David H. Cohen
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View article: K-QA: A Real-World Medical Q&A Benchmark
K-QA: A Real-World Medical Q&A Benchmark Open
Ensuring the accuracy of responses provided by large language models (LLMs) is crucial, particularly in clinical settings where incorrect information may directly impact patient health. To address this challenge, we construct K-QA, a datas…
View article: Addressing Outstanding Problems in the Physics of Massive Stars with the Line Emission Mapper X-ray Probe
Addressing Outstanding Problems in the Physics of Massive Stars with the Line Emission Mapper X-ray Probe Open
We present some of the salient aspects of the scientific motivation for high resolution soft X-ray spectroscopy of early-type stars with the Line Emission Mapper X-ray Probe. The major strength of {\it LEM} for hot star physics is its larg…
View article: KELT-25 b and KELT-26 b: A Hot Jupiter and a Substellar Companion Transiting Young A Stars Observed by TESS
KELT-25 b and KELT-26 b: A Hot Jupiter and a Substellar Companion Transiting Young A Stars Observed by TESS Open
We present the discoveries of KELT-25 b (TIC 65412605, TOI-626.01) and KELT-26 b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A stars. The transit signals were initially detected by the KELT sur…
View article: Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system ϵ Lupi
Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system ϵ Lupi Open
We report detailed X-ray observations of the unique binary system ϵ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital …
View article: Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $ε$ Lupi
Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $ε$ Lupi Open
We report detailed X-ray observations of the unique binary system $ε$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbita…
View article: Helium-like X-ray line complexes show that the hottest plasma on the O supergiant ζ Puppis is in its wind
Helium-like X-ray line complexes show that the hottest plasma on the O supergiant ζ Puppis is in its wind Open
We present an analysis of Chandra grating spectra of key helium-like line complexes to put constraints on the location with respect to the photosphere of the hottest (T ≳ 6 × 106 K) plasma in the wind of the O supergiant ζ Pup and to explo…
View article: <i>Chandra</i> grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption
<i>Chandra</i> grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption Open
We present a uniform analysis of six examples of embedded wind shock (EWS) O star X-ray sources observed at high resolution with the Chandra grating spectrometers. By modelling both the hot plasma emission and the continuum absorption of t…
View article: Adapting to the Digital Age: Strategic Change in the Pulp and Paper Sector
Adapting to the Digital Age: Strategic Change in the Pulp and Paper Sector Open
With the rise of the internet and electronic media, the first two decades of the 21st century have seen a rapid decline in demand for graphic paper. This study examines the strategic actions pulp and paper companies have been taking to ada…
View article: <i>Chandra</i> spectral measurements of the O supergiant ζ Puppis indicate a surprising increase in the wind mass-loss rate over 18 yr
<i>Chandra</i> spectral measurements of the O supergiant ζ Puppis indicate a surprising increase in the wind mass-loss rate over 18 yr Open
New long Chandra grating observations of the O supergiant ζ Pup show not only a brightening of the X-ray emission line flux of 13 per cent in the 18 yr since Chandra’s first observing cycle, but also clear evidence – at more than 4σ signif…
View article: MOBSTER: Establishing a Picture of Magnetic Massive Stars as a Population
MOBSTER: Establishing a Picture of Magnetic Massive Stars as a Population Open
Magnetic massive and intermediate-mass stars constitute a separate population whose properties are still not fully understood. Increasing the sample of known objects of this type would help answer fundamental questions regarding the origin…
View article: Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties -- The MOBSTER Collaboration
Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties -- The MOBSTER Collaboration Open
In this contribution, we present the MOBSTER Collaboration, a large community effort to leverage high-precision photometry from the Transiting Exoplanet Survey Satellite (\textit{TESS}) in order to characterize the variability of magnetic …
View article: Magnetic OB[A] Stars with TESS: probing their Evolutionary and\n Rotational properties -- The MOBSTER Collaboration
Magnetic OB[A] Stars with TESS: probing their Evolutionary and\n Rotational properties -- The MOBSTER Collaboration Open
In this contribution, we present the MOBSTER Collaboration, a large community\neffort to leverage high-precision photometry from the Transiting Exoplanet\nSurvey Satellite (\\textit{TESS}) in order to characterize the variability of\nmagne…
View article: Business Transformation in the British Columbia Forest Industry
Business Transformation in the British Columbia Forest Industry Open
This study aims to define the emerging concept of firm-level business transformation from the perspective of British Columbia-based forest sector executives, and to investigate its drivers, enablers, and barriers. The ten executives interv…
