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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.
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Views of 3 pulsating sdB stars Each with different properties. We wish to understand them and determine how they resemble other pulsating sdB stars.
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Connecting to a larger picture: What can we learn using Asteroseismology? *Stellar evolutionary timescales *Cosmochronology *Stratifying of stellar interiors *Stellar crystallization *Nuclear fusion cross 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.
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A Radial Pulsator: l=0 The entire surface changes.
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A Nonradial Pulsator: l=1 1 line across the surface.
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A Nonradial Pulsator: l=2 2 lines across the surface.
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But when many are combined.... It is hard to distinguish the mode.
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First Goal: Determine the spherical harmonics of pulsation frequencies to constrain models.
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Mode Identification Methods Traditional: Frequencies and spacings: Feige 48 Binary interactions: PG1336-018
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Feige 48 Observed over several years and from multiple campaigns.
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Triplet
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Our Model Solution: Total Mass: 0.4725 M solar Shell Mass: 0.0025 M solar T eff =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.
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Binary sdB pulsator PG1336-018: Observed by WET in 1999 and 2001
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Binary Period is ~2.4 Hours The companion (~M5V) contributes little light to the integrated flux. i=81 o
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PG1336-018 Over 20 Pulsation Frequencies Detected within 2500 mHz ➢ 2.4 hour orbital period. ➢ Tidal forces are comparable to Coriolis force
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Effects to look for. ➢ Eclipse Mapping ➢ Tidal Influence on Pulsations
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Eclipse Mapping
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l=1, m=1
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PG1336-018 An ideal case! ~15 minute eclipses covering ~60% of the pulsator.
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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.
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Tipped Pulsation Axis (Tidal Influence on Pulsations)
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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.
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l=2, m=1
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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.
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And what did we really see?
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Nothing new and/or exciting.
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Here is one!
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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!
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PG0048: An unexpected surprise!
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Every night, something new!
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Detected a total of 29 frequencies. But only 1 of them is detected in every good-quality run.
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Signatures of stochastic oscillations: *Highly variable amplitudes. *Sometimes (or often) damped below detectability *Combinations of data have reduced amplitudes (because of phase differences)
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Simulations of stochastic oscillations
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Best fit results for PG0048: A damping timescale if 4 – 6 hours and a re-excitation timescale of 13 – 19 hours.
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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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