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NGC 7099
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Messier 30 (also M30, NGC 7099, ESO 531-SC21 and GCL 122) is a magnitude +7.7 globular star cluster located 27,140 ±650 light-years away in the constellation Capricornus. 

The cluster was discovered by French astronomer Charles Messier using a 8.38 cm (3.3-inch) refracting telescope at the Hôtel de Cluny (now the Musée national du Moyen Age), in Paris, France on the 3rd August 1764.

Right Ascension 21h 40m 22.12s, Declination -23° 10' 47.5"

M30 is, in general, the last object to be viewed on a Messier Marathon, a competition among amateur astronomers in order to visualize the largest possible number of Messier objects in only a single night.
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Title: Estimating the parameters of globular cluster M 30 (NGC 7099) from time-series photometry
Authors: N. Kains, D. M. Bramich, A. Arellano Ferro, R. Figuera Jaimes, U. G. Jørgensen, S. Giridhar, K.A. Alsubai, J. M. Andersen, V. Bozza, P. Browne, M. Burgdorf, S. Calchi Novati, Y. Damerdji, C. Diehl, P. Dodds, M. Dominik, A. Elyiv, X.-S. Fang, E. Giannini, S.-H. Gu, S. Hardis, K. Harpsøe, T.C. Hinse, A. Hornstrup, M. Hundertmark, J. Jessen-Hansen, D. Juncher, E. Kerins, H. Kjeldsen, H. Korhonen, C. Liebig, M. N. Lund, M. Lundkvist, L. Mancini, R. Martin, M. Mathiasen, M.T. Penny, M. Rabus, S. Rahvar, D. Ricci, K. Sahu, G. Scarpetta, J. Skottfelt, C. Snodgrass, J. Southworth, J. Surdej, J. Tregloan-Reed, C. Vilela, O. Wertz, A. Williams

We present the analysis of 26 nights of V and I time-series observations from 2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to search for variable stars in this cluster and refine the periods of known variables; we then used our variable star light curves to derive values for the cluster's parameters. We used difference image analysis to reduce our data to obtain high-precision light curves of variable stars. We then estimated the cluster parameters by performing a Fourier decomposition of the light curves of RR Lyrae stars for which a good period estimate was possible. We also derive an estimate for the age of the cluster by fitting theoretical isochrones to our colour-magnitude diagram (CMD). Out of 13 stars previously catalogued as variables, we find that only 4 are bona fide variables. We detect two new RR Lyrae variables, and confirm two additional RR Lyrae candidates from the literature. We also detect four other new variables, including an eclipsing blue straggler system, and an SX Phoenicis star. This amounts to a total number of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of the light curves of the RR Lyrae stars to derive cluster parameters using empirical relations. We find a cluster metallicity [Fe/H]_ZW=-2.01 ± 0.04, or [Fe/H]_UVES=-2.11 ± 0.06, and a distance of 8.32 ± 0.20 kpc (using RR0 variables), 8.10 kpc (using one RR1 variable), and 8.35 ± 0.42 kpc (using our SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we estimate an age of 13.0 ± 1.0 Gyr for M 30.

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Messier 30 (also known as M30 or NGC 7099) is a globular cluster of stars in the southern constellation of Capricornus. It was discovered by the French astronomer Charles Messier in 1764, who described it as a circular nebula without a star. In the New General Catalogue, compiled during the 1880s, it was described as a "remarkable globular, bright, large, slightly oval."
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Zooming Into Messier 30



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Using the NASA/ESA Hubble Space Telescope, astronomers have uncovered two distinct kinds of "rejuvenated" stars in the globular cluster Messier 30. A new study shows that both stellar collisions and a process sometimes called vampirism are behind this cosmic "face lift". The scientists also uncover evidence that both sorts of blue stragglers were produced during a critical dynamical event (known as "core collapse") that occurred in Messier 30 a few billion years ago.
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