The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Herve Abgrall - One of the best experts on this subject based on the ideXlab platform.
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high resolution ultraviolet radiation fields of classical t tauri stars
The Astrophysical Journal, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912-1700 ?) radiation field from accreting central stars in classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. The FUV field may also play a critical role in determining the evolution of the inner disk (r < 10?AU), from a gas- and dust-rich primordial disk to a transitional system where the optically thick warm dust distribution has been depleted. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly? emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly? line profiles and remove atomic and molecular disk emission (from H2 and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly?, N V, C IV, He II) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical classical T Tauri star FUV radiation field at 1?AU from the central star is ~107 times the average interstellar radiation field. The Ly? emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly? flux are strongly correlated with C IV flux, suggesting that accretion processes dominate the production of both of these components. On average, only ~0.5% of the total FUV flux is emitted between the Lyman limit (912 ?) and the H2 (0-0) absorption band at 1110 ?. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
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high resolution ultraviolet radiation fields of classical t tauri stars
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912--1700 \AA) radiation field from accreting central stars in Classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly$\alpha$ emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly$\alpha$ line profiles and remove atomic and molecular disk emission (from H$_{2}$ and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly$\alpha$, \ion{N}{5}, \ion{C}{4}, \ion{He}{2}) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical Classical T Tauri Star FUV radiation field at 1 AU from the central star is $\sim$ 10$^{7}$ times the average interstellar radiation field. The Ly$\alpha$ emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly$\alpha$ flux are strongly correlated with \ion{C}{4} flux, suggesting that accretion processes dominate the production of both of these components. On average, only $\sim$ 0.5% of the total FUV flux is emitted between the Lyman limit (912 \AA) and the H$_{2}$ (0 -- 0) absorption band at 1110 \AA. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
Lucianne M Walkowicz - One of the best experts on this subject based on the ideXlab platform.
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the ultraviolet radiation environment around m dwarf exoplanet host stars
The Astrophysical Journal, 2013Co-Authors: Cynthia S Froning, J L Linsky, Aki Roberge, John T Stocke, Feng Tian, Rachel Bushinsky, Jeanmichel Desert, Pablo J D Mauas, Mariela Vieytes, Lucianne M WalkowiczAbstract:The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The combined FUV+NUV spectra are publicly available in machine-Readable Format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV-quiet" M dwarfs are observed. The bright stellar Lyα emission lines are reconstructed, and we find that the Lyα line fluxes comprise ~37%-75% of the total 1150-3100 A flux from most M dwarfs; ≳10^3 times the solar value. We develop an empirical scaling relation between Lyα and Mg II emission, to be used when interstellar H I attenuation precludes the direct observation of Lyα. The intrinsic unreddened flux ratio is F(Lyα)/F(Mg II) = 10 ± 3. The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O_2 and O_3, is shown to be ~0.5-3 for all M dwarfs in our sample, >10^3 times the solar ratio. For the four stars with moderate signal-to-noise Cosmic Origins Spectrograph time-resolved spectra, we find UV emission line variability with amplitudes of 50%-500% on 10^2-10^3 s timescales. This effect should be taken into account in future UV transiting planet studies, including searches for O_3 on Earth-like planets. Finally, we observe relatively bright H_2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot (T(H_2) ≈ 2000-4000 K) molecular gas observed in these objects.
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the ultraviolet radiation environment around m dwarf exoplanet host stars
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Cynthia S Froning, J L Linsky, Aki Roberge, John T Stocke, Feng Tian, Rachel Bushinsky, Jeanmichel Desert, Pablo J D Mauas, Mariela Vieytes, Lucianne M WalkowiczAbstract:The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both FUV and NUV wavelengths. The combined FUV+NUV spectra are publically available in machine-Readable Format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV quiet" M dwarfs are observed. The bright stellar Ly-alpha emission lines are reconstructed, and we find that the Ly-alpha line fluxes comprise ~37-75% of the total 1150-3100A flux from most M dwarfs; > 10^{3} times the solar value. The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O2 and O3, is shown to be ~0.5-3 for all M dwarfs in our sample, > 10^{3} times the solar ratio. For the four stars with moderate signal-to-noise COS time-resolved spectra, we find UV emission line variability with amplitudes of 50-500% on 10^{2} - 10^{3} s timescales. Finally, we observe relatively bright H2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot (T(H2) \approx 2000-4000 K) molecular gas observed in these objects.
E Schindhelm - One of the best experts on this subject based on the ideXlab platform.
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high resolution ultraviolet radiation fields of classical t tauri stars
The Astrophysical Journal, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912-1700 ?) radiation field from accreting central stars in classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. The FUV field may also play a critical role in determining the evolution of the inner disk (r < 10?AU), from a gas- and dust-rich primordial disk to a transitional system where the optically thick warm dust distribution has been depleted. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly? emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly? line profiles and remove atomic and molecular disk emission (from H2 and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly?, N V, C IV, He II) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical classical T Tauri star FUV radiation field at 1?AU from the central star is ~107 times the average interstellar radiation field. The Ly? emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly? flux are strongly correlated with C IV flux, suggesting that accretion processes dominate the production of both of these components. On average, only ~0.5% of the total FUV flux is emitted between the Lyman limit (912 ?) and the H2 (0-0) absorption band at 1110 ?. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
-
high resolution ultraviolet radiation fields of classical t tauri stars
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912--1700 \AA) radiation field from accreting central stars in Classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly$\alpha$ emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly$\alpha$ line profiles and remove atomic and molecular disk emission (from H$_{2}$ and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly$\alpha$, \ion{N}{5}, \ion{C}{4}, \ion{He}{2}) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical Classical T Tauri Star FUV radiation field at 1 AU from the central star is $\sim$ 10$^{7}$ times the average interstellar radiation field. The Ly$\alpha$ emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly$\alpha$ flux are strongly correlated with \ion{C}{4} flux, suggesting that accretion processes dominate the production of both of these components. On average, only $\sim$ 0.5% of the total FUV flux is emitted between the Lyman limit (912 \AA) and the H$_{2}$ (0 -- 0) absorption band at 1110 \AA. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
Cynthia S Froning - One of the best experts on this subject based on the ideXlab platform.
