Issue |
A&A
Volume 418, Number 1, April IV 2004
|
|
---|---|---|
Page(s) | 313 - 324 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20035666 | |
Published online | 02 April 2004 |
Signature of oscillations in coronal bright points
1
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
2
Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
3
Instituto de Astrofísica de Canarias, C/ vía Láctea s/n, 38200 La Laguna, Tenerife, The Canary Islands, Spain
Corresponding author: I. Ugarte-Urra, iuu@star.arm.ac.uk
Received:
12
November
2003
Accepted:
23
January
2004
A detailed study of two consecutive bright points observed simultaneously with the Coronal Diagnostic Spectrometer (CDS), the Extreme ultraviolet Imaging Telescope (EIT) and the Michelson
Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) is presented. The analysis of
the evolution of the photospheric magnetic features and their coronal counterpart shows that there
is a linear dependence between the EIT Fe xii 195 Å flux and the total magnetic flux of the photospheric
bipolarity. The appearance of the coronal emission is associated with the emergence of new magnetic flux and
the disappearance of coronal emission is associated with the cancellation of one of the polarities. In
one of the cases the disappearance takes place ~3–4 h before the full cancellation of the
weakest polarity.
The spectral data obtained with CDS show that one of the bright points experienced short time
variations in the flux on a time scale of 420–650 s, correlated in
the transition region lines (O v 629.73 Å and O iii 599.60 Å) and also the He i
584.34 Å line. The coronal line (Mg ix 368.07 Å) undergoes changes as well, but on a longer scale.
The wavelet analysis of the temporal series reveals that many of these events appear in a random
fashion and sometimes after periods of quietness. However, we have found two cases of an oscillatory
behaviour. A sub-section of the O v temporal series of the second bright point shows a damped
oscillation of five cycles
peaking in the wavelet spectrum at 546 s, but showing in the latter few cycles a lengthening
of that period. The period compares well with that detected in the S vi 933.40 Å
oscillations seen in another bright point observed with the Solar Ultraviolet Measurements of
Emitted Radiation (SUMER) spectrometer, which has a period of 491 s. The derived electron
density in the transition region was cm-3 with some small
variability, while the coronal electron density was
cm-3.
Key words: Sun: oscillations / Sun: corona / Sun: transition region / Sun: UV radiation / Sun: magnetic fields
© ESO, 2004
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