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A list of all the posts and pages found on the site. For you robots out there, there is an XML version available for digesting as well.
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Posts
Future Blog Post
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Blog Post number 4
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Blog Post number 1
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portfolio
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publications
Absolute Dimensions of the F-type Eclipsing Binary V2154 Cygni
Published in The Astrophysical Journal, 2017
Abstract: We report spectroscopic observations of the 2.63 day, detached, F-type main-sequence eclipsing binary V2154 Cyg. We use our observations together with existing uvby photometric measurements to derive accurate absolute masses and radii for the stars that are good to better than 1.5%. We obtain masses of {M}1=1.269+/- 0.017 {M}⊙ and {M}2=0.7542+/- 0.0059 {M}⊙ , radii of {R}1=1.477+/- 0.012 {R}⊙ and {R}2=0.7232+/- 0.0091 {R}⊙ , and effective temperatures of 6770 ± 150 K and 5020 ± 150 K for the primary and secondary stars, respectively. Both components appear to have their rotations synchronized with the motion in the circular orbit. A comparison of the properties of the primary with current stellar evolution models gives good agreement for a metallicity of [{Fe}/{{H}}]=-0.17, which is consistent with photometric estimates, and an age of about 2.2 Gyr. On the other hand, the K2 secondary is larger than predicted for its mass by about 4%. Similar discrepancies are known to exist for other cool stars, and are generally ascribed to stellar activity. The system is in fact an X-ray source, and we argue that the main site of the activity is the secondary star. Indirect estimates give a strength of about 1 kG for the average surface magnetic field on that star. A previously known close visual companion to V2154 Cyg is shown to be physically bound, making the system a hierarchical triple.
Minidisk Dynamics in Accreting, Spinning Black Hole Binaries: Simulations in Full General Relativity
Published in The Astrophysical Journal Letters, 2021
Abstract: We perform magnetohydrodynamic simulations of accreting, equal-mass binary black holes in full general relativity focusing on the impact of black hole spin on the dynamical formation and evolution of minidisks. We find that during the late inspiral the sizes of minidisks are primarily determined by the interplay between the tidal field and the effective innermost stable orbit around each black hole. Our calculations support that a minidisk forms when the Hill sphere around each black hole is significantly larger than the black hole’s effective innermost stable orbit. As the binary inspirals, the radius of the Hill sphere decreases, and minidisks consequently shrink in size. As a result, electromagnetic signatures associated with minidisks may be expected to gradually disappear prior to merger when there are no more stable orbits within the Hill sphere. In particular, a gradual disappearance of a hard electromagnetic component in the spectrum of such systems could provide a characteristic signature of merging black hole binaries. For a binary of given total mass, the timescale to minidisk “evaporation” should therefore depend on the black hole spins and the mass ratio. We also demonstrate that accreting binary black holes with spin have a higher efficiency for converting accretion power to jet luminosity. These results could provide new ways to estimate black hole spins in the future.
Minidisc influence on flow variability in accreting spinning black hole binaries: simulations in full general relativity
Published in mnras, 2023
Abstract: We perform magnetohydrodynamic simulations of accreting, equal-mass binary black holes in full general relativity focusing on the effect of spin and minidiscs on the accretion rate and Poynting luminosity variability. We report on the structure of the minidiscs and periodicities in the mass of the minidiscs, mass accretion rates, and Poynting luminosity. The accretion rate exhibits a quasi-periodic behaviour related to the orbital frequency of the binary in all systems that we study, but the amplitude of this modulation is dependent on the existence of persistent minidiscs. In particular, systems that are found to produce persistent minidiscs have a much weaker modulation of the mass accretion rate, indicating that minidiscs can increase the inflow time of matter on to the black holes, and dampen out the quasi-periodic behaviour. This finding has potential consequences for binaries at greater separations where minidiscs can be much larger and may dampen out the periodicities significantly.
