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'''NGC 7089'''<ref>Hirshfeld, Alan, and Roger W. Sinnott, eds., Sky Catalogue 2000.0, Vol.2, Cambridge, Massachusetts: Sky Publishing Corp. and Cambridge University Press, 1985. (3098,238)</ref><ref>NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J.L.E. Dreyer Sinnott, R.W. (edited by) <Sky Publishing Corporation and Cambridge University Press (1988)></ref>, also known as '''M2''', is a [[globular cluster]] located in the constellation [[Aquarius]].
'''NGC 7089''', also known as '''Messier 2''', is a [[globular cluster]] located in the constellation [[Aquarius (constellation)|Aquarius]].
{{Infobox NGCobject
{{Infobox NGCobject
| number= NGC 7089
| number= NGC 7089
Line 6: Line 6:
| type = [[Globular cluster]]
| type = [[Globular cluster]]
| epoch = 2000.0
| epoch = 2000.0
| ra = 21<sup>h</sup>33.5<sup>m</sup>
| ra = 21<sup>h</sup> 33<sup>m</sup>
| de = -00<sup>o</sup>49<sup>'</sup>
| de = -0° 49ˡ
| app_size = 12.9
| app_size = 16ˡ
| app_mag =   6.5
| app_mag = 6.5
| distance_ly =
| distance_ly = 37.500 light years
| const = Aquarius
| const = Aquarius (constellation){{!}}Aquarius
| radius_ly =
| radius_ly = 174 light years
| redshift =
| redshift =
| other =  M 2
| other =  Messier 2
| source = Hirshfeld, Alan, and Roger W. Sinnott, eds., Sky Catalogue 2000.0, Vol.2, Cambridge, Massachusetts: Sky Publishing Corp. and Cambridge University Press, 1985. (3098,238)
| source =  
| org_source = NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J.L.E. Dreyer Sinnott, R.W. (edited by) <Sky Publishing Corporation and Cambridge University Press (1988)>
| org_source =  
}}
}}
=== Appearance ===
==Discovery and Observational data==
NGC 7089 was first discovered in 1746 by Jean-Dominique Maraldi. French comet hunter [[Charles Messier]] included the cluster on his list of nebulous objects in 1760 as the second entry after the [[Crab Nebula]]. Messier was unable to resolve the cluster into individual stars and thus called it a "nebula". It was [[William Herschel]] who first discovered the true identity of the cluster when he resolved individual stars.


=== Location ===
Messier 2 can be found less than 5° almost due north of [[Beta Aquarii|β Aqr.]] and shines with an apparent magnitude of 6.5, placing it below naked-eye visibility. It is however, easily seen with binoculars or modest amateur telescopes. Larger telescopes are needed to fully resolve the golular into stars.


=== Scientific research  ===
==Physical data==
NGC 7089 is a rather compact globular cluster of type ''II'' and is decidedly elliptical in shape. The cluster has a diameter of about 175 light years and is some 37.500 light years distant.<ref name="Harris">William E. Harris, ''Catalog Of Parameters For Milky Way Globular Clusters'', February 2003, online at: http://www.physics.mcmaster.ca/~harris/mwgc.dat</ref> The brightest individual stars of NGC 7089 are of apparent magnitude +13.1 while the estimated age of the cluster is in the order of 13 X 10<sup>9</sup> years. The absolute magnitude for NGC 7089 is -9.0.<ref name="Harris" />


