Unknown object next to Saturn 8/6/16

[kkara4]

wasnt sure where was best to post this in the forum, mods please move if needed.

I was out imaging Saturn, Mars and Jupiter on 8/6/16. I wanted to test the ASI290mm's capabilities on Saturn's moons, so i cranked the gain to max and increased shutter to 35ms, which showed rhea, tethys and dione no problem. Enceladus and mimas were revealed after stacking and stretching levels in photoshop.

but as i did this, an unexpected object presented itself. it can be seen in the two attached images 12 oclock of Dione. anyone know what it is? i have inserted a stacked and lightly sharpened image of Saturn through red filter taken just afterwards to give scale to the whole image. i believe i am at around 0.077 arcsec/pixel here. I put the motion at around 1arcsecond?

It cant be a moon since its motion is retrograde to the others, and i certainly didnt discover a new moon that bright (you can see it is a bit fainter than mimas). Cant be Phoebe, since too close. i dont think its a star but stellarium is all i know in terms of checking this, i know there are much more advanced ways of checking. i dont think its a satellite (too bright/slow?). Asteroid would be too faint? comet would be too faint?

Image details as follows:

Telescope: Celestron EdgeHD 925
Mount: Losmandy G11, polar alignment happened to be excellent.
Camera: ASI290mm, red filter, max gain @ 35ms, stack of ~430 frames.
image times: Filenames contain times, center of recordings 8/6/16 (11:39:43UT and 11:41:06UT). Times are accurate to +/- few seconds i believe, since i time synced to UT the computer clock about 5 hours prior.
IMage stacking: autostakkert, Alignpoints placed on Rhea, Tethys, Dione, Enceladus, best 50% using COG method (hence the apparent difference in blown out disk since i didnt align on it).
My location: western suburbs of brisbane

i have exhausted every resource i know of up to my ability, but my knowledge of the more advanced sky charts and other utilities is limited, so hopefully the much more knowledgeable folks on here can help identify the object!

Please let me know if more details are required. happy to provide. unfortunately these two images represent the first and last sequences i captured, because i was really only testing and i only just got a chance to process the videos.

[tonybarry]

Hi Krishan,

I cannot determine what object in your images is the source of interest, as you haven't labelled anything.

However please find attached a SkySafari screen shot of Saturn at the time of your first picture (11:39:43pm 2016-06-08). It may help you out.

Regards,
Tony Barry
WSAAG

[AussieTrooper]

I don't see anything to 12 oclock of dione. Might be missing something here.
At 1 oclock there is a 14mag star which appears to move a tiny amount between images. Is this what you are talking about?

[kkara4]

Ben, yep this is what i am talking about. sorry guys ill upload versions with object clearly labelled in a few minutes.

[kkara4]

Thanks Tony, i didnt know sky safari does all the moons like that, i wonder if stellarium can be set to achieve the same thing :question:. i added annotated versions to OP to make things clearer, apologies all for not doing this in the first place :screwy:

[AussieTrooper]

It's just a star.
If you track Saturn, it and it's moons will move very slightly against the background. All stars and anything not orbiting your target for that matter, will appear to move when you compare the two images.
Hope that answers your question.

[kkara4]

thanks Ben, the motion is roughly aligned with RA so that makes sense.

please correct me if im wrong here, just trying to understand:

Saturn moves against the background stars, lets for arguments sake say 360 degrees every 29 years. = about 12.4 degrees per year = 2.04 arcminutes per day = 5 arcseconds per hour = 0.08 arcsecond per minute.

the object moves much more than that (my image scale is around 0.077arcsec per pixel).

since i am equatorially mounted and Saturn always centered, there shouldnt be any drift (and no field rotation since the moons move completely differently and not in line with rotation of the field if there was any).

would you be able to point me to a skychart that shows much fainter stars than the likes of stellarium?

http://theskylive.com/saturn-tracker is great but i cant figure out how to keep the very narrow field of view and change the time, so i can see what that star was catalogued as when it moved past.

[Camelopardalis]

Krishan, I use Sky Safari Pro and it lists it as GSC 6225-1330 at mag 12.49.

The westward drift of Saturn across the sky is more than the rotation of the Earth that we'd see affecting background stars.

[kkara4]

awesome thanks Dunk (and thanks Ben!). I will have to see how i can obtain sky safari.

[AussieTrooper]

It's actually a little more complicated than that.
The perceived motion of Saturn you stated is only true if you were at the centre of the sun. The light pollution there is bad, so I don't recommend it as an observing site.
Additional apparent motion is caused by the earth spinning, it's orbit around the sun, and its orbit around the earth-moon barycentre. This is what causes planets to appear wobble around their orbit and go retrograde.
I use skymap pro (www.skymap.com (http://www.skymap.com)) and have found it to be very good.
It only shows stars down to mag 14, but if you want to see fainter objects, it will overlay an image down to about mag20.

[ZeroID]

Have you downloaded all the Stellarium catalogs ? I'm pretty sure it gets down to better than Mag 15 or so. Not that it necessarily includes all stars anyway but worth checking.

[kkara4]

Thanks Ben cheers, makes sense :)

Thanks for the tip Brent, i certainly havent attempted to download anything extra for it so i have whatever comes default. ill make sure i do what you suggest ASAP.