{{Short description|Open star cluster in the constellation Vela}} {{Infobox open cluster | name = IC 2391 | image = O Velorum Cluster iTelescope.png | caption = A close image of IC 2391 (north is to the left). Credits: iTelescope.net (T59) | epoch = J2000.0 | constellation = Vela | ra = {{RA|08|40.6}} | dec = {{DEC|-53|02}} | dist_ly = 574 ly | dist_pc = 176 pc<ref>{{Cite web|title=IC 2391|url=http://simbad.u-strasbg.fr/simbad/sim-id?mescat.distance=on&Ident=%403033509&Name=IC+2391&submit=display+selected+measurements#lab_meas|access-date=2020-06-11|website=sim-id}}</ref> | appmag_v = 2.5 | size_v = 50′ | mass_kg = | mass_msol = | radius_ly = | v_hb = | age = | notes = | names = Caldwell 85, Cr 191, C 0838-528, Lac II 5 }}
'''IC 2391''' (also known as the '''Omicron Velorum Cluster''' or '''Caldwell 85''') is an open cluster in the constellation Vela consisting of hot, young, blueish stars, some of which are binaries and one of which is a quadruple. Persian astronomer Abd al-Rahman al-Sufi first described it as "a nebulous star" in {{circa|964}}.<ref>{{cite book | last1=Jones | first1=Kenneth Glyn | last2=Society | first2=Webb | title=Webb Society Deep-sky Observer's Handbook: Open and globular clusters | publisher=Enslow Publishers | date=1979 | isbn=978-0-89490-034-1 | url=https://books.google.com/books?id=maCsAAAAIAAJ&q=Deep-sky+Observer%2527s+Handbook:+Open+and+globular+clusters | access-date=2025-04-18}}</ref><ref>{{cite book | last=Rooney | first=Anne | title=The History of Astronomy | publisher=The Rosen Publishing Group, Inc | date=2017-12-15 | isbn=978-1-5081-7703-6 | url=https://books.google.com/books?id=Gd1hDwAAQBAJ&q=The%2520History%2520of%2520Astronomy%2520rooney | access-date=2025-04-18}}</ref> It was re-found by Abbe Lacaille and cataloged as '''Lac II 5'''.
==Description== IC 2391 is centred about 490 light-years away from Earth and can be seen with the naked eye. It contains about 30 stars with a total visual magnitude of 2.5, spread out across 50 arcminutes.
==Member stars== These are some of the prominent members of IC 2391:<ref name=platais>{{cite journal|bibcode=2007A&A...461..509P|arxiv=astro-ph/0611584|title=WIYN open cluster study. XXVI. Improved kinematic membership and spectroscopy of IC 2391|journal=Astronomy and Astrophysics|volume=461|issue=2|pages=509|last1=Platais|first1=I|last2=Melo|first2=C|last3=Mermilliod|first3=J. -C|last4=Kozhurina-Platais|first4=V|last5=Fulbright|first5=J. P|last6=Méndez|first6=R. A|last7=Altmann|first7=M|last8=Sperauskas|first8=J|s2cid=17173564|year=2007|doi=10.1051/0004-6361:20065756}}</ref> {|class="wikitable sortable" !Name!!Apparent<br/>magnitude (V)!!Spectral type!!Distance (LY) |- |HD 74195 (ο Velorum)||3.63 varies<ref>{{cite journal |bibcode=2003AJ....125.2531R |title=Catalog of Galactic OB Stars |last1=Reed |first1=B. Cameron |journal=The Astronomical Journal |date=2003 |volume=125 |issue=5 |page=2531 |doi=10.1086/374771 }}</ref>||style="background:#{{Color temperature|20000|hexval}};"|B3/5(V)<ref name=houk>{{cite book |bibcode=1978mcts.book.....H |date=1978 |title=Michigan catalogue of two-dimensional spectral types for the HD stars |last1=Houk |first1=Nancy }}</ref>||{{val|496|30.5}}<ref>{{cite