A5078016164- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Solar and Space Plasma Dynamics
- Astrophysical Phenomena and Observations
- Atmospheric Ozone and Climate
- Spectroscopy and Laser Applications
- Geomagnetism and Paleomagnetism Studies
- Ionosphere and magnetosphere dynamics
- Stuttering Research and Treatment
- Laser Design and Applications
- Adaptive optics and wavefront sensing
- Respiratory and Cough-Related Research
- Islanding Detection in Power Systems
- Voice and Speech Disorders
- Earthquake Detection and Analysis
- Particle accelerators and beam dynamics
- Methane Hydrates and Related Phenomena
- Magnetic confinement fusion research
- Pulsars and Gravitational Waves Research
- Advanced Fiber Laser Technologies
- Vibration and Dynamic Analysis
Central Michigan University
2025
Howard University
2020-2023
Deleted Institution
2020-2023
Goddard Space Flight Center
2022-2023
University of Delaware
2016-2021
Royal Military College of Canada
2014-2017
Queen's University
2013-2017
Florida Institute of Technology
2016-2017
Building Engineering and Science Talent
2016
Centre for Research in Astrophysics of Québec
2012
The MiMeS (Magnetism in Massive Stars) project is a large-scale, high-resolution, sensitive spectropolarimetric investigation of the magnetic properties O- and early B-type stars. Initiated 2008 completed 2013, was supported by three Large Program allocations, as well various programmes initiated independent principal investigators, archival resources. Ultimately, over 4800 circularly polarized spectra 560 O B stars were collected with instruments ESPaDOnS (Echelle SpectroPolarimetric Device...
ABSTRACT Numerous magnetic hot stars exhibit gyrosynchrotron radio emission. The source electrons were previously thought to be accelerated relativistic velocities in the current sheet formed middle magnetosphere by wind opening field lines. However, a lack of dependence luminosity on power, and strong rotation, has recently challenged this paradigm. We have collected all measurements early-type available literature. When constraints and/or rotational period are not available, we determined...
Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational-wave events involving spectacular black-hole mergers, indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding physics evolution stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observe 250 Z in ultraviolet (UV) with COS STIS...
Abstract Surface magnetic fields have a strong impact on stellar mass loss and rotation and, as consequence, the evolution of massive stars. In this work, we study influence an evolving dipolar surface fossil field with initial strength 4 kG characteristics 15 M⊙ solar metallicity models using Geneva code. Non-rotating rotating considering two different scenarios for internal angular momentum transport are computed, including evolution, mass-loss quenching, braking. Magnetic results in...
Rapidly rotating early-type stars with strong magnetic fields frequently show H$\alpha$ emission originating in Centrifugal Magnetospheres (CMs), circumstellar structures which centrifugal support due to magnetically enforced corotation of the confined plasma enables it accumulate high densities. It is not currently known whether CM escapes via Breakout (CB), or by an unidentified leakage mechanism. We have conducted first comprehensive examination properties all display CM-pattern emission....
Recently, high-precision optical 2~min cadence light curves obtained with \emph{TESS} for targets located in the mission's defined first four sectors have been released. The majority of these high-cadence and measurements currently span $\sim28\,{\rm d}$, thereby allowing periodic variability occurring on timescales $\lesssim14\,{\rm d}$ to potentially be detected. Magnetic chemically peculiar (mCP) A-type stars are well known exhibit rotationally modulated photometric that is produced by...
Light curves and periodograms of 160 B stars observed by the TESS space mission 29 main-sequence from Kepler K2 were used to classify variability type. There are 114 in sample, which 45 classified as possible rotational variables. This confirms previous findings that a large fraction (about 40 percent) A may exhibit modulation. Gaia DR2 parallaxes estimate luminosities, radii equatorial velocities can be deduced. It is shown values projected lower than estimated for nearly all stars, they...
In this paper we introduce the MOBSTER collaboration and lay out its scientific goals. We present first results based on analysis of nineteen previously known magnetic O, B A stars observed in 2-minute cadence sectors 1 2 Transiting Exoplanet Survey Satellite (TESS) mission. derive precise rotational periods from newly obtained light curves compare them to published values. also discuss overall photometric phenomenology massive intermediate-mass propose an observational strategy augment...
The time evolution of angular momentum and surface rotation massive stars is strongly influenced by fossil magnetic fields via braking. We present a new module containing simple, comprehensive implementation such field at the star within Modules for Experiments in Stellar Astrophysics (MESA) software instrument. test two limiting scenarios braking: distributing loss throughout first case, restricting to reservoir second case. perform systematic investigation rotational using grid OB models...
Mercury-manganese (HgMn) stars are late-B upper main sequence chemically peculiar distinguished by large overabundances of heavy elements, slow rotation, and frequent membership in close binary systems. These lack strong magnetic fields typical Bp but occasionally exhibit non-uniform surface distributions chemical elements. The physical origin the extent this spot formation phenomenon remains unknown. Here we use 2-min cadence light curves 64 HgMn observed TESS satellite during first two...
Uncertainties in stellar structure and evolution theory are largest for stars undergoing core convection on the main sequence. A powerful way to calibrate free parameters used of interiors is asteroseismology, which provides direct measurements angular momentum element transport. We report detection classification new variable O B using high-precision short-cadence (2-min) photometric observations assembled by Transiting Exoplanet Survey Satellite (TESS). In our sample 154 stars, we detect a...
