Archived from: http://www.blackskies.org/pn_gc_challenges.htm

PLANETARY NEBULAE IN GLOBULAR CLUSTERS

by Doug Snyder

Four Challenging Observations For The Amateur Astronomer

If you have already read what's below, or don't care too, and just want to surf to these challenge pages, here are links that will take you to the appropriate challenge sections. These pages may take longer to load as they contain finder charts.
GOOD HUNTING & DARK SKIES!

[ Pease 1 | GJJC 1 | JaFu 1 & JaFu 2 ]

I have created this page to serve as a jumping on point to four current observation challenges for amateurs with the desire, patience (and equipment) to attempt to log these four planetaries which are located within the gravitational boundaries of Globular Clusters. It is estimated that globular clusters may contain from 10,000 to over 1,000,000 stars concentrated within a volume of from several 10's of light years to over 200 light years in diameter. All the stars that make up a GC are gravitationally bound with each other and it has been found that a large number of GC's are concentrated around the Galactic Center of our galaxy, the Milky Way. Of the 130+ GC's known and the tens of millions of stars which are contained in them, only four GC's have been found to harbor single planetary nebulae (PNe). For much more information on GC's, the SEDS web site is a great resource for all astronomical objects. Be assured that none of these four objects are easy catches, and the latest two are definitely in the 'possibly impossible' category. But give them a try and prove me wrong!

The Globular Cluster Planetaries

The first PNe to be discovered within a GC has the designations of Pease 1 and K 648. This PNe is deep within the star concentration of the GC M15 (NGC 7078) in the constellation Pegasus. It was first mentioned in a photometric study of M 15 (Messier 15), published in 1921 by Friedrich Kustner (The 'K' in K 648). The true nature of the star was determined in 1927 by astronomer F.G. Pease by using filters and spectrographic methods at Mt. Wilson Observatory. (PASP 40, 342, 1928) It should be noted that although extremely difficult to locate and verify within M15, Pease 1 is being observed by a good number of amateurs with telescopes down to 12.5" (with dark skies, filters, and lots of patience!) But most observations have been reported using 17" or larger telescopes.

The second PNe discovered was found to be near the 'core' of GC M22 (NGC 6656) in Sagittarius. This PNe was first noticed in the IRAS mission catalog as an infrared point source and its original designation was IRAS 18333-2357 (1985). Further study of this point source by a group of astronomers in 1988 which included F.C. Gillett, G.H. Jacoby, R.R. Joyce, and J.G. Cohen led to the determination that this was a newly discovered PNe within a GC. The additional designation attached to this PNe was GJJC1. Their paper on this discovery is Astrophys. J. 338, 862, 1989. This is an extremely difficult object to locate and observe, but as of June, 2001, I have received six positive reports, with telescopes ranging in size from 10" to 36" (in between: 20", 20", 22", 25")

The third & fourth PNe's to be found within GC's came about through a survey of 133 galactic globular clusters conducted exclusively to find PNe's within galactic GC's. This survey, led by astronomers George H. Jacoby and L. Kellar Fulton (among others), led to the announcement of these two discoveries in 1997 (1997AJ....114.2611J). The objects discovered were found to be within the gravitational boundaries of the GC's Palomar 6 in Ophiuchus and NGC 6441 in Scorpius. The newly found PNe's have the designations of JaFu1 (GC Pal6) and JaFu2 (GC NGC6441). Note that both ground based and HST instruments were used to obtain images and data for these objects. There has been no positive observation reports received by me on these two objects (As of June, 2001).

Finder Charts and Data

There are individual sections for both Pease 1 and GJJC 1. These sections were constructed prior to this page being introduced, and so there are separate links to each of them as shown above. Since the last two discoveries are discussed within the same paper by Jacoby and Fulton, I have included the finder charts and data in a section devoted to them. Presently, there are a number of finder charts, and not much data. I plan on incorporating much more data from their paper as I get the opportunity. In the mean time, ANY positive or negative observation reports will be gratefully accepted and posted here on the web site.

Author: Doug Snyder

Hartmut Frommert
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