Conference Proceedings

@inproceedings{2023SPD....5440104M,

title = {Demonstration of Chromospheric Magnetic Mapping with CLASP2.1},

author = {David McKenzie and Ryohko Ishikawa and Javier Trujillo Bueno and Frédéric Auch`ere and Ken Kobayashi and Amy Winebarger and Ryouhei Kano and Donguk Song and Takenori Okamoto and Adam Kobelski and Laurel Rachmeler and Bart De Pontieu and Genevieve Vigil and Luca Belluzzi and Ernest Alsina Ballester and Tanaus'u Pino Aleman and Christian Bethge and Taro Sakao and Jiri Stepan},

year  = {2023},

date = {2023-10-01},

urldate = {2023-10-01},

booktitle = {AAS/Solar Physics Division Meeting},

volume = {55},

pages = {401.04},

series = {AAS/Solar Physics Division Meeting},

abstract = {Probing the magnetic nature of the Sun's chromosphere requires 

 measurement of the polarization profiles of relevant 

 magnetically sensitive spectral lines, many of which are in the 

 ultraviolet spectrum, necessitating observations above the 

 absorbing terrestrial atmosphere. The CLASP series of sounding 

 rocket missions were designed to develop and test a technique 

 for observing the Sun in ultraviolet light, and for quantifying 

 the polarization of that light. By demonstrating successful 

 measurement and interpretation of the polarization in hydrogen 

 Lyman-ensuremathalpha and the Mg II h and k spectral 

 lines, these missions are crucial steps towards routine 

 quantitative characterization of the local thermal and magnetic 

 conditions in the solar chromosphere. In the most recent 

 observations, CLASP2.1, the spectrograph slit was scanned across 

 an active region plage to acquire a two-dimensional map of 

 Stokes V/I, to demonstrate the ability of UV spectropolarimetry 

 to yield chromospheric magnetic fields over a large area. The 

 technique yields a set of simultaneous line-of-sight 

 magnetograms at multiple heights within the plage atmosphere. By 

 combining the CLASP2.1 measurements with magnetograms from 

 Hinode/SOT or SDO/HMI, a wide range of atmospheric heights are 

 mapped, from the photosphere to the upper chromosphere.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2023SPD....5440703F,

title = {Chromospheric horizontal propagating shock waves revealed by fast cadence imaging in Ca II K with DKIST's Visible Broadband Imager},

author = {Catherine Fischer and Friedrich Woeger and Thomas Rimmele and Peter Keys and Oskar Steiner and Vigeesh Gangadharan and Shahin Jafarzadeh and Jose Roberto Canivete Cuissa},

year  = {2023},

date = {2023-10-01},

urldate = {2023-10-01},

booktitle = {AAS/Solar Physics Division Meeting},

volume = {55},

pages = {407.03},

series = {AAS/Solar Physics Division Meeting},

abstract = {The Daniel K. Inouye Solar Telescope is currently acquiring first 

 science data as part of its Operations Commissioning Phase. 

 High-resolution, fast-cadence imaging in the chromospheric Ca II 

 K filter of the Visible Broadband Imager reveals signatures of 

 bright arches emanating radially from the locations of G-band 

 bright points. The G-band bright points denote small-scale 

 magnetic elements harboring strong magnetic fields. Comparison 

 with 3-D simulations suggest that the traveling bright arches 

 are acoustic waves or shock fronts, triggered by the movements 

 of magnetic elements. Inspecting several examples of the events 

 we indeed see the photospheric bright points changing their 

 appearance and position, indicating either a horizontal 

 movement, perhaps swaying, or rotation and seem to be the source 

 location for the bright arches.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2022csss.confE.125R,

title = {Simulations of the small scale surface dynamo of cool main sequence stars},

author = {F. Riva and J. R. Canivete Cuissa and O. Steiner},

doi = {10.5281/zenodo.7540550},

year  = {2022},

date = {2022-12-01},

urldate = {2022-12-01},

booktitle = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},

pages = {125},

series = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},

abstract = {A widely accepted explanation for the origin of the ubiquitous small- 

 scale magnetic field observed on the solar surface is the 

 presence of a small-scale dynamo (SSD) operating in the sub- 

 surface layers of the Sun. To shed light on the functioning of 

 this SSD, a number of numerical studies of a realistic solar 

 atmosphere have been carried out in the past two decades, 

 greatly improving our knowledge on how an SSD operates. 

 Nevertheless, virtually no studies focused on SSD action on the 

 surface of other main-sequence stars. This motivates the work 

 reported here. Hydro and magneto-hydrodynamics simulations of a 

 small partial volume encompassing the surface layers of F5V, 

 G2V, K2V, and K8V main-sequence stars are carried out with the 

 radiative magnetohydrodynamic CO5BOLD code, investigating how 

 SSD action can amplify a tiny seed magnetic field. In 

 particular, the growth rate of the magnetic to kinetic energy 

 ratio is characterized in terms of the Reynolds and magnetic 

 Reynolds numbers of the simulations, and of the effective 

 temperature and surface gravity of each star. It is found that 

 the small-scale dynamo operating in the K2V simulation is the 

 fastest in amplifying the magnetic energy among the four cases 

 considered here. However, similar saturation values of the 

 magnetic to kinetic energy ratio, of about 1%, are found at the 

 surface for all the four stars. Ultimately, we investigate the 

 spatial structure of the magnetic field resulting from SSD 

 action and how it interacts with the plasma in the stellar 

 atmospheres.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2022csss.confE...4C,

title = {Small-scale vortices in stellar atmospheres},

author = {José Roberto Canivete Cuissa and Fabio Riva and Oskar Steiner},

doi = {10.5281/zenodo.7340635},

year  = {2022},

date = {2022-11-01},

urldate = {2022-11-01},

booktitle = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},

pages = {4},

series = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},

abstract = {Over the past two decades, observations and numerical simulations 

 revealed the ubiquitous presence of small-scale vortical motions 

 in the quiet solar atmosphere. Similar swirling flows can be 

 expected to occur in other stellar atmospheres than solar. We 

 investigate the presence and properties of small-scale vortices 

 in the atmosphere of K8, K2, G2, and F5 main sequence stellar 

 models. For that purpose, we analyze numerical simulations 

 encompassing a small region around the stellar surface, ranging 

 from the top layers of the convection zone to the upper 

 photosphere. The simulations are realized with the three- 

 dimensional radiative magneto-hydrodynamical CO5BOLD code and we 

 employ a state-of-the-art automated algorithm for the 

 identification of vortices. Numerous vortical motions are 

 identified in all four stellar models. We present a statistical 

 analysis on the main properties of these swirls, namely their 

 average size, period of rotation, and number density. We find 

 that the fastest vortices are found in the coolest stellar 

 models and we derive a simple scaling law relating the effective 

 temperature of the star to the typical period of rotation of a 

 vortex. Ultimately, we want to study how swirl properties vary 

 according to the strength of the surface magnetic field, which 

 is amplified via the action of a small-scale turbulent dynamo.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{10.1117/12.2629250,

title = {Enhancing the accuracy of solar polarimetry by coalescing slow and fast modulation: method description and first performance tests},

