Object of the Week September 17th 2023 - Palomar 11

Palomar 11

Gcl 114

Globular Cluster

Aquila

R.A. 19h45m14.0s

Dec. -08°00'24" (2000)

Magnitude: 9.80

Size: 10.0

Class XI

Palomar 11 was one of 15 globular clusters discovered on the POSS plates taken with the 48” Schmidt
on Mt Palomar. It is a normal sized globular cluster but is heavily obscured by dust in the Milky Way.
Pal 11 was first found by A.G. Wilson in 1955 and included in a paper published by George Abell in the
same year, although this first list only contained 13 objects. The paper is
http://adsabs.harvard.edu/abs/1955PASP...67..258A It is suggested that Palomar 11 has an age of
about 10.5 billion years and lies at a distance of about 14 kpc from us. It appears to lie about 3.9 kpc
below the plane of the galaxy.

Attachment 5226

Pal 11 appears to be a metal rich cluster that is similar in age and
metallicity to both 47 Tuc and NGC 5927. Pal 11 does not appear to be associated with any of the past
merger populations and streams discovered using the GAIA data and would appear to be a globular
cluster that is actually one of the Milky Way’s own.

Attachment 5227

Palomar 11 has always been a challenge to observe from my latitude at about 52N as both myself and
a colleague were unable to see it with large telescopes (22" and 24") however on a trip to La Palma
observing at around 900m we were able to pick it up with a 12” (30cm) telescope as a faint fuzz. We
could not resolve any stars though. This unfortunately shows the quality of the skies in the UK as it
rises to almost 30 degrees so should have been easily visible. The cluster is quite large and spread
out which makes it quite difficult to see and is probably best observed with a medium to low power
eyepiece. I imagine that those at lower latitudes where it rises higher in the sky will have less trouble
finding it.

As always give it a go and let us know how it goes

With a 20" at 272x:"A bright star on the edge as seen in Uranometria was a clue. With that star off the edge of the filed, a grouping of stars seems like an open cluster. About a class XII (Really = XI)"

I made a number of observations with my former 17.5" and 18" scopes starting in the mid-1980s, but these are my two most recent with my current 24". The first was from the Bumpass Hell parking lot in Lassen National Park (elevation 8187').

24" (7/25/14): this relatively bright Palomar appeared ~3' diameter. Contains a brighter 1.5' central region that was partially resolved at 260x. At 375x, the core contained 5 or 6 brighter mag 14.5-15 stars and an additional 10-15 faint mag 15-16 stars including several within the central 45". A number of stars in the halo sparkled on and off with averted vision or were close to each other, so counting was difficult.

24" (9/7/13): at 200x this easy Palomar globular contained a brighter core and a roundish halo ~2.5' diameter, with several mag 15 and fainter stars resolved. It was well resolved at 375x and 500x into roughly two dozen mag 15/16 (several extremely faint) stars in addition to 5 brighter mag 14.5-15 stars. These stars are distributed over the entire glow, though more concentrated in the 1' core that is slightly elongated SW to NE. Situated 4' SE of mag 8.6 HD 186496 with several brighter mag 12-13 stars scattered outside the halo of the cluster.

Big scopes!

Does this mean that we mortals with a 14" can forget this object?

Sue French included Palomar 11 in one of her Sky & Telescope columns and described it in her 14.5".

At 245x [in my 14.5"], this low surface brightness globular appears about 3' x 2 1/4' aligned NE to SW. It looks mottled, and there are a half dozen superposed stars, at least some of which may be foreground objects (The brightest stars of Pal 11 itself are red giants with apparent mags of around 15.5). A skinny triangle of 11th- and 12th-magnitude stars sits off the NE edge.

I've read a few observations using a 10" from dark sites, including this one from Susan Young at her Bortle 1 site in the Kalahari Desert:

I must confess this one surprised me. I was assuming that the glob’s large size would render it impossible to see. But there it was – a small and very faint glow that didn’t show any central concentration. Averted vision gave it a very, very faint mottling texture that quivered; no stars, simply the very faint quiver of mottling. Very unusual view.

What have others found?

It is faint, even with 16", but also doable with 8" without having a Bortle 1 desert sky. I copy my notes from my Palomar project beneath.

