The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Tim Johannsen - One of the best experts on this subject based on the ideXlab platform.
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a ray Tracing Algorithm for spinning compact object spacetimes with arbitrary quadrupole moments ii neutron stars
The Astrophysical Journal, 2012Co-Authors: Michi Baubock, Dimitrios Psaltis, Feryal Ozel, Tim JohannsenAbstract:A moderately spinning neutron star acquires an oblate shape and a spacetime with a significant quadrupole moment. These two properties affect its apparent surface area for an observer at infinity, as well as the light curve arising from a hot spot on its surface. In this paper, we develop a ray-Tracing Algorithm to calculate the apparent surface areas of moderately spinning neutron stars making use of the Hartle-Thorne metric. This analytic metric allows us to calculate various observables of the neutron star in a way that depends only on its macroscopic properties and not on the details of its equation of state. We use this Algorithm to calculate the changes in the apparent surface area, which could play a role in measurements of neutron-star radii and, therefore, in constraining their equation of state. We show that whether a spinning neutron star appears larger or smaller than its non-rotating counterpart depends primarily on its equatorial radius. For neutron stars with radii ~10 km, the corrections to the Schwarzschild spacetime cause the apparent surface area to increase with spin frequency. In contrast, for neutron stars with radii ~15 km, the oblateness of the star dominates the spacetime corrections and causes the apparent surface area to decrease with increasing spin frequency. In all cases, the change in the apparent geometric surface area for the range of observed spin frequencies is 5% and hence only a small source of error in the measurement of neutron-star radii.
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a ray Tracing Algorithm for spinning compact object spacetimes with arbitrary quadrupole moments ii neutron stars
arXiv: High Energy Astrophysical Phenomena, 2011Co-Authors: Michi Baubock, Dimitrios Psaltis, Feryal Ozel, Tim JohannsenAbstract:A moderately spinning neutron star acquires an oblate shape and a spacetime with a significant quadrupole moment. These two properties affect its apparent surface area for an observer at infinity, as well as the lightcurve arising from a hot spot on its surface. In this paper, we develop a ray-Tracing Algorithm to calculate the apparent surface areas of moderately spinning neutron stars making use of the Hartle-Thorne metric. This analytic metric allows us to calculate various observables of the neutron star in a way that depends only on its macroscopic properties and not on the details of its equation of state. We use this Algorithm to calculate the changes in the apparent surface area, which could play a role in measurements of neutron star radii and, therefore, in constraining their equation of state. We show that whether the spinning neutron star appears larger or smaller than its non-rotating counterpart depends primarily on its equatorial radius. For neutron stars with radii ~10 km, the corrections to the Schwarzschild spacetime cause the apparent surface area to increase with spin frequency. In contrast, for neutron stars with radii ~15 km, the oblateness of the star dominates the spacetime corrections and causes the apparent surface area to decrease with increasing spin frequency. In all cases, the change in the apparent geometric surface area for the range of observed spin frequencies is < 5% and hence only a small source of error in the measurement of neutron star radii.
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a ray Tracing Algorithm for spinning compact object spacetimes with arbitrary quadrupole moments i quasi kerr black holes
arXiv: High Energy Astrophysical Phenomena, 2010Co-Authors: Dimitrios Psaltis, Tim JohannsenAbstract:We describe a new numerical Algorithm for ray Tracing in the external spacetimes of spinning compact objects characterized by arbitrary quadrupole moments. Such spacetimes describe non-Kerr vacuum solutions that can be used to test the no-hair theorem in conjunction with observations of accreting black holes. They are also appropriate for neutron stars with spin frequencies in the 300-600 Hz range, which are typical of the bursting sources in low-mass X-ray binaries. We use our Algorithm to show that allowing for the quadrupole moment of the spacetime to take arbitrary values leads to observable effects in the profiles of relativistic broadened fluorescent iron lines from geometrically thin accretion disks.
Wenting Wang - One of the best experts on this subject based on the ideXlab platform.
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resolving subhaloes lives with the hierarchical bound Tracing Algorithm
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Jiaxin Han, Y P Jing, Huiyuan Wang, Wenting WangAbstract:We develop a new code, the Hierarchical Bound-Tracing (hbt for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that hbt stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding Algorithm with an adaptive source-subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow the growth of satellite subhaloes through accretion from its satellite-of-satellites, hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders and show that hbt is able to well resolve subhaloes in high-density environment and keeps strict physical track of subhaloes merger history. This code is fully parallelized and freely available upon request to the authors.
