Spectral range around HeI6678

[Ernst Pollmann]

It is a shame that almost all Echelle spectra in BeSS only partially reproduce the spectral range around the HeI line at 6678.
Can't that change?

Ernst Pollmann

[Joan Guarro Flo]

Hallo Ernst,

I'm absolutely agree with you, really it's a shame or a pity, but there are a lot of things against, I will try to explain here my personal opinion about it. But you also know that many of observations of Del Sco HeI 6678 on most databases are useless, because don't have a good S/N relation.

First, most echelles are coming collimated to the observer from the shop and he doesn't have any possibility for move a bit the main grating. That would mend the problem.

Second,  most of us use the ATIK460EX, that has a little size chip for our echelles. Tim Lester is the exception, he use a ASI1600MM, size 17.5 x 13.4 mm. in front our ATIK 13.2x9.35 mm. Tim may to choose more configurations than us.

Third, I don't know, I don't understand, why I have another Order composition than the others observers. I can't move my configuration if I want that the NOU_T works. Fortunately it serve very well for catch the HeI 6678.

Fourth, also there are the LHIRES, for the observers that use this excelent spectrograph it's very easy move the grating and observe the Halpha and the HeI 6678 at the same time, with a R=9000.

Fifth, I  don't know if most observers understand or know the importance of your Study Program about Del Sco's HeI 6678 and these observational requirements and particularities.

Sixth,  finaly the decision is free, it depends on each one..

Well, I show for all a graphic of HeI 6678 three days ago.

Friendly, Joan.

[Olivier GARDE]

It's possible with the eshel spectrograph to shift the spectrum in X axis and catch the He I 6678 lines well placed in the order #33, but in this case I can't have H beta in a single order (with an ATIK 460ex H Beta and others Balmer's lines are split in two parts on 2 orders, so not very useful to merge correctly the 2 orders)

So it's a choice, I prefer to have all my Balmer's lines well placed in a single order than have He I 6678 line and If I want to study only HeI 6678, I prefer to use a mono order spectrograph like LHIRES III.

Except with my whoppshel spectrograph where I can have He I 6678 well placed with R=30000.

[Olivier GARDE]

I made some modifications on my eShel to have HeI 6678 better centered on the #34 order and also H alpha line.

Here's the result with the full #34 order with H Alpha and He1 6678


And a crop on the HeI6678 line only


The main problem comes that the H alpha line of Del Sco is very intense compared to the HeI which does not allow to have simultaneously the 2 lines with a good SNR.
HeI emission is very weak on Del Sco....

[Ernst Pollmann]

Hi Joan,
as you know, I used already your excellent HeI6678 spectrum taken with your NOU_T-Echelle (attachment). There are obviously ways with this sort of spectrographs to receive useful spectra with a very well S/N. As your result shows, simply to increase the exposure time did lead to success. An earlier statement in this forum, there is no way to reach that, seems to be disprove.

Hi Olivier,
indeed, to receive an useful HeI6678 spectrum of delta Sco (and for gamma Cas too; see: https://www.aavso.org/gam-cas-campaign-01) with an acceptable S/N is a challange, I know. In this sense your spectrum from 2020-06-24 is really not useful (compare it with the attached spectra sequence) . Also here I would like to recommend, clearly to increase the exposure time, similar to Joan.

Concerning the sense of studying the HeI6678 profile variability you should read the link at this forum:
http://www.spectro-aras.com/forum/viewt ... =14&t=2506

delsco_ 2018-2020.png (57.31 KiB) Viewed 4429 times

Ernst

[Joan Guarro Flo]

Hello,

The observations of HeI6678 in Del Sco are being continuing.

Who of you want to join to us observe this star ?

J.Guarro.