Nova Carinae, at last

[bojan]

At last, some free time and no clouds in Melbourne.
Nova is reddish star in the centre of that frame, taken tonight (08/12/2008) at ~22:00.
After week or so, it is still quite bright.

This image is a small crop (20%) from centre of the full 1.5° frame, taken with Canon 400D, 60 sec, ISO1600, MTO-1000A on basic EQ6 (with DH firmware).

I had no difficulty to point the scope, mount works perfectly with CdC, and GoTo took from Theta Car to nova roughly 20-30 sec. Not very fast but still reasonable and spot-on.

Will try to do some photometry tomorrow.

[Ian Robinson]

What's your estimate of it's current visual magnitude ?

[bojan]

It is about 9, I would guess..
AAVSO charts have comparison stars around nova ranging from 11.5 to 8.2 (visual), so this estimate is very rough.. I will try better with what I have in CdC (Hipparcos data)

EDIT:
8.9, compared to nearby stars from Tycho_2 catalogue.
This estimate was done on stack (8 frames, in DSS) with help of Iris (Aperture photometry (3rings), magnitude constant determined as 24.03).

[avandonk]

Here you go Bojan.

[Terry B]

Did you extract just the green chanel for the estimate?

[bojan]

No, it was done on composite image. My canon is not modified..

[Terry B]

It doesn't need to be modded at all. You just extract the green channel and measure the flux. It much more accurately approximates the "V" photometric filter.

[bojan]

Thanks for the advice :-)
Will do and revert..

[bojan]

Terry,
I have problems with colour channel separation :shrug:
I can suppress R, B channels in DPP, but then Iris outputs silly numbers (background only, but the images of stars are there and they are clearly green)
Could you propose some standard method to do this?
In the meantime, we have to live with RGB magnitude.as estimated earlier (hopefully, there will be more measurement results tonight :)

[Terry B]

If you have a raw image, open it in Iris. Using the "Digital Photo" tab decode the raw file as normal. There is a RGB separation button. This will then create 3 files, one for each colour. You then analyse the green channel.
An article about doing these measurements with a DSLR is at
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2007SASS...26...67H& data_type=PDF_HIGH&whole_paper=YES& type=PRINTER&filetype=.pdf

[bojan]

:thumbsup:
Thank you!
Iris rules.. right?
BTW, last night was cloudless in Melbourne and very cold..
If it stays like like that for next couple of days, there will be some light curves to present here .

[bojan]

OK, the situation so far is as follows.. measurements are taken using G channel data only, as suggested:

Date mag
08/12 9.631
10/12 9.834

It looks like it is fading, as expected.

I did not do error margin analysis (yet).
It would be interesting to know, how IRIS is coping with linearity of the camera... It is always possible that some star images will be saturated, which will compromise the accuracy of measurement.
However, what was done, was done.. so I intend to keep the whole setup and parameters the same for the whole duration of this little project :-)
And I am sure I will learn a lot !

[Terry B]

Well done.
You can get an idea of the linearity by taking exposures of the same starfield at increasing exposures- say 10sec increases until you saturate at least 1 star in the field. Then measure the flux for a variety of stars and plot the graph. You can then see what range of fluxes are linear for your camera.

[bojan]

Thanks for this hint :-)
I was thinking, even just one frame (with rich starfield) can be used to calibrate the camera...
This task was actually ranking pretty high on the list of critical projects for Mt Waverley Observatory (read: my backyard :) )