Collinder 121 (Cr 121) is a loose open cluster/stellar association of stars in the constellationCanis Major,[5] the "greater dog". It is located at a distance of 3,590±720ly (1.10±0.22kpc) from the Sun.[2] This cluster was catalogued by Swedish astronomer Per Collinder in 1931 as entry 121 in his paper titled, On structural properties of open galactic clusters and their spatial distribution. During his study, he found 18–20 stars within an angular area of 60′ × 40′.[6] Of these, eight are members of the Henry Draper Catalog.[7] About 2° to the north is the large cluster NGC 2287 (M 41).[8]
In 1958, it was noted by M. S. Roberts that the Wolf-Rayet starWR 6 (or EZ CMa) coincides with this cluster,[9][10] sparking interest in its study.[11] The red supergiantOmicron1 Canis Majoris is strongly associated with this cluster. Several bright B-type stars with similar space motions are positioned near this supergiant, presumably forming the core of the association.[12] In 1967, the membership list was extended by 28 stars within a 10° radius.[7]O. J. Eggen in 1981 suggested that Cr121 is linked to an OB association of stars 10° to the north, known as CMa OB1.[8]
The results from the Hipparcos satellite drastically changed the membership list, finding 105 stars that formed an OB association rather than a compact cluster.[7][13] However, a 2003 study of lower mass stars in the vicinity lent weight to the original cluster proposal. Instead, this cluster is believed to be coincident with a foreground association designated CMa OB2.[14] As of 2023, data from the Gaia space observatory shows a major association of OB stars is centered at a distance of 803pc. Thus, Cr 121 and CMa OB2 may be the same extended cluster.[15]
12Zeballos, H.; etal. (June 2006), Infante, L.; Rubio, M. (eds.), "Kinematics of stars in the line of sight to the open cluster Collinder21", XI IAU Regional Latin American Meeting of Astronomy, Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias), vol.26, p.185, Bibcode:2006RMxAC..26..185Z.
↑Collinder, Per (1931), "On Structural Properties of Open Galactic Clusters and their Spatial Distribution. Catalog of Open Galactic Clusters", Annals of the Observatory of Lund, 2: B1–B46, Bibcode:1931AnLun...2....1C.
123Hoogerwerf, R.; etal. (August 1997), "New Results for Three Nearby OB Associations", Proceedings of the ESA Symposium 'Hipparcos - Venice '97', 13-16 May, Venice, Italy, ESA SP-402, vol.402, pp.571–574, arXiv:astro-ph/9707088, Bibcode:1997ESASP.402..571H.
↑Roberts, M. S. (1958), "8. The Distribution of Woif-Rayet Stars", Étoiles a raies d'emission: communications présentées au huitième Colloque international d'astrophysique tenu a Liège les 8, 9 et 10 juillet 1957, vol.8, Belgique: Institut d'Astrophysique cointe-Sclessin, pp.76–83, Bibcode:1958LIACo...8...76R.
↑Firmani, C.; etal. (July 1980), "The binary nature of the single-line Wolf-Rayet star EZ CMa=HD 50896", Astrophysical Journal, 239: 607–621, Bibcode:1980ApJ...239..607F, doi:10.1086/158148.
↑Feinstein, Alejandro (July 1967), "Collinder 121: a Young Southern Open Cluster Similar to H and χ Persei", Astrophysical Journal, 149: 107, Bibcode:1967ApJ...149..107F, doi:10.1086/149234.
↑Fleming, Graham D.; etal. (August 2023), "Stellar clustering and the kinematics of stars around Collinder 121 using Gaia DR3", Monthly Notices of the Royal Astronomical Society, 523 (4): 5306−5314, arXiv:2306.08578, Bibcode:2023MNRAS.523.5306F, doi:10.1093/mnras/stad1817.
↑Barclay, Krister D. G.; etal. (January 2024), "Using CHIRON spectroscopy to test the hypothesis of a precessing orbit for the WN4 star EZ CMa", Monthly Notices of the Royal Astronomical Society, 527 (2): 2198–2208, arXiv:2310.15986, Bibcode:2024MNRAS.527.2198B, doi:10.1093/mnras/stad3289.
Further reading
Kaltcheva, Nadia; Makarov, Valeri (October 2007), "The Structure and the Distance of Collinder 121 from Hipparcos and Photometry: Resolving the Discrepancy", The Astrophysical Journal, 667 (2): L155–L157, arXiv:0708.3382, Bibcode:2007ApJ...667L.155K, doi:10.1086/522495.
Pérez-Garrido, A.; etal. (December 2005), "A search for brown dwarfs in Collinder 70 and Collinder 121", Astronomische Nachrichten, 326 (10): 1028–1030, Bibcode:2005AN....326.1028P, doi:10.1002/asna.200510452.
Kaltcheva, N. T.; etal. (December 1999), "Strömgren and Hβ photometry of O and B type stars in star-forming regions. II. Monoceros OB2, Canis Major OB1 and Collinder 121", Astronomy and Astrophysics, 352: 605–608, Bibcode:1999A&A...352..605K.
