The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
You-hua Chu - One of the best experts on this subject based on the ideXlab platform.
-
Variable Hard X-Ray Emission From the Central Star of the Eskimo Nebula
The Astrophysical Journal, 2019Co-Authors: Martín A. Guerrero, Jesús A. Toalá, You-hua ChuAbstract:The central star of NGC 2392 shows the hardest X-Ray Emission among central stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic companion with an orbital period of 1.9 days could provide an explanation for its hard X-Ray Emission, as well as for the collimation of its fast outflow. Here we analyse the available Chandra and XMM-Newton X-Ray observations to determine accurately the spectral and temporal variation properties of the CSPN of NGC 2392. The X-Ray Emission can be described by an absorbed thermal plasma model with temperature 26$^{+8}_{-5}$ MK and X-Ray luminosity (8.7$\pm$1.0)$\times$10$^{30}$ erg s$^{-1}$. No long-term variability is detected in the X-Ray Emission level, but the Chandra light curve is suggestive of short-term variations with a period $\sim$0.26 days. The possible origins of this X-Ray Emission are discussed. X-Ray Emission from the coronal activity of a companion or shocks in the stellar wind can be ruled out. Accretion of material from an unseen main-sequence companion onto the CSPN or from the CSPN wind onto a white dwarf companion are the most plausible origins for its hard X-Ray Emission, although the mismatch between the rotational period of the CSPN and the modulation time-scale of the X-Ray Emission seems to preclude the former possibility.
-
Hard X‐Ray Emission associated with WDs
2010Co-Authors: Jana Bilíková, You-hua Chu, Robert A. Gruendl, Larry A. MaddoxAbstract:Hard X‐Ray Emission associated with white dwarfs (WDs) can be used to diagnose the presence of late‐type binary companions, mass accretion from companions, or physical processes with unknown origins. Since our previous systematic searches for hard X‐Ray Emission associated with WDs, the Galactic WD catalog has been augmented by >10,000 new WDs from the Sloan Digital Sky Survey and new X‐Ray point source catalogs from XMM‐Newton and ROSAT have become available. Therefore, we have extended the search using the updated catalogs, and found 17 new cases of WDs associated with hard X‐Ray Emission. The 32 WDs associated with hard X‐Ray Emission, from the current and previous searches, can be divided into five categories: (1) binary WD with a coronal companion, (2) binary WD with mass transfer from a companion, (3) single hot WD with a hard X‐Ray component peaking near 1 keV in addition to a soft photospheric component, (4) two PG 1159 stars with very faint X‐Ray Emission in the 0.9–2.0 keV band, and (5) two DA W...
-
Hard X-Ray Emission from White Dwarfs
2004Co-Authors: You-hua Chu, Robert A. GruendlAbstract:Hot white dwarfs may exhibit photospheric Emission at X-Ray wavelengths, but their X- Ray Emission should be soft, mutch less than 0.5 keV. Hard X-Ray Emission, at approx. 1 keV, is not expected from white dwarfs, unless they are in binary systems and the hard X-Ray Emission is produced by a late-type companion's coronal activity or by accretion of a companion's material onto the surface of the white dwarf. We proposed to use the ROSAT archive to search for hard X-Ray Emission from white dwarfs in order to determine whether hard X-Ray Emission may provide a sensitive diagnostic for the existence of a binary companion.
