Computer Science
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........10m&link_type=abstract
Thesis (PhD). UNIVERSITY OF GEORGIA, Source DAI-B 60/05, p. 2175, Nov 1999, 98 pages.
Computer Science
1
Rotators, Open Clusters
Scientific paper
Observations of the three most widely studied open clusters, a Persei (50 Myr), the Pleiades (70-115 Myr) and the Hyades (600 Myr), reveal a rotational velocity distribution exhibiting a peak of slow rotators and a tail of rapid rotators among low mass stars. These observations also show that the spin down of rapid rotators with time is a function of mass: young clusters show rapid rotation at earlier spectral types than older clusters. While current angular momentum evolution theories can explain rapid rotation, the coexistent slow rotator peak remains unexplained. Rotational velocities can be determined from rotational periods obtained by photometric monitoring. Low mass stars in young clusters can appear to be variable when stellar rotation, combined with the presence of surface spots, produces detectable levels of modulation in the light curves. Increasing rotational velocities enhance the magnetic dynamo that is responsible for the formation of these spots, thus increasing the areal coverage of the spots. Hence, large variation amplitudes potentially indicate rapid rotation. M35 is an open cluster with an age thought to be similar to that of the Pleiades. In this dissertation, photometric data of M35 was analyzed to select variables having large amplitudes whose light curves might yield rotation periods. Probable M35 members exhibiting light curve dispersions greater than a threshold value were selected as variables or potential fast rotators. However, the observational data were insufficient for a reliable period determination. Nevertheless, an important conclusion was drawn by comparing the dispersion values of K-type members with that of simulated data. This comparison revealed a fraction of fast rotators less than that found in the Pleiades, indicating that M35 is slightly older than the Pleiades. This conclusion was further supported by the fact that the earliest spectral type of the fast rotators in the Pleiades is ~ K2, but fast rotators in M35, as determined from the largest dispersion values, begin to appear only at spectral type ~ K6. Future rotational velocity measurements of M35, as well as the determination of more complete rotational velocity distributions of clusters of various ages, can better constrain the models of angular momentum evolution.
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