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arXiv 0801.2579astro-ph
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轨道偏心率对凌日系外行星探测的影响

Impact of Orbital Eccentricity on the Detection of Transiting Extrasolar Planets

Christopher J. Burke

摘要:

对于轨道周期P&gt;10天的太阳系外行星,径向速度测量发现非圆形轨道偏心率很常见,<e>约为0.3。未来使用凌日技术对太阳系外行星的调查也将对探测这些更长周期的行星具有灵敏度。轨道偏心率以两种相反的方式影响凌日技术对太阳系外行星的探测:行星在近心点附近凌日的概率增加,以及由于凌日持续时间较短而降低凌日的可探测性。对于目前已知的太阳系外行星的偏心率分布,P&gt;10天,行星凌日的概率比等效圆轨道高约1.25倍,平均凌日持续时间比等效圆轨道短约0.88倍。这两个相反的效果几乎取消了一个理想化的现场过境调查与独立的光度测量,主要是由泊松噪声。与假设所有行星都有圆形轨道相比,净效应是过境行星产量适度增加约4%。当恒星的内在变化或相关的光度测量是噪声的主要来源时,凌日的可探测性与凌日持续时间无关。在这种情况下,凌日收益率比圆形轨道假设下的预测值高出约25%。由于开普勒在太阳型恒星的宜居带中寻找地球大小的行星受到内在可变性的限制,因此如果地球大小的行星具有与目前已知的太阳质量行星相似的轨道偏心率分布,开普勒任务的行星产量预计将比圆形轨道的预测高出约25%。

英文摘要:

For extrasolar planets with orbital periods, P>10 days, radial velocity surveys find non-circular orbital eccentricities are common, <e>~0.3. Future surveys for extrasolar planets using the transit technique will also have sensitivity to detect these longer period planets. Orbital eccentricity affects the detection of extrasolar planets using the transit technique in two opposing ways: an enhancement in the probability for the planet to transit near pericenter and a reduction in the detectability of the transit due to a shorter transit duration. For an eccentricity distribution matching the currently known extrasolar planets with P>10 day, the probability for the planet to transit is ~1.25 times higher than the equivalent circular orbit and the average transit duration is ~0.88 times shorter than the equivalent circular orbit. These two opposing effects nearly cancel for an idealized field transit survey with independent photometric measurements that are dominated by Poisson noise. The net effect is a modest ~4% increase in the transiting planet yield compared to assuming all planets have circular orbits. When intrinsic variability of the star or correlated photometric measurements are the dominant source of noise, the transit detectability is independent of the transit duration. In this case the transit yield is ~25% higher than that predicted under the assumption of circular orbits. Since the Kepler search for Earth-sized planets in the habitable zone of a Solar-type star is limited by intrinsic variability, the Kepler mission is expected to have a ~25% higher planet yield than that predicted for circular orbits if the Earth-sized planets have an orbital eccentricity distribution similar to the currently known Jupiter-mass planets.

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