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Zeitschriftenartikel zum Thema „Spectro-Polarimetric“

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Veröffentlicht am 7. Juli 2024

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1

Rousselet-Perraut, K., C. Stehlé, J. B. Le Bouquin, S. Jankov und F. Vakili. „Stellar polarimetry with SPIN (Spectro-Polarimetric INterferometry)“. EAS Publications Series 9 (2003): 123. http://dx.doi.org/10.1051/eas:2003094.

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2

Smith, Craig H., Christopher M. Wright, David K. Aitken und Patrick F. Roche. „Mid-infrared Observations of Magnetic Fields in the Disks of Bi-Polar Outflow Sources“. International Astronomical Union Colloquium 163 (1997): 799–800. http://dx.doi.org/10.1017/s0252921100044067.

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AbstractWe present the results from mid-infrared spectro-polarimetric observations of a number of bi-polar outflow sources. The specto-polarimetric data provides information on the polarization mechanism and the magnetic field direction. The field direction in the disks of the observed sources is most often normal to the ambient field direction and lies in the plane of the disk, indicating a toroidal rather than poloidal field configuration.

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3

van Noort, M. „Spatially coupled inversion of spectro-polarimetric image data“. Astronomy & Astrophysics 548 (12.11.2012): A5. http://dx.doi.org/10.1051/0004-6361/201220220.

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4

Boccaletti, Anthony, Anne-Lise Maire, Raphaël Galicher, Pierre Baudoz, Dimitri Mawet, John Trauger, Jean Schneider et al. „SPICES: A Mission Concept to Characterize Long Period Planets from Giants to Super-Earths“. Proceedings of the International Astronomical Union 8, S293 (August 2012): 429–34. http://dx.doi.org/10.1017/s1743921313013331.

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AbstractSPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) was proposed in 2010 for a five-year M-class mission in the context of ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets located at several AUs (0.5-10 AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses down to super-Earths (~2 Earth radii, ~10 M⊕), possibly habitable. In addition, circumstellar disks as faint as a few times the zodiacal light in the Solar System can be studied. SPICES is based on a 1.5-m off-axis telescope and can perform spectro-polarimetric measurements in the visible (450 - 900 nm) at a spectral resolution of about 40. This paper summarizes the top science program and the choices made to conceive the instrument. The performance is illustrated for a few emblematic cases.

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5

Jordan, Stefan. „Magnetic fields in White Dwarfs and their direct progenitors“. Proceedings of the International Astronomical Union 4, S259 (November 2008): 369–78. http://dx.doi.org/10.1017/s1743921309030749.

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AbstractThe paper provides an overview on the results of the analyses of spectro-polarimetric observations of white dwarfs, subdwarfs, and central stars of planetary nebulae. It will also discuss the question of the origin of the magnetic fields in white dwarfs.

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6

GAN Shi-qi, 甘世奇, 陈向宁 CHEN Xiang-ning, 刘鹏 LIU Peng und 孙健 SUN Jian. „Transmittance spectrum in the liquid crystal spectro-polarimetric system“. Chinese Journal of Liquid Crystals and Displays 32, Nr. 2 (2017): 97–103. http://dx.doi.org/10.3788/yjyxs20173202.0097.

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7

Lepera, E., C. Provenzano, P. Pagliusi und G. Cipparrone. „Liquid Crystal Based Polarization Gratings for Spectro-Polarimetric Applications“. Molecular Crystals and Liquid Crystals 558, Nr. 1 (30.05.2012): 109–19. http://dx.doi.org/10.1080/15421406.2011.653716.

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8

Bommier, V., E. Landi Degl'Innocenti, M. Landolfi und G. Molodij. „UNNOFIT inversion of spectro-polarimetric maps observed with THEMIS“. Astronomy & Astrophysics 464, Nr. 1 (14.12.2006): 323–39. http://dx.doi.org/10.1051/0004-6361:20054576.

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9

Boccaletti, Anthony, Jean Schneider, Wes Traub, Pierre-Olivier Lagage, Daphne Stam, Raffaele Gratton, John Trauger et al. „SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems“. Experimental Astronomy 34, Nr. 2 (29.02.2012): 355–84. http://dx.doi.org/10.1007/s10686-012-9290-5.

