Nova Cen 2013

[pvelez (Pete)]

Greg's post of yesterday about the nova in Centaurus promoted me to go back to my own data.

Inspired by Rolf, I tried to collect data in late December and early January. As it was then an early morning target, I was hampered by some dew issues I had with the STX 16803. A few months back Peter Ward did a great job of cleaning up my sensor and removing accumulated moisture in the chamber (thanks Peter). However, I found that in high humidity moisture would accumulate on the outside of he chamber - it would suddenly appear on my images early in the morning seemingly out of nowhere. The diagnosis was that the window heater worked fine for most of the evening until a critical air saturation level was reached and - Blam! - all the moisture would condense at once leaving a nasty blotch on the images. You can see the remnants of it left of centre on the attached images.

In case anyone has this issue - I solved it by wrapping a dew heater around the camera body. I've only had the issue once since early January - when taking sky flats in the early morning of a very dewey night.

Anyway....I managed some date on 31 December and then a bit more on 13 and 14 January. The brightness of the nova had diminished over the intervening period and the Ha emission lines that were so prominent early - which I think gave Rolf his image that beautiful rosy hue - had faded by the time I took the January data. So my image is plain by comparison.

I have been working through Warren Keller's excellent PI tutorials and playing with this data to trial a few new techniques. So I have 3 alternate images for this nova. With the golden image I used a manual Histogram Transformation stretch which I did by eye while for the other 2 I used a STF stretch which I applied to the Histogram Transformation.

To be honest, I'm not sure which one I prefer. Each time I play with the saturation, the colour gradients in the background stand out like the proverbial dogs b----s. There is also an ongoing battle with an overall green colour cast.

Here is a link to the second image - http://www.pbase.com/equitius/image/154501032

Image details - R (81 mins), G and B (54 mins) in 3 minute subs. Taken from light polluted Sydney with a PW CDK 12.5 and STX 16803.

Pete

[cometcatcher (Kevin)]

Looks great Pete. Certainly a big colour shift it's gone through since Rolf's image.

[Lee]

Nice... Would be hard to find a more crowded field I'd say.
I took an image of the nova on 1 Feb, it certainly came out quite red then...

[Terry B]

Interesting and great images Pete

I looked at the spectra change for the dates you have. My dates are slightly different but this shouldn't matter too much. There was a relative reduction in the overall magnitude including the hydrogen lines between 28th Dec and 11th Jan. There was however a relative increase in the strength of the Ha and Hb lines by the 11th Jan. The continuum for the nova is relatively blue and this is the colour in your image. I think that the reason you have a blue star image is that this is a very bright star compared to the background and very easily saturates the CCD. My ST10XME saturated the nova through any filter with a 5 sec exposure. Your camera has great antiblooming so you don't see the saturation compared to my camera. (my images are also for photometry so they must not saturate to be able to measure them)

I think that any deep red from the Ha has been saturated. I have attached comp graphs of the spectra for the 2 days and they show you the change in the spectra.
Cheers
Terry

[Peter Ward]

Great result.

Also glad to hear the external-dewing issue has been resolved

[pvelez (Pete)]

Originally Posted by Terry B

Interesting and great images Pete

I looked at the spectra change for the dates you have. My dates are slightly different but this shouldn't matter too much. There was a relative reduction in the overall magnitude including the hydrogen lines between 28th Dec and 11th Jan. There was however a relative increase in the strength of the Ha and Hb lines by the 11th Jan. The continuum for the nova is relatively blue and this is the colour in your image. I think that the reason you have a blue star image is that this is a very bright star compared to the background and very easily saturates the CCD. My ST10XME saturated the nova through any filter with a 5 sec exposure. Your camera has great antiblooming so you don't see the saturation compared to my camera. (my images are also for photometry so they must not saturate to be able to measure them)

I think that any deep red from the Ha has been saturated. I have attached comp graphs of the spectra for the 2 days and they show you the change in the spectra.
Cheers
Terry

Thanks Terry

I feel much better about my processing in light of your comments. I was initially bummed that I didn't have the rose hue of Rolf's early image but I understand now why it appears blue.

I will revisit this target in a week or 2 - how is it placed now? I hope its closer to midnight than last year

Pete

[pvelez (Pete)]

Originally Posted by Peter Ward

Great result.

Also glad to hear the external-dewing issue has been resolved

Thanks Peter

Yes, the dew strap was an inspired idea. As its heading up to Coonabarabran this week, I expect humidity will be less of an issue - other than this week!

Despite some wrinkles early on, I'm very happy with the STX - it takes great images and is fast - soooo much faster than the old STL11k

Pete