Yuki Sarugaku

Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions

Context. Near-Earth asteroid 162173 (1999 JU3) is a potential flyby and rendezvous target for interplanetary missions because of its easy-to-reach orbit. The physical and thermal properties of the asteroid are relevant for establishing the scientific mission goals and also important in the context of near-Earth object studies in general. Aims. Our goal was to derive key physical parameters such as shape, spin-vector, size, geometric albedo, and surface properties of 162173 (1999 JU3). Methods. With three sets of published thermal observations (ground-based N-band, Akari IRC, Spitzer IRS), we applied a thermophysical model to derive the radiometric properties of the asteroid. The calculations were performed for the full range of possible shape and spin-vector solutions derived from the available sample of visual lightcurve observations. Results. The near-Earth asteroid 162173 (1999 JU3) has an effective diameter of 0.87 ± 0.03 km and a geometric albedo of 0.070 ± 0.006. The χ 2 -test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of λ ecl = 73°, β ecl = -62° and P sid = 7.63 ± 0.01 h. The most likely thermal inertia ranges between 200 and 600 J m ―2 s ―0.5 K ―1 , about a factor of 2 lower than the value for 25143 Itokawa. This indicates that the surface lies somewhere between a thick-dust regolith and a rock/boulder/cm-sized, gravel-dominated surface like that of 25143 Itokawa. Our analysis represents the first time that shape and spin-vector information has been derived from a combined data set of visual lightcurves (reflected light) and mid-infrared photometry and spectroscopy (thermal emission).

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.

When do internal shocks end and external shocks begin? Early-time broadband modeling of GRB 051111

Even with the renaissance in gamma-ray burst (GRB) research fostered by the Swift satellite, few bursts have both contemporaneous observations at long wavelengths and exquisite observations at later times across the electromagnetic spectrum. We present here contemporaneous imaging with the KAIT robotic optical telescope, dense optical sampling with Lulin, supplemented with infrared data from PAIRITEL and radio to gamma-ray data from the literature. For the first time, we can test the constancy of microphysical parameters in the internal-external shock paradigm and carefully trace the flow of energy from the GRB to the surrounding medium. KAIT data taken ≤1 minute after the start of GRB 051111 and coinciding with the fading gamma-ray tail of the prompt emission indicate a smooth reinjection of energy into the shock. No color change is apparent in observations beginning ∼ 1.5 minutes after the GRB and lasting for the first hour after the burst. There are achromatic flux modulations about the best-fit model at late (t ≈ 104 s) times, possibly due to variations in the external density. We find that the host galaxy extinction is well fit by a curve similar to that of the Small Magellanic Cloud. Low visual extinction, AV ≈ 0.2 mag, combined with high column densities determined from the X-ray and optical spectroscopy (NH > 10 21 cm-2), indicate a low dust-to-metals ratio and a possible overabundance of the light metals. An apparent small ratio of total to selective extinction (RV ≈ 2) argues against dust destruction by the GRB. Time constancy of both the IR/optical/UV spectral energy distribution and the soft X-ray absorption suggests that the absorbing material is not local to the GRB.

Kiso Supernova Survey (KISS) : Survey strategy

The Kiso Supernova Survey (KISS) is a high-cadence optical wide-field supernova (SN) survey. The primary goal of the survey is to catch the very early light of a SN, during the shock breakout phase. Detection of SN shock breakouts combined with multi-band photometry obtained with other facilities would provide detailed physical information on the progenitor stars of SNe. The survey is performed using a 2.2x2.2 deg field-of-view instrument on the 1.05-m Kiso Schmidt telescope, the Kiso Wide Field Camera (KWFC). We take a three-minute exposure in g-band once every hour in our survey, reaching magnitude g~20-21. About 100 nights of telescope time per year have been spent on the survey since April 2012. The number of the shock breakout detections is estimated to be of order of 1 during our 3-year project. This paper summarizes the KISS project including the KWFC observing setup, the survey strategy, the data reduction system, and CBET-reported SNe discovered so far by KISS.

