arXiv subjects

Mark S. Marley

Publications and source records attributed to Mark S. Marley.

220 records · Page 13Linked to original sources

arXiv2001

L-dwarf variability: Magnetic star spots or non-uniform clouds?

The recent discovery of photometric variations in L dwarfs has opened a discussion on the cause of the variations. We argue against the existence of magnetic spots in these atmospheres and favor the idea that non-uniform condensate coverage (i.e. clouds) is responsible for the variations. The magnetic Reynolds number (Rm) in the atmosphere of L dwarfs, which describes how well the gas couples with the magnetic field, is too small (<<1) to support the formation of magnetic spots. In constrast silicate and iron clouds form in the photospheres of L dwarfs. Inhomogeneities in such cloud decks can plausibly produce the observed photometric variations. Further evidence in support of clouds is the tendency for variable L dwarfs to be bluer in J-Ks than the average L dwarf of a given spectral type. This color effect is expected if clear holes appear in an otherwise uniform cloud layer.

astro-ph↗

arXiv2001

Precipitating Condensation Clouds in Substellar Atmospheres

We present a method to calculate vertical profiles of particle size distributions in condensation clouds of giant planets and brown dwarfs. The method assumes a balance between turbulent diffusion and sedimentation in horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are compared with results from previous methods. An adjustable parameter describing the efficiency of sedimentation allows the new model to span the range of predictions made by previous models. Calculations for the Jovian ammonia cloud are consistent with observations. Example calculations are provided for water, silicate, and iron clouds on brown dwarfs and on a cool extrasolar giant planet. We find that precipitating cloud decks naturally account for the characteristic trends seen in the spectra and colors of L- and T-type ultracool dwarfs.

astro-ph↗

arXiv2000

The Onset of Methane in L Dwarfs

We have detected weak absorption features produced by the strong nu(3) methane band at 3.3 microns in two L dwarfs, 2MASSW J1507476-162738 and 2MASSI J0825196+211552, classified by Kirkpatrick et al. (2000) as spectral types L5 and L7.5 respectively. These absorptions occur in objects warmer than any in which methane previously has been detected, and mark the first appearance of methane in the ultracool star-to-brown dwarf spectral sequence.

astro-ph↗

arXiv1997

Atmospheres of Giant Planets from Neptune to Gliese 229B

Stratospheric heating, condensation, convective transport of non-equilibrium species, and deep radiative energy transport are important processes in the atmospheres of the solar jovian planets. They likely affect the atmospheres of extrasolar giant planets and brown dwarfs as well. Stratospheric temperatures control thermal fluxes in strong molecular bands, and may dramatically affect observed spectra. Condensation processes affect the appearance of an object, alter the abundances of atmospheric species, and influence the fluxes of both reflected and emitted radiation. Convection can dredge up non-thermochemical equilibrium species from the deep atmosphere to the observable atmosphere. Finally deep radiative zones can limit the effectiveness of deep convection and alter the boundary condition at which the planet radiates energy to space. Here I discuss the role these processes may play in the atmospheres of brown dwarfs and extrasolar giant planets.

astro-ph↗