Jeonghyun Pyo

OBSERVATIONAL EVIDENCE FOR AN IMPACT ON THE MAIN-BELT ASTEROID (596) SCHEILA

An unexpected outburst was observed around (596) Scheila in 2010 December. We observed (596) Scheila soon after the impact using ground-based telescopes. We succeeded in the detection of a faint linear tail after 2011 February, which provides a clue to determine the dust ejection date. It is found that the dust particles ranging from 0.1-1 ?m to 100 ?m were ejected into the interplanetary space impulsively on December 3.5 ?1.0 day. The ejecta mass was estimated to be (1.5-4.9)?108?kg, suggesting that an equivalent mass of a 500-800?m diameter crater was excavated by the event. We also found that the shape of the light curve changed after the impact event probably because fresh material was excavated around the impact site. We conclude that a decameter-sized asteroid collided with (596) Scheila only eight days before the discovery.

Interpretation of (596) Scheila's Triple Dust Tails

Strange-looking dust cloud around asteroid (596) Scheila was discovered on 2010 December 11.44-11.47. Unlike normal cometary tails, it consisted of three tails and faded within two months. We constructed a model to reproduce the morphology of the dust cloud based on the laboratory measurement of high-velocity impacts and the dust dynamics. As a result, we succeeded in reproducing the peculiar dust cloud by an impact-driven ejecta plume consisting of an impact cone and downrange plume. Assuming an impact angle of 45 Degree-Sign , our model suggests that a decameter-sized asteroid collided with (596) Scheila from the direction of ({alpha}{sub im}, {delta}{sub im}) = (60 Degree-Sign , -40 Degree-Sign ) in J2000 coordinates on 2010 December 3. The maximum ejection velocity of the dust particles exceeded 100 m s{sup -1}. Our results suggest that the surface of (596) Scheila consists of materials with low tensile strength.

REANALYSIS OF THE NEAR-INFRARED EXTRAGALACTIC BACKGROUND LIGHT BASED ON THE IRTS OBSERVATIONS

We reanalyze data of near-infrared background taken by Infrared Telescope in Space (IRTS) based on up-to-date observational results of zodiacal light, integrated star light and diffuse Galactic light. We confirm the existence of residual isotropic emission, which is slightly lower but almost the same as previously reported. At wavelengths longer than 2 {\mu}m, the result is fairly consistent with the recent observation with AKARI. We also perform the same analysis using a different zodiacal light model by Wright and detected residual isotropic emission that is slightly lower than that based on the original Kelsall model. Both models show the residual isotropic emission that is significantly brighter than the integrated light of galaxies.

AKARI OBSERVATION OF THE SUB-DEGREE SCALE FLUCTUATION OF THE NEAR-INFRARED BACKGROUND

We report spatial fluctuation analysis of the sky brightness in the near-infrared from observations toward the north ecliptic pole (NEP) by the AKARI at 2.4 and 3.2 μm. As a follow-up study of our previous work on the Monitor field of AKARI, we used NEP deep survey data, which covered a circular area of about 0.4 square degrees, in order to extend fluctuation analysis at angular scales up to 1000″. We found residual fluctuation over the estimated shot noise at larger angles than the angular scale of the Monitor field. The excess fluctuation of the NEP deep field smoothly connects with that of the Monitor field at angular scales of a few hundred arcseconds and extends without any significant variation to larger angular scales up to 1000″. By comparing excess fluctuations at two wavelengths, we confirm a blue spectral feature similar to the result of the Monitor field. We find that the result of this study is consistent with Spitzer Space Telescope observations at 3.6 μm. The origin of the excess fluctuation in the near-infrared background remains to be determined, but we could exclude zodiacal light, diffuse Galactic light, and unresolved faint galaxies at low redshift based on the comparison with mid- and far-infrared brightness, ground-based near-infrared images.

Low-Resolution Spectrum of the Zodiacal Light with the AKARI InfraRed Camera

We present near- and mid-infrared zodiacal light spectra obtained with the AKARI Infra-Red Camera (IRC). A catalog of 278 spectra of the diffuse sky covering a wide range of Galactic and ecliptic latitudes was constructed. The wavelength range of this catalog is 1.8–5.3 � m with a wavelength resolution of �= Δ� � 20. Advanced reduction methods specialized for the slit spectroscopy of diffuse sky spectra have been developed for constructing the spectral catalog. Based on a comparison analysis of spectra collected in different seasons and ecliptic latitudes, we confirmed that the spectral shape of the scattered component and the thermal emission component of the zodiacal light in our wavelength range does not show any dependence on location and time, but the relative brightness between them varies with location. We also confirmed that the color temperature of the zodiacal emission at 3–5 � mi s 300˙ 10 K at any ecliptic latitude. This emission is expected to originate from sub-micron dust particles in interplanetary space.

