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Arbo D.G.,Institute for Astronomy and Space Physics | Lemell C.,Vienna University of Technology | Burgdorfer J.,Vienna University of Technology
Journal of Physics: Conference Series

We analyze the two-dimensional angular momentum-energy distribution of electrons emitted from argon by short laser pulses. We identify characteristic features of both multiphoton and tunneling ionization in the partial-wave distribution for Keldysh parameters close to unity. We observe a remarkable degree of quantum-classical correspondence in the photoinization process which becomes even more pronounced after intensity averaging over the focal volume. We derive an energy-dependent cut-off for the highest angular momentum accessible within the framework of the strong-field approximation, which accurately reproduces the partial wave distributions found from solutions of the time-dependent Schrödinger equation. © 2015 IOP Publishing Ltd. Source

Edberg N.J.T.,Swedish Institute of Space Physics | Wahlund J.-E.,Swedish Institute of Space Physics | Agren K.,Swedish Institute of Space Physics | Morooka M.W.,Swedish Institute of Space Physics | And 3 more authors.
Geophysical Research Letters

We present electron temperature and density measurements of Titan's cold ionospheric plasma from the Langmuir probe instrument on Cassini from 52 flybys. An expression of the density as a function of temperature is presented for altitudes below two Titan radii. The density falls off exponentially with increased temperature as log(n e) = -2.0log(T e) + 0.6 on average around Titan. We show that this relation varies with location around Titan as well as with the solar illumination direction. Significant heating of the electrons appears to take place on the night/wake side of Titan as the density-temperature relation is less steep there. Furthermore, we show that the magnetospheric ram pressure is not balanced by the thermal and magnetic pressure in the topside ionosphere and discuss its implications for plasma escape. The cold ionospheric plasma of Titan extends to higher altitudes in the wake region, indicating the loss of atmosphere down the induced magnetospheric tail. © 2010 by the American Geophysical Union. Source

Tissera P.B.,Institute for Astronomy and Space Physics
EPJ Web of Conferences

We studied the chemical properties of Milky-Way mass galaxies. We found common global chemical patterns with particularities which reflect their different assembly histories in a hierarchical scenario. We carried out a comprehensively analysis of the dynamical components (central spheroid, disc, inner and outer haloes) and their chemical properties. © Owned by the authors, published by EDP Sciences, 2012. Source

Edberg N.J.T.,Swedish Institute of Space Physics | Andrews D.J.,Swedish Institute of Space Physics | Shebanits O.,Swedish Institute of Space Physics | Agren K.,Swedish Institute of Space Physics | And 11 more authors.
Geophysical Research Letters

We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310 cm-3 during the T85 Titan flyby. This is at least 500 cm-3 higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons. Key Points Titan is located in the magnetosheath of Saturn during the T85 flyby The highest ever ionospheric electron densities at Titan are found during T85 The magnetosheath encounter and the extreme densities are due to a CME impact ©2013. American Geophysical Union. All Rights Reserved. Source

Delva M.,Austrian Academy of Sciences | Mazelle C.,French National Center for Scientific Research | Bertucci C.,Institute for Astronomy and Space Physics
Space Science Reviews

The occurrence of waves generated by pick-up of planetary neutrals by the solar wind around unmagnetized planets is an important indicator for the composition and evolution of planetary atmospheres. For Venus and Mars, long-term observations of the upstream magnetic field are now available and proton cyclotron waves have been reported by several spacecraft. Observations of these left-hand polarized waves at the local proton cyclotron frequency in the spacecraft frame are reviewed for their specific properties, generation mechanisms and consequences for the planetary exosphere. Comparison of the reported observations leads to a similar general wave occurrence at both planets, at comparable locations with respect to the planet. However, the waves at Mars are observed more frequently and for long durations of several hours; the cyclotron wave properties are more pronounced, with larger amplitudes, stronger left-hand polarization and higher coherence than at Venus. The geometrical configuration of the interplanetary magnetic field with respect to the solar wind velocity and the relative density of upstream pick-up protons to the background plasma are important parameters for wave generation. At Venus, where the relative exospheric pick-up ion density is low, wave generation was found to mainly take place under stable and quasi-parallel conditions of the magnetic field and the solar wind velocity. This is in agreement with theory, which predicts fast wave growth from the ion/ion beam instability under quasi-parallel conditions already for low relative pick-up ion density. At Mars, where the relative exospheric pick-up ion density is higher, upstream wave generation may also take place under stable conditions when the solar wind velocity and magnetic field are quasi-perpendicular. At both planets, the altitudes where upstream proton cyclotron waves were observed (8 Venus and 11 Mars radii) are comparable in terms of the bow shock nose distance of the planet, i.e. in terms of the size of the solar wind-planetary atmosphere interaction region. In summary, the upstream proton cyclotron wave observations demonstrate the strong similarity in the interaction of the outer exosphere of these unmagnetized planets with the solar wind upstream of the planetary bow shock. © 2011 Springer Science+Business Media B.V. Source

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