# Presentation: 692019

## Constraints and Measurements of the Equation of State from the White Dwarf Stars

**Constraints and Measurements of the Equation of State from the White Dwarf Stars**

**Don Winget**
**Department of Astronomy and McDonald Observatory**
**University of Texas**
**and**
**Department of Physcis UFRGS Brasil**
**ANL  27 August 2008**

## Some Recommended Reading

**Reviews:**
**Fontaine, Brassard & Bergeron 2001, PASP 113:409**
**Hansen & Liebert 2003, ARA&A 41:465**
**Winget & Kepler 2008, ARA&A in press **
** ****New:**
**Richer et al. 2008, AJ, 135, 2141**
**Hansen et al. 2007, ApJ, 671,380**
**Winget, Kepler, Campos, Montgomery, Girardi &      ****	****Bergeron 2008 submitted to ApJL **
**      ****Classic:**
**Van Horn 1968, ApJ 151:227**

## OUTLINE

**OUTLINE**

- _Astrophysical Context_                     What are White Dwarf Stars—and why should I care? Exploring physics of matter under extreme conditions
- _Individual Stars_: EoS from (spectroscopy, binary studies, and) asteroseismology
- III.  _Ensembles of Stars_: EoS from Luminosity Functions and Color-Magnitude Diagrams

**Notes:**
Emphasize the interplay of theory and observation

## OUTLINE

**OUTLINE**

- _Astrophysical Context_                     What are White Dwarf Stars—and why should I care? Exploring physics of matter under extreme conditions
- _Individual Stars_: EoS from (spectroscopy, binary studies, and) asteroseismology
- III.  _Ensembles of Stars_: EoS from Luminosity Functions and Color-Magnitude Diagrams

**Notes:**
Emphasize the interplay of theory and observation

## Cat’s Eye: What Are White Dwarf Stars?

- _Endpoint_ of evolution for most stars
- _Homogeneous_
- Narrow mass distribution
- Chemically pure layers
- _Uncomplicated_
- Structure
- Composition
- Evolution dominated by** **cooling:  	(oldest=coldest)

- They Shed Their Complexity!

**What Are White Dwarf Stars**

**Notes:**
NGC 6543: HST WFPC2

## ... and Why Should I Care?

- _Representative_ (and personal)
- 98% of all stars, including our sun, will become one
- Archeological history of  star formation in our galaxy
- A way to find _Solar Systems dynamically like ours_
- _Exploration of Extreme physics_
- Matter at extreme densities and temperatures
- 60% of the mass of the Sun compressed into star
-        the size of the Earth
- Chance to study important and  exotic physical processes: plasmon neutrinos, internal crystallization

## Most Importantly ....

- When we talk about white dwarf interiors, we are talking about neutron star crusts ...

- Always remember, a neutron star is just a failed white dwarf, or for purposes of this meeting ....

## Most Importantly ....

- When we talk about white dwarf interiors, we are talking about neutron star crusts ...

*Always remember, a white dwarf is just a failed neutron star ....*

## (log P, log T) plane

**Hot pre-white dwarf**
**model**

**cool white dwarf**
**model**

**Notes:**
Normal mass white dwarf (hot pre-white dwaf model), with a  1.2 Msun cool white dwarf model.

## Physical Properties in White Dwarf Stars

- Various physical processes thought to occur in WDs as they cool

**The DB**
**“****Gap”**

## OUTLINE

- _Individual Stars_: EoS from asteroseismology
- III.  _Ensembles of Stars_: EoS from Luminosity Functions and Color-Magnitude Diagrams

**OUTLINE**

**Notes:**
Emphasize the interplay of theory and observation

## H-R Diagram

-   **5                          4.5                          4**

**4**
**2**
**0**
**-2**
**-4**

- DOV

- DBV

- DAV

- DQV

## Asteroseismology

- _Asteroseismology_: Using normal modes of pulsating WDs to study extreme physics
-  and time itself

