spectro-aras.com

Hi,
First time posting on this forum, back on night of 15/02/18 I had a go at Kappa Dra using my C9.25 and Lhires III with 15um slit,camera is Atik 314L.
Captured four 120sec images which were stacked,dark,flat and flat dark subtracted in BASS. Calibrated using three neon lines of Lhires calibration lamp,no instrument response correction administered.

Regards
Alun

Hi Alun,

If you do not have a reference star spectrum to do an instrument response the continuum shape is meaningless so it is a good idea to rectify the spectrum (ie flatten it by normalising using a fit to the continuum). In this case a straight line fit to the continuum well away from the H alpha line would probably work OK. You can then set the appropriate flag in the (BeSS standard) fits header ready for submission to databases.
(Actually I am bit surprised at the amount of slope in the continuum though. Perhaps it is an effect of BASS but with ISIS, if a flat correction has been done with a halogen lamp, the continuum is an almost horizontal straight line over this short wavelength interval as ISIS compensates for the approximate black body curve of a halogen lamp)

Cheers
Robin

Also your continuum looks rather noisy for such a bright target. A good minimum SNR to aim for on bright targets is an SNR >100. You could increase exposure time but it could also be to do with the narrow 15um slit. Unless your seeing is exceptionally good you could be losing a lot of light. (15um corresponds to just 1.3 arcsec with your scope) 23um (or even 35um though with some loss of resolution relative to the LHIRES design figure of R~17000 at H alpha) would give you more signal. I used to run 23um with my 8 inch f10 and now run 35um with my C11

Cheers
Robin

Hi Robin,

Thank you for the advice. I use the internal lamp of the Lhires III to take my flats,could be possible I didn't take them correctly (too short an exposure).
I used the 15um slit as Kappa Dra was the last target of the night after I'd earlier been concentrating on 28 Tau. I use mainly use BASS for all my calibrating
but just recently downloaded a copy of ISIS and am trying to get used to the software. I input the Kappa Dra data into ISIS and the result was identical to that produced by BASS. Had another go at this star last night using the 23um slit and 600sec exposures,will post results when calibrated.

Best Regards
Alun