Solar photospheric and meteoritic CI chondrite abundance determinations for all elements are summarized and the best currently available photospheric abundances are selected. The meteoritic and solar abundances of a few elements (e.g., noble gases, beryllium, boron, phosphorous, sulfur) are discussed in detail. The photospheric abundances give mass fractions of hydrogen (X ¼ 0:7491), helium (Y ¼ 0:2377), and heavy elements (Z ¼ 0:0133), leading to Z=X ¼ 0:0177, which is lower than the widely used Z=X ¼ 0:0245 from previous compilations. Recent results from standard solar models considering helium and heavy-element settling imply that photospheric abundances and mass fractions are not equal to protosolar abundances (representative of solar system abundances). Protosolar elemental and isotopic abundances are derived from photospheric abundances by considering settling effects. Derived protosolar mass fractions are X 0 ¼ 0:7110, Y 0 ¼ 0:2741, and Z 0 ¼ 0:0149. The solar system and photospheric abundance tables are used to compute self-consistent sets of condensation temperatures for all elements.

We highlight the importance of gaseous TiO and VO opacity on the highly irradiated close-in giant planets. The dayside atmospheres of these planets naturally fall into two classes that are somewhat analogous to the M-and L-type dwarfs. Those that are warm enough to have appreciable opacity due to TiO and VO gases we term ''pM class'' planets, and those that are cooler we term ''pL class'' planets. We calculate model atmospheres for these planets, including pressure-temperature profiles, spectra, and characteristic radiative time constants. We show that pM class planets have temperature inversions (hot stratospheres), appear ''anomalously'' bright in the mid-infrared secondary eclipse, and feature molecular bands in emission rather than absorption. From simple physical arguments, we show that they will have large day/night temperature contrasts and negligible phase shifts between orbital phase and thermal emission light curves, because radiative timescales are much shorter than possible dynamical timescales. The pL class planets absorb incident flux deeper in the atmosphere where atmospheric dynamics will more readily redistribute absorbed energy. This will lead to cooler day sides, warmer night sides, and larger phase shifts in thermal emission light curves. The boundary between these classes ($0.04Y0.05 AU from a Sun-like primary for solar composition) is particularly dependent on the incident flux from the parent star, and less so on other factors. We apply these results to several planets and note that the eccentric transiting planets HD 147506b and HD 17156b alternate between the classes. Thermal emission in the optical from pM class planets is significant redward of 400 nm, making these planets attractive targets for optical detection. The difference in the observed day/night contrast between And b ( pM class) and HD 189733b (pL class) is naturally explained in this scenario. Subject headingg s: planetary systems -radiative transfer

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Opacities and chemical abundance data are crucial ingredients of ultracool dwarf and extrasolar giant planet atmosphere models. We report here on the detailed sources of molecular opacity data employed by our group for this application. We also present tables of Rosseland and Planck mean opacities which are of use in some studies of the atmospheres, interiors, and evolution of planets and brown dwarfs. For the tables presented here we have included the opacities of important atomic and molecular species, including the alkali elements, pressure induced absorption by hydrogen, and other significant opacity sources but neglect opacity from condensates. We report for each species how we have assembled molecular line data from a combination of public databases, laboratory data that is not yet in the public databases, and our own numerical calculations. We combine these opacities with abundances computed from a chemical equilibrium model using recently revised solar abundances to compute mean opacities. The chemical equilibrium calculation accounts for the settling of condensates in a gravitational field, and is applicable to ultracool dwarf and extrasolar planetary atmospheres, but not circumstellar disks. We find that the inclusion of alkali atomic opacity substantially increases the mean opacities over those currently in the literature at densities relevant to the atmospheres and interiors of giant planets and brown dwarfs. We provide our opacity tables for public use and discuss their limitations.Comment: 32 pages, 6 figures, accepted for publication in Astrphysical Journal Supplement, units revised, now includes on-line only data files (available in "source" package from "other formats" link

