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Department of Astronomy Beijing Normal University

Frequency analysis of RR Lyrae stars in the LMC. Bingqiu Chen & Biwei Jiang Beijing Normal University 2010.4. Department of Astronomy Beijing Normal University. Overview. Introduction The data & the method of analysis Variable classification Conclusion Discussion. RR Lyrae stars:

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Department of Astronomy Beijing Normal University

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  1. Frequency analysis of RR Lyrae stars in the LMC Bingqiu Chen & Biwei Jiang Beijing Normal University 2010.4 Department of Astronomy Beijing Normal University

  2. Overview • Introduction • The data & the method of analysis • Variable classification • Conclusion • Discussion

  3. RR Lyrae stars: Period : 0.1 to 1 day Amplitude in V : up to 1.5 magnitudes Spectral type : A5 to F5 Absolute visual magnitude : about +0.5 Mass : about half a solar mass Low metal abundance Z : 0.00001 ~ 0.01 Evolutionary stage: Away from the main sequence & burning Helium in their core. Useful tracer of galactic evolution. Obey a period-luminosity-color relation & used as distanceindicators.( Like the Cepheids) Types : RRab stars, RRc stars , RRd stars, RRe stars RR Lyrae Star

  4. A long-term modulation of the amplitude, shape, and phase of the light and radial velocity curve. Blazhko effect period : 11 to 533 days Occurs in 1/3 RRab stars, & a few RRc stars .(The incidence is lower in LMC). A century of study: Nonradial modes triggered by resonance effects Magnetic field e.g. : Dziembowski and Mizerski (2004). The Blazhko effect

  5. 24906 light curves from the OGLE-III (Soszynski et al. 2009) Exclude I <18m & Observed dots’ number <1000 671 stars Data

  6. Frequency analysis based on a PDM method : f0 In the [1 5] 1/d band Fit the light curve with five harmonics of f0: Frequency analysis with the residual: f1 In the [0.5 5.5] 1/d band Fit the residual with f1 …f2…f3…f4 Visual inspection of lightcurves to check Method

  7. RR-S • Singly-periodic RR Lyrae : • 495 stars 73.7% • RR0: (fundamental mode): 369~74.5% • RR1: (1st overtone mode) : 124~25.1% • RR2: (2nd overtone mode) : 2~0.4%

  8. PDM & fitting

  9. Period distribution

  10. Period–amplitude diagram

  11. RR-01 • Double modes RR Lyrae : 12 ~1.8% • There main pulsation modes are all 1st overtone (RR1-01)

  12. Phased lightcurves

  13. A1 to A0 ratios Wide range A0,only 1 exceeds A1

  14. Petersen diagram

  15. RR-BL1 • RR Lyrae with 1 close frequency component: • Number : 84 stars 12.5% • RR1-BL1: 18 ~ 21.4% • RR0-BL1: 66 ~ 78.6%

  16. Phased lightcurves

  17. Frequency difference: RR0: f1>f0  48 stars 72.7% RR1: f1>f0  3 stars 16.7% RR-BL1

  18. RR-BL2 • RR Lyrae with 2 close symmetric frequencycomponents: 28 4.2% • RR1-BL2 : 12~42.8% • RR0-BL2 : 16~57.2%

  19. Phased lightcurves

  20. Relation of Δf & f0

  21. RR-BL3+ • RR Lyrae with several close components :29 4.2% • RR1-BL3+ : 14~48.3% • RR0-BL3+ : 15~51.7%

  22. RR-BL3+

  23. Relation of Δf & f0

  24. RR-D & RR-unknown 6 RR-D & 17 unknown type double period RR Lyrae stars

  25. Conclusion

  26. Discussion • Blazhko effect occurs more frequently in RR0 than RR1. • The Blazhko period is short in RR1, while sometimes long in RR0 than in RR1. • With the number of oscillating components, the numbers of the RR0-BLn and RR1-BLn stars have a trend to be the same, sothe Blazhko effect depends on the mode of pulsation and thenumber of oscillating components. • For the RR-BL1,RR-BL2, & RR-BL3+, it seems the Blazhko can lead the period to split for any number (1-4) of components, so nonradial mode of oscillation seems better explain for Blazhko effect.

  27. Thank You!

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