The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
A K H Kong - One of the best experts on this subject based on the ideXlab platform.
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the discovery of an x ray uv Stellar Flare from the late k early m dwarf lmc 335
The Astrophysical Journal, 2012Co-Authors: B T H Tsang, R Di Stefano, K L Li, A K H KongAbstract:We report the discovery of an X-ray/UV Stellar Flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The Flare event was recorded continuously in X-ray for its first 10 hr from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be ~(8.4 ± 0.6) × 10–12 erg cm–2 s–1. Combining astrometric information from multiple X-ray observations in the quiescent and Flare states, we identify the NIR counterpart of LMC 335 as the Two Micron All Sky Survey source J05414534–6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100-264) pc, implying a total energy output of the entire event of ~(0.4-2.9) × 1035 erg. This report comprises detailed analyses of this late-K/early-M dwarf Flare event that has the longest time coverage yet reported in the literature. The Flare decay can be modeled with two exponential components with timescales of ~28 minutes and ~4 hr, with a single-component decay firmly ruled out. The X-ray spectra during Flare can be described by two components, a dominant high-temperature component of ~40-60 MK and a low-temperature component of ~10 MK, with a Flare loop length of about 1.1-1.3 Stellar radius.
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THE DISCOVERY OF AN X-RAY/UV Stellar Flare FROM THE LATE-K/EARLY-M DWARF LMC 335
The Astrophysical Journal, 2012Co-Authors: B T H Tsang, R Di Stefano, K L Li, A K H KongAbstract:We report the discovery of an X-ray/UV Stellar Flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The Flare event was recorded continuously in X-ray for its first 10 hr from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be ~(8.4 ± 0.6) × 10–12 erg cm–2 s–1. Combining astrometric information from multiple X-ray observations in the quiescent and Flare states, we identify the NIR counterpart of LMC 335 as the Two Micron All Sky Survey source J05414534–6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100-264) pc, implying a total energy output of the entire event of ~(0.4-2.9) × 1035 erg. This report comprises detailed analyses of this late-K/early-M dwarf Flare event that has the longest time coverage yet reported in the literature. The Flare decay can be modeled with two exponential components with timescales of ~28 minutes and ~4 hr, with a single-component decay firmly ruled out. The X-ray spectra during Flare can be described by two components, a dominant high-temperature component of ~40-60 MK and a low-temperature component of ~10 MK, with a Flare loop length of about 1.1-1.3 Stellar radius.
S. Vennes - One of the best experts on this subject based on the ideXlab platform.
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the extreme ultraviolet continuum of a strong Stellar Flare
The Astrophysical Journal, 2003Co-Authors: D. J. Christian, S. Vennes, M Mathioudakis, Darko Jevremovic, J Dupuis, Adela KawkaAbstract:We present the serendipitous detection of an extreme-ultraviolet Flare on EUVE J0613-23.9B. The Flare showed over a 200-fold increase above the quiescent emission in the DS/Lexan 60-200 ? wavelength band. Optical spectroscopy revealed that the event was associated with an active dM3.5e star. The EUVE spectra are dominated by emission lines formed at temperatures in excess of 107 K. The observation is unique as we have detected, for the first time, a strong Lyman continuum in the EUVE long-wavelength range (320-650 ?). The Flare in the continuum (T ? 20,000-30,000 K) was extremely short, lasting for less than 500 s, while in the DS (T ? 107 K) its duration was ?28 ks. The total energy of the Flare in the DS is ~3 ? 1034 ergs. We have made a fit to the continuum using semiempirical model atmospheres and derived the time-averaged temperature and density structures.
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detection of a strong Stellar Flare from euve j1438 432
The Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:We present extreme-ultraviolet (EUV) observations of a strong Flare from EUVE J1438-432, a source serendipitously detected with the Extreme Ultraviolet Explorer (EUVE) Right Angle Program. The Flare was detected in the Lexan/boron (100 A) band and showed a 16-fold increase over quiescent emission with a rise time of ~10 ks and a decay time of ~40 ks. Optical spectroscopy of objects within the EUVE pointing uncertainty circle revealed a pair of late-type stars (WT 486 and WT 487) both showing Balmer series in emission; either star is a good candidate for production of the Flare. The peak luminosity of the Flare is 5.7 × 1029 ergs s-1 with a total energy of ~5 × 1033 ergs. The Flare energetics are about 2 orders of magnitude lower than the large EUV Flare detected from AU Mic in 1992, but similar to other EUV-detected Flares from late-type stars.
