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My guess would be Fe II] 6541.3569. Fe is abundant, and mostly present as Fe II (Fe+). The upper level of this line is at 102824 cm^-1, which is nearly coincident with the upper level of Lyman-gamma at 972.5368 A. In this situation, Lyman-gamma could pump the upper level of this Fe II line, giving r...

Hi Hugh,

H-alpha remains visible as a weak emission line right through totality, so the area of H-alpha emission must be somewhat larger than the size of the M supergiant's projected disk.

The higher Balmer lines (H-beta, H-gamma, etc) all vanish during total eclipse.

Phil Bennett

Hi Olivier,

I recommend mu Cep. It's a close spectral match to VV Cep (M2 Ia-ab), brighter and fairly close. It's never good to have a standard using up more observing time than the target star.

Phil

Hi Robin, Peter, Ernst, These UV spectra of VV Cep are very useful, especially the record of growth of Fe I and Ti II lines into eclipse -- these lines are formed in the outer atmosphere of the M supergiant and are prominent during the eclipse ingress and egress phases. At these times, the line of s...

Peter, The inverse P Cygni lines in your UV spectrum of VV Cep are the higher Balmer lines (the deep absorption minimum is near line centre). Your spectrum shows, in order of decreasing wavelength: H 2-11 3770.63 A H 2-12 3750.15 A H 2-13 3734.37 A H 2-14 3721.94 A H 2-15 3711.97 A H 2-16 3703.85 A ...

Hi Paolo -- your near-UV observation of VV Cep with mu Cep subtracted is very nice! Just about everything in the subtracted spectrum looks real to me. The Balmer lines show the same inverse P-Cygni profile seen in our Hubble Space Telescope observations. The term "inverse P Cygni" refers t...

The spectrum of VV Cep in the near UV is composite, with the hot component dominating shortward of 4000 A. The hot component is highly variable and is not just the spectrum of the early B-type star; it also includes a substantial (and sometimes dominant) contribution from Balmer continuum emission. ...

Correction: that line in my previous post should read:
Coadding individual images or spectra will also result in a *higher* (not lower) S/N for exactly the same reason: more photons are collected per pixel or detector element.

Phil

Thilo wrote: I wouldn't agree with this statement in general, without having described the method to compute S/N and without describing the method used for filtering. It is often believed that filtering (like binning) improves signal. In fact, this is not generally true, as S/N will remain in the da...

After our object spectrum has been extracted (ie: after image preprocessing, geometry corrected, sky background removed, and signal extracted column by column) and calibrated in wavelength, we have to apply an instrumental correction to adjust the overall profile to correct from: -atmospheric extin...