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resolving subhaloes lives with the hierarchical bound Tracing Algorithm
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Jiaxin Han, Huiyuan Wang, Wenting Wang, Yipeng JingAbstract:We develop a new code, the Hierarchical Bound-Tracing (HBT for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that HBT stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding Algorithm with an adaptive source subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow growth of satellite subhaloes through accretion from its "satellite-of-satellites", hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders and show that HBT is able to well resolve subhaloes in high density environment and keep strict physical track of subhaloes' merger history. This code is fully parallelized and freely available upon request to the authors.
Jiaxin Han - One of the best experts on this subject based on the ideXlab platform.
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resolving subhaloes lives with the hierarchical bound Tracing Algorithm
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Jiaxin Han, Y P Jing, Huiyuan Wang, Wenting WangAbstract:We develop a new code, the Hierarchical Bound-Tracing (hbt for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that hbt stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding Algorithm with an adaptive source-subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow the growth of satellite subhaloes through accretion from its satellite-of-satellites, hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders and show that hbt is able to well resolve subhaloes in high-density environment and keeps strict physical track of subhaloes merger history. This code is fully parallelized and freely available upon request to the authors.
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resolving subhaloes lives with the hierarchical bound Tracing Algorithm
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Jiaxin Han, Huiyuan Wang, Wenting Wang, Yipeng JingAbstract:We develop a new code, the Hierarchical Bound-Tracing (HBT for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that HBT stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding Algorithm with an adaptive source subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow growth of satellite subhaloes through accretion from its "satellite-of-satellites", hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders and show that HBT is able to well resolve subhaloes in high density environment and keep strict physical track of subhaloes' merger history. This code is fully parallelized and freely available upon request to the authors.
Michito Ohm - One of the best experts on this subject based on the ideXlab platform.
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lineament analysis of satellite images using a segment Tracing Algorithm sta
Computers & Geosciences, 1995Co-Authors: Katsuaki Koike, Shuichi Nagano, Michito OhmAbstract:Abstract Regional fault patterns contribute important information for preliminary exploration for mineralized areas and characterization of geologic structure. Faults may correspond with lineaments appearing on remotely sensed images. In this paper, a new lineament identification method, namely the Segment Tracing Algorithm (STA), is proposed, and its application in mountainous areas of southwestern Japan is discussed. The principle of the STA is to detect a line of pixels as a vector element by examining local variance of the gray level in the digital image, and to connect retained line elements along their expected directions. The threshold values for the extraction and the linkage of line elements are direction dependent. The advantages of the proposed method over usual filtering methods are its capability to (1) trace only continuous valleys and (2) extract more lineaments that parallel the sun's azimuth and those located in shadow areas. A LANDSAT Thematic Mapper (TM) subscene was used for the analysis. The band 4 subscene of the LANDSAT TM image was determined to be appropriate for the lineament analysis by comparing several images with a shaded-relief image derived from a digital elevation model (DEM).
Katsuaki Koike - One of the best experts on this subject based on the ideXlab platform.
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lineament analysis of satellite images using a segment Tracing Algorithm sta
Computers & Geosciences, 1995Co-Authors: Katsuaki Koike, Shuichi Nagano, Michito OhmAbstract:Abstract Regional fault patterns contribute important information for preliminary exploration for mineralized areas and characterization of geologic structure. Faults may correspond with lineaments appearing on remotely sensed images. In this paper, a new lineament identification method, namely the Segment Tracing Algorithm (STA), is proposed, and its application in mountainous areas of southwestern Japan is discussed. The principle of the STA is to detect a line of pixels as a vector element by examining local variance of the gray level in the digital image, and to connect retained line elements along their expected directions. The threshold values for the extraction and the linkage of line elements are direction dependent. The advantages of the proposed method over usual filtering methods are its capability to (1) trace only continuous valleys and (2) extract more lineaments that parallel the sun's azimuth and those located in shadow areas. A LANDSAT Thematic Mapper (TM) subscene was used for the analysis. The band 4 subscene of the LANDSAT TM image was determined to be appropriate for the lineament analysis by comparing several images with a shaded-relief image derived from a digital elevation model (DEM).