Counter-rotation and slow precession in aligned eccentric nuclear discs due to gravitational wave recoil kicks
Published in mnras, 2024
Abstract: The M31 nucleus contains a supermassive black hole embedded in a massive stellar disc of apsidally aligned eccentric orbits. It has recently been show that this disc is slowly precessing at a rate consistent with zero. Here, we demonstrate using N-body methods that apsidally aligned eccentric discs can form with a significant ( ∼0.5) fraction of orbits counter-rotating as the result of a gravitational wave recoil kick of merging supermassive black holes. Higher amplitude kicks map to a larger retrograde fraction in the surrounding stellar population, which in turn results in slow precession. We furthermore show that discs wit significant counter-rotation are more stable (i.e. apsidal alignment is most pronounced and long lasting), more eccentric, and have the highest rates of stars entering the black hole’s tidal disruption radius.
talks
Talk 1 on Relevant Topic in Your Field
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Tutorial 1 on Relevant Topic in Your Field
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Talk 2 on Relevant Topic in Your Field
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Conference Proceeding talk 3 on Relevant Topic in Your Field
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teaching
ASTR 1200 - Stars and Galaxies
Undergraduate course, University of Colorado Boulder, Astrophysical and Planetary Sciences Department, 2023
In this course we will be taking a whirlwind tour of the universe. We will peruse the menu of the types of objects that make up the universe including stars, black holes, galaxies, and more! We will explore how these things form, their unique lifecycles, and their eventual fates. We will also explore the history of the entire universe itself and how it is evolving. Throughout this exploration, we will learn about how it is we know what we know, and how science allows us to answer complex questions that range outside of our everyday experience.
PHYS 116 - The Universe and Its Structure
Undergraduate course, Ginnell College, Physics Department, 2024
In this course we will be taking a whirlwind tour of the universe. We will explore our view of the universe from here on earth, and expand to peruse the menu of the types of objects that make up the universe including stars, black holes, galaxies, and more! We will explore how these things form, their unique lifecycles, and their eventual fates. We will also explore the history of the entire universe itself and how it is evolving. Throughout this exploration, we will learn about how it is we know what we know, and how science allows us to answer complex questions that range outside of our everyday experience.
PHYS 132 - Introductory Physics II
Undergraduate course, Ginnell College, Physics Department, 2024
This course is the second part of a yearlong, calculus-based introductory physics sequence, focusing on the application of physical principles, logical reasoning, and mathematical analysis to understand a broad range of electromagnetic phenomena. Topics include electricity, magnetism, light, and early atomic theory. This course meets for six hours each week and involves both classroom and laboratory work.
PHYS 131 - Introductory Physics I
Undergraduate course, Ginnell College, Physics Department, 2025
This course is the first part of a yearlong, calculus-based introductory physics sequence, focusing on the application of physical principles, logical reasoning, and mathematical analysis to understand a broad range of natural phenomena related to force and motion. Topics include Newtonian mechanics, conservation principles, gravity, and oscillation. This course meets for six hours each week and involves both classroom and laboratory work. This course follows the Workshop Physics model. The Workshop approach disposes of the lecture and lab dichotomy of the conventional approach to teaching introductory physics. As such, we will not have formal lectures, and you will use the class meetings for hands-on investigations of topics generally covered in the first semester of college physics.
PHYS 132L - Introductory Physics II Labratory
Undergraduate course, Ginnell College, Physics Department, 2025
Lab will be meeting weekly for approximately three hours. During the lab, you will gain hands-on experience working with the physics concepts covered in lecture. As part of this, you will also become practiced in conducting experiments and interpreting data.
PHYS 234L - Classical Mechanics - Computational Lab
Undergraduate course, Ginnell College, Physics Department, 2025
A study of analytical mechanics, including Lagrangian and Hamiltonian formalisms of particle dynamics, rigid body motion, and harmonic oscillations. Numerical methods laboratory taught in Python.