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Observational properties of pulsating subdwarf B stars. Mike Reed Missouri State University

Observational properties of pulsating subdwarf B stars. Mike Reed Missouri State University With help from many, including Andrzej Baran, Staszek Zola, Michal Siwak, Waldek Ogloza. Views of 3 pulsating sdB stars Each with different properties.

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Observational properties of pulsating subdwarf B stars. Mike Reed Missouri State University

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  1. Observational properties of pulsating subdwarf B stars. Mike Reed Missouri State University With help from many, including Andrzej Baran, Staszek Zola, Michal Siwak, Waldek Ogloza.

  2. Views of 3 pulsating sdB stars Each with different properties. We wish to understand them and determine how they resemble other pulsating sdB stars.

  3. Connecting to a larger picture: What can we learn using Asteroseismology? *Stellar evolutionary timescales *Cosmochronology *Stratifying of stellarinteriors *Stellar crystallization *Nuclear fusioncross sections *Masses, radii, and luminosities of stars (distance scales and population synthesis) *Diffusive processes *Convection *Neutrinos *Elementary particle physics *Helium flash *radiative levitation *binary evolution *Type I supernovae *Mass exchange and loss *Stellar magnetism *Interstellar enrichment *Electroweak theory *Core/Envelope ratios *semiconvection *Stellar equations of state *Stellar winds *Lollypop to Popsicle ratio.

  4. A Radial Pulsator: l=0 The entire surface changes.

  5. A Nonradial Pulsator: l=1 1 line across the surface.

  6. A Nonradial Pulsator: l=2 2 lines across the surface.

  7. But when many are combined.... It is hard to distinguish the mode.

  8. First Goal: Determine the spherical harmonics of pulsation frequencies to constrain models.

  9. Mode Identification Methods Traditional: Frequencies and spacings: Feige 48 Binary interactions: PG1336-018

  10. Feige 48 Observed over several years and from multiple campaigns.

  11. Triplet

  12. Our Model Solution: Total Mass: 0.4725 Msolar Shell Mass: 0.0025 Msolar Teff=29635 K (29,500+/-500) log g = 5.518 (5.50+/-0.05) Near core He exhaustion (0.74% by mass) Predicted a rotation period near 0.4 days, which was detected the following year.

  13. Binary sdB pulsator PG1336-018: Observed by WET in 1999 and 2001

  14. Binary Period is ~2.4 HoursThe companion (~M5V) contributes little light to the integrated flux. i=81o

  15. PG1336-018Over 20 Pulsation Frequencies Detected within 2500 mHz • 2.4 hour orbital period. • Tidal forces are comparable to Coriolis force

  16. Effects to look for. • Eclipse Mapping • Tidal Influence on Pulsations

  17. Eclipse Mapping

  18. l=1, m=1

  19. PG1336-018 An ideal case! ~15 minute eclipses covering ~60% of the pulsator.

  20. Eclipse data for PG1336 • All the in-eclipse modes are new! (Except for 2.) • But not where we expect them to be from splittings seen in the OoE data. • Most modes are splittings away from OoE modes. Results: PG1336 eclipses do not map pulsations as we expect.

  21. Tipped Pulsation Axis(Tidal Influence on Pulsations)

  22. A tipped pulsation axis? • Tidal forces exceed Coriolis force. • Pulsation axis will point at companion- similar to roAp stars. • Orbital motion will precess the pulsation axis, completing one revolution every couple hours.

  23. l=2, m=1

  24. Each tipped pulsation mode has 3 signatures. • Number and separation of peaks in the combined FT • Predictable regions of like phase. • If divided into regions of like phase, a central peak should show up.

  25. And what did we really see?

  26. Nothing new and/or exciting.

  27. Here is one!

  28. What have we learned? 1 good and 1 mediocre l=1, m=1 identifications. 1 reasonable l=2, m=0 identification. 1 reasonable l=2, m=1 identification. On to the models for PG1336!

  29. PG0048: An unexpected surprise!

  30. Every night, something new!

  31. Detected a total of 29 frequencies. But only 1 of them is detected in every good-quality run.

  32. Signatures of stochastic oscillations: *Highly variable amplitudes. *Sometimes (or often) damped below detectability *Combinations of data have reduced amplitudes (because of phase differences)

  33. Simulations of stochastic oscillations

  34. Best fit results for PG0048: A damping timescale if 4 – 6 hours and a re-excitation timescale of 13 – 19 hours.

  35. Results: Feige 48 solved using traditional methods. PG1336 shows indications of inclined pulsation axis which can constrain models. PG0048 shows indications of stochastic oscillations.

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