Have I discovered a nova? ...

[lukebl]

... probably not, but just wondered about the accuracy of the Stellarium maps.

I was going over my images of Comet Siding Spring this morning, to see how I might improve on the images and improve my future attempts at imaging it.

Comparing my image with the Stellarium map, I noticed a fairly bright star on my image which doesn't appear on the Stellarium map. I've downloaded all the Stellarium maps, so it shows stars down to mag 18.5 and should be fairly complete. Judging by the neighbouring stars, the 'stray' appears to be around mag. 14. It didn't move during the exposures, so isn't an asteroid.

So what is it? A nova, or just an inaccuracy in the Stellarium map data?

[iamjulian]

When you say it didn't move during your exposures, how long are you talking? Looks interesting.

[DarkerSky]

I can't say for sure as I don't have the full set of charts from Stellarium to 18.5 mag. What I will say though is that I have found at least on one occasion an inaccuracy with Stellarium. The other evening I was keying a search for some galaxies off a star that was present on stellarium, but was not in the sky.

Still, it is probably worth a more thorough check

[lukebl]

When you say it didn't move during your exposures, how long are you talking?

Only about 30-40 minutes, but in that time the comet moved noticeably, and in my experience asteroids (even fairly distant ones) would change position at least slightly in that period. This object didn't move at all.

[brianb]

There are lots of long period variables with maxima above 15 (and minima below 20), by no means all of them are known (probably somewhat less than 10% are even catalogued). Undiscovered dwarf novae with similar ranges are also reasonably common.

Asteroids near their "stationary points" can indeed appear not to move for several hours ... if you can get the best possible positions from your images (to better than 0.1 arc sec) on a couple of consecutive nights, this should rule out the asteroid theory. As should observations from a different location (on the other side of the earth), solar system objects have a parallax. LPVs, DNe and novae are easily distinguished for their spectra, or by the shape of the light curve.

[NickH]

Did you have a look at the SDSS images in that region (WWT or Simbad/NEDS)

?

[lukebl]

...observations from a different location (on the other side of the earth)...

Hmmm... Lugging my kit over to the antipodes sounds nice, but rather unfeasible, financially as well as practically!

Are there any accurate maps on-line, showing stars down to, say, 18th mag? And if it is a nova or undiscovered variable, what can I do about registering it?

[NickH]

did you run a comparison against the SDSS HST images for those coordinates?

[FraserClarke]

Digitized Sky Survey...

ESO Online Digitized Sky Survey

Put in the coordinates (RA, DEC).

Choose your survey (DSS-1 was taken in the 1950s, DSS-2 taken in the 1980-1990s, and is a bit deeper). DSS-2 red is your best bet..

Either download a FITS file, or display a gif (former will be better for comparing with your image in something like MaximDL etc)

[lukebl]

Wow. Thanks TeaDwarf. What an amazing website. Had a look and, bingo, there's my new star. So it wasn't a nova after all.

The Digitized Sky Survey image also shows loads of fuzzy galaxies in that area which I can just make out in my image, and which I might have otherwise written off as artifacts in my processing. Definitely going to use that website in future.

[mdstuart]

Its not a nova its on the WWT

Microsoft WorldWide Telescope Web Client

Mark

[lukebl]

Its not a nova its on the WWT

Thank Mark. Another great website

[NickH]

Did you have a look at the SDSS images in that region (WWT or Simbad/NEDS)

?

That's exactly what I meant... the URL you got for the digitized sky survey, thought I copied the URL into my reply

http://archive.stsci.edu/cgi-bin/dss_form

(may as well just give up!)

[lukebl]

(may as well just give up!)

No need to be like that. I missed your post , sorry.

[NickH]

Which one...I posted twice!

[Helen]

Yes, its looks like you both posted at the same time (I do miss the functionality on the old forum software which alerted you to posts whicle you were typing )

Some good links in the thread though - thanks guys

Helen

[FraserClarke]

Glad the data helped The link Nick pointed you to is exactly the same survey -- there are several ways to access it.

A pedantic point, which might be interesting background for some people?? ;

DSS == Digitized sky survey. Taken on photographic plates with the 48" Schmidt at Palomar, and covering the whole sky (southern half taken with the 48" Schmidt at the AAO). In the 1990's the plates were scanned to create a 'digitized' version.

SDSS == Sloan Digital Sky Survey. Currently ongoing survey with a 2.5m telescope and an array of CCDs. Very nice data, and a lot deeper than DSS -- but not all sky... this is the stuff GalaxyZoo etc is based on.

[lukebl]

Thanks for the advice, guys.

I know where to look now before I go running off claiming to have discovered a new nova or asteroid, or whatever!

[NickH]

WWT covers SDSS, I have archives for the original DSS data (11 DVD's in fact)

Both are real hunting grounds for as yet undiscovered stuff