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Инфоурок / Астрономия / Статьи / Two types of coronal bright points their characteristics, and evolution

Two types of coronal bright points their characteristics, and evolution

  • Астрономия

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The Physics of Sun and Star Spots

Proceedings IAU Symposium No. 273, 2010

D.P. Choudhary & K.G. Strassmeier, eds.

_c International Astronomical Union 2011

doi:10.1017/S1743921311015511

Two types of coronal bright points their

characteristics, and evolution

Isroil Sattarov1, Nina V. Karachik2, Chori T. Sherdanov3,

Azlarxon M. Tillaboev1, and Alexei A. Pevtsov2

1Tashkent State Pedagogical University, 103 Yusif Kxos Kxojib str.,

Tashkent 100070, Uzbekistan

email: isattar@astrin.uz

2National Solar Observatory, Sunspot, NM 88349, USA

email: apevtsov@nso.edu

3Astronomical Institute of the Academy of Sciences of Uzbekistan

email: chori@astrin.uz

Abstract. Using maximum brightness of coronal bright point’s (CBP) as a criterion, we separate

them on two categories: dim CBPs, associated with areas of a quiet Sun, and bright CBPs,

associated with an active Sun. This study reports on characteristics of two types of CBPs and

their evolution.

Keywords. Solar corona, coronal bright points

1. Introduction and Data

Coronal Bright Points (CBPs, also referred to as X-ray bright points, XBPs) are compact

coronal brightenings observed in X-ray, EUV, and radiowaves. Several authors had

reported on existence of two types of XBPs: XBPs of quiet Sun, uniformly distributed

over the solar surface (both temporally and spatially) and the XBPs with non-statistical

variations in the longitudinal distributions e.g. Golub, Krieger, Vaiana (1975); Sattarov,

et al. (2002, 2005a,b); McIntosh & Gurman (2005). Sattarov (2007) have found that the

number of high latitude CBPs shows negative correlation with sunspot cycle, whereas

number of CBPs in active region belts correlates positively with the cycle. This finding

suggests a more complicated relationship between the CBP number and the solar activity

cycle than had been previously thought. In this report we separate CBPs on two types

using their brightness: “dim” CBPs are connected to quiet Sun regions and “bright”

CBPs related to the active Sun. We investigate the characteristics of the two types of

CBPs and their evolution, including the latitudinal distribution, temporal variation of

CBP’s maximal intensity, area, and the lifetime. We use full disk images observed by

the Extreme-ultraviolet Imaging Telescope (EIT) on board of SOHO. We utilize EIT full

disk synoptic data with spatial resolution of 2.64 arcsec per pixel and six hours cadence

observed (full disk mode) in 195˚A from 1996–2008. For study the evolution of CBPs, we

use EIT data obtained in “CME watch” mode with much higher time cadence. The data

are calibrated following the standard EIT data reduction routine. To identify the coronal

bright points, we employ the automatic procedure developed by us see (Sattarov, et al.

2010).

2. Temporal and latitudinal distribution of CBPs

If the CBPs are related to magnetic fields in the photosphere, one can make a reasonable

assumption that the intensity of CBP must correlate with the magnetic flux. As is


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Figure 1. Cycle variation of average maximal intensity (Imax) of CBP for 1996-2008.

well-known, the magnetic flux on solar surface changes with solar activity, and therefore

the increased level of solar activity would stimulate rise of maximal intensity of CBP and

its decrease would followed by a decline of CBP brightness. Figure 1 presents cycle variation

of average maximal intensity of CPBs during solar Cycle 23, which indicates that

CBPs are (on average) brighter during maximum of solar activity cycle as compared with

periods of solar minimum. At solar minimum in 1996, the average Imax intensity was

about 150 DNs.Thus, we take it as a threshold between the “dim” and “bright” CBPs.

In accordance with this criteria at solar minimum (1996) a majority of CBPs is “dim”

ones. In 1997, number of bright CBPs starts rise quickly, while number of “dim” CBPs

decreases. Latitudinal distribution of “dim” CBPs for 1996 (see Fig.6 in Sattarov, et al.