DR2|5318547273545667584}}</ref> |- |HD 74560 (HY Velorum) sp. binary||4.815<ref name=hog>{{cite journal |bibcode=2000A&A...355L..27H |title=The Tycho-2 catalogue of the 2.5 million brightest stars |last1=Høg |first1=E. |last2=Fabricius |first2=C. |last3=Makarov |first3=V. V. |last4=Urban |first4=S. |last5=Corbin |first5=T. |last6=Wycoff |first6=G. |last7=Bastian |first7=U. |last8=Schwekendiek |first8=P. |last9=Wicenec |first9=A. |journal=Astronomy and Astrophysics |date=2000 |volume=355 }}</ref>||style="background:#{{Color temperature|20000|hexval}};"| B3IV<ref name=houk/>||{{val|490.4|6.9}}<ref>{{cite DR3|5318486456810851072}}</ref> |- |HD 74146 (NZ Velorum) sp. binary||5.19<ref name=ducati>{{cite journal |bibcode=2002yCat.2237....0D |title=VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system |last1=Ducati |first1=J. R. |journal=Vizier Online Data Catalog |date=2002 |volume=2237 }}</ref>||style="background:#{{Color temperature|20000|hexval}};"|B5IV<ref name=houk/>||{{val|497.3|7.5}}<ref>{{cite DR3|5318541982145960064}}</ref> |- |HD 74071 (HW Velorum)||5.44<ref name=hog/>||style="background:#{{Color temperature|20000|hexval}};"|B5V<ref name=houk/>||{{val|519.9|7.5}}<ref>{{cite DR3|5318113550566048256}}</ref> |- |HD 74196 cepheid variable||5.61<ref name=ducati/>||style="background:#{{Color temperature|14000|hexval}};"|B9/A0<ref name=houk/>||{{val|502|4.1}}<ref>{{cite DR3|5318543425255007872}}</ref> |- |HD 74535 (KT Velorum) alpha2 CVn variable||5.47<ref name=hog/>||style="background:#{{Color temperature|20000|hexval}};"|B9III(pSi)<ref name=houk/>||{{val|421|17.5}}<ref>{{cite DR2|5318485043754606848}}</ref> |- |HD 75466 ||6.27<ref name=hog/>||style="background:#{{Color temperature|20000|hexval}};"|B8V<ref name=houk/>||{{val|479|2.8}}<ref>{{cite DR3|5318412686452956800}}</ref> |- |HD 73952 ||6.43<ref name=hog/>||style="background:#{{Color temperature|20000|hexval}};"|B8V<ref name=houk/>||{{val|483|5.8}}<ref>{{cite DR3|5318169866178702976}}</ref> |- |HD 74438, youngest known quadruple star.<ref name="Gaia-ESO Survey">{{cite journal |last1=Merle |first1=T. |last38=Zaggia |first38=S. |title=The Gaia -ESO Survey: double-, triple-, and quadruple-line spectroscopic binary candidates |journal=Astronomy & Astrophysics |date=December 2017 |volume=608 |pages=A95 |doi=10.1051/0004-6361/201730442|arxiv=1707.01720 |bibcode=2017A&A...608A..95M |s2cid=119502806 |doi-access=free }}</ref><ref name="WIYN study">{{cite journal |last1=Platais |first1=I. |last2=Melo |first2=C. |last3=Mermilliod |first3=J.-C. |last4=Kozhurina-Platais |first4=V. |last5=Fulbright |first5=J. P. |last6=Méndez |first6=R. A. |last7=Altmann |first7=M. |last8=Sperauskas |first8=J. |title=WIYN open cluster study: XXVI. Improved kinematic membership and spectroscopy of IC 2391 |journal=Astronomy & Astrophysics |date=January 2007 |volume=461 |issue=2 |pages=509–522 |doi=10.1051/0004-6361:20065756 |arxiv=astro-ph/0611584 |bibcode=2007A&A...461..509P|s2cid=17173564 |doi-access=free }}</ref><ref name="BadAstron">{{cite web |last1=Plait |first1=Phil |title=A weird four-star system may lead the way to catastrophic supernovae |url=https://www.syfy.com/syfy-wire/bad-astronomy-quaternary-star-hd-74438-stars-explode |website=SYFY Official Site |access-date=4 June 2022 |archive-url=https://web.archive.org/web/20220527005009/https://www.syfy.com/syfy-wire/bad-astronomy-quaternary-star-hd-74438-stars-explode |archive-date=27 May 2022 |date=26 May 2022}}</ref>||7.58<ref name=hog/>||style="background:#{{Color temperature|8750|hexval}};"|A2mA5-A8<ref name=houk/>||{{val|472|5.2}}<ref>{{cite DR3|5318169866178702976}}</ref> |} The stars' era of formation is similar to open cluster IC 2602 in neighbouring Carina,<ref>{{cite journal |title=Rotational Velocities and Chromospheric/Coronal Activity of Low-Mass Stars in the Young Open Clusters IC 2391 and IC 2602 |author=Stauffer, J.R. |display-authors=etal |journal=Astrophysical Journal |volume=479 |issue=2 |pages=776–791 |bibcode=1997ApJ...479..776S |doi=10.1086/303930|date=1997 |doi-access=free }}</ref> and has a lithium depletion boundary age of about 50 million years.<ref>{{Cite journal|last1=Navascues|first1=David Barrado y|last2=Stauffer|first2=John R.|last3=Jayawardhana|first3=Ray|date=2004-10-10|title=Spectroscopy of Very Low Mass Stars and Brown Dwarfs in IC 2391: Lithium Depletion and Hα Emission|journal=The Astrophysical Journal|language=en|volume=614|issue=1|pages=386–397|doi=10.1086/423485|issn=0004-637X|bibcode=2004ApJ...614..386B|arxiv=astro-ph/0406436|s2cid=208867491 }}</ref> The latter group averages about the same distance, placed at about 485 light years away.<ref>{{cite DR3}}</ref>
==Argus Association== The components formed at about the same time as a nearer group, known as the "Argus Association" which one motion model suggests began in their own nebula cloud. These are in a similar direction, roughly the Vela constellation, within the local galactic arm.<ref name=Malo2013>{{citation | title=Bayesian Analysis to Identify New Star Candidates in Nearby Young Stellar Kinematic Groups | display-authors=1 | last1=Malo | first1=Lison | last2=Doyon | first2=René | last3=Lafrenière | first3=David | last4=Artigau | first4=Étienne | last5=Gagné | first5=Jonathan | last6=Baron | first6=Frédérique | last7=Riedel | first7=Adric | s2cid=118497872 | journal=The Astrophysical Journal | volume=762 | issue=2 | id=88 | pages=50 | date=January 2013 | doi=10.1088/0004-637X/762/2/88 | bibcode=2013ApJ...762...88M | arxiv=1209.2077 | postscript=. }}</ref> The supposed association may chiefly comprise:<ref name=Malo2013/> {| class="wikitable" |- !Name!!Constellation!!Distance!!Radial velocity |- |Epsilon Pavonis||Pavo||105||−6.7 |- |HD 88955||Vela||100||+7.4 |- |HD 61005||Puppis||119||+22 |}
== References == {{reflist}}
== External links == {{commonscat}} * {{cite web|url=http://messier.seds.org/xtra/ngc/i2391.html|title=Omicron Velorum (IC 2391)|work=SEDS Messier Database|publisher=Students for the Exploration and Development of Space|author=Frommert, Harmut|date=29 March 1998}} * {{wikiSky}} * {{cite simbad|title=IC 2391}} * {{cite web|url=http://www.atlasoftheuniverse.com/openclus.html|title=Open Cluster|work=An Atlas of The Universe}}
{{sky|08|40|18|-|52|54|60|571}} {{Caldwell catalogue}}
2391 Category:Open clusters Category:Vela (constellation) 085b 64 64 {{Vela (constellation)}}