ABSTRACT Title of Dissertation PHYSICAL PROPERTIES OF COMETARY NUCLEI Yanga Rolando Fernandez Do ctor of Philosophy Dissertation directed by Professor Michael F AHearn Department of Astronomy I present results on the physical and thermal prop erties of six cometary nuclei This is a signicant increase in the numb er of nuclei for which physical information is available I have used imaging of the thermal continuum at midinfrared and radio wavelengths and of the scattered solar continuum at optical wavelengths to study the eective radius reectivity rotation state and temp erature of these ob jects Traditionally the nucleus has b een dicult to observe owing to an obscuring coma or extreme faintness I have taken advantage of new midinfrared array detectors to observe more comets than were p ossible b efore I have also codevelop ed a technique to separate the coma and nucleus from a comet image I develop ed a simple mo del of the thermal b ehavior of a cometary nucleus to help interpret the thermal ux measurements the mo del is an extension to the Standard Thermal Mo del for aster oids We have enough nuclei now to see the rst demarcations of the cometary region on an alb edodiameter plot I make a comparison of the cometary nuclei with outer Solar System small b o dies and nearEarth asteroids All of the cometary nuclei studied in this thesis are dark with geometric alb edos b elow and have eective diameters of around to km except for comet HaleBopp C O which is in the next order of magnitude higher I give an extensive discussion of the nuclear characteristics of comets HaleBopp and PEncke the two comets for which I have large datasets PHYSICAL PROPERTIES OF COMETARY NUCLEI by Yanga Rolando Fernandez Dissertation submitted to the Faculty of the Graduate Scho ol of the University of Maryland College Park in partial fulllment of the requirements for the degree of Do ctor of Philosophy Advisory Committee Professor Michael F AHearn Chair Do ctor Alan P Boss Professor Paul D Feldman Do ctor Lucy A McFadden Professor Virginia Trimble Professor Richard J Walker c Copyright by Yanga Rolando Fernandez PREFACE Sections of this thesis have already b een published in scientic p eerreviewed jour nals and conference pro ceedings A discussion of comet Hyakutake app eared in Planetary and Space Science in volume pages A treatment of comet Encke is currently under review by Icarus An overview of comets Temp el Tuttle Wild and Utsunomiya will app ear in the up coming b o ok Cometary Nuclei in Space and Time edited by M F AHearn and published by the Astronomical So ciety of the Pacic which is based on the IAU collo quium held in Nanjing China in May of A pap er on comet HaleBopp app eared in Icarus in July vol ume pages A discussion of the imagepro cessing technique that I call the comatting metho d app ears in a pap er rstauthored by my coinvestigator Dr C M Lisse published in Icarus in July volume pages ii DEDICATION To the two constants of my Universe Mom and Dad iii ACKNOWLEDGEMENTS This thesis is formally credited to one p erson but it is not completed without the assistance of many other p eople of course Mike AHearn has guided me through the bulk of my graduate career and to him I owe many thanks not only for mentoring me through the scientic asp ects of my apprenticeship but through the so ciologi cal and p olitical ones as well The rst scientic talk I heard him give was at the Donn Symp osium in Charlottesville VA in Novemb er of Until then I had b een waing ab out deciding on a concentration for my thesis but after hearing him sp eak ab out his database pap er and seeing his enthusiasm ab out these new break throughs that nally revealed themselves after studying seven dozen comets I really started to understand some of the excitement and allure of studying these buggers So thank you so much Mike for all your help Casey Lisse has b een my other close collab orator in this scientic journey I am grateful for his quick mind innite patience with my questions and wacky humor And of course who can forget the Red Pen I will always lo ok fondly back on these very scientically pro ductive years with him I also owe a deep debt of thanks to Dennis Wellnitz who is such an exp ert on things mechanical and electronic The smashing success of the HaleBopp o ccul tation adventure in a trashdump in upstate Utah would not have happ ened iv without his exp ertise and quick thinking at the critical moments Yet again I think how fortunate I am to have entered Mikes Comet Group just when all these terric p eople were there to help me out I am very grateful to Lucy McFadden for allowing me to start work on an asteroid pro ject in and nally allowing me to realize that I really did like planetary science much more