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J Do D Nascimento - One of the best experts on this subject based on the ideXlab platform.
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erratum the solar Wind in time ii 3d Stellar Wind structure and radio emission
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: D O Fionnagain, A A Vidotto, P Petit, C P Folsom, S V Jeffers, S C Marsden, J Morin, J Do D NascimentoAbstract:This is an erratum to the paper ‘The solar Wind in time - II: 3D Stellar Wind structure and radio emission’, which was published in MNRAS, 483(1), 873, 2019 (O Fionnagain et al. 2019).
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the solar Wind in time ii 3d Stellar Wind structure and radio emission
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: D O Fionnagain, A A Vidotto, P Petit, C P Folsom, S V Jeffers, S C Marsden, J Morin, J Do D NascimentoAbstract:In this work, we simulate the evolution of the solar Wind along its main-sequence lifetime and compute its thermal radio emission. To study the evolution of the solar Wind, we use a sample of solar mass stars at different ages. All these stars have observationally reconstructed magnetic maps, which are incorporated in our 3D magnetohydrodynamic simulations of their Winds. We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionary time-scales, although they can vary in a magnetic cycle time-scale. Stellar Winds are known to emit radiation in the form of thermal bremsstrahlung in the radio spectrum. To calculate the expected radio fluxes from these Winds, we solve the radiative transfer equation numerically from first principles. We compute continuum spectra across the frequency range 100 MHz to 100 GHz and find maximum radio flux densities ranging from 0.05 to 2.2 μJy. At a frequency of 1 GHz and a normalized distance of d = 10 pc, the radio flux density follows 0.24 (Ω/Ω☉)0.9 (d/[10pc])-2μJy, where Ω is the rotation rate. This means that the best candidates for Stellar Wind observations in the radio regime are faster rotators within distances of 10 pc, such as κ1 Ceti (0.73 μJy) and χ1 Ori (2.2 μJy). These flux predictions provide a guide to observing solar-type stars across the frequency range 0.1-100 GHz in the future using the next generation of radio telescopes, such as ngVLA and Square Kilometre Array.
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interplay of tidal evolution and Stellar Wind braking in the rotation of stars hosting massive close in planets
The Astrophysical Journal, 2015Co-Authors: S Ferrazmello, J Do D Nascimento, Tadeu Dos M Santos, Hugo A Folonier, Sz Czismadia, M PatzoldAbstract:This paper deals with the application of the creep tide theory (Ferraz-Mello, Cel. Mech. Dyn. Astron. 116, 109, 2013) to the study of the rotation of stars hosting massive close-in planets. The stars have nearly the same tidal relaxation factors as gaseous planets and the evolution of their rotation is similar to that of close-in hot Jupiters: they tidally evolve towards a stationary solution. However, Stellar rotation may also be affected by Stellar Wind braking. Thus, while the rotation of a quiet host star evolves towards a stationary attractor with a frequency (1 + 6e 2 ) times the orbital mean-motion of the companion, the continuous loss of angular momentum in an active star displaces the stationary solution towards slower values: Active host stars with big close-in companions tend to have rotational periods larger than the orbital periods of their companions. The study of some hypothetical examples shows that because of tidal evolution, the rules of gyrochronology cannot be used to estimate the age of one system with a large close-in companion, no matter if the star is quiet or active, if the current semi-major axis of the companion is smaller than 0.03–0.04 AU. Details on the evolution of the systems: CoRoT LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on hypothetical systems with 1–4 MJup-planets in orbit around a star similar to the Sun are given.
A A Vidotto - One of the best experts on this subject based on the ideXlab platform.
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erratum the solar Wind in time ii 3d Stellar Wind structure and radio emission
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: D O Fionnagain, A A Vidotto, P Petit, C P Folsom, S V Jeffers, S C Marsden, J Morin, J Do D NascimentoAbstract:This is an erratum to the paper ‘The solar Wind in time - II: 3D Stellar Wind structure and radio emission’, which was published in MNRAS, 483(1), 873, 2019 (O Fionnagain et al. 2019).
