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[Text] / N. V. Erkaev [et al.] // Mon. Not. Roy. Astron. Soc. - 2015. - Vol. 448, Is. 2. - P1916-1921, DOI 10.1093/mnras/stv130. - Cited References:28. - The authors acknowledge the support by the FWF NFN project S11601-N16 'Pathways to Habitability: From Disks to Active Stars, Planets and Life', and the related FWF NFN subproject, S11607-N16 'Particle/Radiative Interactions with Upper Atmospheres of Planetary Bodies Under Extreme Stellar Conditions'. PO acknowledges support from the FWF project P22950-N16. NVE acknowledges support by the RFBR grant no. 15-05-00879-a. Finally, the authors thank the International Space Science Institute (ISSI) in Bern, and the ISSI team 'Characterizing stellar-and exoplanetary environments'. . - ISSN 0035-8711. - ISSN 1365-2966РУБ Astronomy & Astrophysics

Аннотация: By considering martian-like planetary embryos inside the habitable zone of solar-like stars we study the behaviour of the hydrodynamic atmospheric escape of hydrogen for small values of the Jeans escape parameter beta < 3, near the base of the thermosphere, that is defined as a ratio of the gravitational and thermal energy. Our study is based on a 1D hydrodynamic upper atmosphere model that calculates the volume heating rate in a hydrogen-dominated thermosphere due to the absorption of the stellar soft X-ray and extreme ultraviolet (XUV) flux. In case of a monatomic gas, we find that when the beta value near the mesopause/homopause level exceeds a critical value of similar to 2.5, there exists a steady hydrodynamic solution with a smooth transition from subsonic to supersonic flow. For a fixed XUV flux, the escape rate of the upper atmosphere is an increasing function of the temperature at the lower boundary. Our model results indicate a crucial enhancement of the atmospheric escape rate, when the Jeans escape parameter beta decreases to this critical value. When beta becomes <= 2.5, there is no stationary hydrodynamic transition from subsonic to supersonic flow. This is the case of a fast non-stationary atmospheric expansion that results in extreme thermal atmospheric escape rates.

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Держатели документа:
Inst Computat Modelling SB RAS, Krasnoyarsk 660036, Russia.
Siberian Fed Univ, Krasnoyarsk 660041, Russia.
Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria.
Graz Univ, Inst Phys, A-8010 Graz, Austria.
Russian Acad Sci, Polar Geophys Inst, Murmansk 183010, Russia.
ИВМ СО РАН

Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Lammer, H.; Odert, P.; Kulikov, Yu. N.; Kislyakova, K.G.; FWF NFN [S11601-N16, S11607-N16]; FWF [P22950-N16]; RFBR [15-05-00879-a]

/ L. Fossati [et al.] // Astron. Astrophys. - 2017. - Vol. 598. - Ст. A90, DOI 10.1051/0004-6361/201629716. - Cited References:48. - We acknowledge the Austrian Forschungsforderungsgesellschaft FFG projects "RASEN" P847963 and "TAPAS4CHEOPS" P853993, the Austrian Science Fund (FWF) NFN project S11607-N16, and the FWF project P27256-N27. N.V.E. acknowledges support by the RFBR grant Nos. 15-05- 00879-a and 16-52-14006 ANF_a. We thank the anonymous referee for the comments that led to a considerable improvement of the manuscript. . - ISSN 1432-0746РУБ Astronomy & Astrophysics

Аннотация: Stimulated by the discovery of a number of close-in low-density planets, we generalise the Jeans escape parameter taking hydrodynamic and Roche lobe effects into account. We furthermore define Lambda as the value of the Jeans escape parameter calculated at the observed planetary radius and mass for the planet's equilibrium temperature and considering atomic hydrogen, independently of the atmospheric temperature profile. We consider 5 and 10 M-circle plus planets with an equilibrium temperature of 500 and 1000 K, orbiting early G-, K-, and M-type stars. Assuming a clear atmosphere and by comparing escape rates obtained from the energy-limited formula, which only accounts for the heating induced by the absorption of the high-energy stellar radiation, and from a hydrodynamic atmosphere code, which also accounts for the bolometric heating, we find that planets whose Lambda is smaller than 15-35 lie in the "boil-off" regime, where the escape is driven by the atmospheric thermal energy and low planetary gravity. We find that the atmosphere of hot ( i.e. T-eq >= 1000 K) low-mass (M-pl <= 5 M-circle plus) planets with Lambda < 15-35 shrinks to smaller radii so that their Lambda evolves to values higher than 15-35, hence out of the boil-off regime, in less than approximate to 500 Myr. Because of their small Roche lobe radius, we find the same result also for hot (i.e. T-eq >= 1000 K) higher mass (M-pl <= 10 M-circle plus) planets with Lambda < 15-35, when they orbit M-dwarfs. For old, hydrogen-dominated planets in this range of parameters, Lambda should therefore be >= 15-35, which provides a strong constraint on the planetary minimum mass and maximum radius and can be used to predict the presence of aerosols and/or constrain planetary masses, for example.

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Держатели документа:
Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria.
SB RAS, Krasnoyarsk Sci Ctr, Fed Res Ctr, Inst Computat Modelling, Krasnoyarsk 36, Russia.
Max Planck Inst Astron, Konigstuhl 17, D-69117 Heidelberg, Germany.
Karl Franzens Univ Graz, Inst Geophys Astrophys & Meteorol, Univ Pl 5, A-8010 Graz, Austria.

