题 目： Spitzer Finds Cosmic Neon's Sweet Spot

报告人： Dr. Robert H. Rubin

Astrophysics Branch, Space Science Division

NASA/Ames Research Center

摘要：

Although neon is the fifth most abundant element in the Universe, it has been difficult getting a precise determination. Spitzer's infrared spectrometer (IRS) can measure all the dominant forms of neon (Ne II and Ne III) in H II regions. In the same spectrum, the IRS can do nearly as well measuring the sulfur abundance. I discuss our recent work that has added significant new data regarding the Ne/S abundance ratio. We observed 25 H II regions in the substantially face-on spiral galaxy M33 and found that the Ne/S ratio was relatively constant with the median value ~16. In order to determine how much the Ne/S ratio can vary or whether or not there is a fairly 'universal' value, we applied precisely the same methodology to other recently published Spitzer observations. We compare with what is predicted from nucleosynthesis, galactic chemical evolution theory. Our observations were also used to find a correlation of higher ionization and lower metallicity with increasing galactocentric distance in M33, and to test the predicted ionizing spectral energy distribution of various stellar atmosphere models. We compare the ratio of fractional ionizations of the observed Ne and S ions with predictions made from photoionization models using several of the state-of-the-art stellar atmosphere model grids.

时 间：2008年10月7日（星期二），上午10:00

地 点：（北京西路2号）紫台大楼3楼327会议室

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紫金山天文台学术委员会学术交流工作委员会

2008年9月27日