20x125, fst 6m0+
not visible

8", 47x, fst 6m5+
even with 31x a small and very faint glow is visible SE of a 9mag star; with 47x the glow is visible more easy and can be hold with averted vision; glow is not concentrated but shows some mottling without showing a star within the GC; surrounded with some faint 13mag stars

16", 257x, fst 7m2
faint, circular, also visible with higher power, 3 stars glimpsed through the halo, no other structure

20", fst 7m+
bright, can easily seen with lower magnification, with higher magnification a dozen of stars can be seen

24", fst 7m0
bright, circular, spectacular resolution into a couple of dozens of stars

27", 293x, fst 7m+
bright and remarkably glow; without an clearly concentration; with 293x a dozen stars pops out the mottled glow; brightest stars form a square figure near the middle of the GC

Quote:

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Originally Posted by Lars53

Big scopes!

Does this mean that we mortals with a 14" can forget this object?

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You certainly should be able to see it. On August 16, 2020 I saw it at 118x as a soft glow in my...new 130mm f/5 Chinese reflector!!

07/15-07/16/20
LINSLAW POINT
SUNSET: 8:53 PM
MOON: 26 days (rose at 2:22 AM; 16% illuminated)
SEEING: 6
TRANSPARENCY: 8
SQM: 21.73-21.63
NELM: not checked
WEATHER CONDITIONS: temps to upper 50s; no dew; mild breeze, pleasant
OTHERS PRESENT: MW, Mike D, Dale F
All observations: 12.5?f/5 Discovery Dob, 14mm ES 82? eyepiece (112x, 0.7? TFOV) unless otherwise noted

1:14
Palomar 11 (Aql): This is the much sought-after and only-seen-once before (at the Oregon Star Party) Palomar 11, on a night where we’ve registered 21.7 to 21.67. The cluster is exceedingly ghostly, but in averted vision it’s actually quite “present”; I’m really surprised at how easy it is here with a 12.5” on this particular night. The cluster is pretty large; it’s about 4’ in diameter. It’s bracketed on the F and P slightly S by 12.5-mag stars that are just on the periphery on each of those sides. From the star on the F, there’s another 1.75’ N slightly P, and from that star NP by about the same distance is the fainter of a pair; that fainter star is 11.5 magnitude, and it has SP it by 0.3’ a 10.5-magnitude star; the 10.5-magnitude star is about 3.5’ N slightly F the middle of the cluster. 3.5’ P the 10.5 magnitude star is the brightest star in the field, which is 8.5 magnitude and is N somewhat P the cluster by 4’. The cluster itself has a very faint granularity to it, considering that it’s barely visible; it seems to have kind of a sprinkling of threshold stars across it, in averted especially, and they flash in and out with averted vision; especially on the P side of the cluster there seems to be a few that are resolved. It’s obviously a very loosely-concentrated object . If I was to take a stab at the magnitude of those cluster stars, I’d say they’re in the 15th magnitude range, and the whole cluster is visible in direct vision about 90% of the time but it certainly doesn’t warrant staring directly at due to lack of visible detail in direct vision. Let’s try the Precious (the 10mm Delos) here– and I bumped the scope (Lots of searching and one dead, unjugged rabbitfish later)….OK, we’re back with Pal 11 in the Delos, because why would I really want to use anything else? This eyepiece really makes the cluster stand out; it just outclasses every other one I’ve got by a huge margin. There’s a lot of suspected granularity now in the cluster; especially on the P side, there seems to be a kind of an arc of a couple of stars, three stars maybe, on the P side of the cluster, but these are very faint; there’s definitely a concentration of stars there on that side. The cluster itself is pretty obvious in the Delos, first time I thought I could say that about a Palomar.

Here are my notes on Palomar 11 from a Central Texas observing site on 2013 August 3rd using my 18" f/4.5:

Easy star-hop from Kappa Aquilae. Rather faint, but "resolved" even in 31mm Nagler. After precise star-hopping, it was easily located in the field and confirmed against neighbouring stars. 10mm Delos insinuates that the feeling of resolution might only be because of foreground stars. Somewhat large, faint glow with a few bright stars (presumably foreground stars) on it. DSS image seems to indicate otherwise, that the feeling of resolution is actually real and there are no real foreground stars. This is confirmed again by averted vision.

Clear Skies
Akarsh