}}Messier 93 or M93, also known as NGC 2447, is an open cluster in the constellation Puppis. It was discovered by Charles Messier then added to his catalogue of comet-like objects on March 20, 1781.[10] Caroline Herschel, the younger sister of William Herschel, independently discovered M93 in 1783, thinking it had not yet been catalogued by Messier.[11] Walter Scott Houston described its appearance as follows:[12]Some observers mention the cluster as having the shape of a starfish. With a fair-sized telescope, this is its appearance on a dull night, but [a four-inch refractor] shows it as a typical star-studded galactic cluster.
It has a Trumpler class of {{nowrap|I 3 r}}, indicating it is strongly concentrated (I) with a large range in brightness (3) and is rich in stars (r).[13]
M93 is at a distance of about 3,380[1] light years from Earth and has a spatial radius of some 5 light years,[4] a tidal radius of {{Val|13.1|2.3|u=ly}},[6] and a core radius of {{Convert|1.3|pc|ly|order=flip|abbr=on|disp=out}}.[17] Its age is estimated at 387.3 million years.[1] The cluster is positioned nearly on the galactic plane and it is following an orbit that varies between {{Convert|8.5|–|8.9|kpc|kly|order=flip|abbr=on}} from the Galactic Center over a period of {{Val|242.7|7.9}} Myr.[1]
54 variable stars have been found in M93, including one slowly pulsating B-type star, one rotating ellipsoidal variable, seven Delta Scuti variables, six Gamma Doradus variables, and one hybrid δ Sct/γ Dor pulsator.[20] Four spectroscopic binary systems in M93 include a yellow straggler component.[21]
References
1. ^1 {{citation | title=Photoelectric Search for Peculiar Stars in Open Clusters - Part Fourteen - NGC1901 NGC2169 NGC2343 CR:132 NGC2423 and NGC2447 | last1=Maitzen | first1=H. M. | journal=Astronomy and Astrophysics Supplement | volume=102 | issue=1 | page=1 | date=November 1993 | bibcode=1993A&AS..102....1M | postscript=. }}
2. ^1 {{citation | first1=Hartmut | last1=Frommert | first2=Christine | last2=Kronberg | title=Messier 93 | work=SEDS Messier pages | publisher=Students for the Exploration and Development of Space (SEDS) | date=September 2, 2007 | url=http://www.messier.seds.org/m/m093.html | accessdate=2018-12-07 | postscript=. }}
3. ^1 {{cite book | last = Houston | first = Walter Scott | authorlink=Walter Scott Houston | title = Deep-Sky Wonders | publisher = Sky Publishing Corporation | year = 2005 | isbn = 978-1-931559-23-2}}
4. ^1 2 3 4 5 6 7 {{Citation | display-authors=1 | last1=Wu | first1 = Zhen-Yu | last2=Zhou | first2 = Xu | last3=Ma | first3 = Jun | last4=Du | first4 = Cui-Hua | title=The orbits of open clusters in the Galaxy | journal=Monthly Notices of the Royal Astronomical Society | volume=399 | issue=4 | pages=2146–2164 | date=November 2009 | arxiv=0909.3737 | bibcode=2009MNRAS.399.2146W | doi=10.1111/j.1365-2966.2009.15416.x | postscript=. }}
5. ^1 {{citation | contribution=Time resolved surveys of stellar clusters | last1=Eyer | first1=L. | last2=Eggenberger | first2=P. | last3=Greco | first3=C. | last4=Saesen | first4=S. | last5=Anderson | first5=R. I. | last6=Mowlavi | first6=N. | title=JENAM 2010, Joint European and National Astronomy Meeting held 6-10 September, 2010 in Lisbon Portugal | pages=212 | date=September 2010 | id=212 | bibcode=2010jena.confE.212E | postscript=. }}
6. ^1 {{citation | title=Red giants and yellow stragglers in the young open cluster NGC 2447 | last1=da Silveira | first1=M. D. | last2=Pereira | first2=C. B. | last3=Drake | first3=N. A. | display-authors=1 | journal=Monthly Notices of the Royal Astronomical Society | volume=476 | issue=4 | pages=4907–4931 | date=June 2018 | doi=10.1093/mnras/sty265 | bibcode=2018MNRAS.476.4907D }}
7. ^1 2 3 4 {{citation | title=Concise Catalog of Deep-Sky Objects: Astrophysical Information for 550 Galaxies, Clusters and Nebulae | series=The Patrick Moore Practical Astronomy Series | first1=Warren H. | last1=Finlay | edition=2nd | publisher=Springer | year=2014 | isbn=978-3319031705 | page=120 | url=https://books.google.com/books?id=eJDIAwAAQBAJ&pg=PA120 }}
8. ^1 2 {{citation | display-authors=1 | last1=Piskunov | first1=A. E. | last2=Schilbach | first2=E. | last3=Kharchenko | first3=N. V. | last4=Röser | first4=S. | last5=Scholz | first5=R.-D. | title=Tidal radii and masses of open clusters | journal=Astronomy and Astrophysics | postscript=. | volume=477 | issue=1 | pages=165–172 | date=January 2008 | doi=10.1051/0004-6361:20078525 | bibcode=2008A&A...477..165P }}
9. ^1 {{citation | title=Towards absolute scales for the radii and masses of open clusters | last1=Piskunov | first1=A. E. | last2=Schilbach | first2=E. | last3=Kharchenko | first3=N. V. | last4=Röser | first4=S. | last5=Scholz | first5=R. -D. | display-authors=1 | journal=Astronomy and Astrophysics | postscript=. | volume=468 | issue=1 | pages=151–161 | date=June 2007 | doi=10.1051/0004-6361:20077073 | bibcode=2007A&A...468..151P | arxiv=astro-ph/0702517 }}
10. ^1 {{citation | title=Gazing at the starry heavens | first1=Michael | last1=Hoskin | journal=Astronomy & Geophysics | volume=57 | issue=1 | date=February 1, 2016 | pages=1.22–1.25 | doi=10.1093/astrogeo/atw038 | bibcode=2016A&G....57a1.22H }}