[论文解读] Transiting exoplanets from the CoRoT space mission - XIX. CoRoT-23b: a dense hot Jupiter on an eccentric orbit

Daniel Rouan, H. Parviainen+41 more|arXiv (Cornell University)|Dec 2, 2011

Stellar, planetary, and galactic studies参考文献 25被引用 2

一句话总结

本文报告了系外行星CoRoT-23b的发现，这是一颗高密度热木星（质量2.8 ± 0.3 MJup，半径1.05 ± 0.13 RJup，密度≈3 g cm⁻³），围绕一颗成熟G0型恒星（年龄≈7 Gyr）运行，轨道中等偏心率（e = 0.16 ± 0.02）。该行星通过CoRoT空间望远镜的光变曲线观测被探测到，并通过地面系外行星径向速度测量得到确认，后续的光变曲线观测排除了背景双星系统造成的假阳性信号。高密度与非零偏心率的组合在热木星中较为罕见，其成因可归因于70亿年来的缓慢潮汐去偏心化过程，与潮汐品质因子Qp > 3×10⁵的模型一致。

ABSTRACT

We report the detection of CoRoT-23b, a hot Jupiter transiting in front of its host star with a period of 3.6314 \pm 0.0001 days. This planet was discovered thanks to photometric data secured with the CoRoT satellite, combined with spectroscopic radial velocity (RV) measurements. A photometric search for possible background eclipsing binaries conducted at CFHT and OGS concluded with a very low risk of false positives. The usual techniques of combining RV and transit data simultaneously were used to derive stellar and planetary parameters. The planet has a mass of Mp = 2.8 \pm 0.3 MJup, a radius of Rpl = 1.05 \pm 0.13 RJup, a density of \approx 3 g cm-3. RV data also clearly reveal a non zero eccentricity of e = 0.16 \pm 0.02. The planet orbits a mature G0 main sequence star of V =15.5 mag, with a mass M\star = 1.14 \pm 0.08 M\odot, a radius R\star = 1. 61 \pm 0.18 R\odot and quasi-solar abundances. The age of the system is evaluated to be 7 Gyr, not far from the transition to subgiant, in agreement with the rather large stellar radius. The two features of a significant eccentricity of the orbit and of a fairly high density are fairly uncommon for a hot Jupiter. The high density is, however, consistent with a model of contraction of a planet at this mass, given the age of the system. On the other hand, at such an age, circularization is expected to be completed. In fact, we show that for this planetary mass and orbital distance, any initial eccentricity should not totally vanish after 7 Gyr, as long as the tidal quality factor Qp is more than a few 105, a value that is the lower bound of the usually expected range. Even if Corot-23b features a density and an eccentricity that are atypical of a hot Jupiter, it is thus not an enigmatic object.

研究动机与目标

• 确认由CoRoT空间任务探测到的凌星行星候选体的行星本质。
• 通过联合光变曲线与光谱分析，确定CoRoT-23b的物理与轨道参数。
• 研究热木星系统中高行星密度与非零轨道偏心率这一非典型组合的成因。

提出的方法

• 利用CoRoT空间望远镜的光变曲线观测，在Corot-23的光 light curve 中检测到类似凌星的信号。
• 在CFHT和OGS进行地面光变曲线后续观测，以排除背景双星系统引起的假阳性信号。
• 获取高精度径向速度测量，以确定行星的质量与轨道偏心率。
• 通过高分辨率光谱分析推导恒星参数，包括有效温度、金属丰度及年龄估算。
• 结合凌星与径向速度数据，联合拟合行星与恒星参数，以获得质量、半径与密度。
• 应用潮汐演化模型，评估长期轨道去偏心化 timescale，以潮汐品质因子Qp作为关键参数。

实验结果

研究问题

• RQ1 CoRoT-23的凌星信号是否与行星起源一致，而非由背景双星系统引起的假阳性？
• RQ2 CoRoT-23b的精确质量、半径与密度是多少？其与其它热木星相比有何特征？
• RQ3 尽管该行星年龄已约70亿年，为何仍表现出显著的轨道偏心率（e = 0.16）？这与潮汐力应使轨道趋于圆形的理论是否矛盾？
• RQ4 高行星密度（≈3 g cm⁻³）是否与行星收缩与演化理论模型一致？
• RQ5 观测到的偏心率能否通过70亿年间的潮汐阻尼机制解释？所需潮汐品质因子（Qp）的范围为何？

主要发现

• CoRoT-23b的质量为2.8 ± 0.3 MJup，半径为1.05 ± 0.13 RJup，因此其密度约为3 g cm⁻³。
• 该行星以3.6314 ± 0.0001天的轨道周期围绕其恒星运行，偏心率e = 0.16 ± 0.02，表明轨道非圆形。
• 其恒星为一颗成熟的G0主序星，质量为1.14 ± 0.08 M⊙，半径为1.61 ± 0.18 R⊙，年龄估计为7 Gyr。
• 高密度与长期行星收缩模型一致，尤其适用于此类质量与年龄的行星。
• 观测到的偏心率与潮汐演化模型不矛盾，只要潮汐品质因子Qp超过3×10⁵，该偏心率可在70亿年内维持稳定。
• 恒星的潮汐特性（Q*/k₂*与Doodson常数）表明，若Q*/k₂* < 10⁷，存在行星被恒星吞噬的风险，但该结论仍属初步。