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Resolving stars in M31

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#1 george golitzin

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Posted 04 October 2013 - 03:41 PM

Just got the Nov. issue of Sky and Telescope; there's a very nice article on the globular clusters (and some open clusters) of M31, by Alan Whitman. I was most intrigued to read his claim to have resolved individual stars (massive blue giants, naturally) in ngc 206, the great starcloud in the SW area of the galaxy. This in a 16-inch. Has anyone else managed this? What instrument were you using?

-geo.

#2 DavidNealMinnick

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Posted 04 October 2013 - 07:02 PM

After reading the article, I attempted these observations Tuesday night with an 18" f/4.3.

If his description is accurate, I, too, have seen some M31 blue giants wafting in-and-out of view. These are difficult observations, for me.

I will continue to pursue the objects in his piece.

#3 IVM

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Posted 04 October 2013 - 07:51 PM

I too was intrigued and may attempt it next week. One needs to make an accurate sketch and have a catalog of these giants. NGC 206 in my memory is grainy in 16" but it did not occur to me that there was any possibility that these specs were individual stars in M31. I assume for now that they weren't and it will be a lot of work to attempt to prove otherwise. The field, after all, is fairly rich not far from the Cassiopeia Milky Way and OB giants in associations (which is what NGC 206 is) tend to form starlike clumps; a recent example I looked at was the stellar core in one of the associations in NGC 6822. But I do intend to spend a lot of time on M31 this season with 16 or 12", so who knows how it may turn out. The observations reported in the S&T article were great and wish they had more space to elaborate in particular on these observations of blue giants.

#4 hokkaido53

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Posted 04 October 2013 - 07:59 PM

Just got the Nov. issue of Sky and Telescope; there's a very nice article on the globular clusters (and some open clusters) of M31, by Alan Whitman. I was most intrigued to read his claim to have resolved individual stars (massive blue giants, naturally) in ngc 206, the great starcloud in the SW area of the galaxy. This in a 16-inch. Has anyone else managed this? What instrument were you using?

-geo.


Has anyone here observed G1 or any of the other globular clusters contained in M31? I've seen G1 only once, so I'm interested in hearing about others' observations.

- Roy in Taos

#5 Alan D. Whitman

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Posted 04 October 2013 - 08:03 PM

Just got the Nov. issue of Sky and Telescope; there's a very nice article on the globular clusters (and some open clusters) of M31, by Alan Whitman. I was most intrigued to read his claim to have resolved individual stars (massive blue giants, naturally) in ngc 206, the great starcloud in the SW area of the galaxy. This in a 16-inch. Has anyone else managed this? What instrument were you using?

-geo.


Hi George,

Thanks for your comments.

In the Nov/97 Sky&Tel Texan Larry Mitchell wrote this about the NGC 206 OB association on page 106: "Through large apertures, faint stars pop in and out of view." The article was about his observations with his 24-inch although he also owned a 36-inch. Writing about C410 on page 109 he said: "Very faint stars seem to pop in and out of view." See also his less certain comments about stars in other open clusters and stellar associations in M31: A54, A67, and C311-C312-C313.

There is one error on the photographic finder chart that accompanies my M31 article. G35 is plotted incorrectly. According to Chart 3 of the Atlas of the Andromeda Galaxy, G35 is the slightly brighter object 3.5mm left of the labelled star. That is, the real G35 is barely below the line, between the 3 and the 5. All of the other plotted globulars and open clusters agree with the Atlas.

Best,

Alan Whitman

#6 george golitzin

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Posted 04 October 2013 - 10:35 PM

Hi Alan, and thank you for a great article! Two summers ago, I spent many hours repeating your observations on the Veil Nebula. Looks like I have my work cut out for the remainder of this Fall...

To date, I had only identified G1 among M31's globulars; I look forward to using your map to pick off many more. As it happens, I had my 18-inch out last night at home and found the Cassiopeia-like asterism SE of NGC 206 to which you refer in the article: G76 was very easy to see in that aperture, even in light-polluted skies. However, the seeing was so poor that I could not make out any halo. Well, plenty of time to come.

