IR from different days

Forums Spectroscopy Instrument response with Lhires IR from different days

Robin Leadbeater

You could try measuring the IR using a high reference resolution spectrum  and see how it compares with you MILES IR.(Unless I am working low to the horizon or at the blue end just use a bright star like Vega, Altair, Regulus for example which can be recorded quickly.) If it is significantly different, it might be safer to just rectify the spectra you have already taken. (You can still submit them the BeSS setting the appropriate flag in the fits header.

To be a bit controversial (and this is just my personal view) I think for relative flux calibrated H alpha spectra, most of the time IR correction of a narrow wavelength range at high resolution is a waste of good observing time. (And may even lead to increased variability, though I need  to quantify this). If you use a flat, You are already getting rid of all instrument affects as they divide out, leaving the flat lamp spectrum  and the atmospheric extinction which hardly varies across the range.  If you are using ISIS, this even removes the small slope due to flat lamp spectrum, assuming a black body at 2750K I believe so the  IR ends up being  effectively a horizontal flat line. In the projects I have been involved in where narrow range spectra have been used, the first step  in analysing the data has been to rectify all the spectra first in any case.