chromospheric plasma dynamics on the emergent Stokes profiles, taking into account the angle-dependent frequency redistribution in the h-k resonance transitions. The results presented here are of interest for the interpretation of spectropolarimetric observations in this important region of the solar UV spectrum. Title: Science Requirement Document (SRD) for the European Solar Telescope (EST) (2nd edition, December 2019) Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.; Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.; Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse, K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.; Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller, T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno, J.; Utz, D.; Zuccarello, F. Bibcode: 2019arXiv191208650S Altcode: The European Solar Telescope (EST) is a research infrastructure for solar physics. It is planned to be an on-axis solar telescope with an aperture of 4 m and equipped with an innovative suite of spectro-polarimetric and imaging post-focus instrumentation. The EST project was initiated and is driven by EAST, the European Association for Solar Telescopes. EAST was founded in 2006 as an association of 14 European countries. Today, as of December 2019, EAST consists of 26 European research institutes from 18 European countries. The Preliminary Design Phase of EST was accomplished between 2008 and 2011. During this phase, in 2010, the first version of the EST Science Requirement Document (SRD) was published. After EST became a project on the ESFRI roadmap 2016, the preparatory phase started. The goal of the preparatory phase is to accomplish a final design for the telescope and the legal governance structure of EST. A major milestone on this path is to revisit and update the Science Requirement Document (SRD). The EST Science Advisory Group (SAG) has been constituted by EAST and the Board of the PRE-EST EU project in November 2017 and has been charged with the task of providing with a final statement on the science requirements for EST. Based on the conceptual design, the SRD update takes into account recent technical and scientific developments, to ensure that EST provides significant advancement beyond the current state-of-the-art. The present update of the EST SRD has been developed and discussed during a series of EST SAG meetings. The SRD develops the top-level science objectives of EST into individual science cases. Identifying critical science requirements is one of its main goals. Those requirements will define the capabilities of EST and the post-focus instrument suite. The technical requirements for the final design of EST will be derived from the SRD. Title: Spectropolarimetry of the Solar Mg II h and k Lines Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; McIntosh, S. Bibcode: 2019ApJ...883L..30M Altcode: 2019arXiv190905574M We report on spectropolarimetric observations across the Mg II h and k lines at 2800 Å made by the Ultraviolet Spectrometer and Polarimeter on board the Solar Maximum Mission satellite. Our analysis confirms the strong linear polarization in the wings of both lines observed near the limb, as previously reported, but also demonstrates the presence of a negatively (i.e., radially oriented) polarized signal between the two lines. We find evidence for fluctuations of the polarization pattern over a broad spectral range, resulting in some depolarization with respect to the pure scattering case when observed at very low spatial and temporal resolutions. This is consistent with recent theoretical modeling that predicts this to be the result of redistribution effects, quantum interference between the atomic levels of the upper term, and magneto-optical effects. A first attempt at a quantitative exploitation of these signals for the diagnosis of magnetic fields in the chromosphere is attempted. In active regions, we present observations of circular polarization dominated by the Zeeman effect. We are able to constrain the magnetic field strength in the upper active chromosphere using an analysis based on the magnetograph formula, as justified by theoretical modeling. We inferred a significantly strong magnetic field (∼500 G) at the 2.5σ level on an exceptionally active, flaring region. Title: PolStar - An Explorer-Class FUV Spectropolarimetry Mission to Map the Environments of Massive Stars Authors: Scowen, Paul; Ignace, Richard; Neiner, Coralie; Wade, Gregg; Beasley, Matt; Bjorkman, Jon; Bouret, Jean-Claude; Casini, Roberto; del Pino Alemán, Tanausu; Edgington, Samantha; Gayley, Ken; Guinan, Ed; Hoffman, Jennifer; Howarth, Ian; Hull, Tony; Manso Sainz, Rafael; Naze, Yael; Nordt, Alison; Owocki, Stan; Petrinec, Steve; Prinja, Raman; Sana, Hugues; Shultz, Matt; Sparks, William; St-Louis, Nicole; Tillier, Clem; Trujillo Bueno, Javier; Vasudevan, Gopal; Woodruff, Bob Bibcode: 2019BAAS...51g.167S Altcode: 2019astro2020U.167S; 2019arXiv191106724S PolStar is an Explorer-class far ultraviolet (FUV) spectropolarimetry mission designed to target massive stars and their environments. PolStar will take advantage of resonance lines only available in the FUV to measure for the first time the magnetic and wind environment around massive stars to constrain models of rotation and mass loss. Title: Magnetic Field Diagnostics with Strong Chromospheric Lines Authors: Manso Sainz, R.; del Pino Alemán, T.; Casini, R. Bibcode: 2019ASPC..526..145M Altcode: 2017arXiv171004155M The complex spectropolarimetric patterns around strong chromospheric lines, the result of subtle spectroscopic and transport mechanisms, are sensitive, sometimes in unexpected ways, to the presence of magnetic fields in the chromosphere, which may be exploited for diagnostics. We apply numerical polarization radiative transfer implementing partially coherent scattering by polarized multi-term atoms, in the presence of arbitrary magnetic fields, in plane-parallel stellar atmospheres to study a few important spectroscopic features: Mg II h-k doublet; Ca II H-K doublet and IR triplet. We confirm the importance of partial redistribution effects in the formation of the Mg II h-k doublet in magnetized atmospheres, as previously pointed out for the non-magnetic case. Moreover, we show, numerically and analytically, that a magnetic field produces measurable modifications of the broadband linear polarization even for relatively small field strengths, while circular polarization remains well represented by the magnetograph formula. We note that this phenomenon has already (unknowingly) been observed by UVSP/SMM, and the interest and possibility of its observation in stars other than the Sun. The interplay between partial redistribution in the H-K doublet of Ca II and metastable level polarization in its IR triplet allow diagnosing the chromospheric magnetic field at different layers and strengths. Our results suggest several new avenues to investigate empirically the magnetism of the solar and stellar chromospheres. Title: Comparison of Scattering Polarization Signals Observed by CLASP: Possible Indication of the Hanle Effect Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.; Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa, Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.; Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso Sainz, R.; De Pomtieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R. Bibcode: 2019ASPC..526..305I Altcode: The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et al. 2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the first time, the linear polarization produced by scattering processes in the hydrogen Lyman-α (121.57 nm) and Si III (120.56 nm) lines of the solar disk radiation. The complexity of the observed scattering polarization (i.e., conspicuous spatial variations in Q/I and U/I at spatial scales of 10″-20″ and the absence of center-to- limb variation at the Lyman-α center; see Kano et al. 2017) motivated us to search for possible hints of the operation of the Hanle effect by comparing: (a) the Lyman-α line center signal, for which the critical field strength (BH) for the onset of the Hanle effect is 53 G, (b) the Lyman-α wing, which is insensitive to the Hanle effect, and (c) the Si III line, whose BH = 290 G. We focus on four regions with different total unsigned photospheric magnetic fluxes (estimated from SDO/HMI observations), and compare the corresponding U/I spatial variations in the Lyman-α wing, Lyman-α center, and Si III line. The U/I signal in the Lyman-α wing shows an antisymmetric spatial distribution, which is caused by the presence of a bright structure in all the selected regions, regardless of the total unsigned photospheric magnetic flux. In an internetwork region, the Lyman-α center shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. We argue that a plausible explanation of this differential behavior is the operation of the Hanle effect.

This work, presented in an oral contribution at this Workshop, has been published on The Astrophysical Journal (Ishikawa et al. 2017). Title: CLASP Constraints on the Magnetization and Geometrical Complexity of the Chromosphere-Corona Transition Region Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa, R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi, K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M. Bibcode: 2018ApJ...866L..15T Altcode: 2018arXiv180908865T The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a suborbital rocket experiment that on 2015 September 3 measured the linear polarization produced by scattering processes in the hydrogen Lyα line of the solar disk radiation. The line-center photons of this spectral line radiation mostly stem from the chromosphere-corona transition region (TR). These unprecedented spectropolarimetric observations revealed an interesting surprise, namely that there is practically no center-to-limb variation (CLV) in the Q/I line-center signals. Using an analytical model, we first show that the geometric complexity of the corrugated surface that delineates the TR has a crucial impact on the CLV of the Q/I and U/I line-center signals. Second, we introduce a statistical description of the solar atmosphere based on a 3D model derived from a state-of-the-art radiation magnetohydrodynamic simulation. Each realization of the statistical ensemble is a 3D model characterized by a given degree of magnetization and corrugation of the TR, and for each such realization we solve the full 3D radiative transfer problem taking into account the impact of the CLASP instrument degradation on the calculated polarization signals. Finally, we apply the statistical inference method presented in a previous paper to show that the TR of the 3D model that produces the best agreement with the CLASP observations has a relatively weak magnetic field and a relatively high degree of corrugation. We emphasize that a suitable way to validate or refute numerical models of the upper solar chromosphere is by confronting calculations and observations of the scattering polarization in ultraviolet lines sensitive to the Hanle effect. Title: A Statistical Inference Method for Interpreting the CLASP Observations Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.; Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi, K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M. Bibcode: 2018ApJ...865...48S Altcode: 2018arXiv180802725S On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) successfully measured the linear polarization produced by scattering processes in the hydrogen Lyα line of the solar disk radiation, revealing conspicuous spatial variations in the Q/I and U/I signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes encode information on the magnetic field of the chromosphere-corona transition region, but they are also sensitive to the three-dimensional structure of this corrugated interface region. With the help of a simple line-formation model, here we propose a statistical inference method for interpreting the Lyα line-center polarization observed by CLASP. Title: Current State of UV Spectro-Polarimetry and its Future Direction Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara, Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi, . Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier; Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts, Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke; Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel; Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan, Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey, Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David; Rachmeler, Laurel; Bethge, Christian Bibcode: 2018cosp...42E1564I Altcode: To obtain quantitative information on the magnetic field in low beta regions (i.e., upper chromosphere and above) has been increasingly important to understand the energetic phenomena of the outer solar atmosphere such as flare, coronal heating, and the solar wind acceleration. In the UV range, there are abundant spectral lines that originate in the upper chromosphere and transition region. However, the Zeeman effect in these spectral lines does not give rise to easily measurable polarization signals because of the weak magnetic field strength and the larger Doppler broadening compared with the Zeeman effect. Instead, the Hanle effect in UV lines is expected to be a suitable diagnostic tool of the magnetic field in the upper atmospheric layers. To investigate the validity of UV spectro-polarimetry and the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP), which is a NASA sounding- rocket experiment, was launched at White Sands in US on September 3, 2015. During its 5 minutes ballistic flight, it successfully performed spectro-polarimetric observations of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly high polarization sensitivity of 0.1% in this wavelength range. CLASP observed the linear polarization produced by scattering process in VUV lines for the first time and detected the polarization signals which indicate the operation of the Hanle effect. Following the success of CLASP, we are confident that UV spectro-polarimetry is the way to proceed, and we are planning the second flight of CLASP (CLASP2: Chromospheric LAyer SpectroPolarimeter 2). For this second flight we will carry out spectro-polarimetry in the Mg II h and k lines around 280 nm, with minimum modifications of the CLASP1 instrument. The linear polarization in the Mg II k line is induced by scattering processes and the Hanle effect, being sensitive to magnetic field strengths of 5 to 50 G. In addition, the circular polarizations in the Mg II h and k lines induced by the Zeeman effect can be measurable in at least plage and active regions. The combination of the Hanle and Zeeman effects could help us to more reliably infer the magnetic fields of the upper solar chromosphere. CLASP2 was selected for flight and is being developed for launch in the spring of 2019.Based on these sounding rocket experiments (CLASP1 and 2), we aim at establishing the strategy and refining the instrument concept for future space missions to explore the enigmatic atmospheric layers via UV spectro-polarimetry. Title: Rayleigh Scattering in Spectral Series with L-term Interference Authors: Casini, R.; Manso Sainz, R.; del Pino Alemán, T. Bibcode: 2017ApJ...850..162C Altcode: 2017arXiv171011491C We derive a formalism