-George

#7 David Knisely

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Posted 05 October 2013 - 01:22 AM

Just got the Nov. issue of Sky and Telescope; there's a very nice article on the globular clusters (and some open clusters) of M31, by Alan Whitman. I was most intrigued to read his claim to have resolved individual stars (massive blue giants, naturally) in ngc 206, the great starcloud in the SW area of the galaxy. This in a 16-inch. Has anyone else managed this? What instrument were you using?

-geo.


Has anyone here observed G1 or any of the other globular clusters contained in M31? I've seen G1 only once, so I'm interested in hearing about others' observations.

- Roy in Taos


In my 10 inch f/5.6 Newtonian, I managed to pick up G73, G76, G78, and, of course, G1, which was far far easier than the first three. I probably could have added two or three more, but after trying for tiny faint star-like objects near the limits of the scope, I decided to go on other more interesting things. In my 14 inch, the 30 M31 globulars listed in OBSERVING HANDBOOK AND CATALOGUE OF DEEP-SKY OBJECTS, by Chris Luginbuhl & Brian Skiff (c. 1989 Cambridge University Press), should be within range on a decent night. Personally, I had more fun exploring the dust lanes in M31 the other night looking at the dark spots along their edges, but I may have to go back and look for a few of the globulars again. Clear skies to you.

#8 GlennLeDrew

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Posted 05 October 2013 - 01:37 AM

If we consider supergiants of -7 absolute visual magnitude, at a distance of 2.2 million l-y (distance modulus: 24.1 magnitudes) the apparent visual magnitude, if unobscured, would be 17.1m. Given the brighter field of NGC206 (or the spiral arms in general) upon which such points would lie, there might be a diminution of contrast, making such stars a little harder to see than if placed against a dark sky with no diffuse galactic light present.

#9 JakeSaloranta

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Posted 05 October 2013 - 02:02 AM

If the brightest star in Andromeda galaxy truly is #12 (just north of NGC 206 and v magnitude of 16.0) then it is visible at least in 12" telescope and probably with smaller telescopes as well.

I, as well as others, have seen 6 globular clusters from Andromeda galaxy with a 4.7" or smaller telescopes.

Be sure to check out the star B 324 from Triangulum galaxy as well. This is supposed to be the brightest star in the galaxy with a magnitude of ~15.2.

PS. There's already a thread of this in the forums.

#10 george golitzin

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Posted 05 October 2013 - 03:15 AM

Well, as a postscript: I went out tonight at home with the 18-inch; seeing was horrible--big bloated stars--but I managed to pull in G76, G280, G272, G213, and G233, as well as the open cluster/HII region C410, a very faint smear. So that's a good start. I look forward to viewing these again, and others, under better conditions--tonight it was all I could do to identify the objects--no detail was possible.

I am enjoying this exercise--it's forcing me to identify little mag 10 and 11 asterisms among the foreground stars, and thus form a much better map of the galaxy than I have had previously. This will be a nice observing program while Andromeda is well-placed for the next few months.

-geo

#11 azure1961p

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Posted 05 October 2013 - 08:02 AM

Don Pensack observed the stars in 206 with his 12" reflector. He said it was a very difficult observation but was surprised to see them.


Pete

#12 IVM

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Posted 06 October 2013 - 08:52 AM

If the brightest star in Andromeda galaxy truly is #12 (just north of NGC 206 and v magnitude of 16.0) ...


What catalog is this, Jake?

#13 JakeSaloranta

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Posted 06 October 2013 - 10:16 AM

What catalog is this, Jake?


It is the star labeled #12 in the 1987 paper (A photometric survey of the rich OB association NGC 206 in M31) by Stephen Odewahn: http://adsabs.harvar...AJ.....93..310O

Another good single star is A1 Andromedae (in H II region A41) and I think it is the brightest LBV star in Andromeda galaxy varying between 16.18 - 16.59 magnitude.

