Richard Ignace
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View article: X-Ray Polarimetry of Accreting White Dwarfs: A Case Study of EX Hydrae
X-Ray Polarimetry of Accreting White Dwarfs: A Case Study of EX Hydrae Open
We present the first first X-ray polarization measurements of a white dwarf (WD), the intermediate polar EX Hya. We measured significant polarization only in the 2–3 keV energy band with a polarization degree of 8% at a 3 σ significance. N…
View article: Chandra/HETG and NuSTAR Observations of V750 Ara, a <i>γ</i> Cas-type Star
Chandra/HETG and NuSTAR Observations of V750 Ara, a <i>γ</i> Cas-type Star Open
We present a 197 ks HETG and 95 ks NuSTAR spectra of the γ Cas-type object V750 Ara. The high-resolution X-ray spectra show that the target is similar to other objects of this class. Data are interpreted under the assumption that the X-ray…
View article: Polarization from Rapidly Rotating Massive Stars
Polarization from Rapidly Rotating Massive Stars Open
Stellar rotation has long been recognized as important to the evolution of stars, by virtue of the chemical mixing it can induce and how it interacts with binary mass transfer. Binary interaction and rapid rotation are both common in massi…
View article: Methods to Test the Source of the Extreme Gas Motions in WS 35
Methods to Test the Source of the Extreme Gas Motions in WS 35 Open
We present theoretical arguments toward the plausibility of a stellar wind to explain the 16,000 km s −1 line broadening in the optical spectra of WS 35, the central star in the Pa 30 nebula. The wind model is discussed in the context of s…
View article: Finite Star Factors with Stellar Limb Darkening for Optically Thin Dipole Scattering in Circumstellar Envelopes
Finite Star Factors with Stellar Limb Darkening for Optically Thin Dipole Scattering in Circumstellar Envelopes Open
A calculation for the finite star correction factors with stellar limb darkening is presented. The application is for dipole scattering, such as free electrons or Rayleigh scattering, in the context of optically thin envelopes that scatter…
View article: Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region?
Variable Polarization of WR 31a: Binary Companion or Corotating Interaction Region? Open
WR 31a (Hen 3-519) is likely a postluminous blue variable (LBV) star that is evolving to become a classical Wolf–Rayet star. Multicolor (UBVR) photopolarimetric observations of WR 31a were obtained over nine nights in early-2007. The linea…
View article: Analyzing Stellar and Interstellar Contributions to Polarization: Modeling Approaches for Hot Stars
Analyzing Stellar and Interstellar Contributions to Polarization: Modeling Approaches for Hot Stars Open
Linear polarimetry of unresolved stars is a powerful method for discerning or constraining the geometry of a source and its environment, since spherical sources produce no net polarization. However, a general challenge to interpreting intr…
View article: Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars
Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars Open
Spectropolarimetric techniques are a mainstay of astrophysical inquiry, ranging from Solar System objects to the Cosmic Background Radiation. This review highlights applications of stellar polarimetry for massive hot stars, particularly in…
View article: Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars
Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars Open
Spectropolarimetric techniques are a mainstay of astrophysical inquiry, ranging from Solar System objects to the Cosmic Background Radiation. This review highlights applications of stellar polarimetry for massive hot stars, particularly in…
View article: X-Shooting ULLYSES: Massive stars at low metallicity
X-Shooting ULLYSES: Massive stars at low metallicity Open
Context . Mass loss governs the evolution of massive stars and shapes the stellar surroundings. To quantify the impact of the stellar winds, we need to know the exact mass-loss rates; however, empirical constraints on the rates are hampere…
View article: Optical Polarimetry of WR 1 Consistent with a CIR and 17 days Rotation
