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Introduction to Binary Stars

Introduction to Binary Stars. Steve B. Howell NOAO. Binary Stars ??. Binary Stars ??. 0 1. Binary Stars -. Binary stars are pairs of stars orbiting each other “connected’ by their mutual gravitational interaction.

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Introduction to Binary Stars

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  1. Introduction to Binary Stars Steve B. Howell NOAO

  2. Binary Stars ??

  3. Binary Stars ?? 0 1

  4. Binary Stars - Binary stars are pairs of stars orbiting each other “connected’ by their mutual gravitational interaction. 50% of stars are binaries: ~100% O/B ~75% M Obs. biases

  5. Binary Stars - • Binary Stars may have orbital periods from seconds to hours to thousands of years • They may contain stars of all kinds, sizes, and masses • They may have circular or elliptical orbits • They are believed to have formed together - same age (not capture) • Close binaries affect each other’s evolution • Long period binaries essentially act as single stars

  6. Binary Stars - Types • Binary stars come in a few types differentiated by their orbital period and/or observational behavior. For example: • Visual double (actually see both components - LONG period). Do not confuse with optical double • Astrometric binaries - see the wobble on the sky

  7. Binary Stars - Types An astrometric and visual binary: Sirius A&B -- an A star (A) and a white dwarf (B) Has a ~50 year orbit. 8.6 light years from Earth Chandra Image

  8. Binary Stars - Types • or • Eclipsing binaries - one/two eclipses per orbit • Spectrum binaries - spectral properties change • Spectroscopic binaries - radial velocity motions (short periods easier to find)

  9. Binary Stars - Types Schematic and real eclipsing binary light curves

  10. Binary Stars - Types Spectral variations over time due to the binary nature of this star

  11. Binary Stars - Types • Or differentiated by other criteria- • Close binaries w/ stellar distortions or mass transfer • Intrinsic brightness changes due to stellar variability • Binaries with components of very different properties: color (WD+RD), mass (Exo-Planet), temperature • Other

  12. Binary Stars - Types Binaries can be close (short orbital period) and show light variations due to … Ellipsoidal shape and/or tidal interaction Interactions such as mass exchange / transfer If the smaller (but more massive) star in an IB is a white dwarf, the binary is called a cataclysmic variable

  13. Binary Stars - Types • All combinations of the previous properties are possible • Many are unknown as they simply have not been seen to vary (line of sight / observed) • Binary Stars are the fundamental way in which we understand stars (and star systems): their formation, evolution & death. • Remember --Three out of every two stars are in a binary system

  14. Binary Stars - What can we learn? • Eclipsing binaries are the best as the light curve can give stellar masses, radii, temperatures,& age estimates

  15. Binary Stars - What can we learn? • Eclipsing (or not) Radial velocity curve can give masses (or mass estimate) RV amplitudes give K1 & K2

  16. Binary Stars - What can we learn? • For a circular orbit Measure semi-major axis, a, from projected orbit & the distance. Relative positions about the center give: M1/M2 = a2/a1 = K2/K1 Kepler’s Law

  17. Mass vs. radius and luminosity

  18. The Oddest Eclipsing Binary? 1987 Epsilon Aurigae “model” from web site -->

  19. The Oddest Eclipsing Binary Life?? Elemarkhorsaurus from the Epsilon Aurigae Binary Star System Caption: Ashraf, do you want to meet my new pet? Look, he is behind you and friendly. He loves the climate and his new home in the Eps Aur binary system. (From flickr)

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