Download or read book Modeling the Astrochemistry of Class 0 1 Protostars Using Time Dependent Dynamics A Case Study of L1527 written by Ashlee Wynter Broussard and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Constraining the Stellar Mass and Disk Radius of L1527 with RadChemT written by Laura Ocampo Alzate and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Determining the Mass of a Class1 0 Protostar L1527 Using Moment Maps written by Andrew Barajas and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Chemistry of the Envelope and Disk in the Protostar L1527 written by Lizxandra Flores Rivera and published by . This book was released on 2018 with total page 87 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Modeling the Infalling and Rotational Motion of the L1527 Protostar s Envelope written by Jonathan Barnes and published by . This book was released on 2017 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Gas Flow from Star Forming Cores Onto Protostellar Disks written by Loraine Sandoval Ascencio and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Solar type Protostars written by and published by . This book was released on 1980 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Revisiting the Chemistry of Star Formation written by Thomas Vidal and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Chemical Evolution in Low mass Star Forming Cores written by Jo-Hsin Chen and published by . This book was released on 2010 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, I focus on the physical and chemical evolution at the earliest stages of low-mass star formation. I report results from the Spitzer Space Telescope and molecular line observations of 9 species toward the dark cloud L43, a survey of 10 Class 0 and 6 Class I protostars with 8 molecular lines, and a survey of 9 Very Low Luminosity Objects (VeLLOs) with 11 molecular lines. From the observational results, CO depletion is extensively observed with C18O(2-1) maps. A general evolutionary trend is also seen toward the Class 0 and I samples: higher deuterium fractionation at higher CO depletion. For the VeLLO candidates and starless cores with N2D(3-2) detection, we found the deuterium ratio of N2D/N2H+ is higher comparing with the Class 0 and I samples. We use DCO+(3-2) maps to trace the velocity structures. Also, HCO+(3-2) blue profiles are seen toward the VeLLO candidate L328, indicating possible infall. To test theoretical models and to interpret the observations, we adopt a modeling sequence with self-consistent calculations of dust radiative transfer, gas energetics, chemistry, and line radiative transfer. In the L43 region described in Chapter 2, a starless core and a Class I protostar are evolving in the same environment. We modeled both sources with the same initial conditions to test the chemical characteristics with and without protostellar heating. The physical model consists of a series of Bonner-Ebert spheres describing the pre-protostellar (PPC) stages following by standard inside-out collapse (Shu 1977). The model best matches the observed lines suggests a longer total timescale at the PPC stage, with faster evolution at the later steps with higher densities. In Chapter 3, we modeled the entire group of Class 0 and I protostars. The trend of decreasing deuterium ratio can be seen after the temperature is high enough for CO to evaporate. After the evaporation, the history of heavy depletion (e.g, from longer PPC timescales or different grain surface properties) no longer affects the line intensities of gas-phase CO. The HCO+ blue profiles, which are used as infall indicators, are predicted to be observed when infall is beyond the CO evaporation front. The low luminosity of VeLLOs cannot be explained by standard models with steady accretion, and we tested an evolutionary model incorporating episodic accretion to investigate the thermal history and chemical behaviors. We tested a few chemical parameters to compare with the observations and the results from Chapter 2 and 3. The modeling results from episodic accretion models show that CO and N2 evaporate from grain mantle surfaces at the accretion bursts and can freeze back onto grain surfaces during the long periods of quiescent phases. Deuterated species, such as N2D+ and H2D+, are most sensitive to the temperature. Possible good tracers for the thermal history include the line intensities of gas-phase N2H+ relative to CO, as well as CO2 and CO ice features.
Download or read book The Impact of Protostellar Feedback on Astrochemistry written by Brandt Gaches and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Star formation is the lynch pin that lies in between the scales of galaxy and planet formation. Observational studies of molecular clouds, the sites of star formation, primarly use molecular line emission, providing dynamical and chemical information. Two of the key parameters of astrochemical models are far-ultraviolet (FUV) flux and the cosmic ray ionization rate. We use analytic accretion histories to predict the bolometric and FUV luminosities of protostar clusters and compare different histories with observed bolometric luminosities. We find that the Tapered Turbulent Core model best represents the observed luminosities and their dispersion. We extend the models to calculate the cosmic ray spectrum of protons accelerated in protostellar accretion shocks. We find that protostars are able to accelerate cosmic rays up to 10 GeV. We predict increased ionization rates within protostellar cores and molecular clouds hosting over 100 protostars. Our model is able to explain the substantial ionization rate, over 1000 times the typical, observed towards the OMC-2 FIR 4 protocluster. We model the impact of the protostellar FUV and cosmic rays on the astrochemistry on the natal molecular cloud. We couple the chemistry to the cosmic ray attenuation to solve the cosmic ray attenuation self-consistently. We find the inclusion of the embedded feedback significantly changes the Carbon chemistry and the CO-to-H2 conversion factor. High-density, optically-thin tracers such as ammonia are noticeably affected. The inclusion of embedded protostellar feedback alters the chemistry throughout molecular clouds, coupling the physics ongoing on the smallest scales of star formation to molecular cloud scale. Our results show that astrochemical modeling should account for ongoing star formation to correctly account for embedded FUV radiation and cosmic rays.
