######################################################################## Master thesis projects ######################################################################## Current: (a) T. Yoshida (b) M. Shimojo (c) S. Yashiro History: (A) R. Kano (Completed, March 1994) (B) M. Takahashi (Completed, March 1994) (C) J. Sato (Completed, March 1994) (D) M. Ohyama (Completed, March 1993) (E) T. Takahashi (Completed, March 1993) (F) K. Yaji (Completed, March 1993) (G) S. Dimascio (Completed, August 1995) ----------------------------------------------------------------------- (a) T. Yoshida - see ar071.yoshida02 Temperature distributions and time variatons of active regions T. Yoshida ( Institute of Astronomy, Univ. of Tokyo ) Master thesis topics Thesis adviser: S. Tsuneta Date used: May-July, 1992 SXT PFI The purpose of this analysis is to get the time scales of the loops' time variations and to see the global temperature structures. Here we sum up the images taken in the intervals of one Yohkoh orbit revvolution (100min) and get the good S/N images. Surprisingly, the Yohkoh-SXT structures don't always coincide with the temperature structures, and sometimes these look quite different. For example, very hot (8MK) regions are in some no-structural diffuse corona above the bright magnetic loops. In the events that whole loops are brighten up after the brightenings occure at the footpoints of the loops, not only those bright loop but also the diffusive loops around the bright loops are heated up to very high temperatures (6MK). The temperatures of the compact steady loops (4MK) are generally higher than the temperatures of the diffusive loops (3MK), and there are low temperature layers (5000km 3MK) around the limbs. Then, the temperatures of the footpoints of loops may be lower than those of the tops. Thus, we can get the new information about the coronal heating mechanism from the temperature maps and their time variations. Preliminary result will be presented in the annual ASJ meeting in the autumn of 1994. ----------------------------------------------------------------------- (b) M. Shimojo - see ar051.shimojo01 Statistical Study of X-ray Jets Observed in SXT/FFI Data M. Shimojo, K. Shibata, ... motivation: The Yohkoh SXT has revealed that the solar corona is full of jet-like features (hereafter, simply called X-ray jets). According to preliminary study by us, the number of X-ray jets is more than 20 per month during Nov. 1991 - March 1992 in full frame images (FFI). These jets are one of new discoveries by Yohkoh. The purpose of this study is to study statistical properties of the X-ray jets using FFI data. how to do it: We will make a catalogue of X-ray jets observed in FFI data. This calalogue include (1) date, time (begin, max, end), (2) place (heliocentric coordinate), (3) length, (4) (apparent) translational velocity, (5) association with XBP, EFR, or AR (with NOAA number), (6) (apparent) shape (7) other comments if available. On the basis of this calalogue, we will study statistical properties of jets, such as velocity, length, occurrence place (lattitude), classification of jets, and so on. note: This study will be done as undergraduate thesis (1993) and master thesis (1994-1995) of M. Shimojo at Tokai University. ----------------------------------------------------------------------------- (c) S. Yashiro A Study of Evolution of Active Region with Yohkoh SXT S. Yashiro (Department of Astronomy, University of Tokyo) Thesis adviser: K. Shibata (collaborator: M. Shimojo) The purpose of this study is to clarify the evolution of active regions, using the soft X-ray images taken with the Soft X-ray Telescope aboard Yohkoh. At first, we derive the time variation of projected area and total soft X-ray intensity of active regions (emerging flux regions or EFRs) using SFD file. We will confirm the results by Ishido et al. (1992) and Su et al. (1992) and examine many cases. (Note that they found that the expansion velocity of EFRs is 2-5 km/s in a few cases, though these studies were published only in the proceeding of the meeting in Japan.) As a preliminary result, we found that the expansion velocity of some EFRs is 1-3 km/s. We will then compare the SXT images with the Kitt Peak magnetograms and study the role of magnetic field in the evolution of active regions. ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- ----------------------------------------------------------------------------- (A) R. Kano -- see ar042.kano02 Scaling Law and Heating Function of Coronal Loops obtained by Yohkoh SXT Ryouhei Kano Institute of Astronomy, University of Tokyo ABSTRACT Yohkoh soft X-ray images clearly demonstrate that the solar corona consists of the loop structures. Thus, it is important to study the heating mechanism of those individual loops for the investigation of the coronal heating mechanism. If we can observationally know which part of the coronal loops is heated, we will be able to constrain the heating models such as the DC current heating and the wave heating models. As a first step toward this attempt, I derive the temperature T, pressure p and length L of 43 steady soft X-ray loops in the active region NOAA 7150, observed by Yohkoh Soft X-ray Telescope (SXT) on 1992 May 2. The transient brightening (micro flares) are excluded in the analysis: only loops which do not show appreciable changes over 30 minutes are used in the analysis. I find that the data set is very much consistent with the scaling law T = 1.4e3 (p L)^{1/3} derived by Rosner, Tucker, Vaiana (1978) within statistical and systematic errors. Since the scaling law is essentially insensitive to the distribution of the heat input (the heating function E_H(s)) along the loops, we can not obtain E_H(s) itself only from the scaling law. An attempt is then made to obtain the heating function E_H(s) directly from the observed temperature gradients with the energy equation, because the energy equation underlying the scaling law is verified by the above analysis. Since the heating function is sensitive to the noise in the derived temperatures, I use the maximum entropy method (MEM), which allows us to obtain the smoothest solution (heating function) among the solutions consistent with the data. The accuracy of the heating function derived by MEM is checked by the numerical simulation for various heat input patterns with noise. The heating function thus obtained for a loop shows that the heat input is concentrated near the loop top. Both the DC current heating and the wave heating with constant damping length do not appear consistent with the heat input distribution. More loops, however, need to be analyzed for definite conclusion. The coronal heating rate is derived for the single loop for the first time: Total heat flux obtained from integration of the heating function is found to be 1.2e7 [erg/cm^2/s]. The major parts of this thesis with some additions will be submitted to the Publications of the Astronomical Society of Japan (PASJ). ----------------------------------------------------------------------- (B) M. Takahashi -- see fl134.takahashi_m01 A flare of 1992 Aug 17 23:58 UT M.Takahashi(Tokai Univ.) J.Sakai(Toyama Univ.) Te.Watanabe T.Sakao T.Kosugi T.Sakurai S.Enome(NAOJ) S.Tsuneta(Univ. of Tokyo) H.Hudson(Univ. of Hawaii) N.Nitta(LPARL) S.Hashimoto(Tokai Univ.) A flare of GOES X-ray class C4.3 was observed in NOAA 7260 on 1992 Aug. 17 at 23:58 UT. All the instruments on board YOHKOH made high time and spatial resolution observations. The soft X-ray time profile in the 3 - 15 keV energy range obtained by Soft X-ray Spectrometer (SXS) shows double peaks around Aug. 18, 00:00 and 00:05 UT. Images of Soft X-ray Telescope (SXT) show that four discrete points brighten in a straight line from northeast to southwest around Aug. 17 23:58 UT, which is also confirmed in Hard X-ray Telescope (HXT) images. We name these four points in SXT images as Points 1, 2, 3 and 4 from northeast of the sun. Four points observed by SXT can be considered as the foot-points of magnetic flux tubes. Moreover HXT contour images show that the fifth point exists between Point 3 and Point 4. The logarithmic scale SXT images indicate the existence of two loops connecting Point 1 with Point 4, and Point 2 with Point 3. Overlaid SXT images on the vector magnetogram obtained by the Solar Flare Telescope (National Astronomical Observatory of Japan) reveal that a magnetic neutral line runs between the second and third points. Obtaining the electron temperature and emission measure by the SXT filter ratio method, the RTV scaling law (Rosner, Tucker, and Viana 1978) implies the connections of Point 1 with Point 4 and of Point 2 with Point 3 in the flare decay phase. The time profile of electron temperature derived from the Bragg Crystal Spectrometer (BCS) also has double peaks. Various information can be obtained from the high resolution soft X-ray line spectra. ----------------------------------------------------------------------- (C) J. Sato -- NO INPUT RECEIVED ----------------------------------------------------------------------- (D) M. Ohyama Coronal Disturbances Associated with Solar-Filament Eruptions (a planned dissertation for the degree of the Master of Science to be submitted to Nagoya University in early 1993) M. Ohyama (Solar-Terrestrial Environment Laboratory, Nagoya Univ.) SXT images showing coronal disturbances associated with filament disappearances (or eruptive