Object of the Week July 25th 2020 - M11

[obrazell]

M11

Wild Duck Cluster, NGC 6705

R.A.: 18h51m05.0s
Dec.: -06°16'12" (2000)
Magnitude: 6.10
Size: 32.0'
Trumpler Class I 2 r

With the bright skies of summer still affecting high northern latitudes it is worth picking a bright target
for this OOTW. Surprisingly not already covered by an OOTW the open cluster M11 in Scutum is one of
the most spectacular sights in a small telescope or binoculars. First discovered by Gottfried Kirsch at
the Berlin observatory in 1681 M11 was first resolved into stars by William Derham in the UK using an
8 foot focal length speculum in 1733, unfortunately he does not give the diameter of the mirror only
that he had to stop using it because it became too tarnished. Messier included it in his catalogue of
comet interlopers in 1764. The nickname of the Wild Duck cluster was given to it by Admiral Smyth
where he compares it to the shape of a flock of wild ducks in flight in his description in the Bedford
Catalogue, no doubt just before he took a shot at them! The brightest stars do indeed form a v shape.
Through a small telescope one bright star stands out amongst the others and the apparent dark shape
which delineates the cluster does indeed make it look like a V. The bright star, HD 174512, is also a
multiple star system. M 11 is one of the Messier objects that are visible to the naked eye. The cluster
is thought to be about 220 million years old and lies at a distance of perhaps 6200 light years from us,
although GAIA may push that out to 7200 lyrs. At this distance the core of the cluster is perhaps 20
light years across. This means that it is the most distant of the Messier open clusters that can be seen
with the naked eye. The cluster contains perhaps 2900 stars and will be expected to disperse due to
galactic tides over the next few million years or so. M 11 lies maybe 6.8 kpc from the galactic centre
and lies in the galactic plane, as perhaps one would expect for a young Pop I cluster.

m11pos.jpg

The brightest stars in it currently have a spectral type of B8, the more massive ones having already
evolved into red giants and gone. The cluster stars also show an enhancement of Alpha process elements
despite its youth, possibly due to the seeding of its birth cloud by a nearby Type II supernova. M11 is also
one of the most massive open clusters known with a possible mass lying between 2500 – 35000 Solar
masses. There is a very nice image of this cluster with the ESO 2.2m telescope at
https://www.eso.org/public/images/eso1430a/. M11 (or the core of it anyway) was also shot by Hubble at
https://www.spacetelescope.org/images/potw1912a/.


m11pan.jpg

PanSTARRS image courtesy of Aladin

As always give it a go and let us know.

[Raul Leon]

Hi here is my observation from 6/18/2207: Messier 11 aka the Wild Duck cluster is an open cluster in Scutum ; magnitude:5.8 ; size:22' ; very bright and compact for an open cluster, many dark lanes intertwine throughout the cluster. One bright star stands out against all others. Interesting clumps of stars in central region. One of the most visually stunning open clusters, I make it a point every summer to observe this marvelous object. I used a 14mm Meade ultra-wide eyepiece at 113x with my 14.5 Starstructure dob f/4.3 messier 11.jpg

[KidOrion]

As many times as I've looked at M11 over the years, I've only recently taken notes on it for the first time.

06/18/20
THE OXBOW
SUNSET: 8:59 PM
MOON: 27 days (set at 6:39 PM; 9% illuminated)
SEEING: 6
TRANSPARENCY: 7
SQM: 21.44
NELM: not checked
WEATHER CONDITIONS: temps to low 50s; slight dew; air still

OTHERS PRESENT: JO, KO (20” TriDob), LR (18”)

All observations: 12.5″f/5 Discovery Dob, 14mm ES 82˚ eyepiece (112x, 0.7˚ TFOV) unless otherwise noted

1:41
Messier 11 (Sct): Not wanting to end yet, although we were all packing up, so one more for the road. I’ve been hesitant to take notes on this one. Words fail; this is the premier open cluster in the sky in impressiveness, detachment, richness, etc. Just F center is the cluster lucida, which is of 8th magnitude. The cluster is roughly diamond- or square-shaped, with corners to the NP, NF, SP, and SF. The cluster is roughly 7’ in main body and has outliers extending out to 9’ x 12’, with a S slightly P-N slightly F axis major axis. Off the N end, 5’ from the lucida, is an arc running NP-SF for 7’ that is a separate detached portion of the cluster. M11 is incredibly rich (200+) and very well detached, even in the dense Scutum Star Cloud. The majority of cluster stars are in the 11.5-13th magnitude range. The cluster also has numerous dark voids within it, and there are a lot of dark nebulae in the area around it; the darkest and largest void is on the cluster’s NF edge between the NF edge of square and the arc to the N, kind of an apple-core shaped void that’s pinched at the middle and is 2.3’ P-F by 1.5’ N-S. The square body of the cluster itself contains four voids, of which two run together. There’s also a triangular void P the lucida on the P corner of the square, which is the least-dense void, roughly equilateral and 1’ on a side. To the S and SF and sweeping around the cluster is another large void that wipes out that edge of cluster, especially on the S; there are a few stars on the F edge of the last void that help make up the right angle on that side of the square, but the void blows out the area due S of the lucida, which is completely barren of stars starting 1’ S of the lucida and stretching further S; so there’s a 1’ area S of lucida with stars and then none, and then the remainder of that corner of the cluster. 1’ F the lucida and stretching SF is another dark nebula. SF the lucida by 4.5’ is the more S of a pair of 9th-magnitude stars separated N-S by 0.75’, with the N of the pair the brighter. On the extreme NF corner of the square of cluster is a very tiny, almost planetary nebula-looking 9” knot of unresolved stars. The dark void S of the lucida also extends much farther to the SP and fans out from there, but is somewhat less opaque with some background glow there—a dark slash through the cluster and beyond the square. A magnificent object!

That's to say nothing of the wonderfully-detailed fields around the cluster, filled with dark nebulae in abundance.