to describe the scattering of polarized radiation over the full spectral range encompassed by atomic transitions belonging to the same spectral series (e.g., the H I Lyman and Balmer series, the UV multiplets of Fe I and Fe II). This allows us to study the role of radiation-induced coherence among the upper terms of the spectral series, and its contribution to Rayleigh scattering and the polarization of the solar continuum. We rely on previous theoretical results for the emissivity of a three-term atom of the Λ-type, taking into account partially coherent scattering, and generalize its expression in order to describe a “multiple Λ” atomic system underlying the formation of a spectral series. Our study shows that important polarization effects must be expected because of the combined action of partial frequency redistribution and radiation-induced coherence among the terms of the series. In particular, our model predicts the correct asymptotic limit of 100% polarization in the far wings of a complete (i.e., {{Δ }}L=0,+/- 1) group of transitions, which must be expected on the basis of the principle of spectroscopic stability. Title: Explicit Form of the Radiative and Collisional Branching Ratios in Polarized Radiation Transport with Coherent Scattering Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R. Bibcode: 2017ApJ...848...99C Altcode: 2017arXiv170900126C We consider the vector emissivity of the polarized radiation transfer in a Λ-type atomic transition, which we recently proposed to account for both complete frequency redistribution (CRD) and partial redistribution (PRD) contributions to the scattered radiation. This expression can concisely be written as ɛ = ( ɛ ( 1 ) - ɛ f . s . ( 2 ) ) + ɛ ( 2 ) , where {{\boldsymbol{\varepsilon }}}(1) and {{\boldsymbol{\varepsilon }}}(2) are the emissivity terms describing, respectively, one-photon and two-photon processes in a Λ-type atom, and where “f.s.” means that the corresponding term must be evaluated assuming an appropriate “flat spectrum” average of the incident radiation across the spectral line. In this follow-up study, we explicitly consider the expressions of these various terms for the case of a polarized multi-term atom to derive the algebraic forms of the branching ratios between the CRD and PRD contributions to the emissivity. In the limit of a two-term atom with non-coherent lower term, our results are shown to be in full agreement with those recently derived by Bommier. Title: Indication of the Hanle Effect by Comparing the Scattering Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.; Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa, Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.; Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R. Bibcode: 2017ApJ...841...31I Altcode: The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding rocket experiment that has provided the first successful measurement of the linear polarization produced by scattering processes in the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In this paper, we report that the Si III line at 120.65 nm also shows scattering polarization and we compare the scattering polarization signals observed in the Lyα and Si III lines in order to search for observational signatures of the Hanle effect. We focus on four selected bright structures and investigate how the U/I spatial variations vary between the Lyα wing, the Lyα core, and the Si III line as a function of the total unsigned photospheric magnetic flux estimated from Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations. In an internetwork region, the Lyα core shows an antisymmetric spatial variation across the selected bright structure, but it does not show it in other more magnetized regions. In the Si III line, the spatial variation of U/I deviates from the above-mentioned antisymmetric shape as the total unsigned photospheric magnetic flux increases. A plausible explanation of this difference is the operation of the Hanle effect. We argue that diagnostic techniques based on the scattering polarization observed simultaneously in two spectral lines with very different sensitivities to the Hanle effect, like Lyα and Si III, are of great potential interest for exploring the magnetism of the upper solar chromosphere and transition region. Title: Polarization Calibration of the Chromospheric Lyman-Alpha SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.; Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.; Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M. Bibcode: 2017SoPh..292...57G Altcode: The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding rocket instrument designed to measure for the first time the linear polarization of the hydrogen Lyman-α line (121.6 nm). The instrument was successfully launched on 3 September 2015 and observations were conducted at the solar disc center and close to the limb during the five-minutes flight. In this article, the disc center observations are used to provide an in-flight calibration of the instrument spurious polarization. The derived in-flight spurious polarization is consistent with the spurious polarization levels determined during the pre-flight calibration and a statistical analysis of the polarization fluctuations from solar origin is conducted to ensure a 0.014% precision on the spurious polarization. The combination of the pre-flight and the in-flight polarization calibrations provides a complete picture of the instrument response matrix, and a proper error transfer method is used to confirm the achieved polarization accuracy. As a result, the unprecedented 0.1% polarization accuracy of the instrument in the vacuum ultraviolet is ensured by the polarization calibration. Title: Discovery of Scattering Polarization in the Hydrogen Lyα Line of the Solar Disk Radiation Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.; Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.; Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.; Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M. Bibcode: 2017ApJ...839L..10K Altcode: 2017arXiv170403228K There is a thin transition region (TR) in the solar atmosphere where the temperature rises from 10,000 K in the chromosphere to millions of degrees in the corona. Little is known about the mechanisms that dominate this enigmatic region other than the magnetic field plays a key role. The magnetism of the TR can only be detected by polarimetric measurements of a few ultraviolet (UV) spectral lines, the Lyα line of neutral hydrogen at 121.6 nm (the strongest line of the solar UV spectrum) being of particular interest given its sensitivity to the Hanle effect (the magnetic-field-induced modification of the scattering line polarization). We report the discovery of linear polarization produced by scattering processes in the Lyα line, obtained with the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket experiment. The Stokes profiles observed by CLASP in quiet regions of the solar disk show that the Q/I and U/I linear polarization signals are of the order of 0.1% in the line core and up to a few percent in the nearby wings, and that both have conspicuous spatial variations with scales of ∼10 arcsec. These observations help constrain theoretical models of the chromosphere-corona TR and extrapolations of the magnetic field from photospheric magnetograms. In fact, the observed spatial variation from disk to limb of polarization at the line core and wings already challenge the predictions from three-dimensional magnetohydrodynamical models of the upper solar chromosphere. Title: A Note on the Radiative and Collisional Branching Ratios in Polarized Radiation Transport with Coherent Scattering Authors: Casini, R.; del Pino Alemán, T.; Manso Sainz, R. Bibcode: 2017ApJ...835..114C Altcode: 2016arXiv161203440C We discuss the implementation of physically meaningful branching ratios between the CRD and partial redistribution contributions to the emissivity of a polarized multi-term atom in the presence of both inelastic and elastic collisions. Our derivation is based on a recent theoretical formulation of partially coherent scattering, and it relies on a heuristic diagrammatic analysis of the various radiative and collisional processes to determine the proper form of the branching ratios. The expression we obtain for the emissivity is {\boldsymbol{\varepsilon }}=[{{\boldsymbol{\varepsilon }}}(1)-{{\boldsymbol{\varepsilon }}}{{f}.{{s}}.}(2)]+{{\boldsymbol{\varepsilon }}}(2), where {{\boldsymbol{\varepsilon }}}(1) and {{\boldsymbol{\varepsilon }}}(2) are the emissivity terms for the redistributed and partially coherent radiation, respectively, and where “f.s.” implies that the corresponding term must be evaluated assuming a flat-spectrum average of the incident radiation. This result is shown to be in agreement with prior literature on the subject in the limit of the unpolarized multi-level atom. Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP) Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando, T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.; Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M. Bibcode: 2016ApJ...832..141K Altcode: High-cadence observations by the slit-jaw (SJ) optics system of the sounding rocket experiment known as the Chromospheric Lyman Alpha Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances that recurrently propagate in either the chromosphere or the transition region or both at a speed much higher than the speed of sound. The CLASP/SJ instrument provides a time series of two-dimensional images taken with broadband filters centered on the Lyα line at a 0.6 s cadence. The multiple fast-propagating intensity disturbances appear in the quiet Sun and in an active region, and they are clearly detected in at least 20 areas in a field of view of 527″ × 527″ during the 5 minute observing time. The apparent speeds of the intensity disturbances range from 150 to 350 km s-1, and they are comparable to the local Alfvén speed in the transition region. The intensity disturbances tend to propagate along bright elongated structures away from areas with strong photospheric magnetic fields. This suggests that the observed fast-propagating intensity disturbances are related to the magnetic canopy structures. The maximum distance traveled by the intensity disturbances is about 10″, and the widths are a few arcseconds, which are almost determined by a pixel size of 1.″03. The timescale of each intensity pulse is shorter than 30 s. One possible explanation for the fast-propagating intensity disturbances observed by CLASP is magnetohydrodynamic fast-mode waves. Title: Laboratory Frequency Redistribution Function for the Polarized Λ -type Three-term Atom Authors: Casini, R.; Manso Sainz, R. Bibcode: 2016ApJ...833..197C Altcode: 2016arXiv161204362C We present the frequency redistribution function for a polarized three-term atom of the Λ-type in the collisionless regime, and we specialize it to the case where both the initial and final terms of the three-state transition are metastable (I.e., with infinitely sharp levels). This redistribution function represents a generalization of the well-known R II function to the case where the lower terms of the transition can be polarized and carry atomic coherence, and it can be applied to the investigation of polarized line formation in tenuous plasmas, where collisional rates may be low enough that anisotropy-induced atomic polarization survives even in the case of metastable levels. Title: Magnetic Diagnostics of the Solar Chromosphere with the Mg II h-k Lines Authors: del Pino Alemán, T.; Casini, R.; Manso Sainz, R. Bibcode: 2016ApJ...830L..24D Altcode: 2016arXiv160705683D We investigated the formation of the Mg II h-k doublet in a weakly magnetized atmosphere (20-100 G) using a newly developed numerical code for polarized radiative transfer in a plane-parallel geometry, which implements a recent formulation of partially coherent scattering by polarized multi-term atoms in arbitrary magnetic-field regimes. Our results confirm the importance of partial redistribution effects in the formation of the Mg II h and k lines, as pointed out by previous work in the non-magnetic case. We show that the presence of a magnetic field can produce measurable modifications of the broadband linear polarization even for relatively small field strengths (∼10 G), while the circular polarization remains well represented by the classical magnetograph formula. Both these results open an important new window for the weak-field diagnostics of the upper solar atmosphere. Title: Frequency Redistribution of Polarized Light in the Λ-Type Multi-Term Polarized Atom Authors: Casini, R.; Manso Sainz, R. Bibcode: 2016ApJ...824..135C Altcode: 2016arXiv160207173C We study the effects of Rayleigh and Raman scattering on the formation of polarized spectral lines in a Λ-type multi-term atom. We fully take into account the partial redistribution of frequency and the presence of atomic polarization in the lower states of the atomic model. Problems that can be modeled with this formalism include, for example, the formation of the Ca II H-K and IR triplet, the analogous system of Ba II, and the Lyβ-Hα system of hydrogenic ions. Title: Spectro-polarimetric observation in UV with CLASP to probe the chromosphere and transition region Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère, Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi, Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa, Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi; Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto; Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca; Carlsson, Mats Bibcode: 2016SPD....4710107K Altcode: The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA sounding-rocket experiment that was performed in White Sands in the US on September 3, 2015. During its 5-minute ballistic flight, CLASP successfully made the first spectro-polarimetric observation in the Lyman-alpha line (121.57 nm) originating in the chromosphere and transition region. Since the Lyman-alpha polarization is sensitive to magnetic field of 10-100 G by the Hanle effect, we aim to infer the magnetic field information in such upper solar atmosphere with this experiment.The obtained CLASP data showed that the Lyman-alpha scattering polarization is about a few percent in the wings and the order of 0.1% in the core near the solar limb, as it had been theoretically predicted, and that both polarization signals have a conspicuous spatio-temporal variability. CLASP also observed another upper-chromospheric line, Si III (120.65 nm), whose critical field strength for the Hanle effect is 290 G, and showed a measurable scattering polarization of a few % in this line. The polarization properties of the Si III line could facilitate the interpretation of the scattering polarization observed in the Lyman-alpha line.In this presentation, we would like to show how the upper chromosphere and transition region are seen in the polarization of these UV lines and discuss the possible source of these complicated polarization signals. Title: CLASP: A UV Spectropolarimeter on a Sounding Rocket for Probing theChromosphere-Corona Transition Regio Authors: Ishikawa, Ryohko; Kano, Ryouhei; Winebarger, Amy; Auchere, Frederic; Trujillo