Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Kawate, Tomoko; Hanaoka, Yoichiro; Ichimoto, Kiyoshi; Miura, Noriaki

doi:10.1111/j.1365-2966.2011.19192.x

Cited by 13 publications

(9 citation statements)

References 13 publications

(20 reference statements)

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“…The time lag of the start of an exposure between the three cameras is less than 8 µs. Assuming the Fried's parameter of 40 mm (Fried 1966;Kawate et al 2011) and wind velocity at the turbulent latitude of 40 m s exactly simultaneous. Motion of the solar image on the slit caused by the local turbulence of air (seeing) was approximately 3 arcsec in amplitude during the run of the observation.…”

Section: Observation and Image Processingmentioning

confidence: 99%

“…The time lag of the start of an exposure between the three cameras is less than 8 µs. Assuming the Fried's parameter of 40 mm (Fried 1966;Kawate et al 2011) and wind velocity at the turbulent latitude of 40 m s −1 , the time scale of the seeing is approximately equal to 1 ms, that is it is much larger than the synchronization accuracy, and thus the exposures of all three cameras can be regarded as exactly simultaneous. Motion of the solar image on the slit caused by the local turbulence of air (seeing) was approximately 3 arcsec in amplitude during the run of the observation.…”

Section: Observation and Image Processingmentioning

confidence: 99%

See 1 more Smart Citation

Differences between Doppler velocities of ions and neutral atoms in a solar prominence

Anan

Ichimoto

Hillier

2017

A&A

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Context. In astrophysical systems with partially ionized plasma the motion of ions is governed by the magnetic field while the neutral particles can only feel the magnetic field's Lorentz force indirectly through collisions with ions. The drift in the velocity between ionized and neutral species plays a key role in modifying important physical processes like magnetic reconnection, damping of magnetohydrodynamic waves, transport of angular momentum in plasma through the magnetic field, and heating. Aims. This paper investigates the differences between Doppler velocities of calcium ions and neutral hydrogen in a solar prominence to look for velocity differences between the neutral and ionized species. Methods. We simultaneously observed spectra of a prominence over an active region in H I 397 nm, H I 434 nm, Ca II 397 nm, and Ca II 854 nm using a high dispersion spectrograph of the Domeless Solar Telescope at Hida observatory, and compared the Doppler velocities, derived from the shift of the peak of the spectral lines presumably emitted from optically-thin plasma.Results. There are instances when the difference in velocities between neutral atoms and ions is significant, e.g. 1433 events (∼ 3 % of sets of compared profiles) with a difference in velocity between neutral hydrogen atoms and calcium ions greater than 3σ of the measurement error. However, we also found significant differences between the Doppler velocities of two spectral lines emitted from the same species, and the probability density functions of velocity difference between the same species is not significantly different from those between neutral atoms and ions. Conclusions. We interpreted the difference of Doppler velocities as a result of motions of different components in the prominence along the line of sight, rather than the decoupling of neutral atoms from plasma.

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“…The time lag of the start of an exposure between the three cameras is less than 8 µs. Assuming the Fried's parameter of 40 mm (Fried 1966;Kawate et al 2011) and wind velocity at the turbulent latitude of 40 m s exactly simultaneous. Motion of the solar image on the slit caused by the local turbulence of air (seeing) was approximately 3 arcsec in amplitude during the run of the observation.…”

Section: Observation and Image Processingmentioning

confidence: 99%

“…The time lag of the start of an exposure between the three cameras is less than 8 µs. Assuming the Fried's parameter of 40 mm (Fried 1966;Kawate et al 2011) and wind velocity at the turbulent latitude of 40 m s −1 , the time scale of the seeing is approximately equal to 1 ms, that is it is much larger than the synchronization accuracy, and thus the exposures of all three cameras can be regarded as exactly simultaneous. Motion of the solar image on the slit caused by the local turbulence of air (seeing) was approximately 3 arcsec in amplitude during the run of the observation.…”

Section: Observation and Image Processingmentioning

confidence: 99%

Differences between Doppler velocities of ions and neutral atoms in a solar prominence

Anan

Ichimoto

Hillier

2017

A&A

Self Cite

View full text Add to dashboard Cite

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“…showed that the typical Fried parameter r 0 at the Hida Observatory was about 4 cm at 600 nm in whole-day and all-season observations 12 . Assuming single ground-layer turbulence with a typical wind speed of 10 m/s, we obtain the Greenwood frequency as f g (typical) =0.427x10/0.04=106.8 (Hz) 13 .…”

Section: System Performancementioning

confidence: 93%

Development of a new solar adaptive optics system at the Hida Observatory

et al. 2014

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We are developing a new adaptive optics (AO) system for the 60cm domeless solar telescope of the Hida Observatory, Japan. The system has a deformable mirror with 97 piezo-actuators, a Shack-Hartmann wavefront sensor with a 10x10-microlens array and standard personal computers. We conducted solar observations in September, 2013, and confirmed that our AO system cancelled image-shifts so that the deviations were within the resolution of the telescope. We report the detailed performances of our new AO system.

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“…In order to obtain accurate polarization signals in ground-based observations, reduction of seeing-induced errors is crucial. A typical Fried's seeing parameter in daytime is several centimeter (Kawate et al 2011) and the seeing changes typically in several milliseconds. Thus, a cycle of the polarization modulation should be completed within several milliseconds.…”

Section: Instruments and Observation Parametersmentioning

confidence: 99%

Infrequent Occurrence of Significant Linear Polarization in Hα Solar Flares

Kawate

Hanaoka

2019

ApJ

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We performed statistical and event studies of linear polarization in the Hα line during solar flares. The statistical study revealed that, among 71 Hα flares analyzed, including 64 GOES flares, only one event shows significant linear polarization signals. Such an infrequent occurrence of significant linear polarization in solar flares is consistent with the result by Bianda et al. (2005), who studied 30 flares and found no polarization signals. In the event showing the significant polarization, the maximum degree of linear polarization was 1.16±0.06%, and the average direction of the polarization deviated by -142.5±6.0 degrees from the solar north. The observed polarization degrees and the directions are consistent with the preceding reports (e.g. Henoux et al. 1990;Emslie et al. 2000;Hanaoka 2003). These strong linear polarization signals did not appear at major flare ribbons, nor did they correlate with either hard or soft X-ray emissions temporally or spatially. Instead they appeared at a minor flare kernel, which corresponds to one of the footpoints of a coronal loop. The active region caused coronal dimming after the soft X-ray peak. The observed flare show no direct evidence that the linear polarization is produced by high energy particles, which are often considered to generate the polarization. On the other hand, our study suggests the possibility that coronal mass ejections, which have been often observed in flares showing linear polarization signals, play an important role for exciting linear polarization at Hα flare kernels.

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Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Cited by 13 publications

References 13 publications

Differences between Doppler velocities of ions and neutral atoms in a solar prominence

Differences between Doppler velocities of ions and neutral atoms in a solar prominence

Development of a new solar adaptive optics system at the Hida Observatory

Infrequent Occurrence of Significant Linear Polarization in Hα Solar Flares

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