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

[TiII] and [NiII] emission from the strontium filament of eta Carinae

We study the nature of the [TiII] and [NiII] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose we employ multilevel models of the TiII and NiII systems which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the TiII ion, for which no atomic data was previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of $10^7$ cm$^{-3}$ and a temperature around 6000 K. In analyzing three observations with different slit orientations recorded between March~2000 and November~2001 we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament, due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of \etacar. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of TiComment: 14 paginas, 12 figure

Parent Stars of Extrasolar Planets. XI. Trends with Condensation Temperature Revisited

We report the results of abundance analyses of new samples of stars with planets and stars without detected planets. We employ these data to compare abundance-condensation temperature trends in both samples. We find that stars with planets have more negative trends. In addition, the more metal-rich stars with planets display the most negative trends. These results confirm and extend the findings of Ramirez et al. (2009) and Melendez et al. (2009), who restricted their studies to solar analogs. We also show that the differences between the solar photospheric and CI meteoritic abundances correlate with condensation temperature.Comment: 7 pages, 11 figures; to be published in MNRA

A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres

We highlight the importance of gaseous TiO and VO opacity on the highly irradiated close-in giant planets. The 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 the ``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 hot stratospheres $\sim$2000 K and appear ``anomalously'' bright in the mid infrared secondary eclipse, as was recently found for planets HD 149026b and HD 209458b. This class of planets absorbs incident flux and emits thermal flux from high in their atmospheres. Consequently, 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. Around a Sun-like primary this boundary occurs at $\sim$0.04-0.05 AU. The eccentric transiting planets HD 147506b and HD 17156b alternate between the classes. Thermal emission in the optical from pM Class planets is significant red-ward of 400 nm, making these planets attractive targets for optical detection. The difference in the observed day/night contrast between ups Andromeda b (pM Class) and HD 189733b (pL Class) is naturally explained in this scenario. (Abridged.)Comment: Accepted to the Astrophysical Journa

Coordinated analysis of two graphite grains from the CO3.0 LAP 031117 meteorite: First identification of a CO Nova graphite and a presolar iron sulfide subgrain

Presolar grains constitute remnants of stars that existed before the formation of the solar system. In addition to providing direct information on the materials from which the solar system formed, these grains provide ground-truth information for models of stellar evolution and nucleosynthesis. Here we report the in-situ identification of two unique presolar graphite grains from the primitive meteorite LaPaz Icefield 031117. Based on these two graphite grains, we estimate a bulk presolar graphite abundance of 5-3+7 ppm in this meteorite. One of the grains (LAP-141) is characterized by an enrichment in 12C and depletions in 33,34S, and contains a small iron sulfide subgrain, representing the first unambiguous identification of presolar iron sulfide. The other grain (LAP-149) is extremely 13C-rich and 15N-poor, with one of the lowest 12C/13C ratios observed among presolar grains. Comparison of its isotopic compositions with new stellar nucleosynthesis and dust condensation models indicates an origin in the ejecta of a low-mass CO nova. Grain LAP-149 is the first putative nova grain that quantitatively best matches nova model predictions, providing the first strong evidence for graphite condensation in nova ejecta. Our discovery confirms that CO nova graphite and presolar iron sulfide contributed to the original building blocks of the solar system.Peer ReviewedPostprint (author's final draft

Comparative Planetary Atmospheres: Models of TrES-1 and HD209458b

We present new self-consistent atmosphere models for transiting planets TrES-1 and HD209458b. The planets were recently observed with the Spitzer Space Telescope in bands centered on 4.5 and 8.0 $\mu$m, for TrES-1, and 24 $\mu$m, for HD209458b. We find that standard solar metallicity models fit the observations for HD209458b. For TrES-1, which has an T_eff ~300 K cooler, we find that models with a metallicity 3-5 times enhanced over solar abundances can match the 1$\sigma$ error bar at 4.5 $\mu$m and 2$\sigma$ at 8.0$\mu$m. Models with solar abundances that included energy deposition into the stratosphere give fluxes that fall within the 2$\sigma$ error bars in both bands. The best-fit models for both planets assume that reradiation of absorbed stellar flux occurs over the entire planet. For all models of both planets we predict planet/star flux ratios in other Spitzer bandpasses.Comment: Accepted to the Astrophysical Journal Letters, May 17, 200

The Cosmic Crystallinity Conundrum: Clues from IRAS 17495-2534

Since their discovery, cosmic crystalline silicates have presented several challenges to understanding dust formation and evolution. The mid-infrared spectrum of IRAS 17495$-$2534, a highly obscured oxygen-rich asymptotic giant branch (AGB) star, is the only source observed to date which exhibits a clear crystalline silicate absorption feature. This provides an unprecedented opportunity to test competing hypotheses for dust formation. Observed spectral features suggest that both amorphous and crystalline dust is dominated by forsterite (Mg\_2 SiO\_4) rather than enstatite (MgSiO\_3) or other silicate compositions. We confirm that high mass-loss rates should produce more crystalline material, and show why this should be dominated by forsterite. The presence of Mg\_2 SiO\_4 glass suggests that another factor (possibly C/O) is critical in determining astromineralogy. Correlation between crystallinity, mass-loss rate and initial stellar mass suggests that only the most massive AGB stars contribute significant quantities of crystalline material to the interstellar medium, resolving the conundrum of its low crystallinity.Comment: 12 pages, 2 figure