Greetings from pissy rainy S Africa, which is why I'm here instead of out at my telescope. You know the feeling.
That out of my hair, has anyone observed a faint streamer which begins at the LMC and trails away into sky dark across Mensa and lower Chamaeleon, to disappear near Tri Austr? It is very dim and I can see it only at my completely non-LP 4500 ft dark site in the Karoo highlands. It gives the LMC a vaguely cometary appearance and looks an awfully lot like a bow shock of the type seen in front of runaway O stars, although much more swept back.
I'm calling it the LMC Streamer for the lack of a catchier title. I don't see it directly adjacent to the LMC because of the LMC's own luminosity, but immediately past the area around the Mensa globulars (see att'd pic) the southerly portion is about the brightness of the gegenschein. The northerly portion disappears before Chamaeleon. I don't think this is an averted imagination object because I see it on any good night and have been observing it for two years since Timo Karhula first described it in a CN post.
I've attached several images. The first is derived from an IIS image by Andrew Lockwood; it emphasises the bow shock close-in to the LMC. (Annotations are mine, sorry about the mess, Andrew.) The second is by Troy Casswell, also an IIS shot, which I had to invert and considerably enhance so it shows the view I see on the sky. The third image is from a professional paper (
Andrew Fox et al 2014 APJ 787:147, non-paywall version on arXiv) which shows a feature called the Leading Arm (again my annotations).
This so-called LMC Steamer is the only visual feature in a vast complex of atomic HI and molecular Ha emission which envelopes the entire MC region and leaves visual tracers as far-ranging as 180 degrees across the galaxy to end near Cygnus. The biggest is the Magellanic Stream, which is an ionisation trail streaming backwards from an LMC-SMC interaction (some say direct hit) some 300 Myr ago. Current MC theory has it that the collision altered their mutual path slightly and set the pair on a course to punch through the outer part of our own MW halo some 50 to 100 Myr in the future. We can't see anything of this gigantic Magellanic Stream because it emits only in HI 21 cm bands. Too bad, if we could see it the spectacle would be brighter and bigger than the MW.
The second main MC emission feature is the Magellanic Bridge, which is a tidal stream of stars and gas torn loose from both galaxies and stretched like a rubber band between them. It doesn't have anything to do with the Streamer feature except that it is a case study in the fact that sizeable numbers of stars (and even some 40 star clusters) can be born in deep space simply from gas ripped loose from a galaxy's HI halo. It's kind of bracing to realise that the Magellanic Stream has the total mass of nearly one billion suns and the Magellanic Bridge grabbed enough gas to make several thousand stars out there in the middle of nowhere. Where do they hide all this stuff when they're not trading punches with each other?
This is all so exciting you must be on the edge of your chairs.
This feature I'm seeing is more important than it looks. It is visible to us, and the only Magellanic collision remnant that is. The Streamer lies amid or on top of the third remnant of the Magellanics interaction, a purely tidal feature called the Leading Arm. The Leading Arm is more complex than the others, with three major components well removed from the near-LMC light band that I see. The Leading Arm nearest the LMC is broken into three clumps. These clumps have a granular character (see the third image). That is quite different from the filamentary character of the other two. Filamentary structures usually imply the influence of magnetic fields, which tend to compress gas into streamlined threads called flux tubes. Flux tubes play a major role in star formation by holding gas collapse at bay until they weaken and enable rapid gas cloud collapse. Granular structures, on the other hand, imply chaotic local turbulence. The turbulence may be energetic enough to cause light emission from non-hydrogen atoms which are part of pretty much any galactic gas body. My emission suspects are the paired Silicon IV bands in the optical violet at 408.9 and 411.6 nm.
Hence the importance of visual corroboration of the Streamer phenomenon I see. This region has not been closely examined using quasar absorption detection described in the Fox 2014 paper. The Streamer, if it exists as I see it, may thus be of some use to the professionals.
To give you some pointers on what to look for, have a look at the attached image by Troy Casswell. The LMC bow shock is clearly marked. Notice how it weakens in the sub-Mensa region, then lightens and broadens abruptly between Mensa and Chamaeleon. Then it goes dark. There are hints at the very bottom of the image near Chamaeleon that it may be brightening again. The luminosity in this image is about times brighter than what I see visually.
The bad news for me is that I do not see the two emission streams to the W and SW of the LMC (marked on the pic). I should see them, but I don't.
Hence I would appreciate your observations, yea or nay, whether you can see this thing. You don't need a telescope, but you do need the darkest skies Oz has to offer.
I'm going to look like an idiot if you come in at 100% nay. I'll sell all my telescopes and take up butterfly chasing. In S Africa they have nice, safe buildings with free food for people who run around chasing butterflies when it's pitch dark.
You can always send me some clear skies as a consolation prize while I chase the butterflies. Sooner would be nice so it doesn't come to the big guys in white jackets point.
=Dana in S A
