Question re binary star systems & possible orbits

[Kate_C]

TL;DR

Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star?

From what I gather, there are S-type, P-type & T-type systems, but I'm having a hard time wrapping my mind around the orbital possibilities. Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star? And could there be daily syzygy with the stars or might it need to be less frequent? If anyone can advise, it would be so appreciated! Thank you!

 

[snorkack]

For a S-type planet, the second star orbits like a superior planet. It therefore has oppositions and superior conjunctions - both of them approximately once a year.
For a P-type planet, the second star orbits like an inferior planet. It therefore has superior and inferior conjunction - total of approximately twice in its own orbital period. Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.

 

[DrStupid]

Would it be theoretically possible to have a planet in a binary star system where there is a daily "pre-sunrise" and a "pre (or post) sunset" due to the dimmer star?

Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).

 

[snorkack]

T-type is problematic, though, due to the mass ratio requirements of Lagrange point stability.

 

[Kate_C]

For a S-type planet, the second star orbits like a superior planet. It therefore has oppositions and superior conjunctions - both of them approximately once a year.
For a P-type planet, the second star orbits like an inferior planet. It therefore has superior and inferior conjunction - total of approximately twice in its own orbital period. Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.

Thank you for clarifying! Very helpful!

 

[Kate_C]

Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).

Great to know! Thank you SO MUCH for your help with this and for the expertise!

 

[Kate_C]

Yes, if the planet is located in the trojan point L5 of the dimmer star (T-type system).

So, if I'm understanding correctly, that would make for a post-sunset in this case by the dimmer star?

 

[snorkack]

So, if I'm understanding correctly, that would make for a post-sunset in this case by the dimmer star?

Both L4 and L5 are equally stable, or not, depending on the mass ratio of primary and secondary.
Elongation to primary star is 60 degrees each case. Whether it is evenstar or morningstar depends on the rotation axis of tertiary.

 

[Kate_C]

Thank you!

 

[stefan r]

...Stars may orbit on quite close orbit, but there is no particular reason for the orbital period of stars to coincide with twice the rotational period of planet.

What if the planet has retrograde rotation? Assume it is close enough to tidal lock with one of the red dwarfs if the dwarf was non-binary. The heavy side of the planet that would otherwise face the star would see the smaller dwarf at sunrise, the stars would eclipse or pass close together (conjunction) at noon (if at zero longitude), and then at sunset the smaller dwarf would still be up later. Why would it slow rotation below 1:1 resonance?

Is there any reason it could not lock into a 2:1 resonance?

 

[Kate_C]

Thank you for weighing, stefan r! I viewed some simulations that appeared to illustrate this and proceeded to write a sci-fi novel around the premise. I'm very glad to know it sounds within the realm of possibility.

 

[snorkack]

What if the planet has retrograde rotation? Assume it is close enough to tidal lock with one of the red dwarfs if the dwarf was non-binary. The heavy side of the planet that would otherwise face the star would see the smaller dwarf at sunrise, the stars would eclipse or pass close together (conjunction) at noon (if at zero longitude), and then at sunset the smaller dwarf would still be up later. Why would it slow rotation below 1:1 resonance?

Is there any reason it could not lock into a 2:1 resonance?

What do you mean - lock of planet rotation to planet orbit, or to star orbit?