OW Geminorum, an unusual star system

[LukeCEL]

Hi everyone! While I was researching, I came across a star system that was very unique, and I knew I had to share it.

OW Geminorum (OW Gem) is an eclipsing binary consisting of two supergiants: one is F2Ib-II and the other is G8IIb (technically a bright giant). The two stars orbit each other every 3 and a half years, so eclipses are very rare.

This unusual configuration poses a conundrum to stellar evolutionary theory, according to Terrell et al. (2003), since it is impossible for the two stars to have formed at the same time. However, they say it's possible that OW Geminorum was once a triple system and two stars in a close binary system merged.

Physical and orbital parameters are from the aforementioned Terrell et al. (2003), while the primary minimum is set to occur at the 2008 primary eclipse. Approximate rotation periods are from Griffin & Duquennoy (1993). Below is the STC code:

Code: Select all

# Terrell et al. (2003), AJ 126 (2), 902
# "The Double Supergiant Binary OW Geminorum"
# https://iopscience.iop.org/article/10.1086/376479
# Period and eclipse minimum from Dvorak (2009), OEJVS 100, 1
# "The 2008 Primary Eclipse of OW Gem"
# http://var.astro.cz/oejv/oejv.php?oejv=100
# Rotation periods from Griffin & Duquennoy (1993), The Obs. 113, 53
# "Spectroscopic binary orbits from photoelectric radial velocities. Paper 109:
# HDE 258878 (OW Gem)"
# https://ui.adsabs.harvard.edu/abs/1993Obs...113...53G/abstract
Barycenter 1004901332 "OW Gem"
{
   RA 97.92404853
   Dec 17.08231543
   Distance 6876.576 # from Gaia DR2 parallax
}

"OW Gem A"
{
   OrbitBarycenter "OW Gem"
   SpectralType "F2Ib-II"
   AbsMag -3.5 # from bolometric magnitude and temperature
   Radius 21497130

   EllipticalOrbit {
      Period          3.445807
      SemiMajorAxis   1.9528 # mass ratio 5.8:3.9
      Eccentricity    0.51718
      Inclination     93.04 # inclination to plane of sky:
      AscendingNode   96.36 # 89.08 +/- 0.02 mas
      ArgOfPericenter 46.87
      MeanAnomaly     344.00
      Epoch           2415779.0 # primary minimum
   }

   RotationPeriod 3912 # 163 d
}

"OW Gem B"
{
   OrbitBarycenter "OW Gem"
   SpectralType "G8IIb"
   AbsMag -1.5 # from bolometric magnitude and temperature
   Radius 22053690

   EllipticalOrbit {
      Period          3.445807
      SemiMajorAxis   2.9042 # mass ratio 5.8:3.9
      Eccentricity    0.51718
      Inclination     93.04 # inclination to plane of sky:
      AscendingNode   96.36 # 89.08 +/- 0.02 mas
      ArgOfPericenter 226.87
      MeanAnomaly     344.00
      Epoch           2415779.0
   }

   RotationPeriod 2928 # 122 d
}

Regards, Luke

[Lafuente_Astronomy]

That is indeed, an interesting system. However, I wonder about this:

However, they say it's possible that OW Geminorum was once a triple system and two stars in a close binary system merged.

Wouldn't the 2 stars that merge actually destroy themselves and create a compact star instead? But since I don't fully know how stars evolve, you can perhaps enlighten me on this? That part, for me, is somewhat confusing

[LukeCEL]

Wouldn't the 2 stars that merge actually destroy themselves and create a compact star instead?

Compact stars are formed when stars die. When two stars merge, they just become a more massive star. Actually, we might have seen this action occur before: V838 Monocerotis' 2002 outburst might have been the result of two stars merging.

[Lafuente_Astronomy]

Compact stars are formed when stars die. When two stars merge, they just become a more massive star. Actually, we might have seen this action occur before: V838 Monocerotis' 2002 outburst might have been the result of two stars merging.

Ahhhh. Thanks for the information

[jujuapapa]

An another unsual system, WDJ0551 + 4135.

The merge of two white dwarfs without giving an SNIa.
Read HERE

[pirogronian]

This unusual configuration poses a conundrum to stellar evolutionary theory, according to Terrell et al. (2003), since it is impossible for the two stars to have formed at the same time

Actually, this is nothing unusuall, but standard astronomy have a long way to admit it.

Most stars revolve in pairs.

Using the same principles, it's aplicable also for far orbiting objects.