Leiden Observatory, Leiden University, Postbus 9513, 2300RA Leiden, The Netherlands.
Nature. 2012 Jun 27;486(7404):502-4. doi: 10.1038/nature11161.
The giant planet orbiting τ Boötis (named τ Boötis b) was amongst the first extrasolar planets to be discovered. It is one of the brightest exoplanets and one of the nearest to us, with an orbital period of just a few days. Over the course of more than a decade, measurements of its orbital inclination have been announced and refuted, and have hitherto remained elusive. Here we report the detection of carbon monoxide absorption in the thermal dayside spectrum of τ Boötis b. At a spectral resolution of ∼100,000, we trace the change in the radial velocity of the planet over a large range in phase, determining an orbital inclination of 44.5° ± 1.5° and a mass 5.95 ± 0.28 times that of Jupiter, demonstrating that atmospheric characterization is possible for non-transiting planets. The strong absorption signal points to an atmosphere with a temperature that is decreasing towards higher altitudes, in contrast to the temperature inversion inferred for other highly irradiated planets. This supports the hypothesis that the absorbing compounds believed to cause such atmospheric inversions are destroyed in τ Boötis b by the ultraviolet emission from the active host star.
环绕 τ 星（τ Bootis）运行的巨行星（被命名为τ Bootis b）是首批被发现的系外行星之一。它是最亮的系外行星之一，也是离我们最近的系外行星之一，其轨道周期只有几天。十多年来，人们已经公布并驳斥了对其轨道倾斜度的测量结果，但迄今仍难以捉摸。在这里，我们报告了在 τ Bootis b 的热昼侧光谱中检测到一氧化碳吸收。在约 10 万的光谱分辨率下，我们在大的相位范围内追踪了行星的径向速度变化，确定了轨道倾斜度为 44.5°±1.5°，质量为木星的 5.95±0.28 倍，证明了对非过境行星进行大气特征描述是可能的。强吸收信号表明，大气温度随着高度的升高而降低，这与其他高辐照行星推断出的温度反转形成对比。这支持了这样一种假设，即在被认为导致这种大气反转的吸收化合物在 τ Bootis b 中被活动母恒星的紫外发射所破坏。
