| 31. |
- Ohta, Yurina, et al.
(författare)
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Extreme asymmetry in the polarized disk of V1247 Orionis
- 2016
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Ingår i: Nippon Tenmon Gakkai obun kenkyu hokoku. - : Oxford University Press (OUP). - 0004-6264. ; 68:4
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Tidskriftsartikel (refereegranskat)abstract
- We present the first near-infrared scattered-light detection of the transitional disk around V1247 Ori, which was obtained using high-resolution polarimetric differential imaging observations with Subaru/HiCIAO. Our imaging in the H band reveals the disk morphology at separations of similar to 0.'' 14-0.'' 86 (54-330 au) from the central star. The polarized intensity image shows a remarkable arc-like structure toward the southeast of the star, whereas the fainter northwest region does not exhibit any notable features. The shape of the arm is consistent with an arc of 0.'' 28 +/- 0.'' 09 in radius (108 au from the star), although the possibility of a spiral arm with a small pitch angle cannot be excluded. V1247 Ori features an exceptionally large azimuthal contrast in scattered, polarized light; the radial peak of the southeastern arc is about three times brighter than the northwestern disk measured at the same distance from the star. Combined with the previous indication of an inhomogeneous density distribution in the gap at less than or similar to 46 au, the notable asymmetry in the outer disk suggests the presence of unseen companions and/or planet-forming processes ongoing in the arc.
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| 32. |
- Rich, Evan A., et al.
(författare)
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Multi-epoch Direct Imaging and Time-variable Scattered Light Morphology of the HD 163296 Protoplanetary Disk
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- We present H-band polarized scattered light imagery and JHK high-contrast spectroscopy of the protoplanetary disk around HD 163296 observed with the High-Contrast Coronographic Imager for Adaptive Optics (HiCIAO) and Subaru Coronagraphic Extreme Adaptive Optics (SCExAO)/Coronagraphic High Angular Resolution Imaging Spectrograph (CHARTS) instruments at Subaru Observatory. The polarimetric imagery resolve a broken ring structure surrounding HD 163296 that peaks at a distance along the major axis of 0 ''.65 (66 au) and extends out to 0 ''.98 (100 au) along the major axis. Our 2011 H-band data exhibit clear axisymmetry, with the NW and SE side of the disk exhibiting similar intensities. Our data are clearly different from 2016 epoch H-band observations of the Very Large Telescope (VLT)/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), which found a strong 2.7 x asymmetry between the NW and SE side of the disk. Collectively, these results indicate the presence of time-variable, non-azimuthally symmetric illumination of the outer disk. While our SCExAO/CHARIS data are sensitive enough to recover the planet candidate identified from NIRC2 in the thermal infrared (IR), we fail to detect an object with JHK brightness nominally consistent with this object. This suggests that the candidate is either fainter in JHK bands than model predictions, possibly due to extinction from the disk or atmospheric dust/clouds, or that it is an artifact of the data set/data processing, such as a residual speckle or partially subtracted disk feature. Assuming standard hot-start evolutionary models and a system age of 5 Myr, we set new, direct mass limits for the inner (outer) Atacama Large Millimeter/submillimeter Array (ALMA)-predicted protoplanet candidate along the major (minor) disk axis of of 1.5 (2) M-J.
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| 33. |
- Rich, Evan A., et al.
(författare)
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NEAR-IR POLARIZED SCATTERED LIGHT IMAGERY OF THE DoAr 28 TRANSITIONAL DISK
- 2015
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 150:3
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Tidskriftsartikel (refereegranskat)abstract
- We present the first spatially resolved polarized scattered light H-band detection of the DoAr 28 transitional disk. Our two epochs of imagery detect the scattered light disk from our effective inner working angle of 0.10 (13 AU) out to 0.50 (65 AU). This inner working angle is interior to the location of the system's gap inferred by previous studies using spectral energy distribution modeling (15 AU). We detected a candidate point source companion 1.08 northwest of the system; however, our second epoch of imagery strongly suggests that this object is a background star. We constructed a grid of Monte Carlo Radiative Transfer models of the system, and our best fit models utilize a modestly inclined (50 degrees), 0.01 M-circle dot disk that has a partially depleted inner gap from the dust sublimation radius out to similar to 8 AU. Subtracting this best fit, axi-symmetric model from our polarized intensity data reveals evidence for two small asymmetries in the disk, which could be attributable to a variety of mechanisms.
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| 34. |
- Rich, Evan A., et al.
