1. Spectrophotometric properties of the nearest pre-main sequence stars 2009. 10. 07 A-Ran Lyo

2. HR diagram Luminosity Temperature Pre-main sequence

3. Lyo et al. 2004a  Hα emission line : accretion disk & chromospheric activity  Li I absorption line : age indicator because Li I is diminished fast during the very early phase of stellar evolution.

4.  ε Chamaelentis cluster : t = 3 - 5 Myr (Feigelson et al. 2003) ~ 6 Myr (Luhman 2004)  η Cha cluster : t = 5 - 8 Myr (Luhman & Steeghs 2004) = 7 - 9 Myr (Lyo et al. 2004)  TW Hydrae association : t ~ 8 - 10 Myr (Webb et al. 1999)  β Pictoris Moving group : t ~ 20±10 Myr (Barrado y Navascues 2001)  Lower Centaurus Crux : t = 17 ~ 23 Myr (Mamajek et al. 2002)  a common kinematic link with the Ophiuchus-Scorpius- Centaurus OB Association

5. Lawson & Feigelson 2000 Pre-main sequence evolutionary models

6. Spectral lines : Effective temperature (spectral type) : Luminosity (surface gravity) : Chemical composition (metallicity)  valuable input for understanding PMS stellar structure and evolution.

8.  Chamaeleontis

9. Lyo et al. 2004b η Chamaeleontis

10. Comparison of η Cha cluster members and dwarfs PC3PC4PC5 CaH TiO CaOH Lyo et al. 2004b

11. Temperature-sensitive indices Lyo et al. 2004b

13. Gravity-sensitive indices Lyo et al. 2004b

14. Lyo et al. 2008

15. Lawson, Lyo, & Bessell 2009, accepted

17. Thank you