**Complex Pulsators**
**Probe interior physics**

**Simple Pulsator **
**=> Stable Clock**

## Surface BrightnessVariations100-1,000 s

*l* = 3 modes

*l *= 1 modes

*l* = 2 modes

- Surface BrightnessVariations100-1,000 s

- Most commonly
- observed
- modes are* l* =1

- Nonradial Gravity
- Modes: g-modes

- Quantum numbers
- l,m,n

## Mike’s convection simulations (standing wave  poloidal mode for l=1, m=0)

- Non-radial Modes
*l*=1,*m*=0
- (standing wave)

## Mike’s convection simulations (travelling sectoral model=1, m=1)

*l*=1,*m*=1
- (travelling wave)

## WANTED! DEAD(Stars)OR ALIVE(Planets)

- A substantially larger sample
- of angry pulsating white dwarf stars,
- last seen at APO, headed east to McDonald...

## The Competitive Edge ...

**The Competitive Edge ...**

##   u’=19.6g’=19.3Argos:15 => 150DAVs600 moreto come ...

**  ****u’=19.6****g’=19.3****Argos:****15 => 150****DAVs****600 more****to come ...**

## Alpha,gamma rates

- Metcalfe 2002

## Asteroseismology of Crystallizing Stars

## Sources of energy loss in WDs

**Are Effects of **
**Plasmon Neutrinos **
**or**
**Axions**
**Measurable **
**Using the ****Techniques of **
**Asteroseismology?**

## Observations of Coolest WDs

**Observations:  finding the coolest white dwarf stars**
**Thin disk**
**Open clusters**
**Thick disk**
**Halo**
**Globular clusters**

## Calculate the ages of the coolest white dwarf stars:White Dwarf Cosmochronology

_**Critical**_** **_**theoretical**_** **_**uncertainties **_**for dating the coolest WDs**
** **_**Outer**_** layers**
**Convection and degeneracy control throttle**
**Deep **_**interiors**_
**Neutrino emission in the hot stars**
**Crystallization and phase separation in coolest**
- Compare with observed distribution, and repeat the cycle... and also...

## The Disk Luminosity Function

- Fontaine, Brassard, & Bergeron (2001)

## shows the lower left portion of the reduced proper motion diagram from SDSS Data Release 2. 

**Notes:**
shows the lower left portion of the reduced proper motion diagram from SDSS Data Release 2. 
Reduced proper motion is defined as H = m + 5logmu + 5
Where m is the apparent magnitude and mu is the proper motion in arcsecs/yr; for a sample with similar kinematics this substitutes for the absolute magnitude of a star.
We have 268 objects with g-r>0.1 meaning that they are cooler than 8000 K, compared to 43 objects in Liebert, Dahn & Monet (1988) luminosity function. 

## LHS1126 Weird DQ Cool WD with Spitzer

**Spitzer Space Telescope Data**

**Cool WDs ****Theory vs Observation**

**Notes:**
LHS 1126 Weird DQ white dwarf with supposedly mixed H/He atmosphere, Teff = 5400K

## The Disk vs M4: Globular clusters are older than the disk ....  

**Hansen & Liebert  (2003)**

## OUTLINE

- _Individual Stars_: EoS from spectroscopy, binary studies, and asteroseismology
- III.  _Ensembles of Stars_: EoS from Luminosity Functions and Color-Magnitude Diagrams

**OUTLINE**

**Notes:**
Emphasize the interplay of theory and observation

## White Dwarf Stars in Clusters

- Explore  white dwarf cooling ages as compared to main sequence isochrone ages
- Open clusters help in establishing constraints on disk age
- Older open clusters sample critical physics of white dwarf cooling

## White Dwarf Stars in Clusters

- Explore  white dwarf cooling ages as compared to main sequence isochrone ages
- Open clusters help in establishing constraints on disk age
- Older open clusters sample critical physics of white dwarf cooling
- Globular Clusters: Finally, we can isolate masses and explore the physics!