Bueno, Javier; Bando, Takamasa; Narukage, Noriyuki; Kobayashi, Ken; Katsukawa, Yukio; Kubo, Masahito; Ishikawa, Shin-nosuke; Giono, Gabriel; Tsuneta, Saku; Hara, Hirohisa; Suematsu, Yoshinori; Shimizu, Toshifumi; Sakao, Taro; Ichimoto, Kiyoshi; Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi, Luca Bibcode: 2015IAUGA..2254536I Altcode: The wish to understand the energetic phenomena of the outer solar atmosphere makes it increasingly important to achieve quantitative information on the magnetic field in the chromosphere-corona transition region. To this end, we need to measure and model the linear polarization produced by scattering processes and the Hanle effect in strong UV resonance lines, such as the hydrogen Lyman-alpha line. A team consisting of Japan, USA, Spain, France, and Norway has been developing a sounding rocket experiment called the Chromospheric Lyman-alpha Spectro-Polarimeter (CLASP). The aim is to detect the scattering polarization produced by anisotropic radiation pumping in the hydrogen Lyman-alpha line (121.6 nm), and via the Hanle effect to try to constrain the magnetic field vector in the upper chromosphere and transition region. In this talk, we will present an overview of our CLASP mission, its scientific objectives, ground tests made, and the latest information on the launch planned for the Summer of 2015. Title: Estimating the magnetic field strength from magnetograms Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R. Bibcode: 2015A&A...577A.125A Altcode: 2015arXiv150307670A A properly calibrated longitudinal magnetograph is an instrument that measures circular polarization and gives an estimation of the magnetic flux density in each observed resolution element. This usually constitutes a lower bound of the field strength in the resolution element, given that it can be made arbitrarily large as long as it occupies a proportionally smaller area of the resolution element and/or becomes more transversal to the observer while still produce the same magnetic signal. However, we know that arbitrarily stronger fields are less likely - hG fields are more probable than kG fields, with fields above several kG virtually absent - and we may even have partial information about their angular distribution. Based on a set of sensible considerations, we derive simple formulae based on a Bayesian analysis to give an improved estimation of the magnetic field strength for magnetographs. Title: Spectro-Polarimetric Imaging Reveals Helical Magnetic Fields in Solar Prominence Feet Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Beck, C.; de la Cruz Rodríguez, J.; Díaz, A. J. Bibcode: 2015ApJ...802....3M Altcode: 2015arXiv150103295M Solar prominences are clouds of cool plasma levitating above the solar surface and insulated from the million-degree corona by magnetic fields. They form in regions of complex magnetic topology, characterized by non-potential fields, which can evolve abruptly, disintegrating the prominence and ejecting magnetized material into the heliosphere. However, their physics is not yet fully understood because mapping such complex magnetic configurations and their evolution is extremely challenging, and must often be guessed by proxy from photometric observations. Using state-of-the-art spectro-polarimetric data, we reconstruct the structure of the magnetic field in a prominence. We find that prominence feet harbor helical magnetic fields connecting the prominence to the solar surface below. Title: Constraining the shaping mechanism of the Red Rectangle through the spectro-polarimetry of its central star Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R.; Corradi, R. L. M.; Leone, F. Bibcode: 2015A&A...574A..16M Altcode: 2014arXiv1410.6365M We carried out high-sensitivity spectro-polarimetric observations of the central star of the Red Rectangle protoplanetary nebula with the aim of constraining the mechanism that gives its biconical shape. The stellar light of the central binary system is linearly polarised since it is scattered on the dust particles of the nebula. Surprisingly, the linear polarisation in the continuum is aligned with one of the spikes of the biconical outflow. Also, the observed Balmer lines, as well as the Ca ii K lines, are polarised. These observational constraints are used to confirm or reject current theoretical models for the shaping mechanism of the Red Rectangle. We propose that the observed polarisation is not very likely to be generated by a uniform biconical stellar wind. Also, the hypothesis of a precessing jet does not completely match observations since it requires a larger aperture jet than for the nebula. Title: Magnetic and Dynamical Photospheric Disturbances Observed During an M3.2 Solar Flare Authors: Kuckein, C.; Collados, M.; Manso Sainz, R. Bibcode: 2015ApJ...799L..25K Altcode: 2015arXiv150104207K This Letter reports on a set of full-Stokes spectropolarimetric observations in the near-infrared He i 10830 Å spectral region covering the pre-flare, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He i 10830 Å emission in the flare. The red component of the He i triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He i Stokes V is substantially larger and appears reversed compared to the usually larger Si i Stokes V profile. The photospheric Si i inversions of the four Stokes profiles reveal the following: (1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare, the magnetic field recovers its pre-flare configuration in a short time (i.e., 30 minutes after the flare). (2) In the photosphere, the line of sight velocities show a regular granular up- and downflow pattern before the flare erupts. During the flare, upflows (blueshifts) dominate the area where the flare is produced. Evaporation rates of ∼ {{10}-3} and ∼ {{10}-4} g cm-2 s-1 have been derived in the deep and high photosphere, respectively, capable of increasing the chromospheric density by a factor of two in about 400 s. Title: Abundance Determinations in Ionized Nebulae and their Sensitivity to Temperature Authors: Rodríguez, M.; Manso Sainz, R. Bibcode: 2014RMxAC..44...22R Altcode: Our main source of uncertainty in the determination of chemical abundances in H II regions and planetary nebulae arises from a discrepancy: the abundances implied by recombination lines are larger than those implied by collisionally excited lines. The discrepancy amounts to a factor of 2 in most objects, but reaches much higher values in some planetary nebulae. There are several possible explanations for this effect. Here we explore a recent proposal and determine what kind of deviations from a Maxwellian electron energy distribution are needed in order to reproduce the measured abundance discrepancies. We note the parallelisms between this explanation and other explanations that are based on the sensitivity to temperature of collisionally excited lines: the presence of metal-rich inclusions within the ionized gas or temperature fluctuations in a chemically homogeneous gas. Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.; Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.; Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway, T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère, F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos, A.; Štěpán, J.; Carlsson, M. Bibcode: 2014ASPC..489..307K Altcode: A sounding-rocket experiment called the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is presently under development to measure the linear polarization profiles in the hydrogen Lyman-alpha (Lyα) line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim for first detection of the linear polarizations caused by scattering processes and the Hanle effect in the Lyα line with high accuracy (0.1%). This is a fist step for exploration of magnetic fields in the upper chromosphere and transition region of the Sun. Accurate measurements of the linear polarization signals caused by scattering processes and the Hanle effect in strong UV lines like Lyα are essential to explore with future solar telescopes the strength and structures of the magnetic field in the upper chromosphere and transition region of the Sun. The CLASP proposal has been accepted by NASA in 2012, and the flight is planned in 2015. Title: Frequency Redistribution Function for the Polarized Two-term Atom Authors: Casini, R.; Landi Degl'Innocenti, M.; Manso Sainz, R.; Landi Degl'Innocenti, E.; Landolfi, M. Bibcode: 2014ApJ...791...94C Altcode: 2014arXiv1406.6129C We present a generalized frequency redistribution function for the polarized two-term atom in an arbitrary magnetic field. This result is derived within a new formulation of the quantum problem of coherent scattering of polarized radiation by atoms in the collisionless regime. The general theory, which is based on a diagrammatic treatment of the atom-photon interaction, is still a work in progress. However, the results anticipated here are relevant enough for the study of the magnetism of the solar chromosphere and of interest for astrophysics in general.

The National Center for Atmospheric Research is sponsored by the National Science Foundation. Title: On the Inversion of the Scattering Polarization and the Hanle Effect Signals in the Hydrogen Lyα Line Authors: Ishikawa, R.; Asensio Ramos, A.; Belluzzi, L.; Manso Sainz, R.; Štěpán, J.; Trujillo Bueno, J.; Goto, M.; Tsuneta, S. Bibcode: 2014ApJ...787..159I Altcode: 2014arXiv1404.0786I Magnetic field measurements in the upper chromosphere and above, where the gas-to-magnetic pressure ratio β is lower than unity, are essential for understanding the thermal structure and dynamical activity of the solar atmosphere. Recent developments in the theory and numerical modeling of polarization in spectral lines have suggested that information on the magnetic field of the chromosphere-corona transition region could be obtained by measuring the linear polarization of the solar disk radiation at the core of the hydrogen Lyα line at 121.6 nm, which is produced by scattering processes and the Hanle effect. The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) sounding rocket experiment aims to measure the intensity (Stokes I) and the linear polarization profiles (Q/I and U/I) of the hydrogen Lyα line. In this paper, we clarify the information that the Hanle effect can provide by applying a Stokes inversion technique based on a database search. The database contains all theoretical Q/I and U/I profiles calculated in a one-dimensional semi-empirical model of the solar atmosphere for all possible values of the strength, inclination, and azimuth of the magnetic field vector, though this atmospheric region is highly inhomogeneous and dynamic. We focus on understanding the sensitivity of the inversion results to the noise and spectral resolution of the synthetic observations as well as the ambiguities and limitation inherent to the Hanle effect when only the hydrogen Lyα is used. We conclude that spectropolarimetric observations with CLASP can indeed be a suitable diagnostic tool for probing the magnetism of the transition region, especially when complemented with information on the magnetic field azimuth that can be obtained from other instruments. Title: Depolarizing Collisions with Hydrogen: Neutral and Singly Ionized Alkaline Earths Authors: Manso Sainz, Rafael; Roncero, Octavio; Sanz-Sanz, Cristina; Aguado, Alfredo; Asensio Ramos, Andrés; Trujillo Bueno, Javier Bibcode: 2014ApJ...788..118M Altcode: 2014arXiv1404.6339M Depolarizing collisions are elastic or quasielastic collisions that equalize the populations and destroy the coherence between the magnetic sublevels of atomic levels. In astrophysical plasmas, the main depolarizing collider is neutral hydrogen. We consider depolarizing rates on the lowest levels of neutral and singly ionized alkali earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II, due to collisions with H°. We compute ab initio potential curves of the atom-H° system and solve the quantum mechanical dynamics. From the scattering amplitudes, we calculate the depolarizing rates for Maxwellian distributions of colliders at temperatures T <= 10,000 K. A comparative analysis of our results and previous calculations in the literature is completed. We discuss the effect of these rates on the formation of scattering polarization patterns of resonant lines of alkali earths in the solar atmosphere, and their effect on Hanle effect diagnostics of solar magnetic fields. Title: Upper Limits to the Magnetic Field in Central Stars of Planetary Nebulae Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R.; Corradi, R. L. M.; Leone, F. Bibcode: 2014ApJ...787..111A Altcode: 2014arXiv1404.2718A More than about 20 central stars of planetary nebulae (CSPNs) have been observed spectropolarimetrically, yet no clear, unambiguous signal of the presence of a magnetic field in these objects has been found. We perform a statistical (Bayesian) analysis of all the available spectropolarimetric observations of CSPN to constrain the magnetic fields in these objects. Assuming that the stellar field is dipolar and that the dipole axis of the objects is oriented randomly (isotropically), we find that the dipole magnetic field strength is smaller than 400 G with 95% probability using all available observations. The analysis introduced allows integration of future observations to further constrain the parameters of the distribution, and it is general, so that it can be easily applied to other classes of magnetic objects. We propose several ways to improve the upper limits found here. Title: Non-coherent Continuum Scattering as a Line Polarization Mechanism Authors: del Pino Alemán, T.; Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2014ApJ...784...46D Altcode: 2014arXiv1401.8094D Line scattering polarization can be strongly affected by Rayleigh scattering at neutral hydrogen and Thomson scattering at free electrons. Often a depolarization of the continuum results, but the Doppler redistribution produced by the continuum scatterers, which are light (hence, fast), induces more complex interactions between the polarization in spectral lines and in the continuum. Here we formulate and solve the radiative transfer problem of scattering line polarization with non-coherent continuum scattering consistently. The problem is formulated within the spherical tensor representation of atomic and light polarization. The numerical method of solution is a generalization of the Accelerated Lambda Iteration that is applied to both the atomic system and the radiation field. We show that the redistribution of the spectral line radiation due to the non-coherence of the continuum scattering may modify the shape of the emergent fractional linear polarization patterns significantly, even yielding polarization signals above the continuum level in intrinsically unpolarizable lines. Title: A search for magnetic fields on central stars in planetary nebulae Authors: Leone, F.; Corradi, R. L. M.; Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2014A&A...563A..43L Altcode: 2014arXiv1401.6282L Context. One of the possible mechanisms responsible for the panoply of shapes in planetary nebulae is the presence of magnetic fields that drive the ejection of ionized material during the proto-planetary nebula phase.
Aims: Therefore, detecting magnetic fields in such objects is of key importance for understanding their dynamics. Still, magnetic fields have not been detected using polarimetry in the central stars of planetary nebulae.
