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

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

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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

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Planetary Nebula Observed by the Hubble Space Telescope

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Sirius and the White Dwarf Sírius B

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White dwarfs pulsate as they cool

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

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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

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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

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Pulsations … Seismology

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Pulsations/Seismology: Y 10 e Y 11

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Pulsations are global

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

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Whole Earth Telescope

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

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Mass distribution 300 stars PG survey

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SDSS We fit all 1872 DA white dwarfs in SDSS

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SDSS T eff determination

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SDSS log g determination

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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

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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

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Most Massive Pulsating WD

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

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Light Curve

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Crystallization O C

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Pulsations Present

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Period in seconds

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Phase Diagram

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Crystallized or not?

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BPM37093 in 1999

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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

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DBV instability strip Bárbara Castanheira - IUE

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DBV GD 358

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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

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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%!

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C( )O S 300

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Mode identification with HST Chromatic amplitude changes

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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

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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

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PNNV – DOV instalibility strip

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Period (sec) PG

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Frequency ( Hz) All PG

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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)

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

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

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

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Most stable optical clock known

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DAV

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G117-B15A 2004 P=215s

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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.

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

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Axions m ax > 1 eV or ax > 1 tan ratio of the vacuum energy of the two Higgs fields

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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

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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).

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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!

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Photon vs neutrino emission

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The Feynman diagram

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Plasma neutrino (Weak interaction)

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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…

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Effects of Neutrinos on Evolutionary Timescales EC GD 358

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

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

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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

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HST: Galaxies formed 1 Gyr after Big-Bang

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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

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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

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Spectra of DA, DB and DO

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Mode identification with SOAR

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

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

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G117-B15A 2004 P=215s

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

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

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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

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

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

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PMT CCD vs PMT

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Measured Amplitude Difference

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Change in Amplitudes

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Amplitude vs Wavelength

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CCD Data Analysis

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That’s all folks!

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Music?

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