塵粒成長對原行星盤能譜分佈演化之作用

Diagnosis of Grain Growth in the Protoplanetary Disks by the Spectral Energy Distribution

黃相輔(Hsiang-Fu Huang)

指導教授 ： 陳文屏

國立中央大學/理學院/天文研究所/碩士(2006年)

摘要

觀測前主序帶時期的原恆星以及部份年輕主序星能譜，常發現到紅外超量的能譜分佈特徵。這些紅外超量現象是由星球周圍較低溫的固態環星物質，吸收恆星能量並再輻射所造成。環星盤被認為是行星誕生的溫床。在此「原行星盤」中，塵粒會經由碰撞及凝聚，由微米尺度成長為公尺大小以上的微行星體，構成行星形成的基石。

我們於本論文中建立一簡易原行星盤數值模型。此模型包含不同塵粒大小、塵粒大小分佈、吸收效率等參數。藉由設定不同的塵粒大小，我們可模擬原恆星不同階段的能譜分佈演化。我們的模型如預期地顯示在此過程中，紅外超量特徵隨塵粒成長而逐漸消退。

此外，我們並以三顆具紅外超量的主序星 (即織女型恆星)：織女星、北落師門、天苑四作為擬合分析的目標，驗證在限制部份參數的條件下，我們的模型可以得到良好的擬合。

關鍵字

太陽系形成 ； 原行星盤 ； 環星物質 ； 前主序星

並列摘要

Infrared excess characteristics are often shown in the spectral energy distribution (SED) of pre-main sequence stars and some young main sequence stars. These excess phenomena are explained by cooler circumstellar material. Those solid grains absorb emission from the central star, and reradiate it. Circumstellar disks are also the wombs of planet formation. Micron-sized grains would grow to above meter-sized plantesimals by collision and coagulation, and become the bricks of planet embryos.

Here we present our simplified protoplanetary disk numerical model. This model considers many parameters such as grain size, grain size distribution, absorption efficiency. By setting different grain size, we can simulate the evolution of protostars’ SEDs. Our result show that IR excess decreases with grain growth, as expected.

In addition, we use our model to fit the SEDs of three main sequence stars with IR excess, i.e. Vega-like stars: Vega, Fomalhaut, and ε Eridani. Under constraining some parameters, our model could get well fitting results.

並列關鍵字

circumstellar matter ； solar system: formation ； planetary systems: protoplanetary disks ； stars: pre-main sequence

參考文獻

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Dullemond, C. P., Hollenbach, D., Kamp, I., D''Alessio, P. 2006. in Protostars and Planets V} (eds Reipurth, B., Jewitt, D., Keil, K.), in press

Friedjung, M. 1985. Astron. Astrophys., 146, 366-368

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