In this paper, we describe an analysis of the MiMeS Survey O-type stars to explore range dipolar field strengths permitted by polarisation spectra that do not yield a magnetic detection. We directly model Stokes V profiles with topology using Bayesian inference. The noise statistics are in excellent agreement those null profiles. Using Monte-Carlo approach conclude which all our sample were host 100\,G, can be ruled out data. Furthermore, if no detection just below their limit, inferred...
ABSTRACT Magnetic fields can drastically change predictions of evolutionary models massive stars via mass-loss quenching, magnetic braking, and efficient angular momentum transport, which we aim to quantify in this work. We use the mesa software instrument compute an extensive main-sequence grid stellar structure evolution models, as well isochrones, accounting for effects attributed a surface fossil field. The is densely populated initial mass (3–60 M⊙), equatorial field strength (0–50 kG),...
The goal of this study was to investigate the relationship between respiratory discomfort and voice measures, including perceived vocal effort selected acoustic parameters. A secondary aim examine whether threat appraisal-measured as susceptibility experience fear suffocation-modulated these relationships. We hypothesized that greater dyspnea would predict worse outcomes, especially in speakers with susceptibility. Repeated measures study. Fifty-eight healthy females were submitted various...
We present the results of a systematic search for new rapidly oscillating Ap (roAp) stars using 2-min cadence data collected by Transiting Exoplanet Survey Satellite (TESS) during its Cycle 1 observations. identify 12 roAp stars. Amongst these we discover star with longest pulsation period, another shortest rotation and six multiperiodic variability. In addition to stars, an analysis 44 known observed TESS 1, providing first high-precision homogeneous sample significant fraction The...
We have carried out a study of radio emission from small sample magnetic O- and B-type stars using the Giant Metrewave Radio Telescope, with goal investigating their magnetospheres at low frequencies. These are lowest frequency measurements ever obtained hot stars. The observations were taken random rotational phases in 1390 610 MHz bands. Out 8 stars, we detect five both O-type observed only band, no detections obtained. explain this result as consequence free-free absorption by...
$\tau$ Sco, a well-studied magnetic B-type star in the Upper Sco association, has number of surprising characteristics. It rotates very slowly and shows nitrogen excess. Its surface field is much more complex than purely dipolar configuration which unusual for massive star. We employ CMFGEN radiative transfer code to determine fundamental parameters CNO helium abundances. Then, we MESA GENEC stellar evolution models accounting effects fields. To reconcile Sco's properties with single-star...
Abstract The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Based on a sample over 550 Galactic B and O-type stars, MiMeS has derived basic characteristics hot, massive stars. Herein we report preliminary results.
OB stars exhibit various types of spectral variability historically associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These features have been proposed to be caused either by magnetic fields or non-radial pulsations. In this second paper series, we revisit canonical phenomenological hydrodynamical modelling used explain formation DACs taking into account modern observations and more realistic theoretical predictions. Using constraints...
Massive stars play a significant role in the chemical and dynamical evolution of galaxies. However, much their variability, particularly during evolved supergiant stage, is poorly understood. To understand variability massive more detail, we present study O9.2Ib $\zeta$ Ori Aa, only currently confirmed to host magnetic field. We have obtained two-color space-based BRIght Target Explorer photometry (BRITE) for Aa two observing campaigns, as well simultaneous ground-based, high-resolution...
OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations. In this paper, we evaluate possible relation between large-scale, dipolar and DAC phenomenon investigating properties a sample 13 exhibiting well-documented behaviour. Using high-precision spectropolarimetric data acquired in part context Magnetism...
Despite their rarity, massive stars dominate the ecology of galaxies via strong, radiatively-driven winds throughout lives and as supernovae in deaths. However, evolution subsequent impact on environment can be significantly affected by presence a magnetic field. While recent studies indicate that about 7% OB Milky Way host stable, organised (fossil) fields at surfaces, little is known very stars, nor properties outside our Galaxy. We aim to continue searching for strong diverse set (VMS)...
We report detailed X-ray observations of the unique binary system $\epsilon$ Lupi, only known short-period consisting two magnetic early-type stars. The components have comparably strong, but anti-aligned fields. orbital and properties imply that magnetospheres overlap at all phases, suggesting possibility variable inter-star magnetospheric interaction due to non-negligible eccentricity orbit. To investigate this effect, we observed emission from Lupi both near away periastron passage, using...
In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent first ultraviolet spectra archetypal object. We examine variability its wind-sensitive resonance lines, comparing it to that other known stars. particular, observed variations in profiles CIV and SiIV doublets between low state high are largest any O-type star, consistent with expected properties 1624-2's magnetosphere. also observe a redshifted absorption component...
We conducted a survey of seven magnetic O and eleven B-type stars with masses above $8M_{\odot}$ using the Very Large Array in 1cm, 3cm 13cm bands. The resulted detection two stars. While detected O-type - HD 37742 47129 are binary systems, stars, 156424 ALS 9522, not known to be binaries. All four were at 3cm, whereas three 1cm only one star was 13cm. significantly more radio luminous than non-detected ones, which is case for non-detections interpreted as due thermal free-free absorption....