Kyoung Wook Min

Plasma blob events observed by KOMPSAT-1 and DMSP F15 in the low latitude nighttime upper ionosphere

[1] In this paper we report plasma blob events (plasma density enhancements) that were observed from KOMPSAT-1 (685-km altitude, 2250 LT) and from DMSP F15 (840-km altitude, 2130 LT) in the low-latitude F region. The blobs were observed mostly along the ±15° magnetic latitudes. Their global distribution showed a seasonal-longitudinal dependence similar to the distribution of the equatorial plasma bubbles. The blobs drifted upward relative to the ambient plasma, and the electron temperatures and H + proportions were lower within the blobs compared to those in the background. The characteristics of the plasma blobs were similar to those of the equatorial plasma bubbles. Therefore, it is suggested that the blobs originated from the lower altitudes by a mechanism that drives an upward drift of the plasma bubbles. The blob events did not occur in a correlated way with the magnetic activity or daily variation of solar activity.

Magnetic signatures of medium-scale traveling ionospheric disturbances as observed by CHAMP

[1] In this work we analyze the global distribution and physical characteristics of nighttime midlatitude magnetic field fluctuations (MMFs) as observed by the CHAMP satellite from 2001 to 2002 (solar maximum) and from 2006 to 2007 (solar minimum). MMFs are defined as medium-scale magnetic fluctuations perpendicular to the mean field, which are not accompanied by plasma density irregularities at the CHAMP altitude (∼400 km). MMFs occur at 15°-40° invariant latitude in the ionospheric F region. The occurrence is rare above the southern Atlantic ocean, and bears little connection to geomagnetic activity. The global MMF occurrence rate depends on season. The occurrence is generally low in equinox, maximizes around east Asia/Oceania and Europe/ northern Atlantic Ocean in June solstice, and peaks above the American continents in December solstice. As the solar cycle declines, the detected MMF occurrence rate also decreases. The MMF occurrence peaks around 2100 LT and slowly decreases toward midnight. In the postmidnight sector, events are practically absent. The MMF occurrence is generally consistent with known features of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), such as the conjugate climatology, and premidnight occurrence peak in the east Asia/Oceania region. But differences in their distributions also exist, implying that factors other than MSTIDs, e.g., ionospheric conductivity, sporadic E layer or plasma instabilities, may play a nonnegligible role in generating MMFs. MMFs have a preferred direction of polarization, which is consistent with that of MSTIDs and again corroborates the close connection between these two phenomena. We interpret the observed magnetic deflections in terms of field-aligned currents (FACs). The estimated wavelength range (∼200-500 km) of associated FAC pairs also agrees well with the size of MSTID density structures.

Results of Ginga/ROSAT Simultaneous Observation of the X-Ray Burst Source 1735–444

We present a detailed analysis of simultaneous Ginga and ROSAT observations of the X-ray burst source 1735-444, during which the source was in an unusually high luminosity state. The source shows the characteristics of an atoll source in the high-intensity (banana) state, with a general correlation between intensity and spectral hardness. A blackbody component contributes ~15%-20% of the total flux when the conventional two-component model is used to fit the spectra. We also observed a bright burst with radius expansion at this very high luminosity. The burst spectrum could not be described by a simple blackbody model. We discuss possible explanations.

MULTI-BAND POLARIMETRY OF THE LUNAR SURFACE. I. GLOBAL PROPERTIES

We have conducted multi-band (U, B, V, R, and I) polarimetric observations of the whole near-side of the Moon for phase angles between 22° and 121° with a spatial resolution of 1.1 km. A median grain size () map of the near-side regolith of the Moon has been constructed using our polarimetry. We find that is a monotonically increasing function of selenographic latitude β; at is estimated to be up to 40% larger than that at the equator. At the same latitude, is larger in the maria than in the highlands, confirming the initial findings of Shkuratov et al. The former is thought to be a result of reduced space weathering effects at high latitudes, where the flux of weathering agents such as micrometeoroids and solar wind particles is smaller. The latter probably indicates that the regolith material in the maria is more resistant to comminution by space weathering than is the material in the highlands. We also find that three photometric or polarimetric maturity indices—optical maturity, and the color ratio of parallel-component polarization ()—have different sensitivities on young small craters and rays of large craters. We present possible causes of these different sensitivities.

Diffuse Far-Ultraviolet Observations of the Lupus Loop Region

Diffuse far-ultraviolet emissions from the Lupus Loop region have been observed with the SPEAR/FIMS instrument. We have detected several important ionic lines, including Si II*, C IV, and N IV], which characterize the warm and hot ionized gas in this region. The spatial variations in the line intensities of Si II* and C IV have also been studied in comparison with X-ray and dust observations. The result shows that they originate from the interface between the hot gas seen in X-rays and the cooler H I shell with which dust is associated. The interface is rather diffuse, and gases with different temperatures seem to coexist in this region. A shock may exist up front in the interface, but its velocity should be very small, as no shock-related distinguishing feature is seen in Hα.

