149 research outputs found
Perfectibilité et spontanéité. Les réflexions de Tetens sur une force fondamentale de l’âme dans le Onzième essai philosophique
The question as to whether the human soul, in the abundance of its theoretical and practical faculties, possesses a fundamental power which unites them, or combines them, or several or none, was one of the controversial fields of European philosophy between Leibniz and Kant. Johann Nikolaus Tetens has presented an independent solution to this problem. At the same time, Tetens is as far removed from speculative dogmatism as from an empirical psychology of the basic power of the soul as a self-activity. Tetens formulates, as it were, conditions of the possibility of a knowledge of the human soul, based on experience, without proceeding methodically empirically
Physical parameter eclipse mapping of the quiescent disc in V2051 Ophiuchi
We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 to 6500 K
Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs
We explore the spectral and atmospheric properties of brown dwarfs cooler
than the latest known T dwarfs. Our focus is on the yet-to-be-discovered
free-floating brown dwarfs in the \teff range from 800 K to 130 K
and with masses from 25 to 1 \mj. This study is in anticipation of the new
characterization capabilities enabled by the launch of SIRTF and the eventual
launch of JWST. We provide spectra from 0.4 \mic to 30 \mic, highlight
the evolution and mass dependence of the dominant HO, CH, and NH
molecular bands, consider the formation and effects of water-ice clouds, and
compare our theoretical flux densities with the sensitivities of the
instruments on board SIRTF and JWST. The latter can be used to determine the
detection ranges from space of cool brown dwarfs. In the process, we determine
the reversal point of the blueward trend in the near-infrared colors with
decreasing \teff, the \teffs at which water and ammonia clouds appear, the
strengths of gas-phase ammonia and methane bands, the masses and ages of the
objects for which the neutral alkali metal lines are muted, and the increasing
role as \teff decreases of the mid-infrared fluxes longward of 4 \mic. These
changes suggest physical reasons to expect the emergence of at least one new
stellar class beyond the T dwarfs. Our spectral models populate, with cooler
brown dwarfs having progressively more planet-like features, the theoretical
gap between the known T dwarfs and the known giant planets. Such objects likely
inhabit the galaxy, but their numbers are as yet unknown.Comment: Includes 14 figures, most in color; accepted to the Astrophysical
Journa
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