# Messier 19

Messier 19
Messier 19 by Hubble Space Telescope; 2.5′ view
Credit: NASA/STScI/WikiSky
Observation data (J2000 epoch)
Class VIII[1]
Constellation Ophiuchus
Right ascension 17h 02m 37.69s[2]
Declination −26° 16′ 04.6″[2]
Distance 28.7 kly (8.8 kpc)[3]
Apparent magnitude (V) +7.47[2]
Apparent dimensions (V) 17′.0
Physical characteristics
Mass 1.10×106[3] M
Metallicity ${\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}$ = –1.53[4] dex
Estimated age 11.90 Gyr[4]
Other designations NGC 6273, GCl 52[2]

Messier 19 or M19 (also designated NGC 6273) is a globular cluster in the constellation Ophiuchus. It was discovered by Charles Messier on June 5, 1764[5] and added to his catalogue of comet-like objects that same year. It was resolved into individual stars by William Herschel in 1784. His son, John Herschel, described it as "a superb cluster resolvable into countless stars".[6] The cluster is located 4.5° WSW of Theta Ophiuchi and is just visible as a fuzzy point of light using 50 mm (2.0 in) binoculars. Using a telescope with a 25.4 cm (10.0 in) aperture, the cluster shows an oval appearance with a 3′ × 4′ core and a 5′ × 7′ halo.[5]

M19 is one of the most oblate of the known globular clusters.[6] This flattening may not accurately reflect the physical shape of the cluster because the emitted light is being strongly absorbed along the eastern edge. This is the result of extinction caused by intervening gas and dust. When viewed in the infrared, the cluster shows almost no flattening.[7] It lies at a distance of about 28.7 kly (8.8 kpc) from the Solar System,[3] and is quite near to the Galactic Center at only about 6.5 kly (2.0 kpc) away.[8]

This cluster contains an estimated 1,100,000 times the mass of the Sun[3] and it is around 11.9 billion years old.[4] The stellar population includes four Cepheids and RV Tauri variables, plus at least one RR Lyrae variable for which a period is known.[9] Observations made during the ROSAT mission failed to reveal any low-intensity X-ray sources.[10]

## References

1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S.
2. ^ a b c d "SIMBAD Astronomical Object Database", Results for NGC 6273, retrieved 2006-11-16.
3. ^ a b c d 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.
4. ^ a b c Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x.
5. ^ a b Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated Guide to Astronomical Wonders, Diy Science, O'Reilly Media, Inc., p. 331, ISBN 0596526857.
6. ^ a b Burnham, Robert (1978), Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Dover Books on Astronomy, 2 (2nd ed.), Courier Dover Publications, p. 1263, ISBN 0486235688.
7. ^ van den Bergh, Sidney (May 2008), "The Flattening of Globular Clusters", The Astronomical Journal, 135 (5): 1731–1737, arXiv:0802.4061, Bibcode:2008AJ....135.1731V, doi:10.1088/0004-6256/135/5/1731.
8. ^ Bica, E.; et al. (April 2006), "Globular cluster system and Milky Way properties revisited", Astronomy and Astrophysics, 450 (1): 105–115, arXiv:astro-ph/0511788, Bibcode:2006A&A...450..105B, doi:10.1051/0004-6361:20054351.
9. ^ Clement, Christine M.; et al. (November 2001), "Variable Stars in Galactic Globular Clusters", The Astronomical Journal, 122 (5): 2587–2599, arXiv:astro-ph/0108024, Bibcode:2001AJ....122.2587C, doi:10.1086/323719.
10. ^ Verbunt, F. (March 2001), "A census with ROSAT of low-luminosity X-ray sources in globular clusters", Astronomy and Astrophysics, 368: 137–159, arXiv:astro-ph/0012261, Bibcode:2001A&A...368..137V, doi:10.1051/0004-6361:20000469.