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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]

/ I. F. Shaikhislamov [et al.] // Astrophys. J. - 2018. - Vol. 866, Is. 1. - Ст. 47, DOI 10.3847/1538-4357/aadf39. - Cited References:48. - This work was supported by grant No. 18-12-00080 of the Russian Science Foundation. H.L., L.F., N.D., M.G., K.G.K., C.P.J. acknowledge the Austrian Science Foundation (FWF) project I2939-N27, FWF-NFN projects S11606-N16, WS11607-N16 and S11604-N16. M.L.K. also acknowledges the FWF projects P25587-N27, P25640-N27 and Leverhulme Trust grant IN-2014-016. Parallel computing simulations, key for this study, have been performed at Computation Center of Novosibirsk State University, SB RAS Siberian Supercomputer Center, and Supercomputing Center of the Lomonosov Moscow State University. . - ISSN 0004-637X. - ISSN 1538-4357РУБ Astronomy & Astrophysics

Аннотация: The absorption of stellar radiation observed by HD 209458b in the resonant lines of O I and C II has not yet been satisfactorily explained. We apply a 2D hydrodynamic multi-fluid model that self-consistently describes the expanding planetary wind, driven by stellar XUV radiation and influenced by tidal forces and the surrounding stellar wind. According to this model, HD 209458b has a hydrogen-dominated plasmasphere, expanding beyond the Roche lobe, in the form of two supersonic streams that propagate toward and away from the star. The species heavier than hydrogen and helium are dragged in the escaping material streams and accelerated up to 50 km s(-1). Our simulations show that, assuming solar abundances, O I and C II produce absorption due to the Doppler resonance mechanism at the level of 6%-10%, which is consistent with the observations. Most of this absorption takes place in the streams. The transit depth in the O I and C II lines is unaffected by the stellar wind, unless it is strong enough to form a compact bowshock around the planet and able to redirect all the escaping material to the tail. In this case, the absorption profile becomes asymmetric due to the prominent blueshifted attenuation. Thus, the spectroscopic measurements enable probing of the planetary wind character, as well as the strength of the stellar wind. The computed absorption at wavelengths of the Si III, Mg I, and Mg II lines at solar abundances appears to be much stronger, compared to the observations. This possibly indicates that Si and Mg may be under-abundant in the upper atmosphere of HD 209458b.

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Держатели документа:
Inst Laser Phys SB RAS, Novosibirsk, Russia.
Austrian Acad Sci, Space Res Inst, Graz, Austria.
Moscow MV Lomonosov State Univ, Skobeltsyn Inst Nucl Phys, Moscow, Russia.
Univ Vienna, Dept Astrophys, Vienna, Austria.
Inst Computat Modelling SB RAS, Krasnoyarsk, Russia.
Siberian Fed Univ, Polytech Inst, Krasnoyarsk, Russia.

Доп.точки доступа:
Shaikhislamov, I. F.; Khodachenko, M. L.; Lammer, H.; Fossati, L.; Dwivedi, N.; Gudel, M.; Kislyakova, K. G.; Johnstone, C. P.; Berezutsky, A. G.; Miroshnichenko, I. B.; Posukh, V. G.; Erkaev, N., V; Ivanov, V. A.; Russian Science Foundation [18-12-00080]; Austrian Science Foundation (FWF) [I2939-N27]; FWF-NFN projects [S11606-N16, WS11607-N16, S11604-N16]; FWF [P25587-N27, P25640-N27]; Leverhulme Trust [IN-2014-016]