author = {Franziska Zeuner and Daniel Gisler and Michele Bianda and Renzo Ramelli and Svetlana V. Berdyugina},

editor = {Christopher J. Evans and Julia J. Bryant and Kentaro Motohara},

url = {http://www.irsol.usi.ch/wp-content/uploads/2022/09/zeuner-etal-spie22.pdf

https://doi.org/10.1117/12.2629250

},

doi = {10.1117/12.2629250},

year  = {2022},

date = {2022-08-29},

urldate = {2022-08-29},

booktitle = {Ground-based and Airborne Instrumentation for Astronomy IX},

volume = {12184},

pages = {121840T},

publisher = {SPIE},

organization = {International Society for Optics and Photonics},

abstract = {The polarimetric zero-level accuracy of spectropolarimetric measurements with ground-based solar telescopes usually suffers from systematic telescopic and instrumental effects which are difficult to model, and therefore, cannot be easily removed during post-measurement data reduction. Here, a novel measurement method to enhance the zero-level accuracy to an unprecedented level of such compromised measurements is presented. The method is comprised of adding a slow polarization modulation (< 1 Hz) before any polarizing component of the telescope to a high-sensitivity polarimeter with fast modulation (> 1 kHz). This additional slow modulation significantly mitigates systematic instrumental polarization signals induced by the telescope and post-focus instruments such as polarimetric offsets or cross-talk between polarization states. We present the results and limitations learned from implementing the method at the 45 cm Gregory-Coudé telescope at IRSOL, Locarno. The slow modulation is performed with a low-cost zero-order retarder film mounted in front of the telescope and is combined with the fast modulating Z¨urich IMaging POLarimeter (ZIMPOL). We find that the ground zero of polarization normalized to the intensity is determined within a few 10^{−5 }. This level is consistently achieved over a wide wavelength range in the visible. An improvement of up to a few orders of magnitude for cases where the polarization offset induced by the telescope is as high as 10^{−2} is achieved. This measurement technique allows for enhancing the zero-level accuracy of solar polarimetry, which is crucial for scattering polarization measurements and their theoretical interpretations.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2022cosp...44.2551C,

title = {Small scale Alfvénic vortices in the solar atmosphere},

author = {José Roberto Canivete Cuissa and Andrea Battaglia and Oskar Steiner},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

booktitle = {44th COSPAR Scientific Assembly. Held 16-24 July},

volume = {44},

pages = {2551},

abstract = {Vortices are one of the fundamental small scale features present in the 

 solar atmosphere. They are ubiquitous at photospheric and 

 chromospheric levels and are often tightly coupled to small 

 scale surface magnetic fields. Therefore, they potentially 

 contribute to the transport of energy towards the upper layers 

 of the solar atmosphere. We study the dynamics and the 

 statistical properties of small scale swirls in realistic 

 radiative magneto-hydrodynamical simulations of the solar 

 atmosphere realized with the CO5BOLD code. To this aim, we 

 employ the swirling strength criterion and its evolution 

 equation to investigate the properties and dynamics of 9 

 identified swirl events. It is found that the studied 

 photospheric and chromospheric swirls are the plasma response to 

 self-consistently launched torsional Alfvén pulses that 

 propagate vertically in the solar atmosphere. To infer the 

 statistical properties of the swirl population in the numerical 

 simulations, we apply a new algorithm for the automatic 

 identification of vortices. This algorithm is based on a state- 

 of-the-art method that combines the rigor of mathematical 

 criteria and the global perspective of morphological techniques. 

 Compared to previous studies, our analysis reveals more and 

 smaller vortical motions in the simulated solar atmosphere. 

 Moreover, it is found that the large majority of the identified 

 swirls in the photosphere show twists in the magnetic field 

 lines compatible with torsional Alfvén waves. Therefore we 

 confirm that the small scale vortices in the lower solar 

 atmosphere are Alfvénic in nature.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2022cosp...44.2521M,

title = {Observation of a small-scale magnetic vortex associated with a chromospheric swirl: signatures of a small-scale magnetic tornado},

author = {Saida Milena Diaz Castillo and Catherine Fischer and Reza Rezaei and Oskar Steiner and Svetlana Berdyugina},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

booktitle = {44th COSPAR Scientific Assembly. Held 16-24 July},

volume = {44},

pages = {2521},

abstract = {High-resolution solar observations revealed the existence of small-scale 

 swirling vortices in chromospheric intensity maps and velocity 

 diagnostics. These events are commonly localized in the quiet 

 sun intergranular space and are often related to small-scale 

 magnetic flux concentrations at the solar surface. Frequently, 

 vortices have been observed in the vicinity of magnetic flux 

 concentrations, indicating a link between swirls and the 

 evolution of the small-scale magnetic fields. Vortices were also 

 studied with MHD numerical simulations of the solar atmosphere, 

 revealing their complexity, dynamics, and magnetic nature. In 

 particular, it has been suggested that the chromospheric 

 swirling plasma motion is due to a coherently rotating magnetic 

 field structure, which again is driven by a photospheric vortex 

 flow at its footpoint. In this contribution, we present a 

 comprehensive description of the evolution of an isolated small- 

 scale magnetic element interacting with a vortex flow, which in 

 turn is related to a chromospheric swirl. We study observations 

 taken with the CRisp Imaging SpectroPolarimeter (CRISP) 

 instrument and the CHROMospheric Imaging Spectrometer (CHROMIS) 

 at the 1m Swedish Solar Telescope (SST) in April 2019 as part of 

 a SOLARNET access program. The data were taken at quiet-Sun 

 disk-center, recording full Stokes photospheric maps in the Fe I 

 line at 617 nm, full Stokes data in the Ca II infrared triplet 

 line at 854 nm, and spectroscopic maps in the 

 Hensuremathalpha 656 nm, Ca II K 393 nm, and Ca II H 396 

 nm lines. Utilizing the multi-wavelength data and applying 

 height-dependent Stokes inversion and local correlation tracking 

 methods, we are able to analyse the magnetic field dynamics in 

 the presence of vortex structures at photospheric and 

 chromospheric layers. The temporal evolution of the magnetic 

 element shows an appreciable increase in the magnetic field 

 strength during the interaction with the vortex flow, reaching 

 kG values for a few minutes. We also find a clear evidence of a 

 Rapid Blue-shift Excursion (RBE) associated with the magnetic 

 field intensification event propagating along the chromospheric 

 vortex. In addition, we explore the polarization signatures in 

 the photosphere to reveal the intrinsic structure of the 

 magnetic element. Marginal but consistent detection of linear 

 polarization signals in the surroundings of the magnetic element 

 before intensification suggests a magnetic field torsion. Our 

 analysis indicates that we have observed a rotating magnetic 

 object reaching from the photosphere to the chromosphere, 

 resembling a small-scale magnetic tornado.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2022cosp...44.2503F,

title = {Acoustic-gravity wave propagation characteristics in 3D radiation hydrodynamic simulations of the solar atmosphere},

author = {Bernhard Fleck and Mats Carlsson and Elena Khomenko and Matthias Rempel and Fabio Riva and Oskar Steiner and Gangadharan Vigeesh},

