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Mizar A - observations of the first known spectroscopic binary

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Posted (edited)

I finished observations of the Mizar A spectroscopic binary.
Calibration for the Hα line made on water lines contained in the Earth's atmosphere.
I used LowSpec spectrograph with 1800 grooves/mm reflective holographic grating, APM APO 107/700, QHY163M camera and HEQ5 mount with guiding.
It turned out that the Earth's movement practically compensated for the radial velocity of the Mizar A system.
Based on the analysis, I received the result:
vr = -8.8 km/s
in fact the system is approaching at a radial velocity of -6.3 km/s.

I also determined the phase plot of radial velocities based on my measurements for the Na (together for both lines) and separately for Hα line:



Error is based on half my spectral resolution (0.2 Å/pix corresponds to rv = 10 km/s). Each measurement corresponds to the stack a few images.

The most important purpose of observing this binary system was to record the historical Ca II line (often called as CaK, 3933.66 Å).
The distances in the violet part of the spectrum are almost 2x smaller than the corresponding shifts for the Hα line. This line initiated the discovery of spectroscopically binary systems, and Mizar A was the first discovered system of this type.

These were the spectroscopic observations in the 19th century:

Source: https://www.leosondra.cz/en/mizar/#b20

I've made several observations of this line in the last two weeks:


Animation showing the changes in the CaK line based on my observations:


Not only the Ca II is split, but the surrounding lines also, shown below in a wider environment:


Balmer hydrogen lines are becoming more dense as Balmer's gap approaches (3646 Å).

Observation result of the Hα line:


And animation showing the changes in this line:


The Na I doublet was much more difficult to observe, because stars with A spectral type contain very faint lines of this metal:


Animation showing the changes in the sodium doublet:


We received the sodium quartet :D

Edited by Bajastro
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First class work and well presented.


Regards Andrew 

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Brilliant stuff. A good example of what the LowSpec can achieve. And well presented.

I'm inspired to dust off my own spectrometer...

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Posted (edited)

Thank you, the LowSpec capabilities are impressive.
The resolution is similar to SQUES Echelle spectrograph results.
I am still thinking about how to improve the guiding module in my spectrograph.

Edited by Bajastro
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Good work, well done.

Clear skies,


Essex UK

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Posted (edited)


Spectra of Mizar, Stars and their spectra Kaler p.177.

What software do you use to reduce your spectra ?



Essex UK


Edited by Jack Martin

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Posted (edited)

@Jack Martin
I'm sorry for late answer. I don't have this book.
I use Bass Project 1.9.9 - version is marked on the right side on the each spectrum (light gray color).

Edited by Bajastro

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