Object of the Week, September 17, 2017 - The UMi dwarf galaxy (UGC 9749) and IC 1110

[Howard B]

Object of the Week, September 17, 2017

The UMi dwarf galaxy (UGC 9749) and IC 1110

Dwarf galaxy and edge on galaxy
Ursa Minor
RA 15h 12m 05s
DEC +67d 21m 45s
Magnitude 14.9
Size: 1.4 x 0.4 arc minutes
(coordinates, magnitude, and size are for IC 1110 because it’s much easier to see than the UMi dwarf galaxy, UGC 9749.)

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These two mismatched galaxies could hardly be more different. The UMi dwarf is a satellite galaxy of the Milky Way and is about 225,000 light years away, while IC 1110 is an edge-on galaxy approximately 157 million light years away.

Their apparent sizes are vastly different too – IC 1110 is a respectable 1.4 x 04 arc minutes but the UMi dwarf is a huge 30 x 19 arc minutes. So even though it's listed magnitude is 11.9, it has a surface brightness so low I can’t find any reference of it. Suffice to say it’s barely brighter than the sky background.

My observing notes from 2013 bear this out:

“IC 1110 was immediately obvious at 131x but not UGC 9749. Only when centering IC 1110 in the field of view did I notice the area where 9749 should be was ever so slightly brighter than elsewhere. The lack of foreground stars here is a help too. This effect was even more pronounced at 253x. 21.77 SQM.”

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My sketch shows only about half the length of the UMi dwarf, but compared to the photo from Wikisky.org it seems to be brightest part.

IC 1110 is just two degrees west from the magnitude 5.13 star, HD 136064 so it’s easy to star hop to, so on the next dark and transparent night…

"GIVE IT A GO AND LET US KNOW"

[Howard B]

Just pinging my original post so it's visible from the home page.

[Steve Gottlieb]

This is an object where dark skies (good transparency) and a wide field are definitely requirements. I've seen it in my 18" and 24", but I've seen reported sightings down to 6". Here's my last observations

24" (7/7/13): the Ursa Minor Dwarf was immediately noticed at 125x (21mm Ethos) with a 50' field of view as an extremely large, roughly oval glow WSW-ENE, extending nearly 30'x20'. The edge was noticed first, particularly along the entire northern side where it has a slightly high contrast than the background. Barely off the ENE end is a mag 10.3 star and roughly at the WSW end is mag 9.4 SAO 16604. A mag 10.7 star is superimposed slightly NE of center. With extended viewing the entire galaxy was seen as an extremely low surface brightness glow and the outline could be traced around fully.

IC 1110, a small edge-on, lies 20' NE of center and 7' further ENE than the mag 10.3 star mentioned above. At 320x it appeared fairly faint, edge-on 4:1 WSW-ENE, 0.6'x0.15', very small bright core, distinct stellar nucleus.

[Uwe Glahn]

Howard,

UMi dwarf is one of a few objects I have no positive result so far. I tried the galaxy with almost every aperture and field under almost perfect skies but could not detect or suspect any sight. I'll stay tuned.