White Dwarf Stars: Crystals and Clocks S.O. Kepler

White Dwarf Stars as Laboratories S.O. Kepler Department of Astronomy UFRGS - Brazil

Stellar Evolution Mass < 10 M sun : White Dwarf 10 M sun < Mass < 25 M sun : Neutron Star 10 M sun < Mass < 25 M sun : Neutron Star Mass > 25 M sun : Black Hole

Planetary Nebula Observed by the Hubble Space Telescope

Sirius and the White Dwarf Sírius B

White dwarfs pulsate as they cool

Intensity Changes With Time Multiperiodic, P=71s to 1500s, amp=4 mma to 300 mma

Pulsating White Dwarfs n Internal structure of the white dwarf (SNIa progenitors) (SNIa progenitors) n Cooling timescale n Age of the oldest stars in our galaxy High energy and high density physics High energy and high density physics

Pulsating White Dwarfs n White Dwarfs ~ 6000 (doubled in 2004) n Variable~ 115 (tripled in 2004) n DOV T eff = K 10 known, M= -1 n DBV T eff = K 13 know, M= 8 13 know, M= 8 n DAV T eff = K 92 known, M=12 92 known, M=12 Structure – SNIa progenitors

Pulsations … Seismology

Pulsations/Seismology: Y 10 e Y 11

Pulsations are global

Observations: 1.6 m telescope Laboratório Nacional de Astrofísica Brasópolis, MG

Whole Earth Telescope

Mass determination n UV spectra n Optical spectra n T ef = K n Massa = 1,1 M sol 0,6 M Sol

Mass distribution 300 stars PG survey

SDSS We fit all 1872 DA white dwarfs in SDSS

SDSS T eff determination

SDSS log g determination

Transição de fase para cristal A parte pontilhada corresponde a P(líquido quântico)/P(gás ideal) > 1. Efeitos quânticos iônicos são importantes à direita desta linha (  1975

DAV instability strip Need high S/N spectra of variables and non-variables to refine Teff and log g Need to find more variables and non-variables to determine log g dependence

Most Massive Pulsating WD

BPM37093 – Diamond in the Sky! 10’ 2 o = 12 x 10’ 17 light yr distant (40 quadrillion km)

Light Curve

Crystallization O C

Pulsations Present

Period in seconds

Phase Diagram

Crystallized or not?

BPM37093 in 1999

Super-Diamond? n Diamond n C crystal n FCC n 3,08A between atoms n 2 shared electrons n T < 8000 K n 10 K atm < P < 1,2x10 8 atm n BPM37093 n C crystal n BCC n 0,01A between nucleons n all electrons are free (degenerate) n T = 7 million K n P = 5x10 18 atm  = 36 Ton/cm 3  = 36 Ton/cm 3 n E ions > 2kT (quantized) n metallic quantum crystal o o

DBV instability strip Bárbara Castanheira - IUE

DBV GD 358

181 periodicities detected n Mass of each layer n M(R): Luminosity -> distance (1/10 uncertainty of parallax) (1/10 uncertainty of parallax) n Rotation law(r) [splitting (k)] n Magnetic field limit (6000 G) n 6 th order harmonics and combinations

Nuclear reaction rate Quantity of 22 Ne dependes mainly onQuantity of 22 Ne dependes mainly on  [C 12  16  Ne 20  Mg 24  ] NonResonantReaction T > 10 8 K and   g/cm 3 Uncertainty is around 50%!

C(  )O S 300

Mode identification with HST Chromatic amplitude changes

GD358 mode identification HST n Bárbara Castanheira l = 1 for k=8 and 9 in 1996 l = 1 for k=8 and 9 in 1996 probably l = 1 for other modes in 2000 probably l = 1 for other modes in 2000

GD358 mode identification HST n Bárbara Castanheira l = 1 for k=8 and 9 in 1996 l = 1 for k=8 and 9 in 1996 probably l = 1 for other modes in 2000 probably l = 1 for other modes in 2000

PNNV – DOV instalibility strip

Period (sec) PG

Frequency (  Hz) All PG

PG : 101 pulsations detected n T eff = K n Total mass : ( / ) M Sun n M(R): Luminosity -> distance n Mass of external layers n no harmonics or linear combination (no convection zone) (no convection zone)