KWFC: four square degrees camera for the Kiso Schmidt Telescope

The Kiso Wide Field Camera (KWFC) is a facility instrument for the 105-cm Schmidt telescope being operated by the Kiso Observatory of the University of Tokyo. This camera has been designed for wide-field observations by taking advantage of a large focal-plane area of the Schmidt telescope. Eight CCD chips with a total of 8k x 8k pixels cover a field-of-view of 2.2 degrees x 2.2 degrees on the sky. The dewar window works as a field flattener lens minimizing an image distortion across the field of view. Two shutter plates moving in parallel achieve uniform exposures on all the CCD pixels. The KWFC is equipped with a filter exchanger composed of an industrial robotic arm, a filter magazine capable of storing 12 filters, and a filter holder at the focal plane. Both the arm and the magazine are installed inside the tube framework of the telescope but without vignetting the beam. Wide-field survey programs searching for supernovae and late-type variable stars have begun in April 2012. The survey observations are performed with a management software system for facility instruments including the telescope and the KWFC. This system automatically carries out observations based on target lists registered in advance and makes appropriate decisions for implementation of observations by referring to weather conditions and status of the instruments. Image data obtained in the surveys are processed with pipeline software in real time to search for candidates of time-variable sources.

SEARCH FOR THE COMET ACTIVITY OF 107P/(4015) WILSON-HARRINGTON DURING THE 2009/2010 APPARITION

We present the optical observations of the Near Earth Object 107P/(4015) Wilson–Harrington during the 2009/ 2010 apparition taken in search of low-level comet activity. Our photometric and spectroscopic data were collected 28–86 days after the perihelion passage on 2009 October 22 in a wide range of solar phase angles of 39 ◦ –68 ◦ .A disk-integrated phase function was constructed, giving a geometric albedo of 0.055 ± 0.012, phase integral of q = 0.34, and Bond albedo of AB = 0.019. The photometric property shows a profile similar to low albedo asteroids and comet nuclei. No emission lines were found in our spectrum, giving a flat reflectance similar to low albedo asteroids. Although we could not find any evidence for cometary activity in our photometric and spectroscopic data, we found an upper limit of 0.001% on the fractional active area. We derived the upper limit of the optical depth of the dust trail and tail, 7 × 10 −10 . We conclude that 107P/(4015) Wilson–Harrington was completely dormant or inactive in the 2009/2010 return.

Machined Immersion Grating with Theoretically Predicted Diffraction Efficiency

An immersion grating composed of a transmissive material with a high refractive index (n>2) is a powerful device for high-resolution spectroscopy in the infrared region. Although the original idea is attributed to Fraunhofer about 200 years ago, an immersion grating with high diffraction efficiency has never been realized due to the difficulty in processing infrared crystals that are mostly brittle. While anisotropic etching is one successful method for fabricating a fine groove pattern on Si crystal, machining is necessary for realizing the ideal groove shape on any kind of infrared crystal. In this paper, we report the realization of the first, to the best of our knowledge, machined immersion grating made of single-crystal CdZnTe with a high diffraction efficiency that is almost identical to that theoretically predicted by rigorous coupled-wave analysis.

DISCOVERY OF DRAMATIC OPTICAL VARIABILITY IN SDSS J1100+4421 : A PECULIAR RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXY?

We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey (KISS). The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z=0.840, however with unusually strong narrow emission lines. The estimated black hole mass of ~ 10^7 Msun implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ~ 4 x 10^2 - 3 x 10^3, which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio- and gamma-ray loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxies

Mid-infrared camera and spectrometer on board SPICA

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for mid- and far-infrared astronomy, envisioned for launch in early 2020s. The core wavelength coverage of this mission is 5 to 200 micron. Mid-infrared Camera and Spectrometer (MCS) will provide imaging and spectroscopic observing capabilities in the mid-infrared region with 4 modules. WFC (Wide Field Camera) has two 5 arcminutes square field of view and covers the wavelength range from 5 to 38 micron. MRS (Mid Resolution Spectrometer) has integral field units by image slicer and covers the wavelength range from 12.2 to 37.5 micron simultaneously using dichroic filter and two sets of spectrometers. HRS (High Resolution Spectrometer) covers the wavelength range from 12 to 18 micron with resolving power 20000 to 30000, and it has optional short wavelength channel which covers from 4 to 8 micron with resolving power 30000. LRS (Low Resolution Spectrometer) adopts prism disperser and covers the wavelength range from 5 to 38 micron with resolving power 50 to 100. Here, we present detailed specifications of MCS, optical design, and estimated performance on orbit.