3D Radiative Transfer Modeling of Embedded Protostellar Regions

3D RADIATIVE TRANSFER MODELING OF EMBEDDED PROTOSTELLAR REGIONS steffen kjær jacobsen Dissertation submitted for the degree of PHILOSOPHIÆ DOCTOR Centre for Star and Planet Formation Niels Bohr Institute & Natural History Museum of Denmark Faculty of Science University of Copenhagen This thesis has been submitted to the PhD School of The Faculty of Science, University of Copenhagen Title 3D Radiative Transfer Modeling of Embedded Protostellar Regions, Author Steffen Kjær Jacobsen Date of Submission 16 April, 2018 Department Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, Faculty of Science, University of Copenhagen Academic Advisor Assoc. Prof. Jes Kristian Jørgensen Typeset using the Palatino and Euler type faces by Hermann Zapf Layout and typography by the author with LATEX2" using the class “classicthesis” developed by André Miede Cover: To friends and family ENGLISH ABSTRACT The formation of stars and planetary systems is a physical as well as a chemical process. Through decades of research, our understanding of star formation has greatly improved, though many aspects are still unknown or heavily debated. Stable, rotationally supported disks of gas and dust around protostars are routinely observed in the interme- diate and later stages of star formation. However, the exact details of how early and how they form, are still open questions. Concurrently with these issues, Complex Organic Molecules (COMs), and even pre- biotic molecules such as simple sugars, have been observed in the gas phase of early, protostellar cores. Their exact formation route and the physical origin of their arrival to the gas phase are heavily debated. It is not known if the observed COMs are linked to the warm disk atmosphere of settled protoplanetary disks, or if they predominantly exist in the gas phase in the warmest, inner regions of protostellar cores, before the emergence of a protoplanetary disk. These questions are important, as the protostellar chemistry acts as a chemical precursor for the composition of the material that ends up in planet formation, and may explain the rich chemistry we see in our own Solar Sys- tem. Using high angular resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA), together with complex 3D radiative transfer codes, we can investigate the innermost environment of young protostars, and hopefully answer some of the questions stated above. In this thesis I present research focusing on the two low-mass protostellar cores, IRAS 16293-2422 and L483, in terms of their dust and gas density, temperature structures, and chemistries. Two of the three research papers presented in this thesis concentrate on IRAS 16293- 2422, with one focusing on the 3D modeling of the envelope, the bridge of dust and gas conjoining the two protostars, and the disk-like emission around each protostar, as well as their individual luminosities. A 3D dust density model is presented, which morphologically matches the 868 µm continuum emission and explains the observed C17O emission through a jump abundance model. This model emu- lates freeze-out of molecules upon the dust grains, when the temperature drops beneath the sublimation temperature of CO on the dust ice-mantles. The individual luminosities of the deeply embedded protostars in IRAS 16293-2422 are found to be LA >18 L and LB 63 L , for radiation source A and B, respectively, which presents the first es- timation of the individual luminosities. The second research paper on IRAS 16293-2422 focuses on the outflows and the kinematics of the observed gas line emission from the v different molecules in the gas phase, and their relation to the bridge of dust and gas. Molecular gas line emission of CO, H2CO, HCN, CS, 17 SiO and C2H reveal that only the dust continuum and C O emission have a physical origin in the bridge of dust and gas, while all other molecular transitions are found to be related to the outflows emanating from radiation source A. The lack of outflow activity from radiation source B leads us to conclude that it is likely on a lower evolutionary stage than radiation source A. The last research paper describes ⇠ 0.100 observations of L483 with ALMA, which reveal that the COMs observed towards L483 reside in the innermost hot region of the envelope, within 40–60 au of the cent- ral protostar, and arise from thermal sublimation of the icy mantle around the dust grains. By analyzing the kinematics of the H13CN J = 4–3 and CS J =7–6 gas line emission, the presence of a Keplerian disk is excluded down to at least a 15 au radius. This means that the observed COMs cannot come from an abrupt transition region be- tween the collapsing envelope and a Keplerian disk, as hypothesized by an earlier research team, or from a warm disk atmosphere. Within 15 au, a small Kepler disk could hypothetically reside. Suggestions are made for future research projects targeting IRAS 16293-2422 and L483, to further constrain the spatial distribution of COMs (which constrains