year  = {2022},

date = {2022-07-01},

urldate = {2022-07-01},

booktitle = {44th COSPAR Scientific Assembly. Held 16-24 July},

volume = {44},

pages = {2503},

abstract = {There has been tremendous progress in the degree of realism of three- 

 dimensional radiation magneto-hydrodynamic simulations of the 

 solar atmosphere in the past decades. Four of the most 

 frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D, 

 and MURaM. Here we test and compare the wave propagation 

 characteristics in model runs from these four codes by measuring 

 the dispersion relation of acoustic-gravity waves at various 

 heights. We find considerable differences between the various 

 models.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2021AAS...23810603M,

title = {Mapping of Solar Magnetic Fields from the Photosphere to the Top of the Chromosphere with CLASP2},

author = {D. McKenzie and R. Ishikawa and J., Trujillo Bueno and F. Auchere and T. Pino Aleman and T. Okamoto and R. Kano and D. Song and M. Yoshida and L. Rachmeler and K. Kobayashi and N. Narukage and M. Kubo and S. Ishikawa and H. Hara and Y. Suematsu and T. Sakao and C. Bethge and B., De Pontieu and G. Vigil and A. Winebarger and E., Alsina Ballester and L. Belluzzi and J. Stepan and A., Asensio Ramos and M. Carlsson and J. Leenaarts},

year  = {2021},

date = {2021-06-01},

urldate = {2021-06-01},

booktitle = {American Astronomical Society Meeting Abstracts},

volume = {53},

pages = {106.03},

series = {American Astronomical Society Meeting Abstracts},

abstract = {Coronal heating, chromospheric heating, and the heating & acceleration 

 of the solar wind, are well-known problems in solar physics. 

 Additionally, knowledge of the magnetic energy that powers solar 

 flares and coronal mass ejections, important drivers of space 

 weather, is handicapped by imperfect determination of the 

 magnetic field in the sun's atmosphere. Extrapolation of 

 photospheric magnetic measurements into the corona is fraught 

 with difficulties and uncertainties, partly due to the vastly 

 different plasma beta between the photosphere and the corona. 

 Better results in understanding the coronal magnetic field 

 should be derived from measurements of the magnetic field in the 

 chromosphere. To that end, we are pursuing quantitative 

 determination of the magnetic field in the chromosphere, where 

 plasma beta transitions from greater than unity to less than 

 unity, via ultraviolet spectropolarimetry. The CLASP2 mission, 

 flown on a sounding rocket in April 2019, succeeded in measuring 

 all four Stokes polarization parameters in UV spectral lines 

 formed by singly ionized Magnesium and neutral Manganese. 

 Because these ions produce spectral lines under different 

 conditions, CLASP2 thus was able to quantify the magnetic field 

 properties at multiple heights in the chromosphere 

 simultaneously, as shown in the recent paper by Ishikawa et al. 

 In this presentation we will report the findings of CLASP2, 

 demonstrating the variation of magnetic fields along a track on 

 the solar surface and as a function of height in the 

 chromosphere; and we will illustrate what is next for the CLASP 

 missions and the demonstration of UV spectropolarimetry in the 

 solar chromosphere.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{9118669,

title = {Solar Radio Observation Using CALLISTO at the USO/PRL, Udaipur},

author = {K. Upadhyay, B. Joshi, P. K. Mitra, R. Bhattacharyya, D. Oberoi and C. Monstein},

url = {http://arxiv.org/abs/2007.01655},

doi = {10.1109/IMaRC45935.2019.9118669},

year  = {2019},

date = {2019-12-01},

booktitle = {2019 IEEE MTT-S International Microwave and RF Conference (IMARC)},

pages = {1-6},

abstract = {This paper presents a detailed description of various subsystems of CALLISTO solar radio spectrograph installed at the USO/PRL. In the front-end system, a log periodic dipole antenna (LPDA) is designed for the frequency range of 40-900 MHz. In this paper LPDA design, its modifications, and simulation results are presented. We also present some initial observations taken by CALLISTO at Udaipur.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..519..113S,

title = {Polarized Line Formation with Incomplete Paschen-Back Effect and Partial Frequency Redistribution},

author = {M. {Sampoorna} and K.N. {Nagendra} and K. {Sowmya} and J.O. {Stenflo} and L.S. {Anusha}},

editor = {K {Werner} and C {Stehle} and T {Rauch} and T {Lanz}},

year  = {2019},

date = {2019-07-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {519},

pages = {113},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {Quantum interference between the hyperfine structure states is known to 

 depolarize the cores of some of the lines in the linearly 

 polarized spectrum of the Sun (the Second Solar Spectrum). The 

 presence of external magnetic fields in the line forming regions 

 modify these signatures through the Hanle, Zeeman, and 

 incomplete/ complete Paschen-Back effects (PBE), depending on 

 the strength of the magnetic field. In an earlier paper, Sowmya 

 et al. (2014) derived the relevant collisionless partial 

 frequency redistribution (PFR) matrix for scattering on a two- 

 level atom with hyperfine structure splitting (HFS) and in the 

 presence of arbitrary strength magnetic fields (including the 

 PBE regime). In the present paper we solve the problem of 

 polarized line transfer in a magnetized atmosphere, including 

 this PFR matrix. For this purpose, we apply a scattering 

 expansion method which is based on orders of scattering 

 approach. We present the results on the combined effects of PBE 

 and PFR on the polarized line profiles using the atomic 

 parameters relevant to the Na I D$_2$ line.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..519..109S,

title = {Effects of Angle-Dependent Partial Frequency Redistribution on Polarized Line Profiles},

author = {M. {Sampoorna} and K.N. {Nagendra} and H. {Frisch} and J.O. {Stenflo}},

editor = {K {Werner} and C {Stehle} and T {Rauch} and T {Lanz}},

year  = {2019},

date = {2019-07-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {519},

pages = {109},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {Scattering of the solar limb-darkened radiation field on atoms and 

 molecules produces linearly polarized spectrum of the Sun 

 (Second Solar Spectrum). Partial frequency redistribution (PFR) 

 plays a fundamental role in shaping the wings of linearly 

 polarized profiles of strong resonance lines. Here we present 

 the effects of the angle-dependent (AD) PFR on resonance 

 polarization both in the presence and absence of magnetic 

 fields. We consider scattering on a two-level atom with 

 unpolarized lower level, and a one-dimensional isothermal 

 atmosphere.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..283R,

title = {Measurement of the Evolution of the Magnetic Field of the Quiet Photosphere over a Solar Cycle},

author = {R {Ramelli} and M {Bianda} and S {Berdyugina} and L {Belluzzi} and L {Kleint}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0283.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {283},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The solar photosphere is filled by magnetic fields tangled at scales much smaller than the resolution capability of solar telescopes. These hidden magnetic fields can be investigated via the Hanle effect. In 2007, we started a synoptic program to explore whether the magnetic flux of the quiet photosphere varies with the solar cycle. For this purpose we applied a differential Hanle effect technique based on observations of scattering polarization in C2 molecular lines around 514.0 nm, taken with a cadence of approximately one month. Our results now span almost one complete solar cycle.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..223B,

title = {Second Solar Spectrum Observations with ZIMPOL},

author = {M {Bianda} and R {Ramelli} and D {Gisler} and L {Belluzzi} and E ~S {Carlin}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0223.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {223},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The observational activity of IRSOL takes advantage of the high-precision instrumentation available, and of the possibility to carry out programs requiring observing time spread over weeks or months. Particular attention is paid to scattering polarization signals modified by the Hanle effect in spectral lines. Several programs at IRSOL are also aimed at getting the technical know-how necessary to exploit the potentialities of the new generation of large-aperture solar telescopes, which will provide observations with unprecedented spatial and temporal resolution without sacrificing spectropolarimetric sensitivity. In this contribution, we provide a brief description of some projects that are presently carried out at IRSOL.

