Low mass sextuple systems?

[Malenfant]

I know of one sextuple star system - Castor - which consists of six stars in three binary pairs.

I'm working on a stellar generation system that randomly generates stars in as realistic way as possible, and I have an option whereby there's a very small chance that you can get a six-star system. Just by chance I managed to naturally generate one, but it consists of six K V stars with masses between 0.5 and 0.7 sols arranged as follows:

Code: Select all

Orbital Config: (S+C)+N+N+(F+N)

S1: K6 V, 0.6 solar masses, solar metallicity, age: 6.0 Ga (Middle Aged)
     S2: K8 V, 0.5 solar masses, solar metallicity, age: 6.0 Ga (Middle Aged), orbital distance 0.1 AU

S3: K4 V, 0.7 solar masses, solar metallicity, age: 6.0 Ga (Middle Aged), orbital distance 10 AU
S4: K8 V, 0.5 solar masses, solar metallicity, age: 6.0 Ga (Middle Aged), orbital distance 150 AU

S5: K5 V, 0.66 solar masses, low metallicity, age: 9.0 Ga (Old), orbital distance 3000 AU
     S6: K7 V, 0.55 solar masses, low metallicity, age: 9.0 Ga (Old) , orbital distance 30 AU


What we have here is S1 and S2 in a close binary pair. S3 orbits the S1/S2 pair at a distance of 10 AU, and S4 orbits the pair at 150 AU. Then 3000 AU from the S1/S2 pair is another binary that is older and has lower metallicity (I assume that very far companions can be captured and so aren't required to have the same age and metallicity as the other stars). This Far binary consists of a K7 V star orbiting a K5 V at a distance of 30 AU.


Given the low mass and maturity of this system though, I'm wondering if it's particularly realistic at all though. Would such a system survive like this for 6 billion years? Are sextuple (and quintuple) systems more likely for high mass stars than low mass stars?

And does anyone see any other problems with this system at all?

[Dollan]

Looks very interesting indeed! Are you going to add a planet generation system to go with it?

I don't see why this would be unrealistic. Xi Scorpii is a quintuple system, with the general mass lying around that of Sol (I've seen some off-handed mentions of a sixth star, but can't find anything official). I know there are other similarly numbered systems, though admittedly these are largely confined to tight binary pairs. Regardless, quad systems are not that unusual, and an additional pair shouldn't be a problem if sufficiently far away from the other two pairs.

...John...

[Malenfant]

Yep, working on the planet generation system...

Do the masses look reasonable? I basically roll up one star then each companion around it has a mass of between 40% and 160% of that star's mass. In this case, that makes them all mid-late K V stars. The Far Binary just happened to end up being a K V system too, but it didn't have to be.

Or should there be more variation?

[Dollan]

The only thing that I wonder about (and bearing in mind that I'm certainly no expert) is that one of the stars in the second binary pair out-masses the stars of the primary pair. Should not the primary pair's total mass be greater than that of the secondary? I know it doesn't outmass it by much, and I may well be incorrect in that assumption.

What are the typical mass ranges for other multiple systems?

Oh! Another question: when this project of yours is all said and done, would one be able to plug in values for a known stellar system and generate worlds from there? In other words, could I put in the values for Alpha Centauri, and get a fairly reasonable result?

...John...

[Ynjevi]

According to the RECONS survey, Gliese 644, the 94th closest system to us is a quintuple system, consisting of three red dwarfs and two as of yet unclassified companions. Gliese 570, the 70th system is quatruple (K5+M1+?+T8). There are two other quatruple systems within 10 parsecs.

[Malenfant]

The only thing that I wonder about (and bearing in mind that I'm certainly no expert) is that one of the stars in the second binary pair out-masses the stars of the primary pair. Should not the primary pair's total mass be greater than that of the secondary? I know it doesn't outmass it by much, and I may well be incorrect in that assumption.

Yeah, I need to figure out what to do about that - the problem with my system is that obviously it generates stars that can be more massive than the primary. What I usually do in that case is swap the stars around so the more massive one in the "primary" (that said, bear in mind that they're all going to be orbiting a centre of mass anyway. In this case it's probably a point in space between the stars).

However, in this case S3 and S4 aren't themselves a pair - they are two stars in their own orbits orbiting the inner pair. Though in reality what is happening is that the S1/S2 binary has its own barycentre, and then the S1/S2 barycentre is orbiting another barycentre that is determined by S1/S2 + the S3 star, and then I guess that this itself is orbiting another barycentre determined by S1/S2 + S3 + S4? And then the whole shebang orbits yet another barycentre around with the Far outermost pair orbits.

