Object of the Week, July 29, 2018 - NGC 6500, NGC 6501, MAC 1756+1820 and Struve 2245

[Howard B]

Galaxy pair with nearby double star and faint background galaxy

Hercules
RA 17 56 00
DEC +18 20 20 (coordinates for NGC 6500)
Magnitude 13.0, 13.1, 16.0, 7.43
Size: 2.2 x 1.6, 1.9 x 1.7, 0.6 x 0.5

Sometimes a view is so pretty that it has to be shared, and that’s exactly the case here. There’s no exotic astrophysics or record setting red shift to talk about here, only a beautiful field of view.

NGC 6500 and NGC 6501 (right to left in my sketch) are a physically associated galaxy pair that make an equilateral triangle with the colorful double star Struve 2245. Neither galaxy is much more than a slightly oval 13th magnitude fuzz ball, but together they make a striking pair nonetheless.

N6500, N6501, MACgalaxy_double star_invert_colored stars_crop.JPG

But it’s the proximity of the yellow-gold and turquoise double star that makes the group really pop - I certainly stayed glued to the eyepiece longer than I would have otherwise during my latest look a couple weeks ago during the Golden State Star Party.

The brightness of the two stars and beautifully complimentary colors give a sparkle and vibrance to contrast with the relatively dim and distant (145 million light years) glow of the two NGC galaxies. Take your time and enjoy.

The subtle part of this view is the 16th magnitude galaxy MAC 1756+1820 that’s hanging out right on the edge of the radiance glow of the double star. You’ll need to know exactly where to look to have a chance for this one, and if the sky isn’t clear and dark enough you may not be able to see it anyway, so this is as much a test of the sky as of your scope and observing skill.

But then this is a field of view that’s worth coming back to many times, and at the very least you’ll always be rewarded with a lovely double star.

"GIVE IT A GO AND LET US KNOW"

[Clear Skies]

Galaxies and double stars: my kind of observing!

This pair of galaxies is known as KPG 526 in Karachentseva's Catalogue of Isolated Galaxies (northern). NGC6500 is KPG 526A, NGC6501 is component B.

I logged a single observation for this pair in september 2013 from the French Alps. 12" SCT @ 179x/27':

NGC6500 (KPG 526A) and NGC6501 (KPG 526B) share the field of view.
NGC6500 is the SSW galaxy: Brighter and slightly larger than NGC6501, slightly elongated NE to SW, brighter in a small, round central part, using AV the faint nucleus is visible.
To the NW is a mag. 13 star, the same distance towards the ENE is a mag. 14 star. To the east is the double star STF2245. 1/4 FoV NNO is a yellow-orange mag. 9 star with a mag. 13 star to its WSW at a PA of approximately 260 (= double star Hipparcos Double Star 2528 / WDS17557+1830). AB split.

NGC6501 is the NNE galaxy: Fainter and slightly smaller than NGC6500, brighter in the middle (a brighter central part than that of NGC6500), using AV the nucleus is visible.

I logged my third observation for STF2245 (WDS17564+1820) at the same time, previous observations were in 2007 and 2013:Two white-yellow mag. 8.5 stars aligned ESE to WNW, a PA of approximately 095/295. AB split, AaAb not visible.

The Karachentseva catalogs are interesting for medium sized and larger apertures (12"+). The northern and southern pairs & triples (KPG, KTG, KTS and Reduzzi-Rampazzo candidates for southern pairs) will be part of CSOG 2.4. Don't expect it before 2020. In the mean time I am on track for a release of CSOG 2.3 in mid-2019 (http://www.clearskies.eu/csog, bottom of page) which will include Holmberg's Catalog of Double and Multiple Galaxies (827 entries).

[Mark McCarthy]

I've seen STF 2245 from my red zone back yard and a full moon to boot, 12.5" 277x: "Very pretty yellow-orange and blue. Alberio like, but fainter and closer together; and the stars are about equal magnitude."

No hint of the galaxies of course. Will have another look next chance I have!