Dwindle, Dwindle Litter Stars --- Hunting for Substellar Objects Young and Old
Wen-Ping Chen1*, Poshih Chiang1, Bhavana Lalchand1, Shih-Yun Tang2
1Graduate Institute of Astronomy, National Central University, Zhongli, Taoyuan, Taiwan
2Department of Physics, National Central University, Zhongli, Taoyuan, Taiwan
* Presenter:Wen-Ping Chen, email:wchen@astro.ncu.edu.tw
With insufficient masses to sustain core hydrogen fusion, substellar objects continue to cool and fade after birth. Those heavier than 13 jupiter masses, called brown dwarfs, can ignite deuterium or lithium, thereby maintaining hydrostatic equilibrium for a short period of time. Those less massive than this do not undertake any nuclear reaction whatsoever in their lives and evolve like planets. So far some 2,000 brown dwarfs and planetary-mass objects are known, all in the field, i.e., already aged. Characterization of the youngest substellar objects by spectroscopy is hampered by their faintness and often confusion with field contaminations. We describe our our international collaboration to select substellar candidates in nearby star-forming regions of 1 to 2 Myr old, when brown dwarfs are being formed or in their earlier evolution. Our sample of substellar populations in star clusters, with well known ages and distances, provide stringent constraints on theoretical modeling of ultracool atmospheres, and of chromospheric activity. We also present how these least-massive members as the most vulnerable in stellar dynamics to get ejected, leading to eventual disintegration of star clusters.

Keywords: brown dwarf, star cluster, star formation