PG modes detected k=   P=21.43s M= M Sun J. Edu S. Costa

Direct Method dP/dt Period (s ) P=516s dP/dt=( )x s/s

But period increases with time! dP/dt=( ) x 10 –11 s/s 1s/300 years

Most stable optical clock known

DAV

G117-B15A 2004 P=215s

Stable? Time scale = 2.2 Gyr Pulsars with dP/dt = s/s have timescale 0.1 Gyr, but PSR B , with P=5.3 ms and dP/dt=1.8x s/s has timescale of 9.5 Gyr.

Axions m ax cos2  < 4 meV E vacuum >2,5GeV &

Axions m ax > 1  eV or  ax > 1 tan  ratio of the vacuum energy of the two Higgs fields

Gravitons? Biesada & Malec (2002) Phys Rev D, 65 dP/dt: the string mass scale M s > 14,3 TeV/c 2 for 6 dimensions for Kaluza-Klein gravitons. The limit is negligible for higher dimensions

Variable G? Asteroseismological bound on G/G from pulsating white dwarfs Omar G. Benvenuto, Enrique García-Berro, and Jordi Isern PHYSICAL REVIEW D 69, (2004).

Why do pulsation periods change? R = 9,6 x 10 8 cm, dR/dt = 1 cm/yr T nucleus =12 million K, dT/dt = 0.05 K/year DAV Cooling dominates!

Photon vs neutrino emission

The Feynman diagram

Plasma neutrino (Weak interaction)

Two keys… n To excite the plasmon we must have n The plasma frequency is much higher for a degenerate gas, and increases with increasing density…

Effects of Neutrinos on Evolutionary Timescales EC GD 358

DBVs: dP/dt and Plasmon Neutrinos: 3-4!

Luminosity Function and Age of the Galaxy Age of the disk:  ± 2 yr Number of Stars Intensity

Age of the Universe Age = (11,5 ± 2,7) billion years Age of Universe = Age of disk + Halo + Formation of galaxy Age of disk + Halo + Formation of galaxy 9 ± 2 1,5 ± 1,5 1 ± 1 billion yr

HST: Galaxies formed 1 Gyr after Big-Bang

White dwarfs in globular cluster M – 8 days of exposure with HST Age= Gyr Age= Gyr Disk corrected we will do other globulars with SOAR

Age of the Universe in 2004 CMB - WMAP = ( ) GyrCMB - WMAP = ( ) Gyr Hubble constant: 1/H = (12 + 1) GyrHubble constant: 1/H = (12 + 1) Gyr Globular clusters: ( ) GyrGlobular clusters: ( ) Gyr Radiactive decay: ( ) GyrRadiactive decay: ( ) Gyr Cooling of white dwarf stars: ( ) GyrCooling of white dwarf stars: ( ) Gyr Distances to SNIa: (0.63/h)Gyr, Distances to SNIa: (0.63/h)Gyr,  10 years ago only white dwarfs gave age smaller than 15 billion years: smaller than 15 billion years: SN1987A NGC6903CenA SNIa

Spectra of DA, DB and DO

Mode identification with SOAR

Find more variables Frequency (Hz) Fractional Amplitude P=647s; A=48mma (V=18.6) P=329s; A=22mma

Detection of extra-solar planets Spectroscopy: detection of radial velocity variation around the center of mass

G117-B15A 2004 P=215s

Jupiter around G117-B15A? P=11.86 years, a=5.2 UA

Saturn around? P=29.46 years, a=9.5 UA

Search for planetary companions monitoring changes in pulse arrival time due to motion of star around barycenter. Orbit around center of mass with planetary companion

Detection Limits on Orbits of the Planets Doppler Sectroscopic Method (Current Limits) Pulsating White Dwarf Method (Current Limits)

Region of Planet Detection Quantitative Theoretical Limits of Stability? Time Squared

PMT CCD vs PMT

Measured Amplitude Difference

Change in Amplitudes

Amplitude vs Wavelength

CCD Data Analysis

That’s all folks!

Music?