[AstroJ]

For the radial velocity measurement...

Can anybody drive me out of the confusion of how to find the dispersion in nm/mm for the 3727 (OII lines) by measuring the center-to-center distance between 3690 and 3799 lines in the attached spectroscopy photograph?

(feel free to redirect my post if it's in the wrong group. I am new to the forum).

Thanks

[mjc123]

Er... am I missing something? You measure the center-to-center distance between the lines (on my screen it's about 15 mm) and divide the difference in wavelength in nm by the distance in mm. What's confusing?
By the way, those numbers look as if they are in Å, so you'll have to convert them to nm.

[AstroJ]

...What's confusing? By the way, those numbers look as if they are in Å, so you'll have to convert them to nm.

I am trying to calculate the radial velocity of the nebula. I have found the wavelength scale (which was my confusion) which turned out to be 0.54nm/mm. Then, the maximum wavelength resulted to be 3.29nm, and since λ0=372.7nm... I am having trouble plugging the values to find the velocity v, for the radial velocity formula, v=Δλ / λ0 * c

Maximum wavelength estimation procedure was: distance in mm between the necklace-like lines which was 6.1mm. That distance multiplied by the wavelength scale 0.54nm, which equals 3.29nm.

Is there something I'm doing wrong here? The velocity is resulting in a very high number.