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.
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.
We wish to understand them and determine how they resemble other pulsating sdB stars.
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.
A Radial Pulsator: l=0
The entire surface changes.
A Nonradial Pulsator: l=1
1 line across the surface.
A Nonradial Pulsator: l=2
2 lines across the surface.
But when many are combined....
It is hard to distinguish the mode.
Determine the spherical harmonics of pulsation frequencies to constrain models.
Mode Identification Methods
Traditional: Frequencies and spacings: Feige 48
Binary interactions: PG1336-018
Observed over several years and from multiple campaigns.
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.
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.
A tipped pulsation axis?
And what did we really see?
Nothing new and/or exciting.
Here is one!
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!
PG0048: An unexpected surprise!
Every night, something new!
Detected a total of 29 frequencies.
But only 1 of them is detected in every good-quality run.
Signatures of stochastic oscillations:
*Highly variable amplitudes.
*Sometimes (or often) damped below detectability
*Combinations of data have reduced amplitudes (because of phase differences)
Simulations of stochastic oscillations
Best fit results for PG0048:
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.