instrument respons LHiResIII-2400l/mm grating
Posted: Fri Sep 18, 2020 4:12 pm
I had a question regarding the correct star for instrument response with LHiResIII and 2400 l/mm grating for H-alpha and HeI @6678 Å.
Generally speaking, I have applied the following rule until today: I use a set of reference stars depending on the period of the year: Altair for summer, Castor for winter and Regulus for spring. I may sometimes also use Vega. I don't take a spectrum from the star every night to determine the instr. response. Usually I use the same correction for a few months. If this is not correct I would like to hear it
So far this has worked quite well, but for some time I have had problems with the correct continuum of the obtained spectra.
With the spectra of gam Cas for the HeI, I notice that the difference is now very clearly visible. The continuum changes as function of the height of the observed star, I suspect that this is the cause, I am not sure.
Example below is the spectrum with instr. response of 15Cas and Altair. 15 Cas is more close to gam Cas and Altair not at all. (blue=Altair for instr. respons - green=15Cas for instr. respons)
Until now I usually only used spectra with the LHiResIII for the BeSS database in high resolution and H-alpha in the centre of the image and instr. response as described above.
The question now is which star is best used to determine the instr. response for LHiResIII and 2400 l/mm grating and is there a difference depended in which part of the spectrum we work - to make the correct choice of the star used for instr. response ?
thanks !
Erik
Generally speaking, I have applied the following rule until today: I use a set of reference stars depending on the period of the year: Altair for summer, Castor for winter and Regulus for spring. I may sometimes also use Vega. I don't take a spectrum from the star every night to determine the instr. response. Usually I use the same correction for a few months. If this is not correct I would like to hear it
So far this has worked quite well, but for some time I have had problems with the correct continuum of the obtained spectra.
With the spectra of gam Cas for the HeI, I notice that the difference is now very clearly visible. The continuum changes as function of the height of the observed star, I suspect that this is the cause, I am not sure.
Example below is the spectrum with instr. response of 15Cas and Altair. 15 Cas is more close to gam Cas and Altair not at all. (blue=Altair for instr. respons - green=15Cas for instr. respons)
Until now I usually only used spectra with the LHiResIII for the BeSS database in high resolution and H-alpha in the centre of the image and instr. response as described above.
The question now is which star is best used to determine the instr. response for LHiResIII and 2400 l/mm grating and is there a difference depended in which part of the spectrum we work - to make the correct choice of the star used for instr. response ?
thanks !
Erik