Доп.точки доступа:
Fossati, L.; Erkaev, N.V.; Еркаев, Николай Васильевич; Lammer, H.; Cubillos, P. E.; Odert, P.; Juvan, I.; Kislyakova, K. G.; Lendl, M.; Kubyshkina, D.; Bauer, S. J.; Austrian Forschungsforderungsgesellschaft FFG projects ["RASEN" P847963, "TAPAS4CHEOPS" P853993]; Austrian Science Fund (FWF) NFN project [S11607-N16]; FWF project [P27256-N27]; RFBR grant [15-05- 00879-a, 16-52-14006 ANF_a]

/ K. G. Kislyakova [et al.] // Astron. Astrophys. - 2019. - Vol. 623. - Ст. A131, DOI 10.1051/0004-6361/201833941. - Cited References:89. - We acknowledge the support by the Austria Science Fund (FWF) NFN project S116-N16 and the subprojects S11607-N16, S11606-N16 and S11604-N16. P.O., H.L., and N.V.E. acknowledge support from the Austrian Science Fund (FWF) project P25256-N27 "Characterizing Stellar and Exoplanetary Environments via Modeling of Lyman-alpha Transit Observations of Hot Jupiters". N.V.E. also acknowledges support by the RFBR grant No 16-52-14006. M.L.K. also acknowledges FWF projects I2939-N27 and the partial support by the Ministry of Education and Science of Russian federation (Grant No. RFMEFI61617X0084). I.F.S. acknowleges support of Russian Science Foundation project 18-12-00080. The software used in this work was in part developed by the DOE NNSA-ASC OASCR Flash Center at the University of Chicago. This research was conducted using resources provided by the Swedish National Infrastructure for Computing (SNIC) at the High Performance Computing Center North (HPC2N), Umea University, Sweden. The authors are very thankful to Dr. David Ehrenreich for providing the Ly-alpha spectra of GJ 436b, which were used in this article. We would also like to sincerely thank Dr. Vincent Bourrier and Baptiste Lavie for original processing of these spectra. . - ISSN 1432-0746РУБ Astronomy & Astrophysics

Аннотация: Aims. We modeled the transit signatures in the Lyman-alpha (Ly-alpha) line of a putative Earth-sized planet orbiting in the habitable zone (HZ) of the M dwarf GJ 436. We estimated the transit depth in the Ly-alpha line for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, a nitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with an amount of hydrogen equal to that of the Earth. For all types of atmospheres, we calculated in-transit absorption they would produce in the stellar Ly-alpha line. We applied it to the out-of-transit Ly-alpha observations of GJ 436 obtained by the Hubble Space Telescope (HST) and compared the calculated in-transit absorption with observational uncertainties to determine if it would be detectable. To validate the model, we also used our method to simulate the deep absorption signature observed during the transit of GJ 436b and showed that our model is capable of reproducing the observations. Methods. We used a direct simulation Monte Carlo (DSMC) code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. It includes several ionization mechanisms, such as charge exchange with the stellar wind, photo- and electron impact ionization, and allows to trace particles collisions. At the lower boundary of the DSMC model we assumed an atmosphere density, temperature, and velocity obtained with a hydrodynamic model for the lower atmosphere. Results. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ 436 only the hydrogen-dominated atmosphere is marginally detectable with the Space Telescope Imaging Spectrograph (STIS) on board the HST. Neither a pure nitrogen atmosphere nor a nitrogen-dominated atmosphere with an Earth-like hydrogen concentration in the upper atmosphere are detectable. We also showed that the Ly-alpha observations of GJ 436b can be reproduced reasonably well assuming a hydrogen-dominated atmosphere, both in the blue and red wings of the Ly-alpha line, which indicates that warm Neptune-like planets are a suitable target for Ly-alpha observations. Terrestrial planets, on the other hand, can be observed in the Ly-alpha line if they orbit very nearby stars, or if several observational visits are available.

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Держатели документа:
Univ Vienna, Dept Astrophys, Turkenschanzstr 17, A-1180 Vienna, Austria.
Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria.
Swedish Inst Space Phys, POB 812, S-98128 Kiruna, Sweden.
Russian Acad Sci, Inst Computat Modelling, Siberian Div, Krasnoyarsk 660036, Russia.
Siberian Fed Univ, Krasnoyarsk, Russia.
Moscow MV Lomonosov State Univ, Skobeltsyn Inst Nucl Phys, Moscow, Russia.
Inst Laser Phys SB RAS, Novosibirsk, Russia.

Доп.точки доступа:
Kislyakova, K. G.; Holmstrom, M.; Odert, P.; Lammer, H.; Erkaev, N., V; Khodachenko, M. L.; Shaikhislamov, I. F.; Dorfi, E.; Gudel, M.; Guedel, Manuel; Kislyakova, Kristina; Austria Science Fund (FWF) NFN project [S116-N16, S11606-N16, S11604-N16, S11607-N16]; Austrian Science Fund (FWF) [P25256-N27]; RFBR [16-52-14006]; FWF [I2939-N27]; Ministry of Education and Science of Russian federation [RFMEFI61617X0084]; Russian Science Foundation [18-12-00080]