The Eridanus Bubble, the Western counterpart of Barnard's Loop

My first post here on this exciting new Forum!


The Eridanus Loop is a huge HII bubble east of Orion and possibly an old SNR. It is known also as Sh2-245. It is suspected to be connected to much brighter Barnard's Loop (Sh2-276) in Orion, forming together the Orion-Eridanus Superbubble.
This picture shows nicely, how this is all connected, to the left is Barnard's Loop and to the right the Eridanus Loop. Here is another nice picture by Axel Mellinger. As you will notice, the Eridanus Loop is considerably fainter than Barnard's Loop. And this is the reason I always thought that this a photographic object only. But it isn't :cool:



http://www.reinervogel.net/artikel/I...chartsmall.jpg

Here is a bigger finder chart.



December 26th of 2012, we had dense fog in the valley and clear sky in the mountains of the Black Forest. The transparency was, however, only moderate, certainly not the best conditions to tackle borderline objects. From Aldebaran it is an easy starhop down to nu Tauri and then you are already there. The brightest part of the Eridanus Loop appears to stretch over 10° (!) in N/S direction, being about 20 to 30' wide. The overall size of the entire Loop is around 20°!


Using my 22" Dob with 7mm exit pupil and H beta filter (Lumicon), I was sweeping over the Loop at different locations along these 10°. And at every one of these locations, the HII emission was visible as a very faint milky band. Two friends of mine, Thomas and Andru, confirmed this observation. The part with the highest contrast appeared to be about 2° South of nu Tauri, directly W of a distinct Y-shaped asterism.
This was much easier than anticipated, in particular under these less than optimal conditions. So we were looking for a challenge.

Thomas had brought along his 100mm binoculars, equipped with H beta filters. With the knowledge of where to find the brightest stretch from the previous observation with the 22", we (or at least I :-) ) were able to locate it also with 100 mm aperture as an extremely faint band. For a comparison, we switched to the brightest part of Barnard's Loop (the S-shaped part NE of M78), which was quite a bit brighter than the observed part of the Eridanus Loop.


While Barnard's Loop is in general not difficult even with my 80mm finder and UHC filter, the Eridanus Loop needs some more aperture and/or better skies. Under regular rural skies (6m5) and H beta filter, 100 mm could be already close to the minimal aperture. Of course, both the Eridanus and Barnard's Loop profit tremendously from perfect sky conditions, but do not strictly depend on it. To me this was the biggest surprise, in particular for the Eridanus Loop.


There is another report of the Eridanus Loop by Dave Riddle using an OIII filter. I haven't thought of using the OIII filter as I suspected the loop to be a classical H beta object.




http://www.reinervogel.net/artikel/I...rtErismall.jpg
Finder chart of the Eridanus Loop (bigger chart)




http://www.reinervogel.net/artikel/I...rnardsmall.jpg
Finder chart for the brightest part of Barnard's Loop (bigger chart)

Reiner,

WELCOME to Deep Sky Forum. What a fantastic first report:)

With the help of people like you we can make this a special place for Deep Sky Observing!

Unbelievable report Reiner and thanks for taking the time to post it.
I'll add the Eridanus Loop to my list of objects to shoot after during my trip to Ft Davis next month.

Thanks!

Great report Reiner. As with Dragan, I also can't wait to see this object. Would look tonite - but since I am in Chicago I don't think I would see much!

Reiner,

Welcome to Deep Sky Forum. This is an awesome observing report. Thanks for sharing it. I wasn't aware of the Eridanus Loop. I'm going to add it to my observing list and give it a try with my 15" Obsession. Just need for the temperatures to warm up some and for the clouds to part.

Hope you have reports on other off-the-beaten path objects that you'll share on DSF.

Clear skies,

Mark

Reiner,

Thanks much for the charts. I've added them to the one I had for last year's Winter Star Party. Unfortunately, uncooperative weather and time spent taking observing requests kept me from getting to the Eri Loop. If I get it this at WSP later this month, I'll be sure to post the observation.

Sue

Thanks Reiner for the heads up on this object. Looks like I should give it a shot!

After years of failed attempts, last night, along with Mauro and Luca, I am finally able to see the brightest part of Barnard's Loop, I am referring in particular to the zone between M78 and 56 Orionis.
Of course I used my little dob 14" with 56 magnification and H-beta filter (6,2 mm exit pupil ), the mirror have now a new coating, SQM 21.45 at 1800 meters above sea level.
It was a very exciting observation.
Ciao!

Observations of the Orion-Eridanus Super Bubble, SH2-245, SH2-264 and the southern arc of Barnard's Loop

Mel Bartels, February 2015

http://bbastrodesigns.com/SH2-245/Th...%20Bubble.html


I've been keen to observe SH2-245, part of the Orion-Eridanus Super Bubble, ever since I read about the nebula on the AmAstro discussion group. I got my chance Tuesday night, February 17, 2015.