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the solar Wind in time ii 3d Stellar Wind structure and radio emission
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: D O Fionnagain, A A Vidotto, P Petit, C P Folsom, S V Jeffers, S C Marsden, J Morin, J Do D NascimentoAbstract:In this work, we simulate the evolution of the solar Wind along its main-sequence lifetime and compute its thermal radio emission. To study the evolution of the solar Wind, we use a sample of solar mass stars at different ages. All these stars have observationally reconstructed magnetic maps, which are incorporated in our 3D magnetohydrodynamic simulations of their Winds. We show that angular-momentum loss and mass-loss rates decrease steadily on evolutionary time-scales, although they can vary in a magnetic cycle time-scale. Stellar Winds are known to emit radiation in the form of thermal bremsstrahlung in the radio spectrum. To calculate the expected radio fluxes from these Winds, we solve the radiative transfer equation numerically from first principles. We compute continuum spectra across the frequency range 100 MHz to 100 GHz and find maximum radio flux densities ranging from 0.05 to 2.2 μJy. At a frequency of 1 GHz and a normalized distance of d = 10 pc, the radio flux density follows 0.24 (Ω/Ω☉)0.9 (d/[10pc])-2μJy, where Ω is the rotation rate. This means that the best candidates for Stellar Wind observations in the radio regime are faster rotators within distances of 10 pc, such as κ1 Ceti (0.73 μJy) and χ1 Ori (2.2 μJy). These flux predictions provide a guide to observing solar-type stars across the frequency range 0.1-100 GHz in the future using the next generation of radio telescopes, such as ngVLA and Square Kilometre Array.
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Radio emission from a young exoplanet and its host star Wind
2018Co-Authors: A A Vidotto, J F DonatiAbstract:Magnetised exoplanets are expected to emit at radio frequencies, similarly to the radio auroral emission of Earth and Jupiter. We predict the radio emission from V830 Tau b, the youngest (2 Myr) detected exoplanet to date, and investigate whether its radio emission can propagate through the Stellar Wind plasma. We model the Wind of the host star using 3D MHD simulations that take into account the reconstructed Stellar surface magnetic field. We find that, although Stellar Winds can power radio emission from exoplanets, if the planet orbits inside the radio photosphere of the Stellar Wind, then the Wind will prevent the propagation of planetary radio emission.
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an evaporating planet in the Wind Stellar Wind interactions with the radiatively braked exosphere of gj 436 b
Astronomy and Astrophysics, 2016Co-Authors: V Bourrier, D Ehrenreich, Yuki Tanaka, A A Vidotto, Lecavelier Des A EtangsAbstract:Observations of the warm Neptune GJ 436 b were performed with HST/STIS at three different epochs (2012, 2013, 2014) in the Stellar Lyman- α line. They showed deep, repeated transits that were attributed to a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas and its dispersion within a large volume around the planet. Yet by itself it cannot explain the specific time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and Stellar Wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and Stellar properties through the direct comparison of simulated and observed spectra. The first epoch of observations is difficult to interpret because of the lack of out-of-transit data. In contrast, the results of our simulations match the observations obtained in 2013 and 2014 well. The sharp early ingresses observed in these epochs come from the abrasion of the planetary coma by the Stellar Wind. Spectra observed at later times during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the Stellar Wind). We find similar properties at both epochs for the planetary escape rate (~2.5 × 10 8 g s -1 ), the Stellar photoionization rate (~2 × 10 -5 s -1 ), the Stellar Wind bulk velocity (~85 km s -1 ), and its kinetic dispersion velocity (~10 km s -1 , corresponding to a kinetic temperature of 12 000 K). We also find high velocities for the escaping gas (~50−60 km s -1 ) that may indicate magnetohydrodynamic (MHD) waves that dissipate in the upper atmosphere and drive the planetary outflow. In 2014 the high density of the Stellar Wind (~3 × 10 3 cm -3 ) led to the formation of an exospheric tail that was mainly composed of neutralized protons and produced a stable absorption signature during and after the transit. The observations of GJ 436 b allow for the first time to clearly separate the contributions of radiation pressure and Stellar Wind and to probe the regions of the exosphere shaped by each mechanism. The overall shape of the cloud, which is constant over time, is caused by the stability of the Stellar emission and the planetary mass loss, while the local changes in the cloud structure can be interpreted as variations in the density of the Stellar Wind.
