spectropolarimetry

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

whawkins — Thu, 01 Aug 2024 15:39:00 +0000

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance whawkins Thu, 08/01/2024 - 09:39

Author:

whawkins

Aug 1, 2024

Corrected Figure 7 of Paper I, showing the polarimetric errors for a stepped waveplate with 150◦ retardance (8-state modulation scheme), with dual-beam analysis, and 10 s integration. For this example, we adopted a non-optimal demodulation scheme consisting of simple additions and subtractions of individual modulated signals.

The Astrophysical Journal: (Published 2012 September 4; submitting a "corrected" Figure 7 of Paper I) We analyze the generation of polarization cross-talk in Stokes polarimeters by atmospheric seeing, and its effects on the noise statistics of spectropolarimetric measurements for both single-beam and dual-beam instruments. We investigate the time evolution of seeing-induced correlations between different states of one modulation cycle and compare the response to these correlations of two popular polarization modulation schemes in a dual-beam system. Extension of the formalism to encompass an arbitrary number of modulation cycles enables us to compare our results with earlier work. Even though we discuss examples pertinent to solar physics, the general treatment of the subject and its fundamental results might be useful to a wider community.

2nd Successful Spectropolarimetry School

whawkins — Wed, 07 Sep 2022 15:36:21 +0000

2nd Successful Spectropolarimetry School whawkins Wed, 09/07/2022 - 09:36

2022 Spectropolarimetry School

Author:

whawkins

Sep 7, 2022

The High Altitude Observatory and the National Solar Observatory organized their second successful Spectropolarimetry School in Boulder, Colorado. This two-week school held at the end of August presented an overview of the field of solar spectropolarimetry and the diagnostic techniques used to analyze and interpret spectropolarimetric observations of the Sun.

Solar magnetism is at the root of all solar activity and is the driving force of Space Weather. The characteristics of the magnetic field are encoded in the polarization of the light emitted by the Sun, and sensitive analysis techniques are necessary to reveal them. This school explored the observations, the theory and the tools that help us determine the state and evolution of the Sun's magnetic field through its polarized spectrum. The curriculum covered theoretical topics such as polarized radiative transfer, polarimetric instrumentation, scattering polarization and the Hanle effect, as well as dozens of hours of hands-on tutorials with different spectral line inversion codes. The school brought together 19 domestic and 7 international participants as well as multiple leading experts from around the world.

Group portrait of the 2022 Spectropolarimetry school students and lecturers taken on the outdoor patio at Center Green 1 building.

On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions

kolinski — Mon, 11 Jul 2022 20:45:28 +0000

On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions kolinski Mon, 07/11/2022 - 14:45

Publication Name: The Astrophysical Journal; Author's names: Centeno, R., de la Cruz Rodriguez, J., del Pino Aleman, T.

Author:

kolinski

Jul 11, 2022

Scattering polarization tends to dominate the linear polarization signals of the Ca II 8542 A line in weakly magnetized areas (B ~ 100 G), especially when the observing geometry is close to the limb. In this paper we evaluate the degree of applicability of existing non-LTE spectral line inversion codes (which assume that the spectral line polarization is due to the Zeeman effect only) at inferring the magnetic field vector and, particularly, its transverse component. To this end, we use the inversion code STiC to extract the strength and orientation of the magnetic field from synthetic spectropolarimetric data generated with the Hanle-RT code. The latter accounts for the generation of polarization through scattering processes as well as the joint actions of the Hanle and the Zeeman effects. We find that, when the transverse component of the field is stronger than ~80 G, the inversion code is able to retrieve accurate estimates of the transverse field strength as well as its azimuth in the plane of the sky. Below this threshold, the scattering polarization signatures become the major contributors to the linear polarization signals and often mislead the inversion code into severely over- or under-estimating the field strength. Since the line-of-sight component of the field is derived from the circular polarization signal, which is not affected by atomic alignment, the corresponding inferences are always good.

Inversion results for observing geometries away from the disk center. The panels show the relative (percent) differences between the magnetic field values retrieved by the STiC inversions and those in the model atmospheres used for the Hanle-RT syntheses. Left and right correspond, respectively, to the Zeeman-only and the full calculation with atomic polarization cases. The top two rows show the results for the strength and the azimuth of the transverse component of the magnetic field, while the bottom panels present the results for the LOS magnetic field.

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm

kolinski — Mon, 11 Jul 2022 20:24:06 +0000

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm kolinski Mon, 07/11/2022 - 14:24

Author:

kolinski

Jul 11, 2022

Alin Paraschiv and Philip Judge present CLEDB, a single point inversion algorithm for determining magnetic parameters using spectro-polarimetric measurements of emission lines formed in the solar corona. We select lines of interest and construct databases for combinations of plasma thermal and magnetic configurations. The method is intended to be applied to two or more lines observed simultaneously. The solutions initially yield magnetic orientation, thermal properties, and the spatial position of the emitting plasma in three dimensions. Multiple possible solutions for each observation are returned, including irreducible degeneracies. The magnetic field strength is separately derived from the simple ratio of observed to database polarization data, after the thermal properties and scattering geometry solutions have been determined.

CLEDB 2-line magnetic inversion algorithm flowchart. An important aspect is the delivery of multiple possible solutions for each observation at the last step. Note that the x-coordinate of the point in space, as well as nearest electron density, are returned along with B. The figure uses the notation Vobs and Vdb for observed and computed values of the amplitudes of the Stokes parameters corresponding to O3 and S3 (B = 1) in the text.

