Vl.~tas in As tronomy, Vol. 31, pp. 73-77, 1988 0083-6656/88 $0.00+ .50

Copyright © 1988 Science Press & Pergamon Journal8 Ltd.

M A G N E T I C AND V E L O C I T Y F I E L D O B S E R V A T I O N S W I T H A S O L A R M A G N E T I C F I E L D T E L E S C O P E ( S M F T )

Li Wei Bhang Hongqi Li J i n g Han Feng Ming Changrong L iu J i a n q i a n g L iu Ken ing

B e i j i n g A s t r o n o m i c a l O b s e r v a t o r y , C h i n a

INTRODUTION

The SMFT (Ai, 1986) is a video vector magnetograph. It was designed

by solar physicists of our country in 1966, and its development was

started in 1972. It was installed at Huairou Solar Observing

Station of Beijing Astronomical Observatory towards the end of 1984.

Since 1985, we have made a series of major improvements, including

the successful use of a computer and a CCD camera in the SMFT.

At present there are three varieties of video magnetographs

in the world. One is the MSFC video vector magnetograph of NASA

(Haygard, 1985) which, however, is not intended for line-of-sight

velocity measurements. Another is the BBSO video magnetograph which

can be used for measurements of longitudinal magnetic field~ and

sight-line velocities of the photosphere. Our telescope can be used

for measurement of the vector magnetic field as well as the line-

of-sight velocities in both the photosphere and the chromosphere'.

In 1986, SMFT had passed appraisal and opened in June of ths year.

We welcome specialists and scholars from all over the world to use

SMFT and cooperate with us in solar physics research.

|. Outline of the SMFT

There are two lines used for the observation of the solar

photosphere and chromosphere respectively. The line Fel %5324. 19A

is suitable for the observation of strong magnetic fields. Calcula-

tions (Ai et al., 1986) have indicated that the linearity deviation

is only 2% even when magnetic strength goes up to 3000G. The line

HB is different from that of Ha in the monochromatic image. The

suppergranule structure is remarkable. At present very few

observations of the solar magnetic field are being made at H~

73

74 Li Wei et ~I.

It is quite a new project to observe the velocity at H~ , especially

suing a two-dimensional treatment with the real time processor

system. Using the solar rotation curve, we have been combining the

empirical calibration with theoretical calculations in our magnetic

field observations. The SMFT (Ai and Hu, 1986) has three modes of

operation: the photoelectric system, the photographic system and

the system of CCD camera with an image processor.

2. The observations of two-dimensional real time sight-line velocity fields and magnetic fields

We have found that, according to our observations with the

photoelectric system, the oscillation period of the chromosphere is

different from that of the photosphere. The former is some 2.3-3.2

minutes, appreciably shorter than that of the photosphere. The

photographic system enables one to achieve a spatial resolution of

] arcsecond with I/4 second exposure times.

The use of a CCD camera and an image processor further makes

the SMFT even more versatile. The size of the observed region is

4'*5'3 (512"512 pixels). The time resolution of an image is 40

seconds when it is taken with 255 frames. The accuracy of the

measured chromospheric velocity field is +30m/s (255 frames, 40 I!

seconds). The resolution in space is 1.5.

Fig.] shows the vector magnetic field of an active region. We

can see that the alignments of the transverse field are along the

sunspot fibers.

67Gi.a~ ~Je v K ~ o r 8 i l l i t o K l l Ot L ie I~lJS)ot{If~J , IJ l?)

• ~ ' ~ ' " : . . : : i : i " i : # ' : i ! i ! ~ i i ~ : i i i : : ~

L~ ' . . . . . . ~ : : : : : : : : : : : : : : : : : : : : : : :

: : ' e ~ ; . " . I ' i ; : : ~ . 4 ~ , : : : . e

Fig. l The vector magnetogram of an active region

Magentic and Velocity Field 75

Fig.2 shows the longitudinal magnetogram of a quiet region. It

was observed in the quiet region near the solar disk centre at

FeI %5324A. The smallest measurable magnetic field is about +3G.

