Globular Clusters in M 31

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Globular Clusters in M 31

Last post 07-08-2008 09:50 PM by DaveMitsky. 3 replies.

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07-03-2008 03:49 AM

ngc2438
Joined on 04-25-2008
Thailand
Posts 121

I'd like to post a older observation of globs in M 31 here, in reference to a discussion in the "Our Galaxy" thread. I have tried to observe globs in M31 only 3 times but it was quite successful. The hunt for globs in M31 is not so difficult because of the low brightness of the clusters (many are brighter than 15 mag) but, because only under perfect seeing conditions some of them will be non-stellar. They don't respond to filters like planetary nebulas. One has to make them out within the many equally faint foreground stars scattered all over.

Here is the Field Guide for your own observation attempt: http://www.robgendlerastropics.com/M31NMmosaicglobs.html

Here is a comprehensive list of all, so far, known globular clusters in M31, incl brightnesses, etc: http://www.bo.astro.it/M31/m31rbcV3.5.dat

Unfortunately I have not yet found a list of data ref open clusters in M31. I have managed to see 3 of those as well (not incl. NGC 206 which is a huge stellar association).

The Report: On 16/17 11 04 I took the chance of perfect seeing and fairly good visibility to hunt for extragalactic globular clusters and open clusters in M31. As reference I did use a picture of M31 from the Night Sky Observer’s Guide. 43 GCs, OCs and stellar Associations are plotted on that map. The brightness and sizes of the objects I did take from the Internet.On earlier occasions I did experience that perfect seeing is much more important to possible resolution of faint stars and almost stellar objects than very clear skies with medium to bad seeing. Seeing last night was better than 1” and naked eye limit approx 5,5mag. M31 was very high in the sky (~60+° during my observations).In order to describe the level of difficulty for observing single objects, I created a 5-level scale: (1) direct vision, easy, (2) direct vision, difficult, averted vision very easy, (3) averted vision only but fairly easy (4) averted vision only, difficult, (5) averted vision only and temporarily visible, extremely difficult.All object observations were done with my 15” f4,5 Obsession scope with 5mm Nagler T6 eyepiece (342x magnification). To locate the area of the objects I did use the Nagler 13mm (131x). G64: (5), 00 40,5 +41 22 02,3, V 15,1 extremely faint and stellar. Seen with AV (averted vision) only. G72: (5), 00 40 52,8 +41 18 54,2, V 15,0 just like G64, stellar and extremely faint. AV only. G73: (2), 00 40,9 +41 41 15, V 15,0 just non-stellar, very faint but directly seen. G73 is in NGC 205! G76: (1), 00 41,1 +40 36 3,6, V 14,2 very easy, directly visible as a stellar object. With AV it turns into a non-stellar smudge. Bright. G87: (5), 00 41 14,7 +40 55 52, V 15,6 most difficult of all objects seen. I could glimpse it only 4,5 times in 10 minutes. I could not confirm whether G87 was stellar or non-stellar. G119: (4-5), 00 41,9 +40 47 2,7, V 15,0 stellar, very difficult with averted vision (AV). G156: (5), 00 42 25,3 +40 57 18, V 15,6 stellar and very faint with AV. G213: (3), 00 43,2 +41 07 2,5, V 14,7 non stellar smudge without core, fairly easy with AV. G226: (4), 00 43 30,3 +41 38 56, V 15,5 non-stellar smudge with averted vision, on the edge of visibility.G244: (5), 00 43,8 +41 37 2,6, V 15,4 pops up only temporarily with averted vision, extremely faint, stellar. G272: (3), V 14,8 features a stellar core and a halo that was seen with averted vision. Fairly easy. G279: (5), 00 44,5 +41 29 2,9, V 15,4 extremely faint smudge with no central brightening or stellar core. ~3”. AV only. G280: (1), 00 44,5 +41 22 2,5, V 14,2 easy, stellar, could be seen directly. C107: (3-4), 00 40,5 +40 36, 4-5” size. No distinct core. Biggest of all observed objects. AV only, not too difficult. C202: (4), 00 42,1 +40 57, stellar and difficult with AV. C410: (5), 00 44,4 +41 21, extremely faint 3-4” smudge of light. AV only. Barely visible. It should be noted that the observed size of objects described as “non-stellar” or as “smudge” was never more than approx 2-3”. It is almost impossible to tell the size when an object is so extremely faint and visible only with averted vision. Therefore a simple description as “non-stellar” is all that can be determined.I was amazed how far and beyond the limit I could push my 15 inch under last night’s conditions. Extremely clear skies provided me with another chance to look for more GCs in M31. I did also observe some objects that I observed on the 16th Nov. GCs that were rather difficult on that day were fairly easy on the 18th as visibility was so much better. The seeing was probably not as good but, good enough for high magnifications. G287: (5), 00 44 42, +41 43 55, V 15,8, extremely faint and stellar. Very difficult even with averted vision (AV)

G305: (4), 00 45 41, +41 45 33, V 15,6, faint but fairly easy with averted vision. Stellar.

G286: (4), V 15,7, requires AV, non-stellar fairly big (3”) smudge of light), no central brightening or core. C? just N of G 272, (5), unknown stellar association in M31, extremely faint. AV only, pops up as a stellar object. Object designation G 270 wrong in Kepple and Sanner. G233: (2), 00 43,6, +41 08 26, V 15,4, fairly easy and directly visible (then stellar). With averted vision non-stellar. Two objects from 16 Nov (G252 and G213) were 2 levels easier to observe than on the 16th. I think that I have reached the limits (here in Sangkhlaburi's location) of my 15 inch last night with the observation of all those objects. It brings the number of objects I have seen in M31 to 22 (!), including Mayall 2 (or G1) a few years earlier through a 12 inch f6.7 Newtonian at 430x.

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07-08-2008 03:53 PM In reply to

zachsdad Joined on 10-02-2007 Wever, IA Posts 1,558	Re: Globular Clusters in M 31 Thanks for the links and the report, ngc2438. I have long been intrigued by the M31 globs and would like to attempt to see them this fall when Andromeda is high once again. Signature Science without religion is lame, religion without science is blind. -- Albert Einstein
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07-08-2008 08:43 PM In reply to

DaveMitsky Joined on 07-25-2001 Pennsylvania, USA Posts 5,863	Re: Globular Clusters in M 31 G1 is one of the easier globulars to detect but even through a 20" aperture it doesn't appear to be much more than a slightly fuzzy star. Dave Mitsky Signature Chance favors the prepared mind. De gustibus non est disputandum.
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07-08-2008 09:50 PM In reply to

DaveMitsky Joined on 07-25-2001 Pennsylvania, USA Posts 5,863	Re: Globular Clusters in M 31 Information on G1 (Mayall II) can be found at http://www.nightskyinfo.com/archive/g1_globular_cluster/ and http://seds.org/messier/more/m031_g1hst.html Dave Mitsky Signature Chance favors the prepared mind. De gustibus non est disputandum.
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