Atmospheric Sulfur Photochemistry on Hot Jupiters

We develop a new 1D photochemical kinetics code to address stratospheric chemistry and stratospheric heating in hot Jupiters. Here we address optically active S-containing species and CO2 at 1200 < T < 2000 K. HS (mercapto) and S2 are highly reactive species that are generated photochemically and thermochemically from H2S with peak abundances between 1-10 mbar. S2 absorbs UV between 240 and 340 nm and is optically thick for metallicities [SH] > 0 at T > 1200 K. HS is probably more important than S2, as it is generally more abundant than S2 under hot Jupiter conditions and it absorbs at somewhat redder wavelengths. We use molecular theory to compute an HS absorption spectrum from sparse available data and find that HS should absorb strongly between 300 and 460 nm, with absorption at the longer wavelengths being temperature sensitive. When the two absorbers are combined, radiative heating (per kg of gas) peaks at 100 microbars, with a total stratospheric heating of about 8 x 10^4 W/m^2 for a jovian planet orbiting a solar-twin at 0.032 AU. Total heating is insensitive to metallicity. The CO2 mixing ratio is a well-behaved quadratic function of metallicity, ranging from 1.6 x 10^-8 to 1.6 x 10^-4 for -0.3 < [M/H] < 1.7. CO2 is insensitive to insolation, vertical mixing, temperature (1200 < T <2000 K), and gravity. The photochemical calculations confirm that CO2 should prove a useful probe of planetary metallicity.Comment: Astrophysical Journal Lett. in press; important revision includes effect of updated thermodynamic data and a new opacity sourc

Microlensing Events from Measurements of the Deflection Angle

Microlensing events are now regularly being detected by monitoring the flux of a large number of potential sources and measuring the combined magnification of the images. This phenomenon could also be detected directly from the gravitational deflection, by means of high precision astrometry using interferometry. Relative astrometry at the level of 10\muas may become possible in the near future. The gravitational deflection can be measured by astrometric monitoring of a bright star having a background star within a small angular separation. This type of monitoring program will be carried out for the independent reasons of discovering planets from the angular motion they induce on the nearby star around which they are orbiting, and for measuring parallaxes, proper motions and orbits of binary stars. We discuss three applications of the measurement of gravitational deflections by astrometric monitoring: measuring the mass of the bright stars that are monitored, measuring the mass of brown dwarfs or giant planets around the bright stars, and detecting microlensing events by unrelated objects near the line of sight to the two stars. We discuss the number of stars whose mass could be measured by this procedure. We also give expressions for the number of expected microlensing events by unrelated objects, which could be stars, brown dwarfs, or other compact objects accounting for dark matter in the halo or in the disk.Comment: submitted to ApJ Letter

A Comparison of Near-Infrared Photometry and Spectra for Y Dwarfs with a New Generation of Cool Cloudy Models

We present YJHK photometry, or a subset, for the six Y dwarfs discovered in WISE data by Cushing et al.. The data were obtained using NIRI on the Gemini North telescope. We also present a far-red spectrum obtained using GMOS-North for WISEPC J205628.90+145953.3. We compare the data to Morley et al. (2012) models, which include cloud decks of sulfide and chloride condensates. We find that the models with these previously neglected clouds can reproduce the energy distributions of T9 to Y0 dwarfs quite well, other than near 5um where the models are too bright. This is thought to be because the models do not include departures from chemical equilibrium caused by vertical mixing, which would enhance the abundance of CO, decreasing the flux at 5um. Vertical mixing also decreases the abundance of NH_3, which would otherwise have strong absorption features at 1.03um and 1.52um that are not seen in the Y0 WISEPC J205628.90+145953.3. We find that the five Y0 to Y0.5 dwarfs have 300 < T_eff K < 450, 4.0 < log g < 4.5 and f_sed ~ 3. These temperatures and gravities imply a mass range of 5 - 15 M_Jupiter and ages around 5 Gyr. We suggest that WISEP J182831.08+265037.8 is a binary system, as this better explains its luminosity and color. We find that the data can be made consistent with observed trends, and generally consistent with the models, if the system is composed of a T_eff = 325 K and log g ~ 4.0 secondary, corresponding to masses of 10 and 7 M_Jupiter and an age around 2 Gyr. If our deconvolution is correct, then the T_eff = 300 K cloud-free model fluxes at K and W2 are too faint by 0.5 - 1.0 magnitudes. We will address this discrepancy in our next generation of models, which will incorporate water clouds and mixing.Comment: 39 pages, 10 Figures, 8 Tables. Accepted by ApJ. This revision replaces Figures 9 and 10 with B & W versions, corrects figure captions for color online only, corrects references. Text is unchanged. Tables 3, 4 and 8 are available at http://www.gemini.edu/staff/sleggett, other model data are available at http://www.ucolick.org/~cmorley/cmorley/Data.htm