*  We<ref>Lee & Carney, Photometry of RR Lyrae Variables in M2, AJ, 117, 2868</ref>have presented BV photometry for 30 RR Lyrae variables, including 13 newly discovered variables, in the Oosterhoff type II globular cluster M2. The methods of searching for periods and new variables were discussed. We have derived pulsational parameters for RR Lyrae variables. With the discovery of new RR Lyrae variables, the mean periods of the RRab and RRc variables are 〈Pab〉 = 0.69 ± 0.02 days and 〈Pc〉 = 0.33 ± 0.01 days, respectively. The number ratio of the RRc type variables to the total number of the RR Lyrae type variables is n(c)/n(ab + c) = 0.40. A comparison with the model instability boundaries shows general agreement, although the detailed comparison is somewhat uncertain in the theoretical fundamental red edge given by Bono et al. (1995b)<ref>Bono, G., Caputo, F., & Marconi, M. 1995b, AJ, 110, 2365</ref>. The RR Lyrae pulsational mode transition occurs between the fundamental period of 0.528 days and 0.556 days. From the star counts along the horizontal branch, two HB color distribution indices have been derived, (B-R)/(B + V + R) = 0.92 and B2/(B + V + R) = 0.46. Our analysis of the secular period-change rates from six RRab variables shows a general agreement with the canonical synthetic HB model predictions by Lee (1991)<ref>Lee, Y.-W. 1991, ApJ, 367, 524</ref>. Finally, the HB star distribution shows that there are no significant blue HB gaps in M2.
The half-mass radius of NGC 7089, ie the distance from the center of the cluster where half of the object's mass is concentrated, is 10 light years while the tidal radius, the point at which the gravitational influence of the cluster falls below that of the Milky Way as a whole, is about 233 light years from the center of the cluster. Stars beyond this distance would escape the cluster's gravitational pull. The overall spectraltype of NGC 7089 is ''F4''.<ref name="Harris" />


=== References ===
Messier 2 follows a highly elongated (e=0.76) orbit around the Milky Way Galaxy taking it from between 23.500 light years to up to about 171.000 light years from the galaxtic center.<ref name="Brosche">Brosche et al, ''Space Motions and Orbits of Globular Clusters'', 1997</ref>
{{reflist}}
 
===Variable stars===
Like many globular clusters, NGC 7089 contains a number of [[variable star]]s, most notable of the ''RR Lyrae'' type. There are also 3 ''W Virginis'' [[Cepheid stars|Cepheid type]] variables known within this object as well as an ''RV Tauri'' star. The first of these variable stars within Messier 2 were discovered in 1895 by Solon Bailey.
 
==References==
{{reflist}}[[Category:Suggestion Bot Tag]]

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NGC 7089, also known as Messier 2, is a globular cluster located in the constellation Aquarius.

NGC 7089
Observation data: 2000.0 epoch
Constellation Aquarius
Right ascension 21h 33m
Declination -0° 49ˡ
Distance 37.500 light years
Type Globular cluster
Apparent dimensions 16ˡ
Diameter in ly 174 light years
Apparent magnitude 6.5
Other designations Messier 2

Discovery and Observational data

NGC 7089 was first discovered in 1746 by Jean-Dominique Maraldi. French comet hunter Charles Messier included the cluster on his list of nebulous objects in 1760 as the second entry after the Crab Nebula. Messier was unable to resolve the cluster into individual stars and thus called it a "nebula". It was William Herschel who first discovered the true identity of the cluster when he resolved individual stars.

Messier 2 can be found less than 5° almost due north of β Aqr. and shines with an apparent magnitude of 6.5, placing it below naked-eye visibility. It is however, easily seen with binoculars or modest amateur telescopes. Larger telescopes are needed to fully resolve the golular into stars.

Physical data

NGC 7089 is a rather compact globular cluster of type II and is decidedly elliptical in shape. The cluster has a diameter of about 175 light years and is some 37.500 light years distant.[1] The brightest individual stars of NGC 7089 are of apparent magnitude +13.1 while the estimated age of the cluster is in the order of 13 X 109 years. The absolute magnitude for NGC 7089 is -9.0.[1]

The half-mass radius of NGC 7089, ie the distance from the center of the cluster where half of the object's mass is concentrated, is 10 light years while the tidal radius, the point at which the gravitational influence of the cluster falls below that of the Milky Way as a whole, is about 233 light years from the center of the cluster. Stars beyond this distance would escape the cluster's gravitational pull. The overall spectraltype of NGC 7089 is F4.[1]

Messier 2 follows a highly elongated (e=0.76) orbit around the Milky Way Galaxy taking it from between 23.500 light years to up to about 171.000 light years from the galaxtic center.[2]

Variable stars

Like many globular clusters, NGC 7089 contains a number of variable stars, most notable of the RR Lyrae type. There are also 3 W Virginis Cepheid type variables known within this object as well as an RV Tauri star. The first of these variable stars within Messier 2 were discovered in 1895 by Solon Bailey.

References

  1. ↑ 1.0 1.1 1.2 William E. Harris, Catalog Of Parameters For Milky Way Globular Clusters, February 2003, online at: http://www.physics.mcmaster.ca/~harris/mwgc.dat
  2. ↑ Brosche et al, Space Motions and Orbits of Globular Clusters, 1997
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