NGC 2359

{{Short description|Emission nebula in the constellation Canis Major}}

{{ Planetary nebula |

| image = 300px

|caption= Thor’s Helmet Nebula imaged on the occasion of ESO’s 50th Anniversary.

| name = Thor’s Helmet Nebula

| type = Emission

| epoch = J2000

| ra = {{RA|07|18|30}}{{cite simbad|title=NGC 2359|access-date=5 October 2012}}

| dec = {{DEC|-13|13.8|}}

| dist_ly = 11,960

| appmag_v =

| size_v =

| constellation = Canis Major

| radius_ly =

| absmag_v =

| notes = HII (ionized) region

| names = GUM 4, LBN 227.66-00.09, SH 2-298, GRS 227.80 -00.20, LBN 1041, RCW 5

}}

NGC 2359 (also known as Thor's Helmet) is an emission nebula[http://seds.org/~spider/ngc/ngc.cgi?2359 SEDS: NGC 2359] {{webarchive|url=https://web.archive.org/web/20100326114605/http://seds.org/~spider/ngc/ngc.cgi?2359 |date=2010-03-26 }} in the constellation Canis Major. The nebula is approximately 3,670 parsecs (11.96 thousand light years) away and 30 light-years in size. The central star is the Wolf-Rayet star WR7, an extremely hot star thought to be in a brief pre-supernova stage of evolution. It is similar in nature to the Bubble Nebula, but interactions with a nearby large molecular cloud are thought to have contributed to the more complex shape and curved bow-shock structure of Thor's Helmet.

It is also catalogued as Sharpless 2-298 and Gum 4.{{cite web |url=http://galaxymap.org/cgi-bin/gum.py?s=1 |title=The Gum Catalog |publisher=Galaxymap.org |access-date=2013-10-06 |archive-date=2013-07-16 |archive-url=https://web.archive.org/web/20130716142645/http://galaxymap.org/cgi-bin/gum.py?s=1 |url-status=dead }}

The nebula has an overall bubble shape, but with complex filamentary structures. The nebula contains several hundred solar masses of ionised material, plus several thousand more of unionised gas. It is largely interstellar material swept up by winds from the central star, although some material does appear to be enriched with the products of fusion and is likely to come directly from the star.{{Cite journal | doi = 10.1086/300995| title = A Study of Neutral and Ionized Gas of the Wolf-Rayet Ring Nebula NGC 2359| journal = The Astronomical Journal| volume = 118| issue = 2| pages = 948| year = 1999| last1 = Cappa | first1 = C. E.| last2 = Goss | first2 = W. M.| last3 = Niemela | first3 = V. S.| last4 = Ostrov | first4 = P. G.| bibcode = 1999AJ....118..948C| s2cid = 123709946| doi-access = free}} The expansion rate of different portions of the nebula varies from 10 km/s to at least 30 km/s, leading to age estimates of 78,500 - 236,000 years. The nebula has been studied at radio and x-ray wavelengths, but it is still unclear whether it was produced at the class O main sequence stage of development, as a red supergiant, luminous blue variable, or mainly as a Wolf-Rayet star.{{Cite journal | doi = 10.1093/mnras/stu1138| title = X-rays from wind-blown bubbles: An XMM-Newton detection of NGC 2359| journal = Monthly Notices of the Royal Astronomical Society| volume = 443| issue = 1| pages = 12–18| year = 2014| last1 = Zhekov | first1 = S. A.| doi-access = free| bibcode = 2014MNRAS.443...12Z|arxiv = 1406.2463 }}

NGC 2361 is a bright knot of nebulosity on one edge of the central ring of NGC 2359.