SOKENDAI 5th year (D3)
(Supervisor: Aoki Wako, Tsujimoto Takuji, Komiyama Yutaka)
Halo stars with asteroseismology and with high-resolution spectroscopy
The long-term high-precision photometric observation by the Kepler mission has enabled us to infer stellar masses of a large number of red giants through stellar oscillation frequencies. The masses can easily be converted to stellar ages, which is one of the fundamental parameters of stars in the context of the Galactic archaeology. Although this approach has been applied to stars belonging to the Galactic disk, application to halo stars has been limited. Here we have identified 26 halo stars in the field that Kepler has observed for four years and conducted high-resolution spectroscopy for them. We refined stellar parameter estimates from the high-resolution spectra through a line-by-line differential analysis and measured detailed chemical abundances. In the talk, I will report the recent progress of this project.
SOKENDAI 3rd year (D1)
(Supervisor: Yusei Koyama, Masato Onodera, Masayuki Tanaka)
Inflow and outflow parameters of nearby galaxies revealed by SDSS and ALFALFA
It is well known that galaxy inflow and outflow play important roles in shaping the history of galaxy evolution. However, any existing telescopes or instruments cannot directly constrain these processes in the distant universe. We here attempt to study the inflow and outflow properties of galaxies by adopting a simple model and by exploiting key observational properties (stellar mass, gas fraction, and metallicity, i.e. “integrated” properties of star formation in the past). We used 3441 local galaxies from the cross-matched SDSS-ALFALFA samples. These galaxies are divided into 24 subsamples by their stellar mass and the offsets from the star-forming main sequence (ΔMS). We fit the galaxies in each subsample (hence at fixed stellar mass and SFR) with the ’leaky-box’ model and obtain their inflow and outflow parameters. We find that, while both inflow and outflow parameters depend on ?MS, only inflow parameters show a trend with stellar mass. In my poster, I will discuss the interpretation of our results in the context of the geometry of star formation within the galaxies as well as the shape of the gravitational potential well of the galaxies (the distribution of baryon and dark matter).