GAIA transient GAIA21dxg / TNS AT2021wui

[Tom Love]

Just to add briefly to the discussion on classification, Gray and Corbally is the current standard text on classification, though it tends to have a lot of focus on detailed analysis of lines in the blue (reflecting where classification studies have traditionally come from), which isn't always the most helpful for amateur spectra. I have found that Walker's Spectral Atlas for amateur astronomers is another really useful book:

https://www.bookdepository.com/Spectral ... 1107165908

This has low resolution spectra taken across the whole visual spectrum, acquired with the kind of instruments and telescopes that we often use, so it provides a quite helpful reference for the kind of data that we tend to generate.

And I'd echo Peter and Hamish's comments that this discussion has been quite interesting and useful.

[Hamish Barker]

Ha ha. Well, I am fairly sure that I have not taken a planet or asteroid's spectrum (this time). <*dramatic music*> or have we?

[Hamish Barker]

There seems to have been a significant change (the brown trace is the latest spectrum) in the H-alpha profile if the observation I made last night is correctly processed:

Hopefully others can manage to take a spectrum to confirm the change. I don't know if this is "normal" for Be stars, or if it indicates that the object is something else.

[Hamish Barker]

clouds clouds clouds, so I have had no chance yet to confirm the the possible change in the spectrum.

[Robin Leadbeater]

There seems to have been a significant change (the brown trace is the latest spectrum) in the H-alpha profile if the observation I made last night is correctly processed:

at2021wui_Halphapeakmoved-or-went-picyg.png

I think these sort of effects are seen in discs and accreting systems due to asymmetry.
It reminds me a bit of the changes seen in the He 6678 line in the X ray binary X Per
http://www.spectro-aras.com/forum/viewt ... =10#p14191

Certainly an interesting system. A pity it is rather faint for high SNR at high resolution

Cheers
Robin

[Hamish Barker]

clear again last night, but I started late so only an hour, so the S/N suffered a bit.

the redshifted Halpha peak is there again. comparing to the spectra which were previously taken, it appears to be a fairly symmetric swing of about +/-400 km/s around H alpha.

I don't know how to plot them staggered on plotspectra to avoid confusion. anyway the legend shows the last plot at the top in black.

at2021wui_20210920-velocity-compare.png (37.28 KiB) Viewed 10285 times

[Hamish Barker]

the lightcurve has continued the very gradual upward trend (if at all).

[Hamish Barker]

worked out how to make the stacked chart.

I wonder if that's a trend showing in the doppler shifting of H alpha. It will be interesting to track if it shifts back and/or displays a long term oscillation.

at2021wui_20210825-to-0920-stacked.png (78.55 KiB) Viewed 10235 times

[Robin Leadbeater]

What are the photospheric absorption lines doing eg Balmer, He ? This would give you a clue as to whether it is due to orbital velocity of a binary system or something specifically to do with the H alpha emission source.

Robin

[Hamish Barker]

He1 ad 5875 and I assume the sodium doublet to the right of it doesn't seem to move. Plotspectra has just crashed so will take me a little while to reload all the spectra again.

at2021wui_20210920_427_He1-5875.png (42.7 KiB) Viewed 10179 times