Observing M101 and a question about star forming regions

[josefk]

This is not exactly an observing report though there are observations, I'm using this post to actually ask a question about observing spiral galaxies and HII star forming regions within them...

A couple of weeks ago i was observing NGC 2903 (with 185mm of aperture) with the express intent of trying to see NGC 2905 within it. I used exit pupils between 1.3mm and 0.6mm (!) with magnifications between x140 to x305. I'm not convinced i observed NGC 2905 but my observing notes for NGC 2903 are:

Seen in all EP’s. All EPS used to try and tease out NGC 2905. Some bright (stellar) spots seen but i don’t think NGC 2905 conclusively. A rough edged and patchy “smudge” with bright soft stellar spots.

This is the eyepiece sketch (unfortunately the bright bits are not correctly located to actually be NGC 2905 in this case 😞)

 

This week with 85mm of aperture and using an exit pupil of 1.5mm (predominantly) and a scale of x56 i observed and sketched M101 like this:

Notes:

Easy find starting at Mizar, (STF 1831 & STF 1831 on the way).

Took a while for it to first reveal itself as an averted vision smudge. Disappeared with any use of red light either to navigate SSP or sketch. Growing dark adaptation brought it more definitely even for direct vision. Large, hazy but with variation in the haziness. at least two stellar points or bright spots within it. No sign of the arm structure. Later returning from M102 with the 14mm in the diagonal it was markedly brighter and more definite.

Sketch:

the tidy version looks like this - it is sketched as i observed it at x56 but in this tidy version i have used the brightness of M101 i could achieve with a 2.6mm exit pupil (x32):

My question is...when we observe nearly face on spiral galaxies and see brighter lumps and bumps are they brighter parts of the galaxy i.e. dense star concentrations and/or (if they are in the right place) even the NGC star forming regions (eg. possibly NGC 5461 at 8 o'clock within M101 above) or is it something else at play? Maybe a foreground star or stars perhaps or even "just" the core of the galaxy that we are not seeing as centrally as we possibly would in good conditions? With averted vision it is not easy to be precise with the exact location of these "bright" spots... 

Its unfeasible for me that i could see a Mag14 NGC within the Mag7.8 M101 with 85mm of aperture though i know that it can be funny how surface brightness works for concentrated objects.

I'd love to hear the thoughts of experienced observers.

Cheers

 

[josefk]

to add another perspective, @cfinn has kindly allowed me to degrade (desaturate) and annotate his recent picture of M101:

 

If i really was picking up for example NGC 5461 within M101 in that lower arm then the nearby galaxies NGC 5474 and NGC 5473 would have been positively jumping out at me (as out of focus "stars") wouldn't they? They weren't and didn't!

Edited May 2 by josefk

[Nik271]

Dear Josef,

 

I think you probably saw NGC2905, it looks to be the bright spot northeast of the core , as in your sketch:

 

 

Herschel saw NGC2903/05 as a 'double nebula' and  most sources identify 2905 with precisely this region, as in this photo:

https://www.wikidata.org/wiki/Q2080000#/media/File:NGC_2903_SDSS.jpg

 

 

 

 

 

 

 

 

[josefk]

Thank you @Nik271 - i have higher confidence to go after NGC 2905 again then for a definitive "tick" with a carefully prepared red light readable map i think.

With M101 sadly i think i have answered my own question with a bit of further reading - any bright spots i would see with my aperture could only be foreground stars x wishful thinking 🙂 

Never mind.

 

[John]

I missed this report - very interesting 🙂

The only star forming region in another galaxy that I've seen without question is NGC 604 which lies within Messier 33. I've seen that often when I had a 12 inch scope and from time to time with smaller scopes, down to 100mm in aperture. A fuzzy spot close to a foreground star a little distance from the core of M33. Apparently this nebula would be humungous for us to observe if it lay within our galaxy, far exceeding Messier 42 in extent and brightness.

Seeing a DSO in another galaxy is an exotic and exciting observing challenge in my book 😀

@Nik271 started a good thread on this one last year:

 

Apologies for the diversion from M 101 !

 

[josefk]

3 hours ago, John said:

seeing a DSO in another galaxy is an exotic and exciting observing challenge in my book 😀

A galaxy alone is wondrous enough but yes it is an exotic and exciting challenge to try and observe something else within such massive structure that far away. I 100% agree. 

I failed with NGC 604 at the time of Nik's thread last year but that thread and my trying (because of that thread) coincided with a bad run of weather so i was always behind my smallest (GnG) scope trying for it at that time. I certainly learnt the star field in that area really well while attempting it and i think i know exactly which foreground star you mean! I've been conscious to try again this spring but M33 had swung around and gotten quite low by the time my opportunity evenings had gotten dark so while conscious of it i haven't actually tried for it since that thread. I will do again though this autumn.

With these challenge objects (challenge always being relative to whatever kit you are using in whatever sky) i am very conscious to try not to fool myself. 

I go out bird spotting and if i wouldn't bet my house on a bird ID i don't count it - i'm the same at night with astro - i don't want any asterix next to items in my observing log. I will go back to NGC 2905 above for example "to be sure".

i think the ones in M101 could be reachable with a good night and maybe 10" aperture - possibly also with O-III or UHC filtering to shake them out. I WILL be trying those again too 🙂 .

I think you could probably create a list of ten or a dozen extra galactic objects that are difficult enough to be very cool and satisfying to observe but that are not so difficult to need a 36" scope half way up a mountain somewhere.