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The Cepheid Galactic Internet astro-ph/0809.0339

The Cepheid Galactic Internet astro-ph/0809.0339. Learned, Kudritzki, Pakvasa & Zee. SETI. Microwave, lasers Difficulties: Resolution, Noise, Power, Ephemeral Other propositions: neutrinos (but power, ephemeral) Artifacts Cepheids …?!. Cepheids.

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The Cepheid Galactic Internet astro-ph/0809.0339

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  1. The Cepheid Galactic Internet astro-ph/0809.0339 Learned, Kudritzki, Pakvasa & Zee

  2. SETI • Microwave, lasers • Difficulties: Resolution, Noise, Power, Ephemeral • Other propositions: • neutrinos (but power, ephemeral) • Artifacts • Cepheids …?!

  3. Cepheids • First recognized P-L relationship by Herietta Leavitt (1908) • Yellow supergiants (~ F type) kind of bright … log(L/Lsun) = 4-5 • ~ 12 visible to the naked eye • ~ 500 in the Galaxy • Periods 1<t<50 days t~ R/v = R/(t*GM/R**2) → t ~ √(R**2/G/M)

  4. Light curves

  5. Oscillation mechanism • He II ionization • Gamma mechanism • Opacity dependence in temperature reversed The relevant layers are unstable: compression → increased T → more opacity (Kappa mechanism)

  6. Period Luminosity relationship • Mv = -2.81 logP – 1.43 OGLE data LMC

  7. Distance ladder

  8. Gaia WILL PROVIDED Parallaxes for LMC Cepheids!!

  9. Modulation • Unstable to compressions (or temperature enhacement) in the relevant layers • A small extra energy deposited can alter (trigger earlier) the oscillation • Neutrinos! • 1 Tev neutrinos would be deposited over 1e6 km

  10. Encoding • Binary

  11. Would it be easy to recognize?

  12. Further details • 1e-6 of the stellar output • Distance: not too close • Self-sustaining device? d=100 AU → R=0.2 AU ~ 30e6 km (1AU~ 150e6 km) • A signal might be buried in the archived data …

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