Objects of the Week, May 24th, 2015 - Double your pleasure - NGC 6441 & Haro 1-36
Objects of the Week, May 24th, 2015 - Double your pleasure - NGC 6441 & Haro 1-36 + Surprise Guest Object, in Scorpius
NGC 6441 = ESO 393-SC034
R.A.: 17h50m13.0s
Dec.: -37°03'06" (2000)
Size: 9.6'
Mag: 7.20 B
H 1-36 = He 2-289, PN G353.5-04.9, PK 353-4.1, ESO 393-31
R.A.: 17h49m48.2s
Dec.: -37°01'29" (Right next to G Sco :>)
Size: 10"
Mag: 12.5 B
I really enjoy observing dissimilar objects in the same field of view, and that's what I have chosen for this week's OOTW.
NGC 6441 is a nice enough globular cluster, and is unique in one sense because it is only one of a few known metal-rich globular clusters. It is about 8 or 9 arc-minutes in diameter (compared to M 13, for example, which is about 20), and is a nice bright 7.2 mag. NGC 6441 was discovered by James Dunlop on May 13, 1826 from Paramatta, Australia and is also cataloged as Dunlop 557.
Using my 25" dob, NGC 6441 is almost all core, and the intense brightness of the core drops off rapidly. It is a dense cluster, with just a few resolved individual stars. There is a 10th mag star about 1.2' SW of the core, HD 161948... more about this guy later.
Your typical eyepiece field of view, when viewing NGC 6441, will undoubtedly include the 3.2 mag star G Sco (HR 6630, HD 161892, SEE 340A, B, C), which frankly dominates the view. Close to G Sco (http://stars.astro.illinois.edu/sow/gsco.html), about 1.3 arc-minutes NNW (PA 330) lies Haro 1-36, originally classified as a planetary nebula, but that identification was later modified to that of Symbiotic Binary star, which, according to Brian Skiff (writing on Amastro a few years ago) "... is a common error since the spectra of the symbiotic stars have numerous very strong emission lines, and are well-known PN mimics. Something like one-third of the things originally called planetary nebulae are not, leading to much confusion in the literature." Thanks, Brian!
Haro 1-36 is a tiny object, and one would think that at mag ~12.5 it might be overwhelmed by G Sco... but it responds strongly to an OIII filter, and with 'blinking' the field, this fellow pops in-and-out admirably. The first time I observed this guy it was a very pleasant surprise, and a real treat! To me it looked slightly elongated, perhaps 6" x 9" or so, and blinking helped verify its identity because it resides in a very rich field of stars.
Surprise guest object; PN G353.5-05.0 = JaFu 2
Let's jump back to NGC 6441, and let me give you another reason why it is unique... it is only one of (4) globular clusters known to contain a planetary nebula, the other (3) being M22 (GJJC 1), M15 (Pease 1), Palomar 6 (JaFu 1), and was unknown until its discovery in 1997 by Jacoby and Fullton. Concerning NGC 6441, planetary nebula JaFu 2 is contained within... but I can find no indication that anyone has recovered this guy visually, so this presentation is just informational... but if anyone has, in fact, observed this object, I'll bet he or she is a member of Deep Sky Forum! I have looked for JaFu 2, but never under ideal conditions, and although I was confident of locating the exact position, I didn't see a hint of the planetary. Be sure to chime in if you have made this observation! The location of JaFu 2 is fairly straightforward. Here is a link to more JaFu 2 information... http://spider.seds.org/spider/MWGC/Add/n6441_jafu2.html ... and here is a pretty good visual guide...
... I've drawn a couple of lines, starting from the aforementioned HD 161948, continuing through the brightest stars in the area to help guide us to the planetary's exact position.
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