32 research outputs found

    Hunting for Stellar Coronal Mass Ejections

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    Coronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum and mass loss of late-type stars, and also shape the environment in which planets form and live. Stellar CMEs can be detected in optical spectra in the Balmer lines, especially in Halpha, as blue-shifted extra emission/absorption. To increase the detection probability one can monitor young open clusters, in which the stars are due to their youth still rapid rotators, and thus magnetically active and likely to exhibit a large number of CMEs. Using ESO facilities and the Nordic Optical Telescope we have obtained time series of multi-object spectroscopic observations of late-type stars in six open clusters with ages ranging from 15 Myrs to 300 Myrs. Additionally, we have studied archival data of numerous active stars. These observations will allow us to obtain information on the occurrence rate of CMEs in late-type stars with different ages and spectral types. Here we report on the preliminary outcome of our studies.Comment: 6 pages, submitted to the proceedings of IAU Symposium 328 'Living Around Active Stars

    The Exosphere as a Boundary: Origin and Evolution of Airless Bodies in the Inner Solar System and Beyond Including Planets with Silicate Atmospheres

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    In this review we discuss all the relevant solar/stellar radiation and plasma parameters and processes that act together in the formation and modification of atmospheres and exospheres that consist of surface-related minerals. Magma ocean degassed silicate atmospheres or thin gaseous envelopes from planetary building blocks, airless bodies in the inner Solar System, and close-in magmatic rocky exoplanets such as CoRot-7b, HD 219134 b and 55 Cnc e are addressed. The depletion and fractionation of elements from planetary embryos, which act as the building blocks for proto-planets are also discussed. In this context the formation processes of the Moon and Mercury are briefly reviewed. The Lunar surface modification since its origin by micrometeoroids, plasma sputtering, plasma impingement as well as chemical surface alteration and the search of particles from the early Earth’s atmosphere that were collected by the Moon on its surface are also discussed. Finally, we address important questions on what can be learned from the study of Mercury’s environment and its solar wind interaction by MESSENGER and BepiColombo in comparison with the expected observations at exo-Mercurys by future space-observatories such as the JWST or ARIEL and ground-based telescopes and instruments like SPHERE and ESPRESSO on the VLT, and vice versa

    Protective effects of halite to vacuum and vacuum-ultraviolet radiation: A potential scenario during a young sun superflare

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    Halite (NaCl mineral) has exhibited the potential to preserve microorganisms for millions of years on Earth. This mineral was also identified on Mars and in meteorites. In this study, we investigated the potential of halite crystals to protect microbial life-forms on the surface of an airless body (e.g., meteorite), for instance, during a lithopanspermia process (interplanetary travel step) in the early Solar System. To investigate the effect of the radiation of the young Sun on microorganisms, we performed extensive simulation experiments by employing a synchrotron facility. We focused on two exposure conditions: vacuum (low Earth orbit, 10-4 Pa) and vacuum-ultraviolet (VUV) radiation (range 57.6-124 nm, flux 7.14 W/m2), with the latter representing an extreme scenario with high VUV fluxes comparable to the amount of radiation of a stellar superflare from the young Sun. The stellar VUV parameters were estimated by using the very well-studied solar analog of the young Sun, Îș1 Cet. To evaluate the protective effects of halite, we entrapped a halophilic archaeon (Haloferax volcanii) and a non-halophilic bacterium (Deinococcus radiodurans) in laboratory-grown halite. Control groups were cells entrapped in salt crystals (mixtures of different salts and NaCl) and non-trapped (naked) cells, respectively. All groups were exposed either to vacuum alone or to vacuum plus VUV. Our results demonstrate that halite can serve as protection against vacuum and VUV radiation, regardless of the type of microorganism. In addition, we found that the protection is higher than provided by crystals obtained from mixtures of salts. This extends the protective effects of halite documented in previous studies and reinforces the possibility to consider the crystals of this mineral as potential preservation structures in airless bodies or as vehicles for the interplanetary transfer of microorganisms.X.C.A. acknowledges CNPEM for the beamtime grantedto the proposal TGM—16126 (LNLS), FAPESP postdoc-toral fellowship (years 2013–2014) (Processo nro: 2012/20106-5), Brazil, and funding from PIP—CONICET 0754,Argentina. M.L. and P.O. acknowledge the Austrian ScienceFund (FWF): P30949-N36, I5711-N for supporting thisproject. J.E.H. acknowledges the financial support of FAPESP (Sao Paulo State) and CNPQ (Brazil) financingagencies. G.F.P.M. acknowledges grant 474972/2009-7from CNPq/Brazil.Peer reviewe

    Are Supermassive Hot Jupiters Providing More Favourable Conditions for Generation of Radio Emission via the Cyclotron Maser Instability? - A Case Study based on Tau Bootis b

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    International audienceWe check if supermassive Hot Jupiters can maintain source regions for radio emission, and whether the emission can propagate to an observer outside the system. Planets identical to the Hot Jupiter Tau Bootis b are investigated, but located at different orbital distances, starting at the actual orbit of 0.046 AU up to 0.2 AU. We find that due to the strong gravity of the supermassive planet Tau Bootis b additional coolings would become very effective. Including these cooling effects, the exobase is very close to the planet, which makes Tau Bootis b a good candidate for radio observations. The case of hydrodynamic escape without cooling effects is considered as well for comparison and we check at which orbital distance the upper atmosphere is in the hydrodynamic rather than in the hydrostatic regime, i.e. where conditions for the Cyclotron Maser Instability (CMI) are favourable. In the hydrodynamic regime the ionosphere is extended up to the magnetopause and can constitute an obstacle for possibly generated radio waves, or the generation via the CMI might even be prevented completely. We find that the transition to more favourable conditions for the CMI occurs at 0.056 AU, where the exobase distance is already close to the magnetosphere standoff distance. Another interesting finding is that, even though the exobase is more extended for smaller orbits, the stronger stellar wind of the young star Tau Bootis causes a higher outflow velocity for the planetary mass loss due to the higher XUV flux. This effect lowers the electron density peak for the actual orbit of Tau Bootis b compared to the larger orbits and could thus make generation and escape of radio waves possible. In a further step of this investigation the star Tau Bootis is replaced by a Sun-like star. In this case the highest electron density peak is found for the closest orbit
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