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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tae-Soo Pyo, Sherry Yeh, Nagayoshi Ohashi) by email : (please change"_at" to @).

April 1, Tuesday, at 11:00 am

" Stellar populations of Galactic satellites "

Sakurako Okamoto

(Kavli Institute for Astronomy and Astrophysics)

Nearby dwarf galaxies provide us a unique opportunity to investigate galaxy formation and evolution through their resolved stars. Thanks to systematic surveys in the SDSS data archive, the number of Galactic dwarf satellites (dSph) is doubled in recent years. The newly discovered ultra faint dwarf (UFD) galaxies are roughly 10 to 100 times fainter than the well-known "classical" dSphs and even fainter than globular clusters, having amorphous morphology and too low surface brightness to be found by the photographic plate. Their star formation histories and detailed structural properties provide a clue to understanding of the galaxy formation at the faint-end and of the Galactic tidal effects for the satellite galaxies. I will present the deep colour-magnitude diagrams (CMDs) of faint Galactic dSphs, including UFD galaxies. The resulting CMDs show that the brighter galaxies have relatively younger populations than these of fainter ones. In the brighter dSphs, the younger populations are more spatially concentrated to the galaxy center than old stars, indicating that the star formation in the central region continued at least a few Gyr. On the other hands, the CMDs of the faintest satellites show a single epoch of star formation as metal-poor Galactic globular clusters, and it is very different from those of massive star clusters that have multiple stellar generations. These results indicate that the gaseous matter in the progenitors of UFDs were removed more effectively than those of brighter dSphs at an occurrence of the initial star formation, and also the star formations in UFDs were regulated by different mechanisms from those of massive star clusters. I will also introduce an up-coming opportunity for studying Galactic Archeology by Hyper Suprime-Cam SSP survey.

Seminars are also held at JAC, CFHT, and IfA.

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