observational properties of pulsating subdwarf b stars. mike reed missouri state university with...
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![Page 1: Observational properties of pulsating subdwarf B stars. Mike Reed Missouri State University With help from many, including Andrzej Baran, Staszek Zola,](https://reader035.vdocument.in/reader035/viewer/2022062309/56649d1a5503460f949efd80/html5/thumbnails/1.jpg)
Observational properties of pulsating subdwarf B stars.
Mike ReedMissouri 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=0The entire surface changes.
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A Nonradial Pulsator: l=11 line across the surface.
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A Nonradial Pulsator: l=22 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 48Observed over several years and
from multiple campaigns.
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Triplet
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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.
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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=81o
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PG1336-018Over 20 Pulsation Frequencies
Detected within 2500 Hz
➢ 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 hoursand 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.