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Messier 19

Globular cluster in Ophiuchus

Field	Value
name	Messier 19
image	[[File:Messier 19.jpg	300px]]
caption	Globular cluster Messier 19 in Ophiuchus
epoch	J2000
class	VIII
constellation	Ophiuchus
ra
dec
dist_ly	28.7 kly
appmag_v	6.8
size_v	17.0
mass_msol
radius_ly	70 ly
metal_fe	–1.53
age	11.90 Gyr
names	NGC 6273, GCl 52

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 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". The cluster is located 4.5° WSW of Theta Ophiuchi and is just visible as a fuzzy point of light using 50 mm binoculars. Using a telescope with a 25.4 cm aperture, the cluster shows an oval appearance with a 3 × 4 core and a 5 × 7 halo.

M19 is one of the most oblate of the known globular clusters. 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. It lies at a distance of about 28.7 kly from the Solar System, and is quite near to the Galactic Center at only about 6.5 kly away.

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

References

"Messier 19".
(August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin.
(May 2010). "Accreted versus in situ Milky Way globular clusters". [[Monthly Notices of the Royal Astronomical Society]].
(November 2011). "Young Radio Pulsars in Galactic Globular Clusters". The Astrophysical Journal.
(2007). "Illustrated Guide to Astronomical Wonders". [[O'Reilly Media, Inc.]].
(1978). "Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System". [[Courier Dover Publications]].
"M 19".
(May 2008). "The Flattening of Globular Clusters". The Astronomical Journal.
(April 2006). "Globular cluster system and Milky Way properties revisited". Astronomy and Astrophysics.
(November 2001). "Variable Stars in Galactic Globular Clusters". The Astronomical Journal.
(March 2001). "A census with ROSAT of low-luminosity X-ray sources in globular clusters". Astronomy and Astrophysics.

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globular-clusters ophiuchus messier-objects ngc-objects astronomical-objects-discovered-in-1764 discoveries-by-charles-messier

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