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Small Wonders: Sagitta and Vulpecula


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Small Wonders:Vulpecula and Sagitta
Tom Trusock9/2006




This monthwe've got two tiny constellations to look at: Vulpecula andSagitta.  The fox and the arrow seem to be a match made in heaven,but on investigation we find that while the arrow has been around forthousands of years, the fox is a fairly recent creation.

The constellation Vulpecula was initially known as Vulpecula et Anser,"foxwith the goose", and was theinvention of 17th century astronomer JohannesHelveius to fill an area left blank on prior star maps.  Known today only as Vulpecula (The Little Fox), the goosemust have been a short meal – allthats remains of the goose is Alpha Vulpecula (named Anser) caught between the teeth like aleftover morsel.

It’s far too late to save this goose.

So if it's too late to save the goose, why shoot the fox?  Thatpresumes the unknown archer is actually shooting at the fox.

Given the timeline, we see we have a bit of a chicken and eggproblem.  Obviously, since it was shot well before the fox came onthe scene, the arrow can’t betargeting the Vulpecula.  Who shot the arrow?  And atwhat? Taking a look at the summer milky one celestial archer screams out –but unless he’s a truly horrid shot, it most likely wasn't Sagittarius– he’s facing the wrong way.  Casting about the sky, we latch ontoanother likely suspect setting in the west – Hercules.  But ifit was Hercules, whom was he shooting act?  If not the fox, we'vegot two other prime suspects, eitherAquilia (the eagle) or Cygnus (the swan)/  Both have just takenflight,undoubtedly shocked into action by the unexpected attack. Whatever the target, it lookslike poor Vulpecula is going to go hungry for a while.

Vulpecula andSagitta lie on the edge of the summer Milky Way, andas such are rich in open clusters and planetary nebulae.  Sagittacontains M71 – a cluster with a history of  identity crisis. (But more on that later. ), while Vulpecula harbors M27 and thespectacular association Cr399 – better known as the Coat Hanger. 

In addition this area is home to a couple of cases of galactic identitycrisis, several appear on the list this month.  Another, not onthe target list, is Merrill's star.  This object is misclassifiedinmost catalogs as a planetary nebula.  In reality it appears to beacool Wolf-Rayet star with an associated  nebula and thus it'sa  "young"object.   Interestingly enough, it's velocity isconsiderable, and it's also thought to be a  "runaway" object.


 
Carl Burton has done an excellent job of capturing it with the aboveimage. And Bill Warden contributed the following.



This isn't much in the way of avisual target - at least in the average amateur telescope.  But ifyou're so inclined, don't let that stop you.  You'll never knowwhatyou are going to see until you look.  Merrill's star can be foundat: 19h11m30.9s RA, +16 deg 51 minutes, 38 seconds Dec. Note, thecoordinates are in epoch 2000.
As per the rest of the area; Interesting targets abound.  Thereare some 69planetary nebulae, an amazing2030 galaxies, 9 quasars (the brightest at mag 16.4) , 8 diffusenebulae, 102 dark nebulae, 21 open clusters, and two globular clusters(both of which are in this months edition).

In fact, some of you will probably want to take a set of binoculars andjust scan the region.

As per the rest: Shall we get started?




Let's begin with a good old fashioned Messier - M71.

M71

Most likely discovered by Philippe Loys de Cheseaux in 1746, it wascataloged by Messier on the 4th of October in 1780.  If you'rereading this in September, you've got a chance to observe it on theanniversary of its being added to the Messier catalog!

For a long time, M71 suffered from some fundamental identityconfusion.  We weren't quite certain what it was.  We had itpegged as someform of cluster, but the jury was out on it being either a dense openclusteror a loose globular.  Confusion reigned as least as late as the50's and 60's. 

We've finally seemed to come to a general consensus (thanks to are-examination of the HR diagram). M71 does, in fact, belong withthe rest of the globulars in the Milky Way.  It's probably soloose because it's a mere 13,000 light years away.  Indeed, it'sone of the closer globular clusters.

I'm sure its relieved to know its status is no longer in doubt.



John Graham's photo of M71 is anexcellent approximation of what I see in a largescope.    I've always thought of this as the angelfish,can you see it, or do I have an overactive imagination?
I've seen M71 with scopes as small as 66 mm, and various people havemanaged to pick out its subtle glow with binoculars.  Largerscopes tend to give a more impressive view, but whatever you use, thisis one pretty cluster.  I've found it takes an 80mm to reallybegin resolving stars on the outskirts.

