Unveiling the Envelope and Disk : a Sub - Arcsecond Surveyof Young Stellar

Title of Dissertation: UNVEILING THE ENVELOPE AND DISK: A SUB-ARCSECOND SURVEY OF YOUNG STELLAR SYSTEMS Leslie W. Looney, Do tor of Philosophy, 1998 Dissertation dire ted by: Dr. Lee G. Mundy, Asso iate Professor Department of Astronomy Nearby (less than 500 light years away) stellar systems are forming that may someday resemble our solar system. By studying these forming stars, we an probe the origins, evolution, and properties of ir umstellar disks that are probably similar to the disk from whi h our planets formed. This thesis endeavors to address some of the major questions in modern star formation and planet formation theory via sub-ar se ond resolution observations of the envelopes and disks surrounding the youngest stars. We present the results of a detailed survey of 24 nearby forming stars with sub-ar se ond = 2.7 mm interferometri observations overing a range of evolutionary states. These multi-array observations fully sample spatial s ales ranging from 0: 004 to 5000, allowing the rst onsistent omparisons of ir umstellar stru tures, as seen in their dust emission. The images show a variety of stru ture and omplexity. The opti al/near-infrared T Tauri stars (DG Tauri, HL Tauri, GG Tauri, and GM Aurigae) have ontinuum emission that is dominated by ompa t (< 100) ir umstellar disks; these disks are resolved in two systems. The embedded near-infrared sour es (SVS13 and L1551 IRS5) have both extended and ompa t ontinuum emission. The deeply embedded sour es (L1448 IRS3, NGC1333 IRAS2, NGC1333 IRAS4, VLA 1623, and IRAS 16293-2422) have ontinuum emission that is dominated by the extended envelope. If these systems have disks, they are not more massive than the expe ted mass of the envelope extrapolated to small s ales. Our sample has a large number of multiple systems; morphologi ally, they an be separated into three types: independent envelope, ommon envelope, and ommon disk. The three types have distin t size s ales whi h are probably indi ative of the fragmentation s ale and formation me hanism for multiple systems. Many of the systems were modeled in the u,v plane. All of the systems ould be well t by the standard power-law models for envelopes and disks. In the more massive envelopes, a selfonsistent temperature pro le was needed to a hieve a eptable ts. Our data on lusively show that the majority of the emission and mass in the embedded systems is due to the envelope. Even though the embedded systems have massive envelopes, any ir umstellar disk is less than 10% of the system mass, and the disk is not more massive than ir umstellar disks in opti al systems. UNVEILING THE ENVELOPE AND DISK: A SUB-ARCSECOND SURVEY OF YOUNG STELLAR SYSTEMS by Leslie W. Looney Dissertation submitted to the Fa ulty of the Graduate S hool of the University of Maryland, College Park in partial ful llment of the requirements for the degree of Do tor of Philosophy 1998 Advisory Committee: Asso iate Professor Lee G. Mundy, Chair/Advisor Professor Robert Dorfman, Cohair Asso iate Professor Ri hard Ellis Professor Jordan Goodman Asso iate Professor Andrew Harris Copyright by Leslie W. Looney 1998 PREFACE This thesis presents the results of sub-ar se ond observations in the = 2.7 mm ontinuum. These observations were made with the Berkeley-Illinois-Maryland Asso iation (BIMA) millimeter Array, whi h operates under funding from the National S ien e Foundation. The key aspe t of this thesis was the evolution of high resolution apability of the BIMA array. The proje t onsisted of adding 7 new outrigger stations to the urrent array whi h in reased the baseline lengths to 1.9 km for the 1997/1998 observing season. This work would not have been possible without the vision and foresight of Lee Mundy, Leo Blitz, and Ja k Wel h, the early work of Bill Eri kson and Arie Grossman, and the ontinued e orts of Lee Mundy, Ja k Wel h, Di k Plambe k, Doug Thornton, Mel Wright, and Ri k Forster. The high resolution imaging of the binary system L1551 IRS5 presented in Chapter 3 has been published by the Astrophysi al Journal (Looney, Mundy, & Wel h 1997, ApJ, 484, L157). Chapters 4 and 5 were written as manus ripts suitable for submission to professional journals. Mu h of the work has been presented at numerous s ienti onferen es, su h as the Protostars and Planets IV onferen e in Santa Barbara, California, the Star Formation Workshop in Santa Cruz, California, the Binary Star Formation Conferen e in Stony Brook, New York, and at meetings of the Ameri an Astronomi al So iety in San Antonio, Toronto, and Washington, D.C. ii DEDICATION For my parents. Without their support, I would never had made it.