Bibcode
Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
Bibliographical reference
Astronomy and Astrophysics, v.418, p.313-324 (2004)
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4
2004
Journal
Citations
37
Refereed citations
37
Description
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 3×1010 cm-3
with some small variability, while the coronal electron density was
5×108 cm-3.