on the excitation mechanism of solar 5-min & solar-like oscillations of stars licai deng (naoc)...
Post on 29-Dec-2015
215 Views
Preview:
TRANSCRIPT
On the excitation mechanism ofSolar 5-min &
solar-like oscillations of stars
Licai Deng (NAOC)Darun Xiong (PMO)
contents
• Background• Our theoretical approach• The numerical models• Solar 5-min, solar-like and Mira-like
oscillations• Main results and conclusions
Background
• The most popular theory: Turbulent stochastic excitation (TSE) mechanismGoldreich & Keeley 1977a,bSamadi et al. 2003Belkacem et al. 2008 …
• However, we think it is still not settled because convective zone can damp out solar oscillationsTheoretically: Balmform 1992a,bObservationally: finite spectral lines of Solar oscillations (Libbrecht 1988)
Observational facts
• δ Scuti star strip (the red edge)• Solar and solar-like oscillations;• Mira-type and pulsating red variables located at
the upper part of RGB and AGB(a series of early work by Eggen; Wood 2000, Soszynski et al. 2004 a,b)
• The lower part and the red-side of HRD: convection!
OGLE: OSARGs & Mira Soszynski et al. 2004
MACHO: Pulsating AGBsWood 2000
Eggen 1977
Our results on Solar oscillations
• For stars with extended convective zone such the Sun, convection work not as damping only; it can be excitation in some cases;
• For the Sun and solar-like less luminous stars, the coupling between convection and oscillations (CCO) effectively damps F-modes and lower order P-modes, while excites intermediate- and high-order P-modes
Cont.• As luminosity increases (along RGB), the most
unstable mode shifts to lower orders;• Our theory provides a consistent solution to:
1). The red edge of Cepheid instability strip;2). Solar 5-min and solar-like oscillations;3). Mira and Mira-like stars (Mira instability strip);
• We think there is no distinct natures in Mira-like and Solar-like oscillations:
CCO Mira-like CCO+TSE Solar-like
The theoretical scheme
• Convection: Nonlocal- and time-dependent convection theory (Xiong 1989, Xiong Cheng & Deng 1997)
• Oscillations: Xiong & Deng 2007
Numerical results
• Solar 5-min oscillations;• Evolutionary models of stars with non-local
convection;• Linear non-adiabatic oscillations:
o A series of model with Z=0.020, M=0.6-3.0M;o Linear non-adiabatic modes: radial P0-P39; non-
radial l=1-4, P0-P39 and for the Sun l=1-25, G4-P39 are calculated;
For Solar 5-min oscillations
• Modes with 3 ≤ Period ≤ 16 min are all unstable; all others outside this range:P < 3 min (P-modes) &P > 16 min P-, F- and G- (not incl. l = 1-5 P1-) modes are stable;
• The amplitude growth rate depends only on oscillation frequency, depend on l;
• These predictions match observations very well.
Instability strips• δ Scuti instability strip• The red-edge of Cepheid instability strip
(RR Lyr: Xiong, Cheng & Deng 1998; δ Scuti : Xiong & Deng
2001) • Mira instability strip
(LPV: Xiong, Deng & Cheng 1998; Xiong & Deng 2007)
• Solar-like oscillations in solar-like stars and low-luminosity red giants(Radial: Xiong, Cheng & Deng 2000, Non-radial: Xiong & Deng 2010)
Stability analysis for P0-P5 Stability analysis for P16-P25
Solid symbols: stable modes (η<0);Open symbols: unstable modes (η>0)
Calculations are made formodels selected along thetrack of a 1 solar mass star
Amplitude Growth Rate (AGR)η=-2πωi/ωr
ω=ωr+iωi
The width of instability in Nr as a function of stellar luminosity
AGR as a function of luminosity for the most unstable modes[radial (red) and non-radial (blue, l =1)] in the models
Conclusion and discussions
• Both CCO and TSE play important roles in stellar oscillations;
• CCO is dominant for Mira type oscillations ;• Solar-like oscillations are caused by CCO & TSE
(TSE may dominate);• There is no distinct difference in solar- and
Mira-like oscillations:(L unstable mode shift to lower order modes).
Thank you !
top related