Ryo Asai

Optical Spectropolarimetry of SN 2002ap: A High-Velocity Asymmetric Explosion*

We present spectropolarimetry of the Type Ic supernova SN 2002ap and give a preliminary analysis: the data were taken at two epochs, close to and 1 month later than the visual maximum (2002 February 8). In addition, we present June 9 spectropolarimetry without analysis. The data show the development of linear polarization. Distinct polarization profiles were seen only in the O I λ7773 multiplet/Ca II IR triplet absorption trough at maximum light and in the O I λ7773 multiplet and Ca II IR triplet absorption troughs a month later, with the latter showing a peak polarization as high as ~2%. The intrinsic polarization shows three clear position angles: 80° for the February continuum, 120° for the February line feature, and 150° for the March data. We conclude that there are multiple asymmetric components in the ejecta. We suggest that the supernova has a bulk asymmetry with an axial ratio projected on the sky that is different from 1 by an order of 10%. Furthermore, we suggest very speculatively that a high-velocity ejecta component moving faster than ~0.115c (e.g., a jet) contributes to polarization in the February epoch.

Decomposition of the Superwind in M 82

We present new optical images (B, V ,a nd Hα) of the archetypical starburst/superwind galaxy M 82 obtained with the 8.2m Subaru Telescope to reveal new detailed structures of the superwind-driven nebula and the highlatitude dark lanes. The emission-line nebula is decomposed into (1) a ridge-dominated component comprising numerous filament/loop sub-structures whose overall morphology appears as a pair of narrow cylinders, and (2) a diffuse component extended over much wider opening angle from the nucleus. We suggest that these two components have different origins. The ridge-dominated component appears as a pair of cylinders rather than a pair of cones. Since this morphological property is similar to that of hot plasma probed by soft X-ray, this component seems to surround the hot plasma. On the other hand, the diffuse component may arise from dust grains which scatter stellar light from the galaxy. Since inner region of this component is seen over the prominent “X”-shaped dark lanes streaming out from the nuclear region and they can be reproduced as a conical distribution of dust grains, there seems to be a dusty cold outflow as well as the hot one probed by soft X-ray and shock-excited optical emission lines. If this is the case, the presence of such high-latitude dust grains implies that neutral gaseous matter is also blown out during the course of the superwind activity.

FOCAS: faint object camera and spectrograph for the Subaru Telescope

Faint object camera and spectrograph, FOCAS, is a Cassegrain optical instrument of Subaru telescope. It has a capability of 6 arcmin FOV direct imaging, low resolution spectroscopy, multi-slit spectroscopy as well as polarimetry. Only the imaging mode has been available so far. The overall design, the observing functions, and the preliminary performance verifications of FOCAS will be presented.

Software structure and its performance on FOCAS instrument control, a MOS design, and an analyzing package

Faint Object Camera And Spectrograph (FOCAS) is completed and now waiting for a commissioning run on the Subaru Telescope atop Mauna Kea. We have developed a software system that includes the control of FOCAS instruments, Multiple Object Slits (MOS) design, and an analyzing package especially for evaluating performances of FOCAS. The control software system consists of several processes: a network interface process, user interface process, a central control engine process, a command dispatcher process, local control units, and a data acquisition system. These processes are mutually controlled by passing messages of commands and their status each other. The control system is also connected to Subaru Observation Software System to achieve high efficiency and reliability of observations. We have two off-line systems: a MOS design program, MDP, and an analyzing package. The MDP is a utility software to select spectroscopy targets in the field of view of FOCAS easily through its GUI and to design MOS plates efficiently. The designed MOS parameters are sent to a laser cutter to make a desirable MOS plate. A special package enables prompt performance check and evaluation of the FOCAS itself during a commissioning period. We describe the overall structure of FOCAS software with some GUI samples.

Multi-object spectroscopy of FOCAS: software and its performance

Faint Object Camera and Spectrograph, FOCAS, is a Cassegrain versatile optical instrument of Subaru telescope. Among various observing modes of FOCAS, the multi-object spectroscopy (MOS) requires dedicated software suite which enables accurate positioning of masks which have over fifty slitlets on faint targets over 6 arcminutes diameter field-of-view (FOV). We have been developing three kinds of software: the image processing software performing combining mosaic CCD images and optics distortion correction, mask designing program (MDP) for the slit arrangement, and pointing offset calculator (POC) for the target acquisition on slits. MDP and POC provide observers a graphical user interface (GUI) for efficient and quick mask designing and target acquisition. Our test has shown that the slit positioning accuracy on targets is about 0.2 arcsec RMS over entire FOV, and is accurate enough for typical observations with 0.4 arcsec slits or wider. We briefly describe our software as well as the pointing accuracy and the required time for the MOS target acquisition with FOCAS.

Dusty ERO Search behind Two Massive Clusters

We performed deep K � -band imaging observations of 2 massive clusters, MS 0451.6−0305 at z =0 .55 and MS 0440.5+0204 at z =0 .19, for searching counterparts of the faint sub-mm sources behind these clusters, which would provide one of the deepest extremely red object (ERO) samples. Comparing our near-infrared images with optical images taken by the Hubble Space Telescope and by the Subaru Telescope, we identified 13 EROs in these fields. The sky distributions of EROs are consistent with the previous results, that there is a sign of strong clustering among detected EROs. Also, the surface density with corrected lensing amplification factors in both clusters are in good agreement with that derived from previous surveys. We found 7 EROs and 3 additional very red objects in a small area (∼ 0.6arcmin 2 ) of the MS 0451.6−0305 field around an extended SCUBA source. Many of their optical and near-infrared colors are consistent with dusty star-forming galaxies at high redshifts (z ∼1.0–4.0), and they may be constituting a cluster of dusty starburst galaxies and/or lensed star-forming galaxies at high redshift. Their red

Stress-induced large anisotropy field modulation in Ni films deposited on a flexible substrate

A tensile strain on the order of a few percent was created in Ni thin films deposited on a flexible polyethylene naphthalate substrate, and the strain-induced change in the magnetic anisotropy was investigated. The magnetic easy axis was reversibly switched by 90° by the application of the stress. The easy axis was orthogonal to the applied stress. The in-plane saturation magnetic field or the uniaxial magnetic anisotropy energy changed linearly in reaction to the applied tensile strain up to a strain of 2.3%. Moreover, a large difference in the saturation magnetic field up to ∼0.3 T, which corresponds to a change in the magnetic anisotropy energy of ∼7 × 104 J/m3, was realized. The effective magnetoelastic coupling constant was almost independent of the thickness of Ni.