Forum Replies Created
-
Posts
-
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
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
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
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
Here is the background subtracted spectrum. (IR end cropped where the fringes dominate). Rather featureless with nothing obvious above the noise (SNR ~15)Robin
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.
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
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
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
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
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
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
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
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
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
Jack said
“I am awaiting Robins response on this one.”
Hi Jack,
Not sure what this relates to. What do you want to know ?
Hi Jack,
It is a fits spectrum profile to BeSS standard as used in the BAA database for example (Are you trying to open it as an image?) It will open in VSpec, ISIS, BASS etc. (change the extension from .fits back to .fit if you are having difficulties)
Cheers
Robin
Hi Jack,
Spectrum profiles (in fits or dat format) are also small enough to be uploaded as attachments here if you need advice and are not ready to submit them to the database. For example here is my latest for VVCep at the blue end. It is a work in progress as I am not 100% happy yet with the instrument response/atmospheric extinction correction so I have not yet committed it to the database. (Note I had to change the extension from .fit to .fits as the forum does not accept .fit )
Robin
Hi Andrew,
I see your name correctly in the forum and on your members page or am I not looking in the right place?
Robin
Hi Jack
ISIS automatically estimates the resolving power from lamp line widths for you and adds it to the fits header (SPE-RPOW) or if you want to manually measure it (for example on different lines across the field) you can produce a spectrum profile using the lamp image and measure them directly using the FWHM function.
In ISIS you can even measure the width of the lines (in pixels) directly off the image using the PSF function – useful for checking if you have best focus.
Cheers
Robin
