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M71's location in the galaxy

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#1 precaud

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Posted 06 August 2014 - 09:38 AM

I recently got Nat Geo's computer-generated Milky Way poster. One of the things that first caught my eye is their placement of M71 near the galactic core and directly in line between us and the core. This is quite different to what I'd read elsewhere, for instance ESA/Hubble describe M71 as "a great ball of ancient stars on the edge of our galaxy. And of course it makes no sense visually, as it is nowhere near Sagittarius. It appears that Nat Geo got it wrong. Anyone else notice this?

 



#2 precaud

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Posted 06 August 2014 - 10:10 AM

It must be a typo, should be M17.



#3 Starman1

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Posted 06 August 2014 - 10:29 AM

Yeah, it's M17.

M71 is passing through the disc of the Milky Way (and they say perhaps for the last time, as it's being heavily disrupted tidally)

It might become more of a "stream" of stars after exiting the disc.



#4 precaud

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Posted 06 August 2014 - 11:18 AM

Thanks for the interesting context, Don. Is the Nat Geo map the best "bird's eye" approximation of the Milky Way out there? In the short term, methinks this is going to change the way I explore it..



#5 havasman

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Posted 06 August 2014 - 11:52 AM

http://www.thinkastronomy.com/M13/

The link is to a free download Where Is M13? a 3D "map" of the galaxy showing directional orientation of objects you select/deselect. It's interesting and can aid in visualizing our relative location. BTW, it has proven to be a safe download.

Good seeing to us all.



#6 kt4hx

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Posted 06 August 2014 - 05:16 PM

Hi John.  Other than the M71 - M17 switcheroo, how do you find the chart?  Also, do they actually have M71 in the correct position and only messed up M17?



#7 kt4hx

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Posted 06 August 2014 - 05:17 PM

Don, do you have a link or other reference for this.  I would like to do some more reading.  Thanks.

 

Yeah, it's M17.

M71 is passing through the disc of the Milky Way (and they say perhaps for the last time, as it's being heavily disrupted tidally)

It might become more of a "stream" of stars after exiting the disc.



#8 Starman1

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Posted 06 August 2014 - 06:57 PM

 

Don, do you have a link or other reference for this.  I would like to do some more reading.  Thanks.

 

Yeah, it's M17.

M71 is passing through the disc of the Milky Way (and they say perhaps for the last time, as it's being heavily disrupted tidally)

It might become more of a "stream" of stars after exiting the disc.

 

first, read:

http://messier.seds.org/m/m071.html

As for the other details, it is what I've read and what I've been told by at least two different astronomers--one at Mt. Wilson and one at Kitt Peak.  I've read it elsewhere but am afflicted with reading too many publications and documents on astrophysics.  I also read Astrophysical Journal for many years.  Archinal & Hynes don't mention it in their seminal work, "Star Clusters" in 2003.  I distinctly remember being told it was being disrupted, like the Sagittarius Dwarf which is being absorbed by the Milky Way.  If I find the source, I'll post it.



#9 kt4hx

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Posted 06 August 2014 - 07:28 PM

 

 

Don, do you have a link or other reference for this.  I would like to do some more reading.  Thanks.

 

Yeah, it's M17.

M71 is passing through the disc of the Milky Way (and they say perhaps for the last time, as it's being heavily disrupted tidally)

It might become more of a "stream" of stars after exiting the disc.

 

first, read:

http://messier.seds.org/m/m071.html

As for the other details, it is what I've read and what I've been told by at least two different astronomers--one at Mt. Wilson and one at Kitt Peak.  I've read it elsewhere but am afflicted with reading too many publications and documents on astrophysics.  I also read Astrophysical Journal for many years.  Archinal & Hynes don't mention it in their seminal work, "Star Clusters" in 2003.  I distinctly remember being told it was being disrupted, like the Sagittarius Dwarf which is being absorbed by the Milky Way.  If I find the source, I'll post it.

