Observations of the Capella spectroscopic binary

[Bajastro]

This system consists of two yellow giants having types G0III and G8III (some sources give K0III), similar masses and brightness. The orbital period of the components is 104 days.

The fact that one of the stars has a later spectral type is very convenient 😀. It has stronger spectral lines of metals, including sodium.

This allows you to immediately recognize which star is approaching and which is currently moving away.

I made 3 observations so far with using a DIY 3D printed LowSpec spectrograph in the version v2 designed by @Paul Gerlach and a 1800 l/mm holographic grating.

Based on these observations, the spectral spread for both observations for the sodium line is 0.79 Å (0.079 nm) or 4 pixels, which gives a difference of radial velocities of 40 km/s.

Assuming that component A belongs to G8III and component B to G0III:

2019-12-03 component A was moving at relative vr to the barycenter of the system of -20 km/s and component B was moving at a  relative vr of +20 km/s.

2020-01-23 component A was moving at a relative vr of +20 km/s and component B was moving at a relative vr of -20 km/s.

I called radial speeds relative, because the radial velocity of the Capella barycenter to the Solar System wasn't included.

 

I took the radial velocity of the Capella barycenter into account and I received this phase plot:

The background is the plot of radial velocities from paper:

M. Weber, K. G. Strassmeier, 2011, The spectroscopic orbit of Capella revisited

https://arxiv.org/pdf/1104.0342.pdf

Edited February 7, 2020 by Bajastro

[Paul Gerlach]

Beautiful results! Makes me very happy to see the LOWSPEC being used this way. And also a bit envious because I don't have my equipment operational😉

[robin_astro]

Nice result.  Did you allow for the change in the radial component of Earths orbital velocity between the dates ie make any heliocentric corrections?  

Cheers

Robin

[Bajastro]

Thanks all.

I didn't use the calibration lamp. So, now I can only observe splitting of the spectral lines depending on the phase. In this case, movements of Solar System bodies were omitted.
But for better measurements precision of spectroscopic binaries with higher eccentricity orbits, I will need a good calibration module soon. My friend is constructing a calibration module for his LowSpec spectrograph.

Edited February 16, 2020 by Bajastro