-
Hard X-Ray Emission Associated with White Dwarfs
The Astronomical Journal, 2003Co-Authors: Ian J. O’dwyer, You-hua Chu, Robert A. Gruendl, Martín A. Guerrero, Ronald F. WebbinkAbstract:We have used the WGACAT to search for hard X-Ray sources associated with white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-Ray sources coincident with WDs showing significant hard X-Ray Emission at energies >0.5 keV. Twelve of these WDs are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces the hard X-Ray Emission, and in the other ten of which the late-type companions' coronal activity emits hard X-Rays. One WD is projected near an AGN which is responsible for the hard X-Ray Emission. The remaining four WDs and two additional white dwarfs with hard X-Ray Emission appear single. The lack of near-IR excess from the apparently single WDs suggests that either X-Ray observations are more effective than near-IR photometry in diagnosing faint companions or a different Emission mechanism is needed. It is intriguing that 50% of the six apparently single WDs with hard X-Ray Emission are among the hottest WDs. We have compared X-Ray properties of 11 hot WDs with different spectral types, and conclude that stellar pulsation and fast stellar winds are not likely the origin of the hard X-Ray Emission, but a leakage of the high-energy Wien tail of Emission from deep in the stellar atmosphere remains a tantalizing source of hard X-Ray Emission from hot DO and DQZO WDs. (This abstract is an abridged version.)Comment: 35 pages, 8 figures, 4 tables, accepted for publication in AJ, April issu
-
Origin of X-Ray Emission from Planetary Nebulae
2001Co-Authors: You-hua Chu, Robert A. GruendlAbstract:We proposed to use the entire ROSAT archive to search for observations of Galactic planetary nebulae, and analyze these observations, in order to determine the origin of X-Ray Emission from planetary nebulae. We have cross-correlated the ROSAT archive with a catalog of Galactic planetary nebulae and found useful ROSAT observations for approx. 80 planetary nebulae. These observations have been analyzed. X-Ray Emission is detected in 13 nebulae. The X-Ray spectra and luminosities of these positive detections have been analyzed, and the 3-sigma upper limits are determined for the non-detections. The X-Ray properties of planetary nebulae are correlated with the distance and extinction of the nebula, and the temperature and surface gravity of the central star, in order to explain the observed X-Ray Emission. The results are reported in a conference and a paper that has been published in the Astrophysical Journal Supplement. We conclude that this program has been successfully completed.
Robert A. Gruendl - One of the best experts on this subject based on the ideXlab platform.
-
Hard X‐Ray Emission associated with WDs
2010Co-Authors: Jana Bilíková, You-hua Chu, Robert A. Gruendl, Larry A. MaddoxAbstract:Hard X‐Ray Emission associated with white dwarfs (WDs) can be used to diagnose the presence of late‐type binary companions, mass accretion from companions, or physical processes with unknown origins. Since our previous systematic searches for hard X‐Ray Emission associated with WDs, the Galactic WD catalog has been augmented by >10,000 new WDs from the Sloan Digital Sky Survey and new X‐Ray point source catalogs from XMM‐Newton and ROSAT have become available. Therefore, we have extended the search using the updated catalogs, and found 17 new cases of WDs associated with hard X‐Ray Emission. The 32 WDs associated with hard X‐Ray Emission, from the current and previous searches, can be divided into five categories: (1) binary WD with a coronal companion, (2) binary WD with mass transfer from a companion, (3) single hot WD with a hard X‐Ray component peaking near 1 keV in addition to a soft photospheric component, (4) two PG 1159 stars with very faint X‐Ray Emission in the 0.9–2.0 keV band, and (5) two DA W...
-
Hard X-Ray Emission from White Dwarfs
2004Co-Authors: You-hua Chu, Robert A. GruendlAbstract:Hot white dwarfs may exhibit photospheric Emission at X-Ray wavelengths, but their X- Ray Emission should be soft, mutch less than 0.5 keV. Hard X-Ray Emission, at approx. 1 keV, is not expected from white dwarfs, unless they are in binary systems and the hard X-Ray Emission is produced by a late-type companion's coronal activity or by accretion of a companion's material onto the surface of the white dwarf. We proposed to use the ROSAT archive to search for hard X-Ray Emission from white dwarfs in order to determine whether hard X-Ray Emission may provide a sensitive diagnostic for the existence of a binary companion.