than studying clusters of galaxies And she has continued to b e a great teacher through my graduate career Thanks Lucy Lastly on the scientic front I have to thank b oth NASA and NSF for there consistent nancial supp ort throughout these last years the telescop e allo cation committees and stas of IRTF KPNO CTIO ESO VLA Lowell Observatory and MKO for there helpful service and p ositive attitude Mike Ressler Bill Homann and Ulli Kau for granting us p ermission to play with their instruments Without all of these p eople I would not have b een so successful in gaining the necessary data to complete this thesis Among other things Ive learned you can have o o dles of fun with only oxygen in your lungs formtting foam is a go dsend theres nothing like jicama and asparagus salad to help you gure out how to drive a stickshift Now planetary science has b een go o d to me if I had not b een studying comets I would not have b een able to travel all over the world and exp erience more of our planet than I had imagined It makes you realize how much of Earths culture and nature is still left to explore Twentyeight trips in grad scho ol and I have only scratched the surface from strolling along Victoria Harb or among the bright lights of Hong Kong to bathing in a giant waterfall in Waipio Valley on the Big Island to b eing the highest human for miles around at the tip of Mt Lassen to watching the v rainb ows app ear and reapp ear on a misty summers day in Sto ckholm I could go on for a while Unfortunately now I have no choice but to submit to this wanderlust Ive picked up and sp end the rest of my life traveling the no oks and crannies of our planet One rep ercussion of all this scamp ering around has b een to instill in me a great sense of appreciation for how lucky I am Though the physical distance b etween me and that subsistence farmer in central Chile that family selling trinkets in Nogales and those p o or homeless blokes near Constitution Avenue may b e small what an incredibly fortunate p erson I am to b e able to go to my warm house my wellsup plied gro cery my steadily paying job We are all just a few small but critical events away from any of these predicaments And now for the other imp ortant p eople of my time here Thanks to Arunav Kartik and Laura I wouldnt have b een able to nish this tome without all of their supp ort and understanding through this crabby and grumpy time esp ecially near the end Mes amis your friendships mean more to me than you imagine The mid to late s would have b een quite a bit more dicult to slog through without you all Lets all nd enough inner p eace and gumption to make the XXIst century b etter than the XXth AK Thank you for keeping my head on straight KS Thank you for keeping me honest LW Thank you for giving me selfcondence Continuing with the imp ortant p eople thanks Don for among other things bringing ice cream and going sledding thanks Leslie for among other things playing racquetball and nding my bike thanks Amy for among other things going to see ob eat movies with me thanks Doug for among other things making me stay loyal vi to the Padres thanks Steve for among other things having practical knowledge in a institute full of geeks thanks Pete for among other things endlessly quoting The Simp ons thanks Alison for among other things endlessly quoting Star Wars Where would we b e without the department sta shielding us from the three to ed sloth that is the university administration To John T Mary Ann and Maggie thanks for your protection Where would I b e if I hadnt babysat the PDS machine during SL impact week To Anne thanks for that job years ago and for your humor in the meantime Where would I b e if I were not able to go to Giant at oclo ck in the morning and buy PopTarts What a country Finally thanks to Carl Sagan for writing Cosmos Halleys Comet for b eing visible right when I was so impressionable may I see you again when Im ninety Voyager for sending back very co ol pictures of Uranus and Neptune vii TABLE OF CONTENTS List of Tables xi List of Figures xii Cometary Nuclei Their History and Imp ortance A Brief Rundown The Role in the Solar System Motivation A Description of Chapters Data Acquisition and Pro cessing Obtaining Optical Data Obtaining Infrared Data Obtaining Radio Data The Ideal Dataset Pro cessing the Data Coma Removal Data Interpretation Philosophy of Thermal Mo deling The Energy of a Nucleus The Augmented Thermal Mo del Rotation of the Nucleus viii The Nucleus of Comet HaleBopp Background Occultation Measurements Thermal Emission and Scattered Light Imaging Summary of HaleBopp Results The Nucleus of Comet Encke Background Observations and Reduction Analysis Discussion Previous Work Summary of Encke Results The Nucleus