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10

Libbrecht, Tine, Jaime de la Cruz Rodríguez, Sanja Danilovic, Jorrit Leenaarts und Hiva Pazira. „Chromospheric condensations and magnetic field in a C3.6-class flare studied via He I D3 spectro-polarimetry“. Astronomy & Astrophysics 621 (Januar 2019): A35. http://dx.doi.org/10.1051/0004-6361/201833610.

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Context. Magnetic reconnection during flares takes place in the corona, but a substantial part of flare energy is deposited in the chromosphere. However, high-resolution spectro-polarimetric chromospheric observations of flares are very rare. The most used observables are Ca II 8542 Å and He I 10830 Å. Aims. We aim to study the chromosphere during a C3.6 class flare via spectro-polarimetric observations of the He I D3 line. Methods. We present the first SST/CRISP spectro-polarimetric observations of He I D3. We analyzed the data using the inversion code HAZEL, and estimate the line-of-sight velocity and the magnetic field vector. Results. Strong He I D3 emission at the flare footpoints, as well as strong He I D3 absorption profiles tracing the flaring loops are observed during the flare. The He I D3 traveling emission kernels at the flare footpoints exhibit strong chromospheric condensations of up to ∼60 km s−1 at their leading edge. Our observations suggest that such condensations result in shocking the deep chromosphere, causing broad and modestly blueshifted He I D3 profiles indicating subsequent upflows. A strong and rather vertical magnetic field of up to ∼2500 G is measured in the flare footpoints, confirming that the He I D3 line is likely formed in the deep chromosphere at those locations. We provide chromospheric line-of-sight velocity and magnetic field maps obtained via He I D3 inversions. We propose a fan-spine configuration as the flare magnetic field topology. Conclusions. The He I D3 line is an excellent diagnostic to study the chromosphere during flares. The impact of strong condensations on the deep chromosphere has been observed. Detailed maps of the flare dynamics and the magnetic field are obtained.

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11

Chesneau, O., K. Rousselet-Perraut und F. Vakili. „Interferometry and Stellar Magnetism“. International Astronomical Union Colloquium 175 (2000): 174–77. http://dx.doi.org/10.1017/s0252921100055792.

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AbstractThe classical detection of magnetic fields in Be stars remains a challenge due to the sensitivity threshold and geometrical cancelation of the field effects. We propose to study the Zeeman effect using Spectro-Polarimetric INterferometry (SPIN) which consists of the simultaneous use of polarimetry and very high angular resolution provided by long baseline interferometers. As monitoring of the instrumental polarisation is mandatory in order to calibrate interferometric observations in any case, the polarised signal is a natural by-product of interferometers. This method will be tested on the GI2T interferometer thanks to its high spectral resolution and its polarimetric capabilities.

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12

Yuan Yinlin, 袁银麟, 郑小兵 Zheng Xiaobing, 吴浩宇 Wu Haoyu, 孟凡刚 Meng Fangang, 康晴 Kang Qing, 陈立刚 Chen Ligang, 李健军 Li Jianjun und 邹鹏 Zou Peng. „A Intensity Modulated Spectro-Polarimetric Analyzer Based on Fourier Transformation“. Acta Optica Sinica 34, Nr. 12 (2014): 1223001. http://dx.doi.org/10.3788/aos201434.1223001.

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13

Walters, Josh, Brian Robinson und Patrick J. Reardon. „Modeling and simulation of a spectro-polarimetric lenslet array imager“. Optical Engineering 52, Nr. 2 (01.02.2013): 023201. http://dx.doi.org/10.1117/1.oe.52.2.023201.

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14

Casini, R., P. G. Judge und T. A. Schad. „REMOVAL OF SPECTRO-POLARIMETRIC FRINGES BY TWO-DIMENSIONAL PATTERN RECOGNITION“. Astrophysical Journal 756, Nr. 2 (27.08.2012): 194. http://dx.doi.org/10.1088/0004-637x/756/2/194.

