Finding radial velocities

I’ve made good progress on a Python code for finding the radial velocity of an object, and expect it to be done soon!  I’m looking forward to finding some radial velocities, and then using the information to determine cluster membership for the brown dwarfs in our sample.

I thought I’d just outline the very basic steps involved in finding radial velocity.

1) Cross correlation: cross correlate two spectra to find how much one is shifted in relation to the other (in pixels).  One of these spectra should be a standard for which the radial velocity is known.

2) Convert this shift in pixels to a shift in velocity.  Note that this is the velocity with respect to the standard object.

3) Subtract the velocity of the standard from the velocity shift to obtain the radial velocity of your object!


Beginning to find radial velocities for our NIRSPEC data

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!