Methods: Circularly polarized light spectra have been obtained with the Focal Reducer and Low Dispersion Spectrograph at the Very Large Telescope of the European Southern Observatory and the Intermediate dispersion Spectrograph and Imaging System at the William Herschel Telescope. Twentythree planetary nebulae that span very different morphology and evolutionary stages have been selected. Most of central stars have been observed at different rotation phases to point out evidence of magnetic variability.
Results: In this paper, we present the result of two observational campaigns aimed to detect and measure the magnetic field in the central stars of planetary nebulae on the basis of low resolution spectropolarimetry. In the limit of the adopted method, we can state that large scale fields of kG order are not hosted on the central star of planetary nebulae. Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon Flare Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael; Asensio Ramos, Andres Bibcode: 2014cosp...40E.568C Altcode: On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar atmosphere on the active region AR 11748. The flare evolution was observed at the German VTT of the Observatorio del Teide using the instrument TIP-II, with spectropolarimetric measurements of the photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet at 1083 nm). Simultaneous spectroscopic data of the chromospheric spectral line of Ca II at 854.2 nm and filtergrams at Halpha were also obtained. The flare evolution as observed from the ground can be compared with the changes observed by AIA@SDO at different ultraviolet wavelengths. The ground observations covered several hours, including the pre-flare, impulsive, gradual and post-flare phases. We present maps of the magnetic field, thermal and dynamical properties of the region during its evolution from pre- to post-flare phase. Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger, A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.; Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.; Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini, R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan, J.; Suematsu, Y.; Holloway, T. Bibcode: 2013SPD....44..142K Altcode: The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV spectropolarimeter optimized for measuring the linear polarization of the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to show linear polarization caused by atomic scattering in the chromosphere and modified by the magnetic field through the Hanle effect. The Hanle effect is sensitive to weaker magnetic fields than Zeeman effect, and is not canceled by opposing fields, making it sensitive to tangled or unresolved magnetic field structures. These factors make the Hanle effect a valuable tool for probing the magnetic field in the chromosphere above the quiet sun. To meet this goal, CLASP is designed to measure linear polarization with 0.1% polarization sensitivity at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is scheduled to be launched in 2015. Title: Signal detection for spectroscopy and polarimetry Authors: Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2013hsa7.conf..771A Altcode: Spectroscopic and spectropolarimetric observations with high spectral resolution provide extremely rich information on the physical conditions of distant celestial objects; sometimes, even the mere presence of a spectroscopic or polarimetric pattern may offer fundamental insights. But these are photon-starving techniques. Signals are often at the noise level or buried in it and, many times, just detection proves difficult. Here we present a Bayesian technique for the detection of spectropolarimetric signals based on the application of the non-parametric relevance vector machine to the observations, which allows computing the evidence for the presence of a signal and its most probable value. Title: Hanle Effect for Stellar Dipoles and Quadrupoles Authors: Manso Sainz, R.; Martínez González, M. J. Bibcode: 2012ApJ...760....7M Altcode: 2012arXiv1209.6187M We derive exact expressions for the degree of lineal polarization over a resolved or integrated stellar disc due to resonance scattering and the Hanle effect from a dipolar or quadrupolar distribution of magnetic fields. We apply the theory of scattering polarization within the formalism of the spherical tensors representation for the density matrix and radiation field. The distribution of linear polarization over the stellar disk for different configurations of the magnetic field is studied and its topology discussed. For an unresolved dipole, the resulting polarization can be expressed in terms of just three functions (of the inclination angle and effective dipole strength) that are calculated numerically and their behavior discussed. Dipolar and (aligned) quadrupoles are considered in some detail, but the techniques here—in particular, the extensive use of the spherical tensor formalism for polarization—can easily be applied to more general field configurations. Title: Anomalous Circular Polarization Profiles in the He I 1083.0 nm Multiplet from Solar Spicules Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R.; Beck, C.; Belluzzi, L. Bibcode: 2012ApJ...759...16M Altcode: 2012arXiv1209.2589M We report Stokes vector observations of solar spicules and a prominence in the He I 1083 nm multiplet carried out with the Tenerife Infrared Polarimeter. The observations show linear polarization profiles that are produced by scattering processes in the presence of a magnetic field. After a careful data reduction, we demonstrate the existence of extremely asymmetric Stokes V profiles in the spicular material that we are able to model with two magnetic components along the line of sight, and under the presence of atomic orientation in the energy levels that give rise to the multiplet. We discuss some possible scenarios that can generate the atomic orientation in spicules. We stress the importance of spectropolarimetric observations across the limb to distinguish such signals from observational artifacts. Title: Signal detection for spectroscopy and polarimetry Authors: Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2012A&A...547A.113A Altcode: 2012arXiv1209.6455A The analysis of high spectral resolution spectroscopic and spectropolarimetric observations constitutes a very powerful way of inferring the dynamical, thermodynamical, and magnetic properties of distant objects. However, these techniques starve photons, making it difficult to use them for all purposes. A common problem is not being able to detect a signal because it is buried on the noise at the wavelength of some interesting spectral feature. This problem is especially relevant for spectropolarimetric observations, because only a small fraction of the received light is typically polarized. We present in this paper a Bayesian technique for detecting spectropolarimetric signals. The technique is based on applying the nonparametric relevance vector machine to the observations, which allows us to compute the evidence for the presence of the signal and compute the more probable signal. The method is suited for analyzing data from experimental instruments onboard space missions and rockets aiming at detecting spectropolarimetric signals in unexplored regions of the spectrum, such as the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment. Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP) Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa, Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa, Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada, Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier; Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Auchère, Frédéric; Carlsson, Mats Bibcode: 2012SPIE.8443E..4FK Altcode: One of the biggest challenges in heliophysics is to decipher the magnetic structure of the solar chromosphere. The importance of measuring the chromospheric magnetic field is due to both the key role the chromosphere plays in energizing and structuring the outer solar atmosphere and the inability of extrapolation of photospheric fields to adequately describe this key boundary region. Over the last few years, significant progress has been made in the spectral line formation of UV lines as well as the MHD modeling of the solar atmosphere. It is found that the Hanle effect in the Lyman-alpha line (121.567 nm) is a most promising diagnostic tool for weaker magnetic fields in the chromosphere and transition region. Based on this groundbreaking research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) to NASA as a sounding rocket experiment, for making the first measurement of the linear polarization produced by scattering processes and the Hanle effect in the Lyman-alpha line (121.567 nm), and making the first exploration of the magnetic field in the upper chromosphere and transition region of the Sun. The CLASP instrument consists of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam spectrograph assembly with a grating working as a beam splitter, and an identical pair of reflective polarization analyzers each equipped with a CCD camera. We propose to launch CLASP in December 2014. Title: Resonance scattering polarization in the magnetosphere of Mercury Authors: López Ariste, A.; Leblanc, F.; Casini, R.; Manso Sainz, R.; Gelly, B.; Le Men, C. Bibcode: 2012Icar..220.1104L Altcode: The conditions of the exosphere of Mercury constitute a prime example of a magnetosphere subject to space weather. We aim at improving the diagnostic of the physical conditions of Na atoms in the exosphere of Mercury, with particular emphasis in the possibility of inferring the magnetic field through polarimetry of the Na D emission lines. We performed spectropolarimetry of the Na D emission lines in the exosphere of Mercury at two different ranges of phases of the planet and interpreted them under present models of resonance scattering polarization applied to the Na atom. We measured successfully the polarization of the Na D2 line while no polarization was seen in D1, as expected. The measured polarization varies with the phase angle but it is roughly a factor two smaller than expected from an isolated emitting atom. Depolarization due to the presence of optical depth explains this factor two and is the most probable explanation for this discrepancy. A framework for the observation of polarization in the emission lines of the exosphere and its interpretation is laid. This opens the possibility to use these measurements for diagnostic of the physical conditions in the exosphere of Mercury, and eventually to infer the magnetic field of Mercury and its variability from observations made with ground telescopes. Title: Dead Calm Areas in the Very Quiet Sun Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Hijano, E. Bibcode: 2012ApJ...755..175M Altcode: 2012arXiv1206.4545M We analyze two regions of the quiet Sun (35.6 × 35.6 Mm2) observed at high spatial resolution (lsim100 km) in polarized light by the IMaX spectropolarimeter on board the SUNRISE balloon. We identify 497 small-scale (~400 km) magnetic loops, appearing at an effective rate of 0.25 loop h -1 arcsec-2 further, we argue that this number and rate are underestimated by ~30%. However, we find that these small dipoles do not appear uniformly on the solar surface: their spatial distribution is rather filamentary and clumpy, creating dead calm areas, characterized by a very low magnetic signal and a lack of organized loop-like structures at the detection level of our instruments, which cannot be explained as just statistical fluctuations of a Poisson spatial process. We argue that this is an intrinsic characteristic of the mechanism that generates the magnetic fields in the very quiet Sun. The spatio-temporal coherences and the clumpy structure of the phenomenon suggest a recurrent, intermittent mechanism for the generation of magnetic fields in the quietest areas of the Sun. Title: Scattering Polarization in the Ca II Infrared Triplet with Velocity Gradients Authors: Carlin, E. S.; Manso Sainz, R.; Asensio Ramos, A.; Trujillo Bueno, J. Bibcode: 2012ApJ...751....5C Altcode: 2012arXiv1203.4438C Magnetic field topology, thermal structure, and plasma motions are the three main factors affecting the polarization signals used to understand our star. In this theoretical investigation, we focus on the effect that gradients in the macroscopic vertical velocity field have on the non-magnetic scattering polarization signals, establishing the basis for general cases. We demonstrate that the solar plasma velocity gradients may have a significant effect on the linear polarization produced by scattering in chromospheric spectral lines. In particular, we show the impact of velocity gradients on the anisotropy of the radiation field and on the ensuing fractional alignment of the Ca II levels, and how they can lead to an enhancement of the zero-field linear polarization signals. This investigation remarks on the importance of knowing the dynamical state of the solar atmosphere in order to correctly interpret spectropolarimetric measurements, which is important, among other things, for establishing a suitable zero-field reference case to infer magnetic fields via the Hanle effect. Title: The Chromospheric Lyman-Alpha SpectroPolarimeter: CLASP Authors: Kobayashi, K.; Kano, R.; Trujillo-Bueno, J.; Asensio Ramos, A.; Bando, T.; Belluzzi, L.; Carlsson, M.; De Pontieu, R. C. B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Katsukawa, Y.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Sakao, T.; Stepan, J.; Suematsu, Y.; Tsuneta, S.; Watanabe, H.; Winebarger, A. Bibcode: 2012ASPC..456..233K Altcode: The magnetic field plays a crucial role in the chromosphere and the transition region, and our poor empirical knowledge of the magnetic field in the upper chromosphere and transition region is a major impediment to advancing the understanding of the solar atmosphere. The Hanle effect promises to be a valuable alternative to Zeeman effect as a method of measuring the magnetic field in the chromosphere and transition region; it is sensitive to weaker magnetic fields, and also sensitive to tangled, unresolved field structures.

