Searching for a Companion Star of Tycho's Type Ia Supernova with Optical Spectroscopic Observations

We report our first results of photometric and spectroscopic observations for Tycho's supernova remnant (SNR Tycho) to search for the companion star of a type Ia supernova (SN Ia). From photometric observations using Suprime-Cam on the Subaru Telescope, we have picked up stars brighter than 22 mag (in $V$-band) for spectroscopy, which are located within a circular region with the radius of 30" around the center of SNR Tycho. If the ejecta of young supernova remnants, such as SNR Tycho, have a sufficient amount of Fe I, we should be able to detect absorption lines at 3720 \AA and 3860 \AA associated with transitions from the ground state of Fe I in the spectrum of the companion star. To identify the companion star of a SN Ia using these characteristic absorption lines of Fe I, we made optical low-resolution spectroscopy of their targets using FOCAS on the Subaru Telescope. In our spectroscopic observations, we obtained spectra of 17 stars in the SNR Tycho region and compare them with template stellar spectra. We detect significant absorption lines from two stars at 3720 \AA. Since widths of their absorption lines are broad, it is likely that the detected absorptions are due to Fe I in the expanding ejecta of SNR Tycho. However, none of stars exhibits a clear red wing in the observed profiles of the absorption, though a star in the background of the SNR should show it. Hence, we suggest another interpretation that the detected absorption lines might be caused by the peculiarity of stars. A star named Tycho(E) has the absorption line at 3720 \AA and its projected position is close to the center of SNR Tycho. Based on our observations, Tycho(E) is a new candidate as the companion star of Tycho's supernova.Comment: 17 pages, 28 figures, accepted for publication in PAS

Re-calibration of SDF/SXDS Photometric Catalogs of Suprime-Cam with SDSS Data Release 8

We present photometric recalibration of the Subaru Deep Field (SDF) and Subaru/XMM-Newton Deep Survey (SXDS). Recently, Yamanoi et al. (2012) suggested the existence of a discrepancy between the SDF and SXDS catalogs. We have used the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8) catalog and compared stars in common between SDF/SXDS and SDSS. We confirmed that there exists a 0.12 mag offset in B-band between the SDF and SXDS catalogs. Moreover, we found that significant zero point offsets in i-band (~ 0.10 mag) and z-band (~ 0.14 mag) need to be introduced to the SDF/SXDS catalogs to make it consistent with the SDSS catalog. We report the measured zero point offsets of five filter bands of SDF/SXDS catalogs. We studied the potential cause of these offsets, but the origins are yet to be understood.Comment: 36 pages, 19 figures(128 EPS files), PASJ accepte

Proper motions with Subaru II. A sample in the Subaru/XMM-Newton Deep Survey field

We search for stars with proper motions in a set of deep Subaru images, covering about 0.48 square degrees to a depth of $i' \simeq 26$, taken over a span of five and a half years. We follow the methods described in \citet{Richmond2009} to reduce and analyze this dataset. We present a sample of 69 stars with motions of high significance, and discuss briefly the populations from which they are likely drawn. Based on photometry and motions alone, we expect that 14 of the candidates may be white dwarfs. Our candidate with the largest proper motion is surprisingly faint and likely to prove interesting: its colors and motions suggest that it might be an M dwarf moving at over 500 km/sec or an L dwarf in the halo.Comment: 10 pages, 5 figures. Accepted by Publications of the Astronomical Society of Japan, to appear in volume 62, February 2010. Revised version: removed PASJ LaTeX tutorial which was mistakenly appended to pape

Catalog of Ultra-diffuse Galaxies in the Coma Clusters from Subaru Imaging Data

We present a catalog of ultra-diffuse galaxies (UDGs) in the Coma cluster. UDGs are a subset of low surface brightness (SB) galaxies with very large effective radii defined by van Dokkum et al. We surveyed the Subaru data archive for deep Suprime-Cam/Subaru R-band images, and used data covering the 1º.7 × 2º.7 region of the Coma cluster. The data are ~1 magnitude deeper than the data of van Dokkum et al (2015a) in limiting SB. This paper explains the details of our sample selection procedure. This UDG catalog includes positions, magnitudes, effective radii, mean and central SBs, and colors (when available). Comparisons with previous galaxy catalogs in the literature are performed, and we show that the current catalog is the largest for UDGs. We also discuss that most of the UDGs are members of the Coma cluster, and the major axis of the UDGs tends to align toward the cluster center (radial alignment)