INFORMATION TO USERS This manuscript)las been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissenation copies are in typewriter face, while others may be from any type ofcomputer printer. The quality orthis reproduction is dependent upon the quality orthe copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely. event that the author did not send UMI a coJ&plete mam1saipt and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the ori~ beginning at the upper left-hand comer and continuing from left to right inequal sections with smaIl overlaps. Each original is also photographed in one exposure and is included in reduced form at the back ofthe book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell &Howell InformatIon Company 300 North Zeeb Road. Ann Amar. MI48106-1346 USA 313!761-47oo 8OO:521-()600 THE EVOLUTION OF ROTATION AND ACTIVITY IN YOUNG OPEN CLUSTERS: THE ZERO-AGE MAIN SEQUENCE A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ASTRONOMY DECEMBER 1995 By Brian Michael Patten Dissertation Committee: Theodore Simon, Chairperson George H. Herbig David Jewitt Barry LaBonte Ralph Freese UMI N~ber: 9615544 Copyright 1995 by Patten, Brian Michael All rights reserved. UMI Microform 9615544 Copyright 1996, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 @Copyright 1995 by Brian Michael Patten III Acknowledgements I would like to thank all the faculty members that have been part of my committee over the course of this work, Ted Simon, George Herbig, Dave Jewitt, Barry LaBonte, Ralph Freese, Ed DeLuca, and Mark Shure for their advice and guidance. I also thank George Fisher, Sandy McClymont, and Ed DeLuca for teaching me a lot of solar physics during my brief tenure as a solar graduate student. Several of my fellow graduate students deserve thanks for their friendship and support over the years: Jeff Goldader, Kristin Blais, Tony Farnham, Matt Senay, and Susan Ridgway. I am grateful to Jeff Goldader and Tony Farnham who created the ]}'JEX macro package that was used to typeset this dissertation. I spent a great deal of time in Chile collecting data for this disseration. My deepest thanks go the outstanding staff of the Cerro Tololo Inter-American Observatory for helping to make my observing runs in Chile as productive and as pleasant as possible. IV 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 30 of Lx about a median Lx value of "'10 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. v Table of Contents Acknowledgements. ......................................................... IV Abstract.................................................................... V List of Tables. .............................................................. VIn List of Figures .............................................................. IX Chapter 1: Introduction................................................... 1 Chapter 2: Observations................................................... 5 2.1 A ROSAT Image of IC 2391. .. .. .. .. .... .. ......... .. .. .. .. .. 5 2.1.1 Source Detection..... 5 2.1.2 Source Photometry....................................... 8 2.1.3 X-ray Spectroscopy. ...................................... 19 2.1.4 X-ray Variability Analysis................................ 21 2.2 A ROSATX-ray Survey oflC 2602.... 27 2.3 Optical Multi-color Photometry and Spectroscopy.............. .. 28 2.4 Proposed New Cluster Members.................................. 45 2.5 Optical Time-Series Photometry. ................................. 50 Chapter 3: Rotation at the ZAMS ......................................... 67 Chapter 4: Coronal Activity at the ZAMS . .. .. .. .. .. .. .. .. .... .. .. .. .. .. 75 4.1 Selection Effects , . 87 4.2 Lx versus Axial Inclination.. .................................... 88 VI 4.3 Binarity ......................................................... 88 4.4 Rotational Modulation. .......................................... 90 4.5 Long-Term Activity Cycles........................ 91 4.6 Lx versus Rotation Rate. ........................................ 92 Chapter 5: The Relation Between Activity and Rotation... ................ 95 Chapter 6: Summary. ................................................... .. 102 Vll List of Tables 1 PSPC Observations of IC 2391 6 2 Detected X-ray Sources in IC 2391......................... .. 10 3 X-ray Variability Tests for IC 2391 Sources ,. '" 24 4 Optical Photometry and Spectroscopy for IC 2391 X-ray Source Candidates 39 5 New Optical Data for Ie 2602 Suspected Members........... 44 6 Rotation Data for Late-Type Stars in IC 2391/IC 2602. ...... 63 7 Variable Stars............................................... 66 8 X-ray Detections of Known or Suspected Members of IC 2391 76 9 X-ray Upper Limits for Known Members of IC 2391.......... 78 10 The Range and Spread of X-ray Activity... .. 85 Vlll List of Figures Figure 1 A 23 ksec ROBAT PSPC Observation of IC 2391. 7 2 Finders for ROBAT PSPC X-ray Sources in IC 2391. ......... 12 3 Distribution of Deviations from the Mean Count Rates....... 26 4 Low Resolution Spectra. .................................... 30 5 Color-Magnitude Diagram for Possible Optical Counterparts to X-ray Sources in IC 2391 46 6 Color-Magnitude Diagram for Known and Suspected IC 2391 and IC 2602 Members....................................... 49 7a Light Curve for SHJM 3..................................... 55 7b Periodogram for SHJM 3 Light Curve........................ 56 7e Light Curve for SHJM 3 Folded to 0.527 day................. 57 8 Folded Light Curves for IC 2391 and IC 2602 Stars with Detected Periods 58 9 Rotation Period Histograms. ................................ 70 10 Rotation Period Distributions for wTTS and CTTS .......... 74 lla Lx versus Vi for IC 2391 and IC 2602 ....................... 79 llb Lx versus Vi for IC 2391/IC 2602 and the Pleiades..... ..... 80 lle Lx versus Vi for IC 2391/IC 2602 and the Hyades........... 81 12 Cumulative Luminosity Function for X-rays.. ................ 84 13 The Decay of X-ray Luminosity with Age.. .................. 86 IX 14 X-ray Luminosity versus Rotation Period.. .... .... ..... .. .. 93 15a Rossby Diagram for X-rays. ................................. 96 15b Rossby Diagram for X-rays, Solar-Type Stars Only.. ......... 97 x Chapter 1 Introduction IC 2391 and IC 2602 are two relatively nearby clusters whose ages (""30 Myr)l are young enough that solar-type members (late-F to mid-K dwarfs) have just arrived, or are just arriving, on the zero-age main sequence (ZAMS). The ZAMS is of some importance to the study of the evolution of angular momentum and the underlying dynamo in solar-type stars because it represents the dividing line between the pre-main sequence (PMS) and main sequence (MS) lives of these stars. In the PMS phase, the angular momentum evolution of these stars is dominated primarily by gravitational contraction and interactions,