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Old 09-04-2011, 09:48 PM
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Paddy (Patrick)
Canis Minor

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Observations 2/4/2011 and a chart correction

A bit more LMC and a couple of bits in Corvus - on following up through the NGC/IC project site, I have found an error on chart 3 on my site - now corrected.

2/4/2011

Telescope 410mm (16”) f4.9 tri-dob reflector
Eyepieces 28mm UWAN, 17,13,9 mm Naglers, Paracorr
Navigation: Night Sky Observer’s Guide (NSOG) My own charts of the Large Magellanic Cloud (3, 4 & 8) http://www.cloudsofmagellan.net.au/


2305

Seeing excellent 1/5
Transparency good 6/7

NGC 1783 OC in LMC

This is readily found 30’ to the NNE of the NGC 1760 complex 175X Large, 3’ dia round smooth cluster with central concentration but no resolvable stars. The core seems to be about half the width of the whole cluster.

Just to the north is NGC 1787

NGC 1787 OC in LMC

175X A wide swathe of 50-60 stars and faint patchy haze some of which lights up with UHC filter. Steve Gottlieb’s notes on NGC/IC project site are 13.1" (2/17/04 - Costa Rica): large cloud of stars, 15'-20' in size, over extensive haze of unresolved stars. 40-50 stars mag 11-13 visible at 105x within the cluster. N1783 is located 15' S.
Discovered by JH (h2731) in LMC. His single observation placed this cluster at 05 00 17.3 -65 50 33 (2000). His description "p Rich cl of S stars which fills
field" appears to described the entire 20'-25' association HW 15 which includes N1783 and SL 178.
The RNGC and N2000.0 position is 04 59.1 -65 44 (2000). This position is from
Lucke and Hodge's "A Catalogue of Stellar Associations in the Large Magellanic Cloud",Astron. J., v. 75, pp. 171-175, and corresponds with the NW portion of the association. ESO and Morel incorrectly place N1787 at 05 01 42 -65 49.4 but this corresponds with SL 178 at the E edge of the association.”


Following the Morel charts and using the image from the NGC/IC project site (which is on SL178, not NGC 1787), my charts included this mis-identification of NGC 1787 - now corrected.

About 30’ ESE of NGC 1783 is NGC 1805

NGC 1805 OC in LMC

175X Quite a bright grainy small cluster with marked central core and a resolvable star on its western edge. About 40” dia. There is a small but distinct bright projection from the core into the halo on the eastern side.

SL 178 OC in LMC

175X Forms the NE vertex of an equilateral triangle with NGCs 1783 and 1805. Much less distinct than 1783 & 1805, this OC is next to a bright star and looks stellar itself until averted vision reveals a faint halo around either a core or star in the centre of the cluster. The halo may touch the adjacent star. The halo is less than 30” across.

The object marked on my chart as NGC 1787 is at the coordinates for SL178.

A line from NGC 1783 through 1783 and extended 3X lead to a bright star and 2 clusters NGC 1859 and 1866 which is very much the brighter of the tow

NGC 1859 OC in LMC
175X Soft but distinct 1’ dia glow with obvious core surrounded by smooth round halo.

NGC 1866 OC in LMC
175X Very bright and very slightly elongated E-W. Smooth texture but averted vision shows a core and some resolution of stars. 2’ x 2.5’

A line from NGC 1866 through 1859 and extended 2x leads to NGC 1831.

NGC 1831 OC in LMC
175X Fairly large 1.5’ dia round distinct OC with slight core and grainy texture to the large soft halo. Very similar in appearance to 1783 and 1866, but a tad fainter.

NGC 1925 OC and emission nebula in LMC
175X A wide swathe of gossamer with a spattering of 20 or so stars. Appears like a thick v-shape with the point to the north covering 15’x10’. UHC filter increases the brightness of the haze considerably. A brightening at the tip of the eastern arm of the V is SL 428

Shapley Lindsay 428 OC in LMC
175X A 30” dia. circular brightening of haze with a few stars in the eastern part of NGC 1925.

NGC 1923 OC and emission nebula in LMC
175X A faint circle of haze just less than 1’ across. Brightens somewhat with UHC filter.

3/4/2011 0005

As the LMC sinks (and transparency deteriorates) I turn my attention to Corvus

NGC 4361 PN in Corvus
250X A distinct soft edged grey disc with central star with a slightly brighter inner disc within a soft halo. This is enhanced by UHC filter but not OIII. There is also a small dark annulus just around the central star.

NGC 4756 GX in Corvus
135X I just catch a glimpse of this brightest member of the Abell 1631 galaxy group and a couple of its neighbours before the cloud rapidly swamps the field of view. 4756 is a distinct N-S oval glow near a faint foreground star with a faint foreground star just inside the halo.
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Old 09-04-2011, 10:26 PM
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michaellxv (Michael)
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Hi Paddy,

It's interesting that your decriptions of these OC in the LMC sound more like GC. I had to go look for some images. I'm guessing it's due to the distance that they don't resolve. Is there any visual clue that its an OC and not a GC that you are looking at?
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Old 10-04-2011, 09:34 AM
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Paddy (Patrick)
Canis Minor

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I don't think that there is a way to tell visually and certainly a lot of them look like GCs. I think the decision is based on assessment of star numbers and spectroscopy - using metallicity to determine the age etc. The story of GCs in the LMC seems to have changed somewhat over the last 15 years or so as it seems that the age and structure of GCs there differ quite a lot from the Milky Way with the LMC GCs being younger, bluer and with fewer stars. So at some times a lot of these seem to have been classified as "Blue Globulars" or "Young Populous Clusters".

From what I've been able to gather there are 13 official GCs in the LMC and I haven't found a definitive list of them so far. I have a way to go in reading the literature though and a fair whack of it is above my amateur head. So I've relied on the NGC/IC project for determining what classifications to use for objects on the charts.

It does seem that the issue comes down to when do you call something a globular cluster.

Any input from someone who knows what they are talking about would be much appreciated.
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