introduction to binary stars steve b. howell noao
TRANSCRIPT
Introduction to Binary StarsIntroduction to Binary Stars
Steve B. Howell
NOAO
Binary Stars ??Binary Stars ??
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Binary Stars ??Binary Stars ??
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Binary Stars - Binary Stars -
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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
Binary Stars - 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
Binary Stars - TypesBinary 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
Binary Stars - TypesBinary Stars - Types
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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
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Chandra Image
Binary Stars - TypesBinary 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)
Binary Stars - TypesBinary Stars - Types
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Schematic and real eclipsing binary light curves
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Binary Stars - TypesBinary Stars - Types
Spectral variations over time due to the binary nature of this star
Binary Stars - TypesBinary 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
Binary Stars - Types 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
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Binary Stars - TypesBinary 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
Binary Stars - What can we learn?Binary Stars - What can we learn?
Eclipsing binaries are the best as the light curve can give stellar masses, radii, temperatures,& age estimates
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Binary Stars - What can we learn?Binary Stars - What can we learn? Eclipsing (or not) Radial velocity curve
can give masses (or mass estimate)
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RV amplitudes give K1 & K2
Binary Stars - What can we learn?Binary Stars - What can we learn? For a circular orbit
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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
Mass vs. radius and luminosityMass vs. radius and luminosity
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The Oddest Eclipsing Binary?The Oddest Eclipsing Binary?
1987 Epsilon Aurigae “model” from web site -->
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The Oddest Eclipsing Binary Life??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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