Ken'ichi Tarusawa

Wide-Field CCD Photometry around Nine Open Clusters

In this paper we study the evolution of the core and corona of nine open clusters using the projected radial density profiles derived from homogeneous CCD photometric data obtained with the 105 cm Kiso Schmidt telescope. The age and galactocentric distance of the target clusters vary from 16 to 2000 Myr and 9 to 10.8 kpc, respectively. Barring Be 62, which is a young open cluster, other clusters show a uniform reddening across the cluster region. The reddening in Be 62 varies from E(B - V)min = 0.70 mag to E(B - V)max = 1.00 mag. The coronae of six of the clusters in the present sample are found to be elongated; however, on the basis of the present sample it is not possible to establish any correlation between the age and shape of the core. The elongated core in the case of the young cluster Be 62 may reflect the initial conditions in the parental molecular cloud. The other results of the present study are as follows: (1) Core radius rc and corona size rcn/cluster radius rcl are linearly correlated. (2) The rc, rcn, and rcl are linearly correlated with the number of stars in that region. (3) In the age range 10-1000 Myr, the core and corona shrink with age. (4) We find that in the galactocentric distance range 9-10 kpc, the core and corona/cluster extent of the clusters increase with the galactocentric distance.

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.

Multicolor Shallow Decay and Chromatic Breaks in the GRB 050319 Optical Afterglow

Multiwavelength observations of the optical afterglow of GRB 050319 were performed from 1.31 to 9.92 hr after the burst. Our R-band light curves, combined with other published data, can be described by the smooth broken power-law function, with α1 = -0.84 ± 0.02 to α2 = -0.48 ± 0.03, 0.04 days after the gamma-ray burst. The optical light curves are characterized by shallow decays—as was also observed in the X-rays—which may have a similar origin, related to energy injection. However, our observations indicate that there is still a puzzle concerning the chromatic breaks in the R-band light curve (at 0.04 days) and the X-ray light curve (at 0.004 days) that remains to be solved.

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.

The University of Tokyo Atacama 1.0-m telescope

The current status of the University of Tokyo Atacama 1.0m telescope project being constructed at the summit of Co. Chajnantor (5,640m) in Atacama, Chile, will be presented. This is an optical/infrared telescope at the worlds highest site. A precipitable water vapor (PWV) amount of 0.4 to 1.3 mm at the summit, much lower than that of 0.9 to 2.8 mm at Mauna Kea, Hawaii. provides excellent atmospheric transmission from the near- to the mid-infrared wavelength. Seeing and weather conditions are confirmed to be suitable for infrared observations at the summit. The telescope is an f/12 Ritchey-Chrétien type with a field of view of 10 arcmin. The telescope is installed in a 6-m dome and controlled from an operation room in a container separated from the dome. The operation room will be directly connected to a base support facility in San Pedro de Atacama by a wireless LAN and a satellite link. A power generator and solar panels are equipped for a main and a back-up power supply, respectively. The ANIR near-infrared camera and the MAX38 mid-infrared camera are equipped on the Cassegrain focus. This telescope will start operation at the beginning of 2009, and will be operated remotely from the base facility in the near future.

Multiband Optical Follow-up Observations of GRB 020813 at the Kiso and Bisei Observatories

Observations were made of the optical afterglow of GRB 020813 (Fox, Blake, & Price) with the Kiso observatory 1.05 m Schmidt telescope and the Bisei astronomical observatory 1.01 m telescope. Four-band (B, V, R, and I) photometric data points were obtained on 2002 August 13 (10:52-16:46 UT), or 0.346-0.516 days after the burst. In order to investigate the early-time (<1 day) evolution of the afterglow, four-band light curves were produced by analyzing the data taken at these two astronomical observatories as well as the publicly released data taken using the Magellan Baade telescope (Gladders & Hall). The light curves can be approximated by a broken power law, of which the indices are approximately 0.46 and 1.33 before and after a break at ~0.2 days, respectively. The optical spectral index stayed approximately constant at ~0.9 over 0.17-4.07 days after the burst. Since the temporal decay index after the break and the spectral index measured at that time are both consistent with those predicted by a spherical expansion model, the early break is unlikely to be a jet break but is likely to represent the end of an early bump in the light curve, as was observed in the optical afterglow of GRB 021004.

