Publications
Gravitational-wave-moderated Accretion: The Case of ES Ceti
Coleman M. S. B., Venumadhav, T., Zackay, B., 2019, MNRAS, submitted
arXiv,
ADS
Solving the Riemann Problem for Realistic Astrophysical Fluids
Chen, Z.,
Coleman M. S. B., Blackman, E. G., Frank, A., 2018, JCP, 388, 490
arXiv,
ADS
Convection Enhances Magnetic Turbulence in AM CVn Accretion Disks
Coleman M. S. B., Blaes O., Hirose S., Hauschildt, P. H., 2018, 857, 52
arXiv,
ADS
Convective Quenching of Field Reversals in Accretion Disc Dynamos
Coleman M. S. B., Yerger E., Blaes O., Salvesen G., Hirose S., 2017, MNRAS, 467, 2625
arXiv,
ADS
Dwarf Nova Outbursts with Magnetorotational Turbulence
Coleman M. S. B., Kotko I., Blaes O., Lasota J.-P., Hirose S., 2016, MNRAS, 462, 3710
arXiv,
ADS
Convection Causes Enhanced Magnetic Turbulence in Accretion Disks in Outburst
Hirose S., Blaes O., Krolik J. H.,
Coleman M. S. B., Sano T., 2014, ApJ, 787, 1
arXiv,
ADS
See my SAO/NASA Astrophysics Data System listing.
orcid.org/0000-0001-5939-5957
Dissertation
Convection Affects Magnetic Turbulence in White Dwarf Accretion Disks
Links:
ProQuest/pdf
Abstract:
In this dissertation we focus on the accretion disks which surround accreting white dwarfs as they are some of the most abundant and well observed accretion disk systems. In many of these systems (e.g. dwarf novae), the accretion disk switches between a low luminosity state (quiescence) and a high luminosity state (outburst). These outbursts enable observers to place numeric constraints on the strength of turbulence (i.e. the α parameter) in these accretion disks. This dissertation focuses on results of local (stratified shearing-box) computer simulations of white dwarf accretion disks, and uses these results to gain a better theoretical understanding of these disks. As expected we find that the magnetorotational instability (MRI) is the predominant source of turbulence in these systems. However, we also find that hydrodynamic convection plays a key role as well. During the high luminosity state the disk becomes convectively unstable and the resulting convection enhances the MRI by seeding it with vertical magnetic field. This provides the first robust theoretical mechanism for enhancing turbulence only in outburst; a result required by observations. This convection also prevents the magnetic dynamo in our simulations from exhibiting the typical behavior of magnetic field reversals propagating vertically throughout the simulation. We also examine how the convection in our simulation changes the prior theoretical understanding of these disks. Specifically, we examine how these disks change luminosity over time by generating synthetic lightcurves using a modified disk instability model. These models can successfully reproduce observed outburst and quiescence durations, as well as outburst amplitudes. However, these lightcurves exhibit reflares in the decay from outburst, which are not generally observed in dwarf novae. Although, we highlight the problematic aspects of the quiescence physics in the disk instability model and MRI simulations that are responsible for this behavior.
Undergraduate Senior Thesis
The Evolution of Supernovae Embedded in Stellar Groups (PDF)
Abstract:
Supernovae (SNe) and the remnants they leave behind dramatically impact the
dynamics of the interstellar medium. They are also likely the source of all but the highest
energy cosmic rays, and they are the means by which heavy elements are produced and
disseminated. The standard model used for the evolution of supernova remnants (SNRs)
has been based on Woltjer’s (1972) simplistic model describing SNRs as spherical shells in
one of four distinct phases of expansion into uniform media. These phases have come to be
known as
free expansion, Sedov, adiabatic blast wave, radiative snowplow, and
dispersal. Yet
the evidence is strong that this cartoon is inadequate as a model for real SNR dynamics.
The distinct phases imagined by Woltjer may be brief or may not occur at all in a given
remnant. Further, SNRs are generally not spherical and do not interact with uniform
media. Thus, different dynamical stages may occur simultaneously within a single remnant,
and structures may be very complex. The observational and theoretical evidence of this
dynamical complexity seriously limits our ability to determine critical issues ranging from
SNR age determination to their role in establishing the structure of the ISM. This thesis
was conceived to address key questions regarding the evolution of supernovae embedded
in the complex environments found in and around young stellar groups by means of three
dimensional, hydrodynamical calculations. Because massive star progenitors in groups are
expected to have their close-in surroundings modified by the winds of their neighboring stars,we consider shocked winds as possible external media for supernova remnant evolution.
Abundant confirmation is provided here of the important notion that the morphology and
visibility of supernova remnants are determined largely by their circumstellar environments.