Small Wonders: Deep Andromeda (Special)
Posted 26 November 2006 - 02:04 PM
Posted 26 November 2006 - 02:07 PM
Posted 26 November 2006 - 03:10 PM
A tiny point of clarification: in the section on G1, it is noted that this object is more massive than Omega Cen, and that G1 might be the core of a stripped dwarf galaxy, and not a "true" globular cluster as a result. Interestingly, Omega Cen itself also shows multiple stellar populations, and many people have recently argued that it also is a good bet that Omega Cen is the core of a dwarf galaxy that has suffered multiple collisions with the Milky Way. At this point, it's probably premature to suggest that either object is not a "true" globular cluster, because we don't yet know much about the rate of dwarf galaxy destruction, and some popular models for galaxy formation actually require the rate of dwarf galaxy destruction to be very very high, so quite a few similar objects might be out there. (That said, most globular clusters have very uniform old stellar populations, so its unlikely that most formed via dwarf galaxy accretion unless this happened a very long time ago).
A final parenthetical note: One interesting controversy about globular clusters in M31 that wasn't noted in the terrific article is that there is quite a bit of controversy about the subset of supposedly "young" globulars in M31 (where "young" in this context means "less than 5 billion years old"). As noted above, most M31 globulars are rather older than this, but a few years ago some astronomers claimed to have discovered a population of young globulars in M31. Last year some observations with Keck's new adaptive optics system were able to resolve these objects and showed quite convincingly that most of these objects were open clusters or asterisms, and not globulars at all. Here's a link to a PDF version of the article:
Comparing Figure 1 of this paper to the HST image of G1 shows that adaptive optics is really beginning to deliver the goods.
Posted 26 November 2006 - 03:55 PM
Roberto, Thank you very much! I really appreciate your input on this, and the LGSAO images from the Keck at the end of the PDF you reference are amazing. May I add your comments as an addendum directly to the article?
Posted 26 November 2006 - 05:05 PM
Sure, feel free to use my comments in whatever way you want.
I tried to send you a PM but I'm a bit of a beginner on the PM system so I'll respond here too in case I messed up the PM. Apologies for any duplication.
Posted 26 November 2006 - 06:20 PM
And thank you again Roberto. I'll drop you an e-mail.
Posted 26 November 2006 - 07:45 PM
Now if only can snag a clear night before this warm weather is all gone.
Posted 26 November 2006 - 07:48 PM
Posted 27 November 2006 - 12:21 AM
Well written as usual, Tom.
One thing I would say is that 10" doesn't really do justice to the fainter globulars in the Andromeda Galaxy, and are really specialty targets for larger aperture reflectors. Magnitude 15 and 16 globulars are not 10" visual targets.
Posted 27 November 2006 - 10:36 AM
Your article reminded me of a magical Fall night spent on Mt. Pinos.
That night we had seeing better than 0.5 arc second (at times WAY better), and the darkness was superb (21.69 per sq.arc.sec). After finding a couple globulars in M31 (G1 was easy), I swung over to NGC206 and ran the magnification on my 12.5" up to 365X and the image held sharp and steady. A horde of individual stars could be seen in NGC206--enough to know I wasn't seeing just foreground stars. I didn't even know how deep I was reaching until I read that there were a handful of supergiant stars in 206 around magnitude 17 to 17.5. There is another bunch around magnitude 19, but I'm sure I wasn't seeing those. NGC 205 that night displayed a core with mottling on one side--the dark spot is usually not visible in photos due to exposure, but stands out in excellent seeing at very (>300X) high powers.
The only other cluster of "impossible" stars similarly resolved on a nearly identical magical night was M14, but that's another story.
Thanks for the "deep" article. It gives me something to shoot for when another superb night comes my way.
Posted 27 November 2006 - 11:02 AM
Posted 27 November 2006 - 11:15 AM
That's a cool story -
It's really amazing how much you can really see in a (relatively) small aperture. Many folks tend to look just at magnitude and think of it as a hard rule while forgetting to take things like point source vs extended, photographic vs visual, airmass, sky conditions, biology, and plain old catalog mistakes into account. I learned a long time ago not to write a target off till I've looked for it. OTOH, It never would have occured to me that you could resolve the stars in NGC 205 with an amateur telescope, knowing that it took baade a perfect night to resolve Andromeda itself. This gives me something to look for.
Posted 27 November 2006 - 11:17 AM
Posted 27 November 2006 - 11:35 AM
Posted 27 November 2006 - 02:53 PM
This is an absolutely wonderful *Small Wonders*! It brought back my M31 globular lust--absolutely full tilt.
I spent quite a bit of time on M31 earlier this Fall, and managed to log NGC 206, G76, G119, G213, G272, G280, and G73. While searching for G213, I noted another object that was not on my observing chart that I had previiously printed up; turned out to be G233!
And no--I don't think you have averted imagination. I was quite certain that G76 had a reasonable *fuzzy* or *fat star* look, as did G213. By my observing notes, there is a star of similar magnitude BEYOND G76 and the tip of the broad-based triangular asterism of faint stars; it appears *starlike* at 387x, whereas G76 is non-stellar.
I used my Discovery 12.5" for all of my observations. The eyepiece set included the UWAN 28 as my basic finder e.p., and then a Pentax 10 XW to navigate within the galaxy. I narrowed down my search with a Pentax 7 XW, and finally viewed the globulars with a UWAN 4 at 387x. This is just enough magnification to separate the globs from stars.
Thanks again for the article--you really made my day!
Added as an *edit*.
Dierctly from my notes of 9/18/2006: Finding G 76 is easy from an asterism of three faint stars; Tyc 2801-2035-1 (mag 11.21), Tyc 2801-2059-1 (mag 12.23), and GSC 2801-2006 (mag 12.17). The obtuse apex of this triangle is Tyc2801-2059-1. and a line drawn from GSC 2801-2006 passing through this apex points directly to G 76. There is a mag 14 starjust beyond G 76 (distal from the apex) which may be confused with the cluster. High power (387x)removes all doubt as to which is a star and which is the globular, since G 76 is a *fat, fuzzy star*.
My recommendation is USE THE HIGHEST MAGNIFICATION POSSIBLE!
Posted 27 November 2006 - 08:25 PM
Posted 28 November 2006 - 12:00 PM
We are awaiting an encore.
Posted 28 November 2006 - 01:58 PM
Posted 28 November 2006 - 06:51 PM
Posted 29 November 2006 - 01:02 PM
Any chance of a PDF version in the near future? I always print them off and keep them in a binder for future reference. Keep up your excellent work!
Again, many sincere thanks!
Posted 29 November 2006 - 03:11 PM
Rodger: Olivier is out of town, but Timm sent me one - it's a little rougher, but definitely printable. I'll attach it.