对“长周期银河造父变星RS船尾座”的评论。I.几何距离从它的光回声”
Comments on "The long-period Galactic Cepheid RS Puppis. I. A geometric distance from its light echoes"
摘要：
明亮的银河系造父变星RS船尾座是独一无二的，它被造父变星的可变光照亮的尘埃星云所包围。在这本杂志最近的一篇论文中，Kervella等人（2008）报告了一个非常精确的到RS Pup的几何距离，基于反射星云中单个结的光变化的测量相位滞后。在这篇评论中，我们检验了距离测量的有效性，以及Feast（2008）基于结的相位滞后确定的星云空间结构的真实性。（Kervella等人假设被照亮的尘埃结平均位于天空平面中（否则不可能从光回波的直接成像中导出几何距离）。我们认为，偏置引入的高效率的前向散射。我们的结论是，大多数节点实际上可能位于天空平面的前面，从而使Kervella等人的结果无效。我们还表明，平坦的赤道盘结构确定的盛宴是不可能的，相反，星云的形态更可能是双极的，其轴相对于天空的平面有显着的倾斜。虽然Kervella等人的距离结果是无效的，我们表明，高分辨率偏振成像有可能产生一个有效的几何距离，这个重要的造父变星。
英文摘要：
The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a dust nebula illuminated by the variable light of the Cepheid. In a recent paper in this journal, Kervella et al. (2008) report a very precise geometric distance to RS Pup, based on measured phase lags of the light variations of individual knots in the reflection nebula. In this commentary, we examine the validity of the distance measurement, as well as the reality of the spatial structure of the nebula determined by Feast (2008) based upon the phase lags of the knots. {Kervella et al. assumed that the illuminated dust knots lie, on average, in the plane of the sky (otherwise it is not possible to derive a geometric distance from direct imaging of light echoes). We consider the biasing introduced by the high efficiency of forward scattering. We conclude that most of the knots are in fact likely to lie in front of the plane of the sky, thus invalidating the Kervella et al. result. We also show that the flat equatorial disk structure determined by Feast is unlikely; instead, the morphology of the nebula is more probably bipolar, with a significant tilt of its axis with respect to the plane of the sky. Although the Kervella et al. distance result is invalidated, we show that high-resolution polarimetric imaging has the potential to yield a valid geometric distance to this important Cepheid.
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