Hydrogen Burning and Pulsations on Low Mass
Helium Core White Dwarfs
Justin D. R. Steinfadt
Lars Bildsten
UCSB
Wild Stars in the Wild West II
14th North American Workshop on
Cataclysmic Variables and Related Objects
March 16, 2009
Creating He-Core White Dwarfs
C/O WDs Truncation of the
AGB Helium WDs
Truncation of the RGB
(Girardi et al. 2000)
Channel must prevent the core mass from growing beyond 0.45-0.48 M
Binary interaction via common envelope
Rapid mass loss via stellar winds induced by high metallicity
Two Possible Channels
Direct Evidence: ZZ Cetis
(courtesy Phil Arras)
Thorough mode period analysis of pulsation spectrum is sensitive to: Total Mass Envelope Mass Core Composition
He-core ZZ Cetis
Low Mass WDs PSR J0218+4232, PSR
J1019+5307, PSR J1911-5958A SDSS
J0022+00, J0022-10, J0822+27, J0849+04, J1053+52, J1056+65, J1234-02, J1426+01, J1436+50, J1630+42, J2252-00, J2345-01
LP 400-22
(Steinfadt et al. 2008)
A Dichotomy in Evolution
(Panei et al. 2007)
(Panei et al. 2007)
0.18 M represents a boundary between two very different classes of models
Highly dependent upon metallicity
Seen in the recent time-dependent evolution codes
Panei et al. 2001, 2007 Serenelli et al. 2002 Driebe et al. 1998
A Dichotomy in Timescales
Building a Hydrostatic Model
He Core No energy generation Isothermal Pure Helium composition
Envelope Nuclear Energy Generation
PP - Chain Pure Hydrogen composition
Radiative and convective heat transportC
ore
Env
elop
eIn
terf
ace
MWD
MENV
Grey Atmosphere
Key Physics MESA - Bill Paxton - http://mesa.sourceforge.net
EOS, Opacity, numerical algorithms, … Diffusive equilibrium chemical profile
Two component plasma of Hydrogen, Helium and electrons
pp Burning Slows Cooling
0 Gyr
5 Gyr
12 Gyr
0 Gyr
5 Gyr
12 Gyr
pp Burning Slows Cooling
0 Gyr
0 Gyr2 Gyr
12 Gyr
2 Gyr
12 Gyr
Pulsation Probes H Shell
c2kh2
N2
p-modes
g-modes
(courtesy Phil Arras)
Non-adiabatic driving will determine where the ZZ Ceti Strip resides (ala Brickhill)
Epsilon mechanism may be possible with the pp burning shell
Period spacing would constrain the WD envelope mass.
Implications of a He-core WD Pulsator
New extension to the ZZ Ceti instability strip New insights into the driving mechanisms Constraints on He-core models through
seismic modeling Is there really a thick Hydrogen envelope? Do low mass He-core WDs have nuclear
burning envelopes?
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