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15

Chesneau, O., S. Wolf und A. Domiciano de Souza. „Hot stars mass-loss studied with Spectro-Polarimetric INterferometry (SPIN)“. Astronomy & Astrophysics 410, Nr. 1 (Oktober 2003): 375–88. http://dx.doi.org/10.1051/0004-6361:20031186.

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16

Socas-Navarro, Hector, Valentín Martínez Pillet, David Elmore, Anna Pietarila, Bruce W. Lites und Rafael Manso Sainz. „Spectro-Polarimetric Observations and Non-Lte Modeling of Ellerman Bombs“. Solar Physics 235, Nr. 1-2 (Mai 2006): 75–86. http://dx.doi.org/10.1007/s11207-006-0049-x.

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17

Huynh, Cong Phuoc, Antonio Robles-Kelly und Edwin R. Hancock. „Shape and Refractive Index from Single-View Spectro-Polarimetric Images“. International Journal of Computer Vision 101, Nr. 1 (29.06.2012): 64–94. http://dx.doi.org/10.1007/s11263-012-0546-3.

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18

Boccaletti, Anthony, Alessandro Sozzetti, Jean Schneider, Pierre Baudoz, Giovanna Tinetti und Daphne Stam. „The SEE-COAST concept“. Proceedings of the International Astronomical Union 5, H15 (November 2009): 718–19. http://dx.doi.org/10.1017/s1743921310011154.

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AbstractThe SEE COAST concept is designed with the objective to characterize extrasolar planets and possibly Super Earths via spectro-polarimetric imaging in reflected light. A space mission complementary to ground-based near IR planet finders is a first secure step towards the characterization of planets with mass and atmosphere comparable to that of the Earth. The accessibility to the Visible spectrum is unique and with important scientific returns.

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19

Zong, W. G., Y. H. Tang, C. Fang, P. Mein, N. Mein und A. A. Xu. „Spectro-polarimetric observation of the fine structure of a quiescent filament“. Astronomy & Astrophysics 412, Nr. 1 (25.11.2003): 267–70. http://dx.doi.org/10.1051/0004-6361:20034115.

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20

Casini, R., und W. Li. „Removal of Spectro-polarimetric Fringes by Two-dimensional Principal Component Analysis“. Astrophysical Journal 872, Nr. 2 (20.02.2019): 173. http://dx.doi.org/10.3847/1538-4357/ab0023.

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21

Lopez-Rodriguez, E., C. Packham, P. F. Roche, A. Alonso-Herrero, T. Díaz-Santos, R. Nikutta, O. González-Martín et al. „Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068“. Monthly Notices of the Royal Astronomical Society 458, Nr. 4 (07.03.2016): 3851–66. http://dx.doi.org/10.1093/mnras/stw541.

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22

Pasetto, Alice, Carlos Carrasco-González, Shane O’Sullivan, Aritra Basu, Gabriele Bruni, Alex Kraus, Salvador Curiel und Karl-Heinz Mack. „Broadband radio spectro-polarimetric observations of high-Faraday-rotation-measure AGN“. Astronomy & Astrophysics 613 (Mai 2018): A74. http://dx.doi.org/10.1051/0004-6361/201731804.

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We present broadband polarimetric observations of a sample of high-Faraday-rotation-measure (high-RM) active galactic nuclei (AGN) using the Karl. G. Jansky Very Large Array (JVLA) telescope from 1 to 2 GHz, and 4 to 12 GHz. The sample (14 sources) consists of very compact sources (linear resolution smaller than ≈5 kpc) that are unpolarized at 1.4 GHz in the NRAO VLA Sky Survey (NVSS). Total intensity data have been modeled using a combination of synchrotron components, revealing complex structure in their radio spectra. Depolarization modeling, through the so-called qu-fitting (the modeling of the fractional quantities of the Stokes Q and U parameters), has been performed on the polarized data using an equation that attempts to simplify the process of fitting many different depolarization models. These models can be divided into two major categories: external depolarization (ED) and internal depolarization (ID) models. Understanding which of the two mechanisms is the most representative would help the qualitative understanding of the AGN jet environment and whether it is embedded in a dense external magneto-ionic medium or if it is the jet-wind that causes the high RM and strong depolarization. This could help to probe the jet magnetic field geometry (e.g., helical or otherwise). This new high-sensitivity data shows a complicated behavior in the total intensity and polarization radio spectrum of individual sources. We observed the presence of several synchrotron components and Faraday components in their total intensity and polarized spectra. For the majority of our targets (12 sources), the depolarization seems to be caused by a turbulent magnetic field. Thus, our main selection criteria (lack of polarization at 1.4 GHz in the NVSS) result in a sample of sources with very large RMs and depolarization due to turbulent magnetic fields local to the source. These broadband JVLA data reveal the complexity of the polarization properties of this class of radio sources. We show how the new qu-fitting technique can be used to probe the magnetized radio source environment and to spectrally resolve the polarized components of unresolved radio sources.