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Detection of a Strong Stellar Flare from EUVE J1438−432
The Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:We present extreme-ultraviolet (EUV) observations of a strong Flare from EUVE J1438-432, a source serendipitously detected with the Extreme Ultraviolet Explorer (EUVE) Right Angle Program. The Flare was detected in the Lexan/boron (100 A) band and showed a 16-fold increase over quiescent emission with a rise time of ~10 ks and a decay time of ~40 ks. Optical spectroscopy of objects within the EUVE pointing uncertainty circle revealed a pair of late-type stars (WT 486 and WT 487) both showing Balmer series in emission; either star is a good candidate for production of the Flare. The peak luminosity of the Flare is 5.7 × 1029 ergs s-1 with a total energy of ~5 × 1033 ergs. The Flare energetics are about 2 orders of magnitude lower than the large EUV Flare detected from AU Mic in 1992, but similar to other EUV-detected Flares from late-type stars.
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Detection of a strong Stellar Flare from euve J1438-432
Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:In this letter we describe a hippocampo-cortical model of spatial\nprocessing and navigation based on a cascade of increasingly complex\nassociative processes that are also relevant for other hippocampal\nfunctions such as episodic memory. Associative learning of different\ntypes and the related pattern encoding-recognition take place at three\nsuccessive levels: (1) an object location level, which computes the\nlandmarks from merged multimodal sensory inputs in the parahippocampal\ncortices; (2) a subject location level, which computes place fields by\ncombination of local views and movement-related information in the\nentorhinal cortex; and (3) a spatiotemporal level, which computes place\ntransitions from contiguous place fields in the CA3-CA1 region, which\nform building blocks for learning temporospatial sequences.\nAt the cell population level, superficial entorhinal place cells encode\nspatial, context-independent maps as landscapes of activity; populations\nof transition cells in the CA3-CA1 region encode context-dependent maps\nas sequences of transitions, which form graphs in prefrontal-parietal\ncortices. The model was tested on a robot moving in a real environment;\nthese tests produced results that could help to interpret biological\ndata. Two different goal-oriented navigation strategies were displayed\ndepending on the type of map used by the system.\nThanks to its multilevel, multimodal integration and behavioral\nimplementation, the model suggests functional interpretations for\nlargely unaccounted structural differences between hippocampo-cortical\nsystems. Further, spatiotemporal information, a common denominator\nshared by several brain structures, could serve as a cognitive\nprocessing frame and a functional link, for example, during spatial\nnavigation and episodic memory, as suggested by the applications of the\nmodel to other domains, temporal sequence learning and imitation in\nparticular.
D. J. Christian - One of the best experts on this subject based on the ideXlab platform.
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the extreme ultraviolet continuum of a strong Stellar Flare
The Astrophysical Journal, 2003Co-Authors: D. J. Christian, S. Vennes, M Mathioudakis, Darko Jevremovic, J Dupuis, Adela KawkaAbstract:We present the serendipitous detection of an extreme-ultraviolet Flare on EUVE J0613-23.9B. The Flare showed over a 200-fold increase above the quiescent emission in the DS/Lexan 60-200 ? wavelength band. Optical spectroscopy revealed that the event was associated with an active dM3.5e star. The EUVE spectra are dominated by emission lines formed at temperatures in excess of 107 K. The observation is unique as we have detected, for the first time, a strong Lyman continuum in the EUVE long-wavelength range (320-650 ?). The Flare in the continuum (T ? 20,000-30,000 K) was extremely short, lasting for less than 500 s, while in the DS (T ? 107 K) its duration was ?28 ks. The total energy of the Flare in the DS is ~3 ? 1034 ergs. We have made a fit to the continuum using semiempirical model atmospheres and derived the time-averaged temperature and density structures.
