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Simultaneous Photometry and Echelle-Spectroscopy of BZ UMa During the 2005 January Outburst

This study presents the simultaneous photometric and echelle-spectroscopic observations of the dwarf nova BZ UMa during its January 2005 outburst. The analysis includes the light curves, line profiles, and Doppler tomography, revealing very strong Balmer emission lines. We observe different stages of the outburst, concluding it to be of the inside-out type based on spectral changes. The results challenge the current Disc Instability Model due to the unusual light curve experienced during the outburst.

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Simultaneous Photometry and Echelle-Spectroscopy of BZ UMa During the 2005 January Outburst

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  1. The dwarf nova BZ UMa Simultaneous photometry and echelle-spectroscopy during the 2005 January Outburst MNRAS, 2006, Coming Soon Vitaly Neustroev (NUI Galway), S.Zharikov and R.Michel

  2. BZ UMa • Period: 97.8 min • Outburst cycle: > 300d • Min: V≈16-17 (17.8) • Max: V≈10.5-11.5 • Very strong Balmer emission lines

  3. Spectrum

  4. Doppler Tomography • April, 2004. Quiescence: Hα

  5. Observations • OAN SPM (Mexico) • Photometry: 2005 Jan 12-13 and 15-17 • Echelle-spectroscopy: 2005 Jan 15-17

  6. Light Curve

  7. Light Curve

  8. Light Curve

  9. Light Curve

  10. Colours

  11. Line profiles

  12. FWHM, Fluxes and EW of Hα

  13. Doppler Tomography • April, 2004. Quiescence: Hα

  14. Doppler Tomography • Jan 15, 2005. Preoutburst: Hα

  15. Doppler Tomography • Jan 16, 2005. Outburst, 1st stage: Hα

  16. Doppler Tomography • Jan 16, 2005. Outburst, 3rd stage: Hα

  17. Doppler Tomography • Jan 17, 2005. Outburst, Decline: Hα

  18. Doppler Tomography • Jan 17, 2005. Outburst, Decline: Hβ

  19. Doppler Tomography • Jan 17, 2005. Outburst, Decline: He I 5876

  20. Inside-Out or Outside-In outburst? • The only way to be sure of the outburst type is from eclipse profile observations during outbursts and BZ UMa is not an eclipsed system. • A very low mass-transfer rate for BZ UMa (≤1015 g/s) implies that theoretically, its outbursts should be of an inside-out type.

  21. Line profiles

  22. Line profiles

  23. Line profiles

  24. Summary • We reported simultaneous photometric and echelle-spectroscopic observations of the dwarf nova BZ UMa during which we were lucky to catch the system at the onset of an outburst. • Using Doppler tomography we found that the unusual emission distribution detected in quiescence held during the outburst. • On the base of the spectral changes during the rising stage we conclude that the 2005 January outburst of BZ UMa was of the inside-out type. • Nevertheless, a highly asymmetrical light curve with a “jump” shows that this outburst cannot easily be fit into the framework of the current Disc Instability Model.

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