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23

Casini, R., A. Asensio Ramos, B. W. Lites und A. López Ariste. „IMPROVED SEARCH OF PRINCIPAL COMPONENT ANALYSIS DATABASES FOR SPECTRO-POLARIMETRIC INVERSION“. Astrophysical Journal 773, Nr. 2 (06.08.2013): 180. http://dx.doi.org/10.1088/0004-637x/773/2/180.

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24

Casini, Roberto, Dennis Gallagher, Anthony Cordova und Matthew Morgan. „Measured performance of shadow-cast coated gratings for spectro-polarimetric applications“. Applied Optics 57, Nr. 25 (28.08.2018): 7276. http://dx.doi.org/10.1364/ao.57.007276.

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25

Maisonneuve, Mathieu, Chiara Valsecchi, Chen Wang, Alexandre G. Brolo und Michel Meunier. „Leukemic marker detection using a spectro-polarimetric surface plasmon resonance platform“. Biosensors and Bioelectronics 63 (Januar 2015): 80–85. http://dx.doi.org/10.1016/j.bios.2014.06.018.

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26

Briand, C., und A. Vecchio. „Chromospheric polarity reversal on sunspots: New insight from spectro-polarimetric measurements“. Astronomy & Astrophysics 403, Nr. 2 (Mai 2003): L33—L36. http://dx.doi.org/10.1051/0004-6361:20030553.

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27

Alouini, M., F. Goudail, N. Roux, L. Le Hors, P. Hartemann, S. Breugnot und D. Dolfi. „Active spectro-polarimetric imaging: signature modeling, imaging demonstrator and target detection“. European Physical Journal Applied Physics 42, Nr. 2 (28.03.2008): 129–39. http://dx.doi.org/10.1051/epjap:2008034.

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28

González, M. J. Martínez, R. Manso Sainz, A. Asensio Ramos, C. Beck, J. de la Cruz Rodríguez und A. J. Díaz. „SPECTRO-POLARIMETRIC IMAGING REVEALS HELICAL MAGNETIC FIELDS IN SOLAR PROMINENCE FEET“. Astrophysical Journal 802, Nr. 1 (13.03.2015): 3. http://dx.doi.org/10.1088/0004-637x/802/1/3.

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29

Maire, Anne-Lise, Raphaël Galicher, Anthony Boccaletti, Pierre Baudoz, Jean Schneider, Kerri Cahoy, Daphne Stam und Wesley Traub. „Atmospheric Characterization of Cold Exoplanets Using a 1.5-m Space Coronagraph“. Proceedings of the International Astronomical Union 8, S293 (August 2012): 289–91. http://dx.doi.org/10.1017/s174392131301301x.

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AbstractWe present numerical results of the science performance of the SPICES mission, which aims to characterize the spectro-polarimetric properties of cold exoplanets and circumstellar disks in the visible. We focus on the instrument ability to retrieve the spectral signatures of molecular species, clouds and surface of super-Earths in the habitable zone of solar-type stars. Considering realistic reflected planet spectra and instrument limitation, we show that SPICES could analyse the atmosphere and surface of a few super-Earths within 5 pc of the Sun.

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30

Hussain, G. A. J., J. D. Alvarado-Gómez, J. Grunhut, J. F. Donati, E. Alecian, M. Oksala, J. Morin et al. „A spectro-polarimetric study of the planet-hosting G dwarf, HD 147513“. Astronomy & Astrophysics 585 (22.12.2015): A77. http://dx.doi.org/10.1051/0004-6361/201526595.