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an evaporating planet in the Wind Stellar Wind interactions with the radiatively braked exosphere of gj436 b
arXiv: Earth and Planetary Astrophysics, 2016Co-Authors: V Bourrier, Alain Lecavelier Des Etangs, D Ehrenreich, Yuki Tanaka, A A VidottoAbstract:The warm Neptune GJ436b was observed with HST/STIS at three different epochs in the Stellar Ly-alpha line, showing deep, repeated transits caused by a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas. Yet by itself it cannot explain the time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and Stellar Wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and Stellar properties through the direct comparison of simulated and observed spectra. Our simulations match the last two epochs well. The observed sharp early ingresses come from the abrasion of the planetary coma by the Stellar Wind. Spectra observed during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the Stellar Wind). We find similar properties at both epochs for the planetary escape rate (2.5x10$^{8}$ g/s), the Stellar photoionization rate (2x10$^{-5}$ /s), the Stellar Wind bulk velocity (85 km/s), and its kinetic dispersion velocity (10 km/s). We find high velocities for the escaping gas (50-60 km/s) that may indicate MHD waves that dissipate in the upper atmosphere and drive the planetary outflow. In the last epoch the high density of the Stellar Wind (3x10$^{3}$ /cm3) led to the formation of an exospheric tail mainly composed of neutralized protons. The observations of GJ436 b allow for the first time to clearly separate the contributions of radiation pressure and Stellar Wind and to probe the regions of the exosphere shaped by each mechanism.
Zhanwen Han - One of the best experts on this subject based on the ideXlab platform.
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effect of binary fraction on horizontal branch morphology under tidally enhanced Stellar Wind
Publications of the Astronomical Society of Japan, 2014Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuemei Chen, Xiaoyu Kang, Zhanwen HanAbstract:Tidally enhanced Stellar Wind may affect horizontal branch (HB) morphology in globular clusters (GCs) by enhancing the mass loss of primary star during binary evolution. Lei et al. (2013a, AA 2013b, A&A, 554, 130) studied the effect of this kind of Wind on HB morphology in detail, and their results indicated that a binary is a possible second-parameter (2P) candidate in GCs. Binary fraction is a very important fact in the tidally-enhanced-Stellar-Wind model. In this paper, we studied the effect of binary fraction on HB morphology by removing the effects of metallicity and age. Five different binary fractions (i.e., 10%, 15%, 20%, 30%, and 50%) are adopted in our model calculations. The synthetic HB morphologies with different binary fractions are obtained at different metallicities and ages. We found that, due to the great influence of metallicity and age, the effect of binary fraction on HB morphology may be masked by these two parameters. However, when the effects of metallicity and age are removed, the tendency of HB morphologies becoming bluer with increasing binary fractions is clearly presented. Furthermore, we compared our results with the observation by Milone et al. (2012, A&A, 540, 16). Our results are consistent with the observation at metal-rich and metal-poor GCs. For the GCs with intermediate metallicity, when the effect of age on HB morphology is removed, a weak tendency of HB morphologies becoming bluer with increasing binary fractions is presented in all regions of GCs, which is consistent with our results obtained in this metallicity range.
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effect of binary fraction on horizontal branch morphology under tidally enhanced Stellar Wind
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuemei Chen, Xiaoyu Kang, Zhanwen HanAbstract:Tidally enhanced Stellar Wind may affect horizontal branch (HB) morphology in globular clusters (GCs) by enhancing the mass loss of primary star during binary evolution. Lei et al. (2013a, 2013b) studied the effect of this kind of Wind on HB morphology in details, and their results indicated that binary is a possible secondparameter (2P) candidate in GCs. Binary fraction is an very important fact in the tidally-enhanced-Stellar-Wind model. In this paper, we studied the effect of binary fraction on HB morphology by removing the effects of metallicity and age. Five different binary fractions (i.e., 10%, 15%, 20%, 30% and 50%) are adopted in our model calculations. The synthetic HB morphologies with different binary fractions are obtained at different metallicities and ages. We found that, due to the great influence of metallicity and age, the effect of binary fraction on HB morphology may be masked by these two parameters. However, when the effects of metallicity and age are removed, the tendency that HB morphologies become bluer with increasing of binary fractions is clearly presented. Furthermore, we compared our results with the observation by Milone et al. (2012). Our results are consistent well with the observation at metalrich and metal-poor GCs. For the GCs with intermediate metallicity, when the effect of age on HB morphology is removed, a weak tendency that HB morphologies become bluer with increasing of binary fractions is presented in all regions of GCs, which is consistent with our results obtained in this metallicity range.
