View source for Messier 71

{{short description|Globular cluster in the constellation Sagitta}}
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{{Infobox globular cluster
| name = Messier 71
| image  	              		= Messier 71, an Unusual Globular Cluster.jpg
| caption = The globular cluster Messier 71 by the [[Hubble Space Telescope]].
| credit = 
| epoch = [[J2000]]
| class = X-XI
| constellation = [[Sagitta]]
| ra = {{RA|19|53|46.49}}<ref name=aj140_6_1830/>
| dec = {{DEC|+18|46|45.1}}<ref name=aj140_6_1830/>
| dist_ly = {{Convert|13.0|kly|kpc|abbr=on|lk=on}}<ref name=apj670_1_363/>
| appmag_v = 8.2<ref>{{cite web |url=https://messier.seds.org/m/m071.html |title=Messier 71 |access-date=30 April 2022 |website=SEDS Messier Catalog}}</ref>
| size_v = 7.2'
| mass_msol = {{Val|1.7|e=4}}<ref name=mnras406_3_2000/>
| radius_ly = 13 ly<ref>distance × sin( diameter_angle / 2 ) = 13 ly. radius</ref>
| metal_fe = –0.78<ref name=apj742_1_51/>
| v_hb =
| age = 9-10 Gyr
| notes =
| names = M71, [[New General Catalogue|NGC]] 6838, [[Collinder catalog|Cr]] 409, GCl 115<ref name="simbad" />
}}

'''Messier 71''' (also known as '''M71''', '''NGC 6838''', or the '''Angelfish Cluster''') is a [[globular cluster]] in the small [[celestial hemisphere|northern]] [[constellation]] [[Sagitta]]. It was discovered by [[Philippe Loys de Chéseaux]] in 1745 and included by [[Charles Messier]] in his catalog of non-[[comet]]-like objects in 1780. It was also noted by [[Johann Gottfried Koehler|Koehler]] at [[Dresden]] around 1775.<ref>{{Cite web|title=New General Catalog Objects: NGC 6800 - 6849|url=https://cseligman.com/text/atlas/ngc68.htm#6838|access-date=2021-03-11|website=cseligman.com}}</ref> Messier 71 is also known as '''NGC 6839''', though this identification is very uncertain.<ref>{{Cite web |title=Your NED Search Results |url=https://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC_6839&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES |access-date=2024-08-28 |website=ned.ipac.caltech.edu}}</ref>

This star cluster is about 13,000 [[light year]]s away from [[Earth]] and spans {{convert|27|ly|pc|0}}. The irregular [[variable star]] ''Z Sagittae'' is a member.<ref name="AAVSO" />

[[File:M71 Crop.png|left|thumb|The M71 globular cluster at the center is surrounded by a dense Milky Way star field.]]M71 was for many decades thought (until the 1970s) to be a densely packed [[open cluster]] and was classified as such by leading [[astronomer]]s in the field of star cluster research due to its lacking a dense central compression, and to its stars having more "[[Metallicity|metals]]" than is usual for an ancient globular cluster; furthermore, it lacks the [[RR Lyrae variable|RR Lyrae]] "cluster" variable stars that are common in most globulars. However, modern photometric [[Photometry (astronomy)|photometry]] has detected a short "[[horizontal branch]]" in the [[Hertzsprung-Russell diagram|H-R diagram]] (chart of temperature versus luminosity) which is characteristic of a globular cluster.  The shortness of the branch explains the lack of RR Lyrae variables and is due to the globular's relatively young age of 9&ndash;10 billion years.  Taking in many or only late series ([[Population I]]) stars explains relatively its stars.  Hence today M71 is designated as a very loosely concentrated globular cluster, much like [[Messier 68|M68]] in [[Hydra (constellation)|Hydra]]. M71 has a mass of about {{solar mass|53,000|link=yes}} and a [[Luminosity#In astronomy|luminosity]] of around 19,000 {{lo|link=yes}}.<ref name="Dalgleish"/>
[[File:M71map.png|thumbnail|Map showing location of M71]]
{{Commons category|Messier 71}}

==See also==
* [[List of Messier objects]]
* [[NGC 6366]]
* [[NGC 6342]]

==References==
{{reflist|refs=
<ref name=aj140_6_1830>{{citation | display-authors=1 | last1=Goldsbury | first1=Ryan | last2=Richer | first2=Harvey B. | last3=Anderson | first3=Jay | last4=Dotter | first4=Aaron | last5=Sarajedini | first5=Ata | last6=Woodley | first6=Kristin | title=The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters | journal=The Astronomical Journal | volume=140 | issue=6 | pages=1830–1837 |date=December 2010 | doi=10.1088/0004-6256/140/6/1830 | bibcode=2010AJ....140.1830G | postscript=. |arxiv = 1008.2755 | s2cid=119183070 }}</ref>

