Date of Award

2004

Document Type

Restricted Thesis

Terms of Use

© 2004 Matthew Miller. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Physics & Astronomy Department

First Advisor

Eric L.N. Jensen

Second Advisor

Keivan Stassun

Abstract

We apply a simple photospheric spot temperature model to photometric variability measurements of T Tauri stars in the Trapezium region of the Orion Nebula Cluster. Our aim is to search for the relationship, if any, between spot temperatures and stellar rotation periods to better understand the relationship between accretion and angular momentum regulation in T Tauri stars. Current magnetic disk-locking models of young stars ascribe spot temperatures hotter than the photosphere to active accretion from a circumstellar disk. If accretion acts to brake stellar rotation, spot temperatures hotter than the photosphere should be more prevalent among slow rotators. From the variability amplitudes at four wavelengths (B, V, R, I), we determine spot temperatures and the areal coverage of the spot on the stellar surface. The results of our model show that we can unambiguously distinguish spots hotter than the photosphere from spots cooler than the photosphere for most stars. Comparisons between spot temperatures and previously determined rotation periods reveal no significant correlation between spot temperatures and stellar rotation. Comparisons between spot temperatures and measurements of near-IR excess, Δ(I-K), reveal possible problems with the accuracy of Δ(I-K) as an indicator of circumstellar disk presence. We confirm this problem by further comparing spot temperatures to Ca II equivalent widths and comparing Δ(I-K) measurements with Ca II equivalent widths corresponding to evidence for accretion from a circumstellar disk. We propose that future studies of the angular momentum evolution of T Tauri stars take considerable care in distinguishing stars with circumstellar disks and possible magnetic disk locking from stars without circumstellar disks or magnetic disk locking. Finally, we argue that our spot temperature and rotation period comparisons support new theories of angular momentum evolution in T Tauri stars that relate the angular momentum evolution of pre-main-sequence stars to the core-envelope decoupling that occurs during the convective-radiative transition.

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