哈勃空间望远镜时间序列测光的行星过境的HD189733：没有月亮，没有戒指，恒星黑子
Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
摘要：
我们用哈勃太空望远镜上的ACS相机监测了这颗巨大的气体行星围绕附近的K矮星HD 189733的三次凌日。由此产生的非常高精度的光变曲线（单个测量的信噪比接近15000，10分钟平均值为35000）允许直接几何测量轨道倾角，半径比和系统的比例：i = 85.68 +- 0.04，Rpl/R*=0.1572 +- 0.0004，a/R*=8.92 +- 0.09。我们推导出恒星和行星半径的改进值，R*=0.755+- 0.011 Rsol，Rpl=1.154 +- 0.017 RJ，以及凌日星历表，Ttr=2453931.12048 +- 0.00002 + n 2.218581 +-0.00002 $。HST的数据还揭示了行星在恒星表面掩盖斑点的明确证据。至少需要一个大的斑点复合体（>80000公里）来解释观测到的通量残差及其颜色演变。这一特征在幅度和相位上与从地面同时观测到的变化是一致的。在HST的光变曲线中，没有证据显示HD 189733 b周围有卫星或环存在。这使我们能够排除地球大小的卫星和土星类型的碎片环在这颗行星周围存在的可能性很高。采样的三次凌日的时间稳定在几秒的水平，不包括外部2：1共振的第二颗大质量行星。
英文摘要：
We monitored three transits of the giant gas planet around the nearby K dwarf HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting very-high accuracy lightcurve (signal-to-noise ratio near 15000 on individual measurements, 35000 on 10-minute averages) allows a direct geometric measurement of the orbital inclination, radius ratio and scale of the system: i = 85.68 +- 0.04, Rpl/R*=0.1572 +- 0.0004, a/R*=8.92 +- 0.09. We derive improved values for the stellar and planetary radius, R*=0.755+- 0.011 Rsol, Rpl=1.154 +- 0.017 RJ, and the transit ephemerides, Ttr=2453931.12048 +- 0.00002 + n 2.218581 +- 0.000002$. The HST data also reveal clear evidence of the planet occulting spots on the surface of the star. At least one large spot complex (>80000 km) is required to explain the observed flux residuals and their colour evolution. This feature is compatible in amplitude and phase with the variability observed simultaneously from the ground. No evidence for satellites or rings around HD 189733b is seen in the HST lightcurve. This allows us to exlude with a high probability the presence of Earth-sized moons and Saturn-type debris rings around this planet. The timing of the three transits sampled is stable to the level of a few seconds, excluding a massive second planet in outer 2:1 resonance.
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