Beginning to find radial velocities for our NIRSPEC data

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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!

One thought on “Beginning to find radial velocities for our NIRSPEC data”

  1. 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?).

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