[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

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

The Influence Of Neutron Capture Rates On The Rare Earth Region Of The r-Process Abundance Pattern

We study the sensitivity of the r-process abundance pattern to neutron capture rates along the rare earth region (A~150 to A~180). We introduce the concepts of large nuclear flow and flow saturation which determine the neutron capture rates that are influential in setting the rare earth abundances. We illustrate the value of the two concepts by considering high entropy conditions favorable for rare earth peak production and identifying important neutron capture rates among the rare earth isotopes. We also show how these rates influence nuclear flow and specific sections of the abundance pattern.Comment: 14 pages, 7 figures, submitted to PR