Seeing environment at a 5640m altitude of Co. Chajnantor in northern Chile

We have carried out a campaign to monitor seeing at a 5640m altitude on the summit of Co. Chajnantor at Atacama, for the 6.5m telescope TAO project planned by the University of Tokyo. The seeing conditions were measured at 0.5μm using a DIMM (Differential Image Motion Monitor) during 8 nights in November 2006 and April 2007. In April, the measurement was done on a 2m-tower to suppress effect of ground-layer turbulence. The best night showed median seeing of 0.38, while the total median seeing is 0.69. This is comparable or even better than most of the major observatories. Together with the high transparency in infrared wavelength owing to the extremely high altitude of 5640m and its accessibility, the summit of Co. Chajnantor is one of the best site for infrared astronomy on the Earth.

The distance to the Coma cluster using the B-band Tully-Fisher relation

The present estimate of the distance to the Coma cluster on the basis of the B-band Tully-Fisher (T-F) relation has conducted photographic surface photometry on all galaxies for which H I line width data in a circle of 4-deg radius centered on the Coma cluster. A detailed estimate is made of the cluster population incompleteness bias for the distance estimation. While the correction for sample incompleteness, in conjunction with the T-F relation, increases the distance modulus, the result cannot be as large as the value indicated by Kraan-Kortweg et al. (1988). 65 refs.

MiniTAO/MAX38 first light: 30-micron band observations from the ground-based telescope

We successfully carried out 30-micron observations from the ground-based telescope for the first time with our newly developed mid-infrared instrument, MAX38, which is mounted on the University of Tokyo Atacama 1.0-m telescope (miniTAO telescope). Thanks to the high altitude of the miniTAO (5,640m) and dry weather condition of the Atacama site, we can access the 30-micron wavelength region from ground-based telescopes. To achieve the observation at 30- micron wavelength, remarkable devices are employed in MAX38. First, a Si:Sb 128x128 array detector is installed which can detect long mid-infrared light up to 38-micron. Second, we developed metal mesh filters for 30-micron region band-pass filter, which are composed of several gold thin-films with cross-shaped holes. Third, a cold chopper, a 6-cm square plane mirror controlled by a piezoelectric actuator, is built into the MAX38 optics for canceling out the atmospheric turbulence noise. It enables square-wave chopping with a 50-arcsecound throw at a frequency more than 5- Hz. Finally, a low-dispersion grism spectrometer (R~50) will provide information on the transmission spectrum of the terrestrial atmosphere in 20 to 40 micron. In this observation, we clearly demonstrated that the atmospheric windows around 30-micron can be used for the astronomical observations at the miniTAO site.

The History of the Mysterious Eclipses of KH 15D. II. Asiago, Kiso, Kitt Peak, Mount Wilson, Palomar, Tautenburg, and Rozhen Observatories, 1954-1997

The unusual pre–main-sequence binary star KH 15D undergoes remarkably deep and long-lasting periodic eclipses. Some clues about the reason for these eclipses have come from the observed evolution of the systems light curve over the last century. Here we present UBVRI photometry of KH 15D from 1954 to 1997 based on photographic plates from various observatories. The system has been variable at the ≈1 mag level since at least 1965. There is no evidence of color variations, with a typical limit of Δ(B - V) < 0.2 mag. We confirm some previously published results that were based on a smaller sample of plates: from approximately 1965 to 1990, the total flux was modulated with the 48 day orbital period of the binary, but the maximum flux was larger, the fractional variations were smaller, and the phase of minimum flux was shifted by almost a half-cycle relative to the modern light curve. All these results are consistent with the recently proposed theory that KH 15D is being occulted by an inclined, precessing, circumbinary ring.