The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
K Hasegawa - One of the best experts on this subject based on the ideXlab platform.
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co observations toward the isolated mid infrared bubble s44 External Triggering of o star formation by a cloud cloud collision
Publications of the Astronomical Society of Japan, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have performed a multi-wavelength study of the mid-infrared bubble S44 to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble S44 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate the spectral type of the embedded star inside the bubble to be O8.5-9 ($\sim 20 M_{\odot}$) from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in S44, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
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co observations toward the isolated mid infrared bubble gal 334 53 00 83 s44 External Triggering of o star formation by a cloud cloud collision
arXiv: Astrophysics of Galaxies, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have perform a multi-wavelength study of the mid-infrared bubble GAL 334.53+00.83 (S44) to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble GAL 334.53+00.83 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate} the spectral type of the embedded star inside the bubble to be O8.5-9 from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in GAL 334.53+00.83, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
S Wing - One of the best experts on this subject based on the ideXlab platform.
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External versus internal Triggering of substorms an information theoretical approach
Geophysical Research Letters, 2014Co-Authors: Jay R Johnson, S WingAbstract:The role of External Triggering of substorms through northward turning of the interplanetary magnetic field has been examined in a number of recent studies. While Hsu and McPherron (2002, 2004) argue that the strong association between External triggers defined by Lyons et al. (1997) and substorm onsets could be responsible for most substorms, Morley and Freeman (2007) argue that the association between northward interplanetary magnetic field (IMF) turnings and substorm onsets are coincidental rather than causal, because the same External triggers are also closely associated with an artificial list of substorm onsets generated with the Minimal Substorm Model, which has no requirement of northward IMF turning. We examine an expanded list of substorms using conditional redundancy, an entropy-based measure of conditional dependency, to examine whether northward IMF turning as an External trigger provides any additional information about substorm onset beyond knowing that there has been a period of sustained loading of energy flux (southward IMF). Our analysis reveals that only a few percent additional information is provided by the northward turning criterion, which is consistent with the statistics of surrogate data sets of External triggers constructed to coincide with 2% of substorms. We therefore conclude that northward turning of the IMF is, in general, coincidentally, rather than causally, associated with substorm onsets.
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External versus internal Triggering of substorms: An information‐theoretical approach
Geophysical Research Letters, 2014Co-Authors: Jay R Johnson, S WingAbstract:The role of External Triggering of substorms through northward turning of the interplanetary magnetic field has been examined in a number of recent studies. While Hsu and McPherron (2002, 2004) argue that the strong association between External triggers defined by Lyons et al. (1997) and substorm onsets could be responsible for most substorms, Morley and Freeman (2007) argue that the association between northward interplanetary magnetic field (IMF) turnings and substorm onsets are coincidental rather than causal, because the same External triggers are also closely associated with an artificial list of substorm onsets generated with the Minimal Substorm Model, which has no requirement of northward IMF turning. We examine an expanded list of substorms using conditional redundancy, an entropy-based measure of conditional dependency, to examine whether northward IMF turning as an External trigger provides any additional information about substorm onset beyond knowing that there has been a period of sustained loading of energy flux (southward IMF). Our analysis reveals that only a few percent additional information is provided by the northward turning criterion, which is consistent with the statistics of surrogate data sets of External triggers constructed to coincide with 2% of substorms. We therefore conclude that northward turning of the IMF is, in general, coincidentally, rather than causally, associated with substorm onsets.
Mikito Kohno - One of the best experts on this subject based on the ideXlab platform.
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co observations toward the isolated mid infrared bubble s44 External Triggering of o star formation by a cloud cloud collision
Publications of the Astronomical Society of Japan, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have performed a multi-wavelength study of the mid-infrared bubble S44 to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble S44 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate the spectral type of the embedded star inside the bubble to be O8.5-9 ($\sim 20 M_{\odot}$) from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in S44, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
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co observations toward the isolated mid infrared bubble gal 334 53 00 83 s44 External Triggering of o star formation by a cloud cloud collision
arXiv: Astrophysics of Galaxies, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have perform a multi-wavelength study of the mid-infrared bubble GAL 334.53+00.83 (S44) to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble GAL 334.53+00.83 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate} the spectral type of the embedded star inside the bubble to be O8.5-9 from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in GAL 334.53+00.83, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
Kun Xu - One of the best experts on this subject based on the ideXlab platform.
