A Spectroscopic Study of Three FU Orionis Objects : Accretion Disks and Wind Signatures

University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-1991 A spectroscopic study of three FU Orionis objects : accretion disks and wind signatures. Alan David Welty University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Welty, Alan David, "A spectroscopic study of three FU Orionis objects : accretion disks and wind signatures." (1991). Doctoral Dissertations 1896 - February 2014. 1807. https://scholarworks.umass.edu/dissertations_1/1807 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. A SPECTROSCOPIC STUDY OF THREE FU ORIONIS OBJECTS: ACCRETION DISKS AND WIND SIGNATURES A Dissertation Presented by ALAN DAVID WEUTY Submitted to the Graduate School of the University of Massachusetts in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Febmary 1991 Department of Physics and Astronomy © Copyright by Alan David Welty 1991 All Rights Reserved A SPECTROSCOPIC STUDY OF THREE FU ORIONIS OBJECTS: ACCRETION DISKS AND WIND SIGNATURES A Dissertation Presented by ALAN DAVID WEUTY Approved as to style and content by: Stephen E. Strom, Chairman Au Suzan Edwards, Member Ronald L. Snell, Member David Van Blerkom, Member Robert V. Krotkov, Outside Member Robert B. Hallock, Department Head Department of Physics and Astronomy to my family Emily, Daniel, and Andrew ACKNOWLEDGMENTS Many people have contributed to this work in many ways. In the broader context of my life, it seems that my mother, Miriam Szanyi, has been an important player. She brought me into the worid and gave me direction in life. Her criticism was always constructive. She was always encouraging. My reasons for becoming an astronomer, other than childhood interest, are something of a mystery to me. However, it is probably more than just coincidence that my choice of career is the same as that of my older brother Daniel, whom I look up to in many ways. I had the good fortune to have a series of exceUent math and science teachers in junior and senior high school in Bethlehem, PA. Mr. Checkley, Mr. Jackson, Mr. Nemeth, Mr. Wetcher, Mrs. Buzzard, and, in particular, Miss Helms gave me a vision that math and science are interesting, important, and fun. My early education in astronomy was given to me by Stewart Sharpless and Judy Pipher, at the University of Rochester. Jack Fix and Bob Mutel, of the University of Iowa, built on that foundation and gave me needed encouragement. I didn't embarrass myself \he first time... The rumors were such tiiat I should be indebted to the Department of Physics and As- tronomy of the University of Iowa for its part in making possible my move to Massachusetts, and the opportunity to work with people here. True or not, I have a feeling that it didn't matter in my case. Thanks are due to the Kitt Peak support staff for their efforts toward productive observing runs at the Mayall telescope, and to the IRAF group for a wonderful product. The secretarial staff at UMass was also very helpful and cheerful during my years here. The students and faculty of the Five College Astronomy Department have left their mark on this document. The title page and abstract heading would not have been the same without them. It seems a small price to pay for the fond memories and friendships. In particular. V Pat Knezek and Lynne HiUenbrand were terrific office mates, and Diane Dutkevitch gave my ear. a reason for being. They and the darts gang (TJ, Jzak, Brother. Ted and James) helped me retain some sanity. Conversations with Kar^n Strom. Ron SneU, and David Van Bleiicom, whether about this work or other topics dear to their hearts, were always useful and enjoyable. These individuals contribute greaUy to the wonderful overall character of the astronomy department at UMass. Input and encouragement from Lee Hartmann and Scott Kenyon of the Center for Astro- physics. Suzan Edwards of the FCAD/Smith CoUege, and Steve Strom of the FCADAJMass were essential for the completion of this work. They provided superb examples for a young astronomer to follow, and much free entertainment Steve Strom deserves special recognition and thanks for his involvement. A dream of mine, to be involved in star fonnation research, had been all but lost. He revived the dream, helped enormously in making it a reality, and paid me for it for more than three years. Through it all he was patient and understanding, and able to motivate me. He saw me as more than just a laborer. He thought of my needs, and the needs of my family, and acted accordingly. His example and his friendship will always be special to me. The heroic endurance of my wife, Emily, through six years of being married to a graduate