The
Diffraction-Limited Near-Infrared Spectropolarimeter
(DL-NIRSP) is one of the first-light instruments for the National Science Foundation’s
Daniel K. Inouye Solar Telescope
(DKIST). DL-NIRSP is ...an integral-field, dual-beam spectropolarimeter intended for studying magnetically sensitive spectral lines in the Sun’s photosphere, chromosphere, and corona with high spectral resolution and polarimetric accuracy. Two novel fiber-optic integral-field units (IFUs), paired with selectable feed optics and a field-scanning mirror provide great flexibility in spatial sampling (
0.03
″
,
0.08
″
, and
0.5
″
) and field coverage (
2
′
×
2
′
). The IFUs allow DL-NIRSP to record all the spectra from a 2D field of view simultaneously, enabling the instrument to study the evolution of highly dynamic events. The spectrograph is an all-reflecting, near-Littrow design, which achieves a resolving power of approximately 125,000. Multiple wavelengths can be observed simultaneously using three spectral arms: one for visible wavelengths (500 – 900 nm) and two for infrared wavelengths (900 – 1350 nm and 1350 – 1800 nm). Each supporting camera sub-system is capable of a 30-Hz frame rate, making it possible to track dynamic phenomena on the Sun.
Abstract
To obtain full Stokes spectra in multi-wavelength windows simultaneously, we developed a new spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory. The new polarimeter ...consists of a 60 cm aperture vacuum telescope on an altazimuth mounting, an image rotator, a high-dispersion spectrograph, and a polarization modulator and an analyzer composed of a continuously rotating waveplate with a retardation that is nearly constant at around 127° in 500–1100 nm. There are also a polarizing beam splitter located close behind the focus of the telescope, fast and large format CMOS cameras, and an infrared camera. A slit spectrograph allows us to obtain spectra in as many wavelength windows as the number of cameras. We characterized the instrumental polarization of the entire system and established a polarization calibration procedure. The cross-talks among the Stokes Q, U, and V have been evaluated to be about 0.06%–1.2%, depending on the degree of the intrinsic polarizations. In a typical observing setup, a sensitivity of 0.03% can be achieved in 20–60 seconds for 500–1100 nm. The new polarimeter is expected to provide a powerful tool for diagnosing the 3D magnetic field and other vector physical quantities in the solar atmosphere.
Spicule Dynamics over a Plage Region Anan, Tetsu; Kitai, Reizaburo; Kawate, Tomoko ...
Publications of the Astronomical Society of Japan,
08/2010, Letnik:
62, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We studied spicular jets over a plage area and derived their dynamic characteristics using Hinode Solar Optical Telescope (SOT) high-resolution images. A target plage region was near to the west limb ...of the solar disk. This location permitted us to study the dynamics of spicular jets without any overlapping effect of spicular structures along the line of sight. In this work, to increase the ease with which we could identify spicules on the disk, we applied the image processing method ‘MadMax’ developed by Koutchmy et al. (1989). It enhances fine, slender structures (like jets), over a diffuse background. We identified 169 spicules over the target plage. This sample permited us to derive statistically reliable results regarding spicular dynamics. The properties of plage spicules can be summarized as follows: (1) In a plage area, we clearly identified spicular jet features. (2) They were shorter in length than the quiet region limb spicules, and followed a ballistic motion under constant deceleration. (3) The majority (80%) of the plage spicules showed a cycle of rise and retreat, while 10% of them faded out without a complete retreat phase. (4) The deceleration of the spicule was proportional to the velocity of ejection (i.e., the initial velocity).
Abstract
We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. using observations ...acquired in the He
i
10830 Å triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s
−1
and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively controlled source function above the sunspot umbra. Strong emission profiles close to the rest wavelengths but with long redshifted tails are also observed at the downflow terminus. From the polarized spectra, we infer longitudinal magnetic field strengths of ∼2.4 kG in the core portion of the He
i
strong emission, which we believe is the strongest ever reported in this line. Photospheric field strengths along the same line of sight are ∼2.8 kG as inferred using the Ca
i
10839 Å spectral line. The temperatures of the highest speed He
i
absorption and the near-rest emission are similar (∼10 kK), while a differential emission measure analysis using Solar Dynamics Observatory/Atmospheric Imaging Assembly data indicates significant increases in radiative cooling for temperatures between ∼0.5 and 1 MK plasma associated with the downflow terminus. Combined we interpret these observations in the context of a strong radiative shock induced by the supersonic downflow impacting the low sunspot atmosphere.
