Sunday, 23 December 2012

Greetings from Gamma Velorum


C P Gaposchkin, when asked to name the best moments in her astrophysics career didn't hesitate: "My first sight of the spectrum of Gamma Velorum".

   What makes it so special? This star ( we now know) has exhausted its hydrogen fuel and has a superabundance of helium: the byproduct of hydrogen fusion. Gamma Velorum now converts helium into carbon. The resulting spectrum is dominated by bright carbon bands (and lesser helium bands) - much like the spectrum of a WWII searchlight!
   The background continuum is that of a larger type O companion - but it's the Wolf-Rayet bands that are so distinctive. This is a 'sketch' compiled from spectroscope views, published plots and a generic white light spectrum. It's as close to the ep view as I can get. Photographs are rather different and dominated by a strong deep violet continuum - but my eye doesn't detect deep violet so well. The strongest part of the visible continuum is green, and the blue and yellow carbon bands make the Gamma Vel primary seem 'greenish' to my eye when viewed (undispersed) in the eyepiece.
   Big question: did CPG see it in colour, or only as a BW photo? We may never know; but I guess 'colour' for it to be her most favourite moment in a career of looking at spectra.
   Christmas greetings to all viewers. (by the way: the two smaller spectra are added for a Christmas effect)