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synthetic horizontal branch morphology for different metallicities and ages under tidally enhanced Stellar Wind
Astronomy and Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Zhanwen HanAbstract:Context. It is believed that some other parameters, except for metallicity (the first parameter), are needed to explain the horizontal branch (HB) morphology of globular clusters (GCs). Furthermore, these parameters are considered to be correlated with the mass loss of the red giant branch (RGB) stars. Unfortunately, the physics of mass loss on the RGB is poorly understood at present. In our previous work, we proposed that tidally enhanced Stellar Wind during binary evolution may affect the HB morphology by enhancing the mass loss of the red giant primary and that we can reproduce the basic morphology of HB in GCs. Aims. We did not consider the effects of other important parameters (e.g., metallicity and age) in our final results there. As a further study, we now investigate the effects of metallicity and age on HB morphology by considering tidally enhanced Stellar Winds during binary evolution. Methods. We incorporated the tidally enhanced-Stellar-Wind model of Tout & Eggleton into Eggleton's Stellar evolution code to study the binary evolution. A group of binary system samples were generated by Monte Carlo simulations. The position of each sample star in a color-magnitude diagram was obtained by transforming temperature and luminosity into B - V color and absolute magnitude. To study the effects of metallicity and age on our final results, we conducted two sets of model calculations: (i) for a fixed age, we used three metallicities, namely Z = 0.0001, 0.001 and 0.02; (ii) for a fixed metallicity, Z = 0.001, we used five ages in our model calculations: 14, 13, 12, 10, 7 Gyr. Results. We found that HB morphology of GCs becomes bluer with decreasing metallicity, and old GCs present bluer HB morphology than young ones. These results are consistent with previous work. Although the envelope-mass distributions of zero-age HB stars produced by tidally enhanced Stellar Wind are similar for different metallicities, the synthetic HB under tidally enhanced Stellar Wind for Z = 0.02 presented a distinct gap between red and blue HB. However, this feature was not seen clearly in the synthetic HB for Z = 0.001 and 0.0001. We also found that higher binary fractions may make HB morphology become bluer, and we discuss the results with recent observations.
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synthetic horizontal branch morphology for different metallicities and ages under tidally enhanced Stellar Wind
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Zhanwen HanAbstract:It is believed that, except for metallicity, some other parameters are needed to explain the horizontal branch (HB) morphology of globular clusters (GCs). Furthermore, these parameters are considered to be correlated with the mass loss of the red giant branch (RGB) stars. In our previous work, we proposed that tidally enhanced Stellar Wind during binary evolution may affect the HB morphology by enhancing the mass loss of the red giant primary. As a further study, we now investigate the effects of metallicity and age on HB morphology by considering tidally enhanced Stellar Winds during binary evolution. We incorporated the tidally enhanced-Stellar-Wind model into Eggleton's Stellar evolution code to study the binary evolution. To study the effects of metallicity and age on our final results, we conducted two sets of model calculations: (i) for a fixed age, we used three metallicities, namely Z=0.0001, 0.001, and 0.02. (ii) For a fixed metallicity, Z=0.001, we used five ages in our model calculations: 14, 13, 12, 10, and 7 Gyr. We found that HB morphology of GCs becomes bluer with decreasing metallicity, and old GCs present bluer HB morphology than young ones. These results are consistent with previous work. Although the envelope-mass distributions of zero-age HB stars produced by tidally enhanced Stellar Wind are similar for different metallicities, the synthetic HB under tidally enhanced Stellar Wind for Z=0.02 presented a distinct gap between red and blue HB. However, this feature was not seen clearly in the synthetic HB for Z=0.001 and 0.0001. We also found that higher binary fractions may make HB morphology become bluer, and we discussed the results with recent observations.
