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MOA-2009-BLG-387L
MOA-2009-BLG-387L is a red dwarf in the Sagittarius constellation that is host to the planet MOA-2009-BLG-387Lb. The star is estimated to be nearly 20,000 light years away and approximately one fifth the mass of the Sun, although large confidence intervals exist, reflecting the uncertainties in both the mass and distance. The star drew the attention of astronomers when it became the lens of gravitational microlensing event MOA-2009-BLG-387L, in which it eclipsed a background star and created distorted caustics, an envelope of reflected or refracted light rays. Analysis of the caustic events and of follow-up observational data led to the planet's discovery, which was reported in February 2011.
==Observational history==
On July 24, 2009, the Microlensing Observations in Astrophysics collaboration (MOA) detected the star MOA-2009-BLG-387L eclipsing a background star in a microlensing event that was named MOA-2009-BLG-387. In a process called gravitational microlensing, the star MOA-2009-BLG-387L became a lens that created two distorted caustic images. In the case of the microlensing event MOA-2009-BLG-387, these caustics produced a series of small "resonating" diffractions; such resonant-caustic events are valued because they tend to yield more information about an orbiting planet.〔
The first caustic event was detected by the South African Astronomical Observatory (SAAO) on July 24, 2009. An alert was issued, which attracted many to cover the caustic event; as such, the end of the first caustic event was well-documented.〔 The microlensing event's second caustic event was seven days later, an unusually long middle period for planetary microlensing events.〔 An alert brought three different telescopes at SAAO and telescopes at ten different observatories to focus on the event.
Follow-up observations on the star MOA-2009-BLG-387L using the NACO imager at the Very Large Telescope array successfully distinguished the star's mass. The collected data from VLT and from observations during the microlensing event was run through a series of models and analyzed. An orbiting planetary body larger than Jupiter (or of a similar size, given uncertainties) was discovered. The discovery of the planet was reported on February 21, 2011 in the journal ''Astronomy and Astrophysics''.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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