OK guys, here's a stacked and cleaned up spectrum from this morning. Easily my best capture with the SA100. I've done a fair bit of research this morning on what I may be seeing. So here goes:
1) The Balmer lines remain prominent. However, they are less so relative to the continuum than on 19 December. This corresponds with a rebrightening of the nova - as the nova brightens, the SA100-measured Balmer lines decrease in relative intensity.
In a study of V5558 Sgr (2007), another nova with a series of rebrightenings after maximum,
Tanaka et al (2011) found that the absorption component of the Balmer P Cygni profiles increased as the nova rebrightens. This is because the rebrightening is owing not to increased temperature, but to increased density, mass flow and photospheric radius of the stellar wind.
The SA100 does not have sufficient resolution to capture both absorption and emission components. The net effect of an increase of the absorption component would be a diminution of the measured emission component, as here. This seems to be an interpretation that is at least plausible.
2) The FeII emisison lines are extremely prominent across the spectrum.There is also evidence of CaII, NaI, NII, and possibly HeII and CII. These latter are less convincing, but are consistent with a FeII nova at this stage.
3) There is no evidence of any forbidden lines. Not unusual, but see below.
4) Perhaps the most interesting feature of the spectrum is OI at 7773. OI at 8446 is present in nearly all novae spectra, but OI 7773 can only form in conditions of a relatively dense wind.
Williams (2013) discusses this in detail and proposes the 8446/7773 ratio as a means of classifying the wind environment of different novae. Williams suggests that where the 8446/7773 ratio is low (as here), and the wind relatively dense, then forbidden lines are (unsurprisingly) slower to emerge.
So there is is - even from a SA100 spectrum there's a bit of evidence from the rebrightenings and the 8446/7773 ratio that this is a nova with a particularly dense wind.