## ComparingTheoreticalmodels:new(er) opacities, interior EOS and atmospheric boundary conditionsHansen & Liebert (2003)

## Fontaine 2001 models and Winget et al. 2008 models 0.5 Msun

## Fontaine 2001 models and Winget et al. 2008 models 0.8 Msun

## Conclusions from model comparisons

- Mass – radius is consistent for all groups
**EoS improvements **( Chabrier et al. 2000 over Lamb & Van Horn 1975 for interiors  and Saumon Chabrier & Van Horn 1993 over Fontaine , Graboske & Van Horn 1977 for the envelope) do not produce (presently) observable differences in the models.
- Improved **atmospheric surface boundary **condition is not as important as has been claimed in the literature ... it produces no observable differences until bolometric luminosities below the largest magnitude globular cluster stars

## Fixing the WD evolutionary tracks in the CMD by simultaneously fitting the main sequence and the WDsgives Z, (m-M) and E

- Data: proper motion screened sample from **Richer et al. 2008, AJ, 135,2131**

**Fixing the WD evolutionary tracks in the CMD by simultaneously fitting the ****main sequence and the WDs****gives Z, (m-M) and E**

- This diagram (and previous ones) determines
- the low-mass limit for WDs at the “clump”= 0.5 Msun

## Luminosity Function for NGC 6397 proper motion screened WD sample

**Luminosity Function for NGC 6397 proper motion screened WD sample**

## What physics might be relevant near the peak of theLuminosity Function (the “clump” in the CMD)?

**Convective Coupling**: The surface convection zone reaches the degeneracy boundary, reducing the insulation of the envelope
**Crystallization**: Ions crystallize with attendant latent heat and phase separation expected from theory

## Fontaine, Brassard & Bergeron (2001)

## Ratio of Coulomb Energy to Ion Thermal Energy

**What is the value of Gamma at and near the “clump” in the observed CMD,  or equivalently, the value of Gamma at the peak of the Luminosity Function?**

**(peak)  = 194 (carbon) = 313 (oxygen)**

**(rise)    = ****182**** (carbon) = ****291**** (oxygen)**

## Conclusions from NGC 6397

- Confirm that **crystallization occurs**
- Confirm that **Debye cooling occurs**
- We can _***measure***_** the       **for crystallization
- We find the first empirical evidence that
-          Van Horn’s 1968 prediction is correct: ***Crystallization is a first order phase transition***
- Low metallicity clusters may not produce significant O in cores of some of the 0.5Msun stars ...
**He mixing **combined with CIA opacities explains the mysterious “blue hook.”

## Observational and theoretical futures for EoS constraints and other physics from white dwarfs

- More fields for NGC 6397 and other globular clusters
- More clusters:  globular and rich, old, open clusters different white dwarf and masses and Z, C/O = C/O(Z)?
- SDSS => enormous increase in the disk and halo white dwarfs
- SDSS => more asteroseismology of high (near Chandra mass) and (He-core) low mass white dwarf stars
- Measurements of evolutionary changes allows study of particle physics aspects and general thermal properties

## Observational and theoretical futures for EoS constraints and other physics (cont’d)

- Measurements of evolutionary changes allows study of particle physics aspects and general thermal properties
- Bayesian analysis of data with different classes of theoretical models for these large observational samples
- New opacity calculations for warm and cool white dwarfs
- Your list goes here ....

## Some Recommended Reading (reprise)

**Reviews:**
**Fontaine, Brassard & Bergeron 2001, PASP 113:409**
**Hansen & Liebert 2003, ARA&A 41:465**
**Winget & Kepler 2008, ARA&A in press **
** ****New:**
**Richer et al. 2008, AJ, 135, 2141**
**Hansen et al. 2007, ApJ, 671,380**
**Winget, Kepler, Campos, Montgomery, Girardi &      ****	****Bergeron 2008 submitted to ApJL **
**      ****Classic:**
**Van Horn 1968, ApJ 151:227**

## The End Thank you