student, cannot go unrecognized. She has held up under the burden, one much heavier than she expected. Through it all she supplied me with love and strength to keep going. And she brought our two beautiful boys into the worid. vi ABSTRACT A SPECTROSCOPIC STUDY OF THREE FU ORIONIS OBJECTS- ACCRETION DISKS AND WIND SIGNATURES FEBRUARY 1991 ALAN DAVID WEUTY, B.S.. UNIVERSITY OF ROCHESTER M.S., UNIVERSITY OF IOWA Ph.D., UNIVERSITY OF MASSACHUSETTS Directed by: Professor Stephen E. Strom It has been suggested that in outburst, FU Ori objects (FUors) are luminous accretion disks surrounding young, low luminosity stars. We obtained high resolution, high signal-to- noise, 3985-4920 A, 4940-6830 A, and 8030-9510 A spectra of V1057 Cyg, Z CMa, and FU Ori at the Mayall telescope at KPNO to examine predictions of the accretion disk model of Kenyon, Hartmann, and Hewett (1988). Synthetic disk spectra are calculated assuming the temperature gradient, T(R), of a classical accretion disk, and assuming that disk photospheres can be modeled by adding contributions from concentric disk aimuli represented by spectra of supergiant stars having Teff ^ T(R). Given the simplicity of the model, we find surprising agreement between observed and synthetic spectra. We examine variation of absorption linewidth with wavelength for synthetic and FUor spectra, and find good correlations for the model and two FUors. We also investigate variation of linewidth with lower excitation potential, and find a subtle effect, less useful as a disk diagnostic. We subtract synthetic spectra from object spectra to investigate overall goodness of fit. For V1057 Cyg and Z CMa, the percentage of lines fit to < 10 mA accuracy rises from ~50% at 4000 A to > 80% at 5000-6800 A. At 8000-9000 A, the goodness of fit is ~50%; Vll the decline attributed to disk flaring. For FU Ori, the goodness of fit is -10% at 4000 A. rising to ~80% longward of 5700 A. We examine residual features in V1057 Cyg and Z CMa. Most of the strongest features are either emission or P Cygni lines, suggesting origin in powerftil winds driven by these objects. For FU Ori, most residuals are absorption features, as expected if FU Ori has lower surface gravity than do supergiants, or if wind absorption is particulariy strong. The signal-to-noise ratio in Z CMa's residual spectrum is sufficient to examine the P Cygni structure in lines of a large range of optical depths. We leave detailed analysis to a subsequent paper, but point here to unusual line structure that may arise in a rotating wind, suggesting tiiat FUor winds carry large amounts of angular momentum. viii TABLE OF CONTENTS Page ACKNOWLEDGMENTS V ABSTRACT vii LIST OF TABLES xii LIST OF HGURES ... xiu Chapter 1. INTRODUCTION ^ The FU Ononis Phenomenon j Early Observations of FU Orionis 1 The Outburst and Evolution of V1057 Cygni. 3 Observations of Z Canis Majoris 5 Characteristics of the Ori FU Objects 5 Suggested Explanations 8 2. MOTIVATION AND GOALS H Project Goals U Further Motivation \2 3. OBSERVATIONS AND DATA REDUCTION 15 Program Requirements 15 Object Selection 16 Observations and Data Reduction 16 4. ACCRETION DISK MODELING 20 Background 20 Method of Model Calculation 20 Broad-Band Energy Distributions 21 High Resolution Spectral Synthesis 22 Details for the Program Objects 27 Quahtative Predictions of the Model 28 5. TESTS OF ACCRETION DISK MODEL PREDICTIONS 31 Measurement Techniques 31 Linewidth Versus Wavelength Results 32 VI 057 Cygni 32 IX Z Canis Majoris FU Orionis ... 37 Cross-Correlation Results . 37 V1057 Cygni Z Canis Majoris .... ~Z FU Orionis 41 Linewidth Versus Excitation Potential Results 41 V1057 Cygni Z Canis Majoris FU Orionis 45 Comparison with Other Objects 4g 6. SYNTHETIC SPECTRUM SUBTRACTION: GOODNESS OF RT 51 Subtraction of Synthetic Disk Spectra 51 V1057 Cygni 51 Z Canis Majoris 53 FU Orionis 53 Goodness of Fit: Method and Results 56 Determination of Best Model Parameters 62 Effects Due to Error in Rotational Velocity Normalization 62 Effects Due to Error in Radial Velocity 64 Effects Due to Error in Disk Temperature Scale 65 Goodness of Fit Test Results for V1057 Cygni 65 Goodness of Fit Test Results for Z Canis Majoris 68 Goodness of Fit Test Results for FU Orionis 68 7. ANALYSIS OF RESIDUAL FEATURES 71 Identification of Residual Features 71 Gravity Sensitivity 73 Temperature Sensitivity 82 Description of Residual Features 83 V1057 Cygni 83 Z Canis Majoris 84 FU Orionis 84 Constraint of Wind Properties 85 8. CONCLUSIONS 87 Summary of Results and Conclusions 87 Directions for Further Study 88 X APPENDIX: COMPLETE RESIDUAL FEATURE LISTS REFERENCES XI LIST OF TABLES Table Page 1.

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