In terms of the light curve, we've had increasingly rapid oscillations since around 6 Jan, with an amplitude of 0.5-1 mag and a period of 1-1.5 days. *Possibly* these are smoothing out recently into a steadier decline, although I'm not betting on it.
The first image below shows the spectra from one of the maxima (8 Jan, V=c.4.5) and one of the minima (V=c.5.1). The lines visible in the two spectra are essentially the same - but the relative intensity of the Balmer lines (especially Ha) is much greater at minimum. These are normalised spectra, not flux calibrated - in other words, we're comparing relative intensity of spectral features, not absolute intensity. So at minimum, the emission lines are relatively stronger compared to the stellar continuum. This lends support to the theory that these oscillations are a product of changes in the optical thickness of the ejecta. As the ejecta fireball becomes optically thin, we see a greater relative intensity of the ionised gas shell (emission lines) and of the UV/FUV radiation from the white dwarf itself. Well, we don't actually "see" the latter, which is why the visual-wavelength magnitude drops.
In the last week, everything has begun to change. The second attachment compares spectra from 17-25 Jan. All the forbidden lines are growing in intensity while the "iron curtain" of FeII emisison lines are beginning to fade in relative intensity. Some other significant changes (marked with triangles):
1) [OIII] at 4363 has emerged - although in my low-resolution spectrum this merges with H gamma at 4340. Good to get a higher-res picture of this area.
2) An entirely new line has emerged around 4670-80. Is this He II? That's not implausible
3) OI at 8446 has gone nuts. According to one theory (e.g. Williams, 2012), this is a product not of the white dwarf emission itself, but of interaction with the material coming off the secondary star.
I won't begin to speculate as to the astrophysical causes. But the spectra and photometry at least suggest we may be entering the transition phase of the nova.
Very little change from last night. Which at least confirms that some of the new things in last night's spectrum were real not artifacts of my clumsy processing or technique.
The only real change seems a slight slant to the blueward. When we have seen this before, it has been when the nova has been rebrightening. Don't tell me we could be on our way up again?!?
Jon,
gathering data around Hb >4670A as I type....
I'll go down to the Hgamma region before fitting the sort filter for Ha and, if I can, out to the [OI] at 8446.
So far so good.
Still processing...
Had some issues trying to get out to 8446A - may need to redo.
Here are the Ha and Hb regions in medium resolution (R=6000/5000)
The P Cyg profiles seen earlier are diminishing and the ragged tops, I'm sure, may mean something???
I have more in the pipeline.
Still processing...
Had some issues trying to get out to 8446A - may need to redo.
Here are the Ha and Hb regions in medium resolution (R=6000/5000)
The P Cyg profiles seen earlier are diminishing and the ragged tops, I'm sure, may mean something???
I have more in the pipeline.
Very interesting Ken. It looks as though there are 4-5 different absorption lines superimposed on a broadening emission line. As you say, P Cyg profiles have given way to this more ragged feature.
Hmmm
The emission line peaks seem to have moved to the red.....
My limited exposure of 8446A didn't seem to show the emission as bright as Ha???!!???
THe SA100 spectrum I got had 8446 dropping below Ha too. It seemed a short outburst ... what is the "OI flash"? I've seen references to it. Honestly, understanding these novae evolution seems a combination of science, intuition, and witchcraft :-)
I took spectra last night with my LISA. Very strong Ha.
I will upload them later today.
The conditions were terrible with a 20Knot easterly blowing making the stars about 20 pixels wide as the scope was buffeted around.
Spectra from last night. It was very windy and this made guiding a challenge.
My measurements from last night 27/1/14
B = 6.026 (err 0.05)
V = 6.097 (err 0.035)
V = 5.178 (err 0.05)
I = 5.121 (err 0.039)
The spectra shows an overall decrease in the continuum since my last spectra (18/1/14) in absolute flux.
There has been an increase in both relative and absolute flux of th eHa line but not the other H lines.
The P Cyg absorption features have now gone.
