演講資訊

摘要：

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, manage to ignite deuterium or lithium in the cores, 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 a few thousand brown dwarfs and planetary-mass objects are known, found almost exclusively, because of their intrinsically low brightness, in the solar proximity, i.e., they are already aged. The youngest substellar objects being bright and warm are readily detectable by OIR imaging, but often are confused with outnumbering reddened background sources. Confirmation by spectroscopy requires large telescopes and is possible only if a reliable list of candidates is available. We describe our efforts to identify substellar candidates in nearby star-forming regions of 1 to 3 Myr old, when brown dwarfs are being formed or in their infancy. Our sample of substellar populations in star clusters, with known ages and distances, provides stringent constraints to confront theoretical modeling of ultracool atmospheres, and of chromospheric activity. We also present how these least-massive members as being the most vulnerable in stellar dynamics get ejected, leading to eventual disintegration of star clusters. I will suggest a possible project to find Galactic old brown dwarfs, and to bootstrap the current seek-and-find approach to the gigantic telescope era.