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NGC 2403

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#1 Starman1

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Posted 14 January 2013 - 01:28 PM

On Saturday night I had a good view of this object through my 12.5".
Here are some specs:
constellation--CAMELOPARDALIS
type--GAL
designation--NGC 2403
alternate designation--UGC 3918
RA---07 36.8
DEC---+65 36
Integrated Magnitude--8.5
Average surface brightness--14.4
Max size--23.40
Min size--11.80
Type--SBc
Distance--11mly

This object is amazing. Most of what you first see is the central core and bar, though it's not obviously a bar but resembles an elliptical shape with a brighter center and "flocculent" remainder (mottled and filled with darker areas).

But this night (SQM of 21.5, or NELM approx, 6.8), with the galaxy culminating, the oval structure appeared to terminate in curved arcs in opposite directions, as if you were seeing a very distorted edge-on or the start of spiral arms leaving the end of the bar.

What struck me was how FAT the central bar was--it made me think the spiral arms were going to leave the field of view (think NGC 1365 where the arms leave the bar at nearly a 90 degree angle).

Continued observing at different magnifications and use of averted vision rewarded me with a view of one spiral arm and about half of the other main arm. I couldn't believe how tight they were to the bar! They were so close to the bar that the oval shape was only widened about 50% by seeing the arms. This barred spiral must be being viewed at a substantial angle for the structure to appear so "squashed".

Now, definitely one arm was significantly brighter than the other. Pictures show this and even show a messier (pun intended) structure than what I saw.
And it doesn't help that there are so many superimposed stars on this galaxy, one of which might have been an HII region, NGC2404, in one of the spiral arms.

This is a spectacular object, and I'd love to see it in a much larger scope under similarly dark skies. I'm definitely going to revisit the object, and I encourage everyone to check out what you can see of it.

Link: http://ngcicproject....s/dss_n2400.asp and choose "NGC 2403 Data" under the top text.

#2 blb

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Posted 14 January 2013 - 02:29 PM

Don, you list this as a bared SBc galaxy, but the NGC/IC project web page lists it as a Sc III galaxy. How do you determin which type of galaxy it really is?
:question:

#3 Starman1

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Posted 14 January 2013 - 03:25 PM

Well, I found several classifications on the web. The one I have came originally from the SAC list.
NED lists it as SAB(s)cd, and 8 million light years.
SIMBAD lists it as ScD and 10.1 to 13.4 million light years.

Most web listings are SAB, in between spiral and barred spiral.

The NED classification is from Vaucouleurs and refers to:
SAB--intermediate between Spiral and Barred spiral
(s)--features show no ring and a normal spiral pattern
cd--slight irregularity to the shape so not a pure "c"

I think SIMBAD has an older listing in classification, but shows multiple determinations of distance, so may be more accurate for distance than NED.

I should change the classification in my List and in my post to read:
SAB(s)cd

#4 IVM

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Posted 14 January 2013 - 03:56 PM

This is a very complex object, one arm segment in which was already described by Herschel. Like you, I am looking forward to reobserving it soon. In particular I want to study more the area of the Hodge star associations 35 and 41, which seemed detectable but confused last time I saw this galaxy: http://ivm-deep-sky....1/ngc-2403.html

#5 uniondrone

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Posted 14 January 2013 - 05:21 PM

Good object. I observed it for the first time a couple of months ago. The central core does a good job of cutting through light pollution, so it is a decent suburban object as well. It seemed brighter than a lot of Messier galaxies to me.

#6 jeff heck

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Posted 14 January 2013 - 07:05 PM

Sounds like another early morning into the galaxies of Leo, Don. Thanks for the link showing the images. I have a two night trip to the dark skies of Kansas tomorrow and Wednesday night, I will add 2903 to the list. :grin:

#7 Starman1

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Posted 14 January 2013 - 08:50 PM

Sounds like another early morning into the galaxies of Leo, Don. Thanks for the link showing the images. I have a two night trip to the dark skies of Kansas tomorrow and Wednesday night, I will add 2903 to the list. :grin:

No, not 2903 in Leo (great in its own right), but NGC 2403 in Camelopardalis.

Coincidentally, though, 2903 is a barred spiral SB(s)d, so a more classical bar and spiral pattern with a little more irregularity than NGC 2403 in CAM.
Hey, if you're going to be up all night, try 2903 too.

While you're at it, if you time it right, NGC1365 could be viewed crossing the meridian earlier in the night. It never ceases to amaze me. It took 12.5" to show me the spiral arms, but what a classic barred spiral. In pictures, it reminds me of the Greek letter Theta. http://apod.nasa.gov...d/ap121124.html

#8 jeff heck

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Posted 14 January 2013 - 09:42 PM

My mistake, Don. I have been looking at observing books the last few days planning my trip, I have ngc numbers showing up in my breakfast cereal. :grin:
I was in Kansas two weeks ago and tried for NGC1365 as the southern horizon there is great but a low fog rolled in making my cemetery observing site look like a "B" movie set. "Plan 9 From Outer Space" comes to mind.

