Ionization in atmospheres of brown dwarfs and extrasolar planets. V. Alfvén Ionization

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfv´en ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization ( 10−7) that they constitute plasmas. We outline the criteria required for Alfv´en ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfv´en ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10−6–1 can be obtained as a result of Alfv´en ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H2, or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfv´en ionization may also be applicable to other astrophysical environments such as protoplanetary disks.

‘All the places we were not supposed to go’: a case study of formative class and gender habitus in adventure climbing

This paper explores the origins of meaning in adventurous activities. Specifically, the paper reports on a study of 10 adventure climbers in the Scottish mountaineering community. The study explores how formative experiences have influenced engagement in adventure climbing. Work has been done on the phenomenology of adventure and how individuals interpret and find meaning in the activity—this paper goes a step further and asks where do these dispositions come from? Using Bourdieu’s ideas of field, habitus and forms of capital to frame these experiences in the wider social environment, early experiences are identified that, for the subjects of this study, provide a framework for their later adoption of the ‘adventure habitus’. Among these influences are mainstream education, adventure education in particular, as well as broader formative experiences relating to factors such as gender and class. In addition, the study suggests that accounts differ between males and females in terms of their attitudes and dispositions towards adventure. This may relate to their respective experiences as well as expanding opportunities for both males and females. However, while the ‘adventure field’ provides a context where women can develop transformative identities, these are nearly always subject to male validation.