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effects of tidally enhanced Stellar Wind on the horizontal branch morphology of globular clusters
Astronomy and Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuefei Chen, Zhanwen HanAbstract:Context. Metallicity is the first parameter to influence the horizontal branch (HB) morphology of globular clusters (GCs). It has been found, however, that some other parameters may also play an important role in affecting the morphology. While the nature of these important parameters remains unclear, they are believed to be likely correlated with Wind mass-loss of red giants, since this mass loss determines their subsequent locations on the HB. Unfortunately, the mass loss during the red giant stages of the Stellar evolution is poorly understood at present. Aims. The Stellar Winds of red giants may be tidally enhanced by companion stars if they are in binary systems. We investigate the evolutionary consequences of red giants in binaries by including tidally enhanced Stellar Winds, and examine the effects on the HB morphology of GCs. Methods. We used Eggleton's Stellar evolution code to study the binary evolution. The tidally enhanced Stellar-Wind model of Tout & Eggleton is incorporated into this code, where the tidal enhancement parameter, B-w, has various values (e.g., 10 000 and 500) to examine the dependency of the final results on this parameter. A Monte Carlo simulation was performed to generate a group of binary systems. The position of each primary star on the HB in the Hertzsprung-Russell diagram in this sample is obtained through interpolations among the constructed HB evolutionary tracks. Finally, a synthetic HB in the color-magnitude diagram is obtained by transforming the effective temperature and luminosity of each primary star on the HB into B - V colors and absolute magnitude. Results. We find that red, blue, and extreme horizontal branch stars are all produced under the effects of tidally enhanced Stellar Wind without any additional assumptions on the mass-loss dispersion. Furthermore, the horizontal branch morphology is found to be insensitive to the tidal enhancement parameter, Bw. We compare our theoretical results with the observed horizontal branch morphology of globular cluster NGC 2808, and find that the basic morphology of the horizontal branch can be well reproduced. The number of blue horizontal branch stars in our calculations, however, is lower than that of NGC 2808.
H Lammer - One of the best experts on this subject based on the ideXlab platform.
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two regimes of interaction of a hot jupiter s escaping atmosphere with the Stellar Wind and generation of energized atomic hydrogen corona
arXiv: Earth and Planetary Astrophysics, 2017Co-Authors: I F Shaikhislamov, H Lammer, M L Khodachenko, K G Kislyakova, L Fossati, C P Johnstone, P A Prokopov, A G Berezutsky, Yu P Zakharov, V G PosukhAbstract:The interaction of escaping upper atmosphere of a hydrogen rich non-magnetized analog of HD209458b with a Stellar Wind of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic model. A realistic sun-like spectrum of XUV radiation which ionizes and heats the planetary atmosphere, hydrogen photo-chemistry, as well as Stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric hydrodynamic outflow. Two different regimes of the planetary and Stellar Winds interaction have been modelled. These are: 1) the "captured by the star" regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe towards the star, and 2) the "blown by the Wind" regime, when sufficiently strong Stellar Wind confines the escaping planetary atmosphere and channels it into the tail. The model simulates in details the hydrodynamic interaction between the planetary atoms, protons and the Stellar Wind, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge-exchange between planetary atoms and Stellar protons. The revealed location and shape of the ENA cloud either as a paraboloid shell between ionopause and bowshock (for the "blown by the Wind" regime), or a turbulent layer at the contact boundary between the planetary stream and Stellar Wind (for the "captured by the star" regime) are of importance for the interpretation of Ly{\alpha} absorption features in exoplanetary transit spectra and characterization of the plasma environments.
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Stellar Wind induced soft x ray emission from close in exoplanets
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: K G Kislyakova, M. Holmström, L Fossati, C P Johnstone, V V Zaitsev, H LammerAbstract:In this paper, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX) which produces soft X-ray emission is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar Wind and the atmospheric neutral particles. In the Solar System, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus and Moon. Since the number of emitted photons is proportional to the solar Wind mass flux, this mechanism is not very effective for the Solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the Stellar Wind. Using the example of HD~209458b, we show that this mechanism alone can be responsible for an X-ray emission of $\approx 10^{22}$~erg~s$^{-1}$, which is $10^6$ times stronger than the emission from the Jovian aurora. We discuss also the possibility to observe the predicted soft X-ray flux of hot Jupiters and show that despite high emission intensities they are unobservable with current facilities.
