Two UCD's in Messier 59

[Jimi Lowrey]

I recently ran across a paper about two UCD's (ultra compact dwarf's) in M59. One M59 UCD-3 I had observed before but the other one UCD-c0 was new to me. I observed both of these rare objects the other night under great transparency and ok seeing. M59-UCD-3 was easy to see at MAG 14.2 but M59-c0 was a lot tougher. I could only see it with AV and could only hold it for a few seconds at a time. I thought that it was a lot dimmer than the 17.6 MAG in the SDSS average of the G and R band. I am confident of my observation as I could see it at the right location many times.

M59-UCD-3
Ra
12 42 11
Dec
+11 38 41
2979

M59-c0
Ra
12 41 55
Dec
+11 40 03
2980

[Robin]

Hi Jimi,

This sounds really interesting! Which paper did you get it from?
I just googled "M59-UCD3" and found this one:
https://arxiv.org/pdf/1506.08828v2.pdf

According to Table 1 and the text below the table it is V = 16.34 +/- 0.05 mag and radius = 0.28"
According to NOMAD catalog there is a 15.79 mag object at this position, while according to your source it is 14.2 mag.
So this dwarf galaxy should be visible for any telescope and observing conditions that reveal stars of 14.2 - 16.39 mag, depending on the source.
Under the conditions that I usually have, I can get to 16.0 to 16.2 mag with 12 inch aperture. So if I take my telescope to really dark skies, this might be visible.
And it makes me wonder how many "point sources" near galaxies are actually dwarf galaxies.

Clear skies

Robin

[Jimi Lowrey]

I do not think from viewing it several times that is as dim as the papers you quoted. Sometimes it is hard to get good photometry on a object because it is so near M 59. There are several papers on this object here is a good one.
http://iopscience.iop.org/article/10.1088/2041-8205/812/1/L2/pdf

I look forward to hearing about your observations + or - of this unusual object.

[Robin]

Hi Jimi,

The paper you cited says g' mag = 16.74 in table 1 and cites a Peng et al. 2006 reference, according to which g' - V = 0.40 mag. This would also mean 16.34 mag.

I tried to give it a go with my 12" Dobsonian this weekend, but I didn't see anything as bright as 14.2 mag there. I was looking at the field on this side of the galaxy for about half an hour and saw something blinking and flickering at the expected position 5 times. It was really hard to discern this from "visual noise" in my retina or between my retina and brain (when observing something at the detection threshold of my vision, I always see something flickering up at random positions, perhaps as bright as objects slightly beyond 16 mag in my 12" Dobsonian. Then I have to filter for signals always flickering up at the same position against signals flickering up at random positions).
Perhaps I really detected some photons coming from this ultra-compact dwarf galaxy, but I think I'm not confident about it either.
But I suspect that it may be visible with 14" or 16" aperture at similar conditions (NELM 6.6 mag).

I saw several field stars down to 15.8 mag around Messier 59. All of them were easier that UCD-3. Please find attached my sketch, in which I marked the suspected position and magnitudes of field stars according to 3UC catalog.

Did anyone else try to observe this object? It would be really interesting to know what minimum aperture is required for a confident detection or how difficult it is for a given aperture.


Clear skies,

Robin