VY CMa nebula [Archive] - Deep Sky Forum

Steve Gottlieb

May 29th, 2016, 04:06 PM

VY CMa is both a unique star and a pretty cool nebula!

I've observed the nebula several times and wrote about this object in the March 2012 Sky & Telescope Going Deep column, titled "Bubbles, Jets, and Exotic Stars", but the nebula was discovered back in 1917!

Here's my text from the S&T article --

"The red hypergiant VY Canis Majoris is one of the largest and intrinsically brightest stars in our galaxy. Roughly 2,000 times the solar diameter, it shines with nearly 500,000 times the Sun’s luminosity. VY CMa is encased in a small, irregular reflection nebula consisting of ejected material from earlier, high-mass-loss outbursts. The intriguing visual target is a small tail or jet that has been likened to the Nike “swoosh” logo.

VY CMa appeared slightly fuzzy or soft when I viewed it at 175× in my 18-inch, like a star that won’t focus in poor seeing. Bumping the magnification to 285×, I clearly saw a tiny orange disk surrounding a brighter center, and I was startled to find a short tail extending out from the star. The best view was at 325× — the central star was cleanly resolved within a very small, 4′′ halo, and the attached jet extended about 8′′, curving slightly to the west-northwest. In Lowrey’s 48-inch, the jet appears as a shiny blue-white saber attached to the orange star. At the other extreme, I wonder what’s the smallest scope that can show this tail?"

I first read about the nebula back in 2005 from the late Mike Kerr in Australia. Here's his post on the 'amastro' yahoo group):

"63cm: Readily apparent at low power as a nebulous mag 8 orange-red star. At 450x a fairly bright, 6"-long, curved nebulous tail is seen attached on the SW side of the star and heading NW. The nebula and star have a striking orange-red colour. A faint 10" diameter nebulous glow surrounds the object with the central star offset to the NE and there appears be a larger extremely faint halo, but it is difficult to estimate its size because of the glare from the bright central star. At 900x a brighter, definitely nonstellar spot is seen at the SE end of the arc near the central star at about the location of B 719 B (Bos 719: 7.8+9.1; 0.7" 211 deg 1970). Surprisingly there is a fair gain with a UHC filter, which substantially dims the central star, shows the 10" diameter nebula well and suggests a halo diameter of about 15". Most of the nebula fades with an OIII or H-beta filter leaving just the central star and subdued nebulous tail. Two mag 13 stars are 0.6' SW. Best viewed at 450x or 650x without a filter.

VY CMa is probably the most strikingly orange-red object I have looked at in my 63-cm scope. The nebulous tail is fairly bright and looks a bit like the Nike 'swoop'. If you haven't looked at VY CMa, add it to your observing list. It is definitely a must see.

The earliest note I've been able to find on the VY CMa nebula is in a 1923 paper by C.D. Perrine, "Spectroscopic Notes on Southern Clusters, Nebulae and Red Stars" (PASP, 35, 229). The paper has a section devoted to VY CMa, where Perrine notes that the nebula was discovered by Guerin in 1917 with the 4.8-inch Repsold Meridian Circle. I assume Guerin was an observer at the Cordoba Observatory, where Perrine was the director. Quoting from the paper:

"Senor Guerin described the object as a nebula about 8" x 12", red, tending toward dark red or scarlet; as containing three nuclei, the preceding of which is the brightest and the point which he observed for position. The general aspect is that of a comet, the tail (which is excessively faint) extending to the east (Power 220). With a power of 500 the tail is seen prolonged in a sinuous form to the south to a length of 2', but preserving its red color to disappearance."