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Stellar Wind induced soft x ray emission from close in exoplanets
The Astrophysical Journal, 2015Co-Authors: K G Kislyakova, M. Holmström, L Fossati, C P Johnstone, V V Zaitsev, H LammerAbstract:In this Letter, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX), which produces soft X-ray emission, is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar Wind and the atmospheric neutral particles. In the solar system, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus, and the Moon. Since the number of emitted photons is proportional to the solar Wind mass flux, this mechanism is not very effective for the solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the Stellar Wind. Using the example of HD 209458b, we show that this mechanism alone can be responsible for an X-ray emission of ≈10{sup 22} erg s{sup –1}, which is 10{sup 6} times stronger than the emission from the Jovian aurora. We discuss also the possibility of observing the predicted soft X-ray flux of hot Jupitersmore » and show that despite high emission intensities they are unobservable with current facilities.« less
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Stellar Wind interaction and pick up ion escape of the kepler 11 super earths
arXiv: Earth and Planetary Astrophysics, 2013Co-Authors: K G Kislyakova, H Lammer, M. Holmström, C P Johnstone, P Odert, N V Erkaev, T Luftinger, M L KhodachenkoAbstract:We study the interactions between Stellar Wind and the extended hydrogen-dominated upper atmospheres of planets and the resulting escape of planetary pick-up ions from the 5 "super-Earths" in the compact Kepler-11 system and compare the escape rates with the efficiency of the thermal escape of neutral hydrogen atoms. Assuming the Stellar Wind of Kepler-11 is similar to the solar Wind, we use a polytropic 1D hydrodynamic Wind model to estimate the Wind properties at the planetary orbits. We apply a Direct Simulation Monte Carlo Model to model the hydrogen coronae and the Stellar Wind plasma interaction around Kepler-11b-f within a realistic expected heating efficiency range of 15-40%. The same model is used to estimate the ion pick-up escape from the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b-f. From the interaction model we study the influence of possible magnetic moments, calculate the charge exchange and photoionization production rates of planetary ions and estimate the loss rates of pick-up H+ ions for all five planets. We compare the results between the five "super-Earths" and in a more general sense also with the thermal escape rates of the neutral planetary hydrogen atoms. Our results show that for all Kepler-11b-f exoplanets, a huge neutral hydrogen corona is formed around the planet. The non-symmetric form of the corona changes from planet to planet and is defined mostly by radiation pressure and gravitational effects. Non-thermal escape rates of pick-up ionized hydrogen atoms for Kepler-11 "super-Earths" vary between approximately 6.4e30 1/s and 4.1e31 1/s depending on the planet's orbital location and assumed heating efficiency. These values correspond to non-thermal mass loss rates of approximately 1.07e7 g/s and 6.8e7 g/s respectively, which is a few percent of the thermal escape rates.
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Stellar Wind interaction and pick up ion escape of the kepler 11 super earths
EGUGA, 2013Co-Authors: K G Kislyakova, H Lammer, M. Holmström, C P Johnstone, P Odert, N V Erkaev, T Luftinger, M L KhodachenkoAbstract:Aims. We study the interactions between Stellar Wind and the extended hydrogen-dominated upper atmospheres of planets and the resulting escape of planetary pick-up ions from the 5 “super-Earths” in the compact Kepler-11 system and compare the escape rates with the effi ciency of the thermal escape of neutral hydrogen atoms. Methods. Assuming the Stellar Wind of Kepler-11 is similar to the solar Wind, we use a polytropic 1D hydrodynamic Wind model to estimate the Wind properties at the planetary orbits. We apply a Direct Simulation Monte Carlo Model to model the hydrogen coronae and the Stellar Wind plasma interaction around Kepler-11b‐f within a realistic expected heating effi ciency range of 15‐40%. The same model is used to estimate the ion pick-up escape from the XUV heated and hydrodynamically extended upper atmospheres of Kepler-11b‐f. From the interaction model we study the infl uence of possible magnetic moments, calculate the charge exchange and photoionization production rates of planetary ions and estimate the loss rates of pick-up H + ions for all five planets. We compare the results between the five “super-Earths” and in a more gene ral sense also with the thermal escape rates of the neutral pl anetary hydrogen atoms. Results. Our results show that for all Kepler-11b‐f exoplanets, a huge neutral hydrogen corona is formed around the planet. The nonsymmetric form of the corona changes from planet to planet and is defined mostly by radiation pressure and gravitational e ffects. Nonthermal escape rates of pick-up ionized hydrogen atoms for Kepler-11 “super-Earths” vary between∼ 6.4×10 30 s −1 and∼ 4.1×10 31 s −1 depending on the planet’s orbital location and assumed heat ing effi ciency. These values correspond to non-thermal mass loss rates of ∼ 1.07× 10 7 g·s −1 and∼ 6.8× 10 7 g·s −1 respectively, which is a few percent of the thermal escape rates.
Zhenxin Lei - One of the best experts on this subject based on the ideXlab platform.
