[Robin Leadbeater]

Hi  Jack

Chromatic Aberration.  The inability of a lens to bring all wavelengths to focus in the same plane. The LHIRES uses an achromatic doublet which shows the usual pronounced chromatism in the Violet/UV so the focus varies across the spectrum. 

Cheers

Robin

[Robin Leadbeater]

I saw the same changes in the similar system AZ Cas in 2012 as it entered eclipse and we lost the spectrum of the hot B star  (Though there is no H Balmer emission in AZ Cas)

http://www.threehillsobservatory.co.uk/astro/spectra_43.htm

Cheers

Robin

[Robin Leadbeater]

I know the feeling. I’ve been doing astronomical spectroscopy for over 10 years now and the curve has still not tailed off yet !

Note, I suspect the spectrum will not have been corrected for instrument response/extinction so the shape of the spectrum will not represent the actual spectral energy distribution. There may be some spectra of standards around taken on the same night though which could be used to produce a (relative) flux calibrated spectrum to give us an idea  of temperature.

Cheers

Robin

[Robin Leadbeater]

Hi George,

It might yet develop features in the spectrum so it will be worth keeping an eye on over the next couple of weeks. In classical novae the H alpha emission lines are relatively strongest after maximum. For example this animation of Nova Del 2013 by amateur Paolo Berardi covering the first week

http://quasar.teoth.it/html/spectra/novadel_15_21.gif

Cheers

Robin

[Robin Leadbeater]

Here are the target binning (blue) and sky subtraction (green) zones I used in ISIS to extract the spectrum of the PNV (The asymmetric sky background zones were deliberately chosen to avoid the cosmic ray hits)

Robin

[Robin Leadbeater]

The spectrum beyond ~7700A (~pixel 500) is unusable in its current state because of the severe optical etalon type interference fringes, common in IR spectrographs. A careful flat correction would be needed to remove them.

Robin

[Robin Leadbeater]

Attached are the spectra with and without sky background subtraction, (pink and blue respectively, to the same Y scale).

The strongest emission line is the O I airglow line at 5577A. There is also O I emission at 6300A and Na D emission (light pollution ?) at 5900A

Robin

[Robin Leadbeater]

Hi George,

Your plot includes the sky background (from air glow, light pollution and from M31) which dominates the spectrum. The strong emission lines are airglow and light pollution. To see the target spectrum you need to just select the target spectrum (the narrow band) subtracting the background first. If you look at my sky background subtracted and wavelength calibrated spectrum you can see there is no emission line, including at H alpha (6563A) currently.

Cheers

Robin

[Robin Leadbeater]

Here is the background subtracted spectrum. (IR end cropped where the fringes dominate).  Rather featureless with nothing obvious above the noise (SNR ~15)

Robin

[Robin Leadbeater]

Hi Nick,

I’ll have a try at extracting it from the background. I don’t understand where all the emission lines in the sky background come from though. They do not look like galactic lines to me. Do they have an unusual light pollution problem or something or perhaps they superimpose the calibration lamp spectrum?

Robin

EDIT:  ok the “emission lines” are actually severe fringing in the IR. I can see the O2 telluric band so should be able to cross check the wavelength calibration.

[Robin Leadbeater]

Hi Nick,

The author of the article,Francois Teyssier is the resident expert amateur on CV spectroscopy  in the ARAS group. He publishes a nominally monthly newsletter on the group’s activities in this area.

http://www.astrosurf.com/aras/novae/InformationLetter/InformationLetter.html

There have been a number of nova confirmations by amateurs recently and followup up spectra tracking the evolution of some targets. We have been getting a lot of support interpreting the data from professional Steve Shore.

I expect the FLOYDS spectrum should settle the matter. It is a rather strange low resolution 2 order echelle instrument though which needs a very specific data reduction pipeline. (looking at the spectrum image, subtracting the sky background should be an interesting challenge !)

Cheers

Robin

[Robin Leadbeater]

Good to hear. mag 16 makes it well within range, possibly with other observers too. I will put out an alert on the ARAS forum

Robin

[Robin Leadbeater]

Hi Nick

In good conditions, mag 17 is just within range at very low resolution (R~130) with my modified ALPY 200 and I don’t know anyone operating fainter currently but the contrast against the galactic background  does not look high based on your image so it could be very tough. I have noted it to have a look but no promises, particularly as there are no clear skies forecast here for the week ahead currently

Cheers

Robin

[Robin Leadbeater]

Thanks Paul,

That’s 6 to date I think, though apart from taking a quick spectrum of the very bright sn2017eaw, I have not really been looking this year so this is the first in 2017. It looks like I have quite a bit more professional competition now though. For example ePESSTO now seems to be submitting half a dozen confirmations a night when it has telescope time.

I was planning to try for another one last night in ngc3172 (at2017gla) but it was so close to the pole (+89.1 deg Dec) that I was literally going round in circles trying to get the mount to point at it ! 

Cheers

Robin

[Robin Leadbeater]

Hi Tony,

It will be interesting to see how your results compare with conventional differential photometry.  It will give us an idea how accurate absolute flux calibration from a typical amateur observatory actually is.  The difficulties compared with conventional differential photometry  are you are dependent on stable atmospheric conditions and  because suitable reference spectra calibrated in absolute flux are rather widely spaced, differential extinction has to be taken into account – the spectroscopic equivalent of all sky photometry.

Cheers

Robin

[Robin Leadbeater]

Hi Jack,

I am not monitoring H alpha as the coverage there already looks pretty good.

I am just covering ~3800-4100 A (which covers H epsilon – H10  including Ca H,K )  This is the same region I monitored during the 2012-2013 eclipse of AZ Cas (A similar but much fainter system.)

http://www.threehillsobservatory.co.uk/astro/spectra_43.htm

The changes are very pronounced and potentially scientifically interesting in this region but I was the only one monitoring AZ Cas there. For VV Cep there are a couple of others working in that region though so hopefully we should get good coverage there for this eclipse.

Cheers

Robin

[Robin Leadbeater]

Hello Jack,

I  had not planned to do that. I just described how it could be done if you wanted to. I suggest you and Marc get together directly to make the comparison.

Cheers

Robin

[Robin Leadbeater]

Hello Jack,

The fits spectrum profile I attached was just to show you how it can be done on the forum. The content is not important. It just happened to be a recent spectrum that I was working on.

Robin 

[Robin Leadbeater]

Hi Jack,

You have a lot of cosmetic defects (the narrow spikes caused by hot pixels.) This is quite surprising with such a  bright target. Are your dark and hot pixel map corrections working OK?

Robin

[Robin Leadbeater]

Jack said

“I am awaiting Robins response on this one.”

Hi Jack,

Not sure what this relates to. What do you want to know ?

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