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the ultraviolet radiation environment around m dwarf exoplanet host stars
The Astrophysical Journal, 2013Co-Authors: Cynthia S Froning, J L Linsky, Aki Roberge, John T Stocke, Feng Tian, Rachel Bushinsky, Jeanmichel Desert, Pablo J D Mauas, Mariela Vieytes, Lucianne M WalkowiczAbstract:The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The combined FUV+NUV spectra are publicly available in machine-Readable Format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV-quiet" M dwarfs are observed. The bright stellar Lyα emission lines are reconstructed, and we find that the Lyα line fluxes comprise ~37%-75% of the total 1150-3100 A flux from most M dwarfs; ≳10^3 times the solar value. We develop an empirical scaling relation between Lyα and Mg II emission, to be used when interstellar H I attenuation precludes the direct observation of Lyα. The intrinsic unreddened flux ratio is F(Lyα)/F(Mg II) = 10 ± 3. The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O_2 and O_3, is shown to be ~0.5-3 for all M dwarfs in our sample, >10^3 times the solar ratio. For the four stars with moderate signal-to-noise Cosmic Origins Spectrograph time-resolved spectra, we find UV emission line variability with amplitudes of 50%-500% on 10^2-10^3 s timescales. This effect should be taken into account in future UV transiting planet studies, including searches for O_3 on Earth-like planets. Finally, we observe relatively bright H_2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot (T(H_2) ≈ 2000-4000 K) molecular gas observed in these objects.
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the ultraviolet radiation environment around m dwarf exoplanet host stars
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Cynthia S Froning, J L Linsky, Aki Roberge, John T Stocke, Feng Tian, Rachel Bushinsky, Jeanmichel Desert, Pablo J D Mauas, Mariela Vieytes, Lucianne M WalkowiczAbstract:The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both FUV and NUV wavelengths. The combined FUV+NUV spectra are publically available in machine-Readable Format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV quiet" M dwarfs are observed. The bright stellar Ly-alpha emission lines are reconstructed, and we find that the Ly-alpha line fluxes comprise ~37-75% of the total 1150-3100A flux from most M dwarfs; > 10^{3} times the solar value. The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O2 and O3, is shown to be ~0.5-3 for all M dwarfs in our sample, > 10^{3} times the solar ratio. For the four stars with moderate signal-to-noise COS time-resolved spectra, we find UV emission line variability with amplitudes of 50-500% on 10^{2} - 10^{3} s timescales. Finally, we observe relatively bright H2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot (T(H2) \approx 2000-4000 K) molecular gas observed in these objects.
E Roueff - One of the best experts on this subject based on the ideXlab platform.
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high resolution ultraviolet radiation fields of classical t tauri stars
The Astrophysical Journal, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912-1700 ?) radiation field from accreting central stars in classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. The FUV field may also play a critical role in determining the evolution of the inner disk (r < 10?AU), from a gas- and dust-rich primordial disk to a transitional system where the optically thick warm dust distribution has been depleted. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly? emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly? line profiles and remove atomic and molecular disk emission (from H2 and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly?, N V, C IV, He II) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical classical T Tauri star FUV radiation field at 1?AU from the central star is ~107 times the average interstellar radiation field. The Ly? emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly? flux are strongly correlated with C IV flux, suggesting that accretion processes dominate the production of both of these components. On average, only ~0.5% of the total FUV flux is emitted between the Lyman limit (912 ?) and the H2 (0-0) absorption band at 1110 ?. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
-
high resolution ultraviolet radiation fields of classical t tauri stars
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: E Schindhelm, Edwin A Bergin, E Roueff, Herve AbgrallAbstract:The far-ultraviolet (FUV; 912--1700 \AA) radiation field from accreting central stars in Classical T Tauri systems influences the disk chemistry during the period of giant planet Formation. Previous efforts to measure the true stellar+accretion-generated FUV luminosity (both hot gas emission lines and continua) have been complicated by a combination of low-sensitivity and/or low-spectral resolution and did not include the contribution from the bright Ly$\alpha$ emission line. In this work, we present a high-resolution spectroscopic study of the FUV radiation fields of 16 T Tauri stars whose dust disks display a range of evolutionary states. We include reconstructed Ly$\alpha$ line profiles and remove atomic and molecular disk emission (from H$_{2}$ and CO fluorescence) to provide robust measurements of both the FUV continuum and hot gas lines (e.g., Ly$\alpha$, \ion{N}{5}, \ion{C}{4}, \ion{He}{2}) for an appreciable sample of T Tauri stars for the first time. We find that the flux of the typical Classical T Tauri Star FUV radiation field at 1 AU from the central star is $\sim$ 10$^{7}$ times the average interstellar radiation field. The Ly$\alpha$ emission line contributes an average of 88% of the total FUV flux, with the FUV continuum accounting for an average of 8%. Both the FUV continuum and Ly$\alpha$ flux are strongly correlated with \ion{C}{4} flux, suggesting that accretion processes dominate the production of both of these components. On average, only $\sim$ 0.5% of the total FUV flux is emitted between the Lyman limit (912 \AA) and the H$_{2}$ (0 -- 0) absorption band at 1110 \AA. The total and component-level high-resolution radiation fields are made publicly available in machine-Readable Format.
