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Author: Ashlee Wynter Broussard Publisher: ISBN: Category : Astrochemistry Languages : en Pages : 0
Book Description
In the early stages of star formation, a protostar is surrounded by an envelope of gas and dust. Over time, material from the protostellar envelope falls inward, accreting onto the protostar and protostellar disk. RadChemT is a code developed to model protostars in the class 0/I phase, which calculates both the radiative transfer and astrochemistry in a dynamical collapse model. RadChemT has been used to successfully model astrochemical abundances for the protostar L1527 (Flores-Rivera et al. 2021), using a simplified assumption for time dependence. The aim of this research is to explore how these astrochemical abundances are impacted when integrating the physical conditions present at earlier times; namely, when temperatures are colder, and densities are lower. This effect originates from the dynamical flow of gas parcels along a streamline, and is separate from luminosity outbursts in the central protostar, which are known to affect abundances. Results of this research will be presented in the context of updates to the chemical modeling of L1527.
Author: Ashlee Wynter Broussard Publisher: ISBN: Category : Astrochemistry Languages : en Pages : 0
Book Description
In the early stages of star formation, a protostar is surrounded by an envelope of gas and dust. Over time, material from the protostellar envelope falls inward, accreting onto the protostar and protostellar disk. RadChemT is a code developed to model protostars in the class 0/I phase, which calculates both the radiative transfer and astrochemistry in a dynamical collapse model. RadChemT has been used to successfully model astrochemical abundances for the protostar L1527 (Flores-Rivera et al. 2021), using a simplified assumption for time dependence. The aim of this research is to explore how these astrochemical abundances are impacted when integrating the physical conditions present at earlier times; namely, when temperatures are colder, and densities are lower. This effect originates from the dynamical flow of gas parcels along a streamline, and is separate from luminosity outbursts in the central protostar, which are known to affect abundances. Results of this research will be presented in the context of updates to the chemical modeling of L1527.
Author: Laura Ocampo Alzate Publisher: ISBN: Category : Astronomy Languages : en Pages : 0
Book Description
Modeling is a fundamental aspect of research in astronomy that helps provide a deeper understanding of theories and the nature of physics. Protostars are a particularly difficult object to study because they are hidden in molecular clouds for much of their formation. Astronomers can use modeling techniques to explore the dynamics of protostars and their environment. L1527 is a protostar that has been researched for decades, using various Monte Carlo radiative transfer codes to replicate Atacama Millimeter/submillimeter Array (ALMA) data. In this project, a simulation is done using Radiation, Dynamics, and Chemistry in Time (RadChemT) modeling package to imitate ALMA data on L1527 protostar adjusting various physical conditions explored by previous scientists. These initial conditions include the mass of the star-like object, the radius of the disk, the mass of the disk, temperature, and density. The goal is to find which combination of characteristics best fits the data. Eight models were created, all with different parameters, that might lead us towards the best fit. Further analysis of these models is needed to distinguish between degeneracies.
Author: Andrew Barajas Publisher: ISBN: Category : Astronomy Languages : en Pages : 0
Book Description
Protostars have been studied and examined for decades; however, many puzzles remain about them, from their mass to the kinematics of the gas surrounding the protostar. Spectral lines coming from protostars contain information on the velocity dispersion of the dust/molecules, which arise from the Doppler effect. The kinematics of the infalling and rotating gas provides information on how solar systems developed what type of star will result from these early stages, or constrains on the mass through assumed Keplerian motions. Here we utilize the spectral line cubes of the ClassO/I Protostar L1527's chemical model from ALMA C18O (2-1) model simulations, created using the software package RadChemT, to develop predicted Moment maps and PV diagrams. Moment maps and PV diagrams give us the kinematics of L1527 that are used to determine its mass. Using ALMA's Data Mining Toolkit (ADMIT), we made moment maps and PV diagrams from observed data for L1527. ADMIT is a set of coding tools that help analyze image data cubes. Through comparisons of the observation and model moment maps, we hope to better determine the mass of L1527 and further solidify the accuracy of the RadChemT model of L1527.
Author: Lizxandra Flores Rivera Publisher: ISBN: 9780438069114 Category : Astrophysics Languages : en Pages : 87
Book Description
Molecule formation is dynamic during the protostar collapse phase, driven by changes in temperature, density, and Ultra-Violet (UV) radiation as gas and dust flows from the envelope onto the forming protoplanetary disk. In this work, we compare two physical models, one describing the envelope as free-falling collapse and the other one includes a rotating-infalling envelope derived from an inside-out collapse. We modeled the chemistry for C 18O to see how its abundance changes over time using as primary input parameters the temperature and density profile that were produced by the dust Radiative Transfer (MCRT) code called HOCHUNK3D (Whitney et al. 2013). For each model, we produce synthetic line emission maps from L1527 IRS to simulate the Class 0/I protostar using RADMC3D code to better interpret the observations from the Atacama Large Millimeter Array (ALMA). High concentrations of gas phase molecules of C18O are found within the 20 AU in areas in the envelope that are close to the surface of the disk. In the outermost part of the disk surface, the C18O freezes out beyond 400 AU, showing a much reduced abundance where the temperature profile drops down below 25 K. In cold regions, the radiation field plays an important role in the chemistry.
