M. Montalto, G. Piotto, S. Desidera, F. De Marchi, H. Bruntt, P. B. Stetson, A. Arellano Ferro, Y. Momany, R. G. Gratton, E. Poretti, A. Aparicio, M. Barbieri, … 展开作者
M. Montalto, G. Piotto, S. Desidera, F. De Marchi, H. Bruntt, P. B. Stetson, A. Arellano Ferro, Y. Momany, R. G. Gratton, E. Poretti, A. Aparicio, M. Barbieri, R. U. Claudi, G. Grundahl, A. Rosenberg
Context. Searching for planets in open clusters allows us to study the effects of dynamical environment on planet formation and evolution.
Aims. Considering the strong dependence of planet frequency on stellar metallicity, we studied the metal rich old open cluster NGC 6791 and searched for close-in planets using the transit technique.
Methods. A ten-night observational campaign was performed using the Canada-France-Hawaii Telescope (3.6m), the San Pedro Mártir telescope (2.1m), and the Loiano telescope (1.5m). To increase the transit detection probability we also made use of the Bruntt et al. (2003) eight-nights observational campaign. Adequate photometric precision for the detection of planetary transits was achieved.
Results. Should the frequency and properties of close-in planets in NGC 6791 be similar to those orbiting field stars of similar metallicity, then detailed simulations foresee the presence of 2-3 transiting planets. Instead, we do not confirm the transit candidates proposed by Bruntt et al. (2003). The probability that the null detection is simply due to chance coincidence is estimated to be 3%-10%, depending on the metallicity assumed for the cluster.
Conclusions. Possible explanations of the null-detection of transits include: (i) a lower frequency of close-in planets in star clusters; (ii) a smaller planetary radius for planets orbiting super metal rich stars; or (iii) limitations in the basic assumptions. More extensive photometry with 3-4m class telescopes is required to allow conclusive inferences about the frequency of planets in NGC 6791.
Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets
Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters
我们提出的金属丰度估计七个疏散星团的分光光度指数的基础上，从中等分辨率光谱。对已知金属丰度的场巨星的观测提供了疏散星团巨星的光谱指数和金属丰度之间的相关性。我们用χ^2分析来拟合分光光度指数与场巨星金属丰度的关系。由此产生的函数允许估计的目标集群巨星的金属丰度的方法中的误差为\pm 0.08 dex。我们推导出七个疏散星团的金属丰度如下：NGC 1245，[m/H]=-0.14 \pm 0.04; NGC 2099，[m/H]=+0.05 \pm 0.05; NGC 2324，[m/H]=-0.06 \pm 0.04; NGC 2539，[m/H]=-0.04 \pm 0.03; NGC 2682（M67），[m/H]=-0.05 \pm 0.02; NGC 6705，[m/H]=+0.14 \pm 0.08; NGC 6819，[m/H]=-0.07 \pm 0.12。这些金属丰度估计将有助于规划未来的太阳系外行星过境搜索，因为行星可能更容易在富含金属的环境中形成。
Planets in Stellar Clusters Extensive Search. I. Discovery of 47 Low-amplitude Variables in the Metal-rich Cluster NGC 6791 with Millimagnitude Image Subtraction Photometry
The central stars of the planetary nebulae NGC 7027 and NGC 6543
NGC 7027和NGC 6543的红外光谱范围从2.4到45微米，用红外空间天文台上的短波光谱仪获得。这些光谱的第一次分析，与光电离模型的帮助下，提出。我们报告的第一次检测到的Ar VI 4.53微米和Ne VI 7.65微米线的光谱NGC7027。与较早的观测结果相比，很明显Ar VI线和可能还有其他线的强度自1981年以来有所增加。我们认为，这种变化的一个可能的解释是中央恒星的光谱能量分布的变化，可能是有效温度的增加。然而，这一结果需要进一步的观察来证实。我们还报告了NGC 6543光谱中未检测到O IV 25.9微米线和首次检测到Na III 7.32微米线。根据中心恒星光谱的黑体近似，预计不会检测到。O（3+）的电离阈值刚好超过He II的极限，而这条线的缺失表明恒星的通量在He II的极限处至少下降了350倍。模拟O IV线可能被证明是对大气模型的一个有价值的测试。