Observing with a 6" from dark skies in California, Eric Graff has thisto say:

...this object appears as a brightnebulous patch over strewn with numerous faint stars in an exceedinglyrich field at 30x. To the west is a bright grouping of stars including6th magnitude 9 Sagittae arranged in a Y-shaped pattern with the prongspointing northward. The indistinct haze of H20 is also included in thewide field view of this globular star cluster. At 60x this object isseen to be elongated north-northeast to south-southwest with many starsresolved around the edges, particularly in the directions of elongationas well as across the face of the cluster. At 120x M-71 displays abright triangular patch to stars near the center, pointing toward thesouth-southwest. The cluster is pretty well resolved across the entireface of the cluster, an indication of its loose structure compared withmany other clusters of this type. A distinctive arc of bright stars tothe northeast and a bright star on the south side of the clustercomplete the scene at high power.

M71 shines with the light of 6,576 suns.

While you're in the area, take a peek 1/2 degree south for the sparseopen cluster Harvard 20.

Now haul out those small scopes and binoculars, next up we're headed toCr399.

Cr 399


This photo by Keith Geary shows this famous grouping of stars.  Cr399goes byseveral different names: Brocchi's Cluster, Al Sufi's Cluster and mostrecognizably, the Coat Hanger.

Brent Archinal and Steven Hynes have an excellent section on Cr 399 intheir book "Star Clusters", where they note that historically we shouldprobably refer to this as Al Sufi's Cluster, as the Persianastronomer  discovered it  in the 10th century AD.  Sufinoted that it was "...a little cloud situated to the north of the twostars of the notch of Vulpecula" One supposed that Vulpecula wasinserted by the translator as a positional reference as it wasn'tactually a constellation for some time to come.  "Star Clusters"further notes that Brian Skiff has shown the group to be an asterisminstead of a true galactic cluster.  Our challenge object for theevening lies nearby so we'll return here at the end of the night.

Can't see a Coat Hanger in the stars above?  It can be difficulttopick out the asterism from the field stars without a sizereference.  If you can't see it in the photo above trycomparing it with the one below.


To see the Coat Hanger you'll need a wide field scope or a set ofbinoculars. The lower the magnification the better the asterism willstand out.  This is definitely one target that looks better in asmall telescope than in a larger one.

Phillip Creed has this to say about the Al Sufi's Cluster:

I was in SE Ohio on the night of 8/21/06and brought my 25x100 binoculars down there. Sky conditions were verytransparent, with a pretty dark sky ("green" on the Clear Sky ClockLight Pollution Map). 25x is about the limit for getting the entirecluster in the field of view. I wasn't expecting the entire field ofview to be filled out by
this, but it was!

The jury is out about just how much one can resolve with the nakedeye.  Obviously from a dark site, it's visible (itwas discovered with the naked eye), but I've heard varyingreports of amateurs being able to resolve a few individual stars. On the best nights I see a slight glow in the area myself, but I'm notcertain if that's Cr 399 or simply a brighter portion of the MilkyWay.  Take a look and decide for yourself.

While you're here, take a peek just off the eastern edge of the CoatHanger - about 20 arc minutes -  and see if you can spot NGC6802.  (This is where a little more aperture might come inhandy.)  Those of you interested in determining just how deepyou're seeing this evening, might want to pick up Luginbuhl and Skiff's"Observing Handbook and Catalogue of Deep-Sky Objects", as it has anicephotometric chart of 6802.

From here, let's head to the northeast five degrees and take a lookat  NGC 6823.

NGC 6823





This is a nice little cluster for a small scope and shows a fairconcentration of stars toward the center.  If you have a hard timepulling it out from the background (not unusual for many openclusters), look for a tiny diamond shapedasterism at the center.  The nebula in the photo isNGC 6820.  6820 extends for a fair region around 6823, but for themost part will be most likely be invisible to the typicalamateur.  Itmight, however, make a good target for an astrophotographer.

Now lets hop three degrees directly east to M27.

M27


Marco Ciocca's excellent photograph shows us a target that isspectacular in any size telescope, and easily spotted in mostbinoculars.   M27, better known as the Dumbbell Nebula wasdiscovered by Messier in 1764.  The fact that it's both nearby(at 1250 light years)  and large (~1 light year in diameter) conspire to make it one of the larger and brighter planetaries in ournight sky.

By now, you may be wondering; "Just where are these Messier objects,anyway?"

Bill Tschumy's "Where is M13?" to the rescue!



Shown above, we see the location of M27 and M71 with respect to the thesolar system (the orange dot).  M71 is the orange dot with theblue circlearound it, and M27 is the blue dot with the cross through it andextending beyond the edges. 

While viewing, take a moment and hop back and forth between the twowith yourtelescope to get a feeling of their absolute sizes.

