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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 @).

October 26, Monday, 11:00 am in 104

" Disk dissipation timescale of pre-main sequence stars "

Yuhei Takagi

(University of Hyogo)

We present the results of the age determination study of pre-main sequence (PMS) stars in the Taurus and the Ophiuchus star-forming regions. Ages of PMS stars with 0.5 - 1.5 solar mass were determined from their surface gravities estimated with high-resolution optical and near-infrared spectroscopy. We used equivalent width ratios of nearby absorption lines such as Fe (8204.9A) / Na (8183.3A, 8194.8A) in I-band and Sc (22057.8A) / Na (22062.4A, 22089.7A) in K-band as surface gravity indicators. Since the continuum veiling is nearly uniform over such a limited wavelength range, the equivalent width ratio directly reflects the parameters of the stellar atmosphere of PMS stars. Ages of the pre-main sequence stars were estimated by comparing the derived surface gravities to the evolutionary model. From a comparison of determined ages and near-infrared color excesses, the inner disk lifetime of young stars in the Taurus and the Ophiuchus are estimated to be 2.4 Myr and 1.2 Myr, respectively (Takagi et al. 2014, 2015) which indicate the disk dissipation timescale depends on the environment of the star-forming regions.

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