Sorry for the delay - some calibration issues....
The central wavelength is listed, each has approx. 140A coverage and R from 4000 to 7000.
These show some interesting detail in the various emission lines....
Jon,
Yes, the Spectra-L200 with the 1200 l/mm grating.......
The hot night meant that the camera cooling was struggling and I didn't have a set of darks for the temp.
I used an old set of darks for a lower temp....
Some belated results from the 27th. Terribly noisy I'm afraid. Still no guiding and I tried to narrow the slit gap slightly which made things worse, plus battling with various other technical issues. Shame as it was an incredible night down here, best we've had in months.
Close up of the Hb and FeII lines show similar structure to Ken's recent results, particularly the redward skew on the Hb line.
Sorry for the delay - some calibration issues....
The central wavelength is listed, each has approx. 140A coverage and R from 4000 to 7000.
These show some interesting detail in the various emission lines....
Based on these I get the feeling we are moving into a different phase. Although the velocities have slowly increased, the absorption systems have maintained pretty much the same profile since they were first picked up. However here there's a definite change.
There has been an increase in both relative and absolute flux of th eHa line but not the other H lines.
I wonder what drives this? In your spectra, the decrement from H beta -> gamma -> delta seems quite normal, but the drop from alpha -> beta is enormous.
I wonder what drives this? In your spectra, the decrement from H beta -> gamma -> delta seems quite normal, but the drop from alpha -> beta is enormous.
I don't know but the same effect was seen in the spectra of nova del last year. The relative strength of the Ha line got up to 120.
Terry
I don't know but the same effect was seen in the spectra of nova del last year. The relative strength of the Ha line got up to 120.
Terry
After thinking about it I realised I'm naively thinking about it in terms of absorption where n=2 is the starting point for all the balmer transitions.
For emission conditions may be favouring n=3, and not the levels for the other balmer lines. We will see the 3 -> 2 transitions (ha) but the 3 -> 1 transition is in the Lyman series (UV).
So it's not such a mystery why the lines are so imbalanced.
""
I'll send something this weekend, Ken. Thanks very much for all of
this. It's really a delight to have this window, for the moment
there's nothing coming in from CTIO or ESO (although I heard we got
something with FEROS I haven't seen the data). You're right that
there are still absorption systems present, the optical depth of the
ejecta remains high even now that the oscillations have stopped. The
development is now more along the lines of V339 Del but slower. The He
I absorption feature is very neat, you see that the detached absorption
is persistent. That again indicates a high opacity in the UV. So
more this weekend, I promise, in the hope it'll be encouraging.
""
Here is my SA100 spectrum from last night. I had a cloud issue, was playing with exposure times and may have saturated the Ha so I wouldn't read anything into the low Ha level.
The forbidden lines at [OIII] 4363, [NI]5755 and [OI] 6300 are really growing.
After thinking about it I realised I'm naively thinking about it in terms of absorption where n=2 is the starting point for all the balmer transitions.
For emission conditions may be favouring n=3, and not the levels for the other balmer lines. We will see the 3 -> 2 transitions (ha) but the 3 -> 1 transition is in the Lyman series (UV).
So it's not such a mystery why the lines are so imbalanced.
Hope that makes sense :/
Malc, there's a good bit on the causes of relative changes in Ha/Hb (the "Balmer decrement") in the Keith Robinson book. As you say it's often to do with the relative optical thickness of the ejecta (in this case) to photons at the energy level to produce Lyman vs Balmer transitions.
There's also something going on here to do with a recombination front, which I think I just about understand :-) Along the lines of - recombination takes place, a 3->2 transition happens emitting an Ha photon, but then the Hydrogen immediately absorbs another photon of the same energy level bumping it back up to 3, because of the density of the Ha at this point in the nova evolution (unlike a nebula, for instance, where the much less dense Hydrogen will be more likely to continue to cascade down to 1).
There's also something going on here to do with a recombination front, which I think I just about understand :-) Along the lines of - recombination takes place, a 3->2 transition happens emitting an Ha photon, but then the Hydrogen immediately absorbs another photon of the same energy level bumping it back up to 3, because of the density of the Ha at this point in the nova evolution (unlike a nebula, for instance, where the much less dense Hydrogen will be more likely to continue to cascade down to 1).
Something like that.
The above makes sense. Although I would expect the same to hold true for the other Balmer lines, so I can't see how this would explain the different intensities of the Balmer series.
I imagine (without any grounding) that it would be more likely to be simply temperature dependent, where the visible ejecta is at a temperature that favours excitation to n=3 and hence the 3->2 H alpha transition is dominant. In much the same way that the temperature of an A class star puts a lot of the hydrogen into n=2 and thus favours absorption in the Balmer lines. That could also account for the decrease in H beta, as the temperature decreases, less and less of the hydrogen is excited to n=4.
Unrelated to the discussion of the relative intensities of the Balmer lines, I don't have a grasp on what mechanism could drive this recombination front outwards through the ejecta. It must be doing this if we ascribe to the idea that the absorption systems are from the ejecta, that there is a velocity gradient embedded in it, and that this recombination front is the cause of the changing observed velocity of the absorption system.
I would imagine the 'sweet spot' for recombination to be highly temperature dependent, and therefore would expect it to migrate inwards to lower velocity over time, not outwards, as the ejecta expands and cools.
Clearly there is some fundamental part of this that I don't get
A bit of nova trivia - given we are now on around day 60, and that we have observed expansion velocities (if that is what they are) of around 2000 km/s, the ejecta should now have a radius of around 70 AU, almost twice the orbit of Pluto!
Using the small angle approximation (θ = D x 206265/d, where D is the size of the object and d is the distance), this figure combined with the estimated distance from the ATCA of 3.3 kpc, this gives an angular size of 0.04 arcseconds.
A bit of nova trivia - given we are now on around day 60, and that we have observed expansion velocities (if that is what they are) of around 2000 km/s, the ejecta should now have a radius of around 70 AU, almost twice the orbit of Pluto!
Using the small angle approximation (θ = D x 206265/d, where D is the size of the object and d is the distance), this figure combined with the estimated distance from the ATCA of 3.3 kpc, this gives an angular size of 0.04 arcseconds.
Anyone fancy trying direct imaging
LOL, even 0.04 arcminutes is still a couple of orders of magnitude too small for anything I've got!
Same pattern tonight. Ha still increasing over Hb.
Malc, you pose some interesting questions. I had a stab at why the processes seem inside out on the ARAS forum. I found some papers on the idea of the recombination front, as I agree it seems counterintuitive. I think the key is the optical thickness at various wavelengths. That's not so much about us seeing the photons from the centre of the nova; it's about the atoms in the periphery of the nova "seeing" the photons at particular wavelengths coming from the centre, getting ionised, then cascading back down. Which is how it moves from inside out not outside in. If you see what I mean.
Actually, reading that back, I'm sure you don't. It's late, I'll have a crack at being coherent in the morning :-)