#9 Tony Flanders

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Posted 15 January 2013 - 05:46 AM

Steve Gottlieb has an article on NGC 2403 in the March issue of Sky & Telescope. He also talks about its exotic companions NGC 2366 and Holmberg II.

#10 Scanning4Comets

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Posted 21 January 2013 - 12:47 AM

I saw this galaxy a long time ago, and revisited it in 2005. I thought it was really bright when I first saw it in a 10". I'm going to re-visit this galaxy again!

Thanks for the great post Don!

Cheers,

#11 David Knisely

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Posted 21 January 2013 - 01:26 AM

This one has always been one of the easier galaxies for me to pick up, but it never has shown much of a "grand design" spiral form. At best, it is a somewhat diffuse oval with a brighter inner oval inner core region and a somewhat patchy outer haze (10 inch Newtonian at 100x). There is a somewhat darker area just north of the core and a number of very faint patches around the outer haze, but nothing that really says "spiral" all that well. Certainly I don't see any real hints of bar-like structure in it. Maybe that will change once it warms up a bit and I can try it in my 14 inch Newtonian. Clear skies to you.

#12 Starman1

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Posted 21 January 2013 - 01:56 PM

David,
The large oval area pretty much IS the bar. Coming off the ends are spiral arms. One of them is easy to follow into the "hook", while the other is exceedingly faint. The two major spiral arms are very tight to the bar, as if taking NGC1365 and tipping it until it is almost edge-on.
So if you see a fairly elongated oval, you're seeing the bar. If you're seeing a fairly fat oval, you're seeing the spiral arms too and then it's a matter of making out the gaps between the bar and spiral arms.
what was interesting to me was how clumpy and mottled the bar was.

short exposure: here
and long exposure: here
Note that some of the superimposed stars are HII regions in the galaxy.

#13 stevecoe

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Posted 21 January 2013 - 03:27 PM

Don, David, et al;

Here is an observation with a 13 inch Newt on a great night:

NGC 2403 13.1" f/5.6 S=7, T=9 Bright, large and elongated 1.5X1 in PA 135 degrees at 135X. This object is bright enough to be seen with the 11X80 finder scope. There are several stars involved with faint spiral structure in the outer sections in this lovely galaxy. The middle is gradually much brighter. From the darkest sites, the spiral arms of this galaxy shimmer and sparkle with mottling.

The drawing is with the same scope.

Clear skies;
Steve Coe

Attached Files



#14 Bill Weir

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Posted 22 January 2013 - 12:18 AM

David,
The large oval area pretty much IS the bar. Coming off the ends are spiral arms. One of them is easy to follow into the "hook", while the other is exceedingly faint. The two major spiral arms are very tight to the bar, as if taking NGC1365 and tipping it until it is almost edge-on.
So if you see a fairly elongated oval, you're seeing the bar. If you're seeing a fairly fat oval, you're seeing the spiral arms too and then it's a matter of making out the gaps between the bar and spiral arms.
what was interesting to me was how clumpy and mottled the bar was.

short exposure: here
and long exposure: here
Note that some of the superimposed stars are HII regions in the galaxy.


One of them is a Super Nova too. It was a really bright sucker. I was able to detect it in as small as 70mm refractor/spotting scope. That was back in early August 2004.

I've always enjoyed this galaxy with my 12.5". If I remember the next time I'm out I think it might deserve a return visit with the 20.

Bill

#15 David Knisely

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Posted 22 January 2013 - 01:56 AM

David,
The large oval area pretty much IS the bar. Coming off the ends are spiral arms. One of them is easy to follow into the "hook", while the other is exceedingly faint. The two major spiral arms are very tight to the bar, as if taking NGC1365 and tipping it until it is almost edge-on.
So if you see a fairly elongated oval, you're seeing the bar. If you're seeing a fairly fat oval, you're seeing the spiral arms too and then it's a matter of making out the gaps between the bar and spiral arms.
what was interesting to me was how clumpy and mottled the bar was.

short exposure: here
and long exposure: here
Note that some of the superimposed stars are HII regions in the galaxy.


The problem is that the core is not elongated enough to really justify calling it a bar. The aspect of the galaxy (61 degree angle of inclination) is such that it should be easy to see any bar-like structure. I see little indication of such. In fact, many of the sources I see on the object classify it as Sc, which I would tend to agree with. The object does show a lot of faint mottled structure including a bit of a linear patch west of the core, but in my 10 inch, the detail never seems to quite join up into a full continuous spiral the same way that M101 tends to do on a really good night. I may revisit this one in my 14 inch, but I am not holding out much hope that doing this will change my view of what type of a galaxy it appears to be. Clear skies to you.

#16 Dave Mitsky

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Posted 22 January 2013 - 03:26 AM

One of them is a Super Nova too. It was a really bright sucker. I was able to detect it in as small as 70mm refractor/spotting scope. That was back in early August 2004.


SN 2004dj was a good one. It got as bright as 11th magnitude.

http://www.rochester...004/n2403s1.jpg - amateur image

http://hubblesite.or.../2004/23/image/ - HST images

Dave Mitsky






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