Umbral flashes are periodic brightness increases routinely observed in the core of chromospheric lines within sunspot umbrae and are attributed to propagating shock fronts. In this work we quantify ...the shock heating energy of these umbral flashes using observations in the near-infrared He i triplet obtained on 2014 December 7 with the SpectroPolarimetric Imager for the Energetic Sun, which is a novel integral field unit spectrograph at the Dunn Solar Telescope. We determine the shock properties (the Mach number and the propagation speed) by fitting the measured He i spectral profiles with a theoretical radiative transfer model consisting of two constant-property atmospheric slabs whose temperatures and macroscopic velocities are constrained by the Rankine-Hugoniot relations. From the Mach number, the shock heating energy per unit mass of plasma is derived to be 2 × 1010 erg g−1, which is insufficient to maintain the umbral chromosphere. In addition, we find that the shocks propagate upward with the sound speed and the Mach number does not depend on the temperature upstream of the shocks. The latter may imply suppression of the amplification of the Mach number due to energy loss of the shocks.
Abstract
In order to investigate the relation between magnetic structures and the signatures of heating in plage regions, we observed a plage region with the He
i
1083.0 nm and Si
i
1082.7 nm lines ...on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph obtained spectra of the ultraviolet Mg
ii
doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg
ii
radiative flux increases with the magnetic field in the chromosphere with a factor of proportionality of 2.38 × 10
4
erg cm
−2
s
−1
G
−1
. The positive correlation implies that magnetic flux tubes can be heated by Alfvén wave turbulence or by collisions between ions and neutral atoms relating to Alfvén waves. Within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere or at the edges of magnetic patches. On the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. In addition to the Alfvén wave turbulence or collisions between ions and neutral atoms relating to Alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere.
Abstract
A flare kernel associated with a C4 class flare was observed in a spectral window including the He i triplet 10830 Å and Si i 10827 Å with a spectropolarimeter on the Domeless Solar ...Telescope at Hida Observatory on 2015 August 9. The observed Stokes profiles of the He i triplet in the flare kernel in its post-maximum phase are well reproduced through inversions considering the Zeeman and the Paschen–Back effects with a three-slab model of the flare kernel, in which two slabs which have upward and downward velocities produce emissions and one slab produces an absorption. The magnetic field strength inferred from the emission components of the He i line is 1400 G, which is significantly stronger than 690 G that is observed at the same location in the same line 6.5 hr before the flare. In addition, the photospheric magnetic field vector derived from the Si i10827 Å is similar to that of the flare kernel. To explain this result, we suggest that the emission in the He i triplet during the flare is produced in the deep layer, around which bombardment of non-thermal electrons leads to the formation of a coronal temperature plasma. Assuming a hydrogen column density at the location where the He i emissions are formed, and a power-law index of non-thermal electron energy distribution, we derived the low-energy cutoff of the non-thermal electron as 20–30 keV, which is consistent with that inferred from hard X-ray data obtained by RHESSI.
Abstract
In this publication, we continue the work started in Quintero Noda et al., examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the ...physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles from the interior of the flux tube are periodically doppler shifted following an oscillation pattern that is also reflected in the amplitude of the circular polarization signals. In addition, we analyse the properties of the Stokes profiles at the edges of the flux tube discovering the presence of linear polarization signals for the Ca ii lines, although they are weak with an amplitude around 0.5 per cent of the continuum intensity. Finally, we compute the response functions to perturbations in the longitudinal field, and we estimate the field strength using the weak-field approximation. Our results indicate that the height of formation of the spectral lines changes during the magnetic pumping process, which makes the interpretation of the inferred magnetic field strength and its evolution more difficult. These results complement those from previous works, demonstrating the capabilities and limitations of the 850-nm spectrum for chromospheric Zeeman polarimetry in a very dynamic and complex atmosphere.
Solar polarimetry through the K i lines at 770 nm Quintero Noda, C; Uitenbroek, H; Katsukawa, Y ...
Monthly notices of the Royal Astronomical Society,
09/2017, Letnik:
470, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We characterize the K i D1 & D2 lines in order to determine whether they could complement the 850 nm window, containing the Ca ii infrared triplet lines and several Zeeman sensitive ...photospheric lines, that was studied previously. We investigate the effect of partial redistribution on the intensity profiles, their sensitivity to changes in different atmospheric parameters, and the spatial distribution of Zeeman polarization signals employing a realistic magnetohydrodynamic simulation. The results show that these lines form in the upper photosphere at around 500 km, and that they are sensitive to the line-of-sight velocity and magnetic field strength at heights where neither the photospheric lines nor the Ca ii infrared lines are. However, at the same time, we found that their sensitivity to the temperature essentially comes from the photosphere. Then, we conclude that the K i lines provide a complement to the lines in the 850 nm window for the determination of atmospheric parameters in the upper photosphere, especially for the line-of-sight velocity and the magnetic field.
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