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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Missouri State University
With help from many, including Andrzej Baran, Staszek Zola, Michal Siwak, Waldek Ogloza.
Each with different properties.
We wish to understand them and determine how they resemble other pulsating sdB stars.
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.
The entire surface changes.
1 line across the surface.
2 lines across the surface.
It is hard to distinguish the mode.
Determine the spherical harmonics of pulsation frequencies to constrain models.
Traditional: Frequencies and spacings: Feige 48
Binary interactions: PG1336-018
Observed over several years and from multiple campaigns.
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.
PG1336-018: Observed by WET in 1999 and 2001
An ideal case!
~15 minute eclipses covering ~60% of the pulsator.
PG1336 eclipses do not map pulsations as we expect.
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!
But only 1 of them is detected in every good-quality run.
*Highly variable amplitudes.
*Sometimes (or often) damped below detectability
*Combinations of data have reduced amplitudes (because of phase differences)
A damping timescale if 4 – 6 hours
re-excitation timescale of 13 – 19 hours.
Feige 48 solved using traditional methods.
PG1336 shows indications of inclined pulsation axis which can constrain models.
PG0048 shows indications of stochastic oscillations.