CLASP is a sounding rocket experiment that aims to observe the Hanle effect polarization of the Lyman α (1215.67Å) line in the solar chromosphere and transition region, and prove the usefulness of this technique in placing constraints on the magnetic field strength and orientation in the low plasma-β region of the solar atmosphere. The Ly-α line has been chosen because it is a chromospheric/transition-region line, and because the Hanle effect polarization of this line is predicted to be sensitive to 10-250 Gauss, encompassing the range of interest. The CLASP instrument is designed to measure linear polarization in the Ly-α line with a polarization sensitivity of 0.1%. The instrument is currently funded for development. The optical design of the instrument has been finalized, and an extensive series of component-level tests are underway to validate the design. Title: Model Selection for Spectropolarimetric Inversions Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González, M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H. Bibcode: 2012ApJ...748...83A Altcode: 2012arXiv1201.5063A Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios (S/Ns) favor models without gradients along the line of sight. If the observations show clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large S/Ns favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future. Title: Analytical maximum likelihood estimation of stellar magnetic fields Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Belluzzi, L. Bibcode: 2012MNRAS.419..153M Altcode: 2011MNRAS.tmp.1583M; 2011arXiv1108.4366M The polarized spectrum of stellar radiation encodes valuable information on the conditions of stellar atmospheres and the magnetic fields that permeate them. In this paper, we give explicit expressions to estimate the magnetic field vector and its associated error from the observed Stokes parameters. We study the solar case where specific intensities are observed and then the stellar case, where we receive the polarized flux. In the second case, we concentrate on the explicit expression for the case of a slow rotator with a dipolar magnetic field geometry. Moreover, we also give explicit formulae to retrieve the magnetic field vector from the least-squares deconvolution (LSD) profiles without assuming mean values for the LSD artificial spectral line. The formulae have been obtained assuming that the spectral lines can be described in the weak-field regime and using a maximum likelihood approach. The errors are recovered by means of the Hermitian matrix. The bias of the estimators is analysed in depth. Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.; Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu, B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.; Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos, A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.; Watanabe, H.; West, E.; Winebarger, A. R. Bibcode: 2011AGUFM.P14C..05K Altcode: We present an overview of the Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket experiment currently under development as collaboration between Japan, USA and Spain. The aim is to achieve the first measurement of magnetic field in the upper chromosphere and transition region of the Sun through the detection and measurement of Hanle effect polarization of the Lyman alpha line. The Hanle effect (i.e. the magnetic field induced modification of the linear polarization due to scattering processes in spectral lines) is believed to be a powerful tool for measuring the magnetic field in the upper chromosphere, as it is more sensitive to weaker magnetic fields than the Zeeman effect, and also sensitive to magnetic fields tangled at spatial scales too small to be resolved. The Lyman-alpha (121.567 nm) line has been chosen because it is a chromospheric/transition-region line, and because the Hanle effect polarization of the Lyman-alpha line is predicted to be sensitive to 10-250 Gauss, encompassing the range of interest. Hanle effect is predicted to be observable as linear polarization or depolarization, depending on the geometry, with a fractional polarization amplitude varying between 0.1% and 1% depending on the strength and orientation of the magnetic field. This quantification of the chromospheric magnetic field requires a highly sensitive polarization measurement. The CLASP instrument consists of a large aperture (287 mm) Cassegrain telescope mated to a polarizing beamsplitter and a matched pair of grating spectrographs. The polarizing beamsplitter consists of a continuously rotating waveplate and a linear beamsplitter, allowing simultaneous measurement of orthogonal polarizations and in-flight self-calibration. Development of the instrument is underway, and prototypes of all optical components have been tested using a synchrotron beamline. The experiment is proposed for flight in 2014. Title: Scattering Polarization and Hanle Effect in Stellar Atmospheres with Horizontal Inhomogeneities Authors: Manso Sainz, Rafael; Trujillo Bueno, Javier Bibcode: 2011ApJ...743...12M Altcode: 2011arXiv1108.2958M Scattering of light from an anisotropic source produces linear polarization in spectral lines and in the continuum. In the outer layers of a stellar atmosphere the anisotropy of the radiation field is typically dominated by the radiation escaping away, but local horizontal fluctuations of the physical conditions may also contribute, distorting the illumination and, hence, the polarization pattern. Additionally, a magnetic field may perturb and modify the line scattering polarization signals through the Hanle effect. Here, we study such symmetry-breaking effects. We develop a method to solve the transfer of polarized radiation in a scattering atmosphere with weak horizontal fluctuations of the opacity and source functions. It comprises linearization (small opacity and Planck function fluctuations are assumed), reduction to a quasi-plane-parallel problem through harmonic analysis, and the problem's numerical solution by generalized standard techniques. We apply this method to study scattering polarization in atmospheres with horizontal fluctuations in the Planck function and opacity. We derive several very general results and constraints from considerations on the symmetries and dimensionality of the problem, and we give explicit solutions of a few illustrative problems of special interest. For example, we show (1) how the amplitudes of the fractional linear polarization signals change when considering increasingly smaller horizontal atmospheric inhomogeneities, (2) that in the presence of such inhomogeneities even a vertical magnetic field may modify the scattering line polarization, and (3) that forward scattering polarization may be produced without the need for an inclined magnetic field. These results are important for understanding the physics of the problem and as benchmarks for multidimensional radiative transfer codes. Title: The Hanle Effect from Space for Measuring the Magnetic Fields of the Upper Solar Chromosphere Authors: Trujillo Bueno, J.; Stepan, J.; Belluzzi, L.; Manso Sainz, R. Bibcode: 2011AGUFM.P11F1626T Altcode: We present some theoretical predictions concerning the amplitudes and magnetic sensitivities of the linear polarization signals produced by scattering processes in some UV and FUV spectral lines of the upper chromosphere and transition region, such as Ly-alpha and Mg II k. To this end, we have calculated the atomic level polarization (population imbalances and quantum coherences) induced by anisotropic radiation pumping in semi-empirical and hydrodynamical models of the solar atmosphere, taking into account radiative transfer and the Hanle effect caused by the presence of organized and random magnetic fields. The amplitudes of the emergent linear polarization signals are found to vary typically between a fraction of a percent and a few percent, depending on the scattering geometry and the strength and orientation of the magnetic field. The results shown here encourage the development of UV polarimeters for sounding rockets and space telescopes with the aim of opening up a true diagnostic window for magnetic field measurements in the upper chromosphere and transition region of the Sun. Title: Polarization Diagnostics of Solar Magnetic Fields Authors: Manso Sainz, R. Bibcode: 2011AGUFM.P14C..01M Altcode: The solar atmosphere is a highly ionized medium which is the playground of magnetic fields. In the deepest layer (the photosphere), magnetic fields disturb the 'normal' fluid motions forcing the plasma to behave incounterintuitive ways; in the outer layers (the chromosphere and the corona) magnetic fields rule, making the plasma levitate or even ejecting it out of the gravitational well of the Sun, with important consequences for us here on Earth. However, magnetic fields are elusive. The only quantitative evidence of their presence is through the polarization state of the light emitted by the plasma they are playing with. Remote sensing of magnetic fields from 150 million km away through spectropolarimetry is a challenge on applied physics as well as an art. It requires the application of quantum mechanics, radiative transfer theory, and advanced optics to the interpretation and analysis of spectropolarimetric observations. I will review standard diagnostic techniques and recent developments on this field. I will discuss their limitations and how to overcome them through the complementary aspects of different diagnostic techniques, spectral regions, and statistical analysis. Finally, I will review what are the main areas for progress in this regard: most notably, the 'measurement' of magnetic fields in the extremely dilute and weakly magnetized outer layers of the sun. Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP) Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano, Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu, Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi; Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim, Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats Bibcode: 2011SPIE.8148E..0HN Altcode: 2011SPIE.8148E..16N The solar chromosphere is an important boundary, through which all of the plasma, magnetic fields and energy in the corona and solar wind are supplied. Since the Zeeman splitting is typically smaller than the Doppler line broadening in the chromosphere and transition region, it is not effective to explore weak magnetic fields. However, this is not the case for the Hanle effect, when we have an instrument with high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect linear polarization produced by the Hanle effect in Lyman-alpha line (121.567 nm) and to make the first direct measurement of magnetic fields in the upper chromosphere and lower transition region. To achieve the high sensitivity of ~ 0.1% within a rocket flight (5 minutes) in Lyman-alpha line, which is easily absorbed by materials, we design the optical system mainly with reflections. The CLASP consists of a classical Cassegrain telescope, a polarimeter and a spectrometer. The polarimeter consists of a rotating 1/2-wave plate and two reflecting polarization analyzers. One of the analyzer also works as a polarization beam splitter to give us two orthogonal linear polarizations simultaneously. The CLASP is planned to be launched in 2014 summer. Title: Erratum: "Scattering Polarization of the Ca II IR Triplet for Probing the Quiet Solar Chromosphere" (2010, ApJ, 722, 1416) Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2011ApJ...737..106M Altcode: No abstract at ADS Title: Advection and dispersal of small magnetic elements in the very quiet Sun Authors: Manso Sainz, R.; Martínez González, M. J.; Asensio Ramos, A. Bibcode: 2011A&A...531L...9M Altcode: We track small magnetic structures on very quiet regions (internetwork) of the Sun. We follow the footpoints of small-scale magnetic loops that appear on the photosphere at granular scales using spectropolarimetric and magnetographic data obtained with Hinode. We find two different regimes for their wanderings. Within granules (where they appear), they seem to be passively advected by the plasma - which is justified by their relatively low magnetic flux (~1016 Mx), and magnetic field strength (~200 G). The plasma flow thus traced is roughly laminar with a characteristic mean velocity of 2 km s-1 and very low vorticity. Once the magnetic markers reach intergranular lanes, they remain there and are buffeted by the random flows of neighbouring granules and turbulent intergranules, follow random walks, and disperse across the solar surface with a diffusion constant of 195 km2 s-1. While on their intergranular random walking, they may fall close to whirlpools (on scales ≲400 km) associated with convective downdrafts, similar to the events recently reported in mesogranular and supergranular cell boundaries tracking magnetic bright points, which provides additional evidence that these events are ubiquitous on the solar surface. Title: A Sounding Rocket Experiment for Spectropolarimetric Observations with the Lyα Line at 121.6 nm (CLASP) Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano, R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe, H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.; de Pontieu, B.; Carlsson, M.; Casini, R. Bibcode: 2011ASPC..437..287I Altcode: A team consisting of Japan, USA, Spain, and Norway is developing a high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP), which is proposed to fly with a NASA sounding rocket in 2014. CLASP will explore the magnetism of the upper solar chromosphere and transition region via the Hanle effect of the Lyα line for the first time. This experiment requires spectropolarimetric observations with high polarimetric sensitivity (∼0.1%) and wavelength resolution (0.1 Å). The final spatial resolution (slit width) is being discussed taking into account the required high signal-to-noise ratio. We have demonstrated the performance of the Lyα polarimeter by extensively using the Ultraviolet Synchrotron ORbital Radiation Facility (UVSOR) at the Institute for Molecular Sciences. In this contribution, we report these measurements at UVSOR together with the current status of the CLASP project. Title: Non-detection of Magnetic Fields in the Central Stars of the Planetary Nebulae NGC 1360 and LSS 1362 Authors: Leone, Francesco; Martínez González, María J.; Corradi, Romano L. M.; Privitera, Giovanni; Manso Sainz, Rafael Bibcode: 2011ApJ...731L..33L Altcode: 2011arXiv1104.1042L The presence of magnetic fields is an attractive hypothesis for shaping planetary nebulae (PNe). We report on observations of the central star of the two PNe NGC 1360 and LSS 1326. We performed spectroscopy on circularly polarized light with the Focal Reducer and Low Dispersion Spectrograph at the Very Large Telescope of the European Southern Observatory. Contrary to previous reports, we find that the effective magnetic field, which is the average over the visible stellar disk of longitudinal components of the magnetic fields, is null within errors for both stars. We conclude that direct evidence of magnetic fields on the central stars of PNe is still missing—either the magnetic field is much weaker (<600 G) than previously reported, or more complex (thus leading to cancellations), or both. Certainly, indirect evidence (e.g., MASER emission) fully justify further efforts to point out the strength and morphology of such magnetic fields. Title: On the Inversion of Stokes Profiles with Local Stray-light Contamination Authors: Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2011ApJ...731..125A Altcode: 2011arXiv1102.4703A Obtaining the magnetic properties of non-resolved structures in the solar photosphere is always challenging and problems arise because the inversion is carried out through the numerical minimization of a merit function that depends on the proposed model. We investigate the reliability of inversions in which the stray-light contamination is obtained from the same observations as a local average. In this case, we show that it is fundamental to include the covariance between the observed Stokes profiles and the stray-light contamination. The ensuing modified merit function of the inversion process penalizes large stray-light contaminations simply because of the presence of positive correlations between the observables and the stray light, fundamentally produced by spatially variable systematics. We caution that if the wrong merit function is used, artificially large stray-light contaminations might be inferred. Since this effect disappears if the stray-light contamination is obtained as an average over the full field of view, we recommend taking into account stray-light contamination using a global approach. Title: Elementary Theory of Scattering Polarization in Complex Atoms Authors: Manso Sainz, R. Bibcode: 2011ASPC..437...19M Altcode: Scattering polarization in complex atoms poses interesting theoretical problems and is interesting for diagnostic plasma purposes. Here, an elementary theory on the generation and transfer of scattering polarization and Hanle effect in complex atoms (chiefly, transition metals and rare earths) is introduced. It is based on the quantum mechanical formulation of polarization transfer. The exposition is self-contained and can be (and has been) applied to treat very general problems. Numerical methods of solution are reviewed. I discuss non-trivial problems arising not from the formalism itself, but from its application to systems (complex atoms) with intrinsic spectroscopic peculiarities. In particular, they have a large number of relevant atomic levels massively interconnected between them by a huge amount of (resonant or quasi-resonant) spectral lines. This gives rise to surprising effects such as depolarization by interlocking, level over-polarization, and special Hanle effect regimes. Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun Revealed by SUNRISE/IMaX Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste, A.; Schmidt, W.; Barthol, P.; Gandorfer, A. Bibcode: 2011ApJ...730L..37M Altcode: 2011arXiv1103.0145M We present observational evidence for oscillations of magnetic flux density in the quiet areas of the Sun. The majority of magnetic fields on the solar surface have strengths of the order of or lower than the equipartition field (300-500 G). This results in a myriad of magnetic fields whose evolution is largely determined by the turbulent plasma motions. When granules evolve they squash the magnetic field lines together or pull them apart. Here, we report on the periodic deformation of the shapes of features in circular polarization observed at high resolution with SUNRISE. In particular, we note that the area of patches with a constant magnetic flux oscillates with time, which implies that the apparent magnetic field intensity oscillates in antiphase. The periods associated with this oscillatory pattern are compatible with the granular lifetime and change abruptly, which suggests that these oscillations might not correspond to characteristic oscillatory modes of magnetic structures, but to the forcing by granular motions. In one particular case, we find three patches around the same granule oscillating in phase, which means that the spatial coherence of these oscillations can reach 1600 km. Interestingly, the same kind of oscillatory phenomenon is also found in the upper photosphere. Title: Are magnetic fields shaping PNe? Authors: Matínez González, M. J.; Leone, F.; Corradi, R.; Manso Sainz, R.; Privitera, G. Bibcode: 2011iac..talk..255M Altcode: 2011iac..talk..206M No abstract at ADS Title: Detecting photons with orbital angular momentum in extended astronomical objects: application to solar observations Authors: Uribe-Patarroyo, N.; Alvarez-Herrero, A.; López Ariste, A.; Asensio Ramos, A.; Belenguer, T.; Manso Sainz, R.; Lemen, C.; Gelly, B. Bibcode: 2011A&A...526A..56U Altcode: Context. The orbital angular momentum (OAM) of the photon is a property of light from astronomical objects that has not yet been measured. We propose a method of measuring the OAM spectrum of light from an extended natural source, the Sun. Relating the OAM spectrum of different solar areas to its structures could lead to a novel remote sensing technique.