 

 

 

Thanks Don.  I find it interesting that Archinal & Hynes didn't mention it in their work.  Though I have read Hynes' book on Planetary Nebulae from 1991, I never have gotten around to Star Clusters.  I will also continue digging on my own to see what I can come up on this.

 


Edited by kt4hx, 06 August 2014 - 07:29 PM.


#10 precaud

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Posted 06 August 2014 - 08:38 PM

Hi John.  Other than the M71 - M17 switcheroo, how do you find the chart?  Also, do they actually have M71 in the correct position and only messed up M17?

Hi Alan,

I find the chart by looking down at the floor, where it is currently splayed...  :p

 

In the absence of any alternative (it's the only poster-size simulated Milky Way overview I know of in print), I like it. It doesn't have very many objects placed on it, a dozen or so, but there are enough to get your bearings. I would definitely like to have seen more, but this was made for the public, not for astronomers. More objects are placed on the elongated edgewise view along the top of the map, along with the location of the various arms (I assume it is a cross-section taken perpendicular to our orientation to the core). It should be good enough for getting started observing objects that lie in a particular arm, which is what I have in mind.



#11 GlennLeDrew

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Posted 07 August 2014 - 05:16 AM

That Nat Geo Milky Way poster has a number of other errors. On one of the smaller strip charts it has a certain class of object given reversed longitudes, making for mirrored locations. Bad!

 

As for M71. It's a quite rich cluster, and is thus rather strongly bound. It will require more than one disk shock to disrupt it. This is far from its last disk crossing as a bound structure, where each such crossing might strip perhaps several or ten per cent of the members.



#12 Sarkikos

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Posted 07 August 2014 - 06:54 AM

Hard to believe Star Clusters does not mention that M71 "is passing through the disc of the Milky Way (and they say perhaps for the last time, as it's being heavily disrupted tidally)" and that "it might become more of a "stream" of stars after exiting the disc."  Unless what Glenn says about M71's stability is closer to the truth.  I ordered Star Clusters a couple days ago. I had intended to buy it and finally did. I'll have to check out what it says about M71.
 
M71 is one of my must-see objects when Sagitta is up.  It certainly is easy to find. Right on the shaft of the arrow.  Nearby is another easy-to find M glob: M56. It's about half-way between Sulafat and Albireo.
 
Mike

Edited by Sarkikos, 07 August 2014 - 11:21 AM.


#13 precaud

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Posted 07 August 2014 - 07:32 AM

That Nat Geo Milky Way poster has a number of other errors. On one of the smaller strip charts it has a certain class of object given reversed longitudes, making for mirrored locations. Bad!

Yeah, I caught a couple of those last night, NGC6124 and 6231 are incorrectly placed in the Cygnus Arm in the strip chart. Sheesh.



#14 GlennLeDrew

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Posted 07 August 2014 - 01:38 PM

Open clusters which reside in and near the disk (i.e., do not experience large vertical oscillation which takes them well above/below the midplane, outside the thin disk) are much more affected by giant molecular clouds than by disk shocking. This has the result that some 80% of open clusters do not remain bound for longer than about 500 million years, or two trips about the Galaxy at the Sun's galactocentric distance.

 

Clusters which experience significant vertical oscillation, as does M71, can remain bound for rather longer at given cluster mass. The encounters with those ~1 million solar mass clouds are much reduced in frequency.



#15 Starman1

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Posted 07 August 2014 - 06:26 PM

Open clusters which reside in and near the disk (i.e., do not experience large vertical oscillation which takes them well above/below the midplane, outside the thin disk) are much more affected by giant molecular clouds than by disk shocking. This has the result that some 80% of open clusters do not remain bound for longer than about 500 million years, or two trips about the Galaxy at the Sun's galactocentric distance.

 

Clusters which experience significant vertical oscillation, as does M71, can remain bound for rather longer at given cluster mass. The encounters with those ~1 million solar mass clouds are much reduced in frequency.

Yup.

M71 is identified as having virtually no core or central condensation, is small (<30 light years), and its outer stars are sparse.

As a candidate for disruption, it'd be high on my list.








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