Dolphin Head Nebula Sh 2-308 & Collinder 121
History
In 1931 Swedish astronomer Per Collinder published his «Catalogue of Open Galactic Clusters» based on a survey of Lundmark using the Franklin-Adams plates and Collinder using the Franklin-Adams charts. Cluster nr. 121 (Collinder 121, Cr 121) is listed there with dimensions of circa 60×40 arcminutes and containing 18-20 stars. [455]
In the 1950-ies the American astronomer Stewart Sharpless did a survey for H II regions on the photo plates of «Palomar Observatory Sky Survey» made with the 48-inch Schmidt telescope. In 1959 he published his revised catalogue of H II regions where the nebula is listed as number 308 (Sh 2-308, S 308). He described it as a medium brightness nebula of irregular form with filamentary structure and a diameter of 35 arcminutes. [310]
Due to its shape revealed on long exposure photography the nebula got the nickname «Dolphin Head Nebula» or just «Dolphin Nebula».
Physical Properties
Collinder 121 is a small open cluster containing ~20 main-sequence B-stars spanning an area of 50×35 arcminutes and the red supergiant star ο1 Canis Majoris which according to Gaia DR3 is at a distance of ~777 parsec. [145]
Sh 2-308 is a Wolf-Rayet bubble surrounding the 6.9 mag and WN4b spectral type star EZ Canis Majoris (HD 50896, WR 6). Wolf-Rayet stars are a class of massive stars descended from stars greater than 20 solar masses. They are characterized by the presence of strong broad emission lines in their spectra, which indicates a strong outflow of stellar wind, forming a bubble in the excited interstellar medium surrounding the star. Sh 2-308 is one of two known Wolf-Rayet bubbles emmitting X-ray. The other one is NGC 6888. [39] According to Gaia DR 3 the distance to the star is ~1537 parsec and therefore possibly unrelated to Collinder 121, which center lies ~50 arcminutes further south. [145]
| Name | Type | RA (J2000.0) |
Dec (J2000.0) |
PM [mas/y] |
Parall. [mas] |
Rvel [km/s] |
z | SP Type |
Magnitudes | Identifiers |
|---|---|---|---|---|---|---|---|---|---|---|
| Collinder 121 | OpC | 06h 56m 20s | -24° 43' 48" | -5.11 | 31.4 | 0.000105 | B 3.02; V 2.6 | C 0652-245; Cl Collinder 121; OCl 619.0; [KPR2004b] 115; [KPS2012] MWSC 1018 | ||
| Sh 2-308 | WR* | 06h 54m 13s | -23° 55' 42" | -4.322 | 0.6505 | 164 | 0.000547 | WN4b | U 5.74; B 6.63; V 6.91; G 6.583162; R 7.74; J 6.353; H 6.226; K 5.893 | 1RXS J065413.8-235543; 2E 0652.1-2351; 2E 1743; 2MASS J06541303-2355422; 2XMM J065413.0-235542; ALS 98; BRAN 2; CD-23 4553; CEL 1426; CMC 172546; CMC 203719; CPD-23 1588; CSV 6527; Cl Collinder 121 4; GC 9061; GCRV 4522; GEN# +5.11210004; GSC 06522-03270; Gaia DR1 2922367972368451072; Gaia DR2 2922367976673391232; Gaia DR3 2922367976673391232; HD 50896; HIC 33165; HIP 33165; HR 2583; Hen 3-20; IRAS 06521-2351; JP11 4532; LBN 1052; LBN 234.57-10.00; LMA IC 1613 10; LS 98; MR 6; N30 1504; PPM 251223; RCW 11; SAO 172546; SH 2-308; SKY# 12250; TD1 8528; TIC 78959225; TYC 6522-3270-1; UBV 6842; UBV M 12581; UBV M 40625; UCAC4 331-017802; V* EZ CMa; WR 6; WRAY 15-2; YZ 113 4156; [BNJ2003] XMM 1; [TSA98] J065412.01-235541.40; uvby98 511210004 |
Finder Chart
The Dolphin-Head Nebula Sh 2-308 is located in the constellation Canis Maior. On 3 January it is in opposition to the Sun and culminates at local midnight. The best time for observation is in the months from November until February.
