Other
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23..131r&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 131-132
Other
1
Scientific paper
The magnetohydrodynamic chromospheric phenomena, observed in the Sun and other low mass stars, are linked to the stellar angular momentum evolution, by the interaction of differential rotation with the convective motions. They are strongly correlated with stellar age, as the magnetized wind arising from active regions carries away angular momentum and slows down the stellar rotation. There is evidence that the angular momentum decay with time follows different paths from star to star, not being monotonical. Also, the Sun might be an exceptionally quiet star for its age. In this work we present results of a project to compare age-activity relations as obtained from different chromospheric indicators, for solar type-stars with well determined atmospheric parameters, metallicities and ages. The stellar sample comprises 180 stars with Halpha observations and 60 stars with the Ca II HK and IR triplet observations. We show that for the Ca II H and K lines, a strong age effect is seen in the first 1 Gyr, making this index suitable for discriminating age for very young stars. But its sensitivity levels off abruptly after 2 Gyr, and it shows some scatter, presumably due to cycle modulation and transient events such as flares. For the infrared Ca II triplet a smoother age-activity relation is found, making it more suitable for moderately old stars. For Halpha a well behaved and tight relation is seen, making this index adequate to determine ages for moderately old and very old stars. We also establish a dependence on metallicity, suggesting a more complex scenario for the rotational slow-down than commonly presupposed.
Lyra Wladimir
Porto de Mello Gustavo F.
Rodrigues R. K. G.
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