List of Figures

View Image Figure 1:
Light curve inversion results for the RS CVn star σ Gem (Berdyugina & Henry, in preparation). The first and third columns are maps of the spot filling factor. Darker regions indicate larger values. Observed and calculated V band light curves are shown in the second and fourth columns by crosses and lines, respectively. The images also illustrate a flip-flop event that occurred in 1988: the active region near the phase 0.5 has diminished for about one year, while the region near the phase 0.0 has increased in size (see discussion of the flip-flop phenomenon in Section 6.2).
View Image Figure 2:
Spectral line profiles for a model fast rotating star with no spots (dashed line) and with a spot moving across the disk as the star rotates (solid line). See also animation at External Linkhttp://www.astro.phys.ethz.ch/staff/berdyugina/private/StellarActivity/StellarAct.html
View Image Figure 3:
Observed circular polarisation in the spectrum (panel b) is a sum of opposite polarity Stokes V profiles due to spots located at different Doppler shifts (panel a). From Semel (1989). See also explanatory animations by P. Petit at External Linkhttp://webast.ast.obs-mip.fr/people/petit/zdi.html
View Image Figure 4:
Zeeman–Doppler images of the young active K0 dwarf AB Dor. From Donati and Collier Cameron (1997).
View Image Figure 5:
Calculated (solid line) and observed (dashed line) Stokes V profile for the TiO γ(0,0)R3 band head in a sunspot. The field strength is 3 kG and the filling factor is 0.75 for an angle between the magnetic vector and the line of sight of 0°. Vertical dashes indicate positions of lines included in the spectral synthesis. From Berdyugina (2002).
View Image Figure 6:
Doppler image of the RS CVn type star HD 12545 at the time of its largest amplitude of brightness variations. From Strassmeier (1999).
View Image Figure 7:
Spot temperature contrast with respect to the photospheric temperature in active giants (squares) and dwarfs (circles). Thin lines connect symbols referring to the same star. The thick solid line is a second order polynomial fit to the data excluding EK Dra. Dots in circles indicate solar umbra (ΔT = 1700 K) and penumbra (ΔT =750 K) (based on data in Table 5).
View Image Figure 8:
Magnetic field measurements for active dwarfs (circles) and giants (squares) versus the photosphere temperature. Big circles indicate the sunspot umbra (B = 3 kG) and penumbra (B = 1.5 kG). The thick solid line is a linear fit to the data, excluding the sunspot umbra (based on data in Table 6).
View Image Figure 9:
Magnetic field measurements for active dwarfs (circles) and giants (squares) versus the filling factor. Big circles indicate the sunspot umbra (B = 3 kG) and penumbra (B = 1.5 kG). The thick solid line is a linear fit to the data, excluding the sunspot umbra (based on data in Table 6).
View Image Figure 10:
Filling factors of spots (open symbols) and magnetic fields (filled symbols) on the surfaces of active dwarfs (circles) and giants (squares) versus the photosphere temperature. The thick solid line is a polynomial fit to the spot filling factors. The dashed line is a fit to the magnetic field filling factor, excluding the Sun. A big circle emphasises the sunspot umbra (f ∼ 1%) (based on data in Tables 5 and 6).
View Image Figure 11:
Active longitudes, flip-flops, and sunspot-like cycles on the RS CVn star σ Gem (Berdyugina and Henry, 2005), young solar analogue AB Dor (Järvinen et al., 2005b), and the Sun (Berdyugina and Usoskin, 2003). The three plots upper panels show phases of spot concentrations (filled and open circles denote primary and secondary regions, respectively). The migration paths of active longitudes are emphasised by solid lines. Flip-flops are marked by vertical dashed lines. They occur when the primary region jumps to the opposite active longitude. For the Sun, only half-year average phases are shown and a linear drift of the active longitudes in the Carrington system is subtracted for better visibility. Lower panels in the plots show variations of the stellar brightness and sunspot area. Note that minimum brightness corresponds to maximum spotted area for both σ Gem and AB Dor, in contrast to the Sun (e.g., Amado et al., 2001).
View Image Figure 12:
Two Doppler images of the young active K0 dwarf AB Dor (on the left) and a cross-correlation image (on the right) showing that near-equatorial spots rotate faster than high-latitude regions. From Donati and Collier Cameron (1997). See also animation by J.-F. Donati at External Linkhttp://webast.ast.obs-mip.fr/people/donati/diffrot2.html
View Image Figure 13:
Chromospheric Ca ii emission cycles for Sun-like stars, illustrating the regular cyclic variation that is common in such stars. The Ca ii emission is plotted in Mount Wilson “S-Index” units. From Radick (2000).
View Image Figure 14:
Spot cycles in the solar irradiance and V magnitudes of the RS CVn binary σ Gem and two young solar analogues AB Dor and LQ Hya. Note that the maximum of the spot area corresponds to the maximum irradiance on the Sun and minimum brightness on the stars.
View Image Figure 15:
Doppler images of the RS CVn star II Peg in the pole-on projection illustrating a flip-flop that occurred between the end of 1997 and mid of 1998. From Berdyugina et al. (1999a).