},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..287R,

title = {Atlas of the Solar Intensity Spectrum and its Center-to-Limb Variation},

author = {R {Ramelli} and M {Bianda} and M {Setzer} and M {Enegelhard} and F {Paglia} and J O {Stenflo} and G {Küveler} and R {Plewe}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0287.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {287},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The solar limb darkening function is well known and is widely employed in models of the solar atmosphere. However, there has been a lack of systematic spectrally resolved measurements. Therefore we recently decided to start an observing campaign with the Gregory-Coudé Telescope at IRSOL in Locarno in order to produce a spectral atlas obtained at 10 different heliocentric angles θ, chosen so that μ = cos θ covers the interval from 0.1 to 1.0 in step of 0.1. The measurements carried out till now include the spectral range from 439 nm to 666 nm. The collected data provide information about the anisotropy of the emergent radiation field on the solar surface, allowing a better modeling of the Second Solar Spectrum. In addition the data give observational constraints that should be taken into account when modeling the solar atmosphere.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..305I,

title = {Comparison of Scattering Polarization Signals Observed by CLASP: Possible Indication of the Hanle Effect},

author = {R {Ishikawa} and J {Trujillo Bueno} and H {Uitenbroek} and M {Kubo} and S {Tsuneta} and M {Goto} and R {Kano} and N {Narukage} and T {Bando} and Y {Katsukawa} and S {Ishikawa} and G {Giono} and Y {Suematsu} and H {Hara} and T {Shimizu} and T {Sakao} and A {Winebarger} and K {Kobayashi} and J {Cirtain} and P {Champey} and F {Auch{`e}re} and J {{Š}t{ě}pán} and L {Belluzzi} and A {Asensio Ramos} and R {Manso Sainz} and B {De Pomtieu} and K {Ichimoto} and M {Carlsson} and R {Casini}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0305.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {305},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {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-ensuremathalpha (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-ensuremathalpha 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-ensuremathalpha line center signal, for which the 

 critical field strength (B$_Ħ$) for the onset of the Hanle 

 effect is 53 G, (b) the Lyman-ensuremathalpha wing, which 

 is insensitive to the Hanle effect, and (c) the Si III line, whose B$_Ħ$ = 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-ensuremathalpha wing, 

 Lyman-ensuremathalpha center, and Si III line. The U/I 

 signal in the Lyman-ensuremathalpha 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-ensuremathalpha 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. 

 textbackslashtextbackslashThis work, presented in an oral 

 contribution at this Workshop, has been published on The 

 Astrophysical Journal (Ishikawa et al. 2017).},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..133J,

title = {Numerical Methods for the Radiative Transfer Equation of Polarized Light},

author = {G {Janett} and O {Steiner} and L {Belluzzi}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0133.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {133},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The quest of the ``best formal solver'' available is still open and the 

 lack of a clear comparison between the different numerical 

 methods proposed by the community does not facilitate a 

 conclusion. This work presents a reference paradigm for the 

 characterization of formal solvers, based on the concepts of 

 order of accuracy, stability and computational cost. This 

 overview aims to facilitate the comprehension of the advantages 

 and weaknesses of the already existing formal solvers and of 

 those yet to come.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..119A,

title = {The Transfer of Resonance Line Polarization with PRD in the General Hanle-Zeeman Regime},

author = {E {Alsina Ballester} and L {Belluzzi} and J {Trujillo Bueno}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0119.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {119},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {We present numerical radiative transfer calculations of the four Stokes 

 parameters of the radiation emerging from one-dimensional model 

 atmospheres. In this investigation we account for the impact of 

 partial frequency redistribution (PRD) in scattering and the 

 joint action of the Hanle and Zeeman effects. Strong resonance 

 lines of interest for chromospheric magnetic field diagnostics 

 have been considered, namely the Ca I line at 4227 Å and 

 the Mg II k line at 2795 Å. The Stokes profiles of these 

 lines have been obtained by considering two-level atomic models, 

 both in the absence and in the presence of magnetic fields. We 

 draw attention to the fact that the magneto-optical terms of the 

 transfer equations for Stokes Q and U are responsible for an 

 interesting and previously unnoticed magnetic sensitivity of 

 their scattering polarization profiles beyond the Doppler core. 

 This important discovery contributes to paint a more detailed 

 picture of the influence of relatively weak magnetic fields on 

 the observable linear polarization signals of strong 

 chromospheric lines, highlighting the importance of a PRD 

 treatment for such lines.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526...29L,

title = {Relaxation Phenomena Due to Collisions with Neutral Perturbers in Hyperfine Structure Multiplets},

author = {E {Landi Degl'Innocenti} and L {Belluzzi}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0029.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {29},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {A connection is established between the depolarizing rates, due to 

 collisions with neutral perturbers, of the statistical tensors 

 of a hyperfine structure multiplet and those of the statistical 

 tensors of the parent fine structure level. This connection is 

 described by a simple equation involving a 12-j symbol of the 

 second kind. An application is performed to derive an analytical 

 expression for the scattering matrix of a hyperfine structured 

 two-level atom in the presence of collisions and a magnetic 

 field. Numerical results are presented.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2019ASPC..526..361M,

title = {CLASP2: The Chromospheric LAyer Spectro-Polarimeter},

author = {D ~E {McKenzie} and R {Ishikawa} and J {Trujillo Bueno} and F {Auchére} and L ~A {Rachmeler} and M {Kubo} and K {Kobayashi} and A ~R {Winebarger} and C ~W {Bethge} and N {Narukage} and R {Kano} and S {Ishikawa} and B {de Pontieu} and M {Carlsson} and M {Yoshida} and L {Belluzzi} and J {{Š}t{ě}pán} and T {del Pino Alemán} and E {Alsina Ballester} and A {Asensio Ramos}},

editor = {L {Belluzzi} and R {Casini} and M {Romoli} and J {Trujillo Bueno}},

url = {http://aspbooks.org/custom/publications/paper/526-0361.html},

year  = {2019},

date = {2019-05-01},

booktitle = {Astronomical Society of the Pacific Conference Series},

volume = {526},

pages = {361},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The hydrogen Lyman-ensuremathalpha line at 121.6 nm and the Mg k 