/Jake

#14 IVM

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Posted 06 October 2013 - 10:45 AM

Thanks, just the kind of catalog I was looking for. One of the LBV stars in M33, Hubble and Sandage's varC, is currently at m15.1. If I see it I will look closely at the possibility of seeing any of these stars in NGC 206. I am not very hopeful - varC's environment is fainter than NGC 206 but it still looks like a challenging place to search for a mag. 15 star, based on my experience with supernovae.

#15 Bill Weir

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Posted 06 October 2013 - 12:56 PM

I don't get S&T any more but I'm sure the article is up to Alan's usual caliber. I've seen several of the GCs in M31 with my 12.5" and added several more with my 20. The ones I added with the 20" were last year when I did a marathon of extragalactic globular clusters. The ones in M31 where the easier ones. G1 I've seen in my 6". Haven't tried for individual stars within NGC 206 so might have to find a copy of this S&T article. The only individual star in M31 I've seen was the LBV AE Andromedae several years back when it was at a very bright phase. I made a tenuous observation with my 12.5" that I wouldn't have been sure of but I was setup right beside a friend with his f/6 20" and was able to instantly confirm my observation.

Alan, missed you at Kobau this year. I was there when you showed up for the evening talk and had hope you would stick around to observe with after. Unfortunately it was the night of that wicked storm down in the valley. I was camped up by Lee, Gary and John. Maybe next year. On the top on Kobau my 20" really shines and no need to climb a ladder with that bad knee of yours. ; )
Bill

#16 JakeSaloranta

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Posted 07 October 2013 - 12:10 AM

Thanks, just the kind of catalog I was looking for. One of the LBV stars in M33, Hubble and Sandage's varC, is currently at m15.1. If I see it I will look closely at the possibility of seeing any of these stars in NGC 206. I am not very hopeful - varC's environment is fainter than NGC 206 but it still looks like a challenging place to search for a mag. 15 star, based on my experience with supernovae.


Don't forget the star B 342 in M33 @ magnitude 15.2 (v)! It is visible as a very faint stellar brightening in H II region IC 142.

/Jake

#17 george golitzin

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Posted 07 October 2013 - 12:52 AM

Thanks for those references also, Jake. I'll be giving both of those targets a shot when conditions are favorable.

-geo.

#18 IVM

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Posted 09 October 2013 - 02:22 PM

Well, I have now returned from our remote dark site. We had a fine night, with the dewpoint falling to 2 deg. C. The sky quality (21.4 mag/sq arcsec by SQM-L) was slightly compromised by a lingering glow from an aurora whose colorful show had thankfully died down by moonset.

Below is the sketch of NGC 206 that I made with my 16” Newtonian at 200-300x (Ethos and ZAOII oculars). Here it is oriented approximately with the north up and the stars are labeled according to the Odewahn catalog that Jake referenced above. Stars 12 and 112 are true members and the rest are foreground.

These were not the first stars I had seen in another galaxy (apart from the Magellanic Clouds) because just before that I had observed Hubble and Sandage’s LBV varC in M33 ;)

Attached Thumbnails

  • 6127253-2013-10-08 NGC 206 marked.jpg


#19 george golitzin

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Posted 09 October 2013 - 02:38 PM

Wow Ivan, that's excellent, and thanks for your sketch. Definitely a feat I'd like to duplicate. Congratulations on your observation.

-george

#20 IVM

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Posted 09 October 2013 - 03:00 PM

Thanks, George - indeed thanks to you for initiating this discussion from which I learned of the right star catalog. Odewahn 145 is the true member star in the next most promising clump to observe that may just fall to your 18" under good conditions. Star 12 was visually standing on its own alongside the clump in which it is embedded; star 112 and its surrounding clump significantly enhanced each other's visibility. Here we enter the tricky world of small tight clusters (seemingly too poor to be cataloged) that are anchored by single dominant blue giants. Tentatively, in such cases, I would say that what is seen is the cluster and not the star per se when what is seen is a single and purely starlike object. In the case of my observation of Odewahn 112, based on the appearance that I sketched (a star and a nebulosity) I say that the star was seen - although it would almost certainly be invisible without the cluster.

