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ヨネハラ アツノリ
YONEHARA ATSUNORI
米原 厚憲 所属 京都産業大学 理学部 宇宙物理・気象学科 職種 教授 |
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| 言語種別 | 英語 |
| 発行・発表の年月 | 2016/12 |
| 形態種別 | 研究論文 |
| 査読 | 査読あり |
| 標題 | The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass |
| 執筆形態 | その他 |
| 掲載誌名 | The Astrophysical Journal |
| 巻・号・頁 | 833(2),pp.article id. 145 |
| 著者・共著者 | D. Suzuki,D. P. Bennett,T. Sumi,I. A. Bond,L. A. Rogers,F. Abe,Y. Asakura,A. Bhattacharya,M. Donachie,M. Freeman,A. Fukui,Y. Hirao,Y. Itow,N. Koshimoto,M. C. A. Li,C. H. Ling,K. Masuda,Y. Matsubara,Y. Muraki,M. Nagakane,K. Onishi,H. Oyokawa,N. Rattenbury,To. Saito,A. Sharan,H. Shibai,D. J. Sullivan,P. J. Tristram,A. Yonehara |
| 概要 | We report the results of the statistical analysis of planetary signals<br />
discovered in MOA-II microlensing survey alert system events from 2007 to 2012.<br /> We determine the survey sensitivity as a function of planet-star mass ratio,<br /> $q$, and projected planet-star separation, $s$, in Einstein radius units. We<br /> find that the mass ratio function is not a single power-law, but has a change<br /> in slope at $q \sim 10^{-4}$, corresponding to $\sim 20 M_{\oplus}$ for the<br /> median host star mass of $\sim 0.6 M_{\odot}$. We find significant planetary<br /> signals in 23 of the 1474 alert events that are well characterized by the<br /> MOA-II survey data alone. Data from other groups are used only to characterize<br /> planetary signals that have been identified in the MOA data alone. The<br /> distribution of mass ratios and separations of the planets found in our sample<br /> are well fit by a broken power-law model of the form $dN_{\rm pl}/(d{\rm log}<br /> q\ d{\rm log} s) = A (q/q_{\rm br})^n s^m \, {\rm dex}^{-2}$ for $q > q_{\rm<br /> br}$ and $dN_{\rm pl}/(d{\rm log} q\ d{\rm log} s) = A (q/q_{\rm br})^p s^m \,<br /> {\rm dex}^{-2}$ for $q < q_{\rm br}$, where $q_{\rm br}$ is the mass ratio of<br /> the break. We also combine this analysis with the previous analyses of Gould et<br /> al. and Cassan et al., bringing the total sample to 30 planets. This combined<br /> analysis yields $A = 0.61^{+0.21}_{-0.16}$, $n =-0.93\pm 0.13$, $m =<br /> 0.49_{-0.49}^{+0.47}$ and $p = 0.6^{+0.5}_{-0.4}$ for $q_{\rm br}\equiv<br /> 1.7\times 10^{-4}$. The unbroken power law model is disfavored with a $p$-value<br /> of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken<br /> power-law model. These results imply that cold Neptunes are likely to be the<br /> most common type of planets beyond the snow line. |
| DOI | 10.3847/1538-4357/833/2/145 |
| arXiv ID | arXiv:1612.03939 |
| PermalinkURL | http://arxiv.org/abs/1612.03939v1 |