fl208.ohyama03 Posted: 10-JUN-95 Updated: 24-Feb-96, 10-Nov-96 Events specified: See text
M.Ohyama (STElab.,Nagoya) and K.Shibata (NAOJ)
X-ray plasmoid ejection in eruptive flares has been discovered by the soft X-ray telescope (SXT) aboard YOHKOH. Some of limb flares show that plasmoids are ejected with a form of blobs. Using the filter-ratio-method, we will analyze SXT images to derive the temperature and emission measure structure of plasmoids in the flares listed in Table I. Preliminary analyses show that: (1) The density of plasmoids is larger than that of the surroundings. (2) The temperature of plasmoids is 8 to 11 MK. (3) There is a possibility that hotter regions exist below plasmoids. Table I. List of Plasmoid Ejection in Flares
911102 16:20 - 17:10
911202 04:50 - 05:31
921004 22:10 - 22:45
921005 09:20 - 09:50
930217 10:30 - 10:55
930514 21:45 - 22:25
931111 11:15 - 11:30
The preliminary results will be presented at the IAU Colloqium No. 153 which will be held in May 22-26, 1995.
Update 10-Nov-96
We submitted a paper whose authors are M. Ohyama and K. Shibata to PASJ today. We send the abstract of the paper to TBB.
Title: Preflare Heating and Mass Motion in a Solar Flare Associated with a Hot Plasma Ejection
Authors: Masamitsu Ohyama (Nagoya Univ./NAOJ) and Kazunari Shibata (NAOJ)
Abstract:
An X-ray plasma ejection associated with an impulsive flare was observed near the solar limb on 11 November 1993 with the Yohkoh soft X-ray telescope. We examined the physical condition as well as the morphological evolution of the ejecta and the flare. The results are the following: (1) The shape of the ejecta was a loop before the start of the ejection. (2) The ejected loop appeared after its footpoint brightened and started
to rise slowly long before the impulsive phase at about 10 km/s,
(the preflare slow rise), but was suddenly accelerated to about 130 km/s
just before or at about the onset of the impulsive phase (the main rise).
(3) The ejected material was already heated to 11 +/- 4 MK before the main
rise.
(4) The electron density of the ejecta (about 4.5x10^9 - 1.4x10^{10} /cm^3
was larger than the typical density of the active region corona.
(5) The mass of the ejecta was about 10^{14} g.
These results suggest chromospheric evaporation due to preflare heating.
We compare these results with a model of magnetic reconnection, and it is
suggested that reconnection may already be occurring in the preflare phase,
leading to heating of the ejected material (possibly plasmoids) and causing
chromospheric evaporation. The reconnection rate (or the speed of the inflow
into the neutral point) is also estimated for the preflare, the impulsive,
and the gradual phases.
Update 24-Feb-96
The following results were obtained and reported during IAU Colloq. No. 153, held at Makuhari, Japan, in June 1995. A short extended abstract with some figures will be published in the Proc. of IAU Colloq. 153 in 1996 or 1997.
Title : X-ray plasma ejection in an eruptive flare on 1992 October 5
M. Ohyama (STElab., Nagoya Univ. / NAOJ ) & K. Shibata (NAOJ)
In this study we have analyzed an X-ray plasma ejection (or plasmoid) in an eruptive flare (< M2.0) on 1992 October 5 which occurred behind the west limb. The plasma ejection is seen as a blob-like feature (i.e., it has the local intensity maximum). The time-height diagram for the ejection shows that the plasma ejection was ejected at an apparent velocity of 200-450 km/s, and that the acceleration occurred during the impulsive phase. We derived the temperature and emission measure of the plasma ejection assuming isothermality, then obtained also the other physical parameters of both the plasma ejection and the flare region (Table 1).
Results:
(1) The plasma ejection was ejected at an apparent velocity of 200-450 km/s, and the acceleration occurred during the impulsive phase.
(2) Temperature of the plasma ejection is 6 - 13 MK which is lower than that of the flare region.
(3) Mass of the plasma ejection is about 2*10^13 g.
(4) Kinetic energy of the plasma ejection is smaller than thermal energy content of the plasma ejection.
(5) Thermal energy content of the plasma ejection is smaller than that of the flaring region.
Table 1. Physical parameters of plasma ejection and flare region.
Temperature and emission measure are derived from a beryllium and
thick aluminum filter combination after taking 3x3-pixel sums of
the intensity in order to improve statistics. Then the other physical
parameters are obtained assuming the line-of-sight thickness ~ 10^4 km.
(Ejection) 09:25:16 and 09:25:18 UT.
(Flare region) 09:24:58 and 09:25:00 UT.
The kinetic energy is calculated using the velocity ~ 200 - 300 km/s.
Temperature [10^6 K] | 6 - 13 | 8 - 17 Emission measure [10^28 cm^(-5)] | 7 - 20 | 60 - 800 Electron density [10^9 cm^(-3)] | 8 - 15 | 25 - 90 Mass [10^(13) g] | ~2 | 9 - 10 Gas pressure [dyn cm^(-2)] | 20 - 40 | 70 - 280 Thermal energy content [10^(28) erg] | 4 - 5 | 20 - 30 Kinetic Energy [10^(27) erg] | 3 - 10 | -----