Author: Jonathan Barnes Publisher: ISBN: 9781369846409 Category : Astronomy Languages : en Pages : 33
Book Description
Protostars are stars in their earliest stages of development. They are born in giant molecular clouds of gas that can be as dense as 104 solar masses and as cool as 10K. When the gravity is strong enough, the gas collapses in on itself creating the star. The envelope of gas that surrounds the protostar in its development also plays a role in creating a solar system. Some physical properties such as the mass of the protostar can be gathered by modeling the infalling and rotational motion of the gas of the envelope. [can determine the mass of the growing protostar]. We developed a method to measure protostar masses quickly and conveniently by data-mining the ALMA archive and using automated processing tools. ADMIT is a processing tool that automatically models, via spectral line identification, the infalling and rotational motion, of the gas, with a PV diagram and moment maps including the 2nd moment. We validate our method by modeling the motion of the gas in the L1527 protostar's envelope and comparing to and already known model. This same method should work on other protostar's with ALMA data to determine its mass.
Author: Loraine Sandoval Ascencio Publisher: ISBN: Category : Astronomy Languages : en Pages : 0
Book Description
Investigating the dynamics in protostellar disks is key to understanding the evolution of protostars, their developing structure, and the formation of planets. The components of a class 0/I Young Stellar Object (YSO) such as L1527 include the protostar, outflowing gas, a protostellar disk, and a gaseous infalling envelope. The protostar accretes mass which initially travels from the envelope and then into the disk. Studies have shown the outer disk regions of young YSO systems may exhibit shocks at the disk-envelope boundary. This causes deviations from simple dynamics such as circular Keplerian motions and can govern the size of the eventual planetary system. RadChemT developed by Flores-Rivera et al. (2021) modeled L1527 to have an infalling rotating envelope and a circular Keplerian disk inside of the disk radius, 75 au. In this work, we model shocks and implement elliptical orbits post-shock to describe C18O (2-1) gas motions inside the disk for the RadChemT model. We generate spectral line cubes and position-velocity diagrams to visualize and interpret our model. The results of the updated modeling method are compared with the prior method and observed data from the Atacama Large Millimeter/submillimeter Array (ALMA). Since L1527 is an approximately edge-on system, we can resolve the kinematics and shock physics in diagrams. Generating a consistent model enables us to constrain the protostar's mass using Doppler velocity techniques, explain similar motions in other YSOs, and potentially provide novel clues on planet formation.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The formation of a 1 M/sub 0 protostar in spherical symmetry has been followed in time dependent hydrodynamics with a detailed description of the equation of state and a careful treatment of radiative transport. The comparison of the dynamic evolution with observation is made in terms of the Hertzprung-Russell diagram. It is found that the evolution following from Larson's initial condition produces quantitatively and qualitativley better agreement than that following from the initial condition of Hayashi, including the first appearance of the object as an infrared source. Of particular importance for a correct physical understanding of the formation process is an adequate description of the accretion shock. Pressure ionization and electrodegeneracy effects are of increasing importance for the internal structure of lower mass objects.
Author: Thomas Vidal Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Astrochemical studies of star formation are of particular interest because they provide a better understanding of how the chemical composition of the Universe has evolved, from the diffuse interstellar medium to the formation of stellar systems and the life they can shelter. Recent advances in chemical modeling, and particularly a better understanding of grains chemistry, now allow to bring new hints on the chemistry of the star formation process, as well as the structures it involves. In that context, the objective of my thesis was to give a new look at the chemistry of star formation using the recent enhancements of the Nautilus chemical model. To that aim, I focused on the sulphur chemistry throughout star formation, from its evolution in dark clouds to hot cores and corinos, attempting to tackle the sulphur depletion problem. I first carried out a review of the sulphur chemical network before studying its effects on the modeling of sulphur in dark clouds. By comparison with observations, I showed that the textsc{Nautilus} chemical model was the first able to reproduce the abundances of S-bearing species in dark clouds using as elemental abundance of sulphur its cosmic one. This result allowed me to bring new insights on the reservoirs of sulphur in dark clouds. I then conducted an extensive study of sulphur chemistry in hot cores and corinos, focusing on the effects of their pre-collapse compositions on the evolution of their chemistries. I also studied the consequences of the use of the common simplifications made on hot core models. My results show that the pre-collapse composition is a key parameter for the evolution of hot cores which could explain the variety of sulphur composition observed in such objects. Moreover, I highlighted the importance of standardizing the chemical modeling of hot cores in astrochemical studies. For my last study, I developed an efficient method for the derivation of the initial parameters of collapse of dark clouds via the use of a physico-chemical database of collapse models, and comparison with observations of Class 0 protostars. From this method, and based on a sample of 12 sources, I was able to derive probabilities on the possible initial parameters of collapse of low-mass star formation.
Author: Ian W. M. Smith Publisher: Springer Science & Business Media ISBN: 3642317308 Category : Science Languages : en Pages : 353
Book Description
Astrochemistry and Astrobiology is the debut volume in the new series Physical Chemistry in Action. Aimed at both the novice and experienced researcher, this volume outlines the physico-chemical principles which underpin our attempts to understand astrochemistry and predict astrobiology. An introductory chapter includes fundamental aspects of physical chemistry required for understanding the field. Eight further chapters address specific topics, encompassing basic theory and models, up-to-date research and an outlook on future work. The last chapter examines each of the topics again but addressed from a different angle. Written and edited by international experts, this text is accessible for those entering the field of astrochemistry and astrobiology, while it still remains interesting for more experienced researchers.
Author: Ashlee Wynter Broussard
Author: Ashlee Wynter Broussard
Author: Laura Ocampo Alzate
Author: Andrew Barajas
Author: Lizxandra Flores Rivera
Author: Jonathan Barnes
Author: Loraine Sandoval Ascencio
Author: 
Author: Thomas Vidal
Author: Tom Gehrels
Author: Ian W. M. Smith