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Detection of spicules termed Rapid Blue-shifted Excursions as seen in the chromosphere via Hα and the transition region via Si iv 1394 line emission  

Nived Vilangot Nhalil   Submitted: 2022-07-06 05:11

We show signatures of spicules termed Rapid Blue-shifted Excursions (RBEs) in the Si iv 1394 emission line using a semi-automated detection approach. We use the Hα filtergrams obtained by the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope and co-aligned Interface Region Imaging Spectrograph data using the SJI 1400 channel to study the Spatio-temporal signature of the RBEs in the transition region. The detection of RBEs is carried out using an oriented coronal loop tracing algorithm on Hα Dopplergrams at 35 km s-1. We find that the number of detected features is significantly impacted by the time-varying contrast values of the detection images, which are caused by the changes in the atmospheric seeing conditions. We detect 407 events with lifetime greater than 32 sec. This number is further reduced to 168 RBEs based on the Hα profile and the proximity of RBEs to the large scale flow. Of these 168 RBEs, 89 of them display a clear Spatio-temporal signature in the SJI 1400 channel, indicating that a total of ~53% are observed to have co-spatial signatures between the chromosphere and the transition region.

Authors: Nived Vilangot Nhalil, Juie Shetye, J. Gerry Doyle
Projects: None

Publication Status: MNRAS (accepted)
Last Modified: 2022-07-06 13:25
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Doubling of minute-long Quasi-Periodic Pulsations from super-flares on a low mass star  

Nived Vilangot Nhalil   Submitted: 2022-06-17 10:40

Using the ULTRASPEC instrument mounted on the 2.4-m Thai National Telescope, we observed two large flares, each with a total energy close to 1034 erg with sub-second cadence. A combination of a wavelet analysis, a Fourier transform plus an empirical mode decomposition, reveals quasi-period pulsations (QPP) which exhibit an apparent doubling of the oscillation period. Both events showed oscillations of a few minutes over a interval of several minutes, and despite the availability of sub-second cadence, there was no evidence of sub-minute oscillations. The doubling of the QPP periods and shorter lifetime of shorter-period QPP modes strongly favour resonant dynamics of magnetohydrodynamic waves in a coronal loop. We estimate loop lengths to be 0.2-0.7 R*, in agreement with a typical length of solar coronal loops. These observations presents rare and compelling evidence for the presence of compact plasma loops in a stellar corona.

Authors: J. Gerry Doyle, Puji Irawati, Dmitrii Y. Kolotkov, Gavin Ramsay, Nived Vilangot Nhalil, Vik S. Dhillon, Tom R. Marsh, Ram Kesh Yadav
Projects: None

Publication Status: MNRAS (accepted)
Last Modified: 2022-06-21 11:12
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Implications of spicule activity on coronal loop heating and catastrophic cooling  

Nived Vilangot Nhalil   Submitted: 2021-11-25 05:11

We report on the properties of coronal loop foot-point heating with observations at the highest resolution, from the CRisp Imaging Spectro-Polarimeter (CRISP) located at the Swedish 1-m Solar Telescope (SST) and co-aligned NASA Solar Dynamics Observatory (SDO) observations, of Type II spicules in the chromosphere and their signatures in the EUV corona. Here, we address one important issue, as to why there is not always a one-to-one correspondence, between Type II spicules and hot coronal plasma signatures, i.e. beyond TR temperatures. We do not detect any difference in their spectral properties in a quiet Sun region compared to a region dominated by coronal loops. On the other hand, the number density close to the foot-points in the active region is found to be an order of magnitude higher than in the quiet Sun case. A differential emission measure analysis reveals a peak at ∼5 105 K on the order of 1022 cm-5 K-1. Using this result as a constraint, we conduct numerical simulations and show that with an energy input of 1.25 1024 erg (corresponding to ∼10 RBEs contributing to the burst) we manage to reproduce the observation very closely. However, simulation runs with lower thermal energy input do not reproduce the synthetic AIA 171 signatures, indicating that there is a critical number of spicules required in order to account for the AIA 171 signatures in the simulation. Furthermore, the higher energy (1.25 1024 ergs) simulations reproduce catastrophic cooling with a cycle duration of ∼5 hours, matching a periodicity we observe in the EUV observations.

Authors: V N Nived, E Scullion, J G Doyle, R Susino, P Antolin, D Spadaro, C Sasso, S Sahin, M Mathioudakis
Projects: SDO-AIA,Swedish Solar Telescope (SST)

Publication Status: Published in MNRAS
Last Modified: 2021-11-26 09:15
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Abstracts by Author
Detection of spicules termed Rapid Blue-shifted Excursions as seen in the chromosphere via Hα and the transition region via Si iv 1394 line emission
Doubling of minute-long Quasi-Periodic Pulsations from super-flares on a low mass star
Implications of spicule activity on coronal loop heating and catastrophic cooling

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