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.