Mapping of the sun was made at 3.1mm (98 GHz) and 8.3mm (36 GHz) wavelengths with a 45m dish radio telescope at the Nobeyama Cosmic Radio Observatory. The depressions associated with large H alpha filaments are derived to be -0.2 at 8.3mm and -0.05 at 3.1mm, which are darker than the values inferred by Raoult et al. (1979

Hiel, E.

Ishiguro, M.

Kosugi, T.

Shibasaki, K.

English

NASA Technical Reports Server

N87-20887
DARK FILAMENTS OBSERVED AT 8.3ram AND 3. lmm WAVELENGTHS
E. Hiei, M. Ishiguro, T. Kosugi, and K. Shibasaki*
Tokyo Astronomical Observatory, Mitaka, Tokyo 181
*Research Institute of Atmospherics, Nagoya University,
Toyokawa, Aichi 442
ABSTRACT
Mapping of the sun was made at 3.1mm (98 GHz) and 8.3mm (36 GHz)
wavelengths with a 45m dish radio telescope at the Nobeyama
Cosmic Radio Observatory. The depressions associated with large
Ha filaments are derived to be -0.2 at 8.3mm and -0.05 at
3.1mm, which are darker than the values inferred by Raoult et al.
(1979).
INTRODUCTION
The radio observations of the filaments are valuable for studying
the physical conditions in and surrounding the prominences. The
spatial resolutions of ,h^ ._A;^ nh_o_,_tinn_, ......_,,_ ,_,_ ............. hnwever, are worse
than those in the optical ones, and the determinations of the
size and the brightenss temperature of the filaments are more or
less affected by the antenna beam-width.
Many dark filaments have been observed at millimetric and
centimetric wavelengths as brightness depressions on the disk.
These observations are sunlnarized in Table I. Raoult et al.
(1979) made a synthesis of the millimetric and centimetric
observations of the quiescent prominences on the disk by
correcting the instrumental beam-width and derived a spectrum of
the brightness temperature of the radio filaments between 3.5mm
and 6cm wavelengths. Apushkinskii and Topchilo (1976 a)
presented the brigtness temperatures of 70 filaments, selected
from 300 radio filaments observed at the Lebedev Physics
Institute and 70 at the Crimea Astrophysical Observatory, and
derived the height dependence of the temperature in the
prominences. The prominence-corona transition region was studied
by Chiuderi-Drago et al. (1975), Lantos and Raoult (1980), and
Schmahl (1979). The weakening in the brightnes_ depression after
disparition brusque was observed (Kundu and Lantos, 1977). A
radio observation of a prominence at mm-wavelength during a solar
eclipse was carried out in order to obtain the structure and
physical parameters of the prominence (Simon and WickstrOm 1971,
Apushkinskii et al. 1976). Radio flux enhancements associated
with the filaments were observed at 169 MHz (Axis et al., 1971)
I09
_:_3_:_CEOIT_iGPAGE _ NOT FILMED
https://ntrs.nasa.gov/search.jsp?R=19870011454 2020-03-20T11:51:49+00:00Z
TABLE 1 OBSERVATION OF FILAMENTS
Wavelength HPBW
(arc min)
Telescope Reference
1.2 mm
2.0
2.0
2.25
3.1
3.2
3.3
3.5
3.5
4.0
4.0
4.0
6.0
6.0
7.0
8.0
8.0
8.0
8.15
8.3
8.5
9.0
9.5
1.2 cm
1.3
1.35
1.36
1.6
1.95
2.0
2.0
2.0
2.0
2.8
2.8
3.8
3.8
3.8
6.0
6.0
6.0
6.0
11
2O
1.78 m
1.88
3.75
1.2 36ft NRAO
1.2 22m Crimea
22m Lebedev
22m Crimea
0.28(17") 45m Nobeyama
3.0
2.8
1.2
1.2
1.0
1.2
0.9
1.7
1.6
Kundu
Efanov
Apushkinskii et al.
Efanov et al.
Hiei et al.
15ft Aerospace C. Simon
15ft Aerospace C. Simon & WickstrOm
36ft NRAO Kundu
Kundu & Lantos
36ft NRAO Buhl & Tlamicha
22m Crimea Efanov
22m Lebedev Apushkinskii & Tsyganov
13.7m Helsinki Kundu et al.
22m Crimea Efanov et al.
22m Lebedev Apushkinskii et al.
120ft Haystack Schmahl et al.
22m Lebedev
22m Crimea
22m Lebedev
22m Crimea
0.77(46") 45m Nobeyama
22m Lebedev
3.5 36ft NRAO
1.5 85ft NRL
Khangil'din
Efanov
Apushkinskii
Efanov et al.
Hiei et al.
Apushkinskii et al.
Kundu
Kundu & McCullough
0.67
2.4
1.5
1.4
3.0
2.1
2.0
2.2
1.0
2.2
1.25
1.25
4.4
4.1
4.4
2.6
2.5
0.25(15")
5.0
100m Effelsberg Kundu et al.
22m Crimea Efanov
120ft Haystack Pramesh et al.
120ft Haystack Schmahl et al.
22m Crimea Efanov
140ft NRAO Chiuderi-Drago & Felli
140ft NRAO Tlamicha
120ft Haystack Schmahl et al.
