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Title: Discovery of a Probable SX Phoenicis Star in M107 (NGC 6171)
Authors: Thayne A. McCombs, Erik D. Reinhart, Andrew N. Darragh, Elliott W. Johnson, Brian W. Murphy

Using V images taken in May and June 2012 with the SARA Consortium's 0.9-meter telescope located at Kitt Peak National Observatory, we searched for variable stars in the globular cluster M107 (NGC 6171). The search was accomplished using the ISIS v2.2 image subtraction software. We refined the positions of the previously known variables and confirmed the 21 RR Lyrae variables from Clement's Catalogue of Variable Stars in Globular Clusters (Clement et al. 2001). We also discovered a previously unknown variable which is likely an SX Phoenicis star. For this SX Phoenicis star we measured a fundamental pulsation frequency 19.0122/day (P=0.05257 days) and a mean amplitude of 0.046 magnitudes in the V band. This variable had an average V-band magnitude of 17.72, nearly 2 magnitudes dimmer than the horizontal branch of M107, typical of SX Phoenicis stars and blue stragglers lying just beyond the main sequence turn-off in globular clusters.

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Hubble Has an Audience of Stellar Flashbulbs

670020main1_m107-670.JPG

The NASA/ESA Hubble Space Telescope has captured a crowd of stars that looks rather like a stadium darkened before a show, lit only by the flashbulbs of the audience's cameras. Yet the many stars of this object, known as Messier 107, are not a fleeting phenomenon, at least by human reckoning of time - these ancient stars have gleamed for many billions of years.
Messier 107 is one of more than 150 globular star clusters found around the disc of the Milky Way galaxy. These spherical collections each contain hundreds of thousands of extremely old stars and are among the oldest objects in the Milky Way.

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NGC 6171
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A Swarm of Ancient Stars

We know of about 150 of the rich collections of old stars called globular clusters that orbit our galaxy, the Milky Way. This sharp new image of Messier 107, captured by the Wide Field Imager on the 2.2-metre telescope at ESO's La Silla Observatory in Chile, displays the structure of one such globular cluster in exquisite detail. Studying these stellar swarms has revealed much about the history of our galaxy and how stars evolve.
The globular cluster Messier 107, also known as NGC 6171, is a compact and ancient family of stars that lies about 21 000 light-years away. Messier 107 is a bustling metropolis: thousands of stars in globular clusters like this one are concentrated into a space that is only about twenty times the distance between our Sun and its nearest stellar neighbour, Alpha Centauri, across. A significant number of these stars have already evolved into red giants, one of the last stages of a star's life.

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Messier 107
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Globular Cluster M107 (also known as Messier Object 107 or NGC 6171) is a very loose globular cluster in the constellation Ophiuchus. It was discovered by Pierre Méchain in April 1782 and independently by William Herschel in 1793. It wasn't until 1947 that Helen Sawyer Hogg added it and three other objects discovered by Méchain to the list of Messier objects.
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