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effect of binary fraction on horizontal branch morphology under tidally enhanced Stellar Wind
Publications of the Astronomical Society of Japan, 2014Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuemei Chen, Xiaoyu Kang, Zhanwen HanAbstract:Tidally enhanced Stellar Wind may affect horizontal branch (HB) morphology in globular clusters (GCs) by enhancing the mass loss of primary star during binary evolution. Lei et al. (2013a, AA 2013b, A&A, 554, 130) studied the effect of this kind of Wind on HB morphology in detail, and their results indicated that a binary is a possible second-parameter (2P) candidate in GCs. Binary fraction is a very important fact in the tidally-enhanced-Stellar-Wind model. In this paper, we studied the effect of binary fraction on HB morphology by removing the effects of metallicity and age. Five different binary fractions (i.e., 10%, 15%, 20%, 30%, and 50%) are adopted in our model calculations. The synthetic HB morphologies with different binary fractions are obtained at different metallicities and ages. We found that, due to the great influence of metallicity and age, the effect of binary fraction on HB morphology may be masked by these two parameters. However, when the effects of metallicity and age are removed, the tendency of HB morphologies becoming bluer with increasing binary fractions is clearly presented. Furthermore, we compared our results with the observation by Milone et al. (2012, A&A, 540, 16). Our results are consistent with the observation at metal-rich and metal-poor GCs. For the GCs with intermediate metallicity, when the effect of age on HB morphology is removed, a weak tendency of HB morphologies becoming bluer with increasing binary fractions is presented in all regions of GCs, which is consistent with our results obtained in this metallicity range.
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effect of binary fraction on horizontal branch morphology under tidally enhanced Stellar Wind
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuemei Chen, Xiaoyu Kang, Zhanwen HanAbstract:Tidally enhanced Stellar Wind may affect horizontal branch (HB) morphology in globular clusters (GCs) by enhancing the mass loss of primary star during binary evolution. Lei et al. (2013a, 2013b) studied the effect of this kind of Wind on HB morphology in details, and their results indicated that binary is a possible secondparameter (2P) candidate in GCs. Binary fraction is an very important fact in the tidally-enhanced-Stellar-Wind model. In this paper, we studied the effect of binary fraction on HB morphology by removing the effects of metallicity and age. Five different binary fractions (i.e., 10%, 15%, 20%, 30% and 50%) are adopted in our model calculations. The synthetic HB morphologies with different binary fractions are obtained at different metallicities and ages. We found that, due to the great influence of metallicity and age, the effect of binary fraction on HB morphology may be masked by these two parameters. However, when the effects of metallicity and age are removed, the tendency that HB morphologies become bluer with increasing of binary fractions is clearly presented. Furthermore, we compared our results with the observation by Milone et al. (2012). Our results are consistent well with the observation at metalrich and metal-poor GCs. For the GCs with intermediate metallicity, when the effect of age on HB morphology is removed, a weak tendency that HB morphologies become bluer with increasing of binary fractions is presented in all regions of GCs, which is consistent with our results obtained in this metallicity range.
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synthetic horizontal branch morphology for different metallicities and ages under tidally enhanced Stellar Wind
Astronomy and Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Zhanwen HanAbstract:Context. It is believed that some other parameters, except for metallicity (the first parameter), are needed to explain the horizontal branch (HB) morphology of globular clusters (GCs). Furthermore, these parameters are considered to be correlated with the mass loss of the red giant branch (RGB) stars. Unfortunately, the physics of mass loss on the RGB is poorly understood at present. In our previous work, we proposed that tidally enhanced Stellar Wind during binary evolution may affect the HB morphology by enhancing the mass loss of the red giant primary and that we can reproduce the basic morphology of HB in GCs. Aims. We did not consider the effects of other important parameters (e.g., metallicity and age) in our final results there. As a further study, we now investigate the effects of metallicity and age on HB morphology by considering tidally enhanced Stellar Winds during binary evolution. Methods. We incorporated the tidally enhanced-Stellar-Wind model of Tout & Eggleton into Eggleton's Stellar evolution code to study the binary evolution. A group of binary system samples were generated by Monte Carlo simulations. The position of each sample star in a color-magnitude diagram was obtained by transforming temperature and luminosity into B - V color and absolute magnitude. To study the effects of metallicity and age on our final results, we conducted two sets of model calculations: (i) for a fixed age, we used three metallicities, namely Z = 0.0001, 0.001 and 0.02; (ii) for a fixed metallicity, Z = 0.001, we used five ages in our model calculations: 14, 13, 12, 10, 7 Gyr. Results. We found that HB morphology of GCs becomes bluer with decreasing metallicity, and old GCs present bluer HB morphology than young ones. These results are consistent with previous work. Although the envelope-mass distributions of zero-age HB stars produced by tidally enhanced Stellar Wind are similar for different metallicities, the synthetic HB under tidally enhanced Stellar Wind for Z = 0.02 presented a distinct gap between red and blue HB. However, this feature was not seen clearly in the synthetic HB for Z = 0.001 and 0.0001. We also found that higher binary fractions may make HB morphology become bluer, and we discuss the results with recent observations.
