Universe Today Astronomy Picture of the Week: NGC 3199 – The Interstellar Snow Plough

One thing is certain, Wolf-Rayet stars produce some interesting
science. In this week’s portrait we see a distorted bubble produced
by a moving star blowing a strong stellar wind into a surrounding
uniform interstellar medium – yet is isn’t uniform. What exactly is
going on here?

Hanging out some 11,736 light years away in the southern constellation
of Carina (RA 10:17:24.0 Dec -57:55:18), NGC 3199 is classed as a
diffuse nebula or supernova remnant. Discovered by John Herschel in
1834, it has been known throughout historic astronomy observations as
bright, large, crescent-shaped nebula with embedded stars, but modern
astronomy shows it as much more. It’s being pushed along by
Wolf-Rayet star 18.

Says Dr. Michael Corcoran: “Wolf-Rayet stars (named for their
discoverers) are very large, massive stars (stars which are about 20
times bigger than the sun) nearly at the end of their stellar lives.
As these stars age, material which the stars have cooked up in their
central nuclear furnaces (like carbon and oxygen) gradually reach the
surface of the star. When enough material reaches the surface, it
absorbs so much of the intense light from the star that an enormously
strong wind starts to blow from the star’s surface. This wind becomes
so thick that it totally obscures the star – so when we look at a
Wolf-Rayet star, we’re really just seeing this thick wind. The amount
of material which the wind carries away is very large – typically, a
mass equivalent to that of the entire earth is lost from the star each
year. The mass loss is so large that it significantly shortens the
star’s life, and as you can imagine has important effects on the space
surrounding the star too. We think that very massive stars become
Wolf-Rayet stars just before they explode as supernova (though no one
has yet seen such a star explode).

At magnitude 11, NGC 3199 is observable with larger amateur
telescopes, but the crescent shape is cause for study by some of the
finest research telescopes and astronomers in the world. Through
optical observations, the ring nebula and cavities around WF stars have
painted a history of mass loss in these highly evolved stellar
curiosities. By studying molecular gases associated with Wolf-Rayet
stars, it appears that some materials seem to be avoiding optical
emission.

In reading scientific reports submitted by A. P. Marston, molecular
gas has already been observed around Wolf-Rayet Star 18 – the first to
confirm the presence of HCN, HCO+, CN, and HNC and molecules. This
makes the Wolf-Rayet ring nebula NGC 3199 very unique and filled
associated molecular gas that took the form clumpy ejecta and
interstellar material. At one time, NGC 3199’s formation was believed
to be caused by bow shock, but current data now shows the associated
Wolf Rayet star is moving at a right angle to its enveloping
environment. Could this be an indication that something else is at
work here? Astronomers seem to think so.

According to their information, it is possible the northern area of
the optically bright nebula is being torn apart by a possible blowout
of Wolf Rayet wind. This, in turn, affects the surrounding ejecta and
could very well account for the observed velocity. By modeling
molecular abundances, the central Wolf Rayet star could be contributing a
portion of its material to this nebula as ejecta. Despite its still
unsolved mysteries, NGC 3199 is a stunning portrait. J.E. Dyson and
Ghanbari summed it up best when they described it as an “interstellar
snow plough”.

This week’s awesome astronomy picture is the work of Ken Crawford, taken at Macedon Ranges Observatory.

Says Ken: “This image was taken using an Apogee CCD Camera that uses primarily Narrow Band data which is color mapped mixed with RGB for natural star colors and back ground balancing. The bright blue area shows lots of OIII (ionized oxygen) signal which really shows the direction of the star movement well. The star is said to be moving at about 60 km/s through the interstellar gas.”