Achernar in emission

[Jon]

Malcolm Locke has posted in some other forums his observation that Achernar is currently in emission at the Ha wavelength. My own spectrum from Friday is attached - you can see the characteristic split lines indicating a rotating disc of ionised hydrogen, at relatively high inclination (i.e. edge on to us). The blue peak is from the side of the disc coming towards us; the red peak is the other side, receding from us.

This might be of interest to folk with an SA 100. You won't see the split at the low resolution of the SA100. But there's a good chance, with a star as bright as Achernar, that you can get a decent look at the spectrum visually at the eyepiece. I've never seen an emission line with my own eyes - I'll give it a try myself once the clouds clear.

[Rob_K]

Nice work Jon! I took a low-res spectrum of Achernar with an SA100 last night and could see no appreciable emissions at the Ha line. Could it be over that quickly? Emission lines look good at the eyepiece - I saw N Cen 2013 (V1369 Cen) last year when it was bright, through a 114mm f8 reflector & SA100 grating. My scope is temporarily out of service so I didn't get a chance to check Achernar visually last night.

Cheers -

Rob

[robin_astro]

Hi Rob,

Looking at Jonathan's high resolution spectrum, the emission is embedded in a broad absorption. At the Star Analyser resolution the emission and absorption will combine so the net emission may disappointingly be quite weak

Cheers
Robin

[malclocke]

I'd probably agree with Robin that the SA100 might not show this. The emission is only 20% stronger than the continuum.

Attached is an SA100 spectrum I took of Achernar last year with a very far from optimal set-up comprising a dob and an 8 bit guide camera. The spectrum is almost featureless, but it would be interesting to see results from more competent SA100 users.

[Jon]

Ah, drat! Thanks Robin and Malc - but it would have been nice to see an emission line visually ...

[robin_astro]

Given it is such a bright target, the best bet with the Star Analyser would probably be to record it with the grating in front of a camera lens. That would potentially give the best resolution because the beam is collimated through the grating. 10-15A resolution is possible with this kind of setup which should be enough to isolate the emission from the broad absorption

Cheers
Robin

[Rob_K]

This is the best I could do last night (13:37, 02 Dec 2014 UT) between clouds with SA100 and 200mm lens on Canon 650D. Calibration is approximate.

Cheers -

[robin_astro]

Hi Rob,

Yes would say you have got it. Not so obvious in the large scale version but in the smaller image the eye is definitely drawn by the lighter line. Not very spectacular though sadly

Robin