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The evolution of rotation and activity in young open clusters : the zero-age main sequence

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Title:The evolution of rotation and activity in young open clusters : the zero-age main sequence
Authors:Patten, Brian Michael
Keywords:Cool stars -- Luminosity function
Cool stars -- Rotation
Date Issued:1995
Abstract:I have undertaken a program of ground- and space-based observations to measure photometric rotation periods and X-ray luminosities for late-type stars in the young open clusters IC 2391 and IC 2602. With cluster ages of ~30 Myr, IC 2391 and IC 2602 are ideal sites in which to observe conditions at the ZAMS since the solar-type stars in these clusters have not been on the main sequence long enough to undergo significant magnetic braking. The ROBAT survey of IC 2391 revealed 80 X-ray sources, 44 of which were found to be associated with stars which are now classified as new cluster members. Among the solar-type stars in both IC 2391 and IC 2602, I find a factor of ~25 spread in the distribution of rotation periods, which range from 0.21 to 4.86 day. I also find a factor of ~10-20 spread in the range of Lx about a median Lx value of ~10^30 erg S^-1 for both clusters. These results show conclusively that stars arrive on the ZAMS with a wide range of rotation rates and coronal activity levels. When compared to data from older clusters, such as the Pleiades and the Hyades, there is an overall decline observed in both the rotation rates and median X-ray luminosity of cluster members with increasing age, however, while the spread in the range of rotation rates decreases to a small value, the spread in the range of Lx values as a fraction of the median is observed to increase with age. This behavior is best explained through a dependence of Lx on Prot which is weak in the young clusters and strong in the older clusters. The Rossby diagram shows there is a tight correlation between Lx/ Lbol and the Rossby number, Prot divided by the convective turnover time. Young, rapidly rotating, main sequence stars lie along a plateau of magnetic saturation, where Lx has a weak dependence on rotation period, while older, more slowly rotating stars lie in a region on the Rossby diagram where Lx has a strong dependence on rotation period.
Description:Thesis (Ph. D.)--University of Hawaii at Manoa, 1995.
Includes bibliographical references (leaves 106-112).
x, 112 leaves, bound ill. (some col.) 29 cm
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Astronomy

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