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31

Pinto, M., R. M. Curado da Silva, J. M. Maia, N. Simões, J. Marques, L. Pereira, A. M. F. Trindade et al. „Polarimetric analysis of a CdZnTe spectro-imager under multi-pixel irradiation conditions“. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 840 (Dezember 2016): 69–76. http://dx.doi.org/10.1016/j.nima.2016.09.054.

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32

Demidov, M. L., und H. Balthasar. „On Multi-Line Spectro-Polarimetric Diagnostics of the Quiet Sun’s Magnetic Fields“. Solar Physics 276, Nr. 1-2 (08.11.2011): 43–59. http://dx.doi.org/10.1007/s11207-011-9863-x.

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33

Takahashi, J., T. Matsuo und Y. Itoh. „Feasibility of spectro-polarimetric characterization of exoplanetary atmospheres with direct observing instruments“. Astronomy & Astrophysics 599 (28.02.2017): A56. http://dx.doi.org/10.1051/0004-6361/201628206.

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34

Tumendemberel, Begzsuren, Luvsanbat Khurelbaatar, Yukihiro Takahashi, Turtogtokh Tumenjargal und Erdenebaatar Dashdondog. „Measurement of single Coffea canephora leaf spectro-polarimetric bidirectional reflectance factor dataset“. Data in Brief 53 (April 2024): 110204. http://dx.doi.org/10.1016/j.dib.2024.110204.

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35

Wolleben, Maik, T. L. Landecker, E. Carretti, J. M. Dickey, A. Fletcher, B. M. Gaensler, J. L. Han et al. „GMIMS: the Global Magneto-Ionic Medium Survey“. Proceedings of the International Astronomical Union 4, S259 (November 2008): 89–90. http://dx.doi.org/10.1017/s1743921309030117.

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AbstractThe Global Magneto-Ionic Medium Survey (GMIMS) is a project to map the diffuse polarized emission over the entire sky, Northern and Southern hemispheres, from 300 MHz to 1.8 GHz. With an angular resolution of 30–60 arcmin and a frequency resolution of 1 MHz or better, GMIMS will provide the first spectro-polarimetric data set of the large-scale polarized emission over the entire sky, observed with single-dish telescopes. GMIMS will provide an invaluable resource for studies of the magneto-ionic medium of the Galaxy in the local disk, halo, and its transition.

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36

Basu, Aritra, Andrew Fletcher, Sui Ann Mao, Blakesley Burkhart, Rainer Beck und Dominic Schnitzeler. „An In-depth Investigation of Faraday Depth Spectrum Using Synthetic Observations of Turbulent MHD Simulations“. Galaxies 7, Nr. 4 (23.11.2019): 89. http://dx.doi.org/10.3390/galaxies7040089.

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In this paper, we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. To directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although most of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to the presence of a Faraday-rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously.

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37

de Boer, J., M. Langlois, R. G. van Holstein, J. H. Girard, D. Mouillet, A. Vigan, K. Dohlen et al. „Polarimetric imaging mode of VLT/SPHERE/IRDIS“. Astronomy & Astrophysics 633 (Januar 2020): A63. http://dx.doi.org/10.1051/0004-6361/201834989.

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Context. Polarimetric imaging is one of the most effective techniques for high-contrast imaging and for the characterization of protoplanetary disks, and it has the potential of becoming instrumental in the characterization of exoplanets. The Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on the Very Large Telescope (VLT) contains the InfraRed Dual-band Imager and Spectrograph (IRDIS) with a dual-beam polarimetric imaging (DPI) mode, which offers the capability of obtaining linear polarization images at high contrast and resolution. Aims. We aim to provide an overview of the polarimetric imaging mode of VLT/SPHERE/IRDIS and study its optical design to improve observing strategies and data reduction. Methods. For H-band observations of TW Hydrae, we compared two data reduction methods that correct for instrumental polarization effects in different ways: a minimization of the “noise” image (Uϕ), and a correction method based on a polarimetric model that we have developed, as presented in Paper II of this study. Results. We use observations of TW Hydrae to illustrate the data reduction. In the images of the protoplanetary disk around this star, we detect variability in the polarized intensity and angle of linear polarization that depend on the pointing-dependent instrument configuration. We explain these variations as instrumental polarization effects and correct for these effects using our model-based correction method. Conclusions. The polarimetric imaging mode of IRDIS has proven to be a very successful and productive high-contrast polarimetric imaging system. However, the instrument performance is strongly dependent on the specific instrument configuration. We suggest adjustments to future observing strategies to optimize polarimetric efficiency in field-tracking mode by avoiding unfavorable derotator angles. We recommend reducing on-sky data with the pipeline called IRDAP, which includes the model-based correction method (described in Paper II) to optimally account for the remaining telescope and instrumental polarization effects and to retrieve the true polarization state of the incident light.