(2010)) follows cosine function . The latitudinal distribution of bright CBPs (See Fig. 7

in Sattarov, et al. (2010)) for 1998 and 2002 exhibits two humps similar to latitudinal

distribution of sunspots. However, in these years of high solar activity, both types of

CBPs are present; bright CBP being predominant in active region belts, and dim CBPs

are more abundant near the equator.

3. Evolution of coronal bright points

To study temporal evolution of CBPs we use EIT data obtained in “CME Watch”

mode on 26 September 1997 (start of cycle 23) and 21 December 2002 (second maximum

of the cycle). We find that CBPs have different area at maximum of its brightness, from

10 up to 200 pixels, and we study evolution of CBPs of different area (Figure 2).

On Fig.2 one can see the evolutions of two types CBP have small difference by area, but

amplitude variation of intensity differs. The difference is small for bright CBP and large

for “dim” ones. Fig.3 presents the temporal variations in intensity and area of small CBP

of quiet Sun type. A small flare-like brightening had occurred at the beginning of CBP

development (see peak in intensity in Figure 3, right). After the intensity spike, CBP

area remains glaring during 5-10 hour. CBPs of larger size also show flare-like changes in

intensity (see examples in Figure 2). Area of CBP shown in Figure 2 is 8 pixels or circle

with radius 4 arc sec or 16 MHS. It represents an example of small, quiet Sun CBP during

solar minimum of activity. Based on the examples shown in Figure 2, we speculate that



Two types of coronal bright points


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Figure 2. Examples of temporal variation an area (upper panel for each example) and intensity

(lower panel for each example) of CBPs of different size and maximum intensity for periods of

low (left column) and high (right) levels of solar activity.



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Figure 3. Temporal variation an area and intensity for CBP on September 26 1997.

large CBPs may be comprised of smaller CBPs that exhibit flare-like activity similar to

example shown in Figure 3.

4. Discussion and Conclusions

We find that the active and quiet Sun coronal bright points exhibit flare-like variation

in their maximum intensity. The amplitude of intensity variations is higher for small

CBPs and lower for larger ones. Small quiet Sun CBPs may show repeated flare-like

spikes with amplitude gradually decreasing during half a day period. This flaring slowly

increases background around the CBP. Large CBPs also show such repeated flaring up

albeit with smaller amplitude as compared with small CBPs. The repeat flaring in large

CBPs may be related to elementary CBPs that collectively form large CBP. This our

finding is in agreement with early studies, which found that X-ray bright point may

consist of several kernels that flare-up one after the other. Small CBPs may consist of a

I. Sattarov et al.

single kernel (one elementary CBP), which would explain higher amplitude variations in

their intensity as compared with larger CBPs.

Acknowledgements

The presentation of this paper at the IAU Symposium 273 was made possible due

to partial support from the National Science Foundation grant numbers ATM 0548260,

AST 0968672 and NASA - Living With a Star grant number 09-LWSTRT09-0039.

References

Golub, L., Krieger, A. S., & Vaiana, G. S. 1975, Solar Phys., 42, 131

McIntosh, S. W. & Gurman, J. B. 2005, Solar Phys., 228, 285

Sattarov, I., Pevtsov, A. A., Karachik, N. V., Sherdanov, C. T., & Tillaboev, A. M. 2010, Solar

Phys., 262, 321

Sattarov, I., Pevtsov, A. A., Karachik, N. V., & Sherdanov, C. T. 2007, Adv. Sp. Res. 39, 1777

Sattarov, I., Pevtsov, A. A., Karachik, N. V., & Sattarova, B. J. 2005a, ASP Conf. Ser., 346,

363

Sattarov, I., Pevtsov, A. A., Karachik, N. V., & Sattarova, B. J. 2005b, ASP Conf. Ser., 346,

395

Sattarov, I., Pevtsov, A. A., Hojaev, A. S., & Sherdonov, C. T. 2002, Astrophys. J., 564, 1042


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Дата добавления 05.07.2016
Раздел Астрономия
Подраздел Статьи
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