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX

kolinski — Mon, 11 Jul 2022 18:57:40 +0000

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX kolinski Mon, 07/11/2022 - 12:57

Publication: The Astrophysical Journal; Authors: Aatiya Ali, Alin Razvan Paraschiv, Kevin Reardon, and Philip Judge

Author:

kolinski

Jul 11, 2022

The infrared solar spectrum contains a wealth of physical data about the Sun and is being explored using modern detectors and technology with new ground-based solar telescopes. One such instrument will be the ground-based Cryogenic Near-IR Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope (DKIST), which will be capable of sensitive imaging of the faint infrared solar coronal spectra with full Stokes polarization states. Highly ionized emission lines have been observed in galaxies and the solar corona. Quantifying the accuracy of spectral inversion procedures requires a precise spectroscopic calibration of observations. A careful interpretation of the spectra around prominent magnetic dipole lines is essential for deriving physical parameters and particularly for quantifying the off-limb solar coronal observations from DKIST. In this work, we aim to provide an analysis of the spectral regions around the infrared coronal emission lines of Fe xiii 1074.68 nm, Fe xiii 1079.79 nm, Si x 1430.10 nm, and Si ix 3934.34 nm, aligning with the goal of identifying solar photospheric and telluric lines that will help facilitate production of reliable inversions and data products from four sets of solar coronal observations.

Fe XIII 1074.68 nm emission over atmospheric absorption (normalized) in the He I Cryo-NIRSP wavelength range with all labeled candidate lines. The green curve represents the atmospheric spectra that are convolved with a Gaussian function correspondent to the Cryo-NIRSP 0"5 slit spectral resolution of 0.027 nm.

Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun

kolinski — Thu, 18 Nov 2021 19:07:10 +0000

Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun kolinski Thu, 11/18/2021 - 12:07

Publication Name: ApJ First; HAO Author's Name: Philip Judge

Author:

kolinski

Nov 18, 2021

We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro- Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca II 8542 Å and Hα lines as well as in the photospheric Fe I line.

Snapshots in Hα 6563 Å, Ca II 8542.11 Å, and Stokes-V of Fe 6302 Å, and Doppler difference images constructed in Ca II 8542 Å showing selected swirling events.

We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca II and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures.

Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare

kolinski — Thu, 18 Nov 2021 19:02:39 +0000

Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare kolinski Thu, 11/18/2021 - 12:02

Publication Name: ApJL; First HAO Author's Name: Philip Judge

Author:

kolinski

Nov 18, 2021

We examine spectropolarimetric data from the CoMP instrument, acquired during the evolution of the September 10th 2017 X8.2 solar flare on the western solar limb. CoMP captured linearly polarized light from two emission lines of Fe XIII at 1074.7 and 1079.8 nm, from 1.03 to 1.5 solar radii. We focus here on the hot plasma-sheet lying above the bright flare loops and beneath the ejected CME.

Intensity and polarization data surrounding the current sheet formed on Sept 10 2017.

The polarization has a striking and coherent spatial structure, with unexpectedly small polarization aligned with the plasma-sheet. By elimination, we find that small-scale magnetic field structure is needed to cause such significant depolarization, and suggest that plasmoid formation during reconnection (associated with the tearing mode instability) creates magnetic structure on scales below instrument resolution of 6 Mm. We conclude that polarization measurements with new coronagraphs, such as the upcoming DKIST, will further enhance our understanding of magnetic reconnection and development of turbulence in the solar corona.

Design of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer

kolinski — Tue, 16 Nov 2021 21:14:23 +0000

Design of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer kolinski Tue, 11/16/2021 - 14:14

Publication: ApJ; First HAO Author: Alfred de Wijn; Authors as listed in article: A.G. de Wijn, J. de la Cruz Rodríguez, G.B. Scharmer, G. Sliepen, and P. Sütterlin

Author:

kolinski

Nov 16, 2021

Example spectro-polarimetric data of Active Region 12471 in the Fe I lines at 630.2 nm. The observation was recorded on 2019-05-10 around 09:10 UT. Top row: images of the Stokes parameter in the blue wing of the 630.25 nm line at −90 mÅ from line center. Spectra at the black, red, and blue crosses are shown in the bottom row. The locations of the spectral sampling are indicated by crosses.

In 2014 HAO built a polarimetric modulator for the CRISP instrument on the Swedish 1-m Solar Telescope in La Palma, using the principles of polychromatic modulation previously developed by HAO scientists. This paper discusses the processes by which the modulator was designed, built, and tested. The modulator was installed and had been in use since 2015. It is working at close to optimal efficiency and has produced considerable scientific output.

Link to paper: Design and Performance Analysis of a Highly Efficient Polychromatic Full Stokes Polarization Modulator for the CRISP Imaging Spectrometer

spectropolarimetry

Erratum: Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

Recent News

2nd Successful Spectropolarimetry School

Recent News

On the (Mis)interpretation of the Scattering Polarization Signatures In the Ca II 8542 A line Through Spectral Line Inversions

Recent News

Efficient and Automated Inversions of Magnetically-Sensitive Forbidden Coronal Lines: CLEDB - The Coronal Line Emission DataBase Magnetic Field Inversion Algorithm

Recent News

A Spectroscopic Survey of Infrared 1–4 μm Spectra in Regions of Prominent Solar Coronal Emission Lines of Fe XIII, Si X, and Si IX

Recent News

Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun

Recent News

Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare

Recent News

Design of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer

Recent News