FAR-ULTRAVIOLET COOLING FEATURES OF THE ANTLIA SUPERNOVA REMNANT

We present far-ultraviolet observations of the Antlia supernova remnant obtained with Far-Ultraviolet Imaging Spectrograph (FIMS, also called SPEAR). The strongest lines observed are C IV λλ1548, 1551 and C III λ977. The C IV emission of this mixed-morphology supernova remnant shows a clumpy distribution, and the line intensity is nearly constant with radius. The C III λ977 line, although too weak to be mapped over the whole remnant, is shown to vary radially. The line intensity peaks at about half the radius and drops at the edge of the remnant. Both the clumpy distribution of C IV and the rise in the C IV to C III ratio toward the edge suggest that central emission is from evaporating cloudlets rather than thermal conduction in a more uniform, dense medium.

Vertical Scale Height of the Topside Ionosphere Around the Korean Peninsula: Estimates from Ionosondes and the Swarm Constellation

In this study, we estimated the topside scale height of plasma density (Hm) using the Swarm constellation and ionosondes in Korea. The Hm above Korean Peninsula is generally around 50 km. Statistical distributions of the topside scale height exhibited a complex dependence upon local time and season. The results were in general agreement with those of Tulasi Ram et al. (2009), who used the same method to calculate the topside scale height in a mid-latitude region. On the contrary, our results did not fully coincide with those obtained by Liu et al. (2007), who used electron density profiles from Arecibo Incoherent Scatter Radar (ISR) between 1966 and 2002. The disagreement may result from the limitations in our approximation method and data coverage used for estimations, as well as the inherent dependence of Hm on Geographic LONgitude (GLON).

FUV Interstellar Absorption Toward the Lupus Loop Region (abstract)

Far‐ultraviolet (FUV) observation of interstellar absorption toward the Lupus Loop region (SNR 330.0+15.0) is presented. Using Hipparcos, more accurate distance estimates to 52 B‐type stars in Lupus are obtained. When a distance of 155±8 pc to the supernova remnant is adopted, most stars seem to lie in the foreground. Seven stars lie in the background, allowing a clearer interpretation of absorption lines. Prior to Hipparcos, research suffered from distance uncertainties, leading to confusion as to whether the origin of an observed absorption line was stellar or interstellar. FUV emission studies detected ionic lines inferred to be tracers of warm and hot (104<106° K) interstellar plasma. Important cooling lines (e.g., C IV, O VI, S II, and N IV) from diffuse warm gas have been reported. Assuming that these lines are caused by the same plasma, a detailed absorption analysis is performed toward seven background stars in Lupus. The ionic lines detected in emission are also well detected in absorption, sugge...

Space Radiation Experiments on Kitsat-1 and Kitsat-2

ABSTRACT The results of the space radiation experiments carried out on board the first two Korean technology demonstration microsatellites are presented in this paper. The first satellite: KITSAT-1, launched in August 1992, carries a radiation monitoring payload Cosmic Ray Experiment (CRE) for characterizing the low-Earth orbit radiation environment. CRE measures the linear energy transfer of the high energy particle flux, total radiation dose, and the single event upsets (SEU). The second satellite: KITSAT-2, launched in September 1993, carries various types of memories which have been monitored to test the possibility of the future use of these memories in space. These two satellites, which are similar in structures but different in orbits, provide a unique opportunity to study the effects of the radiation environment characterized by the orbit. The result shows that the SEU characteristics observed in the two satellites are different: single bit errors are dominant in the low inclination KITSAT-1 orbit, while multiple bit errors are prevalent on KITSAT-2 in the high inclination orbit. It is also found that monolithic memories are more vulnerable to the ionizing radiation than the hybrid memories.

THE CORE COLLAPSE OF GLOBULAR CLUSTERS WITH STELLAR EVOLUTION

The orbit averaged Fokker-Planck equation is used to study the dynamical evolution of globular clusters. Stellar evolutions according to their masses are incorporated in the model. The initial density distribution is chosen by Plummers model with the initial mass function index α=0.65, 1.35, 2.35, and 3.35. The mass-loss rate is given by the model of Fusi-Pecci and Renzini. It is found that the stellar mass loss acts as an energy source, and thereby affects the dynamical evolution of globular clusters by slowing down the evolution rate and extending the core collapse time. Also, the dynamical length scale is extended.