Object of the Week December 9th, 2018 - NGC 1851

Object of the Week - NGC 1851 = ESO 305-SC016 = Mel 30 C 73 - Globular Cluster in COLUMBA

R.A.: 05h14m06.0s Dec.: -40°02'48" (2000)
Apparent Size: 12.0'
Magnitude: 7.10

From my +33° latitude, today’s OOTW, NGC 1851, is not a particularly flashy object, but it is a fascinating and fairly unique globular cluster nonetheless. It is located at declination -40°, low in the western corner of the small and faint constellation Columba, the Dove, which is mostly directly south of Lepus, the Hare, which is itself mostly directly south of Orion, the Hunter. It never gets too high above the horizon for me, about 15° or so, and it is probably even lower for many readers here. Still, it is a nice surprise for everyone who looks at it for the first time. I vividly remember the first time I star-hopped to NGC 1851 about 35 years ago with my brand-new C-8, I was surprised just how pretty it was and how its core was unexpectedly bright. It is one of the most compact GC’s known. I’ll bet it is a wonderful sight from Down Under. Here is a nice photo by Damian Peach from Siding Spring, Australia…

https://britastro.org/system/files/s...?itok=y9xN3aHL

But wait! There is more to the story than NGC 1851 being just another bright Globular Cluster. It seems that NGC 1851 is a possible remnant of a dwarf galaxy! This would put it in rare company, for only about 8 or 10 other objects can say the same thing. Studies show that there are at least (2) subpopulations of stars formed at different times, with each showing different metallicity measurements, making this an ‘anomalous’ cluster. So, there are apparently (2) scenarios to consider… one is that NGC 1851 is one of several globular clusters left over from a dwarf galaxy that was previously ripped to shreds by the Milky Way, ,or that NGC 1851 is the ‘kernel’, or core, of a former dwarf galaxy… but in either case it appears to be of extragalactic origin. I need to say that I have learned much of this from the recent availability of Volume 6 of The Annals of the Deep Sky (Jeff Kanipe & Dennis Webb), and there is still even more to the story, so check it out for yourselves.

In any case, this is a terrific object, especially if you can get yourself way down south for a really good view.

As always, give it a go and let us know.

Great choice Paul and very interesting that this may be a remnant of a dwarf galaxy. I observed this globular cluster from 40 degrees north using my 20" telescope in 2012 and noted "brighter than M 79 but not resolved in stars due to the low elevation above the horizon". Sounds indeed as if I need to observe this one from more southern latitudes.


Clear skies, Wouter

I viewed it both in 18x50 IS binoculars and in a 150 mm telescope from central Australia. My notes say: "Resolved telescopically at the high power. Very pretty." The high power was up to about 280x, with a Pentax zoom.

Likewise in 1998 from Aruba, I saw it with a pair of 11x80 binoculars: "Bigger than a star; quite bright and easy to see near an asterism of a trapezium."

Practically invisible from Middle Europe and a horizon test for the best locations in the High Alps (47°N) it is a stunning object from more southern locations.

16" SCT, 308x, NELM 7m0+, Seeing II-III (Sahara Sky, 30°N)
fully resolved; compact and unsteady center; large outer zone

24" Newton, 141x, NELM 7m5+, Seeing III (Hakos/Namibia, 23°S)
dominated by the bright and very compact core; quick light decrease towards the outer zones; no uniform concentration to its middle; drak lane/zone to the southern side

Hi,
Here's my observation from 1/6/2014: globular cluster in Columba; mag:7.1 size:10' ;fairly bright with a very bright almost stellar core; 14.5 Starstructure Dob f/4.3 ;8mm Ethos 198x magnification Attachment 3269

I had a great view of NGC 1851 through a 13.1-inch travelscope that I brought to Costa Rica (+10° latitude) --

At 200x this compact globular was very bright, strongly concentrated with an intense 1.5' core and a 4-5' fainter halo. The core was very lively and there were ~30 stars resolved [brightest cluster members are mag 13.2], mostly in the loose halo. A neat loop of stars emerges from the core and runs NNE-SSW along the west edge of the core.

From October 2008:

NGC 1851
Columba
Globular Cluster
October 28, 2008
03:30 MDT, 09:30 UT
15-inch reflector, 272x
NELM +6.5
New Mexico Skies

This is a large and very bright globular with a round, blazing core embedded in a round, very bright and rich halo. Well seen at high magnification, the richness of the outer halo works against resolution; the stars are fairly tightly packed and very even in brightness, leading to a mottled appearance with resolved stars overlaid.

Attachment 3270