1 / 18

On the excitation mechanism of Solar 5- min & solar-like oscillations of stars

On the excitation mechanism of Solar 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.

siusan
Download Presentation

On the excitation mechanism of Solar 5- min & solar-like oscillations of stars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. On the excitation mechanism ofSolar 5-min &solar-like oscillations of stars Licai Deng (NAOC) Darun Xiong (PMO)

  2. contents • Background • Our theoretical approach • The numerical models • Solar 5-min, solar-like and Mira-like oscillations • Main results and conclusions

  3. 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)

  4. 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!

  5. Eggen 1977 MACHO: Pulsating AGBs Wood 2000 OGLE: OSARGs & Mira Soszynski et al. 2004

  6. 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

  7. 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

  8. The theoretical scheme • Convection: Nonlocal- and time-dependent convection theory (Xiong 1989, Xiong Cheng & Deng 1997) • Oscillations: Xiong & Deng 2007

  9. Numerical results • Solar 5-min oscillations; • Evolutionary models of stars with non-local convection; • Linear non-adiabatic oscillations: • A series of model with Z=0.020, M=0.6-3.0M; • 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;

  10. 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.

  11. 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)

  12. Stability analysis for P0-P5 Stability analysis for P16-P25

  13. Calculations are made formodels selected along thetrack of a 1 solar mass star Amplitude Growth Rate (AGR)η=-2πωi/ωrω=ωr+iωi Solid symbols: stable modes (η<0); Open symbols: unstable modes (η>0)

  14. The width of instability in Nr as a function of stellar luminosity

  15. AGR as a function of luminosity for the most unstable modes[radial (red) and non-radial (blue, l =1)] in the models

  16. 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).

  17. Thank you !

More Related