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Frequency Compensation Range Amplification for the Stabilized Optoelectronic Oscillator
2018 Asia Communications and Photonics Conference (ACP), 2018Co-Authors: Yao Zeng, Xiaoyang Wang, Kun XuAbstract:A novel stabilization scheme based on the frequency conversion pair has been proposed and experimentally demonstrated to improve the frequency-drift compensation range for the stabilized optoelectronic oscillator. The cavity length is adjusted by controlling the phase shift of oscillation signal at relative low frequency via frequency division and frequency multiplication. In the proof-of-concept experiment, a 10 GHz signal has been successfully generated with the phase noise about -123 dBc/Hz at 10 kHz offset frequency assisted by the External Triggering. The optoelectronic resonant cavity is tuned at 5 GHz via divide-by-2 prescaler and frequency doubler, and the frequency compensation range can be enlarged more than 3 times compared with conventional phase-locked-loop based stabilization method. Finally, the stability of the locked optoelectronic oscillator is improved from 4.1×10-7 to 1.1×10-10 at 1000s averaging time.
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Stabilized Optoelectronic Oscillator With Enlarged Frequency-Drift Compensation Range
IEEE Photonics Technology Letters, 2018Co-Authors: Ziyan Zhao, Yao Zeng, Tian Zhang, Yue Zhou, Kun XuAbstract:To improve the frequency-drift compensation range for the stabilized optoelectronic oscillator, a novel stabilization scheme based on the frequency conversion pair has been proposed and experimentally demonstrated. The cavity length is adjusted by controlling the phase shift of oscillation signal at relatively low frequency via frequency division and frequency multiplication. In the proof-of-concept experiment, a 10-GHz signal has been successfully generated with the phase noise about -123 dBc/Hz at 10-kHz offset frequency assisted by the External Triggering. The optoelectronic resonant cavity is tuned at 5 GHz via a divide-by-2 prescaler and a frequency doubler, and the frequency compensation range can be enlarged more than three times compared with a conventional phase-locked-loop-based stabilization method. Finally, the stability of the locked optoelectronic oscillator is improved from 4.1 × 10-7 to 1.1 × 10-10 at 1000-s averaging time.
Shinji Fujita - One of the best experts on this subject based on the ideXlab platform.
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co observations toward the isolated mid infrared bubble s44 External Triggering of o star formation by a cloud cloud collision
Publications of the Astronomical Society of Japan, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have performed a multi-wavelength study of the mid-infrared bubble S44 to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble S44 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate the spectral type of the embedded star inside the bubble to be O8.5-9 ($\sim 20 M_{\odot}$) from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in S44, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
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co observations toward the isolated mid infrared bubble gal 334 53 00 83 s44 External Triggering of o star formation by a cloud cloud collision
arXiv: Astrophysics of Galaxies, 2018Co-Authors: Mikito Kohno, Kengo Tachihara, Shinji Fujita, Yusuke Hattori, Kazufumi Torii, Atsushi Nishimura, Misaki Hanaoka, S Yoshiike, Rei Enokiya, K HasegawaAbstract:We have perform a multi-wavelength study of the mid-infrared bubble GAL 334.53+00.83 (S44) to investigate the origin of isolated high-mass star(s) and the star-formation process around the bubble formed by the HII region. In this paper, we report the results of new CO observations ($^{12}$CO, $^{13}$CO $J=$1-0, and $^{12}$CO $J=$3-2) toward the isolated bubble GAL 334.53+00.83 using the NANTEN2, Mopra, and ASTE radio telescopes. We found two velocity components in the direction of the bubble, at $-84$ km s$^{-1}$ and $-79$ km s$^{-1}$. These two clouds are likely to be physically associated with the bubble,both because of the enhanced $^{12}$CO $J=$3-2/1-0 intensity ratio from a ring-like structure affected by ultraviolet radiation from embedded high-mass star(s) and from the morphological correspondence between the 8 $\mu$m emission and the CO distribution. Assuming a single object, we estimate} the spectral type of the embedded star inside the bubble to be O8.5-9 from the radio-continuum free-free emission. We hypothesize that the two clouds collided with each other 3 Myr ago, Triggering the formation of the isolated high-mass star in GAL 334.53+00.83, as also occurred with RCW 120 and RCW 79. We argue that this scenario can explain the origin of the isolated O-star inside the bubble.
