Starship Asterisk*

zb4ms wrote:Spectroscopy would give a better indication of the true nature of these sources.

Who wants to volunteer for this?

dokkum wrote:Perhaps a globular cluster that is being tidally disrupted?

As good of a guess as any. It seems unlikely that it would have formed like that. Could be the stripped core of another dwarf. If that's the case, I find it interesting that it looks like it's completely abandoned and off to the side by itself. It'd be like all but the closest stars either joined up with the other dwarf or went flying all over the place, leaving a weird shaped core behind. Dwarf galaxies certainly are an interesting bunch. Too bad the big spirals steal the show so often.

Chris wrote:
It might be a galaxy. Or it might be an unusual form of cluster that simply hasn't been properly classified.

It absolutely doesn't look like a galaxy to me.

We can be almost certain that this object is small, in view of its small angular size combined with the fact that we see no evidence of any obvious redshift reddening in its color. But it certainly doesn't look like a typical dwarf galaxy. Dwarf galaxies are usually either loose, like Leo 1, or compact, like M32. To my knowledge, they just aren't small, compact and surrounded by a starry halo where many of the individual stars are quite bright compared with the overall brightness of the galaxy itself. It is globular clusters that look that way, not galaxies.

The shape of this object is weird for a globular cluster, but its stellar content, size, compactness and strikingly star-rich halo make it very weird for a dwarf galaxy. It might technically be a large galaxy surrounded by numerous globular clusters, but it is too unreddened and really too grainy for that.

Ann

Ann wrote:

Geck wrote:
PGC 47857 is a synonym for NGC 5238.

My software says that PGC 47857 is located in the lower part of NGC 5238. According to my software, the magnitude of NGC 5238 is 13.7, while the magnitude of PGC 47857 is 16.2. So there must be some people who think that NGC 5238 and PGC 47857 are not the same.

Ann

You have told me before, Ann, but I've forgotten the name of the software you use - could you remind me? Many thanks.

Margarita

geckzilla wrote:Yeah, that's the squishy football ellipsoid globular cluster wannabe. The more obscure an object is, the less likely it is to have been looked at thoroughly. Such entries in SED or SIMBAD could be wrong.

I looked it up here in case they had a spectrum, but no joy. It's again classified as a galaxy. Is that the default for "it's not in our galaxy and it's a long way away"?! I'm way out of my depth here, but it's fun!

M

Ann wrote:

Chris wrote:
It might be a galaxy. Or it might be an unusual form of cluster that simply hasn't been properly classified.

It absolutely doesn't look like a galaxy to me.

Nor to me. But I've seen enough odd things in astronomical images to not allow my visual impression to sway me too much.

I don't trust that there's actually a star halo around this object. I've seen similar illusions.

I don't trust color. We don't consistently see redshift, and in any case, this image is not made from filters which create an image with accurate color.

We don't even have a solid definition for what a galaxy is. There are dwarf and irregular galaxies that overlap globular clusters in size, mass, and composition.

What I know is that this seems to be a peculiar object. It is substantially more elliptical than any other globular cluster I've been able to identify. It appears to have a disc bisecting it (I don't believe this is a diffraction artifact, as there is at least one other object in the image with a similar size which is brighter and has no diffraction artifacts). I think the most likely explanation is that it's either an incompletely formed globular (one model says they form irregular, and become globular because of tidal effects), or a previously globular cluster that has become disrupted.

In any case, we can do little more than make educated guesses until somebody points some instruments that way and collects more data.

Alice posted about this on Facebook in the astronomer's group (which I don't have access to!) and one of them pointed out this globular cluster, which is cool and just to show that there are some very elliptical GCs.
http://www.bo.astro.it/M31/hstcatalog/W ... /B088.html

geckzilla wrote:Alice posted about this on Facebook in the astronomer's group (which I don't have access to!) and one of them pointed out this globular cluster, which is cool and just to show that there are some very elliptical GCs.
http://www.bo.astro.it/M31/hstcatalog/W ... /B088.html

Yeah, but that still only has an ellipticity of about 0.25, about the same as the most flattened LMC examples in the paper I referenced earlier. This is much less than the object in your image, which is at least e = 0.4, possibly more.

MargaritaMc wrote:

Ann wrote:

Geck wrote:
PGC 47857 is a synonym for NGC 5238.

My software says that PGC 47857 is located in the lower part of NGC 5238. According to my software, the magnitude of NGC 5238 is 13.7, while the magnitude of PGC 47857 is 16.2. So there must be some people who think that NGC 5238 and PGC 47857 are not the same.

Ann

You have told me before, Ann, but I've forgotten the name of the software you use - could you remind me? Many thanks.

Margarita

It's this one. My good friend Arne Lindengard helped me buy it and install it.

Ann

If you called it what it is, which is Guide, instead of "my software" then it would be less awkward.

geckzilla wrote:If you called it what it is, which is Guide, instead of "my software" then it would be less awkward.

Do you know this program, geck? Its data is drawn from http://www.usno.navy.mil/USNO/astrometr ... -prod/ucac, so that looks good. But I looked at the Guide website and the last update was 2012 - which makes me cautious about entering credit card details.

I use Stellarium, but I haven't checked it to see if it has info about this object under discussion. (I'm on the Android tablet only, as the builders are in and we are living in the basement.)

MargaritaMc wrote:Do you know this program, geck? Its data is drawn from http://www.usno.navy.mil/USNO/astrometr ... -prod/ucac, so that looks good. But I looked at the Guide website and the last update was 2012 - which makes me cautious about entering credit card details.

I'd be cautious about Guide. It's pretty long in the tooth, and kind of non-standard with respect to current Windows interface guidelines. It's more for plotting charts than exploring the sky.

There is a ton of free planetarium software out there, and a lot of online tools, as well. At the school we use Cartes du Ciel, which can use a huge range of catalogs.

Thanks Chris. I'd just come across Cartes du Ciel in a web search, so I will follow that up. I've also discovered that Stellarium now has an Android version, so I've installed that on my tablet.
Mostly Stellarium is sufficient for my needs, but sometimes (like now) I would like to explore more deeply without having to find my way through several different web site databases. (Even tho it is satisfying to get a hang on how they work.)

For simply looking up objects I've taken to Aladin as of late. If I need to simulate something then I use Stellarium. I may be biased toward Stellarium because I used to know the guy who did the constellation art.

geckzilla wrote:For simply looking up objects I've taken to Aladin as of late. If I need to simulate something then I use Stellarium. I may be biased toward Stellarium because I used to know the guy who did the constellation art.

Thanks for the tip about Aladin. I've now got the previewer on my Tablet home screen.

Do you ever use lookUP, from Stuart (Strudel?)l? I've had it on my browser for months and ( ) forgot about it.
Here's what it returns about "The Object Under Discussion"!
http://www.strudel.org.uk/lookUP/?name= ... B513547.6+

SDSS J133445.99+513547.6 (RA 13:34:46.0, Dec +51:35:47 FK5 J2000) Object of unknown nature.

M

PS. Love the Stellarium constellation artwork!

Edit: because I had had a senior moment over the name of the originator of lookUP ...