I set up my 6 inch [15cm] f2.8 and my 13.2 inch [34cm] f3.0 side by side and settled into views of the Orion Nebula as my eyes dark-adapted. Soon I was able to see Barnard's Loop to the east of the Orion Nebula and faint Milky Way dust to the west.

The two scopes proved a lethal combination of super wide field, 4+ degrees in the 6 inch, and lots of aperture with a 1.8 degree field in the 13.2 inch.

The Horsehead was visible without a filter in the 13.2 inch and on the edge of visibility in the 6 inch. With a H-Beta filter in the 13.2 inch, the Horsehead stood out nicely with the Flame Nebula and Zeta Orionis in the same field - very attractive. My new SQM read 21.1 while my older model read 21.3. Not the best of nights but I take what I can get.

After review of images of SH2-245 (I started with LBN 839 without much results until I found it in the Sharpless catalog at approximately 4hrs RA, 4 deg Dec), The images suggested that this nebula was tad dimmer than the nebula enveloping Lambda Orionis, SH2-264 and Barnard's Loop. I've seen both nebula with the 13.2 inch with some margin to spare, so I had hopes. Of course, one never knows - sometimes the object is visible and sometimes it just cannot be seen.

Finding this object was one of the easiest star hops I've encountered. Nu Tauri is an easy hop from the Hyades open cluster. It has a companion star visible to the unaided eye. A short distance below is a fainter pair with magnitude 5.3. I aimed my 13.2 inch at the fainter pair which according to deep digital images was adjacent to the brightest portion of SH2-245. There it was! Instantly visible as a bright streak, there was no need for averted vision or studying the field carefully until whatever nebulosity present slowly comes into conscious view.
Attachment 1526

I returned to the 6 inch and was rewarded with an obvious streak, though not as bright. I followed the streak northward as it expanded in width and then followed the streak southward for 10 degrees. Dimmer, but still visible, I could trace the nebula through a split that looked like a 'Y'. The east end faded into the background, while the west end faded into the Zodiacal Light. SH2-245 is also called the 'Fishhook Nebulae'.
Attachment 1527

Observations by others can be found at http://www.deepskyforum.com/showthre...Barnard-s-Loop and http://www.visualdeepsky.org/logs/msg03151.html.

I returned to the top of Orion and sketched another nebula, SH2-264 with some detail and dark regions using the 6 inch. I could fit two-thirds of the nebula into a single field of view. Not quite as detailed as the view through the 13.2 inch, but much more of the nebula viewable at one time gave a more satisfying view.
Attachment 1528

Curious, I swung south below M42, the Orion Nebula and was able to pick up the southern arc of Barnard's Loop.
Attachment 1529

I tried an H-Beta filter on all these objects. It dimmed the field but didn't really enhance the contrast much.

At this point I went through the dew point with moisture accumulating on the telescopes. The SQM indicated deteriorating conditions and soon the sky was fogged over.

A satisfying evening that left me with the desire to observe more of the 'Y' portion of SH2-245 under better skies. Next time!

eod

Last night I set up my 71 mm WO ZenitStar at Hotel Pachon next to the Rubin Observatory construction site. My work comes with some privileges occasionally :) Anyway, I used a 35 mm Panoptic eye piece (12x, 5.7º FOV) with a new 2" Lumicon H-Beta filter to observe Barnard's Loop in its entirety from the northern part down to the southern part beyond Rigel. I was surprised about how wide it seemed: the arc was over a degree wide!

M 42 and IC 434 (together with NGC 1975/7 and NGC 2024) were visible together in a single FOV.

I tried to see the Eridanus Bubble near and south of Nu Tau but unfortunately didn't see anything at all.

My SQM gave values between 21.65 and 21.77 and I had the feeling that the sky was a tad hazy. Jupiter wasn't as crisp as I have seen it there and there definitively was some murk over the western horizon. I'll try again with my 94 mm refractor as soon as I have the chance.

The Eridanus Bubble is much more difficult than Barnards Loop Wouter.

I gave the brightest streamer (Sh 2-245) a go some years ago. I had no chance with a small binocular (8x30, 8.8° field, Hß) but finally succeed with my 4-inch binocular telescope which gave me 5° field.

All in all I had the impression that aperture also rules here. So with your 94mm (f/5.5, 4,5° field?) you surely have more chances to see the bubble.

sketch: 4" binocular, 14x, Hß, NELM 6m5+
Attachment 4928
home

Thanks for the encouragement Uwe!

My 94 mm indeed is an F/5.5. I also have a 31 mm Nagler which would yield a slightly higher magnification (and therefore smaller exit pupil) but also a slightly larger FOV. I'll try both as soon as I have the chance to see which one works best.

This paper, trying to come with a better formation history of Barnard's Loop, appeared on ArXiv today:

https://arxiv.org/abs/2212.01405

Re: A 3D View of Orion: I. Barnard’s Loop

This is a very interesting article, offering some new insights into the astrophysics of the Barnard's Loop area.

Thank you for sharing,
Jiri