<ref name=mnras406_3_2000>{{citation | last1=Marks | first1=Michael | last2=Kroupa | first2=Pavel | title=Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=406 | issue=3 | pages=2000–2012 |date=August 2010 | doi=10.1111/j.1365-2966.2010.16813.x | doi-access=free | bibcode=2010MNRAS.406.2000M | postscript=. |arxiv = 1004.2255 | s2cid=118652005 }} Mass is from M<sub>PD</sub> on Table 1.</ref>

<ref name="simbad">{{cite simbad | title=M 71 | access-date=2006-11-17 }}</ref>

<ref name=apj670_1_363>{{citation | display-authors=1 | last1=Hessels | first1=J. W. T. | last2=Ransom | first2=S. M. | last3=Stairs | first3=I. H. | last4=Kaspi | first4=V. M. | last5=Freire | first5=P. C. C. | title=A 1.4 GHz Arecibo Survey for Pulsars in Globular Clusters | journal=The Astrophysical Journal | volume=670 | issue=1 | pages=363–378 |date=November 2007 | doi=10.1086/521780 | bibcode=2007ApJ...670..363H | postscript=. |arxiv = 0707.1602 | s2cid=16914232 }}</ref>

<ref name=apj742_1_51>{{citation | display-authors=1 | last1=Boyles | first1=J. | last2=Lorimer | first2=D. R. | last3=Turk | first3=P. J. | last4=Mnatsakanov | first4=R. | last5=Lynch | first5=R. S. | last6=Ransom | first6=S. M. | last7=Freire | first7=P. C. | last8=Belczynski | first8=K. | title=Young Radio Pulsars in Galactic Globular Clusters | journal=The Astrophysical Journal | volume=742 | issue=1 | page=51 |date=November 2011 | doi=10.1088/0004-637X/742/1/51 | bibcode=2011ApJ...742...51B | postscript=. |arxiv = 1108.4402 | s2cid=118649860 }}</ref>

<ref name="AAVSO">{{cite web |title=Z Sge |url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=27350 |website=The International Variable Star Index |publisher=AAVSO |access-date=1 March 2021}}</ref>

<ref name="Dalgleish">{{cite journal |last1=Dalgleish |first1=H. |last2=Kamann |first2=S. |last3=Usher |first3=C. |last4=Baumgardt |first4=H. |last5=Bastian |first5=N. |last6=Veitch-Michaelis |first6=J. |last7=Bellini |first7=A. |last8=Martocchia |first8=S. |last9=Da Costa |first9=G. S. |last10=Mackey |first10=D. |last11=Bellstedt |first11=S. |last12=Pastorello |first12=N. |last13=Cerulo |first13=P. |title=The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity |journal=Monthly Notices of the Royal Astronomical Society |date=March 2020 |volume=492 |issue=3 |pages=3859–3871 |doi=10.1093/mnras/staa091 |bibcode=2020MNRAS.492.3859D |doi-access=free |arxiv=2001.01810 }}</ref>

}}

== Gallery ==
<gallery>
File:M71.jpg|Till Credner and Sven Kohle, Calar Alto Observatory.
 File:M71 - Noao-m71.jpg|M71 in visible light by the [[National Optical Astronomy Observatory|NOAO]].
 File:NGC 6838 2MASS.jpg|M71 in [[infrared]] by the [[Astronomical survey|survey]] [[2MASS]].
 File:NGC 6838 DSS.jpg|M71 in visible light by the [[Astronomical survey|survey]] [[Digitized Sky Survey|DSS]].
</gallery>

==External links==
* {{WikiSky}}
* [http://messier.seds.org/m/m071.html Messier71 @ SEDS Messier pages]
* [http://gclusters.altervista.org/cluster_4.php?ggc=M+71 Messier 71, Galactic Globular Clusters Database page]
* [http://www.perseus.gr/Astro-DSO-NGC-6838.htm Messier 71, LRGB CCD image based on two hours total exposure]
* [https://esahubble.org/images/potw1018a/ Messier 71: an Unusual Globular Cluster], [[ESA]]\[[Hubble Space Telescope|Hubble]] picture of the week.
* {{cite web|title=M71 – Globular Cluster|url=http://www.deepskyvideos.com/videos/messier/M71.html|work=Deep Sky Videos|publisher=[[Brady Haran]]|author=McCormac, James|author2=Szymanek, Nik |author-link2=Nik Szymanek }}

{{Portal bar|Astronomy|Stars|Outer space}}
{{Messier objects}}
{{NGC objects: 6001-7000}}
{{Sky|19|53|46.11|+|18|46|42.3|12000}}

[[Category:Globular clusters|Messier 071]]
[[Category:Sagitta|Messier 071]]
[[Category:Messier objects|071]]
[[Category:NGC objects|Messier 071]]
[[Category:Astronomical objects discovered in 1745|?]]