 line at 279.5 nm are especially relevant for deciphering the 

 magnetic structure of the chromosphere since their line-center 

 signals are formed in the chromosphere and transition region, 

 with unique sensitivities to magnetic fields. We propose the 

 Chromospheric LAyer Spectro-Polarimeter (CLASP2), to build upon 

 the success of the first CLASP flight, which measured the linear 

 polarization in H I Lyman-ensuremathalpha. The existing 

 CLASP instrument will be refitted to measure all four Stokes 

 parameters in the 280 nm range, including variations due to the 

 anisotropic radiation pumping, the Hanle effect, and the Zeeman 

 effect.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2017SPD....4811010R,

title = {CLASP2: The Chromospheric LAyer Spectro-Polarimeter},

author = {L {Rachmeler} and D {E McKenzie} and R {Ishikawa} and J {Trujillo Bueno} and F {Auchère} and K {Kobayashi} and A {Winebarger} and C {Bethge} and R {Kano} and M {Kubo} and D {Song} and N {Narukage} and S {Ishikawa} and B {De Pontieu} and M {Carlsson} and M {Yoshida} and L {Belluzzi} and J {Stepan} and T {del Pino Alemná} and E A {Ballester} and A {Asensio Ramos}},

url = {http://adsabs.harvard.edu/abs/2017SPD....4811010R},

year  = {2017},

date = {2017-08-01},

booktitle = {AAS/Solar Physics Division Meeting},

volume = {48},

pages = {110.10},

series = {AAS/Solar Physics Division Meeting},

abstract = {We present the instrument, science case, and timeline of the CLASP2 

sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha 

Spectro-Polarimeter) sounding rocket flight in 2015 resulted in the 

first-ever linear polarization measurements of solar hydrogen 

Lyman-alpha line, which is sensitive to the Hanle effect and can be used 

to constrain the magnetic field and geometric complexity of the upper 

chromosphere. Ly-alpha is one of several upper chromospheric lines that 

contain magnetic information. In the spring of 2019, we will re-fly the 

modified CLASP telescope to measure the full Stokes profile of Mg II h 

amp k near 280 nm. This set of lines is sensitive to the upper 

chromospheric magnetic field via both the Hanle and the Zeeman effects. },

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2017MmSAI..88...54V,

title = {On the effect of vorticity on the propagation of internal gravity waves.},

author = {G {Vigeesh} and O {Steiner} and F {Calvo} and M {Roth}},

year  = {2017},

date = {2017-05-01},

journal = {Mem. Societa Astronomica Italiana},

volume = {88},

pages = {54},

abstract = {We compare different models of solar surface convection to study 

vorticity and how it can influence the propagation of internal gravity 

waves. We conclude that simulations performed with higher grid 

resolution may have a reduced gravity wave flux in the lower part of the 

atmosphere due to strong vorticity. We also show that the vertical 

extent of the allowed region of propagation depends on the magnetic 

field inclination. },

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2017MmSAI..88...37S,

title = {CO5BOLD for MHD: progresses and deficiencies .},

author = {O. Steiner and F. Calvo and R. Salhab and G.Vigeesh},

year  = {2017},

date = {2017-01-01},

journal = {Mem. Societa Astronomica Italiana},

volume = {88},

pages = {37},

abstract = {The magnetohydrodynamics module of CO5BOLD has been steadily improved 

over the past decade and has been used for various solar and stellar 

physical applications. We give an overview of current work with it and 

of remaining and newly emerged shortcomings. },

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2016CEAB...40...79W,

title = {The Electron Density in a Quiescent Prominence},

author = {Wiehr, E. Stellmacher, G. and Bianda, M.},

year  = {2016},

date = {2016-02-01},

journal = {Central European Astrophysical Bulletin},

volume = {40},

pages = {79-85},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2016SPD....47.1208S,

title = {The Sun's spectrally resolved center-to-limb variation},

author = {Stenflo, J.O.},

year  = {2016},

date = {2016-01-01},

booktitle = {AAS/Solar Physics Division Meeting},

volume = {47},

pages = {12.08},

series = {AAS/Solar Physics Division Meeting},

abstract = {The center-to-limb variation (CLV) of the Sun's continuous spectrum is 

well known and has served as a major observational constraint on models 

of the solar atmosphere. The CLV however also varies dramatically with 

wavelength inside each spectral line. Here we report on two new atlases 

that show the properties of the CLV with high spectral resolution. One 

is a fully resolved spectral atlas from 4084 to 9950 AA of the 

ratio between the near limb spectrum, at 10 arcsec inside the limb, and 

the disk center spectrum, both recorded with the FTS at NSO/Kitt Peak. 

The other atlas gives the same kind of information but covers the whole 

range of limb distances by giving the ratio spectra for the nine $mu$ 

positions 0.1, 0.2, łdots, 0.9. This set of nine atlases for different 

$mu$ have been recorded over the last couple of years with the solar 

facility at IRSOL (Istituto Ricerche Solari Locarno) in Switzerland. We 

find that the CLV is spectrally as richly structured as the ordinary 

intensity spectrum, but the structuring is different and contains 

diagnostic information that is not contained in the intensity spectrum. 

Here we illustrate the properties of the new spectral structures and 

discuss what they mean. },

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..372S,

title = {A revisit to model the Cr i triplet at 5204-5208 Å and the Ba ii D2 line at 4554 Å in the Second Solar Spectrum},

author = {Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Bianda, M. and Sampoorna, M. and Ramelli, R.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..372S},

doi = {10.1017/S1743921315005074},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

booktitle = {Polarimetry},

volume = {305},

pages = {372-376},

series = {IAU Symposium},

abstract = {In our previous attempt to model the Stokes profiles of the Cr i triplet at 5204-5208 Å and the Ba ii D2 at 4554 Å, we found it necessary to slightly modify the standard FAL model atmospheres to fit the observed polarization profiles. In the case of Cr i triplet, this modification was done to reduce the theoretical continuum polarization, and in the case of Ba ii D2, it was needed to reproduce the central peak in Q/I. In this work, we revisit both these cases using different standard model atmospheres whose temperature structures closely resemble those of the modified FAL models, and explore the possibility of synthesizing the line profiles without the need for small modifications of the model atmosphere.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..154S,

title = {Paschen-Back effect involving atomic fine and hyperfine structure states},

author = {Sowmya, K. and Nagendra, K.N. and Sampoorna, M. and Stenflo, J.O.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..154S},

doi = {10.1017/S1743921315004688},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

booktitle = {Polarimetry},

volume = {305},

pages = {154-158},

series = {IAU Symposium},

abstract = {The linear polarization in spectral lines produced by coherent scattering is significantly modified by the quantum interference between the atomic states in the presence of a magnetic field. When magnetic fields produce a splitting which is of the order of or greater than the fine or hyperfine structure splittings, we enter the Paschen-Back effect (PBE) regime, in which the magnetic field dependence of the Zeeman splittings and transition amplitudes becomes non-linear. In general, PBE occurs for sufficiently strong fields when the fine structure states are involved and for weak fields in the case of hyperfine structure states. In this work, we apply the recently developed theory of PBE in the atomic fine and hyperfine structure states including the effects of partial frequency redistribution to the case of Li i 6708 Å doublet. We explore the signatures of PBE in a single scattering event and their applicability to the solar magnetic field diagnostics.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..146C,

title = {Chromospheric diagnosis with forward scattering polarization},

author = {Carlin, E.S.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..146C},

doi = {10.1017/S1743921315004676},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

