Further studies of non-maxwellian effects associated with the thermal escape of a planetary atmosphere

Abstract The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Lyα line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the $\sim 56\%$ absorption found in Lyα transits, simultaneously with the lack of absorption in Hα transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Lyα observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s−1 with a temperature of [3 − 4] × 105 K. The stellar and planetary mass loss rates are found to be 2 × 10−15 M⊙ yr−1 and ∼[6 − 10] × 109 g s−1, respectively, for a stellar EUV luminosity of [0.8 − 1.6] × 1027 erg s−1. For the parameters explored in our simulations, none of our models present any significant absorption in the Hα line in agreement with the observations.

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Direct observation of long-lived cyanide anions in superexcited states

Communications Chemistry ◽

10.1038/s42004-021-00450-0 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Xiao-Fei Gao ◽

Jing-Chen Xie ◽

Hao Li ◽

Xin Meng ◽

Yong Wu ◽

...

Keyword(s):

Direct Observation ◽

Electron Attachment ◽

Planetary Atmosphere ◽

Interstellar Space ◽

Dissociative Electron Attachment ◽

Circumstellar Envelopes ◽

Vibrational States ◽

Cyanide Anion ◽

Exceptional Stability ◽

Electronic Ground

AbstractThe cyanide anion (CN−) has been identified in cometary coma, interstellar medium, planetary atmosphere and circumstellar envelopes, but its origin and abundance are still disputed. An isolated CN− is stabilized in the vibrational states up to ν = 17 of the electronic ground-state 1Σ+, but it is not thought to survive in the electronic or vibrational states above the electron autodetachment threshold, namely, in superexcited states. Here we report the direct observation of long-lived CN− yields of the dissociative electron attachment to cyanogen bromide (BrCN), and confirm that some of the CN− yields are distributed in the superexcited vibrational states ν ≥ 18 (1Σ+) or the superexcited electronic states 3Σ+ and 3Π. The triplet state can be accessed directly in the impulsive dissociation of BrCN− or by an intersystem transition from the superexcited vibrational states of CN−. The exceptional stability of CN− in the superexcited states profoundly influences its abundance and is potentially related to the production of other compounds in interstellar space.

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Luminescence from Droplet-Etched GaAs Quantum Dots at and Close to Room Temperature

Nanomaterials ◽

10.3390/nano11030690 ◽

2021 ◽

Vol 11 (3) ◽

pp. 690

Author(s):

Leonardo Ranasinghe ◽

Christian Heyn ◽

Kristian Deneke ◽

Michael Zocher ◽

Roman Korneev ◽

...

Keyword(s):

Quantum Dots ◽

Penetration Depth ◽

Gaas Substrate ◽

Room Temperature ◽

Green Laser ◽

Significant Loss ◽

Blue Laser ◽

Ambient Conditions ◽

Thermal Escape ◽

Intensity Loss

Epitaxially grown quantum dots (QDs) are established as quantum emitters for quantum information technology, but their operation under ambient conditions remains a challenge. Therefore, we study photoluminescence (PL) emission at and close to room temperature from self-assembled strain-free GaAs quantum dots (QDs) in refilled AlGaAs nanoholes on (001)GaAs substrate. Two major obstacles for room temperature operation are observed. The first is a strong radiative background from the GaAs substrate and the second a significant loss of intensity by more than four orders of magnitude between liquid helium and room temperature. We discuss results obtained on three different sample designs and two excitation wavelengths. The PL measurements are performed at room temperature and at T = 200 K, which is obtained using an inexpensive thermoelectric cooler. An optimized sample with an AlGaAs barrier layer thicker than the penetration depth of the exciting green laser light (532 nm) demonstrates clear QD peaks already at room temperature. Samples with thin AlGaAs layers show room temperature emission from the QDs when a blue laser (405 nm) with a reduced optical penetration depth is used for excitation. A model and a fit to the experimental behavior identify dissociation of excitons in the barrier below T = 100 K and thermal escape of excitons from QDs above T = 160 K as the central processes causing PL-intensity loss.

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Collisionless Hydrodynamic Generators in a Planetary Atmosphere

The Earth’s Electric Field ◽

10.1016/b978-0-12-397886-8.00003-x ◽

2014 ◽

pp. 53-86

Author(s):

Michael C. Kelley

Keyword(s):

Planetary Atmosphere

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Stellar activity and magnetic shielding

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992961 ◽

2009 ◽

Vol 5 (S264) ◽

pp. 385-394 ◽

Cited By ~ 2

Author(s):

J.-M. Grießmeier ◽

M. Khodachenko ◽

H. Lammer ◽

J. L. Grenfell ◽

A. Stadelmann ◽

...

Keyword(s):

Dipole Moment ◽

Magnetic Dipole ◽

Magnetic Dipole Moment ◽

Direct Interaction ◽

Planetary Atmosphere ◽

Stellar Activity ◽

Planetary Environment ◽

Atmospheric Loss ◽

Planetary Magnetic Field ◽

Planetary Habitability

AbstractStellar activity has a particularly strong influence on planets at small orbital distances, such as close-in exoplanets. For such planets, we present two extreme cases of stellar variability, namely stellar coronal mass ejections and stellar wind, which both result in the planetary environment being variable on a timescale of billions of years. For both cases, direct interaction of the streaming plasma with the planetary atmosphere would entail servere consequences. In certain cases, however, the planetary atmosphere can be effectively shielded by a strong planetary magnetic field. The efficiency of this shielding is determined by the planetary magnetic dipole moment, which is difficult to constrain by either models or observations. We present different factors which influence the strength of the planetary magnetic dipole moment. Implications are discussed, including nonthermal atmospheric loss, atmospheric biomarkers, and planetary habitability.

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