Aims: We present a method for measuring the OAM spectrum of solar photons.
Methods: The THEMIS (Télescope Héliographique pour l'Étude du Magnetisme et les Instabilités Solaires is a 0.9 m solar telescope property of the French CNRS-INSU at the Spanish Observatorio del Teide.) telescope is being used with a novel phase-diversity technique. A spatial light modulator is placed on one pupil image, and an ad-hoc optical setup allows the measurement of two simultaneous phase-diverse images in the same CCD, with equal optical paths.
Results: Preliminary results show that very good seeing is mandatory for this kind of observation. The method works in the laboratory, and good seeing conditions in the 2010 campaign are being awaited. Title: Scattering Polarization of the Ca II IR Triplet for Probing the Quiet Solar Chromosphere Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2010ApJ...722.1416M Altcode: 2010arXiv1007.0727M The chromosphere of the quiet Sun is a very important stellar atmospheric region whose thermal and magnetic structure we need to decipher in order to unlock new discoveries in solar and stellar physics. To this end, we need to identify and exploit observables sensitive to weak magnetic fields (B <~ 100 G) and to the presence of cool and hot gas in the bulk of the solar chromosphere. Here, we report on an investigation of the Hanle effect in two semi-empirical models of the quiet solar atmosphere with different chromospheric thermal structures. Our study reveals that the linear polarization profiles produced by scattering in the Ca II IR triplet have thermal and magnetic sensitivities potentially of great diagnostic value. The linear polarization in the 8498 Å line shows a strong sensitivity to inclined magnetic fields with strengths between 0.001 and 10 G, while the emergent linear polarization in the 8542 Å and 8662 Å lines is mainly sensitive to magnetic fields with strengths between 0.001 and 0.1 G. The reason for this is that the scattering polarization of the 8542 Å and 8662 Å lines, unlike the 8498 Å line, is controlled mainly by the Hanle effect in their (metastable) lower levels. Therefore, in regions with magnetic strengths noticeably larger than 1 G, their Stokes Q and U profiles are sensitive only to the orientation of the magnetic field vector. We also find that for given magnetic field configurations the sign of the Q/I and U/I profiles of the 8542 Å and 8662 Å lines is the same in both atmospheric models, while the sign of the linear polarization profile of the 8498 Å line turns out to be very sensitive to the thermal structure of the lower chromosphere. We suggest that spectropolarimetric observations providing information on the relative scattering polarization amplitudes of the Ca II IR triplet will be very useful to improve our empirical understanding of the thermal and magnetic structure of the quiet chromosphere. Title: Small Magnetic Loops Connecting the Quiet Surface and the Hot Outer Atmosphere of the Sun Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; Bellot Rubio, L. R. Bibcode: 2010ApJ...714L..94M Altcode: 2010arXiv1003.1255M Sunspots are the most spectacular manifestation of solar magnetism, yet 99% of the solar surface remains "quiet" at any time of the solar cycle. The quiet sun is not void of magnetic fields, though; they are organized at smaller spatial scales and evolve relatively fast, which makes them difficult to detect. Thus, although extensive quiet Sun magnetism would be a natural driver to a uniform, steady heating of the outer solar atmosphere, it is not clear what the physical processes involved would be, due to lack of observational evidence. We report on the topology and dynamics of the magnetic field in very quiet regions of the Sun from spectropolarimetric observations of the Hinode satellite, showing a continuous injection of magnetic flux with a well-organized topology of Ω-loop from below the solar surface into the upper layers. At first stages, when the loop travels across the photosphere, it has a flattened (staple-like) geometry and a mean velocity ascent of ~3 km s-1. When the loop crosses the minimum temperature region, the magnetic fields at the footpoints become almost vertical and the loop topology resembles a potential field. The mean ascent velocity at chromospheric height is ~12 km s-1. The energy input rate of these small-scale loops in the lower boundary of the chromosphere is (at least) of 1.4 × 106-2.2 × 107 erg cm-2 s-1. Our findings provide empirical evidence for solar magnetism as a multi-scale system, in which small-scale low-flux magnetism plays a crucial role, at least as important as active regions, coupling different layers of the solar atmosphere and being an important ingredient for chromospheric and coronal heating models. Title: Scattering Polarization in the Fe I 630 nm Emission Lines at the Extreme Limb of the Sun Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.; Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot Rubio, L. Bibcode: 2010ApJ...713..450L Altcode: Spectro-polarimetric observations with the Solar Optical Telescope onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines at the solar limb. The emission shell extends for less than 1'' thereby making it extremely difficult to detect from ground-based observatories viewing the limb through the Earth's atmosphere. The linear polarization signal is clearly due to scattering and it is predominantly oriented in the radial direction. Using a comprehensive atomic model of iron, we are able to interpret qualitatively the observed signals, including the radial orientation of the linear polarization. The Hanle effect causes the linear polarization of the Fe I 630 nm lines to be sensitive to magnetic fields between ~0.1 G and ~40 G, and also to be sensitive to the field's topology for stronger fields. The overall degree of observed polarization can be reproduced by randomly oriented horizontal magnetic fields of strength ≈2 G. The discovery of their scattering polarization signals thus opens a new diagnostic opportunity for these lines. Title: The stochastic, intermittent nature of quiet Sun magnetism Authors: Martinez González, M. J.; Manso Sainz, R.; López Ariste, A.; Bellot Rubio, L. R.; Bianda, M. Bibcode: 2010iac..talk....1M Altcode: 2010iac..talk..153M No abstract at ADS Title: Statistical Analysis of the very Quiet Sun Magnetism Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos, A.; López Ariste, A.; Bianda, M. Bibcode: 2010ApJ...711L..57M Altcode: 2010arXiv1001.4551M The behavior of the observed polarization amplitudes with spatial resolution is a strong constraint on the nature and organization of solar magnetic fields below the resolution limit. We study the polarization of the very quiet Sun at different spatial resolutions using ground- and space-based observations. It is shown that 80% of the observed polarization signals do not change with spatial resolution, suggesting that, observationally, the very quiet Sun magnetism remains the same despite the high spatial resolution of space-based observations. Our analysis also reveals a cascade of spatial scales for the magnetic field within the resolution element. It is manifest that the Zeeman effect is sensitive to the microturbulent field usually associated with Hanle diagnostics. This demonstrates that Zeeman and Hanle studies show complementary perspectives of the same magnetism. Title: Polarimetric Diagnostics of Unresolved Chromospheric Magnetic Fields Authors: Casini, R.; Manso Sainz, R.; Low, B. C. Bibcode: 2009ApJ...701L..43C Altcode: 2008arXiv0811.0512C For about a decade, spectropolarimetry of He I λ10830 has been applied to the magnetic diagnostics of the solar chromosphere. This resonance line is very versatile as it is visible both on disk and in off-limb structures, and it has a good sensitivity to both the weak-field Hanle effect and the strong-field Zeeman effect. Recent observations of an active-region filament showed that the linear polarization was dominated by the transverse Zeeman effect, with very little or no hint of scattering polarization. This is surprising, since the He I levels should be significantly polarized in a conventional scattering scenario. To explain the observed level of atomic depolarization by collisional or radiative processes, one must invoke plasma densities larger by several orders of magnitude than currently known values for prominences. We show that such depolarization can be explained quite naturally by the presence of an unresolved, highly entangled magnetic field, which averages to give the ordered field inferred from spectropolarimetric data, over the typical temporal and spatial scales of the observations. We present a modeling of the polarized He I λ10830 in this scenario, and discuss its implications for the magnetic diagnostics of prominences and spicules, and for the general study of unresolved magnetic field distributions in the solar atmosphere. Title: Variability of the polarization profiles of the Ba II D{2} line in the solar atmosphere Authors: López Ariste, A.; Asensio Ramos, A.; Manso Sainz, R.; Derouich, M.; Gelly, B. Bibcode: 2009A&A...501..729L Altcode: Resonance-scattering polarization and the Hanle effect are powerful but seldom exploited probes into the magnetism of the quiet solar atmosphere. They are also very interesting checks of the quantum theory of atomic polarization. The Ba ii D2 line has been known for more than 20 years as presenting a conspicuous signal of resonance scattering polarization thanks to its atomic configuration and the presence of five different isotopes of Ba, two of which present a hyperfine structure.A model that considers most of the known ingredients of the atomic polarization of Ba ii related to the formation of the D2 line was presented in 2007. We intend to observe all the variability of the Stokes profiles of this line in conditions of resonance scattering to verify the general validity of the model and to ascertain the use of the model for magnetic field diagnostics in the quiet solar chromosphere and in spicules. The new CCD cameras at THEMIS and the recently commissioned tip-tilt tracking system gave us the opportunity to perform the required observations with unprecedented precision and reliability, resulting in data ready to confront the present theory.The Stokes Q profiles, both off-limb and on disk, appear to verify this theory in qualitative terms. The observed departures in terms of overall signal amplitude and relative ratios among the three spectral features point to a refinement of the theory for quantitative purposes, perhaps including radiative-transfer effects. We observed, on the other hand, anomalous Stokes V profiles in the absence of Zeeman effect that remain unexplained.The qualitative agreement between the theory and the observations encourages an increased effort to also match the observations from a quantitative point of view, including the observed anomalous Stokes V profiles. Title: Magnetic field strength of active region filaments Authors: Kuckein, C.; Centeno, R.; Martínez Pillet, V.; Casini, R.; Manso Sainz, R.; Shimizu, T. Bibcode: 2009A&A...501.1113K Altcode: 2009arXiv0904.4876K Aims: We study the vector magnetic field of a filament observed over a compact active region neutral line.
Methods: Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 Å spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and PCA-based atomic polarization inversions.
Results: The inferred magnetic field strengths in the filament are around 600-700 G by all these three methods. Longitudinal fields are found in the range of 100-200 G whereas the transverse components become dominant, with fields as high as 500-600 G. We find strong transverse fields near the neutral line also at photospheric levels.