-
Hard X-Ray Emission Associated with White Dwarfs
The Astronomical Journal, 2003Co-Authors: Ian J. O’dwyer, You-hua Chu, Robert A. Gruendl, Martín A. Guerrero, Ronald F. WebbinkAbstract:We have used the WGACAT to search for hard X-Ray sources associated with white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-Ray sources coincident with WDs showing significant hard X-Ray Emission at energies >0.5 keV. Twelve of these WDs are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces the hard X-Ray Emission, and in the other ten of which the late-type companions' coronal activity emits hard X-Rays. One WD is projected near an AGN which is responsible for the hard X-Ray Emission. The remaining four WDs and two additional white dwarfs with hard X-Ray Emission appear single. The lack of near-IR excess from the apparently single WDs suggests that either X-Ray observations are more effective than near-IR photometry in diagnosing faint companions or a different Emission mechanism is needed. It is intriguing that 50% of the six apparently single WDs with hard X-Ray Emission are among the hottest WDs. We have compared X-Ray properties of 11 hot WDs with different spectral types, and conclude that stellar pulsation and fast stellar winds are not likely the origin of the hard X-Ray Emission, but a leakage of the high-energy Wien tail of Emission from deep in the stellar atmosphere remains a tantalizing source of hard X-Ray Emission from hot DO and DQZO WDs. (This abstract is an abridged version.)Comment: 35 pages, 8 figures, 4 tables, accepted for publication in AJ, April issu
-
Origin of X-Ray Emission from Planetary Nebulae
2001Co-Authors: You-hua Chu, Robert A. GruendlAbstract:We proposed to use the entire ROSAT archive to search for observations of Galactic planetary nebulae, and analyze these observations, in order to determine the origin of X-Ray Emission from planetary nebulae. We have cross-correlated the ROSAT archive with a catalog of Galactic planetary nebulae and found useful ROSAT observations for approx. 80 planetary nebulae. These observations have been analyzed. X-Ray Emission is detected in 13 nebulae. The X-Ray spectra and luminosities of these positive detections have been analyzed, and the 3-sigma upper limits are determined for the non-detections. The X-Ray properties of planetary nebulae are correlated with the distance and extinction of the nebula, and the temperature and surface gravity of the central star, in order to explain the observed X-Ray Emission. The results are reported in a conference and a paper that has been published in the Astrophysical Journal Supplement. We conclude that this program has been successfully completed.
Martín A. Guerrero - One of the best experts on this subject based on the ideXlab platform.
-
Variable Hard X-Ray Emission From the Central Star of the Eskimo Nebula
The Astrophysical Journal, 2019Co-Authors: Martín A. Guerrero, Jesús A. Toalá, You-hua ChuAbstract:The central star of NGC 2392 shows the hardest X-Ray Emission among central stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic companion with an orbital period of 1.9 days could provide an explanation for its hard X-Ray Emission, as well as for the collimation of its fast outflow. Here we analyse the available Chandra and XMM-Newton X-Ray observations to determine accurately the spectral and temporal variation properties of the CSPN of NGC 2392. The X-Ray Emission can be described by an absorbed thermal plasma model with temperature 26$^{+8}_{-5}$ MK and X-Ray luminosity (8.7$\pm$1.0)$\times$10$^{30}$ erg s$^{-1}$. No long-term variability is detected in the X-Ray Emission level, but the Chandra light curve is suggestive of short-term variations with a period $\sim$0.26 days. The possible origins of this X-Ray Emission are discussed. X-Ray Emission from the coronal activity of a companion or shocks in the stellar wind can be ruled out. Accretion of material from an unseen main-sequence companion onto the CSPN or from the CSPN wind onto a white dwarf companion are the most plausible origins for its hard X-Ray Emission, although the mismatch between the rotational period of the CSPN and the modulation time-scale of the X-Ray Emission seems to preclude the former possibility.
-
Hard X-Ray Emission Associated with White Dwarfs
The Astronomical Journal, 2003Co-Authors: Ian J. O’dwyer, You-hua Chu, Robert A. Gruendl, Martín A. Guerrero, Ronald F. WebbinkAbstract:We have used the WGACAT to search for hard X-Ray sources associated with white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-Ray sources coincident with WDs showing significant hard X-Ray Emission at energies >0.5 keV. Twelve of these WDs are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces the hard X-Ray Emission, and in the other ten of which the late-type companions' coronal activity emits hard X-Rays. One WD is projected near an AGN which is responsible for the hard X-Ray Emission. The remaining four WDs and two additional white dwarfs with hard X-Ray Emission appear single. The lack of near-IR excess from the apparently single WDs suggests that either X-Ray observations are more effective than near-IR photometry in diagnosing faint companions or a different Emission mechanism is needed. It is intriguing that 50% of the six apparently single WDs with hard X-Ray Emission are among the hottest WDs. We have compared X-Ray properties of 11 hot WDs with different spectral types, and conclude that stellar pulsation and fast stellar winds are not likely the origin of the hard X-Ray Emission, but a leakage of the high-energy Wien tail of Emission from deep in the stellar atmosphere remains a tantalizing source of hard X-Ray Emission from hot DO and DQZO WDs. (This abstract is an abridged version.)Comment: 35 pages, 8 figures, 4 tables, accepted for publication in AJ, April issu
Joseph Nordgren - One of the best experts on this subject based on the ideXlab platform.
