Observational properties of pulsating subdwarf B stars.

Mike ReedMissouri 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 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.

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

A Nonradial Pulsator: l=11 line across the surface.

A Nonradial Pulsator: l=22 lines across the surface.

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

First Goal:

Determine the spherical harmonics of pulsation frequencies to constrain

models.

Mode Identification Methods

Traditional: Frequencies and spacings: Feige 48

Binary interactions: PG1336-018

Feige 48Observed over several years and

from multiple campaigns.

Triplet

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.

Binary sdB pulsator

PG1336-018: Observed by WET in 1999 and 2001

Binary Period is ~2.4 Hours

The companion (~M5V) contributes little light to the

integrated flux. i=81o

PG1336-018Over 20 Pulsation Frequencies

Detected within 2500 Hz

➢ 2.4 hour orbital period.

➢ Tidal forces are comparable to Coriolis force

Effects to look for.

➢ Eclipse Mapping

➢ Tidal Influence on Pulsations

Eclipse Mapping

l=1, m=1

PG1336-018

An ideal case!~15 minute

eclipses covering ~60% of the

pulsator.

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.

Tipped Pulsation Axis

(Tidal Influence on

Pulsations)

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.

l=2, m=1

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.

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 hoursand a

re-excitation timescale of 13 – 19 hours.

Results:Feige 48 solved using traditional

methods.

PG1336 shows indications of inclined pulsation axis which can constrain

models.

PG0048 shows indications of stochastic oscillations.