Conclusions: Our analysis indicates that strong (higher than 500 G, but below kG) transverse magnetic fields are present in active region filaments. This corresponds to the highest field strengths reliably measured in these structures. The profiles of the helium 10 830 Å lines observed in this active region filament are dominated by the Zeeman effect. Title: A Possible Polarization Mechanism of EUV Coronal Lines Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2009ASPC..405..423M Altcode: The alignment generated in the ground level of Fe X by scattering in the coronal red line λ6374, can be efficiently transferred by collisions to upper levels; the ensuing spontaneous emission in allowed EUV transitions (as 174.5~Å and 177~Å) is then linearly polarized. The polarization thus generated would be sensitive to the electronic density (Ne) and to the magnetic field orientation although not to the field strength. At Ne∼ 10^7~cm-3 the linear polarization would be ∼1% just over the solar surface and ∼5% at 0.2R_⊙, rapidly decaying for Ne> 10^8~cm-3. The mechanism works for other spectral lines and ions too. Title: Near-IR internetwork spectro-polarimetry at different heliocentric angles Authors: Martínez González, M. J.; Asensio Ramos, A.; López Ariste, A.; Manso Sainz, R. Bibcode: 2008A&A...479..229M Altcode: 2007arXiv0710.5219M Aims:The analysis of near infrared spectropolarimetric data at the internetwork in different regions on the solar surface could offer constraints that reject current modeling of these quiet areas.
Methods: We present spectro-polarimetric observations of very quiet regions for different values of the heliocentric angle for the Fe i lines at 1.56 μm, from disc centre to positions close to the limb. The spatial resolution of the data is 0.7{-}1''. We analyse direct observable properties of the Stokes profiles as the amplitude of circular and linear polarisation, as well as the total degree of polarisation. The area and amplitude asymmetries are also studied.
Results: We do not find any significant variation in the properties of the polarimetric signals with the heliocentric angle. This means that the magnetism of the solar internetwork remains the same regardless of the position on the solar disc. This observational fact discards the possibility of modeling the internetwork as a network-like scenario. The magnetic elements of internetwork areas seem to be isotropically distributed when observed at our spatial resolution. Title: Are collisions with neutral hydrogen important for modeling the second solar spectrum of Ti I and Ca II? Authors: Derouich, M.; Trujillo Bueno, J.; Manso Sainz, R. Bibcode: 2007A&A...472..269D Altcode: 2007arXiv0705.1968D Context: The physical interpretation of scattering line polarization offers a novel diagnostic window for exploring the thermal and magnetic structure of the quiet regions of the solar atmosphere.
Aims: We evaluate the impact of isotropic collisions with neutral hydrogen atoms on the scattering polarization signals of the 13 lines of multiplet 42 of Ti i and on those of the K line and of the IR triplet of Ca ii, with emphasis on the collisional transfer rates between nearby J-levels.
Methods: We calculate the linear polarization produced by scattering processes in a plane-parallel layer illuminated by the radiation field from the underlying solar photosphere. We consider realistic multilevel models and solve the statistical equilibrium equations for the multipolar components of the atomic density matrix.
Results: We give suitable formulae for calculating the collisional rates as a function of temperature and hydrogen number density. We confirm that the lower levels of the 13 lines of multiplet 42 of Ti i are completely depolarized by elastic collisions. Upper-level depolarization caused by the collisional transfer rates between nearby J-levels turns out to have an unnoticeable impact on the emergent linear polarization amplitudes, except for the λ4536 and λ4544.7 lines. Concerning the Ca ii lines, we show that the collisional rates play no role in the polarization of the upper level of the K line, while they have a rather small depolarizing effect on the atomic polarization of the metastable lower levels of the Ca ii IR triplet.
Conclusions: Although the collisional transfer rates seem to play a minor role for most of the lines we considered in this paper, except, for example, for the magnetically insensitive λ4536 line of Ti i, they might be important for other atomic or molecular systems with closer J-levels (e.g., hyperfine structured multiplets and/or molecules). Therefore, future research in this direction will be worthwhile.

Appendices A and B are only available in electronic form at http://www.aanda.org Title: Turbulent fields in the quiet sun from Hanle and Zeeman effects with THEMIS Authors: López Ariste, A.; Malherbe, J. M.; Manso Sainz, R.; Asensio Ramos, A.; Ramírez Vélez, J. C.; Martínez González, M. Bibcode: 2007sf2a.conf..596L Altcode: The measurement of the Sr I line with full polarimetry and spatial resolution with THEMIS has provided the unexpected result of an apparent correlation between the Hanle effect signals and the Zeeman effect signals on this line. Traditionnally, Hanle effect signals in linear polarisation have been interpreted as the signature of unorganized, turbulent fields, while Zeeman effect signals -mostly in circular polarisation- were interpreted as structured fields. The correlation between both observed by THEMIS requires a change of mind respect to the picture of the quiet sun, with fewer structured fields and a turbulent field visible also in deep magnetograms. This picture is supported also by recent results with Mn lines with strong coupling with its hyperfine structure and of center-to-limb histograms of Zeeman amplitudes. Title: Scattering Polarization of the Ca II Infrared Triplet as Diagnostic of the Quiet Solar Chromosphere Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2007ASPC..368..155M Altcode: In observations close to the edge of the solar disk, the Ca II infrared triplet has a scattering polarization pattern at the level of 10-3 in its two strongest lines and at the 10-4 level in the weakest. This polarimetric sensitivity is now accessible with modern spectropolarimeters and scattering polarization has been observed by several authors in the Ca II infrared triplet. We discuss here the interest of observing these lines for the detection and mapping of magnetic fields in the quiet solar chromosphere. To this end, we investigate theoretically the sensitivity of the polarization pattern to the presence of magnetic fields through the Hanle effect. We find that the Ca II 8542 Å and 8662 Å lines are mostly sensitive to fields between 0.001 and 0.1 G, the former is also weakly sensitive to fields between 1 and 10 G. Otherwise the polarization signals are dependent only on the magnetic field geometry, but not on its intensity. The 8498 Å line is highly sensitive in the whole regime 0.001-10 G, but its polarization signal is much lower. Diagnostic diagrams giving the Q/I vs. U/I values at the line core for several magnetic field configurations and intensities are presented. We also discuss the sensitivity of the scattering polarization signals to the temperature gradient of the atmospheric model. Title: A synthetic stellar polarization atlas from 400 to 1000 nm Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2007A&A...465..339S Altcode: 2006astro.ph.12388S Context: With the development of new polarimeters for large telescopes, the spectro-polarimetric study of astrophysical bodies is becoming feasible and, indeed, more frequent. In particular, this is permitting the observational study of stellar magnetic fields.
Aims: With the aim to optimize and interpret this kind of observations, we have produced a spectral atlas of circular polarization in a grid of stellar atmospheric models with effective temperatures between 3500 and 10 000 K, surface gravities log(g)=3.5-5, metallicities between 10-2 and 1, and magnetic field strengths of 100, 1000 and 5000 G.
Methods: We have computed the emergent Stokes I and V flux spectra in LTE of more than 105 spectral lines.
Results: The atlas and several numerical tools are available in electronic format and may be downloaded from http://download.hao.ucar.edu/pub/PSA/. In this paper we review and discuss some of its most relevant features, such as which spectral regions and individual lines harbor the strongest signals, what are interesting lines to observe, how to disentangle field strength from filling factor, etc.

Full line lists and spectra are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/ qcat?J/A+A/465/339 Title: VizieR Online Data Catalog: Synthetic stellar polarization 400-1000nm (Socas-Navarro+ 2007) Authors: Socas-Navarro, H.; Asensio Ramos, A.; Manso Sainz, R. Bibcode: 2007yCat..34650339S Altcode: No abstract at ADS Title: The Effect of Turbulent Electric Fields on the Scattering Polarization of Hydrogen Lines Authors: Casini, R.; Manso Sainz, R. Bibcode: 2006ASPC..358..429C Altcode: We reviewed the polarization properties of hydrogen lines in the presence of electric and magnetic fields. We first considered the case of completely depolarized hydrogen atoms. Under this assumption, the hydrogen lines manifest complex polarization signatures due to the combined Stark and Zeeman effect tep{c0 CL93}. One can derive convenient analytic expressions for the 1st and 2nd-order moments of the Stokes profile, which nicely summarize the fundamental properties of hydrogen polarization for both cases of deterministic and micro-turbulent electric and magnetic fields tep{c0 CL94,c0 CL95,c0 Ca97}. In particular, it is demonstrated the ``additivity'' of the Stark and Zeeman effects on such integral properties of the line polarization emitted by a gas of depolarized hydrogen atoms. We then generalized the problem to include the possibility of atomic polarization induced in the hydrogen atoms by anisotropic excitation mechanisms (e.g., in chromospheric and coronal plasmas). The complexity of the problem makes it intractable by analytic means, and one must resort to numerical tools. The results show that, in the presence of atomic polarization, the ``additivity'' of the electric and magnetic effects is lost, and an intricated interplay of the two effects occurs tep{c0 Ca05}. In particular, we considered two hydrogen lines of diagnostic relevance-Lyα and Hα-formed in a magnetized plasma, and demonstrated the modifications of the scattering polarization that are induced by the additional presence of turbulent, electric microfields of various strengths (typically, the normal field strength of the Holtsmark theory, for various electron densities of the plasma). We showed that the additional presence of these electric microfields can significantly enhance the amount of net circular polarization (NCP) of the Hα line for a given magnetic strength, which can be produced by the so-called alignment-to-orientation transfer mechanism tep[e.g.,][]{c0 La82,c0 Ke84,c0 LL04}, even if the electric microfield distribution is perfectly isotropic tep[see Fig. ref{c0 NCP};][]{c0 CM06}. We argued that this mechanism could explain the large levels of NCP that have recently been detected in several quiescent prominences tep{c0 LA05}, and discussed the implications of this study for the diagnostics of magnetic fields in the solar atmosphere using hydrogen lines. Title: Scattering polarization of hydrogen lines in the presence of turbulent electric fields Authors: Casini, R.; Manso Sainz, R. Bibcode: 2006JPhB...39.3241C Altcode: 2005astro.ph.11148C We study the broadband polarization of hydrogen lines produced by scattering of radiation, in the presence of isotropic electric fields. In this paper, we focus on two distinct problems: (a) the possibility of detecting the presence of turbulent electric fields by polarimetric methods and (b) the influence of such fields on the polarization due to a macroscopic, deterministic magnetic field. We found that isotropic electric fields decrease the degree of linear polarization in the scattered radiation, with respect to the zero-field case. On the other hand, a distribution of isotropic electric fields superimposed onto a deterministic magnetic field can increase significantly the degree of magnetic-induced, net circular polarization. This phenomenon has important implications for the diagnostics of magnetic fields in plasmas using hydrogen lines, because of the ubiquitous presence of the Holtsmark microscopic electric field from neighbouring ions. In particular, previous solar magnetographic studies of the Balmer lines of hydrogen may need to be revised because they neglected the effect of turbulent electric fields on the polarization signals. In this work, we give explicit results for the Lyman α and Balmer α lines. Title: A qualitative interpretation of the second solar spectrum of Ce ll Authors: Manso Sainz, R.; Landi Degl'Innocenti, E.; Trujillo Bueno, J. Bibcode: 2006A&A...447.1125M Altcode: 2005astro.ph.11011M This is a theoretical investigation on the formation of the linearly polarized line spectrum of ionized cerium in the sun. We calculate the scattering line polarization pattern emergent from a plane-parallel layer of Ce ii atoms illuminated from below by the photospheric radiation field, taking into account the differential pumping induced in the various magnetic sublevels by the anisotropic radiation field. We find that the line polarization pattern calculated with this simple model is in good qualitative agreement with reported observations. Interestingly, the agreement improves when some amount of atomic level depolarization is considered. We find that the best fit to the observations corresponds to the situation where the ground and metastable levels are depolarized to about one fifth of the corresponding value obtained in the absence of any depolarizing mechanism. One possibility to have this situation is that the depolarizing rate value of elastic collisions is exactly D=10^6~s-1, which is rather unlikely. Therefore, we interpret that fact as due to the presence of a turbulent magnetic field in the limit of saturated Hanle effect for the lower-levels. For this turbulent magnetic