their formation routes), and the timeline for the emergence of protoplanetary disks. vi DANSK RESUMÉ Dannelsen af stjerner er en fysisk, såvel som en kemisk proces. Tak- ket være åtiers forskning er vores forståelse af stjernedannelse blevet betragteligt bedre på trods af, at mange aspekter stadig er ukendte eller omdiskuterede. Stabile, rotationelt understøttede protoplanetariske skiver af støv og gas omkring protostjerner bliver rutinemæssigt observeret i de mellemste og sene stadier af stjernedannelse. Dog er de præcise detaljer omkring, hvordan og hvor tidligt de dannes, stadig åbne spørgsmål. Samtidig med disse problemer, så er komplekse organiske molekuler (KOMs) og selv prebiotiske molekyler såsom simple slags sukker, blevet observeret i gasfasen i tidlige protostellare kerner. Deres præcise formationsrute og den fysiske mekanisme bag deres ankomst til gasfasen, er kraftigt debateret. Det vides ikke, om de observerede KOMs er tilstede i den varme atmosfære af en flad protoplanetarisk skive, eller om de mestendels eksisterer i den varme gasfase i de varmeste, inderste områder af protostellare kerner, før protoplanetariske skiver opstår. Disse spørgsmål er vigtige, da den protostellare kemi agerer som en forgænger for sammensætningen af det materiale, der indgår i planet dannelse, hvilket muligvis kan forklare den komplekse kemi vi ser i vores eget solsystem. Ved at bruge høj opløsnings observationer fra Atacama Large Mil- limeter/submillimeter Array (ALMA), sammen med komplekse 3D strålingstransports koder, kan vi undersøge de inderste regioner af unge protostjerner og forhåbentligt besvare nogle af de spørgsmål vi har stillet ovenover. I denne afhandling præsenterer jeg forskning vedrørende de to lav-masse protostellare kerner, IRAS 16293-2422 og L483, deres støv og gasdensitet, temperaturfordeling og kemi. To ud af de tre forskningsartikler, som bliver præsenteret i denne afhandling omhandler IRAS 16293-2422, hvor den ene fokuserer på 3D modellering af selve skyen, broen af støv og gas, der sammen- binder de to protostjerner, og den skivelignende emission omkring hver protostjerne, såvel som deres individuelle luminositet. En 3D støvdensitets-model præsenteres, som morfologisk svarer til 868 µm kontinuum emissionen, og forklarer den observerede C17O emission vha. en springmodel i mængden af molekyler i gasfasen. Denne model efterligner effekten af udfrysning af molekyler på overfladen af støvkorn, når temperaturen på støvkornene falder under sublima- tionstemperaturen af CO. De individuelle luminositeter af de dybt indlejrede protostjerner i IRAS 16293-2422 bestemmes til at være LA > 18 L og LB 63L , for henholdsvist strålingskilde A og B, hvilket er første gang de individuelle luminositeter estimeres. Den næste forskningsartikel om IRAS 16293 fokuserer på udstrøm- ningerne af materiale og kinematikken af den observerede gaslinje- vii emission fra de forskellige molekyler i gasfasen, og deres relation til broen af støv og gas. Molekylær gaslinje-emission fra CO, H2CO, 17 HCN, CS, SiO og C2H afslører, at kun støvkontinuumet og C O emissionen har et fysisk ophav i broen af støv og gas, imens emissionen fra alle andre molekylære overgange er relateret til udstrømningerne af gas fra strålingskilde A. Manglen på udstrømninger fra strålings- kilde B får os til at konkludere, at den sandsynligvis er på et lavere evolutionært stadie end strålingskilde A. Den sidste forskningsartikel omhandler ⇠0.100 observationer af L483 med ALMA, som afslører at de observerede KOMs i L483 befinder sig i det inderste, varme område af skyen, indenfor 40–60 au af den centrale protostjerne, og kommer af den termale sublimation af isla- get omkring støvkornene. Igennem en analyse af kinematikken fra H13CN J = 4–3 og CS J =7–6 gaslinje-emissionen, kan tilstedeværelsen af en Kepler skive ned til i hvert fald 15 au udelukkes. Dette betyder at de observerede KOMs ikke kan komme fra et abrupt overgangsom- råde imellem den kollapsende sky og en Kepler skive, som foreslået af et tidligere forskningshold, ej heller fra en varm skive atmosfære. Indenfor 15 au kan en lille Kepler skive hypotetisk set eksistere. Til slut bliver der givet foreslag til fremtidige forskningsprojekter, der retter sig imod IRAS 16293-2422 og L483, som bedre vil kunne bestemme den rumlige fordeling af KOMs (hvilket giver mere infor- mation omkring formationsruterne), samt bedre bestemme tidslinjen for dannelsen af protoplanetariske skiver. viii A prudent man should always follow in the path trodden by great men and imitate those who are most excellent. — Niccolò Machiavelli ACKNOWLEDGMENTS I want thank my supervisor Jes Jørgensen for his guidance and sup- port throughout my PhD studies. I am also indebted to my colleagues at StarPlan for their advice and help whenever I needed it. Special thanks are given to Lars Kristensen, Hannah Calcutt, Jon Ramsay, and Christian Brinch. I also want to thank our administrators Marianne Bentsen and Lene Bentzen, the submm group at StarPlan, and all the other members of StarPlan.

Load more