Theta Aurigae – A Double Star?

I do not think you are going to see two stars orbiting about a common center of mass in a short time scale, in the same way you might see Ganymede going around Jupiter. Short period binary systems are so close together you will not separate the stars visually, but you can easily detect the varying brightness as one star passes in front of the other, if they are so oriented. Check out the Eclipsing Binary stars recommended for observation in the variable star section. W Ursa Majoris is one star I have monitored and it has a short period of about 7 hrs so if you start at the right time you can easily plot a light curve in a night.

According to the Washington Double Star Catalogue
http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=B/wds/wds
the separation was 2.1 arcsec in 1871 and 4.2 in 2019. This reference has it as 3.9 arcsec in 2002
https://arxiv.org/abs/1012.3383
so also consistent with it widening currently.
Visual doubles is not my field but I guess 4 arcsec separation with a 5 magnitude difference in brightness could be pretty tough

Cheers
Robin

I’m not a double star observer myself but I seem to recall that Zeta Her was often touted as a ‘fast’ binary (period 34.5 years). A quick internet search suggests the separation is currently 1.5″ but not changing significantly. However the PA is changing by 5deg per year so maybe that change is detectable over a period of say two years.

Your best bet is to contact the Deep Sky Section which has a double star group. Their Newsletters may also be of help here as they generally include double star info. The link is:- https://britastro.org/document_folder/baa-document-store/sections/deep-sky-section

Thank you, that is very helpful. Now take a little time to think about some elementary geometry.

The definition of a parsec is the distance at which one astronomical unit subtends one second of arc. A parsec is about 3.2 light years, and Jupiter orbits the sun at a distance of 5AU in 12 years. Seen from a parsec away, Jupiter would be at most 5″ from the sun. A more massive object would orbit more quickly at the same distance, or be further away for the same period, ’tis true, but we’re talking order of magnitude estimates here.

The nearest star, alpha Centauri, is 1.3 parsecs away and although it is a multiple system the separations are many AU and the orbital periods are much more than a decade.

The only one which stands a chance of meeting your requirement is Sirius which is 2.7 parsecs away and where the companion is at most 11″ from the primary; the orbital period is about 50 years. A fair number of people have imaged Sirius B, myself included (see the gallery), but it is far from being an easy object.

Good luck!

If you want to measure stellar movements over a short period of time I would suggest that you start with stars of high proper motion. Barnard’s star is the easiest target and its movement can be measured within a week or two if you are careful. It moves around 11″ per annum, or 1″ per month. Careful astrometry should be good to around 0.3″ with amateur equipment. Again, see the gallery for my animated GIF which shows the movement from one summer to the next.

Paul

• This reply was modified 2 years, 7 months ago by Dr Paul Leyland. Reason: Fix tyop
• This reply was modified 2 years, 7 months ago by Dr Paul Leyland.

Dr Paul Leyland wrote:

The nearest star, alpha Centauri, is 1.3 parsecs away and although it is a multiple system the separations are many AU and the orbital periods are much more than a decade.

Thinking about it, if you are prepared to use a robotic telescope and/or travel to the southern hemisphere and are willing to relax your orbital period requirement to 80 years, alpha Cen is also a possibility.