prominences) will be analyzed to understand relevant physical processes. Since the phenomena showed a variety of appearances, it is required to study as possible as many events to obtain statistically significant results. (Supervisor: Takashi Watanabe) Point 4 and of Point 2 with Point 3 in the flare decay phase. The time profile of electron temperature derived from the Bragg Crystal Spectrometer (BCS) also has double peaks. Various information can be obtained from the high resolution soft X-ray line spectra. ----------------------------------------------------------------------- (E) T. Takahashi X-ray synoptic maps and comparison with magnetic synoptic structure (a planned dissertation for the degree of the Master of Science to be submitted to Tokyo University in early 1993) T. Takahashi (Department of Astronomy, University of Tokyo) X-ray synoptic maps are created, and its structures are compared with Kitt Peak and WSO magnetic synoptic sturucture. Long term evolution of solar magnetic structure will become evident. The rigidly rotating components including dark channel and differentially rotating components including active regions will be studied. The location of coronal holes predicted by potential field calcuration will be compared with X-ray holes. (Supervisor: ??) ----------------------------------------------------------------------- (F) K. Yaji Hard X-ray Frares Associated with Evolution of Active Region NOAA 7270 (a planned dissertation for degree of the Master of Arts and Sciences to be submitted to Tokyo University in early 1993) K. Yaji (College of Arts and Sciences, University of Tokyo) In early September, 30 flares (more than C5.0 class by GOES) occurred at NOAA 7270. 16 hard X-ray flares of them were observed with YOHKOH, and some were simultaneously with heliograph in Nobeyama. Each of the flares is defferent in the HXTtime profiles and the HXT images. What does determin such caracteristics of the flares? We hope that a set of the flares at NOAA 7270 give answers for this question. First, we compare the connection between the character(impulsive or gradual,etc...) of the HXT time profiles and the location(for the sunspots) of flares. And, we study the HXT images, the HXT spectrum , the SXT images, the heliograph data and so on. Flare events to analyse All Flares(mainly more than C5.0 class) that occurred in NOAA 7270 from Sep.4 to Sep.9 (Supervisor: Takeo Kosugi) ------------------------------------------------------------------------ (G) S. Dimascio An analysis of the bright knots at the tops of solar flare loops using soft X-ray data from the Yohkoh mission. Submitted: August 1995 Simone Dimascio (University College London) The purpose of this study was to carry out a computer analysis on soft X-ray images of solar flares obtained by the Soft X-ray Telescope on board the Yohkoh spacecraft. This instrument has commonly revealed the presence of bright knots at the top of many flare loops, so this investigation was undertaken to study these features. An intensive search was made through the Yohkoh data archive to identify images that would be suitable for analysis. At the same time, familiarisation had to be gained with the software and techniques required to display X-ray images, manipulate them and analyse them. Eight flares were eventually short-listed for study. Initial analysis included studying the shape and size of the loop top source and how this varied over the lifetime of the flares. The results seem to indicate that this loop top region remained approximately constant in area well into the decay phase of the flares. An initial attempt to simplify the problem by reducing the flare loops to one-dimensional structures failed and so this technique was abandoned. A method of analysis that has not been done before was attempted. A program was written to measure the average intensity per pixel contained within contours of increasing areas concentric around the loop top. Though it was uncertain whether this would yield any useful information, it did in fact clearly demonstrate the differing degrees of compactness of the loop top source observed in different events. The results were looked at in different ways to study the features of the data, but more importantly, a measure of the compactness of the loop top regions was obtained by comparing the results with those expected for normal flares with no loop-top enhancement. Finally a brief investigation of the effects of instrumental scattering was undertaken. The results from this suggested that this could be an important effect that needs consideration in any future work of this kind. (Supervisor: Joseph I. Khan) ------------------------------------------------------------------------