Solar and stellar chromospheric activity

Solar and stellar chromospheric activity

Katarzyna MikułaAstronomical Institute, University of Wrocław

March 28th, 2014

1st SOLARNET Spring SchoolMarch 24th – April 4th, 2014,

Wrocław, Poland

Katarzyna Mikuła, Astronomical Institute, University of Wrocław



Wrocław, Poland

1. Observations in Ca II H & K lines2. HK Project3. Stellar chromospheric activity4. Main results5. Summary

Outline




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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?




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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




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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):

MV = 27.59 – 14.94 log W0(K)

Similar relationships were found for other resonance lines, such as Mg II k and Ly α.




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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.




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HK Project

HK Project continued under the direction of S. Baliunas (1977 – 2003)

Mount Wilson Observatory S index:

SMWO = α[(H+K)/(R+V)]

Another observations: O. Wilson – observed the Moon as a solar proxy National Solar Observatory (1974) Sacramento Peak (1976)




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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 activityExamples of HK Project observations (Hall et al. 2007b).




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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.




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Observations of Ca II H & K

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




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Grand minima

The Maunder Minimum: 1645 – 1715.

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

Two different populations:I. SMWO ~ 0.17II. SMWO ~ 0.15

SMWO for the Sun: ~0.17 – 0.18 - active Sun ~0.14 - zero magnetic activity




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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).




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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




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Bibliography

1. Hall, J.C., 2008, Living Reviews in Solar Physics, 5, 22. Wilson, P., 1994, Solar and Stellar Activity Cycles, CAS3. Fares, R., 2013, IAU Symp. 3024. Fletcher , L., 2012, ASP Conference Series, 448, 15. Bruevich, E.A. & Rozgacheva, I.K., 2012 eprint arXiv:1204.57056. Wilson, O., 1978, ApJ, 226, 3797. Donahue, R.A. & Baliunas, S., 1992, ApJ, 393, 638. Baliunas S. et al., 1995, ApJ, 438, 269




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Thank you for your attention!

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Solar and stellar chromospheric activity