(författare)
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The fundamental stellar parameters of FGK stars in the SEEDS survey Norman, OK 73071, USA
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 472:2, s. 1736-1752
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Tidskriftsartikel (refereegranskat)abstract
- Large exoplanet surveys have successfully detected thousands of exoplanets to-date. Utilizing these detections and non-detections to constrain our understanding of the formation and evolution of planetary systems also requires a detailed understanding of the basic properties of their host stars. We have determined the basic stellar properties of F, K and G stars in the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey from Echelle spectra taken at the Apache Point Observatory's 3.5m telescope. Using ROBOSPECT to extract line equivalent widths and TemperatureGravity microtrubulentVelocity ITerations to calculate the fundamental parameters, we have computed T-eff, log(g), v(t), [Fe/H], chromospheric activity and the age for our sample. Our methodology was calibrated against previously published results for a portion of our sample. The distribution of [Fe/H] in our sample is consistent with that typical of the Solar neighbourhood. Additionally, we find the ages of most of our sample are < 500 Myr, but note that we cannot determine robust ages from significantly older stars via chromospheric activity age indicators. The futuremeta-analysis of the frequency ofwide stellar and sub-stellar companions imaged via the SEEDS survey will utilize our results to constrain the occurrence of detected comoving companions with the properties of their host stars.
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| 35. |
- Ryu, Tsuguru, et al.
(författare)
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HIGH-CONTRAST IMAGING OF INTERMEDIATE-MASS GIANTS WITH LONG-TERM RADIAL VELOCITY TRENDS
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 825:2
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Tidskriftsartikel (refereegranskat)abstract
- A radial velocity (RV) survey for intermediate-mass giants has been in operation for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct-imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to gamma Hya B (0.61(-0.14)(+0.12)M(circle dot)), HD 5608 B (0.10 +/- 0.01M(circle dot)), and HD 109272 B (0.28 +/- 0.06M(circle dot)). For the remaining targets (iota Dra, 18 Del, and HD 14067), we exclude companions more massive than 30-60 M-Jup at projected separations of 1 ''-7 ''. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets iota Dra b, HD 5608 b, and HD 14067 b.
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| 36. |
- Schröder, Stefanus, et al.
(författare)
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Characterization of the MASCOT landing area by Hayabusa2
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 666
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Tidskriftsartikel (refereegranskat)abstract
- Context. After landing on C-type asteroid Ryugu, MASCOT imaged brightly colored, submillimeter-sized inclusions in a small rock. Hayabusa2 successfully returned a sample of small particles from the surface of Ryugu, but none of these appear to harbor such inclusions. The samples are considered representative of Ryugu.Aims. To understand the apparent discrepancy between MASCOT observations and Ryugu samples, we assess whether the MASCOT landing site, and the rock by implication, is perhaps atypical for Ryugu.Methods. We analyzed observations of the MASCOT landing area acquired by three instruments on board Hayabusa2: a camera (ONC), a nearinfrared spectrometer (NIRS3), and a thermal infrared imager (TIR). We compared the landing area properties thus retrieved with those of theaverage Ryugu surface.Results. We selected several areas and landforms in the landing area for analysis: a small crater, a collection of smooth rocks, and the landing site itself. The crater is relatively blue and the rocks are relatively red. The spectral and thermophysical properties of the landing site are very closeto those of the average Ryugu surface. The spectral properties of the MASCOT rock are probably close to average, but its thermal inertia may besomewhat higher.Conclusions. The MASCOT rock can also be considered representative of Ryugu. Some of the submillimeter-sized particles in the returned samples stand out because of their atypical spectral properties. Such particles may be present as inclusions in the MASCOT rock.
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| 37. |
- Yamada, Toru, et al.
