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The discovery path of the inverse square root of age relations for �solar-type stars

Andrew Skumanich�High Altitude Observatory

National Center for Atmospheric Research

50Years of the Skumanich Relations Conference� March 8, 2022

High Altitude Observatory (HAO) – National Center for Atmospheric Research (NCAR)

The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research

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1953 Vyssotsky & Skumanich - dG stars spectrally differentiated, A (G-band) & B (none)

dG A have small residual dispersions (17 km/s) : YOUNG, HK emission?

dG B contains the Sun, have larger dispersions (24 km/s): OLD, like SUN

1953 Delhaye - dMe stars: small residual motion compared to dM: 🡪 dMe young

"ces étoiles formeraient donc un sous-système très plat et pourraient être très jeunes."

["These stars form a small scale-height galactic plane system & might be very young."]

1957 Vyssotsky & Dyer – Confirms Delhaye : dMe (11 km/s) & dM (30 km/s) 🡪 dMe young

1963 Wilson – Younger Open Clusters have stronger HK emission: Age vs. Cluster difference?

1964 Skumanich – A = dGe (18 km/s), B = dG (29 km/s) 🡪 dGe young

1964 Wilson & Skumanich – HKe field stars are near Zero Age line 🡪 d*e stars young

1966 Wilson – High rotation states decrease with onset of HK emission along Main Sequence

1967 Kraft - Clusters dGe & Field dGe stars show that Rotation declines with Age

1968 Wilson - Photometer flux measurements of HK lines

1972 Skumanich - Square Root Relations

Ca II Emission, Kinematics, Clusters, Rotation & Age

Solar DISK Ca II K

Main Sequence

The temporal history of stellar properties may be �measured by various types of ‘clocks’

1) Stellar nuclear reaction rate:

Gives rise to the luminosity or power radiated and the surface temperature or color
The Hertzsprung –Russell diagram relates luminosity with color
As the reaction rate begins to deplete the nuclear fuel the star begins to migrate across the diagram

2) Stellar kinematics:

Turbulence within interstellar clouds decays with time 🡪 early epoch stars will have larger internal velocities than later stars
After formation, star collisions with high velocity clouds further increase their velocity 🡪 higher velocities indicate older ages

3) Magnetic energy:

4) ‘Metallic’ (Carbon, Calcium, etc.) content:

Hertzsprung-Russell Diagram for Field Stars – �Mount Wilson (1935)

HR Diagram Open Clusters – �Vatican Conference �(Sandage 1958)