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synthetic horizontal branch morphology for different metallicities and ages under tidally enhanced Stellar Wind
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Zhanwen HanAbstract:It is believed that, except for metallicity, some other parameters are needed to explain the horizontal branch (HB) morphology of globular clusters (GCs). Furthermore, these parameters are considered to be correlated with the mass loss of the red giant branch (RGB) stars. In our previous work, we proposed that tidally enhanced Stellar Wind during binary evolution may affect the HB morphology by enhancing the mass loss of the red giant primary. As a further study, we now investigate the effects of metallicity and age on HB morphology by considering tidally enhanced Stellar Winds during binary evolution. We incorporated the tidally enhanced-Stellar-Wind model into Eggleton's Stellar evolution code to study the binary evolution. To study the effects of metallicity and age on our final results, we conducted two sets of model calculations: (i) for a fixed age, we used three metallicities, namely Z=0.0001, 0.001, and 0.02. (ii) For a fixed metallicity, Z=0.001, we used five ages in our model calculations: 14, 13, 12, 10, and 7 Gyr. We found that HB morphology of GCs becomes bluer with decreasing metallicity, and old GCs present bluer HB morphology than young ones. These results are consistent with previous work. Although the envelope-mass distributions of zero-age HB stars produced by tidally enhanced Stellar Wind are similar for different metallicities, the synthetic HB under tidally enhanced Stellar Wind for Z=0.02 presented a distinct gap between red and blue HB. However, this feature was not seen clearly in the synthetic HB for Z=0.001 and 0.0001. We also found that higher binary fractions may make HB morphology become bluer, and we discussed the results with recent observations.
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effects of tidally enhanced Stellar Wind on the horizontal branch morphology of globular clusters
Astronomy and Astrophysics, 2013Co-Authors: Zhenxin Lei, Fenghui Zhang, Xuefei Chen, Zhanwen HanAbstract:Context. Metallicity is the first parameter to influence the horizontal branch (HB) morphology of globular clusters (GCs). It has been found, however, that some other parameters may also play an important role in affecting the morphology. While the nature of these important parameters remains unclear, they are believed to be likely correlated with Wind mass-loss of red giants, since this mass loss determines their subsequent locations on the HB. Unfortunately, the mass loss during the red giant stages of the Stellar evolution is poorly understood at present. Aims. The Stellar Winds of red giants may be tidally enhanced by companion stars if they are in binary systems. We investigate the evolutionary consequences of red giants in binaries by including tidally enhanced Stellar Winds, and examine the effects on the HB morphology of GCs. Methods. We used Eggleton's Stellar evolution code to study the binary evolution. The tidally enhanced Stellar-Wind model of Tout & Eggleton is incorporated into this code, where the tidal enhancement parameter, B-w, has various values (e.g., 10 000 and 500) to examine the dependency of the final results on this parameter. A Monte Carlo simulation was performed to generate a group of binary systems. The position of each primary star on the HB in the Hertzsprung-Russell diagram in this sample is obtained through interpolations among the constructed HB evolutionary tracks. Finally, a synthetic HB in the color-magnitude diagram is obtained by transforming the effective temperature and luminosity of each primary star on the HB into B - V colors and absolute magnitude. Results. We find that red, blue, and extreme horizontal branch stars are all produced under the effects of tidally enhanced Stellar Wind without any additional assumptions on the mass-loss dispersion. Furthermore, the horizontal branch morphology is found to be insensitive to the tidal enhancement parameter, Bw. We compare our theoretical results with the observed horizontal branch morphology of globular cluster NGC 2808, and find that the basic morphology of the horizontal branch can be well reproduced. The number of blue horizontal branch stars in our calculations, however, is lower than that of NGC 2808.
