Geometry and physical conditions in the stellar wind of AG Carinae
Geometry and physical conditions in the stellar wind of AG Carinae
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AG Carinae 星风中的几何和物理条件
DOI：
10.1086/174241
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
S. Shore
中科院分区：
文献类型：
--
作者：
C. Leitherer;R. Allen;B. Altner;A. Damineli;L. Drissen;T. Idiart;O. Lupie;A. Nota;C. Robert;W. Schmutz;S. Shore
船底座AG是发光蓝变星（LBVs）的原型之一。自1990年以来，这颗恒星在其视觉连续体中不断变亮。我们报道了一种多仪器和波长观测运动，以监测AG Car的当前活动阶段。地面光度法、偏振法、光谱学、空间紫外光谱法和光谱偏振法已经获得。从紫外和光学波长的偏振变化，我们检测到显著的本征偏振。P（sub int）大于或等于0.5%对于一颗炽热明亮的恒星来说是一个很大的值，这表明在AG Car的风中偏离了球对称。本征极化在2个月或更短的时间尺度上是可变的。1992年5月，测量到的紫外偏振（本征+星际）下降到0.5%，1992年7月又恢复到1%。结果被解释为在赤道平面上密度增强的可变外流。对于大麦哲伦星云（LMC）中的相关天体R127，也提出了类似的模型。这种几何形状让人想起围绕AG Car的气体星云和尘埃“喷流”的大规模形态。因此，很可能是靠近恒星表面的物理条件导致了AG Car周围空间分辨的星周物质的几何形状。尽管光球条件发生了剧烈变化，但质量损失率并没有增加。我们没有发现风密度和恒星半径呈正相关的证据。这使得模型不太可能解释流出物中不透明度效应导致的半径增加。造成温度和半径变化的机制尚不清楚，但最有可能起源于亚光球区。
AG Carinae is one of the prototypes of the class of Luminous Blue Variables (LBVs). Since 1990 the star has continuously brightened in its visual continuum. We report on a multi-instrument and -wavelength observing campaign to monitor the current activity phase of AG Car. Ground-based photometry, polarimetry, spectroscopy, and space-ultraviolet spectroscopy and spectropolarimetry have been obtained. From the variability of the polarization at ultraviolet and optical wavelengths we detect significant intrinsic polarization. P(sub int) greater than or equal to 0.5% is a large value for a hot, luminous star, suggesting departure from spherical symmetry in the wind of AG Car. The intrinsic polarization is variable on a timescale of 2 months or less. The measured ultraviolet polarization (intrinsic + interstellar) dropped to 0.5% in 1992 May and returned to 1% in 1992 July. The results are interpreted in terms of a variable outflow with a density enhancement in the equatorial plane. A similar model was suggested for the related object R127 in the Large Magellanic Cloud (LMC). This geometry is reminiscent of the large-scale morphology of the gas nebula and dust 'jet' surrounding AG Car. It is therefore likely that physical conditions close to the stellar surface are responsible for the geometry of the spatially resolved circumstellar material around AG Car. Despite the drastic change of the photospheric conditions, the mass-loss rate did not increase. We find no evidence for a positive correlation between wind density and stellar radius. This makes models that explain the radius increase by opacity effects in the outflow unlikely. The mechanism responsible for the temperature and radius variations is still unknown but most likely has its origin in subphotospheric regions.