booktitle = {Polarimetry},

volume = {305},

pages = {146-153},

series = {IAU Symposium},

abstract = {Is it physically feasible to perform chromospheric diagnosis using spatial maps of scattering polarization at the solar disk center? To investigate it we synthesized polarization maps (in 8542 Angstroms) resulting from MHD solar models and NLTE radiative transfer calculations that consider Hanle effect and vertical macroscopic motions. After explaining the physical con- text of forward scattering and presenting our results, we arrive at the definition of Hanle polarity inversion lines. We show how such features can give support for a clearer chromospheric diagnosis in which the magnetic and dynamic effects in the scattering polarization could be disentangled},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..136S,

title = {Coherence structure of D1 scattering},

author = {Stenflo, J.O.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..136S},

doi = {10.1017/S1743921315004664},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

booktitle = {Polarimetry},

volume = {305},

pages = {136-145},

series = {IAU Symposium},

abstract = {The extensive literature on the physics of polarized scattering may give the impression that we have a solid theoretical foundation for the interpretation of spectro-polarimetric data. This theoretical framework has however not been sufficiently tested by experiments under controlled conditions. While the solar atmosphere may be viewed as a physics laboratory, the observed solar polarization depends on too many environmental factors that are beyond our control. The existence of a symmetric polarization peak at the center of the solar Na D1 line has remained an enigma for two decades, in spite of persistent efforts to explain it with available quantum theory. A decade ago a laboratory experiment was set up to determine whether this was a problem for solar physics or quantum physics. The experiment revealed a rich polarization structure of D1 scattering, although available quantum theory predicted null results. It has now finally been possible to formulate a well-defined and self-consistent extension of the theory of quantum scattering that can reproduce in great quantitative detail the main polarization structures that were found in the laboratory experiment. Here we give a brief overview of the new physical ingredients that were missing before. The extended theory reveals that multi-level atomic systems have a far richer coherence structure than previously believed.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..127T,

title = {Atomic Scattering Polarization. Observations, Modeling, Predictions},

author = {Trujillo Bueno, J. and Del Pino Alemán, T. and Belluzzi, L.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..127B},

doi = {10.1017/S1743921315004652},

year  = {2015},

date = {2015-10-01},

urldate = {2015-10-01},

booktitle = {Polarimetry},

volume = {305},

pages = {127-135},

series = {IAU Symposium},

abstract = {This paper highlights very recent advances concerning the identification of new mechanisms that introduce polarization in spectral lines, which turn out to be key for understanding some of the most enigmatic scattering polarization signals of the solar visible spectrum. We also show a radiative transfer prediction on the scattering polarization pattern across the Mg ii h & k lines, whose radiation can only be observed from space},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2015IAUS..305..381S,

title = {Modeling the center-to-limb variation of the Ca i 4227 Å line using FCHHT models},

author = {Supriya, H.D. and Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Bianda, M. and Ravindra, B. and Ramelli, R. and Anusha, L.S.},

editor = {Nagendra, K.N. and Bagnulo, S. and Centeno, R. and Martínez González, M.J.},

url = {http://adsabs.harvard.edu/abs/2015IAUS..305..381S},

doi = {10.1017/S1743921315005098},

year  = {2015},

date = {2015-01-01},

urldate = {2015-01-01},

booktitle = {Polarimetry},

volume = {305},

pages = {381-386},

series = {IAU Symposium},

abstract = {The Ca i 4227 Å is a chromospheric line exhibiting the largest degree of linear polarization near the limb, in the visible spectrum of the Sun. Modeling the observations of the center-to-limb variations (CLV) of different lines in the Second Solar Spectrum helps to sample the height dependence of the magnetic field, as the observations made at different lines of sight sample different heights in the solar atmosphere. Supriya et al. (2014) attempted to simultaneously model the CLV of the (I, Q/I) spectra of the Ca i 4227 Å line using the standard 1-D FAL model atmospheres. They found that the standard FAL model atmospheres and also any appropriate combination of them, fail to simultaneously fit the observed Stokes (I, Q/I) profiles at all the limb distances (μ) satisfying at the same time all the observational constraints. This failure of 1-D modeling approach can probably be overcome by using multi-dimensional modeling which is computationally expensive. To eliminate an even wider choice of 1-D models, we attempt here to simultaneously model the CLV of the (I, Q/I) spectra using the FCHHT solar model atmospheres which are updated and recent versions of the FAL models. The details of our modeling efforts and the results are presented.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014ASPC..489..213S,

title = {The Role of Quantum Interference and Partial Redistribution in the Solar Ba II D2 4554 Å Line},

author = {Smitha, H.N. and Nagendra, K.N. and Stenflo, J.O. and Sampoorna, M.},

editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},

url = {http://adsabs.harvard.edu/abs/2014ASPC..489..213S},

year  = {2014},

date = {2014-10-01},

urldate = {2014-10-01},

booktitle = {Solar Polarization 7},

volume = {489},

pages = {213},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The Ba <font size=2>II D2 line at 4554 Å is a good example, where the F-state interference effects due to the odd isotopes produce polarization profiles, which are very different from those of the even isotopes that do not exhibit F-state interference. It is therefore necessary to account for the contributions from the different isotopes to understand the observed linear polarization profiles of this line. In this paper we present radiative transfer modeling with partial frequency redistribution, which is shown to be essential to model this line. This is because complete frequency redistribution cannot reproduce the observed wing polarization. We present the observed and computed Q/I profiles at different limb distances. The theoretical profiles strongly depend on limb distance (μ) and the model atmosphere which fits the limb observations fails at other μ positions.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014ASPC..489..167B,

title = {Solar Cycle Variations of the Second Solar Spectrum},

author = {Bianda, M. and Ramelli, R. and Gisler, D. and Stenflo, J.O.},

editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},

url = {https://www.irsol.usi.ch/data/Papers/SPW7-bianda_4.pdf},

year  = {2014},

date = {2014-10-01},

urldate = {2014-10-01},

booktitle = {Solar Polarization 7},

volume = {489},

pages = {167},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The average strength of the spatially unresolved turbulent magnetic field in the Sun's photosphere can be measured with the Hanle effect. The possible variations of this average value over time scales of a solar cycle is the topic of an ongoing synoptic program at IRSOL that was started in 2008. The scattering polarization of C2 molecular lines around 5140 Å is regularly measured, typically once per month. These lines allow the application of the differential Hanle effect to determine the turbulent field strength. Here we report about the behavior of the determined field strength during the beginning active phase of the solar cycle and about our intention to start a new synoptic program based on the Hanle effect in the Sr I 4607 Å line, with which turbulent field strengths are found that are an order of magnitude larger than those determined with the molecular C2 lines. These synoptic programs allow us to explore the nature of the magnetic fields at the small-scale end of the magnetic scale spectrum and to determine the possible role of a local dynamo for the generation of these fields.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014ASPC..489...99L,

title = {Theoretical Schemes for the Interpretation of Solar Polarimetric Observations: An Overview and Some New Ideas},

