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Resolving Starspots

This study explores the use of photometry, Doppler imaging, and interferometry to resolve starspots on active stars. It discusses the methods used, presents results from previous studies, and outlines future plans for research.

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Resolving Starspots

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  1. Resolving Starspots Heidi Korhonen Fellow in Garching since Sep. 2007

  2. SST

  3. Starspots from photometry Long-term V band photometry of FK Com (Korhonen et al. 2001a) Phased light-curves for 1990-1993 and results from the light-curve inversions (Korhonen et al. 2002)

  4. Spot longitudes Korhonen et al. 2009 to be submitted

  5. Starspots with high resolution, Doppler imaging • In Doppler imaging the distortions appearing in the observed line profile due to the presence of spots and moving due to the stellar rotation • Ill-posed inversion problem • Many methods for solving: aximum Entropy Method (e.g., Vogt et al 1987 ), Tikhonov Regularization (e.g., Piskunov et al 1990), Occamian Approach (Berdyugina 1998), Principal Components Analysis (Savanov & Strassmeier 2005) From Svetlana Berdyugina

  6. Doppler imaging results: EK Dra “the young Sun” Järvinen et al 2007

  7. Starspots from photometry Korhonen et al. 2002

  8. More than decade of starspots Korhonen et al. 2007

  9. Active longitudes on FK Com from photometryand Doppler imaging Korhonen et al. 2007

  10. Mean longitudinal magnetic field Korhonen et al. 2009

  11. Simultaneous Doppler image • Three main active regions on the surface: • Phase 0.00-0.15 at an average latitude of 58º, ΔT=1500 K • Phase 0.20-0.35 at an average latitude of 61º, ΔT=900 K • Phase 0.25-0.30 at the equator, ΔT=900 K Korhonen et al. 2009

  12. <Bz> vs. spots • V and I band photometry from the Vienna automatic photometric telescope in Arizona (squares and crosses) • The light curve calculated from the Doppler image (solid line) • <Bz> from FORS1 (lowest panel) • Unfortunately no evidence for the polarity of the second active longitude Korhonen et al. 2009

  13. Starspots with interferometry • Another method for studying starspots is to use optical interferomtery • Unfortunately most active stars are apparently small, and spots naturally even much smaller • Possibly indirect methods like determining the photocentre using a molecular line and continuum can be used (on going study using VLTI & AMBER)

  14. Conclusions • Spots on active stars often occur much closer to the pole than the sunspots do • Spots are also seen on rotational poles, something that is not easily explained by theory • Many active stars show preferred longitudes for the activity • So far no conclusive measurement of spot polarities at the different active longitudes in stars showing flip-flops exists

  15. Future plans • Investigate the magnetic field configuration of active longitudes with higher spectral resolution, Narval observations in April 2009 unfortunately hampered by bad weather • Reduce and analyse the interferometry data (AMBER) for studying starspots , and compare the result to contemporaneous Doppler image (some data from late 2008 and more to come mid 2009)

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