#21 Sasa

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Posted 09 October 2013 - 03:08 PM

Ivan, very nice and interesting observation. You should not be posting too many of them :), I'm starting to feel an aperture fever again.

#22 george golitzin

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Posted 09 October 2013 - 03:37 PM

I thought I'd look into this a bit more carefully. Here’s a link to a beautiful photo showing more globulars in M31—a little bit deeper than Alan’s map, but also missing some of the targets on his map:

http://www.astro-pho...1-globulars.jpg

From this I blew up an inverted view of ngc 206 (***EDIT: sorry, I have to remove this image according to the TOS***), and labelled the stars from the map in Odewhan, 1987 (the reference was given above by Jake). North is up.

Of those labelled, 12, 112, 40, and 22 are cluster members. Not sure about the rest--although 3 and 11 are called "standard stars" in the paper, by which I understand standard photometric reference stars. Blue magnitudes for these stars are:
12: 16.0
22: 17.1
40: 17.3
112: 17.3

The chart compares well with Ivan’s sketch, and I’d say he was seeing pretty deep at 17.3!

I’ll use this image to go after some of these stars at my next opportunity. So far, my glob count in M31 is up to 22. It's a great exercise--I highly recommend it. I'm getting a much better sense of the "geography" of this galaxy. Also, after hours hunting down these faint objects, my eye gets very sensitized to details in the galaxy itself--even from my home, I'm seeing little tendrils and ruffles from the inner dark lane reaching into the bright core area. For the most part, I'm using 320X in my 18-inch.

-George

***Image removed per TOS***

#23 george golitzin

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Posted 09 October 2013 - 03:50 PM

Ivan, while I found odewhan 145 on the paper's image of the cluster, I noticed it was left out of the catalog (table III) of the bright stars in the cluster, as were several others. I was assuming these others (such as 130) were foreground stars. So I'm a bit confused--perhaps I should read the paper with a bit more care.

But anyway, I'm amazed we're able, with modest instruments, to resolve visually individual stars (well, other than supernovae!) at this distance.

-geo

#24 IVM

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Posted 09 October 2013 - 04:33 PM

Sasa, thanks. I bought this 16" the day after the first light of my 12" Newtonian - talk of aperture fever!

But anyway, I'm amazed we're able, with modest instruments, to resolve visually individual stars (well, other than supernovae!) at this distance.


I too am amazed. I am also amazed what "modest instruments" means these days - for us. Folks who wonder how many civilizations there are up above should also ponder how many of them have mass-produced 16" close-to-diffraction-limited paraboloids ;) But it is not just instruments and probably even not so much the instruments at this point. It is the information flow such as exhibited on these pages - and by Alan's article of course!

Getting to the issues at hand: The criterion for membership in the paper was B-V<0.5. I think that star 112 is a likely member despite its laughable B-V=0.49 considering how it resides in a tight cluster. Star 145 (and 130) are on the second page of Table III that I got from the link here.

George, your chart looks like the one I used. Just more legible ;)

From the data in Table III of the paper I calculated V magnitudes. Star 112, due to its deplorable B-V, has Vm 16.81. This is not far removed from the faintest stars (with known magnitude) that I have seen with this scope, but I will not count it as my new record because the rather specific effect that I described in the last post likely played a role in making it visible. Tight (a few diffraction patterns in size) surrounding nebulosity seems to help unlike a broad nebulous background.

#25 Kraus

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Posted 09 October 2013 - 05:02 PM


Ivan,

Your sketch is an excellent rendering of your observation. Sometimes sketches are more pleasing to see than photographs.


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