I’m (for the most part) finished entering our reduced NIRSPEC data into the database. Now I can begin to determine the radial velocities for these objects. In order to find radial velocities, you cross correlate your object’s spectrum with the spectrum of a calibrator whose radial velocity is known. The x-axis “shift” between the two spectra allows you to determine the radial velocity. I’m pretty sure there are a couple of things I need to do before cross-correlating to find the radial velocities (like applying a heliocentric velocity correction to account for our motion around the sun). But we already have a cross correlation code written by another member of our group, and so hopefully things will move pretty quickly from here!

Make sure you re-bin your spectrum onto a wavelength scale that is uniform in log(lambda), or you will only measure the shift of the middle portion of your spectrum rather than the full spectrum. This is because

z = Delta L / L

Where L = lambda. In calculus notation, this is approximately

dz = dL / L = d ln(L)

Thus, a uniform step in z results in a uniform step in the natural log of lambda. See Tonry & Davis (197?).