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38

Kitiashvili, Irina N. „Spectro-polarimetric properties of small-scale plasma eruptions driven by magnetic vortex tubes“. Publications of the Astronomical Society of Japan 66, SP1 (27.11.2014): S8. http://dx.doi.org/10.1093/pasj/psu114.

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39

Alemanno, G., E. Garcia-Caurel, J. Carter, F. Poulet, R. Brunetto, A. Alèon-Toppani, R. G. Urso et al. „Determination of optical constants from Martian analog materials using a spectro-polarimetric technique“. Planetary and Space Science 195 (Januar 2021): 105138. http://dx.doi.org/10.1016/j.pss.2020.105138.

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40

Kokhanovsky, A. A., A. B. Davis, B. Cairns, O. Dubovik, O. P. Hasekamp, I. Sano, S. Mukai et al. „Space-based remote sensing of atmospheric aerosols: The multi-angle spectro-polarimetric frontier“. Earth-Science Reviews 145 (Juni 2015): 85–116. http://dx.doi.org/10.1016/j.earscirev.2015.01.012.

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41

Demidov, M. L., und H. Balthasar. „Spectro-Polarimetric Observations of Solar Magnetic Fields and the SOHO/MDI Calibration Issue“. Solar Physics 260, Nr. 2 (02.10.2009): 261–70. http://dx.doi.org/10.1007/s11207-009-9443-5.

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42

Hou, Jun-Feng, Zhi Xu, Shu Yuan, Yu-Chao Chen, Jian-Guo Peng, Dong-Guang Wang, Jun Xu et al. „Spectro-polarimetric observations at the NVST: I. instrumental polarization calibration and primary measurements“. Research in Astronomy and Astrophysics 20, Nr. 4 (April 2020): 045. http://dx.doi.org/10.1088/1674-4527/20/4/45.

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43

Brown, John C., und Lorna L. Richardson. „Wolf-Rayet star variability and wind inhomogeneities“. Symposium - International Astronomical Union 163 (1995): 186–90. http://dx.doi.org/10.1017/s0074180900201940.

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The wind structure diagnostic possibilities offered by combined study of photo-, spectro-, and polari-metric variability are discussed using data from the Montreal group. These demand the presence in the wind of localised density inhomogeneities and in particular of large ‘blobs’ denser than the ‘mean’ wind and put bounds on the size, mass, and density of individual blobs and their distributions, with implications for theories of blob formation. Blobs responsible for polarimetric variability must be present at the stellar surface rather than forming in the wind, and the relation of this to spectrometric indications that blobs are only detectable at several stellar radii is discussed.

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Marshall, Jonathan P., Daniel V. Cotton, Peter Scicluna, Jeremy Bailey, Lucyna Kedziora-Chudczer und Kimberly Bott. „Polarimetric and radiative transfer modelling of HD 172555“. Monthly Notices of the Royal Astronomical Society 499, Nr. 4 (16.10.2020): 5915–31. http://dx.doi.org/10.1093/mnras/staa3195.