This barycentre stuff gets kinda complicated when you're dealing with more than two stars

What are the typical mass ranges for other multiple systems?

I've not done a fully rigorous check of that, but generally it looks like masses aren't usually that far apart. It seems to be more common for the components (at least in Near or Close orbits) to be similar in age/mass, and Far companions can be different. Look at Sirius for example, if you rewind that in time then the progenitor star for Sirius B was probably slightly more massive than Sirius A. Alpha Centauri A and B are fairly close in mass, and C (Proxima) is rather different but that's a Far companion. Spica is mostly B V stars. And so on.

Oh! Another question: when this project of yours is all said and done, would one be able to plug in values for a known stellar system and generate worlds from there? In other words, could I put in the values for Alpha Centauri, and get a fairly reasonable result?

That's what I'm hoping Currently it's all done by dice rolls and tables, but I'm hoping to get it automated in a computer program once I learn a language that's more conducive for such things that Fortran .

[Cormoran]

Malenfant,

When you translate your system into a program, will you be including the following?

1/ Use of real stellar data (to populate the near spaces for instance)?

2/ Celestia output?

I've been pursuing a similar project for about 20 years (ever since I bought 2300AD actually), and would love to see your results.

best regards,

Cormoran

[Dollan]

Ooo, wouldn't that be nice. With the touch of a button, populate the known Local Neighborhood with reasonable solar systems....

...John...

[Malenfant]

Here's the stc for the sextuple system if anyone's interested. These nested barycentres can get confusing!

(I just put placeholder values for the stars, they're not really accurate, so ignore the comments there).

Code: Select all

Barycenter "Sextet"
{
RA         45
Dec       45
Distance  100
}
#-------------------------------
Barycenter "S1234"
{
   OrbitBarycenter "Sextet"

   EllipticalOrbit {             
      Period          87705.80
      SemiMajorAxis   3000
      Eccentricity    0
      ArgOfPericenter 0
   }
}

Barycenter "S56"
{
   OrbitBarycenter "Sextet"

   EllipticalOrbit {               
      Period          87705.80
      SemiMajorAxis   3000 
      ArgOfPericenter 180
   }
}
#--------------------------
"S5"
{
OrbitBarycenter "S56"
SpectralType "K5V"
AbsMag  7.58 # Luminosity = 0.08 Sol
Radius 375983

   EllipticalOrbit {               
      Period          149.38
      SemiMajorAxis   30 
      ArgOfPericenter 0
   }
}

"S6"
{
OrbitBarycenter "S56"
SpectralType "K7V"
AbsMag  7.65 # Luminosity = 0.08 Sol
Radius 325000

   EllipticalOrbit {               
      Period          149.38
      SemiMajorAxis   30 
      ArgOfPericenter 180
   }
}

#-------------------------------
Barycenter "S123"
{
   OrbitBarycenter "S1234"

   EllipticalOrbit {             
      Period          1211.36
      SemiMajorAxis   150 
      ArgOfPericenter 0
   }
}

"S4"
{
OrbitBarycenter "S123"
SpectralType "K8V"
AbsMag  8.00 # Luminosity = 0.08 Sol
Radius 300000

   EllipticalOrbit {               
      Period          1211.36
      SemiMajorAxis   150 
      ArgOfPericenter 180
   }
}
#-------------------------------
Barycenter "S12"
{
   OrbitBarycenter "S123"

   EllipticalOrbit {             
      Period          23.57
      SemiMajorAxis   10
      ArgOfPericenter 0
   }
}

"S3"
{
OrbitBarycenter "S12"
SpectralType "K4V"
AbsMag  7.0 # Luminosity = 0.08 Sol
Radius 400000
   EllipticalOrbit {               
      Period          23.57
      SemiMajorAxis   10
      ArgOfPericenter 180
   }
}
#-----------------------

400010 "S1"
{
OrbitBarycenter "S12"
SpectralType "K6V"
AbsMag  7.75 # Luminosity = 0.08 Sol
Radius 350000

   EllipticalOrbit {               
      Period          0.014013
      SemiMajorAxis   0.06 
      ArgOfPericenter 0
   }
}

"S2"
{
OrbitBarycenter "S12"
SpectralType "K8V"
AbsMag  8.0 # Luminosity = 0.08 Sol
Radius 300000

   EllipticalOrbit {               
      Period          0.014013
      SemiMajorAxis   0.06 
      ArgOfPericenter 180
   }
}

#-------------------------------