Through a 4" telescope, the nebula shows it's typical Dumbbell shape,but pump up the aperture and it turns into afootball!    In smaller scopes I haven't managed topick out any of the foreground stars, but they easily become visiblewhen using something 8" or larger.  What's the smallestaperture you can pick out at least one foreground star with?  Howmany can you pick out with what size telescope?

Try using an OIII or UHC filter on M27 and see what effect is has.

There seems to have been some controversy surrounding the Dumbbell'scentral star.  Most modern sources put the magnitude at around 14,but older catalogs have it a bit brighter.  Is there a chance it'svariable?  With my 18" scope, the central star is quite obvious,but I've never checked to see just how small an aperture it can be seenin.  Take a peek and let me know.



While there may be somequestion about the variability of the central star, we do know there'sat least one variable visible in this image of the Dumbbell.  IntheOctober 2006 "Sky and Telescope", Sue French notes that the Czechamateurastronomer Leos Ondra discovered the Goldilocks variable whilescrutinizing different images of M27 in 1991.  So keep those eyespeeled, you'll never know what you might find.  John Grahamcontributed this excellent image of the Dumbbell for the article, I wasthe one who made it into a finder chart - John, forgive me for markingup such a beautiful image.

We'll leave M27 with a final image from Josh Dominico.  Can youspot the Goldilocks Variable?


Now hop 4 and 3/4 degrees northeast for another chapter in "GalacticIdentity Crisis".



NGC 6885 and/or 6882 / Caldwell37




These "two" clusters lie near 20Vulpeculae. One is centered on the star, while the other off set. Maybe.  Observers often report two apparent clusters in this area,but which is which?  For the answer we turn again to "StarClusters".  William Herschel discovered these two clusters onsuccessive nights, and his descriptions for these two objects arenearly identical, as are the positions - only 15' apart. Galacticconfusion has reigned supreme since.  

The best guess at this time, until someone can travel back in time andbe with Herschel on those evenings, is that 6885 is a duplicateobservation of 6882.

In 1930, Trumpler realized that there were two groupings here, butdidn't name the second.  It remained for Collinder to assign aname to this "new" group - Collinder 416.  However, Collinder mademistakes here too; apparently flipping the sizes and magnitudes of thetwo groups.  Additionally, he indicated that the star 20 Vul is inboth groups and assigned two different catalog numbers to it.

Problems continued in the Lund catalog.

In the Caldwells, I'd guess that Moore was referring to the clustercentered on 20 Vulwhen he choose this for inclusion in his catalog, but we'd probably bebest off asking him. Incidentally, for those looking for moreinformation on this celestial mystery, Steven James O'Meara has a goodwrite-up in his book "The Caldwell Objects".

On the other hand, maybe the best thing for you to do is get out andlook foryourself.



Rony De Laet, observing with anEXT 90 from Bekkevoort, Belgium captured the region with the abovesketch.  He writes:

At first sight, the cluster isinconspicious and suppressed by the brighter star 20 Vul. After a whilethe fainter stars of the cluster pop into view. Finally some clustermembers seem to have some nebulosity. This might be the glow of fainterstars beyond the limit of the ETX.

And with that, I'll close the section on 688-... uhh, whatever, andhead off to some good old fashioned Planetary Nebulae.  Travel 6degrees south of the 688X confusion, or 1 3/4 degrees east from eta Sge(the tipof the arrow) for the first one: 6886.

NGC 6886



Bill Warden's shot of NGC 6886makes it look like there's a fairly nice planetary here - Hah! Thismost likely isn't a target that will provide the thrills of M27, forwell - anyone. The challenge and enjoyment in this target lies inspotting it.  Here, take a look at the DSS image of the field:


I found it to remain star likeuntil nearly 500x in my scopes.  The "giveaway" is its color, butthisisn't even obvious till around 200x.  There are several differentapproaches you can take to this one - nail the field, then scan aroundat high power, or try blinking an OIII filter and see what star staysbright.
By the way,  nice job Bill.

If you're a true die hard, you might find this negative, reversed DSSimage helpful in narrowing down the field.



I wish I could say that our next target was easier, but - well, that'snot true.  After the big, bright and spectacular targets, it'snice to have a few challenging ones, right?  So drop 3 and 1/2degrees southeast and start your hunt for IC 4997.  (At least thisis going to give us a chance to see how accurate the placement of thesePlanetary Nebulae are in SkyMap Pro, eh?)

IC 4997



Another needle in a haystack, this is really a target for a largerscope.  Use high powers, 200x plus for your best shot.  Theblue green color should be a giveaway when comparing it to the stars inthe area, but if you run into problems try blinking an OIII filter.

