May Challenge Object - NGC2359

[iceman (Mike)]

Hi all.

We'd love you to take part in the May Observing Challenge. Please post your observing reports and sketches for NGC2359 in this thread. Discussions about the object can also be in this thread.

Please ensure scanned sketches obey the image posting guidelines when you attach them.

For deep-space images of the object, see the "Deep Space" astrophotography forum.

[iceman (Mike)]

I'm going to update the notes for this one, to suggest that it be one of the first you tackle this month, and make sure you get to it early in the evening.

Canis Major is setting fast, so this will be the last chance you get to observe Thors Helmet this year.

[hector (Andrew)]

I dont know if anyone here reads Sky and Space but i have an article on Wolf-Rayet stars which included Thors Helmet.
Some of you may find it useful if you can track it down.
Andrew

[hector (Andrew)]

I dont know if anyone here reads Sky and Space but i have an article on Wolf-Rayet stars which included Thors Helmet.
Some of you may find it useful if you can track it down.
Andrew

[ausastronomer (John Bambury)]

Andrew,

That article appeared in the Nov/Dec 2004 Issue on page 72. It was a very informative piece BTW.

CS-John B

[Astroman (Andrew Wall)]

I saw this with a Nagler EP at a dark site, haven't been able to track it down again from my backyard

Easy to see with a UHC filter though.

[hector (Andrew)]

HD56925 is the WR star that has created the nebulae NGC2359 known as Thor’s helmet. William Herschel discovered the nebulae in 1785. The nebulae complex is about 30 light years across and is 15,000 light years distant. The WR bubble is located inside a neutral hydrogen cloud and is interacting with this cloud. The expanding shock front and the intense radiation from the WR star has given the hydrogen cloud the energy to fluoresce. The WR bubble contains 20 solar masses of stellar material.
This is a great visual object and can be glimpsed in a 5” scope as a faint haze around the WR star, which appears to be about 12th magnitude. It is actually quite a challenge for scopes of this size. A 12” scope gives a good view of the nebula showing a partial ring around the WR star. This arc of nebulosity is on the western side about 1’ from the star. The arc is about 3’ long and 30” wide. Also visible is the southern arm giving the nebulae an inverted p shape. The arm appears to be 1’ wide and 3’ long. This arm gives the overall complex an apparent size of about 6’. It is with the 20” that the nebula really stands out. Without a filter using a 16mm Nagler at 159x the first thing I notice in the eyepiece is that the WR star appears to be offset from the middle of complete ring of nebulosity. This offset is only slight and is to the west. The ring is brighter to the west where it appears well defined against the background sky. The nebula is more diffuse as it swings around to the south and east loosing some of its brightness. The center of the nebula appears to be hollow making it look like a doughnut. The bubble is about 3’ across. To the south the arm is very bright and has a higher surface brightness than the rest of the nebula. It is 1’ wide and 3’ long with a well-defined southern edge and is pointed to the southwest. A star of 11th magnitude lies at the joining point between the bubble and arm to the south. The Northern arm is barely visible and can be traced for only 1.5’. Several stars of 13th magnitude and fainter lie scattered across the field of the eyepiece. Using a UHC filter changes the view dramatically. The ring structure around the WR star is now completely shaded with nebulosity, although the central portion is quite faint and diffuse. The portion of the bubble to the northwest is the brightest near a line of 3 stars of 12th magnitude. The arm to the south is definitely the brightest section of the nebulae and now extends to just on 6’ long. The extended portion of the arm is much fainter and changes direction slightly to point almost due west. At it’s widest this arm is now 1.5’. The northern arm is now visible without averted vision and appears to be about 5’ long and slightly narrower than the arm to the south. It is more diffuse than the southern arm extending to the northwest. Changing the eyepiece to a 32mm widefield and using an [OIII] reveals a much fainter envelope of nebulosity surrounding the WR bubble. This envelope appears to extend the size of the complex to about 14’ across. The brightest portion of this envelope appears to be an extension of the northern arm on the eastern side of the bubble. This extended arm appears to be 4’ long. Also noticeable in the halo is a dark lane orientated east west just to the north of the extended arm.

[dhumpie]

Hi Guys,

We (Andrew durick_astro_south) and I hunted this down from Mark's place at Glenore Grove on Sat. Nice views through Andrew's 12.5" and we could clearly see the hollow in the middle and the arm which gives it the "Thor's Helmet" or P shape to it. I tracked it down in my C6 (6"f/5) as well and sketched it at 61x (Meade 24.5mm SWA and 2x Orion Shorty barlow). Will scan my sketch when I have the time and upload it here. The P shape was still apparent in the 6" (with the UHC of course) and i was amazed by how much detail i could see in the 6". The brightness was almost the same and the overall shape apparent. The difference was in the intricate detail seen in the 12.5" that was not visible or less apparent in the 6".

Darren

[astro_south (Andrew)]

To add on from Darren's comments - the view with and without the UHC is markedly different. The nebula is visble in the 12.5" without the filter, but the filtered view reveals the helmet shape very clearly. The conditions weren't ideal with some high level cloud so I didn't explore a range of magnifications. I used a 13mm T6 Nagler for 147x and this framed the object nicely. I will certainly return to this object at the next opportunity to try out different magnifications and for a longer inspection.

Thanks to Mark (Hodson) for supplying the observing site and for printing out a finder map when scans in the general area (from memory) failed to locate it