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© 2012. The American Astronomical Society. All rights reserved. Artículo firmado por 21 autores. S.E.M. thanks Arjen van der Wel for discussion and Angela Adamo and Anibal Garcia for their helpful comments on the manuscript. E.A. and A.B. thank the Centre National d'Etudes Spatiales for financial support., We examine the effect of circumstellar dust extinction on the near-IR (NIR) contribution of asymptotic giant branch (AGB) stars in intermediate-age clusters throughout the disk of M100. For our sample of 17AGB-dominated clusters we extract optical-to-mid-IR spectral energy distributions (SEDs) and find that NIR brightness is coupled to the mid-IR dust emission in such a way that a significant reduction of AGB light, of up to 1 mag in the K band, follows from extinction by the dust shell formed during this stage. Since the dust optical depth varies with AGB chemistry (C-rich or O-rich), our results suggest that the contribution of AGB stars to the flux from their host clusters will be closely linked to the metallicity and the progenitor mass of the AGB star, to which dust chemistry and mass-loss rate are sensitive. Our sample of clusters-each the analogue of a similar to 1 Gyr old post-starburst galaxy-has implications within the context of mass and age estimation via SED modeling at high-z: we find that the average similar to 0.5 mag extinction estimated here may be sufficient to reduce the AGB contribution in the (rest-frame) K band from similar to 70%, as predicted in the latest generation of synthesis models, to similar to 35%. Our technique for selecting AGB-dominated clusters in nearby galaxies promises to be effective for discriminating the uncertainties associated with AGB stars in intermediate-age populations that plague age and mass estimation in high-z galaxies., Centre National d'Etudes Spatiales (CNES), Francia, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CB(b)3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe)(2)SiO4] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO3) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe)(3)Si2O5(OH)(4)], while the other is a nontronite [Na,Fe-2(Si,Al)(4)O-10(OH)(2).nH(2)O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al)(2)O-6]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.

We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CB(b)3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe)(2)SiO4] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO3) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe)(3)Si2O5(OH)(4)], while the other is a nontronite [Na,Fe-2(Si,Al)(4)O-10(OH)(2).nH(2)O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al)(2)O-6]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey is an SiO maser survey of 28,062 infrared-selected evolved stars primarily in the Galactic plane. By cross-matching the BAaDE target sources with nine different infrared catalogs, we have constructed a catalog with wavelength coverage from 0.71 to 80 m. Using this catalog, we fit the data for each source to a model spectral energy distribution (SED) generated with the radiation transport program DUSTY in order to obtain characteristics such as bolometric flux, source effective temperature, and the optical depth of the circumstellar envelope. The overall goal of the BAaDE survey is to extract a gravitational potential in order to model Galactic dynamics, by providing line-of-sight velocities and positions for each source. The results would be greatly enhanced if, in addition to the positions and velocities, we could also provide a distance estimate. We explore a new method of estimating distances to the BAaDE sources by creating a series of template SEDs, differentiated by infrared color in the region of the spectrum covered by the Midcourse Space Experiment (MSX; 8.28 – 21.34 m). We calibrate the first of these template SEDs using similarly colored Red Giant stars with known parallax-distances, and obtain an empirical relation between the bolometric flux and distance of sources with similarly shaped SED.

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey is an SiO maser survey of 28,062 infrared-selected evolved stars primarily in the Galactic plane. By cross-matching the BAaDE target sources with nine different infrared catalogs, we have constructed a catalog with wavelength coverage from 0.71 to 80 m. Using this catalog, we fit the data for each source to a model spectral energy distribution (SED) generated with the radiation transport program DUSTY in order to obtain characteristics such as bolometric flux, source effective temperature, and the optical depth of the circumstellar envelope. The overall goal of the BAaDE survey is to extract a gravitational potential in order to model Galactic dynamics, by providing line-of-sight velocities and positions for each source. The results would be greatly enhanced if, in addition to the positions and velocities, we could also provide a distance estimate. We explore a new method of estimating distances to the BAaDE sources by creating a series of template SEDs, differentiated by infrared color in the region of the spectrum covered by the Midcourse Space Experiment (MSX; 8.28 – 21.34 m). We calibrate the first of these template SEDs using similarly colored Red Giant stars with known parallax-distances, and obtain an empirical relation between the bolometric flux and distance of sources with similarly shaped SED.

More than 80% of the stars in the Universe are expected to have initial masses below eight to ten times the mass of our sun. These low mass stars, including our sun, become cool red giants during one of the final evolutionary stages of their life: the Asymptotic Giant Branch (or AGB) phase. AGB stars are among the main producers of carbon and heavy (s-process) elements in the Universe. These elements are synthesized inside the star and mixed to the stellar atmosphere where stellar winds are responsible for the loss of more than 50% of the stellar mass, hence, AGB stars are strong polluters of the interstellar medium. The ejected material can clump together into dusty particles which may serve as ingredients for the birth of new stars and planets. When most of the AGB stellar envelope is lost, the AGB star stops releasing nuclear energy from interior processes and swaps its giant face for a planetary nebulae look, whereafter it fades away as a white dwarf.The dredge-up of carbon and s-process elements into the AGB atmosphere causes an important chemical anomaly among them: initial oxygen-rich stars (M stars) are transformed into carbon-rich stars (C stars). As a consequence, a group of oxygen-rich AGB stars exists which makes the transition between M and C stars. These transition stars are classified as S.Although AGB stars are identified as producers of heavy elements, their nucleosynthesis and mixing processes are weakly constrained due to large uncertainties on their estimated temperature, gravity and chemical composition. Stronger constraints on the atmospheric parameter space, hence interior processes, of AGB stars can be obtained by investigating the atmosphere of S stars. Since they are transition objects on the AGB, they trace the rise of the s-process. S stars are less numerous than C stars, but their optical spectra are brighter making it easier to identify atomic and molecular lines. Therefore, S stars belong to the most interesting objects alo, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

We report on and discuss the detection of an emission feature at 14.98 mu m from the oxygen-rich, semi-regularly pulsating asymptotic Giant Branch star R Crateris, a feature which we suggest to be due to the 2(0)(1) Q-branch of circumstellar CO2. We also suggest a reasonable excitation mechanism, which could explain the height, the width and the asymmetry of the feature., Addresses: Ryde Nils, Univ Uppsala, Astron Observ, S-75120 Uppsala, Sweden. Univ Uppsala, Astron Observ, S-75120 Uppsala, Sweden. Onsala Space Observ, S-43992 Onsala, Sweden. Stockholm Observ, S-13336 Saltsjobaden, Sweden.