Alpy – radial velocities of PNe

Forums Spectroscopy Measuring radial velocity of planetary nebulae with Alpy? Alpy – radial velocities of PNe

Paul Luckas

Hi all,

Just to close the loop on this; I ended up measuring the radial velocities of 3 planetary nebulae with published values ranging from -13 km/s to 194 km/s. I used PlotSpectra’s point and click measurement tool, averaging the velocities of the prominent H and OIII emission lines.

All three ended up within 15 km/s of the published values – which is closer to what I expected vs my original post on the matter. Of note, the spectra were hastily acquired (ie, resulting in low S/N) between rain and clouds.

I’ve attached a couple of profiles. Nebulium 😉 dominates these objects, as expected, and in the case of the attached NGC 6629, the black body profile of the hot central star appears (perhaps?) to be peaking through at shorter wavelengths, although I did not correct for instrument response (I mention this only as my other two show little sign of a central star via the continuum which could be targeting, or target). Despite the low resolution of the Alpy, there are some interesting differences in the features of the acquired profiles which I’m yet to fully investigate. NII 6583Å is clearly visible in NGC 6818, with its sibling on the other side of H-a not quite developed at this resolution.

A recommended activity for Alpy owners / beginners.

Thanks, Robin, for the links to the ISIS CCF information above.