학술논문
MOA-2012-BLG-505Lb: A Super-Earth-Mass Planet that Probably Resides in the Galactic Bulge
Document Type
Report
Author
Nagakane, M; Sumi, T; Koshimoto, N; Bennett, D. P; Bond, I. A; Rattenbury, N; Suzuki, D; Abe, F; Asakura, Y; Barry, R; Bhattacharya, A; Donachie, M; Fukui, A; Hirao, Y; Itow, Y; Li, M. C. A; Ling, C. H; Masuda, K; Matsubara, Y; Matsuo, T; Muraki, Y; Ohnishi, K; Ranc, C; Saito, To; Sharan, A; Shibai, H; Sullivan, D. J; Tristram, P. J; Yamada, T; Yonehara, A
Source
Astrophysical Journal. 154(1)
Subject
Language
English
ISSN
1538-4357
0004-637X
0004-637X
Abstract
We report the discovery of a super-Earth-mass planet in the microlensing event MOA-2012-BLG-505. This event has the second shortest event timescale of t(sub E) = 10 ± 1 days where the observed data show evidence of a planetary companion. Our 15 minute high cadence survey observation schedule revealed the short subtle planetary signature. The system shows the well known close/wide degeneracy. The planet/host-star mass ratio is q = 2.1 × 10(exp −4) and the projected separation normalized by the Einstein radius is s = 1.1 or 0.9 for the wide and close solutions, respectively. We estimate the physical parameters of the system by using a Bayesian analysis and find that the lens consists of a super-Earth with a mass of 6.7(sup +10.7)(sub -3.6) Mꚛ orbiting around a brown dwarf or late-M-dwarf host with a mass of 0.10(sup +0.16)(sub -0.05) Mꙩ with a projected star–planet separation of 0.9(sup +0.3)(sub -0.2) au. The system is at a distance of 7.2 ± 1.1 kpc, i.e., it is likely to be in the Galactic bulge. The small angular Einstein radius (θ(sub E) = 0.12 ± 0.02 mas) and short event timescale are typical for a low-mass lens in the Galactic bulge. Such low-mass planetary systems in the Bulge are rare because the detection efficiency of planets in short microlensing events is relatively low. This discovery may suggest that such low-mass planetary systems are abundant in the Bulge and currently ongoing high cadence survey programs will detect more such events and may reveal an abundance of such planetary systems.