1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland

Solar and stellar chromospheric activity

Katarzyna Mikuła Astronomical Institute, University of Wrocław March 28 th , 2014

Outline

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

Solar and stellar chromospheric activity

Chromosphere and activity

What is the chromosphere?

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) 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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.

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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.

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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) 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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).

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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. 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

Observations of Ca II H & K

The distribution of activity in 815 southern Sun-like stars (Henry et al. 1996).

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

Grand minima

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland The Maunder Minimum: 1645 – 1715.

Baliunas & Jastrow (1990) - study of magnetic activity for 70 solar-type stars.

Two different populations : I.

II.

S S MWO MWO ~ 0.17

~ 0.15

S MWO for the Sun : ~0.17 – 0.18 - active Sun ~0.14 - zero magnetic activity Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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).

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

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 1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity

Thank you for your attention!

1 st SOLARNET Spring School March 24 th – April 4 th , 2014, Wrocław, Poland Katarzyna Mikuła, Astronomical Institute, University of Wrocław

Solar and stellar chromospheric activity