长周期的银河造父变星RS船尾座- I。一个几何距离从它的光回声
The long-period Galactic Cepheid RS Puppis - I. A geometric distance from its light echoes
摘要：
背景：明亮的造父变星RS Pup被一个反射中央恒星光线的拱星星云所包围。造父变星发出的光在尘埃星云中的传播产生了壮观的光回波，可以在距离恒星很远的地方观察到。这种现象在这类恒星中是独一无二的。目的：对于这颗相对遥远的恒星，依巴谷的三角视差精度较低。仔细观察光的回波有可能提供一个非常准确的，几何距离RS小狗。方法：利用NTT/EMMI仪器获得了RS Pup的一系列CCD图像，覆盖了恒星的变化周期（P=41.4d）。这使我们能够跟踪恒星周围星云特征上的光波阵面的进展。我们精确地测量了星周星云几个区域光度变化的相位滞后。结果：根据我们的相位滞后测量，我们得出了到RS Pup的几何距离为1992 +/- 28 pc。该距离受1.4%的总不确定性的影响，并且对应于pi = 0.502 +/-0.007 mas的视差和mu = 11.50 +/-0.03的距离模数。结论：我们得出的几何距离是迄今为止对造父变星最精确的，也是对任何恒星最精确的。RS Pup似乎有点被忽视，特别有希望调查造父变星的质量损失历史。由于其高度精确的距离，它也必然成为周期光度图中长周期部分的重要光度基准。
英文摘要：
Context: The bright southern Cepheid RS Pup is surrounded by a circumstellar nebula reflecting the light from the central star. The propagation of the light variations from the Cepheid inside the dusty nebula creates spectacular light echoes that can be observed up to large distances from the star itself. This phenomenon is currently unique in this class of stars. Aims: For this relatively distant star, the trigonometric parallax available from Hipparcos has a low accuracy. A careful observation of the light echoes has the potential to provide a very accurate, geometric distance to RS Pup. Methods: We obtained a series of CCD images of RS Pup with the NTT/EMMI instrument, covering the variation period of the star (P=41.4d). This allowed us to track the progression of the light wavefronts over the nebular features surrounding the star. We measured precisely the phase lag of the photometric variation in several regions of the circumstellar nebula. Results: From our phase lag measurements, we derived a geometric distance of 1992 +/- 28 pc to RS Pup. This distance is affected by a total uncertainty of 1.4%, and corresponds to a parallax of pi = 0.502 +/- 0.007 mas and a distance modulus of mu = 11.50 +/- 0.03. Conclusions: The geometric distance we derived is by far the most accurate to a Cepheid, and among the most accurate to any star. RS Pup appears both as somewhat neglected and particularly promising to investigate the mass-loss history of Cepheids. Thanks to its highly accurate distance, it is also bound to become an important luminosity fiducial for the long period part of the period-luminosity diagram.
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