Radial Velocity - using echelle

[Andrew Smith]

Just an update. I have implemented a strict protocol of taking Ar calibrations either side of my Rho Cas spectra and tried to keep to a standard 6 x 300 sec exposures for Rho Cas. Doing this I have managed just two observations and even one of those was before astronomical twilight ended and even then the fog limited me to 5 exposures of Rho Cas.

Nonetheless, I have processed them as follows. I used the RA & Dec from the image header and VSPEC to calculate the Heliocentric correction then SPLAT-VO to do Gaussian fits to the Fe I line at 5572 and also the Ar calibration line at 5572. This allows me to do a small (~0.016A) correction to the wavelength scale. I followed a standard procedure for the measurements using the same areas etc.

For the 26th March 2015 I got an RV of -45.40 Km/s and for 6th April -46.75 Km/s. Kobel et al 2003 give a value of -47+/-2 Km/s for the stars rest RV.

As a check I used ISIS and it RV difference tool to measure the difference in the RV of the whole of order 40 (which contains the Fe I line at 5572) and it gave a difference of -0.932 Km/s which compared well with the difference of -1.3Km/s from the absolute approach. Comparing the two Ar order 40 spectra gave a reassuring 0.0 Km/s difference!

I still need to do more to look for and quantify the errors buy quantifying the errors due to the reduction procedure and by trying some standard RV stars.

Any additional comments and advice are welcome.

Regards Andrew