Search NASA⌕ Search

Engineering topics

Tamura, Motohide

Publications and source records attributed to Tamura, Motohide.

26 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

A Discovery of a Candidate Companion to a Transiting System KOI-94: A Direct Imaging Study for a Possibility of a False Positive

We report a discovery of a companion candidate around one of Kepler Objects of Interest (KOIs), KOI-94, and results of our quantitative investigation of the possibility that planetary candidates around KOI-94 are false positives. KOI-94 has a planetary system in which four planetary detections have been reported by Kepler, suggesting that this system is intriguing to study the dynamical evolutions of planets. However, while two of those detections (KOI-94.01 and 03) have been made robust by previous observations, the others (KOI-94.02 and 04) are marginal detections, for which future confirmations with various techniques are required. We have conducted high-contrast direct imaging observations with Subaru/HiCIAO in H band and detected a faint object located at a separation of approximately 0.6 sec from KOI-94. The object has a contrast of approximately 1 × 10(exp −3) in H band, and corresponds to an M type star on the assumption that the object is at the same distance of KOI-94. Based on our analysis, KOI-94.02 is likely to be a real planet because of its transit depth, while KOI-94.04 can be a false positive due to the companion candidate. The success in detecting the companion candidate suggests that high-contrast direct imaging observations are important keys to examine false positives of KOIs. On the other hand, our transit light curve reanalyses lead to a better period estimate of KOI-94.04 than that on the KOI catalogue and show that the planetary candidate has the same limb darkening parameter value as the other planetary candidates in the KOI-94 system, suggesting that KOI-94.04 is also a real planet in the system.

Subaru/HiCIAO↗
NASA NTRS2012

Coronagraph Focal-Plane Phase Masks Based on Photonic Crystal Technology: Recent Progress and Observational Strategy

Photonic crystal, an artificial periodic nanostructure of refractive indices, is one of the attractive technologies for coronagraph focal-plane masks aiming at direct imaging and characterization of terrestrial extrasolar planets. We manufactured the eight-octant phase mask (8OPM) and the vector vortex mask (VVM) very precisely using the photonic crystal technology. Fully achromatic phase-mask coronagraphs can be realized by applying appropriate polarization filters to the masks. We carried out laboratory experiments of the polarization-filtered 8OPM coronagraph using the High-Contrast Imaging Testbed (HCIT), a state-of-the-art coronagraph simulator at the Jet Propulsion Laboratory (JPL). We report the experimental results of 10-8-level contrast across several wavelengths over 10% bandwidth around 800nm. In addition, we present future prospects and observational strategy for the photonic-crystal mask coronagraphs combined with differential imaging techniques to reach higher contrast. We proposed to apply a polarization-differential imaging (PDI) technique to the VVM coronagraph, in which we built a two-channel coronagraph using polarizing beam splitters to avoid a loss of intensity due to the polarization filters. We also proposed to apply an angular-differential imaging (ADI) technique to the 8OPM coronagraph. The 8OPM/ADI mode avoids an intensity loss due to a phase transition of the mask and provides a full field of view around central stars. We present results of preliminary laboratory demonstrations of the PDI and ADI observational modes with the phase-mask coronagraphs.

coronagraphy↗
NASA NTRS1993

Magnetic field in a low-mass protostar disk - Millimeter polarimetry of IRAS 16293-2422

We have measured the millimeter polarization of IRAS 16293-2422, a low-mass protostar candidate embedded in the east streamer of the Rho Ophiuchi dark cloud. The source has a linear polarization at 1.1 mm of (2.8 +/- 0.5) percent at a position angle of 144 deg +/- 5 deg with a 19 arcsec beam. If this polarization is due to thermal emission from magnetically aligned nonspherical grains in a dust disk around the central (proto)star, then the magnetic field threads across the disk at a position angle of 54 deg +/- 5 deg projected on the sky. This direction is the same as that of the minor axis of the elongated circumstellar gas disk (of scale 1600 AU) and of the direction of one of the quadratic outflows. There is no positive evidence for a twisted magnetic field in the dust disk, which constrains the hydromagnetic models for molecular outflows, at least for this source.

Tamura, Motohide↗
NASA NTRS1992

Circumnuclear pileups of dust and gas in M82

Red H-alpha and R-band CCD images of the M82 galaxy were obtained and compared with corresponding NIR S III forbidden-line and I-band images and with a smaller Br-gamma infrared-array image of the central 500 pc. Results furnish evidence of circumnuclear pileup in M82, probably toroidal in form, which is dynamically linked to the central (bilobal) starburst and which is now collimating the subsequent eruptions and emergent radiation.

Waller, William H.↗
NASA NTRS1992

Infrared morphology of mass outflow from GL 2591

Results are presented of a spectrophotometric study of a young stellar object, GL 2591, at wavelengths covering 2.10 to 2.27 microns, employing the KPNO long-slit cryogenic spectrometer. H2 emission was discovered in this source. A map of the v = 1-0 S(1) emission line shows a bipolar structure extending over 0.9 d (d/2 kpc) pc in an east-west direction roughly centered around GL 2591 IRS, with four bright knotty peaks. Br-gamma emission was detected in this source. A map of the Br-gamma emission line delineates a monopolar jetlike structure emanating over 0.2 d (d/2 kpc)pc from NIRS 1 to the southwest. The map of 2-micron continuum emission shows a multilooplike structure extending predominantly to the west. The dust distribution derived from this continuum map reveals a monopolar shell structure composed of several clumps. The spatial distribution of the H2, Br-gamma and 2-micron continuum emission is consistently explained by an outflow and dust disk model around GL 2591, if this emission is interpreted as shocked gas, ionized, gas, and swept-up dust, respectively, associated with the outflow from GL 2591.

Tamura, Motohide↗
NASA NTRS1992

The molecular hydrogen emission around L1551 IRS 5 - Shock-heated molecular gas at the base of the molecular outflow

Spatially resolved observations of the v = 1-0 S(1) molecular hydrogen emission toward L1551 IRS 5 using the grating spectrometer at KPNO are presented. The S(1) emission consists of a ridge component extending toward west along the optical jet from its peak on IRS 5 and a diffuse component which traces the innermost region of the cavity enclosed by the molecular outflow. The ridge component represents shock-heated molecular gas at the root of the optical jet. The diffuse component is too bright to be of scattered origin; it most likely arises from shock-heated gas within the cavity and could represent an acceleration process of the molecular outflow.

Yamashita, Takuya↗
NASA NTRS1991

Two micron morphology of candidate protostars

Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.

Tamura, Motohide↗