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Solar and stellar chromospheric activity
Katarzyna Mikuła
Astronomical Institute, University of Wrocław
March 28th, 2014
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
1. Observations in Ca II H & K lines2. HK Project3. Stellar chromospheric activity4. Main results5. Summary
Outline
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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?
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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):
MV = 27.59 – 14.94 log W0(K)
Similar relationships were found for other resonance lines, such as Mg II k and Ly α.
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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.
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
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)
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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).
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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.
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
Observations of Ca II H & K
The distribution of activity in 815 southern Sun-like stars (Henry et al. 1996).
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
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
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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).
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 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
Katarzyna Mikuła, Astronomical Institute, University of Wrocław
Solar and stellar chromospheric activity
1st SOLARNET Spring School
March 24th – April 4th, 2014,
Wrocław, Poland
Thank you for your attention!