It is easy to distinguish the supergranule configurations in this

picture. Features characterized by mixed opposite polarities are

universal in the quiet regions (Hu et al., ]983). The white features

are of positive and the black are of negative polarity.

f p ~ . . . ~ ' . ~ ' • .

. ~ . * . ,

• (" ~ •

Fig.2. The magnetogram of a quiet Fig.3. The velocitygram of a region (Sep I0, 1987 UT0048) prominence(Jul.17, 1987

UTOi41)

The magnetic fields with opposite polarities of polar regions

have been obtained. Regular observations have been carried ou~ in

order to study, the long-period changes.

Fig.3 show~ the velocitygram of a prominence. This prominence

is at a height of about 50000km (Zhang et al., 1987). Dark and

bright features represent opposite flows respectively. These

velocity field patterns indicate not only material flow, but also

give us information about the magnetic field because prominence

matter is frozen in the magnetic field. Fig.4 gives the

observations of an active region. After analysing these data

( see Fig.4 ) with Dr. Ai Gouxiang, we found that the

76 LI Wel et at.

neutral line of the line-of-sight velocity field corresponds to that

of the magnetic field (Ai, et al., ]987). We also confirmed that

everyflare occurs at the positions close to the neutral line being

intruded by opposote polarities. When intrusion and extrusion

balance each other in strength, eruption will be possible (Li et

al., 1987). So far, three large flares have been observed with

active regions. All of them exhibited very similar features.

We have gotten the fibril longitudinal magnetic field with a

resolution in space of I~5 (see Fig.5). A close inspection of Fig.5

reveals some fibril structure and small bright (positive polarity)

points. It appears that bright fibrils in the magnetogram correspond

to the filament~ of sunspot penumbra. The flow is much stronger

between two opposite polarities (see Fig.5) than the remainder of

the spot where almost no opposite polarity exists.

, . . -.~ .8854 2 5 5 8 7 B 3 6

,a

L

a. The magnetogram b. H6 velocitygram Fig.4 Observations of an active region

0

878815 ' 8 5 Z 7 ~55 R R . 4 N 6 I

a. The photograph b. H~ velocitygram Fig.5 Observation of sunspot fiber at FeI5324A.

From Fig.6, we can see the structure of the photospheric

network agrees with the magnetogram, and the velocity network with

Magentic and Velocity Field 77

¢~ ,qp,.'*

, 4

. o

q ' ~ . . I r "

a. The magnetogram b. HB velocitygram Fig.6 The magnetic and velocity fields of an enhanced network

matter flow downwards (2-3 km/s, bright features) has some

interrelationship with the photospheric network. The velocity fields

draw the outline of the contour of the supergranulation. (Gibson,

1981).

At the center of the 5324A line, we have observed the bright

points which were named "5324 bright points" by us. This kind of

image was observed at the solar disk center. The relevant data will

be analysed in detail.

REFERENCES

Ai Guoxiang, Hu Yuefeng (1986) Publications of The_Beiji~g Astronomical Observatory, 8, i.

Ai Guoxing, Li Wei et al. (1986) Publications of The Beljing Astronomical Observatory, 8, II.

Ai Guoxiang, Li Wei et al., (1987) Science Bulletin, (in press). Gibson, E.G.,'(1981) The Quiet Sun. Haguard, M.J., (1985) Proceedings of Kunmin 8 Workshop on Solar

Physics and Interplanetary Travellin~ Phenomena, vol.2 eds. De Jager and B. Chen 1216.

Hu Wenrui, Lin Yuanzhang et al. (1983) The Solar Flares. Li Jing, Ai Guoxing et al., (1987) submitted to Acta Astrophysics

Sinica. Zhang Hongqi, Ai Guoxiang et al. (1987) Science Bulletin, (in preaa)