CORONAL BRIGHT AND DARK POINTS: SOME
RESULTS OF JOINT INVESTIGATION
D.V Prosovetsky 1
and L.K. Kashapova2
Institute of Solar-Terrestrial Physics, P.O. Box 4026, Irkutsk, 664033, Russia
1 [email protected] 2 [email protected]
Abstract
We present the investigation results carried out on the basis of simultaneous observations of Large Solar Vacuum telescope (HeI λ 10830 Å) and Siberian Solar
Radio telescope (5.2 cm). The data of Nobeyama radioheliograph, YOHKOH
and TRACE were also used at analysis. Coronal bright points are observed
within the considerable height range – from the corona and the transition region
to low lays of solar chromosphere. In visible spectral region ( HeIλ 10830 Å)
they are known as "dark points". It is assumed that the phenomenon arises as
a result of energy release in the interaction locations of a emerging magnetic
flux and existing magnetic fields. The mechanism of their origin and evolution
has not been enough investigate. A one of reasons is a deficit of information
about the correlation between emission parameters of these objects in different ranges of electromagnetic spectrum. The most promising investigation is
seemed a comparison of the spectral their properties in visible region with parameters obtained from observation in microwaves, X-ray and UV. Authors are
comparing radiation parameters obtained for the group of objects in different
spectral ranges and discuss possible phenomenological models.
Keywords:
Coronal bright points, mechanisms of energy transfer
1.
Introduction
The coronal bright points are the most spreading kind of a solar activity
and they are registered in broad range of electromagnetic spectrum. However,
the observation is showing a partial matching of coronal points at the different wavelengths (see, for example, Fu, Kundu & Schmahl 1987; Maksimov,
Prosovetski, & Krissinel 2001). The same emission features of the coronal
objects, expanded by heights, as can be a evidence of the BP’s spatial structure properties as reproduce the characteristics of energy transference from its
release location to the emission levels. Multiwave observations, giving the information about the radiation from broad range of solar atmospheric levels,
2
AR8257
The operating
height of slit
The slit of
spectrograph
Figure 1. The slit of spectrograph of the Large Solar Vacuum Telescope on solar disk at 02:34
UT on 28th June, 1998.
allow us to estimate the composition and processes within the coronal bright
points more correctly.
2.
The results of observations
The present contribution uses the observational data obtained on spectrograph of Large Solar Vacuum Telescope (LSVT) and Siberian Solar Radio
Telescope (SSRT, 5.2 cm) and Nobeyama radioheliograph (NRH, 1.76 cm).
The scanning of solar disk by the slit of LSVT’s spectrograph was made
nearby the active region AR 8257 on 28 June, 1998 from 2:07 UT till 2:37 UT
(Fig 1). The dark points in He I λ10830 Å on the spectrograms (Fig 2), obtained by CCD-camera, were extracted (Fig 3).The line-of-sight velocities and
optical depth were determined in the dark points according to the method described in (Skomorovsky et al. 2001). We spatially compare the dark points
observed in IR helium with microwave sources (Fig 4) and defined the brightness temperatures and the sizes of corresponding microwave sources. It was
investigated 12 dark points at all. The six microwave sources corresponded to
them, moreover, each of source at 5.2 cm had the pair at 1.76 cm wavelength.
Coronal bright and dark points: some results of joint investigation
3
Figure 2. The spectrogram at a point in time 2:34 UT. DP1 and DP2 are the identified dark
points in HeI 10830Å, QR is quit Sun.
Figure 3. The spectral profile of dark point DP2 (Fig 2). The dashed line is the quit region
spectra, the solid line is the dark point spectra.
4
DP2
DP1
BP
Figure 4. The profiles of brightness temperature with subtracted the quit Sun level on the slit
location on 5.2 cm (solid line) and 1.76 cm (dashed line) wavelength. The crosshatched regions
correspond to dark point locations (DP1 and DP2).
3.
Discussion
The ratio of brightness temperatures for the microwave sources (without
level of quiet Sun), coincided with dark points in He I λ10830 Å, are about
0.112. This indicates the thermal brake gear of optically thin plasma as mechanism of microwave radiation (Maksimov, Prosovetski, & Krissinel 2001). The
comparison of the matter motion directions observed in dark points with the
microwave source presence shows that the microwave bright point presented
only if the line-of-sight velocity of dark point was directed from the observer.
Moreover, the dark points without the pairs at 5.2 and 1.76 cm wavelengths
located farther from the microwave source maximums. It’s notably that the
"recessive" from observer dark points located along the loops seen according
to TRACE’s data in UV-rays (see Fig. 5).
Based on the model of a quasi-stationary loop (Vesecky, Antiochos, & Underwood 1979; Kankelborg et al. 1996), the estimations of coronal bright
points and the line-of-sight velocities from the He I λ10830 Å observations
allow us to conclude that the thermal flux moving from the lower layers of
solar atmosphere can’t support the conditions for the microwave source origin with the observed brightness temperature. At the same time the absolute
value of thermal flux, estimated by microwave irradiation on the assumption of
the thermal mechanism, is quite enough for giving to the matter the measured
chromospheric velocities. So, we can assume that, the energy was released into
the corona, for example, as the reconnection result of the existent and emerg-
Coronal bright and dark points: some results of joint investigation
5
Figure 5. The DP’s location on the UV image of the solar region (TRACE). The signs "+" are
corresponding to DP’s moving from the observer, the circles are corresponding to DP’s moving
to the observer.
Figure 6.
A schematic model of energy transport into the coronal bright points.
ing magnetic fields, and transported by the thermal flux to the lower layers of
solar atmosphere in order to support the conditions for observed effects (see
Fig. 6).
6
Acknowledgments
This work was supported by Lavrentev’s young scientist grant of SB RAS,
grants NSh-477.2003.2 and NSh-733.2003.2 of the State Support of Leading
Scientific Schools of Russia Federation, the state Scientific Technical Program
"Astronomy" and grant I0208.1173 of the Federal Purpose Program "Integration". Dr. L.K. Kashapova acknowledges European Astronomical Society and
Russian Foundation of Basic Research for the supporting of participation in
JENAM-2004.
References
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Maksimov, V.P., Prosovetski, D.V., & Krissinel, B.B. (2001). Astronomy Letters 27, 181–185.
Skomorovsky, V.I., Firstova, N.M., Kashapova, L.K. et al. (2001). Solar Phys., 199, 37–45.
Vesecky, J.F., Antiochos, S.K., & Underwood, J.H. (1979). Astrophys. J. 233, 987–997.