Spitzer observations of molecules and dust in evolved stars in nearby galaxies

Molecules and dust are formed in and around the asymptotic giant branch (AGB) stars and supernovae (SNe), and are ejected into the interstellar medium (ISM) through the stellar wind. The dust and gas contain elements newly synthesised in stars, thus, dying stars play an important role on chemical enrichment of the ISM of galaxies. However, quantitative analysis of molecules and dust in these stars had been difficult beyond our Galaxy. The high sensitivity instruments on board the Spitzer Space Telescope have enabled us to study dust and molecules in these stars in nearby galaxies. Nearby galaxies have wide range of metallicities, thus the impact of the metallicity on dust and gas production can be studied. This study will be useful for chemical evolution of galaxies from low to high metallicities.Comment: 1 page; IAU Highlights of Astronomy, vol 15 (SpSp1 IR and Sub-mm Spectroscopy a New Tool for Studying Stellar Evolution

Revealing infrared populations of nearby galaxies using the Spitzer Space Telescope

Due to their brightness in infrared, asymptotic giant branch (AGB) stars are in important evolutionary stage to be understood at this wavelength. In particular, in next decades, when the infrared optimised telescopes, such as the JWST and the ELT are in operation, it will be essential to include the AGB phase more precisely into the population synthesis models. However, the AGB phase is still one of the remaining major problems in the stellar evolution. This is because the AGB stellar evolution is strongly affected by the mass-loss process from the stars. It is important to describe mass loss more accurately so as to incorporate it into stellar evolutionary models. Recent observations using the Spitzer Space Telescope (SST) enabled us to make a significant progress in understanding the mass loss from AGB stars. Moreover, the SST large surveys contributed to our understanding of the role of AGB stars in chemical enrichment process in galaxies. Here we present the summary of our recent progress.Comment: 4 pages, 2 figures, 1 table; IAU S262 proceeding

Holographic Renormalization Group Structure in Higher-Derivative Gravity

Classical higher-derivative gravity is investigated in the context of the holographic renormalization group (RG). We parametrize the Euclidean time such that one step of time evolution in (d+1)-dimensional bulk gravity can be directly interpreted as that of block spin transformation of the d-dimensional boundary field theory. This parametrization simplifies the analysis of the holographic RG structure in gravity systems, and conformal fixed points are always described by AdS geometry. We find that higher-derivative gravity generically induces extra degrees of freedom which acquire huge mass around stable fixed points and thus are coupled to highly irrelevant operators at the boundary. In the particular case of pure R^2-gravity, we show that some region of the coefficients of curvature-squared terms allows us to have two fixed points (one is multicritical) which are connected by a kink solution. We further extend our analysis to Minkowski time to investigate a model of expanding universe described by the action with curvature-squared terms and positive cosmological constant, and show that, in any dimensionality but four, one can have a classical solution which describes time evolution from a de Sitter geometry to another de Sitter geometry, along which the Hubble parameter changes drastically.Comment: 26 pages, 6 figures, typos correcte