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detection of a strong Stellar Flare from euve j1438 432
The Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:We present extreme-ultraviolet (EUV) observations of a strong Flare from EUVE J1438-432, a source serendipitously detected with the Extreme Ultraviolet Explorer (EUVE) Right Angle Program. The Flare was detected in the Lexan/boron (100 A) band and showed a 16-fold increase over quiescent emission with a rise time of ~10 ks and a decay time of ~40 ks. Optical spectroscopy of objects within the EUVE pointing uncertainty circle revealed a pair of late-type stars (WT 486 and WT 487) both showing Balmer series in emission; either star is a good candidate for production of the Flare. The peak luminosity of the Flare is 5.7 × 1029 ergs s-1 with a total energy of ~5 × 1033 ergs. The Flare energetics are about 2 orders of magnitude lower than the large EUV Flare detected from AU Mic in 1992, but similar to other EUV-detected Flares from late-type stars.
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Detection of a Strong Stellar Flare from EUVE J1438−432
The Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:We present extreme-ultraviolet (EUV) observations of a strong Flare from EUVE J1438-432, a source serendipitously detected with the Extreme Ultraviolet Explorer (EUVE) Right Angle Program. The Flare was detected in the Lexan/boron (100 A) band and showed a 16-fold increase over quiescent emission with a rise time of ~10 ks and a decay time of ~40 ks. Optical spectroscopy of objects within the EUVE pointing uncertainty circle revealed a pair of late-type stars (WT 486 and WT 487) both showing Balmer series in emission; either star is a good candidate for production of the Flare. The peak luminosity of the Flare is 5.7 × 1029 ergs s-1 with a total energy of ~5 × 1033 ergs. The Flare energetics are about 2 orders of magnitude lower than the large EUV Flare detected from AU Mic in 1992, but similar to other EUV-detected Flares from late-type stars.
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Detection of a strong Stellar Flare from euve J1438-432
Astronomical Journal, 1999Co-Authors: D. J. Christian, S. VennesAbstract:In this letter we describe a hippocampo-cortical model of spatial\nprocessing and navigation based on a cascade of increasingly complex\nassociative processes that are also relevant for other hippocampal\nfunctions such as episodic memory. Associative learning of different\ntypes and the related pattern encoding-recognition take place at three\nsuccessive levels: (1) an object location level, which computes the\nlandmarks from merged multimodal sensory inputs in the parahippocampal\ncortices; (2) a subject location level, which computes place fields by\ncombination of local views and movement-related information in the\nentorhinal cortex; and (3) a spatiotemporal level, which computes place\ntransitions from contiguous place fields in the CA3-CA1 region, which\nform building blocks for learning temporospatial sequences.\nAt the cell population level, superficial entorhinal place cells encode\nspatial, context-independent maps as landscapes of activity; populations\nof transition cells in the CA3-CA1 region encode context-dependent maps\nas sequences of transitions, which form graphs in prefrontal-parietal\ncortices. The model was tested on a robot moving in a real environment;\nthese tests produced results that could help to interpret biological\ndata. Two different goal-oriented navigation strategies were displayed\ndepending on the type of map used by the system.\nThanks to its multilevel, multimodal integration and behavioral\nimplementation, the model suggests functional interpretations for\nlargely unaccounted structural differences between hippocampo-cortical\nsystems. Further, spatiotemporal information, a common denominator\nshared by several brain structures, could serve as a cognitive\nprocessing frame and a functional link, for example, during spatial\nnavigation and episodic memory, as suggested by the applications of the\nmodel to other domains, temporal sequence learning and imitation in\nparticular.
Suzanne L. Hawley - One of the best experts on this subject based on the ideXlab platform.
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Synergy Between Solar and Stellar Flares: Challenges and Perspectives
Proceedings of the International Astronomical Union, 2020Co-Authors: Suzanne L. HawleyAbstract:AbstractI will review the current status of Stellar Flare observations and models, highlight similarities and differences with solar Flares, and plead for additional data and insight from the “Sun as a Star”.
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Splinter Session "Solar and Stellar Flares"
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Lyndsay Fletcher, Suzanne L. Hawley, Hugh S. Hudson, Gianna Cauzzi, K. V. Getman, M. Giampapa, Petr Heinzel, Colin P. Johnstone, Adam F. Kowalski, Rachel OstenAbstract:This summary reports on papers presented at the Cool Stars-16 meeting in the splinter session "Solar and Stellar Flares." Although many topics were discussed, the main themes were the commonality of interests, and of physics, between the solar and Stellar Flare communities, and the opportunities for important new observations in the near future.
