Had the chance to play with the T60 telescope on top of the Pic du Midi, and an Alpy 600 at the focus :
The reference star :
The RMS of the spectral calibration was 0.33762 which I guess is ok. Isis also said R=537 (not sure how it is calculated).
The "science" target was the liner galaxy M66.
It is interesting to have a look at a raw spectrum image. Here a screen capture with the region used for binning and sky removal :
Not much light pollution up here... but the green air glow line (558 nm) is readily visible
At the first look, there are emission lines in the galaxy spirals not found in the bulge, maybe active HII regions. There is also an emission line in the bulge :
With the aim of determining the galaxy radial velocity, we choose to look at the bulge with its late G-K stars with plenty of lines to analyze :
Next as a reference K-type star at rest, I looked in the Pickles library for the most similar profile. M66 spectrum is in blue, the K2iii Pickles star in red :
Before CCF analysis, as advised in Christian Buil pages, divided both spectra by the respective continuum :
It is quite clear that M66 is redshifted relative to the reference star at rest. The heliocentric velocity of the target was -3 km/s, close to negligible. The CCF function :
There is a small bug in Isis resulting in aberrant results unless reverting target with reference (resulting in a sign error). So the result here is a radial velocity of +695 km/s (M66 receding from us). This is close to the published figure
Realigning with Vr correction, we obtain reasonably superposed spectra :
Now we can analyze the galaxy for atoms. But before I would like to estimate the error on the Vr measurement. I am not sure how. I guess I can convert the calibration error (RMS=0.33762) and/or the given R to velocities ? Any advice ?
Thanks for reading, clear skies,
Jean-Philippe
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