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Post Info TOPIC: Messier 71


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NGC 6838
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Messier 71 (also known as M71, GCL 115 or NGC 6838) is a magnitude +8.2 globular cluster located 13 000 light-years (~4000 pc) away in the constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1746 and observed by Charles Messier on the 4th October 1780. It was also noted by Koehler at Dresden around 1775.
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The diameter of the cluster is approximately. 27 years light. You can find it in the sky midway between the stars gamma and delta Sagittae. M71 can be seen by a good pair of binoculars.

Picture 275 
Date: 18.04.15 


39 x 4 second frames captured with a 8" f5 reflector and Canon EOS 350D.
Motorised EQ5 Mount.
Prime focus.



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Posts: 131433
Date:
Messier 71
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Title: Chandra X-Ray Observatory Observations of the Globular Cluster M71
Authors: R. F. Elsner, C. O. Heinke, H. N. Cohn, P. M. Lugger, J. E. Maxwell, I. H. Stairs, S. M. Ransom, J. W. T. Hessels, W. Becker, R. H. H. Huang, P. D. Edmonds, J. E. Grindlay, S. Bogdanov, K. Ghosh, M. C. Weisskopf

We observed the nearby, low-density globular cluster M71 (NGC 6838) with the Chandra X-ray Observatory to study its faint X-ray populations. Five X-ray sources were found inside the cluster core radius, including the known eclipsing binary millisecond pulsar (MSP) PSR J1953+1846A. The X-ray light curve of the source coincident with this MSP shows marginal evidence for periodicity at the binary period of 4.2 h. Its hard X-ray spectrum and luminosity resemble those of other eclipsing binary MSPs in 47 Tuc, suggesting a similar shock origin of the X-ray emission. A further 24 X-ray sources were found within the half-mass radius, reaching to a limiting luminosity of 1.5 10^30 erg/s (0.3-8 keV). From a radial distribution analysis, we find that 18±6 of these 29 sources are associated with M71, somewhat more than predicted, and that 11±6 are background sources, both galactic and extragalactic. M71 appears to have more X-ray sources between L_X=10^30--10^31 erg/s than expected by extrapolating from other studied clusters using either mass or collision frequency. We explore the spectra and variability of these sources, and describe the results of ground-based optical counterpart searches.

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