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The Impact of Protostellar Feedback on Astrochemistry
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
Tree-based solvers for adaptive mesh refinement code flash - IV. An X-ray radiation scheme to couple discrete and diffuse X-ray emission sources to the thermochemistry of the interstellar medium
X-ray radiation, in particular radiation between 0.1 and 10 keV, is evident from both point-like sources, such as compact objects and T-Tauri young stellar objects, and extended emission from hot, cooling gas, such as in supernova remnants. The X-ray radiation is absorbed by nearby gas, providing a source of both heating and ionization. While protoplanetary chemistry models now often include X-ray emission from the central young stellar object, simulations of star-forming regions have yet to include X-ray emission coupled to the chemo-dynamical evolution of the gas. We present an extension of the treeray reverse ray trace algorithm implemented in the flash magnetohydrodynamic code which enables the inclusion of X-ray radiation from 0.1 keV < Eγ < 100 keV, dubbed xraythespot. xraythespot allows for the use of an arbitrary number of bins, minimum and maximum energies, and both temperature-independent and temperature-dependent user-defined cross-sections, along with the ability to include both point and extended diffuse emission and is coupled to the thermochemical evolution. We demonstrate the method with several multibin benchmarks testing the radiation transfer solution and coupling to the thermochemistry. Finally, we show two example star formation science cases for this module: X-ray emission from protostellar accretion irradiating an accretion disc and simulations of molecular clouds with active chemistry, radiation pressure, and protostellar radiation feedback from infrared to X-ray radiation
The design and implementation of a 16-bit, low-power, high performance, microprocessor based digital signal processing unit
Call number: LD2668 .T4 EECE 1987 G32Master of ScienceElectrical and Computer Engineerin
Aluminum-26 Enrichment in the Surface of Protostellar Disks Due to Protostellar Cosmic Rays
The radioactive decay of aluminum-26 (Al) is an important heating
source in early planet formation. Since its discovery, there have been several
mechanisms proposed to introduce Al into protoplanetary disks, primarily
through contamination by external sources. We propose a local mechanism to
enrich protostellar disks with Al through irradiation of the
protostellar disk surface by cosmic rays accelerated in the protostellar
accretion shock. We calculate the Al enrichment, [Al/Al],
at the surface of the protostellar disk in the inner AU throughout the
evolution of low-mass stars, from M-dwarfs to proto-Suns. Assuming constant
mass accretion rates, , we find that irradiation by MeV cosmic rays
can provide significant enrichment on the disk surface if the cosmic rays are
not completely coupled to the gas in the accretion flow. Importantly, we find
that low accretion rates, M yr, are able
to produce canonical amounts of Al, . These accretion rates are experienced at the
transition from Class I- to Class II-type protostars, when it is assumed that
calcium-aluminum-rich inclusions condense in the inner disk. We conclude that
irradiation of the inner disk surface by cosmic ray protons accelerated in
accretion shocks at the protostellar surface may be an important mechanism to
produce Al. Our models show protostellar cosmic rays may be a viable
model to explain the enrichment of Al found in the Solar System.Comment: Accepted to ApJ, in pres
The Oxford Face Matching Test:Short-form alternative
A recently published test of face perception, the Oxford Face Matching Test, asks
participants to make two judgements: whether two faces are of the same individual; and how
perceptually similar the two faces are. In the present study, we sought to determine to what
extent the test can be shortened by removing the perceptual similarity judgements, and
whether this impacts test performance. In Experiment 1, participants completed two versions
of the test, with and without similarity judgements, in separate sessions in counterbalanced
order. The version without similarity judgements took approximately 40% less time to
complete. Performance on the matching judgements did not differ across versions and the
correlation in accuracy across the two versions was comparable to the originally reported
test-retest reliability value. Experiment 2 validated the version without similarity judgements
against other measures, demonstrating moderate relationships with other face matching,
memory and self-report face perception measures. These data indicate that a test version
without the similarity judgements can substantially reduce administration time without
impacting on test performance
The evolution of HCO in molecular clouds using a novel chemical post-processing algorithm
Modeling the internal chemistry of molecular clouds is critical to accurately
simulating their evolution. To reduce computational expense, 3D simulations
generally restrict their chemical modeling to species with strong heating and
cooling effects. We address this by post-processing tracer particles in the
SILCC-Zoom molecular cloud simulations. Using a chemical network of 39 species
and 299 reactions (including freeze-out of CO and HO), and a novel
iterative algorithm to reconstruct a filled density grid from sparse tracer
particle data, we produce time-dependent density distributions for various
species. We focus upon the evolution of HCO, which is a critical formation
reactant of CO but is not typically modeled on-the-fly. We analyse the
evolution of the tracer particles to assess the regime in which HCO
production preferentially takes place. We find that the HCO content of the
cold molecular gas forms in situ around n_\textrm{HCO^+}\simeq10^3-
cm, over a time-scale of approximately 1 Myr, rather than being
distributed to this density regime via turbulent mixing from deeper in the
cloud. We further show that the dominant HCO formation pathway is dependent
on the visual extinction, with the reaction H + CO contributing 90% of
the total HCO production flux above . Using our novel
grid reconstruction algorithm, we produce the very first maps of the HCO
column density, (HCO), and show that it reaches values as high as
cm. We find that 50% of the HCO mass is located in an
-range of 10-30, and in a density range of
- cm. Finally, we compare our (HCO) maps to
recent observations of W49A and find good agreement.Comment: 23 pages including appendix, 20 figures, submitted to MNRAS, comments
are welcom
Longevity Basis Risk A methodology for assessing basis risk
This technical report details the methodology developed on behalf of the LBRWG to assess longevity basis risk. A user-guide which provides a high level summary of this report has also been produced. Together these documents form the key outputs of the first phase of a longevity basis risk project
commissioned and funded by the IFoA and the LLMA, and undertaken on our behalf by Cass Business School and Hymans Robertson LLP
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