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How to determine the age of young stars
Contents
• Lithium Depletion Boundary
• Astro-Seismology
• Gyrochronology
• Further methods
Lithium Depletion Boundary
Lithium Depletion Boundary
• Pre main sequence stars (PMS)
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Contracting gas cloud
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes
• Hydrogen at ~ 10 million K
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes
• Hydrogen at ~ 10 million K • Deuterium at ~ 1 million K • Lithium at ~ 3 million K
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes
• Hydrogen at ~ 10 million K • Deuterium at ~ 1 million K • Lithium at ~ 3 million K
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes • Lithium burning
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes • Lithium burning
• Extremely temperature dependent (~ T20)
Lithium Depletion Boundary
• Pre main sequence stars (PMS) • Fusion processes • Lithium burning
• Extremely temperature dependent (~ T20) • More massive stars → reach fusion temperature faster
→ Li is rapidly consumed
Lithium Depletion Boundary
• Low-mass stars • Energy transport primarily through convection
Lithium Depletion Boundary
• Low-mass stars • Energy transport primarily through convection
→ Star is thoroughly mixed and chemically uniform
Lithium Depletion Boundary
How to apply?
Lithium Depletion Boundary
How to apply: 1. Cluster of stars (same age)
2. Determine Li-abundance
3. Plot stars in colour-magnitude-diagram
4. Look for boundary
Lithium Depletion Boundary
1. Cluster of stars (same age)
2. Determine Li-abundance
3. Plot stars in colour-magnitude-diagram
4. Look for boundary
Lithium Depletion Boundary
• Applies for: • Young star (clusters) ~ 100 Myr • Low-mass < 0.4 M
• Accuracy ~ 3-10%
Astero-Seismology
• PMS with mass ~ 1-6 M
Astero-Seismology
• PMS with mass ~ 1-6 M
• Properties of atmosphere • Temperature • Luminosity → Similar to older stars
Astero-Seismology
• PMS with mass ~ 1-6 M
• Properties of atmosphere • Temperature • Luminosity → Similar to older stars
Astero-Seismology
• PMS with mass ~ 1-6 M
• Properties of atmosphere • Temperature • Luminosity
• Difference between young & older stars → Inner structure
Astero-Seismology
• Seismic waves tell about interior
Astero-Seismology
• Seismic waves tell about interior • Velocity & deflection are functions of density, opacity,…
Astero-Seismology
• Seismic waves tell about interior • Velocity & deflection are functions of density, opacity,…
• Frequency as a function of age
Gyrochronology
• empirical method for low mass stars
• ejection and capture of charged particles in the magnetic field
• deceleration • → d(t,M)
http://www.cfht.hawaii.edu/en/news/V830/
Gyrochronology
• empirical method for low mass stars
• ejection and capture of charged particles in the magnetic field
• deceleration • → d(t,M)
http://www.cfht.hawaii.edu/en/news/V830/
https://de.wikipedia.org/wiki/NGC_6819
Gyrochronology
http://www.nature.com/nature/journal/v517/n7536/full/nature14118.html
Gyrochronology
http://www.nature.com/nature/journal/v517/n7536/full/nature14118.html
Further methods
• Nebular emission lines
→ ionization of surrounding gas• UV stellar wind lines • IR features from giants & supergiants • many more…
Further methods
• Nebular emission lines → ionization of surrounding gas • UV stellar wind lines • IR features from giants & supergiants • many more…
Questions?