For those who may not know what "blinking" is; One holds an OIII filterbetween your eye and the eyepiece and flips it in and out. Closely examine the field, looking for a "star" that stays about thesame magnitude with the filter in place.  That's the planetary.

When you've got it, you'll know. At 200x in large scopes, it's smalland circular with not much detail to be seen even at higher powers.

Die hards can again opt for using this negative, reversed DSS image.



The bonus planetary for the month isn't any easier.

I didn't put this in the "official" target list, but if you're aplanetary nebula nut like myself, you can't leave the region without atleast taking a peek for Abell 74. (Notice I didn't say at.)



Identified on the above map as PK 72-17.1, this is a difficult targetand requires dark skies and LOTS of aperture.  I haven't been ableto pick it up in my 18", but CN'er Alvin Huey has a record of it withhis 22" telescope.  If you go looking for it on DSS plates, lookclosely.  Very closely - it's almost impossible to spot.

If the Abell planetaries interest you, I highly recommendAlvin's book - "The Abell Planetary Observer's Guide".  It's awonderful resource.

Frustrated?  Well, take heart, the next target is easier.

NGC 6940



In a small scope, this cluster ismore of a bright semi concentrated haze.  An 8" telescope willshow a grouping of around 70-80 stars, while largertelescopes further enrich the view.  Look for a reddish star nearthe center.
Vedran Vrhovac observing fromCroatia with an 8 inch f6 dob at 38x contributes the following:

Open cluster placed in the rich field ofMilky Way stars. My estimated dimension of the cluster are 40’x 15’ andit consist of about 70 mag 10 to 11 stars. In central part of thecluster there is a one mag 9 orange star. Cluster also reminds me on afish with head on west and tail on east.

This brings us to our last object for the evening.

Challenge Object - Palomar 10

The second globular cluster in the region is a lot harder to spot thanits brother.



Pal 10 is  located 34,556light years away from us and has a luminosity of only 509 suns. Pal 10was discovered via a survey of the DSS plates in 1955 by A GWilson.  Once again Bill Tschumy's "Where is M13" can give us abetter idea where, in reference to us, our neighbor lies.


Pal 10 isn't the easiest object to find, aperture and dark skies arehighly recommended.  The general area isn't all that difficult tospot though,it's near one of this month's showpieces: Al Sufi's cluster. 


Again, you'll probably want to usea negative, reversed DSS image.



As with any difficult target, I'd recommend you only use this articleas a starting point.  I'd encourage you to print out charts tomatch your scope and equipment.    Make use of the MASTDSS, MegaStar, SkyMap Pro, Sky Tools 2 or RealSky till you findsomething you'recomfortable with.

I find searching for the esoteric and difficult targets sharpens yourskills as an observer and allows for a better appreciation of thosetrue showpieces of the night sky. Plus it's just darn cool to seesomething not too many other folks have.

Finally, I'd like to take a moment to thank all the readers whosubmitted observations and photos this month.  The included onesare just the tip of the iceberg. Unfortunately, respect for othersbandwidth limitationsrequire me to restrict the photos to just a smallsample of what readers submitted.

As always, I'm gratified that folks find this column useful.

Till next time -

Tom T.

Additional Links / Resources / References

The Abell Planetary ObserversGuide
Review:  http://www.cloudynights.com/item.php?item_id=1409
Available From: http://www.faintfuzzies.com/
By Alvin Huey

Star Clusters
Available From: http://www.amazon.com/Star-Clusters-Brent-A-Archinal/dp/0943396808
By Brent A.Archinal and Steven J. Hynes

Some comments on NGC 6882/6885
http://www.freelists.org/archives/az-observing/11-2003/msg00165.html
by Brent A.Archinal

Abundances in globular clusterred giants. III - M71, M67, and NGC 2420
http://adsabs.harvard.edu/abs/1980ApJ...241..981C
By Cohen, J. G.



Ifyou liked this article, you may want to check out the rest of theseries.
http://www.cloudynights.com/category.php?category_id=170

I'd love to hear of your experiences under the night sky - please feelfree to
e-mail me or send any observing reports to: tomt@cloudynights.com
Please indicate if I can cite your observations in future columns.

Photographic Images CourtesyDSS: copyright notice
http://archive.stsci.edu/dss/acknowledging.html

Star Charts Courtesy ChrisMarriott, SkyMap Pro 10 Used with Permission
http://www.skymap.com

Locational Images Courtesy BillTschumy, Where is M13? Used with Permission
http://www.thinkastronomy.com/




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