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ABSTRACT The debris disc around HD 172555 was recently imaged in near-infrared polarized scattered light by the Very Large Telescope’s Spectro-Polarimetric High-contrast Exoplanet REsearch instrument. Here we present optical aperture polarization measurements of HD 172555 by the HIgh Precision Polarimetric Instrument (HIPPI), and its successor HIPPI-2 on the Anglo-Australian Telescope. We seek to refine constraints on the disc’s constituent dust grains by combining our polarimetric measurements with available infrared and millimetre photometry to model the scattered light and continuum emission from the disc. We model the disc using the 3D radiative transfer code hyperion, assuming the orientation and extent of the disc as obtained from the SPHERE observation. After correction for the interstellar medium contribution, our multiwavelength HIPPI/-2 observations (both magnitude and orientation) are consistent with the recent SPHERE polarization measurement with a fractional polarization p = 62.4 ± 5.2 ppm at 722.3 nm, and a position angle θ = 67° ± 3°. The multiwavelength polarization can be adequately replicated by compact, spherical dust grains (i.e. from Mie theory) that are around 1.2 μm in size, assuming astronomical silicate composition, or 3.9 μm, assuming a composition derived from radiative transfer modelling of the disc. We were thus able to reproduce both the spatially resolved disc emission and polarization with a single grain composition model and size distribution.

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Bertrang, Gesa H. M., und Henning Avenhaus. „Planet-disk interactions in HD 169142? Tracing ellipticity, structures, and offsets“. Proceedings of the International Astronomical Union 14, S345 (August 2018): 241–43. http://dx.doi.org/10.1017/s1743921318008281.

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AbstractIn Bertrang et al. (2018), we present new data of the protoplanetary disk surrounding the Herbig Ae/Be star HD 169142 obtained in the very broad-band (VBB) with the Zurich imaging polarimeter (ZIMPOL), a subsystem of the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) at the Very Large Telescope (VLT). Our Polarimetric Differential Imaging (PDI) observations probe the disk as close as 0.″3 (3.5au) to the star and are able to trace the disk out to ~1.″08 (~126 au). We find an inner hole, a bright ring bearing substructures around ~0.″18 (21au), and an elliptically shaped gap stretching from 0.″25 to 0.″47 (29–55 au). Outside of 0.″47, the surface brightness drops off, discontinued only by a narrow annular brightness minimum at ~0.″63–0.″74 (74–87 au). These observations confirm features found in less-well resolved data as well as reveal yet undetected indications for planet-disk interactions, such as small-scale structures, star-disk offsets, and potentially moving shadows.

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46

Bhowmik, T., A. Boccaletti, P. Thébault, Q. Kral, J. Mazoyer, J. Milli, A. L. Maire et al. „Spatially resolved spectroscopy of the debris disk HD 32297“. Astronomy & Astrophysics 630 (24.09.2019): A85. http://dx.doi.org/10.1051/0004-6361/201936076.

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Context. Spectro-photometry of debris disks in total intensity and polarimetry can provide new insight into the properties of the dust grains therein (size distribution and optical properties). Aims. We aim to constrain the morphology of the highly inclined debris disk HD 32297. We also intend to obtain spectroscopic and polarimetric measurements to retrieve information on the particle size distribution within the disk for certain grain compositions. Methods. We observed HD 32297 with SPHERE in Y, J, and H bands in total intensity and in J band in polarimetry. The observations are compared to synthetic models of debris disks and we developed methods to extract the photometry in total intensity overcoming the data-reduction artifacts, namely the self-subtraction. The spectro-photometric measurements averaged along the disk mid-plane are then compared to model spectra of various grain compositions. Results. These new images reveal the very inner part of the system as close as 0.15″. The disk image is mostly dominated by the forward scattering making one side (half-ellipse) of the disk more visible, but observations in total intensity are deep enough to also detect the back side for the very first time. The images as well as the surface brightness profiles of the disk rule out the presence of a gap as previously proposed. We do not detect any significant asymmetry between the northeast and southwest sides of the disk. The spectral reflectance features a “gray to blue” color which is interpreted as the presence of grains far below the blowout size. Conclusions. The presence of sub-micron grains in the disk is suspected to be the result of gas drag and/or “avalanche mechanisms”. The blue color of the disk could be further investigated with additional total intensity and polarimetric observations in K and H bands respectively to confirm the spectral slope and the fraction of polarization.

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47

Mackay, D. H., B. Schmieder, A. López Ariste und Y. Su. „Modelling and observations: Comparison of the magnetic field properties in a prominence“. Astronomy & Astrophysics 637 (30.04.2020): A3. http://dx.doi.org/10.1051/0004-6361/201936656.