(författare)
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Application of many-body dissipative particle dynamics to determine liquid characteristics
- 2015
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Ingår i: International Journal of Numerical Methods for Heat & Fluid Flow. - 1758-6585. ; 25:7, s. 1619-1637
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Tidskriftsartikel (refereegranskat)abstract
- Purpose - The purpose of this paper is to find out the applicability of the many-body dissipative particle dynamics (MDPD) method for various real fluids by specifically focusing on the effects of the MDPD parameters on the MDPD fluid properties. Design/methodology/approach - In this study, the MDPD method based on van der Waals (vdw) equation of state is employed. The simulations are conducted by using LAMMPS with some modifications of the original package to include the many-body features in the simulation. The simulations are investigated in a three-dimensional Cartesian box solution domain in which MDPD particles are distributed. In order to evaluate the MDPD liquid characteristics for a stationary liquid film, self-diffusivity, viscosity, Schmidt number (Sc) and surface tension, are estimated for different MDPD parameters. The parameters are carefully selected based on previous studies. A set of single-droplet simulations is also performed to analyze the droplet characteristics and its behavior on a solid-wall. Besides, the relationship between the characteristic length in the DPD simulations and scaling parameters for the stationary liquid-film case is discussed by employing the Ohnesorge number. Findings - The results show that the liquid properties in the MDPD simulations can be widely ranged by varying the MDPD parameters. The values are highly influenced by the many-body feature in the conservative force which is not included in the original DPD method. It is also found that the wetting ability of the MDPD fluid on solid walls can be easily controlled by changing a many-body parameter. The characteristic length between the MDPD reduced unit and real unit is related for the stationary liquid-film case by employing the Ohnesorge number. Originality/value - The present parametric study shows that the liquid properties in the MDPD method can vary by carefully controlling the MDPD parameters, which demonstrates the high-potential applicability of the method for various real fluids. This will contribute to research areas in multi-phase transport phenomena at nano and sub-micron scales in, for example, fuel cells, batteries and other engineering devices involving porous media.
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| 38. |
- Yamada, Toru, et al.
(författare)
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Diffusive-Ballistic Heat Transport in a Two-Dimensional Square Plate Using Energy Conserving Dissipative Particle Dynamics
- 2014
-
Ingår i: ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology Volume 4: Heat and Mass Transfer Under Extreme Conditions. - 9780791855508 ; 4, s. 004-016
-
Konferensbidrag (refereegranskat)abstract
- Diffusive-ballistic heat transport in a two-dimensional square plate was simulated using energy conserving dissipative particle dynamics (DPDe). The solution domain was considered to be a two-dimensional square plate surrounded by walls at constant temperatures, where DPD particles are uniformly distributed. The effects of phonon mean free path was incorporated by its relation to the cutoff radius of energy interaction. This cutoff radius was obtained based on Knudsen number (Kn) using the existing phonon-boundary scattering models. The simulations for 0.1 < Kn < 10 were conducted with different modifications of the cutoff radius. The results are presented in form of temperature distributions in the solution domain and the effect of Knudsen number is discussed.
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| 39. |
- Yamada, Toru, et al.
(författare)
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Diffusive-ballistic heat transport in thin films using energy conserving dissipative particle dynamics
- 2013
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 61, s. 287-292
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusive-ballistic heat transport in thin films was simulated using energy conserving dissipative particle dynamics (DPDe). The solution domain was considered to be two-dimensional with DPD particles distributed uniformly under constant temperature boundary conditions at the top and bottom walls and periodic boundaries at the side walls. The effects of phonon mean free path were incorporated by its relation to the cutoff radius of energy interaction. This cutoff radius was based on the Knudsen number using the existing phonon-boundary scattering models. The simulations for 0.1 < Kn < 10 were obtained with the different modifications of the cutoff radius. The results were presented in form of a nondimensional temperature profile across the thin film and were compared with the semi-analytical solution of the equation of phonon radiative transport (EPRT). When the phonon-boundary scattering is not considered, the DPDe simulation results have more discrepancies compared with the EPRT solution as Kn increases, indicating that the phonon-boundary scattering plays an important role when the heat transport across the film becomes more ballistic. The results demonstrate that the DPDe can simulate the diffusive-ballistic heat transport for a broad range of Kn, but phonon-boundary scattering should be considered for the accurate simulation of the ballistic heat transport. (C) 2013 Elsevier Ltd. All rights reserved.
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| 40. |
- Yamada, Toru, et al.
(författare)
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Dissipative particle dynamics simulations of water droplet flows in a submicron parallel-plate channel for different temperature and surface-wetting conditions
- 2016
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 70:6, s. 595-612
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Tidskriftsartikel (refereegranskat)abstract
- The effects of temperature-dependent thermophysical properties on droplet flow characteristics in a parallel-plate channel at submicron scale are investigated. The dissipative particle dynamics method with many-body (MDPD) and energy conservation (DPDe) configurations (MDPDe) was used. Droplet flows were simulated to study the effects of the temperature difference between top and bottom walls, body force on MDPDe particles, and wall-wetting conditions. The effects on the droplet flow were discussed. Droplet flows with a subzero wall temperature were simulated. An ice layer was formed on the wall. Its thickness and shape changed depending on surface wetting, temperature gradient, and body force.
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