1. Solar and stellar chromospheric activity Katarzyna Mikuła Astronomical Institute, University of Wrocław March 28 th, 2014 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland

2. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland 1.Observations in Ca II H & K lines 2.HK Project 3.Stellar chromospheric activity 4.Main results 5.Summary Outline

3. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Chromosphere and activity Indicators of chromospheric activity: UV lines: Ly α, O I (1304 Å), C I (1557 Å, 1561 Å), Si II (1808 Å, 1817 Å), Mg II h & k (2796 Å, 2803 Å) VIS lines: Ca II H & K (3968 Å, 3934 Å) What is the chromosphere?

4. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Observations in Ca II H & K Eberhard & Schwarzschild (1913) – discovered emission in Ca II H & K lines in Arcturus and other stars spectra Wilson (1963) and Wilson & Skumanich (1964) – from observations (Mount Wilson Observatory) they discovered that chromospheric activity of main-sequence stars decreases with age Result of the observations was confirmed by Skumanich (1972): t -1/2

5. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Long-term observations in Ca II H & K Linear relation between the absolute magnitude and the logarithm of the K line emission widths (Wilson - Bappu effect): M V = 27.59 – 14.94 log W 0 (K) Similar relationships were found for other resonance lines, such as Mg II k and Ly α.

6. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland HK Project Systematic program of Ca II H & K observations of main-sequnece stars. First phase: 1966 – 1977 Does the chromospheric activity of main-sequence stars vary with time, and if so, how? ~Olin Wilson Wilson, O., 1978, Chromospheric Variations in Main-sequence Stars.

7. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland HK Project HK Project continued under the direction of S. Baliunas (1977 – 2003) Mount Wilson Observatory S index: S MWO = α [(H+K)/(R+V)] Another observations: O. Wilson – observed the Moon as a solar proxy National Solar Observatory (1974) Sacramento Peak (1976)

8. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Observations of Ca II H & K From HK Project observations (to 1991): 60 % of stars exhibited periodic, cyclic variations 25 % - irregular or periodic variability 15 % - flat activity Examples of HK Project observations (Hall et al. 2007b).

9. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland HD 114710 MWO series can be used: Identify rotation periods Diferrential rotation via drifts Donahue & Baliunas (1992) – reported detection of a drift in the apparent rotation period in β Com = HD 114710. Solar cycle : 1. activity is low, ARs appear at high latitudes 2. the mean latitude of ARs moves toward the equator (shortest rotation period). HD 114710 cycle : rotation period increase from cycle maximum through cycle minimum.

10. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Observations of Ca II H & K The distribution of activity in 815 southern Sun-like stars (Henry et al. 1996).

11. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Grand minima The Maunder Minimum: 1645 – 1715. Baliunas & Jastrow (1990) - study of magnetic activity for 70 solar-type stars. Two different populations: I.S MWO ~ 0.17 II.S MWO ~ 0.15 S MWO for the Sun: ~0.17 – 0.18 - active Sun ~0.14 - zero magnetic activity

12. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Grand minima HK flux variations for two stars (HD 10476 and HD 3651) with similar mass and rotation. Left: HD14538 appears to have made a transition from a at activity state to short cycle in 2000 (Hall et al. 2007b). Right: HD 3651 shows evidence of having entered a at activity state around 1980 (Baliunas et al. 1995).

13. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Summary Long-term observations of stellar chromospheric activity – over 60 years of observations in Ca II H & K lines The most of stars reveal activity cycles similar to solar activity cycle The samples of stars are not large – we cannot understand chromospheric activity to the end Studying of solar/stellar dynamo

14. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Bibliography 1.Hall, J.C., 2008, Living Reviews in Solar Physics, 5, 2 2.Wilson, P., 1994, Solar and Stellar Activity Cycles, CAS 3.Fares, R., 2013, IAU Symp. 302 4.Fletcher, L., 2012, ASP Conference Series, 448, 1 5.Bruevich, E.A. & Rozgacheva, I.K., 2012 eprint arXiv:1204.5705 6.Wilson, O., 1978, ApJ, 226, 379 7.Donahue, R.A. & Baliunas, S., 1992, ApJ, 393, 63 8.Baliunas S. et al., 1995, ApJ, 438, 269

15. Katarzyna Mikuła, Astronomical Institute, University of Wrocław Solar and stellar chromospheric activity 1 st SOLARNET Spring School March 24 th – April 4 th, 2014, Wrocław, Poland Thank you for your attention!