8 research outputs found
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Grain Destruction in Interstellar Shocks
Interstellar shock waves can erode and destroy grains present in the shocked
gas, primarily as the result of sputtering and grain-grain collisions.
Uncertainties in current estimates of sputtering yields are reviewed. Results
are presented for the simple case of sputtering of fast grains being stopped in
cold gas. An upper limit is derived for sputtering of refractory grains in
C-type MHD shocks: shock speeds v_s \gtrsim 50 \kms are required for return
of more than 30\% of the silicate to the gas phase. Sputtering can also be
important for removing molecular ice mantles from grains in two-fluid MHD shock
waves in molecular gas. Recent estimates of refractory grain lifetimes against
destruction in shock waves are summarized, and the implications of these short
lifetimes are discussed.Comment: To appear in Shocks in Astrophysics, ed. T.J. Millar. Talk given at
conference Shocks in Astrophysics, Manchester, Jan. 1995. 13 pages with 6
figures: uuencoded compressed postscript. Also available as POPe-633 on
http://astro.princeton.edu/~library/prep.htm
Exoplanetary AtmospheresâChemistry, Formation Conditions, and Habitability
Characterizing the atmospheres of extrasolar planets is the new frontier in exoplanetary science. The last two decades of exoplanet discoveries have revealed that exoplanets are very common and extremely diverse in their orbital and bulk properties. We now enter a new era as we begin to investigate the chemical diversity of exoplanets, their atmospheric and interior processes, and their formation conditions. Recent developments in the field have led to unprecedented advancements in our understanding of atmospheric chemistry of exoplanets and the implications for their formation conditions. We review these developments in the present work. We review in detail the theory of atmospheric chemistry in all classes of exoplanets discovered to date, from highly irradiated gas giants, ice giants, and super-Earths, to directly imaged giant planets at large orbital separations. We then review the observational detections of chemical species in exoplanetary atmospheres of these various types using different methods, including transit spectroscopy, Doppler spectroscopy, and direct imaging. In addition to chemical detections, we discuss the advances in determining chemical abundances in these atmospheres and how such abundances are being used to constrain exoplanetary formation conditions and migration mechanisms. Finally, we review recent theoretical work on the atmospheres of habitable exoplanets, followed by a discussion of future outlook of the field.M. AgĂșndez acknowledges funding support from Spanish MINECO through grants CSD2009-00038, AYA2009-07304, and AYA2012-32032 and from the European Research Council (ERC Grant 610256: NANOCOSMOS). J. Moses thanks the NASA Exoplanet Research program NNX15AN82G for support. Y. Hu is supported by the National Natural Science Foundation of China 435 (NSFC) under grants 41375072 and 41530423