field we obtain a lower limit of 0.8 Gauss and an upper limit of 200-300 Gauss. Title: Line Formation Theory for the Multiterm Atom with Hyperfine Structure in a Magnetic Field Authors: Casini, R.; Manso Sainz, R. Bibcode: 2005ApJ...624.1025C Altcode: Within the framework of the quantum theory of polarized line formation, in the limit of complete frequency redistribution and of the collisionless regime, we derive explicit formulae describing the statistical equilibrium and the radiative emission of a multiterm atom with hyperfine structure, in the presence of an external magnetic field. The formulae we obtained for the radiative rates of the statistical equilibrium equations and for the radiative coefficients of the transfer equation for polarized radiation can be applied to investigate the formation of spectral lines for which both fine-structure and hyperfine-structure effects are important (e.g., the D1 and D2 lines of Na I in the solar atmosphere). Title: Shocks in the Quiet Solar Photosphere: A Rather Common Occurrence Authors: Socas-Navarro, H.; Manso Sainz, R. Bibcode: 2005ApJ...620L..71S Altcode: 2004astro.ph.10568S We present observations of the quiet solar photosphere in the Fe I lines at 6302 Å where at least four different spatial locations exhibit upward-directed supersonic flows. These upflows can only be detected in the circular polarization profiles as a double-peaked structure in the blue lobe of both Fe I lines. We have detected cases of either magnetic polarity in the data. The polarization signals associated with the upflows are very weak, which is probably why they had not been seen before in this type of observation. We propose that the observed flows are the signature of aborted convective collapse, similar to the case reported by Bellot Rubio et al. Our data indicate that this phenomenon occurs frequently in the quiet Sun, which means that many magnetic elements (although the fraction is still unknown) are destroyed even before they are formed completely. The spectral signatures of supersonic upflows reported here are probably present in most spectropolarimetric observations of sufficient signal-to-noise ratio and spatial resolution. Title: Concerning the Existence of a ``Turbulent'' Magnetic Field in the Quiet Sun Authors: Manso Sainz, Rafael; Landi Degl'Innocenti, Egidio; Trujillo Bueno, Javier Bibcode: 2004ApJ...614L..89M Altcode: 2004astro.ph..8360M We report on the a5F-y5Fo multiplet of Ti I and its interest for the study of ``turbulent'' magnetic fields in the quiet solar photosphere. In particular, we argue that the sizable scattering polarization signal of the 4536 Å line (whose lower and upper levels have Landé factors equal to zero), relative to the rest of the lines in the multiplet, gives direct evidence for the existence of a ubiquitous, unresolved magnetic field. We cannot determine precisely the strength of the magnetic field, but its very existence is evidenced by the differential Hanle effect technique that this Ti I multiplet provides. Title: Observation of the Molecular Zeeman Effect in the G Band Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Bianda, M.; Manso Sainz, R.; Uitenbroek, H. Bibcode: 2004ApJ...611L..61A Altcode: 2004astro.ph..7332A; 2004astro.ph..7332R Here we report on the first observational investigation of the Zeeman effect in the G band around 4305 Å. Our spectropolarimetric observations of sunspots with the Zürich Imaging Polarimeter at the Istituto Ricerche Solari Locarno confirm our previous theoretical prediction that the molecular Zeeman effect produces measurable circular polarization signatures in several CH lines that are not overlapped with atomic transitions. We also find both circular and linear polarization signals produced by atomic lines whose wavelengths lie in the G-band spectral region. Together, such molecular and atomic lines are potentially important for empirical investigations of solar and stellar magnetism. For instance, a comparison between observed and calculated Stokes profiles suggests that the thermodynamical and/or magnetic properties of the photospheric regions of sunspot umbrae are horizontally structured with a component that might be associated with umbral dots. Title: Zero-Field Dichroism in the Solar Chromosphere Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2003PhRvL..91k1102M Altcode: 2003astro.ph.11455M; 2003astro.ph.11455S; 2003PhRvL..91k1102S We explain the linear polarization of the Ca ii infrared triplet observed close to the edge of the solar disk. In particular, we demonstrate that the physical origin of the enigmatic polarizations of the 866.2 and 854.2nm lines lies in the existence of atomic polarization in their metastable 2D3/2 , 5/2 lower levels, which produces differential absorption of polarization components (dichroism). To this end, we have solved the problem of the generation and transfer of polarized radiation by taking fully into account all the relevant optical pumping mechanisms in multilevel atomic models. We argue that “zero-field” dichroism may be of great diagnostic value in astrophysics. Title: A Multilevel Radiative Transfer Program for Modeling Scattering Line Polarization and the Hanle Effect in Stellar Atmospheres Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2003ASPC..307..251M Altcode: No abstract at ADS Title: Towards the Understanding of the Second Solar Spectrum of Ti I Authors: Manso Sainz, R.; Landi Degl'Innocenti, E. Bibcode: 2003ASPC..307..425M Altcode: No abstract at ADS Title: A qualitative interpretation of the second solar spectrum of Ti I Authors: Manso Sainz, R.; Landi Degl'Innocenti, E. Bibcode: 2002A&A...394.1093M Altcode: The first theoretical investigation of the formation of the linearly polarized solar line spectrum of a complex atom, neutral titanium, is presented. The process of formation of line polarization is modeled by simply considering a plane-parallel layer of Ti I atoms illuminated from below by the photospheric radiation field, and accounting for the differential pumping induced in the various magnetic sublevels by the anisotropic radiation field. The calculated line polarization pattern is in good qualitative agreement with reported observations, thus showing that the generation of population imbalances between magnetic sublevels due to the radiation field anisotropy is the basic physical mechanism responsible for the observed polarization pattern in the Fraunhofer spectrum of Ti I. The role of depolarizing collisions on the polarized spectrum of Ti I is also investigated. Title: Remote sensing of chromospheric magnetic fields via the Hanle and Zeeman effects Authors: Trujillo Bueno, J.; Manso Sainz, R. Bibcode: 2002NCimC..25..783T Altcode: 2007arXiv0711.2584T The only way to obtain reliable empirical information on the intensity and topology of the weak magnetic fields of the quiet solar chromosphere is via the measurement and rigorous physical interpretation of polarization signals in chromospheric spectral lines. The observed Stokes profiles reported here are due to the Hanle and Zeeman effects operating in a weakly magnetized plasma that is in a state far from local thermodynamic equilibrium. The physical origin of their enigmatic linear polarization Q and U components is the existence of atomic polarization in their metastable lower-levels, which permits the action of a dichroism mechanism that has nothing to do with the transverse Zeeman effect. It is also pointed out that the population imbalances and coherences among the Zeeman sublevels of such long-lived atomic levels can survive in the presence of horizontal magnetic fields having intensities in the gauss range, and produce significant polarization signals. Finally, it is shown how the most recent developments in the observation and theoretical modelling of weak polarization signals are facilitating fundamental new advances in our ability to investigate the magnetism of the outer solar atmosphere via spectropolarimetry. Title: Selective absorption processes as the origin of puzzling spectral line polarization from the Sun Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.; Merenda, L.; Manso Sainz, R. Bibcode: 2002Natur.415..403T Altcode: 2002astro.ph..1409T Magnetic fields play a key role in most astrophysical systems, from the Sun to active galactic nuclei. They can be studied through their effects on atomic energy levels, which produce polarized spectral lines. In particular, anisotropic radiation `pumping' processes (which send electrons to higher atomic levels) induce population imbalances that are modified by weak magnetic fields. Here we report peculiarly polarized light in the HeI 10,830-Å multiplet observed in a coronal filament located at the centre of the solar disk. We show that the polarized light arises from selective absorption from the ground level of the triplet system of helium, and that it implies the presence of magnetic fields of the order of a few gauss that are highly inclined with respect to the solar radius vector. This disproves the common belief that population imbalances in long-lived atomic levels are insignificant in the presence of inclined fields of the order of a few gauss, and opens up a new diagnostic window for the investigation of solar magnetic fields. Title: Polarization by scattering processes and the Hanle effect in weakly magnetized stellar atmospheres Authors: Manso Sainz, Rafael Bibcode: 2002PhDT.......308M Altcode: No abstract at ADS Title: Metastable-level Atomic Polarization and the Diagnostic Problem of Chromospheric Magnetic Fields Authors: Trujillo Bueno, J.; Manso Sainz, R. Bibcode: 2001ASPC..248...83T Altcode: 2001mfah.conf...83T No abstract at ADS Title: Modeling the Scattering Line Polarization of the Ca II Infrared Triplet Authors: Manso Sainz, R.; Trujillo Bueno, J. Bibcode: 2001ASPC..236..213M Altcode: 2001aspt.conf..213M No abstract at ADS Title: Iterative Methods for the Non-LTE Transfer of Polarized Radiation: Resonance Line Polarization in One-dimensional Atmospheres Authors: Trujillo Bueno, Javier; Manso Sainz, Rafael Bibcode: 1999ApJ...516..436T Altcode: This paper shows how to generalize to non-LTE polarization transfer some operator splitting methods that were originally developed for solving unpolarized transfer problems. These are the Jacobi-based accelerated Λ-iteration (ALI) method of Olson, Auer, & Buchler and the iterative schemes based on Gauss-Seidel and successive overrelaxation (SOR) iteration of Trujillo Bueno and Fabiani Bendicho. The theoretical framework chosen for the formulation of polarization transfer problems is the quantum electrodynamics (QED) theory of Landi Degl'Innocenti, which specifies the excitation state of the atoms in terms of the irreducible tensor components of the atomic density matrix. This first paper establishes the grounds of our numerical approach to non-LTE polarization transfer by concentrating on the standard case of scattering line polarization in a gas of two-level atoms, including the Hanle effect due to a weak microturbulent and isotropic magnetic field. We begin demonstrating that the well-known Λ-iteration method leads to the self-consistent solution of this type of problem if one initializes using the ``exact'' solution corresponding to the unpolarized case. We show then how the above-mentioned splitting methods can be easily derived from this simple Λ-iteration scheme. We show that our SOR method is 10 times faster than the Jacobi-based ALI method, while our implementation of the Gauss-Seidel method is 4 times faster. These iterative schemes lead to the self-consistent solution independently of the chosen initialization. The convergence rate of these iterative methods is very high; they do not require either the construction or the inversion of any matrix, and the computing time per iteration is similar to that of the Λ-iteration method. Title: Quiet and Active Granulation Properties Authors: Manso Sainz, R.; Rodríguez Hidalgo, I.; Collados, M. Bibcode: 1999ASSL..239..197M Altcode: 1999msa..proc..197M The preliminary results of a classical spectroscopic analysis of a facular region at mu=0.78 of ~100 arcsec x 50 arcsec are presented. The variation with magnetic activity of several spectroscopic parameters has been studied, showing clear evidence that granulation properties are modified. Title: Thermodynamical properties of granulation in active regions. Authors: Rodríguez Hidalgo, I.; Collados, M.; Manso Sainz, R.; Barkler, J. Bibcode: 1999joso.proc..195R Altcode: A two-dimensional spectroscopic study of two solar active regions is presented. A magnetic filling factor has been defined, and a new technique to separate large and small spatial scale motions has been used. Different types of features in the fields of view have been classified according to their magnetic and convective properties, and have been analysed with varying magnetic activity. Title: The Hanle effect in 1D, 2D and 3D Authors: Manso Sainz, R.; Trujillo-Bueno, J. Bibcode: 1999ASSL..243..143M Altcode: 2007arXiv0710.5430M; 1999sopo.conf..143M This paper addresses the problem of scattering line polarization and the Hanle effect in one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) media for the case of a two-level model atom without lower-level polarization and assuming complete frequency redistribution. The theoretical framework chosen for its formulation is the QED theory of Landi Degl'Innocenti (1983), which specifies the excitation state of the atoms in terms of the irreducible tensor components of the atomic density matrix. The self-consistent values of these density-matrix elements is to be determined by solving jointly the kinetic and radiative transfer equations for the Stokes parameters. We show how to achieve this by generalizing to Non-LTE polarization transfer the Jacobi-based ALI method of Olson et al. (1986) and the iterative schemes based on Gauss-Seidel iteration of Trujillo Bueno and Fabiani Bendicho (1995). These methods essentially maintain the simplicity of the Lambda-iteration method, but their convergence rate is extremely high. Finally, some 1D and 2D model calculations are presented that illustrate the effect of horizontal atmospheric inhomogeneities on magnetic and non-magnetic resonance line polarization signals.