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the effect of a strong Stellar Flare on the atmospheric chemistry of an earth like planet orbiting an m dwarf
Astrobiology, 2010Co-Authors: Antigona Segura, Lucianne M Walkowicz, Victoria S Meadows, James F Kasting, Suzanne L. HawleyAbstract:Abstract Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high-energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 Flare from the M dwarf AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect, we estimated a proton flux associated with the Flare of 5.9 × 108 protons cm−2 sr−1 s−1 for particles with energies >10 MeV. Then we calculated the abundance of nitrogen oxides produced by the Flare by scaling the production of these compounds during a large solar proton event called the Carrington event. The simulations were performed with a 1-D photochemical model coupled to a 1-D radiative/convective model...
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x ray heated models of Stellar Flare atmospheres theory and comparison with observations
Astrophysical Journal Supplement Series, 1992Co-Authors: Suzanne L. Hawley, G H FisherAbstract:A sequence of five model atmospheres consisting of the photosphere, chromosphere, and transition region is computed. The models represent the response of the gas in a magnetically confined loop to intense Flare energy release. It is assumed that the energy release is confined to the corona, and the effects of chromospheric evaporation and indirect heating of the lower atmosphere by X-rays emitted from the coronal plasma are included. Line and continuum surface fluxes are presented in the wavelength range 1000-9000 A and are compared with those observed during a giant Flare on the M dwarf star AD Leo
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the response of the chromosphere during a Stellar Flare
Memorie della Societa Astronomica Italiana, 1991Co-Authors: Suzanne L. HawleyAbstract:New multi-wavelength observations of a giant Flare on the dMe star AD Leo have been obtained. These observations provide an unparalleled picture of the response of the lower atmosphere during an energetic Flare. A set of chromospheric models was developed, featuring a coronal loop geometry, energy balance throughout the entire loop form photosphere to corona, and a rigorous treatment of the radiative transfer in the important, optically thick, chromospheric emission lines.
F Reale - One of the best experts on this subject based on the ideXlab platform.
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geometry diagnostics of a Stellar Flare from fluorescent x rays
The Astrophysical Journal, 2008Co-Authors: Paola Testa, Jeremy J Drake, Barbara Ercolano, F Reale, David P Huenemoerder, L Affer, G Micela, D GarciaalvarezAbstract:We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum of the single G-type giant HR 9024 during a large Flare. In analogy to solar X-ray observations, we interpret the observed Fe Ka line as being produced by illumination of the photosphere by ionizing coronal X-rays, in which case, for a given Fe photospheric abundance, its intensity depends on the height of the X-ray source. The HETGS observations, together with three-dimensional Monte Carlo calculations to model the fluorescence emission, are used to obtain a direct geometric constraint on the scale height of the flaring coronal plasma. We compute the Fe fluorescent emission induced by the emission of a single flaring coronal loop that well reproduces the observed X-ray temporal and spectral properties according to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is in good agreement with the observed value within observational uncertainties, pointing to a scale height . Comparison of the HR 9024 Flare with that recently observed on II Peg by Swift indicates the 0.3R∗ latter is consistent with excitation by X-ray photoionization. Subject headings: hydrodynamics — plasmas — stars: coronae — X-rays: stars
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Flare diagnostics from loop modeling of a Stellar Flare observed with xmm newton
Advances in Space Research, 2006Co-Authors: F RealeAbstract:Abstract XMM-Newton data of an X-ray Flare observed on Proxima Centauri provide detailed and challenging constraints for Flare modeling. The comparison of the data with the results of time-dependent hydrodynamic loop modeling of this Flare allows us to constrain not only the loop morphology, but also the details of the heating function. The results show that even a complex Flare event like this can be described with a relatively few – though constrained – components: two loop systems, i.e., a single loop and an arcade, and two heat components, an intense pulse probably located at the loop footpoints followed by a low gradual decay distributed in the coronal part of the loop. The similarity to at least one solar event (the Bastille Day Flare in 2000) indicates that this pattern may be common to solar and Stellar Flares.
