Messier 71

Messier 71
M71 from Hubble Space Telescope; 3.35′ view Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class	X-XI
Constellation	Sagitta
Right ascension	19^h 53^m 46.49^s[1]
Declination	+18° 46′ 45.1″[1]
Distance	13.0 kly (4.0 kpc)[2]
Apparent magnitude (V)	+6.1[3]
Apparent dimensions (V)	7′.2
Physical characteristics
Mass	1.7×10^4[4] M☉
Radius	13 ly[5]
Metallicity	$\begin{smallmatrix}\left[{Fe}/{H}\right]\end{smallmatrix}$ = –0.78[6] dex
Estimated age	9-10 Gyr
Other designations	M71, NGC 6838, GCl 115[3]

Messier 71 (also known as M71 or NGC 6838) is a globular cluster in the constellation Sagitta. It was discovered by Philippe Loys de Chéseaux in 1746 and included by Charles Messier in his catalog of comet-like objects in 1780. It was also noted by Koehler at Dresden around 1775.

M71 is at a distance of about 12,000 light years away from Earth and spans some 27 light years across. The irregular variable star Z Sagittae is a member of this cluster.

M71 was long thought (until the 1970s) to be a densely packed open cluster and was classified as such by leading astronomers in the field of star cluster research due to its lacking a dense central compression, and to its stars having more "metals" than is usual for an ancient globular cluster; furthermore, it lacks the RR Lyrae "cluster" variable stars that are common in most globulars. However, modern photometric photometry has detected a short "horizontal branch" in the H-R diagram of M71, which is characteristic of a globular cluster. The shortness of the branch explains the lacking of the RR Lyrae variables and is due to the globular's relatively young age of 9-10 billion years. The relative youth of this globular also explains the abundance of "metals" in its stars. Hence today M71 is designated as a very loosely concentrated globular cluster, much like M68 in Hydra. M71 has a luminosity of around 13,200 Suns.

Map showing location of M71

References

1. Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
2. Hessels, J. W. T.; et al. (November 2007), "A 1.4 GHz Arecibo Survey for Pulsars in Globular Clusters", The Astrophysical Journal 670 (1): 363–378, arXiv:0707.1602, Bibcode:2007ApJ...670..363H, doi:10.1086/521780.
3. "SIMBAD Astronomical Database". Results for NGC 6838. Retrieved 2006-11-17.
4. Marks, Michael; Kroupa, Pavel (August 2010), "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way", Monthly Notices of the Royal Astronomical Society 406 (3): 2000–2012, arXiv:1004.2255, Bibcode:2010MNRAS.406.2000M, doi:10.1111/j.1365-2966.2010.16813.x. Mass is from M_PD on Table 1.
5. distance × sin( diameter_angle / 2 ) = 13 ly. radius
6. Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal 742 (1): 51, arXiv:1108.4402, Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51.

External links

• Messier 71 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
• Messier71 @ SEDS Messier pages
• Messier 71, Galactic Globular Clusters Database page
• Messier 71, LRGB CCD image based on two hours total exposure
• Messier 71: an Unusual Globular Cluster, ESA\Hubble picture of the week.
• McCormac, James; Szymanek, Nik. "M71 – Globular Cluster". Deep Space Videos. Brady Haran.

Coordinates: 19^h 53^m 46.11^s, +18° 46′ 42.3″