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Title: Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption

Abstract

We present a study on the evolution of the small-scale velocity field in a solar filament as it approaches the eruption. The observation was carried out by the Solar Dynamics Doppler Imager (SDDI) that was newly installed on the Solar Magnetic Activity Research Telescope at Hida Observatory. The SDDI obtains a narrowband full-disk image of the Sun at 73 channels from H α − 9.0 Å to H α + 9.0 Å, allowing us to study the line-of-sight (LOS) velocity of the filament before and during the eruption. The observed filament is a quiescent filament that erupted on 2016 November 5. We derived the LOS velocity at each pixel in the filament using the Becker’s cloud model, and made the histograms of the LOS velocity at each time. The standard deviation of the LOS velocity distribution can be regarded as a measure for the amplitude of the small-scale motion in the filament. We found that the standard deviation on the previous day of the eruption was mostly constant around 2–3 km s{sup −1}, and it slightly increased to 3–4 km s{sup −1} on the day of the eruption. It shows a further increase, with a rate of 1.1 m s{supmore » −2}, about three hours before eruption, and another increase, with a rate of 2.8 m s{sup −2}, about an hour before eruption. From this result we suggest that the increase in the amplitude of the small-scale motions in a filament can be regarded as a precursor of the eruption.« less

Authors:
;  [1]; ; ; ;  [2]
  1. Graduate School of Advanced Integrated Studies in Human Survivability, Kyoto University, Sakyo, Kyoto 606-8306 (Japan)
  2. Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471 (Japan)
Publication Date:
OSTI Identifier:
22654441
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 843; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; CLOUDS; DISTRIBUTION; EVOLUTION; MASS; PRECURSOR; SOLAR FLARES; SUN; TELESCOPES; VELOCITY