author = {Landi Degl'Innocenti, E. and Belluzzi, L.},

editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},

url = {https://www.irsol.usi.ch/data/Papers/landi_belluzzi_spw7.pdf},

year  = {2014},

date = {2014-10-01},

urldate = {2014-10-01},

booktitle = {Solar Polarization 7},

volume = {489},

pages = {99},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {The theoretical scheme based on the density matrix formalism, and self-consistently derived from the principles of Quantum Electrodynamics, is presently one of the most solid frameworks for the interpretation of solar polarimetric observations. This scheme has been highly successful, mainly for the interpretation of polarimetric signals that can be described in the so-called limit of complete frequency redistribution (CRD). However, it suffers from the severe limitation that partial frequency redistribution (PRD) effects cannot be accounted for. The metalevel theory can handle PRD effects, but all the attempts for its generalization to account consistently for collisions and lower-level coherences have failed. The redistribution matrix approach is very suitable for taking PRD effects into account. However, it can consistently describe only two-level atoms with unpolarized lower level. New heuristic approaches have been proposed for treating two-term atoms, but they are based on rather crude approximations and their validity and physical consistency are far from being firmly established. Some few reflections that may lead to the establishment of a self-consistent set of equations, fully derived from first principles, are put forward. These reflections are based on the introduction of the Fourier transform of the density matrix.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014ASPC..489...21D,

title = {Conversion of the 6302 / 6301 Stokes V Line Ratio to the 5250 / 5247 Ratio for the Diagnostics of Quiet-Sun Magnetic Fields},

author = {Demidov, M.L. and Stenflo, J.O. and Bianda, M. and Ramelli, R.},

editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},

url = {http://adsabs.harvard.edu/abs/2014ASPC..489...21D},

year  = {2014},

date = {2014-10-01},

urldate = {2014-10-01},

booktitle = {Solar Polarization 7},

volume = {489},

pages = {21},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {Observations in the "green" spectral lines Fe I 5247.06 and 5250.22 Å and in the "red" lines Fe I 6301.50 and 6302.50 Å are widely used to explore the properties of solar magnetic fields. The green line pair was introduced in 1973 as part of the line-ratio technique, which has been a powerful tool for investigations of intrinsic magnetic field properties at spatially unresolved scales (magnetic flux tubes with kG strengths). The red line pair has recently played a major role for magnetic-field diagnostics due to the large amount of high-quality data provided by the Hinode space observatory. These red lines however differ not only in the values of their Landé factors, but also in their line-formation properties, with the consequence that the magnetic-field information in their line ratio gets tangled up with thermodynamic effects. In contrast, as the green Fe I 5247.06 and 5250.22 Å lines differ only in their Landé factors, the magnetic field effects become cleanly separated from the thermodynamics, which allows the intrinsic magnetic field parameters to be extracted without ambiguties. The red and green line-ratio values are however statistically correlated. By determining the statistical regression function that relates them, it becomes possible to convert the "contaminated" and ambiguous red line ratio into the green line ratio, with which a reliable direct interpretation in terms of intrinsic field strengths is possible. To determine how the two line ratios are related we have made Stokesmeter observations in these four spectral lines with two solar instruments equipped with high-precision spectropolarimeters, ZIMPOL-3 at IRSOL (Locarno, Switzerland), and the STOP telescope at the Sayan Solar Observatory (Irkutsk, Russia). Most of the obtained results are based on IRSOL observations of quiet-sun magnetic fields. In the case of STOP the full-disk magnetograms of large-scale solar magnetic fields are analyzed. A major advantage at IRSOL is the possibility to observe the green and red line pairs simultaneously on the same CCD chip. We have determined how the two line ratios decrease with increasing Stokes V amplitude and increase with increasing distance from disk center. The relation that allows us to convert the observed values for the red line ratio into the corresponding values for the green line ratio has been found and given in analytical form.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014ASPC..489....3S,

title = {Nature of Quiet-Sun Magnetic Fields},

author = {Stenflo, J.O.},

editor = {Nagendra, K.N. and Stenflo, J.O. and Qu, Q. and Sampoorna, M.},

url = {http://adsabs.harvard.edu/abs/2014ASPC..489....3S},

year  = {2014},

date = {2014-10-01},

urldate = {2014-10-01},

booktitle = {Solar Polarization 7},

volume = {489},

pages = {3},

series = {Astronomical Society of the Pacific Conference Series},

abstract = {Since the magnetic structuring continues to scales of order 10-100 m, far smaller than can possibly be resolved, and since the polarization signals are weak on the quiet Sun, one needs to apply robust diagnostic techniques that do not get biased by measurement noise, are independent of telescope resolution, and have minimal model dependence, in order to reliably determine the intrinsic properties of quiet-sun magnetic fields. Such techniques make use of ensemble averages as the observable signatures of the spatially unresolved domain. Here we show how such concepts are applied to derive the field strengths, sizes, and angular distributions from the observed Hanle depolarization and from the symmetry properties of the transverse Zeeman effect.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2014SPIE.9147E..3GR,

title = {First successful deployment of the ZIMPOL-3 system at the GREGOR telescope},

author = {Ramelli, R. and Gisler, D. and Bianda, M. and Bello González, N. and Berdyugina, S. and Soltau, D.},

url = {https://www.irsol.usi.ch/data/Papers/ramelli-spie14.pdf},

doi = {10.1117/12.2056934},

year  = {2014},

date = {2014-01-01},

urldate = {2014-01-01},

booktitle = {Ground-based and Airborne Instrumentation for Astronomy V},

volume = {9147},

pages = {91473G},

series = {procspie},

abstract = {Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is routinely used at IRSOL, Locarno. The fast modulation allows to "freeze" intensity variations due to seeing, and to achieve a polarimetric sensitivity below 10-5 if the photon statistics is large enough. In October 2013 the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by the authors for the first time in this occasion},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2013IAUS..294..119S,

title = {Nature of the solar dynamo at small scales},

author = {Stenflo, J.O.},

editor = {Kosovichev, A.G. and de Gouveia Dal Pino, E. and Yan, Y.},

url = {http://adsabs.harvard.edu/abs/2013IAUS..294..119S},

doi = {10.1017/S1743921313002342},

year  = {2013},

date = {2013-07-01},

urldate = {2013-07-01},

booktitle = {Solar and Astrophysical Dynamos and Magnetic Activity},

volume = {294},

pages = {119-130},

series = {IAU Symposium},

abstract = {It is often claimed that there is not only one, but two different types of solar dynamos: the one that is responsible for the appearance of sunspots and the 11-yr cycle, frequently referred to as the ``global dynamo'', and a statistically time-invariant dynamo, generally referred to as the ``local dynamo'', which is supposed to be responsible for the ubiquitous magnetic structuring observed at small scales. Here we examine the relative contributions of these two qualitatively different dynamos to the small-scale magnetic flux, with the following conclusion: The local dynamo does not play a significant role at any of the spatially resolved scales, nearly all the small-scale flux, including the flux revealed by Hinode, is supplied by the global dynamo. This conclusion is reached by careful determination of the Sun's noise-corrected basal magnetic flux density while making use of a flux cancellation function determined from Hinode data. The only allowed range where there may be substantial or even dominating contributions from a local dynamo seems to be the scales below about 10 km, as suggested by observations of the Hanle depolarization effect in atomic spectral lines. To determine the fraction of the Hanle depolarization that may be due to the action of a local dynamo, a synoptic program is being initiated at IRSOL (Istituto Ricerche Solari Locarno).},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2013MmSAI..84..413B,

