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RE: M22
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Title: The first confirmed microlens in a globular cluster
Authors: P. Pietrukowicz, D. Minniti, Ph. Jetzer, J. Alonso-Garcia, A. Udalski
(Version v2)

In 2000 July/August a microlensing event occurred at a distance of 2.33 arcmin from the center of the globular cluster M22 (NGC6656), observed against the dense stellar field of the Milky Way bulge. We have used the adaptive optics system NACO at the ESO Very Large Telescope to resolve the two objects that participated in the event: the lens and the source. The position of the objects measured in 2011 July is in agreement with the observed relative proper motion of M22 with respect to the background bulge stars. Based on the brightness of the microlens components we find that the source is a solar-type star located at a distance of 6.0 1.5 kpc in the bulge, while the lens is a 0.18 0.01 Solar mass dwarf member of the globular cluster located at the known distance of 3.2 0.2 kpc from the Sun.

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Posts: 131433
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Title: The first confirmed microlens in a globular cluster
Authors: P. Pietrukowicz, D. Minniti, Ph. Jetzer, J. Alonso-Garcia, A. Udalski

In July/August 2000 a microlensing event occurred at a distance of 2.33 arcmin from the center of the globular cluster M22 (NGC6656), observed against the dense stellar field of the Milky Way bulge. We have used the adaptive optics system NACO at the ESO VLT to resolve the two objects that participated in the event: the lens and the source. The position of the objects measured in July 2011 is in agreement with the observed relative proper motion of M22 with respect to the background bulge stars. Based on the brightness of the microlens components we find that the source is a solar-type star located at a distance of 6.9 1.5 kpc in the bulge, while the lens is a 0.18 0.01 Msun dwarf member of the globular cluster located at the known distance of 3.2 0.2 kpc from the Sun.

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The Sagittarius Globular Cluster, a spectacular globule of nearly 100,000 stars, as seen through the Astrochannels 14" telescope and video camera.



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The globular cluster M22, contains over 100,000 stars. These stars formed together and are gravitationally bound. Stars orbit the centre of the cluster, and the cluster orbits the centre of our Galaxy.


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So far, about 140 globular clusters are known to exist in a roughly spherical halo around the Galactic centre. Globular clusters do not appear spherically distributed as viewed from the Earth, and this fact was a key point in the determination that our Sun is not at the centre of our Galaxy.

Globular clusters are very old.
There is a straightforward method of determining their age, and this nearly matches the 13.7 billion-year age of our entire universe.

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