We present an analysis of the 0.95Y14.5 m spectral energy distributions of nine field ultracool dwarfs with spectral types ranging from L1 to T4.5. Effective temperatures, gravities, and condensate cloud sedimentation efficiencies are derived by comparing the data to synthetic spectra computed from atmospheric models that self-consistently include the formation of condensate clouds. Overall, the model spectra fit the data well, although the agreement at some wavelengths remains poor due to remaining inadequacies in the models. Derived effective temperatures decrease steadily through the L1YT4.5 spectral types, and we confirm that the effective temperatures of ultracool dwarfs at the L/T transition are nearly constant, decreasing by only $200 K from spectral types L7.5 to T4.5. The condensate cloud properties vary significantly among the L dwarfs in our sample, ranging from very thick clouds to relatively thin clouds with no particular trend with spectral type. The two objects in our sample with very red J À K s colors are, however, best fitted with synthetic spectra that have thick clouds, which hints at a possible correlation between the near-infrared colors of L dwarfs and the condensate cloud properties. The fits to the two T dwarfs in our sample (T2 and T4.5) also suggest that the clouds become thinner in this spectral class, in agreement with previous studies. Restricting the fits to narrower wavelength ranges (i.e., individual photometric bands) almost always yields excellent agreement between the data and models. Limitations in our knowledge of the opacities of key absorbers such as FeH, VO, and CH 4 at certain wavelengths remain obvious, however. The effective temperatures obtained by fitting the narrower wavelength ranges can show a large scatter compared to the values derived by fitting the full spectral energy distributions; deviations are typically $200 K and, in the worst cases, up to 700 K.

The optical and infrared colors of L and T dwarfs are sensitive to cloud sedimentation and chemical equilibrium processes in their atmospheres. The i ′ − z ′ vs. J − K color-color diagram provides a window into diverse atmospheric processes mainly because different chemical processes govern each color, and cloud opacity largely affects J − K but not i ′ − z ′ . Using theoretical atmosphere models that include for the first time a self-consistent treatment of cloud formation, we present an interpretation of the i ′ − z ′ vs. J − K color trends of known L and T dwarfs. We find that the i ′ − z ′ color is extremely sensitive to chemical equilibrium assumptions: chemical equilibrium models accounting for cloud sedimentation predict redder i ′ − z ′ colors-by up to 2 magnitudes-than models that neglect sedimentation. We explore the previously known J − K color trends where objects first become redder, then bluer with decreasing effective temperature. Only models that include sedimentation of condensates are able to reproduce these trends. We find that the exact track of a cooling brown dwarf in J − K (and i ′ − z ′ ) is very sensitive to the details of clouds, in particular to the efficiency of sedimentation of condensates in its atmosphere. We also find that clouds still affect the strength of the J, H, and K band fluxes of even the coolest T dwarfs. In addition, we predict the locus in the i ′ − z ′ vs. J − K color-color diagram of brown dwarfs cooler than yet discovered.

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We examine the spectra and infrared colors of the cool, methane-dominated atmospheres at T eA 1400 K expected for young gas giant planets. We couple these spectral calculations to an updated version of the Marley et al. giant planet thermal evolution models that include formation by core accretion-gas capture. These relatively cool ''young Jupiters'' can be 1-6 mag fainter than predicted by standard cooling tracks that include a traditional initial condition, which may provide a diagnostic of formation. If correct, this would make true Jupiter-like planets much more difficult to detect at young ages than previously thought. Since Jupiter and Saturn are of distinctly supersolar composition, we examine emitted spectra for model planets at both solar metallicity and a metallicity of 5 times solar. These metal-enhanced young Jupiters have lower pressure photospheres than field brown dwarfs of the same effective temperatures arising from both lower surface gravities and enhanced atmospheric opacity. We highlight several diagnostics for enhanced metallicity. A stronger CO absorption band at 4.5 m for the warmest objects is predicted. At all temperatures, enhanced flux in K band is expected due to reduced collisional induced absorption by H 2 . This leads to correspondingly redder near-infrared colors, which are redder than solar metallicity models with the same surface gravity by up to 0.7 in J À K and 1.5 in H À K. Molecular absorption band depths increase as well, most significantly for the coolest objects. We also qualitatively assess the changes to emitted spectra due to nonequilibrium chemistry. Subject headingg s: planetary systems -planets and satellites: formation -radiative transfer