-
Instrumentation for soft X-Ray Emission spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2000Co-Authors: Joseph Nordgren, Jinghua GuoAbstract:Abstract An account is presented of developments in instrumentation for soft X-Ray Emission spectroscopy (SXES) based on synchrotron radiation. An account for grating spectrometers for soft X-Ray Emission spectroscopy is given, and some considerations regarding synchrotron radiation applications of the spectroscopy are presented. A few points that relate to the new features of resonant SXES and polarization dependent studies are discussed in some detail. A brief discussion on future developments in SXES instrumentation is included.
-
SELECTIVELY EXCITED X-Ray Emission SPECTRA OF N2
Journal of Electron Spectroscopy and Related Phenomena, 1996Co-Authors: Peter Glans, P. Skytt, Kerstin M. Gunnelin, Jinghua Guo, Joseph NordgrenAbstract:Abstract Resonant and non-resonant X-Ray Emission spectra of N2 are presented. The role of the parity selection rule in the case of homonuclear diatomic molecules is discussed thoroughly and illustrated by the X-Ray Emission spectra. We also discuss how the parity selection rule and the angular anisotropy of the resonant X-Ray Emission may affect intensities in a fluorescence yield measurement of N2. Simulated vibrational band profiles calculated using the lifetime–vibrational interference formula are found to be in excellent agreement with the experimental Emission bands.
-
Ab initio calculations of X-Ray Emission from C60
Chemical Physics Letters, 1994Co-Authors: Junji Guo, P. Skytt, Yi Luo, Olav Vahtras, Nial Wassdahl, Hans Ågren, Joseph NordgrenAbstract:Abstract The X-Ray Emission spectrum of the C 60 molecule is analyzed by ab initio Hartree-Fock calculations. The dependency of the X-Ray Emission intensities on the size of the applied basis sets indicate that the obtained large basis set results provide a true representation of the one-particle X-Ray Emission spectrum of C 60 . The results are found to be useful for assigning structures in the experimental spectrum.
Ronald F. Webbink - One of the best experts on this subject based on the ideXlab platform.
-
Hard X-Ray Emission Associated with White Dwarfs
The Astronomical Journal, 2003Co-Authors: Ian J. O’dwyer, You-hua Chu, Robert A. Gruendl, Martín A. Guerrero, Ronald F. WebbinkAbstract:We have used the WGACAT to search for hard X-Ray sources associated with white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-Ray sources coincident with WDs showing significant hard X-Ray Emission at energies >0.5 keV. Twelve of these WDs are in known binary systems, in two of which the accretion of the close companion's material onto the white dwarf produces the hard X-Ray Emission, and in the other ten of which the late-type companions' coronal activity emits hard X-Rays. One WD is projected near an AGN which is responsible for the hard X-Ray Emission. The remaining four WDs and two additional white dwarfs with hard X-Ray Emission appear single. The lack of near-IR excess from the apparently single WDs suggests that either X-Ray observations are more effective than near-IR photometry in diagnosing faint companions or a different Emission mechanism is needed. It is intriguing that 50% of the six apparently single WDs with hard X-Ray Emission are among the hottest WDs. We have compared X-Ray properties of 11 hot WDs with different spectral types, and conclude that stellar pulsation and fast stellar winds are not likely the origin of the hard X-Ray Emission, but a leakage of the high-energy Wien tail of Emission from deep in the stellar atmosphere remains a tantalizing source of hard X-Ray Emission from hot DO and DQZO WDs. (This abstract is an abridged version.)Comment: 35 pages, 8 figures, 4 tables, accepted for publication in AJ, April issu