Brightness map of the zodiacal emission from the AKARI IRC All-Sky Survey

The first Japanese infrared space mission AKARI successfully scanned the whole sky with its two main instruments, the Infrared Camera (IRC) and the Far-Infrared Surveyor (FIS). The AKARI All-Sky Survey provides us with an invaluable opportunity to examine the zodiacal emission (ZE) over the entire sky in the leading as well as the trailing direction of the Earth’s motion. We describe our efforts to reduce the ZE brightness map from the AKARI’s survey in the 9 μm waveband. Compared with the interplanetary dust cloud model of Kelsall et al. (1998), the map requires an increase of the contribution of the resonance ring component to the ZE brightness by about 20%. We paid special attention to the north and south ecliptic pole brightnesses. The symmetry plane’s inclination and longitude of ascending node need to be modified from those in Kelsall et al. (1998) to reach a best fit to the observed pole brightness difference.

MODELING OF THE ZODIACAL EMISSION FOR THEAKARI/IRC MID-INFRARED ALL-SKY DIFFUSE MAPS

The zodiacal emission, which is the thermal infrared (IR) emission from the interplanetary dust (IPD) in our Solar System, has been studied for a long time. Nevertheless, accurate modeling of the zodiacal emission has not been successful to reproduce the all-sky spatial distribution of the zodiacal emission, especially in the mid-IR where the zodiacal emission peaks. We therefore aim to improve the IPD cloud model based on Kelsall et al. 1998, using the AKARI 9 and 18 micron all-sky diffuse maps. By adopting a new fitting method based on the total brightness, we have succeeded in reducing the residual levels after subtraction of the zodiacal emission from the AKARI data and thus in improving the modeling of the zodiacal emission. Comparing the AKARI and the COBE data, we confirm that the changes from the previous model to our new model are mostly due to model improvements, but not temporal variations between the AKARI and the COBE epoch, except for the position of the Earth-trailing blob. Our results suggest that the size of the smooth cloud, a dominant component in the model, is by about 10% more compact than previously thought, and that the dust sizes are not large enough to emit blackbody radiation in the mid-IR. Furthermore we significantly detect an isotropically-distributed IPD component, owing to accurate baseline measurement with AKARI.

Calibration of TEPC for CubeSat Experiment to Measure Space Radiation

Copyright

Conceptual Design of the NISS onboard NEXTSat-1

The NISS onboard NEXTSat-1 is being developed by Korea astronomy and space science institute (KASI). For the study of the cosmic star formation history, the NISS performs the imaging spectroscopic observation in the near-infrared range for nearby galaxies, low background regions, star-forming regions and so on. It is designed to cover a wide field of view ( deg) and a wide wavelength range from 0.95 to by using linear variable filters. In order to reduce the thermal noise, the telescope and the infrared sensor are cooled down to 200 K and 80 K, respectively. Evading a stray light outside the field of view and making the most use of limited space, the NISS adopts the off-axis reflective optical system. The primary and the secondary mirrors, the opto-mechanical part and the mechanical structure are designed to be made of aluminum material. It reduces the degradation of optical performance due to a thermal variation. This paper presents the study on the conceptual design of the NISS.

System design of the compact IR space imaging system MIRIS

Multi-purpose Infra-Red Imaging System (MIRIS) is the main payload of the Korea Science and Technology Satellite-3 (STSAT-3), which is being developed by Korea Astronomy & Space Science Institute (KASI). MIRIS is a small space telescope mainly for astronomical survey observations in the near infrared wavelengths of 0.9~2 μm. A compact wide field (3.67 x 3.67 degree) optical design has been studied using a 256 x 256 Teledyne PICNIC FPA IR sensor with a pixel scale of 51.6 arcsec. The passive cooling technique is applied to maintain telescope temperature below 200 K with a cold shutter in the filter wheel for accurate dark calibration and to reach required sensitivity, and a micro stirling cooler is employed to cool down the IR detector array below 100K in a cold box. The science mission of the MIRIS is to survey the Galactic plane in the emission line of Paschen-α (Paα, 1.88 μ;m) and to detect the cosmic infrared background (CIB) radiation. Comparing the Paα map with the Hα data from ground-based surveys, we can probe the origin of the warm-ionized medium (WIM) of the Galaxy. The CIB is being suspected to be originated from the first generation stars of the Universe and we will test this hypothesis by comparing the fluctuations in I (0.9~1.2 um) and H (1.2~2.0 um) bands to search the red shifted Lyman cutoff signature. Recent progress of the MIRIS imaging system design will be presented.