Time: 14:30pm - 16:30 16th Mar. 2018 (Friday)
Venue: R521, IoA, 2nd General Building 綜二館R521
Speaker: Prof. Ting-Hui Lee 李亭慧 (Western Kentucky University)
Titles: Chemical Abundances of Planetary Nebulae in Our Galaxy
Planetary Nebulae (PNe) are the ionized gaseous shells ejected by Sun-like stars near the ends of their lives. By obtaining spectra of the light from these nebulae, the amount of the heavy elements in each nebula can be determined. From C, N, O and He abundances, we can probe the nuclear reactions that went on in these stars, and even how massive they were and how long they lived. From the abundances of alpha-elements (O, Ne, S, Ar), which mostly pass through the star's nuclear fires unchanged, the original chemical environment where the nebula was formed can also be determined. In this talk, I will summarize the current progress of PN chemical abundance analyses and how these can be used to constrain nucleosynthesis models and the evolution of our Galaxy.
Speaker: Prof. Steven Gibson (Western Kentucky University)
Titles: Gas and Dust in the Dark Neutral Medium
Star formation requires cold, dense, gravitationally bound clouds, which must themselves form somehow from warmer ambient material. How does this process occur, and where? The cold, diffuse interstellar clouds making this transition are hard to detect in standard HI 21cm and CO 2.6mm emission-line surveys, but they can be observed in HI self-absorption, narrow-line HI emission, and in thermal continuum emission from dust grains that may also play an important role in the gas physics. I will describe how such "dark neutral medium" clouds can be mapped over large areas of the Galaxy, what we have learned so far, and the challenges involved in their analysis.