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- 검색키워드
- 저자 : ( David Henley ) (검색결과 4 건)
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THE ORIGIN OF THE X-RAY EMISSION FROM THE HIGH-VELOCITY CLOUD MS30.7-81.4-118
Henley, David B.,Shelton, Robin L.,Kwak, Kyujin IOP Publishing 2014 The Astrophysical journal Vol.791 No.1
<P>A soft X-ray enhancement has recently been reported toward the high-velocity cloud MS30.7-81.4-118 (MS30.7), a constituent of the Magellanic Stream. In order to investigate the origin of this enhancement, we have analyzed two overlapping XMM-Newton observations of this cloud. We find that the X-ray enhancement is similar to 6 or similar to 100 pc across, and is concentrated to the north and west of the densest part of the cloud. We modeled the X-ray enhancement with a variety of spectral models. A single-temperature equilibrium plasma model yields a temperature of (3.69(-0.44)(+0.47)) x 10(6) K and a 0.4-2.0 keV luminosity of 7.9 x 10(33) erg s(-1). However, this model underpredicts the on-enhancement emission around 1 keV, which may indicate the additional presence of hotter plasma (T 107 K), or that recombination emission is important. We examined several different physical models for the origin of the X-ray enhancement. We find that turbulent mixing of cold cloud material with hot ambient material, compression or shock heating of a hot ambient medium, and charge exchange reactions between cloud atoms and ions in a hot ambient medium all lead to emission that is too faint. In addition, shock heating in a cool or warm medium leads to emission that is too soft (for reasonable cloud speeds). We find that magnetic reconnection could plausibly power the observed X-ray emission, but resistive magnetohydrodynamical simulations are needed to test this hypothesis. If magnetic reconnection is responsible for the X-ray enhancement, the observed spectral properties could potentially constrain the magnetic field in the vicinity of the Magellanic Stream.</P>
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Henley, David B.,Kwak, Kyujin,Shelton, Robin L. IOP Publishing 2012 The Astrophysical journal Vol.753 No.1
<P>In order to determine if the material ablated from high-velocity clouds (HVCs) is a significant source of low-velocity high ions (C IV, NV, and OVI) such as those found in the Galactic halo, we simulate the hydrodynamics of the gas and the time-dependent ionization evolution of its carbon, nitrogen, and oxygen ions. Our suite of simulations examines the ablation of warm material from clouds of various sizes, densities, and velocities as they pass through the hot Galactic halo. The ablated material mixes with the environmental gas, producing an intermediate-temperature mixture that is rich in high ions and that slows to the speed of the surrounding gas. We find that the slow mixed material is a significant source of the low-velocity OVI that is observed in the halo, as it can account for at least similar to 1/3 of the observed OVI column density. Hence, any complete model of the high ions in the halo should include the contribution to the OVI from ablated HVC material. However, such material is unlikely to be a major source of the observed CIV, presumably because the observed C IV is affected by photoionization, which our models do not include. We discuss a composite model that includes contributions from HVCs, supernova remnants, a cooling Galactic fountain, and photoionization by an external radiation field. By design, this model matches the observed OVI column density. This model can also account for most or all of the observed C IV, but only half of the observed NV.</P>
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Southeast Asian Studies and the Reality of Southeast Asia
Henley, David Korea Institute for ASEAN Studies 2020 Suvannabhumi Vol.12 No.2
Southeast Asianists have a perennial tendency to question the reality of the region in which they are specialized. Yet while scholars have doubted, Southeast Asians at large have become increasingly sure that Southeast Asia does exist, and increasingly inclined to identify with it. This article summarizes a range of evidence to that effect, from opinion poll research and from the history of ASEAN and other pan-Southeast Asian institutions, and uses it to construct a critique of the relativistic view that Southeast Asia is a fluid and ill-defined concept. Southeast Asians today tend to see Southeast Asia as a cultural as well as a geographical and institutional unit. The nature of the perceived cultural unity remains unclear, and further research is called for in this area. There are reasons to think, however, that it reflects real inheritances from a shared past, as well as shared aspirations for the future.
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Southeast Asian Studies and the Reality of Southeast Asia
( David Henley ) 부산외국어대학교 아세안연구원(구 부산외국어대학교 동남아지역원) 2020 Suvannabhumi Vol.12 No.2
Southeast Asianists have a perennial tendency to question the reality of the region in which they are specialized. Yet while scholars have doubted, Southeast Asians at large have become increasingly sure that Southeast Asia does exist, and increasingly inclined to identify with it. This article summarizes a range of evidence to that effect, from opinion poll research and from the history of ASEAN and other pan-Southeast Asian institutions, and uses it to construct a critique of the relativistic view that Southeast Asia is a fluid and ill-defined concept. Southeast Asians today tend to see Southeast Asia as a cultural as well as a geographical and institutional unit. The nature of the perceived cultural unity remains unclear, and further research is called for in this area. There are reasons to think, however, that it reflects real inheritances from a shared past, as well as shared aspirations for the future.
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