# Multiple star system near Sun: better choices

I'm looking for a star system between 15 and 36 ly from Sun with these characteristics:

• composed by 2 or more stars
• one of the stars should be a late G/ K type star (it doesn't matter for the other/s)
• both should have at least 2.5 AUs of stability for planets
• maximum distance beetween stars: less than 150/200 AUs

If it's possible (but this is a plus), the stars should be not very young and have a few known/colonisable stars near them. If a planet orbiting them would a circumbinary orbit it is also ok. A brown dwarf doesn't count as star.

I want to put 1 or 2 planet(s) in the habitable zone of one star. Which would be the best star systems with these characteristics from 15 to 36 light years from Sun?

A good answer should include at least 2 star systems, the reasons why you've chosen them and the source of the data.

• Do you have any specific reason(s) for picking these numbers (including the distance range)? Jan 10, 2016 at 15:24
• Yes, of course. For the number of stars, in my planet the presence of another light in the sky is part of the religion and influences a lot the science. The type of the star matter for the distance between planet and star (I need it be short but not so short that he planet is tidially locked). The stable space is to have more than 2 planet orbiting the stars. Jan 11, 2016 at 13:50
• The maximum distance between the stars matters 'cos of the brightness of the second star. The not-too-young age of the stars is needed to have life naturally evolved in one planet. The distance 15-36 ly is to have no-so-strict contacts with the Earth (the people here are too far to trade with it, but near enough to come back if they want). Jan 11, 2016 at 13:50

# Xi Boötis

Basic statistics:

• Distance from the Solar System: 22 light-years
• Spectral types: G8 Ve and K4 Ve
• Masses: 0.86 and 0.70 solar masses
• Semi-major axis: 33.14 AU
• Maximum semi-major axis for planetary orbit around Xi Boötis A: 3.8 AU
• Maximum semi-major axis for planetary orbit around Xi Boötis B: 3.5 AU
• Minimum semi-major axis for circumbinary planetary orbit: 108 AU
• Age: 200 million years

I chose Xi Boötis because it is really one of the only candidates that match nearly all the criteria. Both stars are of the correct spectral type. Additionally, it admits orbits with semi-major axes in the ranges you gave.

Sources:

• not that I understand much of this high-science, but you might have a minor typo. Are there supposed to be two list items with the description "Maximum semi-major axis for planetry orbit around Xi Bootis A:"? Jan 10, 2016 at 16:38
• @HenryTaylor My bad. The second should be about the secondary star. Thanks for pointing that out. Jan 10, 2016 at 16:40
• Do Xi got the Boötis? Xi dooooo Jun 25, 2018 at 18:27

What about good old α Centauri? It is closer than your distance limit, but otherwise fits really well.

• spectral types G2V, K1V
• star separation from 11 to 35 AU
• aged around the same as the Sun

And there are stable planetary orbits possible. Summary: orbits around binary components are possible (in the orbital plane of the stars) up to 2.5 AU or 4 AU for retrograde orbits. Orbits around the binary are stable roughly from 70 AU up.

There are even some inconclusive hints there might be a planet already detected.

And as a bonus, you get Proxima Centauri.

• It works pretty well, although it's closer than 15 ly from the Sun . . . :-) Jan 10, 2016 at 17:12
• I'm sorry but I really need it to be farer then 15 ly. Jan 11, 2016 at 13:52

I found out this systems: P Eridani

• Distance from the Solar System: 26,6 ly
• Stars: a K2 V and a K3 V
• Minimum and maximum distance between stars: 29,7 to 97,7 AUs
• Age: around 4.6 Gy

The two stars are about the same mass. As it is thought that a planet must not excede 1/5 of the minimum distance between stars to have its stability guaranteed, than we have 5,9 AUs of stability around both stars: the habitable zones are deeply in it. For a circumbinary orbit we have a minimum distance of 390 AUs.

Additionaly, there are a few G and K stars near it.