230126 - Sh2-308 "Dolphin Head" nebula
|
click image to enlarge
|
ASTRO:
type=Planetary nebula (pre-supernova) mag=7.0 const=Cassiopeia dist=5400 ly size=60 ly IMAGE: location=EB Driveway BrtlCls=4 exposure=CMOS OSC 45x420s (5.3h), Gain120 EQUIPMENT: camera=ZWO ASI2600MC-Pro optics=ES102 w1.0x fltnr, F=714mm, f/7 filter=Optolong L-eXtreme NB mount=Celestron AVX guiding=Orion 60x240mm, ZWO ASi224MC SOFTWARE: acquisition=Stellarium, APT, PHD2, processing=PixInsight (wRCAstro), PhotoshopCC, LrC |
|
Sh2-308, (or Sharpless 308), also designated RCW 11, and LBN 1052, is known as The Dolphin Head nebula. Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged in the second edition of Stewart Sharpless' famous 1959 nebula catalog, it lies appx 5,400 light-years away toward the constellation of the "Big Dog" Canis Major, and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of appx 60 light-years at its estimated distance. The massive star that created the bubble, is Wolf-Rayet 6, also known as EZ Canis Majoris (...derived from the magnitude-succession of stars in its home constellation), and is seen in this image as the bright one at the center of the nebula. Wolf-Rayet stars usually have over 20 times the mass of our Sun; and, this one fits that understanding very well. Wolf-Rayet's are theorized to be in a brief, pre-supernova phase of massive star evolution. This particular star's fast stellar winds create the bubble-shaped nebula as they blow at appx 3.8 million mph, and sweep up slower moving material from an earlier phase of WR6's evolution.
The Dolphin was formed about 70,000 years ago when WR6 threw off its outer hydrogen layers, revealing inner layers of heavier elements. WR6's spectral type indicates it is very hot and luminous. Its spectrum shows that it is devoid of hydrogen at its stellar surface. It is expected to eventually explode in a supernova. When it does, the resulting event horizon will subsume the nebula.
Sh2-308 is part of a larger H-II region located near the center of the Canis Major constellation. Gas clouds lying within the Dolphin Head caricature itself are composed mostly of ionized oxygen, which gives it its characteristic blue color. In contrast, the background clouds lying beyond the object are mostly red-colored ionized hydrogen. The Dolphin Head lies about 8 degrees south of Sirius, the brightest star in our night sky.
The most favorable time of year to observe the nebula is between the months of December and April. Its southern declination makes it easier to observe from the Southern Hemisphere, but it may also be viewed from southerly latitudes in the Northern Hemisphere. Relatively faint emissions captured by a special filter in this deep-sky image are dominated by the glow of ionized oxygen atoms. Amateur astrophotographers will frequently "map" the faint cloud to a blueish hue in their photographs when taken with high-power amateur instruments and with the help of a narrow band filter sensitive to the OIII emission line wavelength of light.
The Dolphin was formed about 70,000 years ago when WR6 threw off its outer hydrogen layers, revealing inner layers of heavier elements. WR6's spectral type indicates it is very hot and luminous. Its spectrum shows that it is devoid of hydrogen at its stellar surface. It is expected to eventually explode in a supernova. When it does, the resulting event horizon will subsume the nebula.
Sh2-308 is part of a larger H-II region located near the center of the Canis Major constellation. Gas clouds lying within the Dolphin Head caricature itself are composed mostly of ionized oxygen, which gives it its characteristic blue color. In contrast, the background clouds lying beyond the object are mostly red-colored ionized hydrogen. The Dolphin Head lies about 8 degrees south of Sirius, the brightest star in our night sky.
The most favorable time of year to observe the nebula is between the months of December and April. Its southern declination makes it easier to observe from the Southern Hemisphere, but it may also be viewed from southerly latitudes in the Northern Hemisphere. Relatively faint emissions captured by a special filter in this deep-sky image are dominated by the glow of ionized oxygen atoms. Amateur astrophotographers will frequently "map" the faint cloud to a blueish hue in their photographs when taken with high-power amateur instruments and with the help of a narrow band filter sensitive to the OIII emission line wavelength of light.