Citation Formats

Seki, Daikichi, Isobe, Hiroaki, Otsuji, Kenichi, Ishii, Takako T., Sakaue, Takahito, and Hirose, Kumi, E-mail: seki@kwasan.kyoto-u.ac.jp. Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption. United States: N. p., 2017. Web. doi:10.3847/2041-8213/AA7559.
Seki, Daikichi, Isobe, Hiroaki, Otsuji, Kenichi, Ishii, Takako T., Sakaue, Takahito, & Hirose, Kumi, E-mail: seki@kwasan.kyoto-u.ac.jp. Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption. United States. doi:10.3847/2041-8213/AA7559.
Seki, Daikichi, Isobe, Hiroaki, Otsuji, Kenichi, Ishii, Takako T., Sakaue, Takahito, and Hirose, Kumi, E-mail: seki@kwasan.kyoto-u.ac.jp. 2017. "Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption". United States. doi:10.3847/2041-8213/AA7559.
@article{osti_22654441,
title = {Increase in the Amplitude of Line-of-sight Velocities of the Small-scale Motions in a Solar Filament before Eruption},
author = {Seki, Daikichi and Isobe, Hiroaki and Otsuji, Kenichi and Ishii, Takako T. and Sakaue, Takahito and Hirose, Kumi, E-mail: seki@kwasan.kyoto-u.ac.jp},
abstractNote = {We present a study on the evolution of the small-scale velocity field in a solar filament as it approaches the eruption. The observation was carried out by the Solar Dynamics Doppler Imager (SDDI) that was newly installed on the Solar Magnetic Activity Research Telescope at Hida Observatory. The SDDI obtains a narrowband full-disk image of the Sun at 73 channels from H α − 9.0 Å to H α + 9.0 Å, allowing us to study the line-of-sight (LOS) velocity of the filament before and during the eruption. The observed filament is a quiescent filament that erupted on 2016 November 5. We derived the LOS velocity at each pixel in the filament using the Becker’s cloud model, and made the histograms of the LOS velocity at each time. The standard deviation of the LOS velocity distribution can be regarded as a measure for the amplitude of the small-scale motion in the filament. We found that the standard deviation on the previous day of the eruption was mostly constant around 2–3 km s{sup −1}, and it slightly increased to 3–4 km s{sup −1} on the day of the eruption. It shows a further increase, with a rate of 1.1 m s{sup −2}, about three hours before eruption, and another increase, with a rate of 2.8 m s{sup −2}, about an hour before eruption. From this result we suggest that the increase in the amplitude of the small-scale motions in a filament can be regarded as a precursor of the eruption.},
doi = {10.3847/2041-8213/AA7559},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 843,
place = {United States},
year = 2017,
month = 7
}
  • Both large-amplitude longitudinal (LAL) oscillations and material drainage in a solar filament are associated with the flow of material along the filament axis, often followed by an eruption. However, the relationship between these two motions and a subsequent eruption event is poorly understood. We analyze a filament eruption using EUV imaging data captured by the Atmospheric Imaging Array on board the Solar Dynamics Observatory and the Hα images from the Global Oscillation Network Group. Hours before the eruption, the filament was activated, with one of its legs undergoing a slow rising motion. The asymmetric activation inclined the filament relative tomore » the solar surface. After the active phase, LAL oscillations were observed in the inclined filament. The oscillation period increased slightly over time, which may suggest that the magnetic fields supporting the filament evolve to be flatter during the slow rising phase. After the oscillations, a significant amount of filament material was drained toward one filament endpoint, followed immediately by the violent eruption of the filament. The material drainage may further support the change in magnetic topology prior to the eruption. Moreover, we suggest that the filament material drainage could play a role in the transition from a slow to a fast rise of the erupting filament.« less
  • We present a possible O VIII X-ray absorption line at z = 0.117 {+-} 0.001 which, if confirmed, will be the first one associated with a broad H I Ly{beta} (BLB: FWHM = 160{sup +50} {sub -30} km s{sup -1}) absorber. The absorber lies along the line of sight to the nearby (z = 0.1372) Seyfert 1 galaxy PKS 0558-504, consistent with being a WHIM filament. The X-ray absorber is marginally detected in two independent XMM-Newton spectra of PKS 0558-504, a long {approx}600 ks guest-observer observation and a shorter, {approx}300 ks total, calibration observation, with a combined single line statisticalmore » significance of 2.8{sigma} (2.7{sigma} and 1.2{sigma} in the two spectra, respectively). When fitted with our self-consistent hybrid-photoionization WHIM models, the combined XMM- Newton spectrum is consistent with the presence of O VIII K{alpha} at z = (0.117 {+-} 0.001). This model gives best-fitting temperature and equivalent H column density of the absorber of log T = 6.56{sup +0.19} {sub -0.17} K, and log N{sub H} = (21.5 {+-} 0.3)(Z/Z {sub 0.01sun}){sup -1} cm{sup -2}, and predicts the marginal contribution of only two more lines within the XMM- Newton Reflection Grating Spectrometer band pass, Ne IX K{alpha} ({lambda} = 13.45 A) and Fe XVII L ({lambda} = 15.02 A), both with equivalent widths well within the 1{sigma} sensitivity of the combined XMM-Newton spectrum of PKS 0558-504 (EW{sup 1}{sigma} < 3 mA). The lack of detection of associated O VI in the archival FUSE spectrum of PKS 0558-504 allows us to infer a tighter lower limit on the temperature, of log T>6.52 K (at 1{sigma}). The statistical significance of this single X-ray detection is increased by the detection of BLB and complex H I Ly{beta} absorption in archival FUSE spectra of PKS 0558-504, at redshifts z = 0.1183 {+-} 0.0001 consistent with the best-fitting redshift of the X-ray absorber. The FUSE spectrum shows a broad (FWHM = 160{sup +50} {sub -30} km s{sup -1}) absorption complex, which we identify as H I Ly{beta} z {sub BLB} = (0.1183 {+-} 0.0001). The single line statistical significance of this line is 4.1{sigma} (3.7{sigma} if systematics are considered). A possible H I Ly{alpha} is marginally hinted in an archival low-resolution ({Delta}{lambda} {approx} 6 A) International Ultraviolet Explorer (IUE) spectrum of PKS 0558-504, at a redshift of z = (0.119 {+-} 0.001) and with single line significance of 1.7{sigma}. Thus, the combined significance of the three (XMM- Newton, FUSE, and IUE) independent tentative detections, is 5.2{sigma} (5.0{sigma} if the H I Ly{alpha} is not considered, and 4.6{sigma} if the systematics in FUSE are considered). The detection of both metal and H lines at a consistent redshift, in this hot absorbing system, allows us to speculate on its metallicity. By associating the bulk of the X-ray absorber with the BLB line detected in the FUSE spectrum at z {sub BLB} = 0.1183 {+-} 0.0001, we obtain a metallicity of 1%-4% Solar. Although the absorber is only blueshifted by {approx}-6000 km s{sup -1} from the systemic redshift of PKS 0558-504, the identification of the absorbing gas with a high velocity nuclear ionized outflow, is unlikely. The physical, chemical, and dynamical properties of the detected absorber are all quite different from those typically found in the warm absorber (WA) outflows, commonly detected in Seyferts and higher luminosity quasars. WA outflow velocities typically span a range of few hundreds to {approx}1-2 thousands km s{sup -1}; WA metallicities, when measured, are typically found to be at least Solar; high-ionization WAs are virtually always found to coexist with lower-ionization X-ray and UV phases. All this strongly suggests that the absorber, if confirmed, is an intervening WHIM system.« less
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