combining spectra taken months apart: dopcor

westmoquette wrote on Mar 08, 2011

I have a set of IFU observations taken at the same coords and spectrograph setup, but ~two years apart. Before I can co-add them, I need to correct for the different geocentric velocities at the time of observations - i.e. correct to the heliocentric velocity frame. Is dopcor the correct task to use? I have been running it like so:
dopcor( "IFUframe1.fits", "IFUframe1_dopcor.fits", -10.42, isvel+, add-, dispers+, flux- )
dopcor( "IFUframe2.fits", "IFUframe2_dopcor.fits", 0.76, isvel+, add-, dispers+, flux- )

After I have done this, how should I co-add the frames in such a way that the wavelength shifts are respected?

Regards,
Mark

---

Francisco Valdes wrote on Mar 08, 2011

The key step is modifying the wavelength solution to account for the geocentric velocities. The task RVCORRECT can be used to calculate a correction and DOPCOR can be used to modify the wavelength solution (without actually rebinning). What you need to do is correct to the same standard of rest (say to heliocentric). The last step for coadding is to use SCOMBINE. This will use the corrected wavelength solutions to resample to a common pixel sampling before coadding.

Frank Valdes

---

Last post on Mar 08, 2011