Download or read book Protostars Planets written by Tom Gehrels and published by . This book was released on 1978 with total page 756 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physical Processes in Circumstellar Disks Around Young Stars written by Paulo J. V. Garcia and published by University of Chicago Press. This book was released on 2011-05-15 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: Circumstellar disks are vast expanses of dust that form around new stars in the earliest stages of their birth. Predicted by astronomers as early as the eighteenth century, they weren’t observed until the late twentieth century, when interstellar imaging technology enabled us to see nascent stars hundreds of light years away. Since then, circumstellar disks have become an area of intense study among astrophysicists, largely because they are thought to be the forerunners of planetary systems like our own—the possible birthplaces of planets. This volume brings together a team of leading experts to distill the most up-to-date knowledge of circumstellar disks into a clear introductory volume. Understanding circumstellar disks requires a broad range of scientific knowledge, including chemical processes, the properties of dust and gases, hydrodynamics and magnetohydrodynamics, radiation transfer, and stellar evolution—all of which are covered in this comprehensive work, which will be indispensable for graduate students, seasoned researchers, or even advanced undergrads setting out on the study of planetary evolution.
Download or read book Astrochemistry and Astrobiology written by Ian W. M. Smith and published by Springer Science & Business Media. This book was released on 2012-10-28 with total page 353 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book NgVLA written by Eric James Murphy and published by . This book was released on 2018 with total page 830 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Diffuse Interstellar Bands written by A.G.G.M. Tielens and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: The mystery of the diffuse interstellar bands has been variously a curiosity, a co nundrum, and a nuisance for astronomers in the seven decades since the features were first noticed, but recently they have become a forefront issue in astrophysics. Ever since Paul Merrill, in a series of papers starting in 1934, pointed out the interstellar and unidentified nature of the bands, a Who's Who of twentieth century astronomers have tried their hands at solving the problem of identifying the carriers. Henry Norris Russell, Pol Swings, Otto Struve, Paul Ledoux, W. W. Morgan, Walter Adams, Jesse Greenstein, Lawrence Aller, and Gerhard Herzberg all briefly entered the stage, only to move on quickly to other problems where the chances for progress appeared more realistic. In more recent times a number of equally prominent scientists have pursued the bands, but generally only as a sideline to their real astronomical research. But in the past decade, and particularly in the past three years, the view of the search for the diffuse band absorbers as an interesting but perhaps quixotic quest has changed. Today there are several astronomers, as well as laboratory chemists, who are devoting substantial research time and resources to the problem and, as perhaps the most reliable indicator of the newly elevated status of research in this field, some research grants have now been awarded for the study of the bands.
Download or read book Introduction to Astrochemistry written by Satoshi Yamamoto and published by Springer. This book was released on 2017-02-13 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: This important book describes the basic principles of astrochemistry—an interdisciplinary field combining astronomy, physics, and chemistry—with particular emphasis on its physical and chemical background. Chemical processes in diffuse clouds, dense quiescent molecular clouds, star-forming regions, and protoplanetary disks are discussed. A brief introduction to molecular spectroscopy and observational techniques is also presented. These contents provide astronomers with a comprehensive understanding of how interstellar matter is evolved and brought into stars and planets, which is ultimately related to the origin of the solar system. The subject matter will also be understandable and useful for physical chemists who are interested in exotic chemical processes occurring in extreme physical conditions. The book is a valuable resource for all researchers beginning at the graduate level.
Download or read book Machine Learning in Chemistry written by Jon Paul Janet and published by American Chemical Society. This book was released on 2020-05-28 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent advances in machine learning or artificial intelligence for vision and natural language processing that have enabled the development of new technologies such as personal assistants or self-driving cars have brought machine learning and artificial intelligence to the forefront of popular culture. The accumulation of these algorithmic advances along with the increasing availability of large data sets and readily available high performance computing has played an important role in bringing machine learning applications to such a wide range of disciplines. Given the emphasis in the chemical sciences on the relationship between structure and function, whether in biochemistry or in materials chemistry, adoption of machine learning by chemistsderivations where they are important
