Nova V1405 Cassiopeia spectra (Remco Kemperman)

Nova V1405 Cassiopeia spectra

I have had another spectroscopic go at nova V1405 Cassiopeia on september 25th. It is still going strong from the start in march 2021. It has actually brightened up again a bit in the last month. This time I compared the spectrum against what I took on july 22nd.

The hydrogen emmission lines seem to be stronger this time. And the expansion of the shell has increased since july. The expension speed is measurable through the P-Cygni profiles in the spectrum.

Those profiles are emission peaks (at the lab value of an element) with a absorption dip in front. What this means is that the emitted light at the center is partially absorpted by the gas shel that is expanding towards us due to the blast. This happens at such a speed that this absorption dip is shifted in wavelength to the blue end of the spectrum. The wavelength difference between peak and dip corresponds to the expansion speed.
22nd of july I measured/estimated it at 1260 km/s
25th of september at 1820 km/s

The iron emmision lines (Fe ii) I saw in july are weakened a bit in september.

Spectra were taken from the backyard with:
Skywatcher 150/750PDS on HEQ5 mount
QHY 294M camera
Star analyzer 100 lines/mm diffraction grating
55x70s exposures for the spectrum, stacked in Pixinsight
spectra were analyzed with R-spec Astro.

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