100m Effelsberg Butz et al.
120ft Haystack Pramesh et al.
100m Effelsberg FOrst et al.
100m Effelsberg Kundu et al.
120ft Haystack Pramesh et al.
120ft Haystack Schm_hl et al.
120ft Haystack Straka et al.
100m Effelsberg Chiuderi-Drago et al.
100m Effelsberg Kundu et al.
WSRT Rao & Kundu
VLA Kundu
100m Effelsberg Kundu et al.
VLA Kundu
Nanfay Axisa et al.
Culgoora Dulk & Sheridan
Culgoora Dulk & Sheridan
1970
1972
1976a
1969
1986
1965
1971
1970,1972b
1977
1970
1972
1973
1978
1972
1976a
1971
1964
1972
1976a,1976c
1969
1986
1976a
1970
1972a
1978
1972
1977
1971
1972
1970
1969
1971
1975
1977
1973
1978
1977
1981
1975
1975
1978
1980
1985
1978
1985
1971
1974
1974
110
ORlGlMAl PAGE IS 
B POOR QUALrrY 
1984 JULY 1 7  (36GHz) 
1984 JULY 18 (36GHz) 
1984 JULY 22 (36GHz) 
111 
and at 80 and 160 MHz (Dulk and Sheridan, 1974). Recent
understanding of the radio observations of the filaments are
reported by Kundu (1979, 1985).
High quality maps at 36 GHz (8.3mm) and 98 GHz (3.1mm) were
obtained with a 45-m radio telescope at the Nobeyama Cosmic Radio
Observatory from 16 July to 22 July 1984. Their brightness
temperature and its time change are discussed.
OBSERVATION ANDANALYSIS
The radio telescope and observation were described in detail by
Kosugi et al. (1985) and only a short description is made here.
The angular resolutions of the 45-m dish telescope is of 46
arcsec (36 GHz) and 17 arcsec (98 GHz) at a half-power beam-
width. The whole disk of the Sun were radially scanned in order
to minimize the variation of the atmospheric attenuation due to
the change of the weather condition during the observation. One
scan length of 0.9" was made in 25 sec and the increment in the
scan angle is 0.75" . Total 240 scans per 180" were carried out
in 2 hours. In this radial-scan method the sudden change in the
atmospheric attenuation within 25 sec is unavoidable, but the
slow variation is corrected by using the brightness at the disc
center.
The observations at 36 GHz were made at 5-7h UT on 16th,
0.5-2.5h UT on 17th, 0.5-2.5h UT on 18th, l-3h UT on 19th, 23h on
21st - lh UT on 22nd, l-3h UT on 22nd, and 3-5h UT on 22nd July
1984, and the observations at 98 GHz at 6-8h UT on 17th, l-3h UT
on 19th, 23h on 21st - lh UT on 22nd, l-3h UT on 22nd, and 3-5h
UT on 22nd July 1984. Simultaneous observations at 36 GHz and 98
GHz were made by using a beam splitter on 19th and 22nd July
1984.
Figures 1 show the radio maps and Ha filtergrams observed
at Mitaka.
The comparison between the radio (36 GHz) and Ha features
of the dark filaments shows the following results.
I) all Ha filaments correspond to the depressions on the disk,
but not all depressions correspond to Ha filaments,
2) the positions of enhanced regions and the depressions move
from east to west day by day. No systematic differnece in
the positions between the radio maps and Ha filtergrams is
found. Therefore the height of the depression is about the
same as Ha filaments within the accuracy of the
observation,
3) depression becomes deep when the size of Ha filament
becomes large. This suggests that the instrumental dilution
still affects the depression,
4) radio filaments, that can not be seen in Ha filtergrams,
exist along the neutral line of the magnetic field,
5) there were three filaments, which could be seen at Ha
filtergrams only in l-2days. The depression seems to be
appeared simultaneously with its corresponding Ha dark
112
7)
8)
filament, and the depression became weak but still seen
after the disappearance of the Ha dark filament,
6) sometimes the depression appeared earlier than the Ha dark
filament. On the depression in north-west disk on July 17,
no Ha filament is seen, and on July 18, an Ha filament
appeared there and the depression become darker than that on
July 17. On July 19 the Ha filament was seen near the
limb. Another example is seen at the depression near the
disk center (south) on July 19. On July 18, the Ha
filament is not seen, and the depression is also weaker than
that on July 19,