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Context. Direct magnetic field measurements in solar prominences occur infrequently and are difficult to make and interpret. As a consequence, alternative methods are needed to derive the main properties of the magnetic field that supports the prominence mass. This is important for our understanding of solar prominences, but also for understanding how eruptive prominences may affect space weather. Aims. We present the first direct comparison of the magnetic field strength derived from spectro-polarimetric observations of a solar prominence, with corresponding results from a theoretical flux rope model constructed from on-disc normal component magnetograms. Methods. We first used spectro-polarimetric observations of a prominence obtained with the magnetograph THEMIS operating in the Canary Islands to derive the magnetic field of the observed prominence by inverting the Stokes parameters measured in the He D3 line. Next, we constructed two data-constrained non-linear force-free field (NLFFF) models of the same prominence. In one model we assumed a strongly twisted flux rope solution, and in the other a weakly twisted flux rope solution. Results. The physical extent of the prominence at the limb (height and length) is best reproduced with the strongly twisted flux rope solution. The line-of-sight average of the magnetic field for the strongly twisted solution results in a magnetic field that has a magnitude of within a factor of 1−2 of the observed magnetic field strength. For the peak field strength along the line of sight, an agreement to within 20% of the observations is obtained for the strongly twisted solution. The weakly twisted solution produces significantly lower magnetic field strengths and gives a poor agreement with the observations. Conclusions. The results of this first comparison are promising. We found that the flux rope insertion method of producing a NLFFF is able to deduce the overall properties of the magnetic field in an observed prominence.

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Pietrow, A. G. M., D. Kiselman, J. de la Cruz Rodríguez, C. J. Díaz Baso, A. Pastor Yabar und R. Yadav. „Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 Å line“. Astronomy & Astrophysics 644 (30.11.2020): A43. http://dx.doi.org/10.1051/0004-6361/202038750.

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Context. It has so far proven impossible to reproduce all aspects of the solar plage chromosphere in quasi-realistic numerical models. The magnetic field configuration in the lower atmosphere is one of the few free parameters in such simulations. The literature only offers proxy-based estimates of the field strength, as it is difficult to obtain observational constraints in this region. Sufficiently sensitive spectro-polarimetric measurements require a high signal-to-noise ratio, spectral resolution, and cadence, which are at the limit of current capabilities. Aims. We use critically sampled spectro-polarimetric observations of the Ca II 8542 Å line obtained with the CRISP instrument of the Swedish 1-m Solar Telescope to study the strength and inclination of the chromospheric magnetic field of a plage region. This will provide direct physics-based estimates of these values, which could aid modelers to put constraints on plage models. Methods. We increased the signal-to-noise ratio of the data by applying several methods including deep learning and PCA. We estimated the noise level to be 1 × 10−3 Ic. We then used STiC, a non-local thermodynamic equilibrium inversion code to infer the atmospheric structure and magnetic field pixel by pixel. Results. We are able to infer the magnetic field strength and inclination for a plage region and for fibrils in the surrounding canopy. In the plage we report an absolute field strength of |B| = 440 ± 90 G, with an inclination of 10° ±16° with respect to the local vertical. This value for |B| is roughly double of what was reported previously, while the inclination matches previous studies done in the photosphere. In the fibrillar region we found |B| = 300 ± 50 G, with an inclination of 50° ±13°.

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O'Sullivan, S. P., C. R. Purcell, C. S. Anderson, J. S. Farnes, X. H. Sun und B. M. Gaensler. „Broad-band, radio spectro-polarimetric study of 100 radiative-mode and jet-mode AGN“. Monthly Notices of the Royal Astronomical Society 469, Nr. 4 (15.05.2017): 4034–62. http://dx.doi.org/10.1093/mnras/stx1133.

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50

Domínguez Cerdeña, I., F. Kneer und J. Sánchez Almeida. „High resolution 2D spectro-polarimetric observations of the quiet Sun in two iron lines“. Astronomische Nachrichten 324, Nr. 4 (Juni 2003): 327. http://dx.doi.org/10.1002/asna.200310113.

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