Object of the Week June 5th, 2016 - NGC 4236

NGC4236
UGC7306

Draco

Galaxy

RA 12 16 43.3
DEC 69 27 47

Mag 10.1

Size 22.0' x 7.2'

Class SB(s)dm

Discovered by William Herschel on April 6th , 1793, NGC4236 is a large, diffuse barred spiral galaxy located in Draco. Spanning 22' by 7' minutes, don't let the apparent magnitude of 10 fool you. With its large surface area, this galaxy can definitely be a challenging object depending on scope size and sky conditions. One observing tip about this object is that "mo power isn't necessarily mo better". This is an object where lower power is definitely your friend.

My last observation were made with my 25" May of 2015. I noted:
Best view at 185x. NW-SE elongation. Faint and diffuse with brighter core region running length of the galaxy. Star within a few minutes of the core.
With AV, steady mottling throughout with a brightest patch at the SE end.

Though I don't usually write the most detailed notes of my observations, I did notice i made mention of a bright patch at the SE end of the galaxy. During my research for this weeks OOTW, I discovered that Fritz Zwicky had incorrectly mislabeled this star forming region of NGC4236 as an entirely different galaxy. Or did he? Megastar labels this patch as a galaxy but other online sources label it as an HII region. Can someone chime in?

"Give it a go and let us know!"

Attachment 2122
©Bernhard Hubl

I just observed this two nights ago, in 21.42 SQML skies with a 20-inch: " Large, long maybe 6:1 NNW-SSE elongation, low surface brightness halo with a gradually brightening core and a sudden sharp stellar nucleus [which could just be a fortuitously placed foreground star]. Several foreground stars and perhaps fainter non-stellar patches on the SSE tip. Detected with AV and then can hold in DV, there is a bulge in the halo on the SW facing side of the NNW tip."

The "bulge" I find in Aladin using the NED filter are identified as HII regions (the brighter being HK83 16, 17, & 18). One of the brighter "non-stellar patches" on the SSE tip (it is in line with the major axis of the halo) Aladin has as VII Zw 446.

I have an unfinished sketch of this galaxy with my 4" Newtonian (waiting for a clear sky). About 70% of the stars are in place but all the rest is still waiting to be captured. NGC 4236 is visible in the 4" scope under a good sky. I don't remember from last time but I'm sure there won't be many details with such a small scope.

Dragan, I think there is a typo. The author of the attached image is Bernhard Hubl.

Similarly, while in downtown Chicago the bar can be a few minutes from the car (once you find the parking), in this case the star was probably a few minutes from the bar, not "car". Seriously, it's a great target, Dragan. I viewed it just last week again and again was not satisfied with the visibility of the finer features. The night was excellent (SQM 21.78) but I got to this galaxy late, when it was almost even with Polaris. This 10 years after first seeing it with a large scope, a glaring gap in my study of galactic structure.

Nice object Dragan,

there is very much detail possible even with mid size telescopes. I gave it a try several years back with my old 14.5" travel scope and was amazed about the result in the eyepiece.

14-5", 109x-202x, NELM 6m5+
Attachment 2123

Woops!

Actually, my notes read "Core" Correction made.

Thanks Ivan!

And I took care of the photo credit Peter.

Thanks you guys!

Quote:

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Originally Posted by Ivan Maly

Similarly, while in downtown Chicago the bar can be a few minutes from the car (once you find the parking), in this case the star was probably a few minutes from the bar, not "car". Seriously, it's a great target, Dragan. I viewed it just last week again and again was not satisfied with the visibility of the finer features. The night was excellent (SQM 21.78) but I got to this galaxy late, when it was almost even with Polaris. This 10 years after first seeing it with a large scope, a glaring gap in my study of galactic structure.

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Here are notes with my 18-inch from 2008. You can match up the features pretty well with Uwe's sketch!

This huge, low surface brightness galaxy extends roughly 12'x3', oriented NNW-SSE. There is only a very weak central brightening with no obvious core. A very faint star appears to be superimposed near the geometric center and just to the south is a slightly elongated brightening (possibly the core).

Another brighter region is near the north end of the galaxy. This patch seems elongated at 45° to the major axis, appearing to extend out to the west of the main glow on the north end. Images reveal this is a gigantic HII complex and is catalogued in NED as NGC 4236:[HK83] 15, 16 and 17, from Hodge and Kennicutt's Atlas of HII regions (1983AJ, 88, 296).

The south end is also splotchy and at the very south tip are two very faint "stars" that seemed slightly fuzzy. These are also small HII knots, catalologued as NGC 4236:[HK83] 02 and 03. One or both of the knots also carry the designation VII Zw 446, described by Zwicky as a "blue patchy compact [galaxy]".

Quote:

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Originally Posted by Steve Gottlieb

The south end is also splotchy and at the very south tip are two very faint "stars" that seemed slightly fuzzy. These are also small HII knots, catalologued as NGC 4236:[HK83] 02 and 03. One or both of the knots also carry the designation VII Zw 446, described by Zwicky as a "blue patchy compact [galaxy]".

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So Steve, 7ZW446 officially an HII region mislabeled by Zwicky, correct?

NED has multiple entries at similar positions -- one for VII Zw 446 as a compact galaxy and two for NGC 4236:[HK83] 02 and 03 as HII regions. But since Hodge & Kennicutt's classification was based on an H-alpha image of the galaxy, I'd say that's more likely.