National Tsing Hua University Institutional Repository:Spherical episodic ejection of material from a young star
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    National Tsing Hua University Institutional Repository > 理學院 > 天文研究所 > 期刊論文 >  Spherical episodic ejection of material from a young star


    题名: Spherical episodic ejection of material from a young star
    作者: Torrelles JM;Patel NA;Gomez JF;Ho PTP;Rodriguez LF;Anglada G;Garay G;Greenhill L;Curiel S;Canto J
    教師: 賀曾樸
    日期: 2001
    出版者: Nature Publishing Group
    關聯: NATURE,Volume: 411,Issue: 6835,Pages: 277-280,Published: MAY 17 2001
    摘要: The exact processes by which interstellar matter condenses to form young stars are of great interest, in part because they bear on the formation of planets like our own from the material that fails to become part of the star. Theoretical models suggest that ejection of gas during early phases of stellar evolution is a key mechanism for removing excess angular momentum, thereby allowing material to drift inwards towards the star through an accretion disk(1,2). Such ejections also limit the mass that can be accumulated by the stellar core(1,2). To date, these ejections have been observed to be bipolar and highly collimated, in agreement with theory. Here we report observations at very high angular resolution of the proper motions of an arc of water-vapour masers near a very young, massive star in Cepheus. We rnd that the arc of masers can be fitted to a circle with an accuracy of one part in a thousand, and that the structure is expanding. Only a sphere will always produce a circle in projection, so our observations strongly suggest that the perfectly spherical ejection of material from this star took place about 33 years earlier. The spherical symmetry of the ejecta and its episodic nature are very surprising in the light of present theories.
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