title = {The project of installing a ZIMPOL 3 polarimeter at GREGOR in Tenerife},

author = {Bianda, M. and Ramelli, R. and Stenflo, J. and Berdyugina, S. and Gisler, D. and Defilippis, I. and Bello González, N.},

year  = {2013},

date = {2013-01-01},

urldate = {2013-01-01},

journal = {Mem. Societa Astronomica Italiana},

volume = {84},

pages = {413},

abstract = {A project of collaboration between Kiepenheuer Institut für Sonnenphysik, KIS, and Istituto Ricerche Solari Locarno, IRSOL, includes the installation of a ZIMPOL_3 high resolution polarimeter at the 1.5 meter aperture solar telescope GREGOR in Tenerife. Important scientific topics are expected to be investigated, in particular in the case of events showing faint amplitude polarization signatures like scattering polarization effects, and the Hanle effect. This project has also a technical importance, this combination can be used as test bench for future polarimeters to be installed on the new generation solar telescopes.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2013CEAB...37..487W,

title = {The Hot Skin of Prominence Structures},

author = {Wiehr, E. and Stellmacher, G. and Ramelli, R. and Bianda, M.},

url = {https://www.irsol.usi.ch/data/Papers/HvarVortrag12.pdf},

year  = {2013},

date = {2013-01-01},

urldate = {2013-01-01},

journal = {Central European Astrophysical Bulletin},

volume = {37},

pages = {487-494},

abstract = {We observe various emission lines in solar prominences and compare the widths of He II 4686 Å, He I 4472 Å (triplet) and He I 5015 Å (singlet) with those of the optically thin Hγ and Mg b_2 lines. The latter two yield a thermal line broadening of 9000<T_{kin}<11 000 K, which fits the width of He I 5015 Å (singlet). However, He I 4471 Å (triplet) shows an excess of 1.1 indicating an excitation of the triplet in 1.2 times hotter prominence regions. He II 4686 Å is 1.65 times broader and thus emitted in 2.73 times hotter regions of the prominence-corona transition layer, PCTR. The linear radiance relations He tripl/He II=50 and Hγ/He tripl=11.8 suggest a PCTR between each fine-structure thread and the surrounding hot coronal gas.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Setzer2013,

title = {Computersteuerung für einen Sonnenspektrografen},

author = {Setzer, M. and Lübke, S. and Küveler, G. and Zuber, A. and Bianda, M. and Ramelli, R.},

year  = {2013},

date = {2013-01-01},

booktitle = {München DIV Deutscher Industrieverlag 2013},

pages = {359},

series = {Tagungsband AALE 2013},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2012EAS....55...59F,

title = {Forward-scattering Hanle effect in the solar Ca i 4227 Å line},

author = {Frisch, H. and Anusha, L.S. and Bianda, M. and Holzreuter, R. and Nagendra, K.N. and Ramelli, R. and Sampoorna, M. and Smitha, H.N. and Stenflo, J.O.},

editor = {Faurobert, M. and Fang, C. and Corbard, T.},

url = {http://www.eas-journal.org/action/displayAbstract?fromPage=online&aid=8626040},

doi = {10.1051/eas/1255007},

year  = {2012},

date = {2012-06-01},

urldate = {2012-06-01},

booktitle = {EAS Publications Series},

volume = {55},

pages = {59-63},

series = {EAS Publications Series},

abstract = {High sensitivity spectropolarimetric observations of the four Stokes parameters of the solar Ca I 4227 Å line have been performed in October 2010 at IRSOL with the ZIMPOL polarimeter, near the disk center, outside an active region (Bianda et al. 2011). They were analyzed in Anusha et al. 2011 with a combination of detailed radiative transfer modelling of the Hanle effect for the linear polarization and weak field Zeeman approximation for the circular polarization. This approach made possible a unique determination of the magnetic field vector at various positions along the slit of the spectrograph. A summary of the observations and of their analysis is presented here},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2012EAS....55..381S,

title = {Atmospheric fluctuations below 0.1 Hz during drift-scan solar diameter measurements},

author = {Sigismondi, C. and Raponi, A. and De Rosi, G. and Bianda, M. and Ramelli, R. and Caccia, M. and Maspero, M. and Negrini, L. and Wang, X.},

editor = {Faurobert, M. and Fang, C. and Corbard, T.},

url = {http://arxiv.org/abs/1112.6187},

doi = {10.1051/eas/1255054},

year  = {2012},

date = {2012-01-01},

urldate = {2012-01-01},

booktitle = {EAS Publications Series},

volume = {55},

pages = {381-383},

series = {EAS Publications Series},

abstract = {Measurements of the power spectrum of the seeing in the range 0.001-1 Hz have been performed in order to understand the criticity of the transits method for solar diameter monitoring.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{2012EGUGA..14.8670E,

title = {Multiwavelength imaging polarimetry of Venus at various phase angles},

author = {Einarsen, L.J. and Rodenhuis, M. and Snik, F. and Keller, C.U. and Stam, D.M. and de Kok, R.J. and Bianda, M. and Ramelli, R.},

editor = {Abbasi, A. and Giesen, N.},

url = {http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012EGUGA..14.8670E&link_type=ARTICLE&db_key=AST&high=},

year  = {2012},

date = {2012-01-01},

urldate = {2012-01-01},

booktitle = {EGU General Assembly Conference Abstracts},

volume = {14},

pages = {8670},

series = {EGU General Assembly Conference Abstracts},

abstract = {Venus is the only planet with an atmosphere that we can observe from the ground at a large range of phase angles. Therefore it constitutes an important benchmark for direct observations of exoplanets, which will soon become available. Moreover, polarimetric observations at various phase angles and wavelengths provide a unique way to characterize any (exo-)planetary atmosphere. For instance, the famous study by Hansen & Hovenier (1974) which combines disk-integrated polarimetric observations and modeling has unambiguously shown that Venus' upper atmosphere consists of sulphuric acid droplets of ~1 um in diameter. We present new spatially resolved observations of Venus using the imaging polarimeters ExPo at the William Herschel Telescope and ZIMPOL at the IRSOL telescope. These observations are taken in narrow-band filters from 364--648 nm, and span phase angles from 10--49 degrees. We find that the degree of polarization varies strongly with wavelength and phase angle, as generally predicted by the model by Hansen & Hovenier. However, the polarization behaviour near the equator differs considerably from that at the poles, hinting at different atmospheric compositions and/or stratifications. In the intensity images we detect a significant shift of the location of maximum intensity with wavelength. These observations allow us to refine the model by Hansen & Hovenier, and we present the preliminary results of our efforts to do so.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Setzer2012,

title = {Automatisierung eines Sonnenspektrografen},

author = {Setzer, M. and Küveler, G. and Zuber, A. and Bianda, M. and Ramelli, R.},

url = {https://www.irsol.usi.ch/data/Papers/setzer2012.pdf},

year  = {2012},

date = {2012-01-01},

booktitle = {VIP 2012},

series = {Viruelle Instrumente in der Praxis},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}