View article: Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties (MOBSTER) – I. First-light observations of known magnetic B and A stars
Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties (MOBSTER) – I. First-light observations of known magnetic B and A stars Open
In this paper we introduce the MOBSTER collaboration and lay out its scientific goals. We present first results based on the analysis of 19 previously known magnetic O, B, and A stars observed in 2-min cadence in sectors 1 and 2 of the Tra…
View article: KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin
KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin Open
We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright ( V ∼ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of days, a radius of , and a relativel…
View article: Extreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star
Extreme resonance line profile variations in the ultraviolet spectra of NGC 1624-2: probing the giant magnetosphere of the most strongly magnetized known O-type star Open
In this paper, we present high-resolution HST/COS observations of the extreme\nmagnetic O star NGC 1624-2. These represent the first ultraviolet spectra of\nthis archetypal object. We examine the variability of its wind-sensitive\nresonanc…
View article: The KELT Follow-up Network and Transit False-positive Catalog: Pre-vetted False Positives for TESS
The KELT Follow-up Network and Transit False-positive Catalog: Pre-vetted False Positives for TESS Open
The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. The KELT images have a pixel scale of ∼23″ pixel −1 —very similar to that of N…
View article: Magnetic massive stars as progenitors of ‘heavy’ stellar-mass black holes
Magnetic massive stars as progenitors of ‘heavy’ stellar-mass black holes Open
Journal Articles
View article: Magnetic B stars observed with BRITE: Spots, magnetospheres, binarity, and pulsations
Magnetic B stars observed with BRITE: Spots, magnetospheres, binarity, and pulsations Open
Magnetic B-type stars exhibit photometric variability due to diverse causes, and consequently on a variety of timescales. In this paper we describe interpretation of BRITE photometry and related ground-based observations of 4 magnetic B-ty…
View article: Magnetic B stars observed with BRITE: Spots, magnetospheres, binarity,\n and pulsations
Magnetic B stars observed with BRITE: Spots, magnetospheres, binarity,\n and pulsations Open
Magnetic B-type stars exhibit photometric variability due to diverse causes,\nand consequently on a variety of timescales. In this paper we describe\ninterpretation of BRITE photometry and related ground-based observations of 4\nmagnetic B…
View article: A JVLA survey of the high-frequency radio emission of the massive magnetic B- and O-type stars
A JVLA survey of the high-frequency radio emission of the massive magnetic B- and O-type stars Open
We conducted a survey of seven magnetic O and eleven B-type stars with masses\nabove $8M_{\\odot}$ using the Very Large Array in the 1cm, 3cm and 13cm bands.\nThe survey resulted in a detection of two O and two B-type stars. While the\ndet…
View article: A multi-wavelength view of NGC 1624-2
A multi-wavelength view of NGC 1624-2 Open
Large magnetometric surveys have contributed to the detection of an increasing number of magnetic massive stars, and to the recognition of a population of magnetic massive stellar objects with distinct properties. Among these, NGC 1624-2 p…
View article: Testing the Wind-shock Paradigm for B-Type Star X-Ray Production with θ Car
Testing the Wind-shock Paradigm for B-Type Star X-Ray Production with θ Car Open
We present Chandra X-ray grating spectroscopy of the B0.2V star, θ Carina. θ Car is in a critical transition region between the latest O-type and earliest B-type stars, where some stars are observed to have UV-determined wind densities muc…
View article: IAU volume 12 issue S329 Cover and Front matter
IAU volume 12 issue S329 Cover and Front matter Open
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View article: KELT-17B: A HOT-JUPITER TRANSITING AN A-STAR IN A MISALIGNED ORBIT DETECTED WITH DOPPLER TOMOGRAPHY
KELT-17B: A HOT-JUPITER TRANSITING AN A-STAR IN A MISALIGNED ORBIT DETECTED WITH DOPPLER TOMOGRAPHY Open
We present the discovery of a hot Jupiter transiting the V = 9.23 mag main-sequence A-star KELT-17 (BD+14 1881). KELT-17b is a , hot-Jupiter in a 3.08-day period orbit misaligned at −115.°9 ± 4.°1 to the rotation axis of the star. The plan…
View article: An ‘analytic dynamical magnetosphere’ formalism for X-ray and optical emission from slowly rotating magnetic massive stars
An ‘analytic dynamical magnetosphere’ formalism for X-ray and optical emission from slowly rotating magnetic massive stars Open
Slowly rotating magnetic massive stars develop "dynamical magnetospheres"\n(DM's), characterized by trapping of stellar wind outflow in closed magnetic\nloops, shock heating from collision of the upflow from opposite loop\nfootpoints, and …
View article: Creating an X-ray Nebula in the Laboratory: Spectral Diagnostics of Neon Photoionization Experiments on the Z-Machine
Creating an X-ray Nebula in the Laboratory: Spectral Diagnostics of Neon Photoionization Experiments on the Z-Machine Open
Presented 1/7/2003 at the American Astronomical Society Meeting.