E-Print Archive

There are 3897 abstracts currently viewable.


Search:

Advanced Search
Options
Main Page Add New E-Print Submitter
Information
Feedback
News Help/FAQ About Preferences
Manage Key Phrase
Notification
Signature of slow acoustic oscillations in a non-flaring loop observed by EIS/Hinode  

Dr. A. K. Srivastava   Submitted: 2009-09-10 22:04

egin{abstract} % Text of abstract We study intensity oscillations near the apex of a coronal loop to find the signature of MHD oscillations.We analyse the time series of the strongest Fe XII 195.12 Å image data, observed by 40'' SLOT of the EUV Imaging Spectrometer (EIS) onboard the Hinode spacecraft. Using a standard wavelet tool, we produce power spectra of intensity oscillations at location 'L3' near the apex of a clearly visible coronal loop. We detect intensity oscillations of a period of approx 322,s with a probability of 96 %. This oscillation period of approx 322 s is found to be in good agreement with theory of the second harmonics of standing slow acoustic oscillations of P2nd slow approx 313 pm 31,s. We detect, for the first time, the observational signature of second harmonics of slow acoustic oscillations in the non-flaring coronal loop. Such oscillations have been observed in the past in hot and flaring coronal loops only, but have been predicted recently to exist in comparatively cooler and non-flaring coronal loops as well. In addition, we also find the periodicities sim 497 s and sim 592 s with the probability 99-100% at the 'L1' and 'L2' locations respectively near the clearly visible western footpoint of the loop. We interpret these oscillations to be likely associated with the first harmonics (fundamental mode) of slow acoustic oscillations. Using the period ratios P_1/P_2~ 1.54, and 1.84 , we estimate the density scale heights in the EUV loop as sim 10 Mm and 21 Mm respectively, in which the latter value (sim 21 Mm) is compared well with the loop half length. We also find an evidence of propagating bright blob at its lower bound sub-sonic speed of approx 6.4 km s-1, suggesting that they are caused by the mass flow from one end to the other in the coronal loop.We also suggest that standing oscillations, and propagating bright blobs caused probably by the pulse of plasma flow, co-exist in comparatively cooler and non-flaring coronal loop. end{abstract}

Authors: A.K. Srivastava; B.N. Dwivedi
Projects: Hinode/EIS

Publication Status: New Astronomy, 2010, Vol. 15, pp. 8-15
Last Modified: 2009-09-11 08:18
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Observations of X-ray oscillations in XI Boo: Evidence of fast kink mode in the stellar loops  

Dr. A. K. Srivastava   Submitted: 2009-04-28 00:50

We report the observations of X-ray oscillations during the flare in a cool active star xi Boo for the first time. xi Boo was observed by EPIC/MOS of XMM-Newton satellite. The X-ray light curve is investigated with wavelet and periodogram analyses. Both analyses clearly show oscillations of the period of sim 1019 s. We interpret these oscillations as a fundamental fast-kink mode of magneto-acoustic waves.

Authors: J.C. Pandey; A.K. Srivastava
Projects: None

Publication Status: ApJL, 5 pages, 3 figures, 2 tables
Last Modified: 2009-04-28 10:18
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Observation of multiple sausage oscillations in cool post-flare loop  

Dr. A. K. Srivastava   Submitted: 2008-06-06 03:53

Using simultaneous high spatial (1.3 arc sec) and temporal (5 and 10 s) resolution Hα observations from the 15 cm Solar Tower Telescope at ARIES, we study the oscillations in the relative intensity to explore the possibility of sausage oscillations in the chromospheric cool postflare loop. We use standard wavelet tool, and find the oscillation period of ~ 587 s near the loop apex, and ~ 349 s near the footpoint. We suggest that the oscillations represent the fundamental and the first harmonics of fast sausage waves in the cool postflare loop. Based on the period ratio P1/P2 ~ 1.68, we estimate the density scale height in the loop as ~ 17 Mm. This value is much higher than the equilibrium scale height corresponding to Hα temperature, which probably indicates that the cool postflare loop is not in hydrostatic equilibrium. Seismologically estimated Alfvén speed outside the loop is ~ 300-330 km s-1. The observation of multiple oscillations may play a crucial role in understanding the dynamics of lower solar atmosphere, complementing such oscillations already reported in the upper solar atmosphere (e.g., hot flaring loops).

Authors: A.K. Srivastava, T.V. Zaqarashvili, W. Uddin, B.N. Dwivedi, Pankaj Kumar
Projects: None

Publication Status: Accepted in MNRAS
Last Modified: 2008-09-23 21:00
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

Subject will be restored when possible  

Dr. A. K. Srivastava   Submitted: 2008-03-14 01:39

Aims. To study intensity oscillations in the solar chromosphere/corona above a quiet-Sun magnetic network. Methods. We analyse the time series of He II 256.32, Fe XI 188.23 and Fe XII 195.12 spectral lines observed by EUV Imaging Spectrometer (EIS) on board Hinode near the south pole. Then we use a standard wavelet tool to produce power spectra of intensity oscillations above the magnetic network. Results. We get ~7 min intensity oscillations in all spectral lines and ~13 min intensity oscillations only in He II with the probability of ~96-98 %, which probably reflects the process of magneto-acoustic wave propagation above the network. Conclusions. We suggest that field-free cavity areas under bipolar magnetic canopies in the vicinity of magnetic network may serve as resonators for the magneto-acoustic waves. The cavities with photospheric sound speed and granular dimensions may produce the waves with the observed periods. The waves may propagate upwards in the transition region/corona and cause observed intensity oscillations.

Authors: A.K. Srivastava, D. Kuridze, T.V. Zaqarashvili, & B.N. Dwivedi
Projects: Hinode/EIS

Publication Status: Accepted in A&A Letters (unedited version from arXive.)
Last Modified: 2008-09-23 21:14
Go to main E-Print page  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 


Key
Go to main E-Print pageGo to main E-Print page.
Download PreprintDownload Preprint.
Submitter's HomepageSubmitters Homepage.
Edit EntryEdit Entry.
Delete AbstractDelete abstract.

Abstracts by Author
Signature of slow acoustic oscillations in a non-flaring loop observed by EIS/Hinode
Observations of X-ray oscillations in XI Boo: Evidence of fast kink mode in the stellar loops
Observation of multiple sausage oscillations in cool post-flare loop
Subject will be restored when possible

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University