AGB拱星包层速度流场和天体水脉泽时变的初步研究
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摘要
本文分为两个部分：第一部分讨论了AGB星的拱星包层，并研究
了包层的速度流场。第二部分则讨论了天体水脉泽的时变，并给出了
初步的研究结果。
在AGB阶段，恒星大量的质量流失形成了很厚的由气体和尘埃构
成的星周包层。研究拱星包层能够：确定恒星的质量损失率；研究脉
泽分子的激发机制和研究粒子的形成、辐射转移、辐射驱动流体力学
以及分子化学等。拱星包层内物质的外流速度直接决定了恒星质量损
失率，由此对恒星从AGB向PN的演化产生重要的影响。
为了研究拱星包层内的速度流场，我们建立了具有轴对称旋转膨
胀的包层模型。通过求解包层内气体和尘埃的运动方程，得到了拱星
包层速度流场的解析解。解的结果表明：物质外流速率随其与赤道面
的交角增加而增大，沿极轴方向达到最大：物质外流量的情形则相反。
时变是天体脉泽最重要的特征之一。它主要表现在谱线强度、线
宽及线心速度随时间的变化。对脉泽时变的详细研究是探索恒星形成
区域、晚型星包层和活动星系核演变的重要手段。
我们对恒星形成区水脉泽的时变进行了初步的研究。这种现象可
能起因于非饱和脉泽区域的涨落、星际散射以及脉泽抽运率的变化等。
通过利用Drawspec软件包对W3（OH）和NGC6334C源中的水脉泽数据
进行处理，我们得到了强度变化的时标分别为19天和8天，以及强度
和线宽的相关变化。这些结果可能是由于两个小的、浓密的分子云以
足够的相对速度碰撞形成的。
This thesis consists of two parts: In part one, we discuss circumstellar
envelopes of AGB stars, and study the outflow velocity in envelope. The
maser variability is discussed in part two. The results of observations of
water masers are presented.
During the AGB phase the stars begin to expel matter at a high rate
(10~(-7)-l0(-4)M_(?)/yr). The process 1asts for about l0~5yr and builds a
circumstellar envelope which is a good testing ground for ideas and theories
about astrophysical progresses: mass loss, maser excitation and radiative
transfer; formation of solid state particles; molecular chemistry; radiation
driven hydrodynamics. Hence, it is very important for star evolution from
AGB to PN.
In order to study the velocity fields of circumstellar envelopes, a
model of an axial-symmetrically rotating and expanding envelope of AGB
stars has been put up. The results show that the mass-loss rate enhanced
towards the equatorial plane and the outflow velocities increase
monotonously with latitude above equatorial plane and reach maximum in
the pole.
The time variation is one of the most important features of
astronomical masers, which shows the variability of the peak line intensity,
the line width at the half power points, and the line center velocity and the
time scales range from yeas to a few days. Its detailed study is an important
probe in the dynamics of the star-forming regions, circumstellar envelopes
and active galactic nuclei. We report the observing results of a short time
scale monitoring of the 22 GHz water maser emission in W3(OH) and
NGC6334C.The timescales of 19 and 8 day have been detected, and the
variations are also accompanied by some changes in the linewidth. The time
variations were probably caused by a collisional pump which led to change
in the pump input.
了包层的速度流场。第二部分则讨论了天体水脉泽的时变，并给出了
初步的研究结果。
在AGB阶段，恒星大量的质量流失形成了很厚的由气体和尘埃构
成的星周包层。研究拱星包层能够：确定恒星的质量损失率；研究脉
泽分子的激发机制和研究粒子的形成、辐射转移、辐射驱动流体力学
以及分子化学等。拱星包层内物质的外流速度直接决定了恒星质量损
失率，由此对恒星从AGB向PN的演化产生重要的影响。
为了研究拱星包层内的速度流场，我们建立了具有轴对称旋转膨
胀的包层模型。通过求解包层内气体和尘埃的运动方程，得到了拱星
包层速度流场的解析解。解的结果表明：物质外流速率随其与赤道面
的交角增加而增大，沿极轴方向达到最大：物质外流量的情形则相反。
时变是天体脉泽最重要的特征之一。它主要表现在谱线强度、线
宽及线心速度随时间的变化。对脉泽时变的详细研究是探索恒星形成
区域、晚型星包层和活动星系核演变的重要手段。
我们对恒星形成区水脉泽的时变进行了初步的研究。这种现象可
能起因于非饱和脉泽区域的涨落、星际散射以及脉泽抽运率的变化等。
通过利用Drawspec软件包对W3（OH）和NGC6334C源中的水脉泽数据
进行处理，我们得到了强度变化的时标分别为19天和8天，以及强度
和线宽的相关变化。这些结果可能是由于两个小的、浓密的分子云以
足够的相对速度碰撞形成的。
This thesis consists of two parts: In part one, we discuss circumstellar
envelopes of AGB stars, and study the outflow velocity in envelope. The
maser variability is discussed in part two. The results of observations of
water masers are presented.
During the AGB phase the stars begin to expel matter at a high rate
(10~(-7)-l0(-4)M_(?)/yr). The process 1asts for about l0~5yr and builds a
circumstellar envelope which is a good testing ground for ideas and theories
about astrophysical progresses: mass loss, maser excitation and radiative
transfer; formation of solid state particles; molecular chemistry; radiation
driven hydrodynamics. Hence, it is very important for star evolution from
AGB to PN.
In order to study the velocity fields of circumstellar envelopes, a
model of an axial-symmetrically rotating and expanding envelope of AGB
stars has been put up. The results show that the mass-loss rate enhanced
towards the equatorial plane and the outflow velocities increase
monotonously with latitude above equatorial plane and reach maximum in
the pole.
The time variation is one of the most important features of
astronomical masers, which shows the variability of the peak line intensity,
the line width at the half power points, and the line center velocity and the
time scales range from yeas to a few days. Its detailed study is an important
probe in the dynamics of the star-forming regions, circumstellar envelopes
and active galactic nuclei. We report the observing results of a short time
scale monitoring of the 22 GHz water maser emission in W3(OH) and
NGC6334C.The timescales of 19 and 8 day have been detected, and the
variations are also accompanied by some changes in the linewidth. The time
variations were probably caused by a collisional pump which led to change
in the pump input.
引文
1．孙锦：分子天文学和恒星形成，摘自《90年代天体物理学》，李启斌 李宗伟 汲培文 编，高等教育出版社，p．330
2.Reid, M.J., and Moran,J. M.(1988).In Galactic and Extragalactic Radio Astronomy, ed. G. L. Verschuur & K.Ⅰ.Kellermann, p.255. New York: Springer-Verlag
3.Elitzue, M.Astronomical Masers, Published by Kluwer Academic publishers.,1992
4.Astrophsical Masers, ed. by Clegg, A. W. & Nedoluha,G.E.,SpringerVerlg, Berlin Heidlberg, 1993
5.Habing, H. J., A&AR., 7(1996).
2.Reid, M.J., and Moran,J. M.(1988).In Galactic and Extragalactic Radio Astronomy, ed. G. L. Verschuur & K.Ⅰ.Kellermann, p.255. New York: Springer-Verlag
3.Elitzue, M.Astronomical Masers, Published by Kluwer Academic publishers.,1992
4.Astrophsical Masers, ed. by Clegg, A. W. & Nedoluha,G.E.,SpringerVerlg, Berlin Heidlberg, 1993
5.Habing, H. J., A&AR., 7(1996).