a contour line on the radio map of July 17 (Figure I) shows
1/8 level of the average brightness of the quiet Sun. The
protuberances in east-south limb and in north-west limb are
corresponding to the Ha prominences (McCabe 1986),
at 96 GHz (3.1mm), depression corresponding to an Ha
filament is seen but weaker than that at 36GHz.
These observations may suggest that an Ha filament appear
at a pre-existing depression channel. Therefore some depressions
come from the prominences and the prominence-corona interface,
and some appear before the appearance of an Ha filament and are
seen after its disappearance. The other depressions, which are
not corresponding to the dark filaments, is due to the different
physical conditions of the chromosphere-corona transition region.
v v
20
10
0
TP-1)( Te
-0.2
-0.1
.... Pr. P,B.......-_''''x/_0 _- -_0
Pr. A / ......x""""
i .,....,-.X-
/
/0
(p.._"
Pr.A
//,,...o..,,,,, Pr.B /-'_
I I I I I I I
16 17 18 19 20 21 22 July 1984
Figure 2
113
The diagram (Figure 2) shows the change of the value of
depressions. The ordinate is (T_/T -i) and the abscissa the day
of July. The depression of prominence A (Pr. A) at 8.3nTn becomes
darker and darker, and again weaker. The depression of
prominence B (Pr. B) becomes darker and darker. The above shows
the width (size) of Pr. A and B. The size of Pr. A on 16 and IT
July is smaller than the antenna beam-width of 46 arcsec and the
observed brightness is thought to be affected by the background
quiet Sun. On 18 and 19 July, the size of Pr. A is about the
same size as the beam-width, and the depression shows a value,
not seriously affected by the quiet Sun. On July 19, the size of
Pr. A is the same as that on July 18, but the depression becomes
weak. Therefore, this depression is thought to be real. This
will be due to the change of physical state in Pr. A, or to the
change of the filling factor of the prominence.
The depression of -0.2 at 8.3mm for Pr. A and Pr. B is the
lowest value at our observations.
The mean value of the depression at 8.3mm wavelength
derived by Raoult et al. (1979) is about -0.I, which still seems
to be affected by the background bright disk due to the lack of
the spatial resolution.
If we take 8000" K as the brightness temperature of the
quiet Sun at 8.3mm, and the depression is to be -0.2, then the
temperature of the prominence is estimated to be _ 6600" K,
which is consistent with the temperature derived from the
spectroscopic study of the quiescent prominence. The temperature
and electron number densitYl, 0 _.ollowing Hirayama's review (1985)
are Te_6500" K, and ne_10 " In this case the optical depth
of the prominence at 8.3mm becomes I at only 40km depth, and
therefore the optical depth at 8.3mm is quite large in quiescent
prominences.
At 3.1n_n, the depression is as small as -0.05. If we take
6500" K as the electron temperature of the prominence, the
brightness temperature is estimated to be 6200" K.
The optical depth at 3.1mm becomes 1 at 280km depth. If the
width of the filamentary structures of the prominence is about
300km, the each filament has r=l at 3.1mm.
If the optical depth of the filament is large, then the
res'idual brightness of the depression and the peak brightness
above the limb should be the same. But if there exists some
differnce between them, it means that filling factor must be
taken into account in order to explain the difference.
CONCLUDING REMARKS
I) A group of the depressions on the radio map is larger than
that of Ha filaments. The depressions are due to H=
filaments, or pre/apr_s-filament state, or different
physical state at the transition region between the
114
2)
3)
chromosphere and the corona.
T /T ratio is equal or smaller than 0.8 at 8.3mm and about
0_95 at 3.1mm. 10.5
If we adopt the prominence model of Te=6500K and ne=10
then r=l at 8.3mm corresponds to 40km length, and at 3.1mm
to 280km length.
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116


Dark filaments observed at 8.3mm and 3.1mm wavelength

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