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CZ Lacertae A Blazhko RR Lyrae star with multiperiodic modulation

CZ Lacertae A Blazhko RR Lyrae star with multiperiodic modulation. Ádám SÓDOR Konkoly Observatory of the Hungarian Academy of Sciences 200 8 .0 9 . 09 . , Wien, Österreich JENAM 2008, Symposium 4 Asteroseismology and Stellar Evolution. Multiperiodic modulation. Telescope.

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CZ Lacertae A Blazhko RR Lyrae star with multiperiodic modulation

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  1. CZ Lacertae A Blazhko RR Lyrae star with multiperiodic modulation • Ádám SÓDOR • KonkolyObservatory • of the Hungarian • Academyof Sciences • 2008.09.09., Wien, Österreich • JENAM 2008, Symposium 4 • Asteroseismology • and Stellar Evolution

  2. Multiperiodic modulation Telescope Multiperiodic modulation was suggested by earlier observations, e.g. by the MACHO and OGLE surveys. Several such stars were extensively observed first by our RR Lyrae survey project. An example is our ongoing observation of V759 Cyg:

  3. The data of CZ Lacertae Telescope • Previous observations • Konkoly pe. observations (7 nights) • Bookmeyer (29 V data points) • Hipparcos epoch photometry • Our observations • 24” automatic telescope, CCD • 2 seasons: Sep 2004. – Dec 2005. • 4 bands: BV(RI)C • 7000 – 8000 data points / band • Reduction • IRAF • ISIS Image Subtraction Method (Alard 2000, A&AS, 144, 235) Hipparcos epoch photometry on CZ Lac

  4. Light curve – season 1 Telescope V light curve of season 1 folded with P0 = 0.4322 d

  5. Light curve – season 1 Telescope V light curve of season 1 shows a complex amplitude variation

  6. Fourier spectrum – season 1 Telescope Dirty spectrum Clean spectrum clean algorithm: Roberts et al. (1987, AJ, 93, 968)

  7. Fourier spectrum – season 1 Telescope Vicinity of k·f0 peaks in the clean Fourier spectrum f0 = 2.31388 c/d The two pairs of modulation peaks are similarly strong. 1f0 2f0 3f0 4f0 -fm2 -fm1 +fm1 +fm2 amplitude [mag] frequency [c/d]

  8. Light curve solution – season 1 Telescope Fit to the V light curve with 3 base frequencies f 0 = 2.31388, fm1 = 0.054 c/d, fm2 = 0.067 c/d using 72 linear combination harmonic components reducedr.m.s. = 15 mmag fm1 / fm2 = 0.80085 ± 0.00007 ≈ 4:5 1f0 2f0 3f0 4f0 amplitude [V mag] -fm2+fm1 +fm2-fm1 -fm2/2 +fm1+fm2 +fm2/2 frequency [c/d]

  9. Light curve – seasons 1 & 2 Telescope V light curves of seasons 1 & 2 folded with P0 = 0.4322 d season 1 season 2

  10. Light curve – season 2 Telescope V light curve of season 2 also shows a complex amplitude variation

  11. Fourier spectrum – season 2 Telescope Vicinity of k·f0 peaks in the clean Fourier spectrum f0 = 2.31388 c/d 1f0 2f0 3f0 4f0 amplitude [mag] -fm2 -fm1 +fm2 +fm1 frequency [c/d]

  12. Light curve solution – season 2 Telescope Fit of the V light curve with 3 base frequencies f 0 = 2.31388, fm1 = 0.053 c/d, fm2 = 0.070 c/d using 69 linear combination harmonic components reducedr.m.s. = 12 mmag fm1 / fm2 = 0.762 ± 0.001 ≈ 3:4 1f0 2f0 3f0 4f0 amplitude [V mag] frequency [c/d]

  13. Changes between the seasons Telescope Comparison of V light curve solutions Modulation frequencies and amplitudes changed 3f0 season 1 season 2

  14. Changes between the seasons Telescope Changes in the pulsation and modulation frequencies Relative change of the pulsation frequency (f0 2 – f0 1)/f0 1 = (7 ± 2)·10-6 Relative change of the modulation frequencies (fm1 2 – fm1 1)/fm1 1 = –0.0181 ± 0.0003 (fm22 – fm2 1)/fm2 1 = +0.0328 ± 0.0011

  15. Changes between the seasons Telescope Comparison of V light curve solutions The modulation component amplitudes at different pulsation harmonic orders season 1 season 2

  16. Changes between the seasons Telescope Mean V light curves of season 1 and season 2 The mean pulsation amplitude decreased 0.03 mag with the decreasing modulation amplitudes season 1 season 2

  17. Summary & conclusion Telescope • Summary • CZ Lac is the first extensively observed Blazhko star with double periodic modulation. • The frequency ratio of the two modulations changed from 4:5 to about 3:4. • The modulation properties changed rapidly between the two seasons. • Conclusion • Multiperiodic modulation seems to be more unstable than the monoperiodic ones. • Multiperiodic modulation renders earlier Blazhko models that bind the modulation frequency to the rotation of the star invalid. • There is not yet any model that explains the multiperiodic modulation. • The multiperiodicity is one more property of Blazhko stars • that should be explained by any forthcoming model.

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