Optical Polarimetry of WR 1 Consistent with a CIR and 17 days Rotation Open
New visible-band linear polarimetry of the star WR 1 (HD 4004) is presented. This early N-rich Wolf–Rayet star has previously been reported as harboring a Corotating Interaction Region structure threading its wind, implying a stellar rotat…
View article: A Time-dependent Spectral Analysis of γ Cassiopeiae
A Time-dependent Spectral Analysis of γ Cassiopeiae Open
We investigated the temporal and spectral features of γ Cassiopeiae’s X-ray emission within the context of the white dwarf (WD) accretion hypothesis. We find that the variabilities present in the X-ray data show two different signals, one …
View article: Astronomy in Appalachia: Five Lessons in Designing a Planetarium Show
Astronomy in Appalachia: Five Lessons in Designing a Planetarium Show Open
Cultural Astronomy sits at the intersection of our study of the universe and the human experience, exploring how we observe the stars, interpret their motions, and incorporate them into our perspectives of the nature of reality. "Astronomy…
View article: The Polstar UV Spectropolarimetry Mission
The Polstar UV Spectropolarimetry Mission Open
The Polstar small explorer concept is for an ultraviolet (UV) spectropolarimetry space telescope mission with a focus on massive star astrophysics. The instrument waveband will be from 115 nm - 286 nm for spectroscopy and 122 nm - 286 nm f…
View article: X-Shooting ULLYSES: Massive stars at low metallicity
X-Shooting ULLYSES: Massive stars at low metallicity Open
On the route toward merging neutron stars and stripped-envelope supernovae, binary population synthesis predicts a large number of post-interaction systems with massive stars that have been stripped of their outer layers. However, observat…
View article: Chandra HETG X-Ray Spectra and Variability of π Aqr, a γ Cas-type Be Star
Chandra HETG X-Ray Spectra and Variability of π Aqr, a γ Cas-type Be Star Open
High-resolution X-ray spectra of π Aqr, a γ Cas-type star, obtained with the Chandra/HETG spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe; a strong, hard continuum; and a lack of He-like ions, indicating the prese…
View article: Chandra HETG X-ray Spectra and Variability of $π$ Aqr, a $γ$ Cas-type Be star
Chandra HETG X-ray Spectra and Variability of $π$ Aqr, a $γ$ Cas-type Be star Open
High-resolution X-ray spectra of $π\,$Aqr, a $γ\,$Cas-type star, obtained with the Chandra/HETG grating spectrometer, revealed emission lines of H-like ions of Mg, Si, S, and Fe, a strong, hard continuum, and a lack of He-like ions, indica…
View article: Using CHIRON spectroscopy to test the hypothesis of a precessing orbit for the WN4 star EZ CMa
Using CHIRON spectroscopy to test the hypothesis of a precessing orbit for the WN4 star EZ CMa Open
The bright WN4 star EZ CMa exhibits a 3.77 d periodicity in photometry, spectroscopy, and polarimetry, but the variations in the measurements are not strictly phase-locked, exhibiting changes in reference times, amplitudes, and the shape o…
View article: Using CHIRON Spectroscopy to Test the Hypothesis of a Precessing Orbit for the WN4 star EZ CMa
Using CHIRON Spectroscopy to Test the Hypothesis of a Precessing Orbit for the WN4 star EZ CMa Open
The bright WN4 star EZ CMa exhibits a 3.77 day periodicity in photometry, spectroscopy, and polarimetry but the variations in the measurements are not strictly phase-locked, exhibiting changes in reference times, amplitudes, and the shape …
View article: Modeling Variable Linear Polarization Produced by Co-Rotating Interaction Regions (CIRs) Across Optical Recombination Lines of Wolf-Rayet Stars
Modeling Variable Linear Polarization Produced by Co-Rotating Interaction Regions (CIRs) Across Optical Recombination Lines of Wolf-Rayet Stars Open
Massive star winds are structured both stochastically ("clumps") and often coherently (Co-rotation Interaction Regions, or CIRs). Evidence for CIRs threading the winds of Wolf-Rayet (WR) stars arises from multiple diagnostics including lin…
View article: The RS Oph Outburst of 2021 Monitored in X-Rays with NICER
The RS Oph Outburst of 2021 Monitored in X-Rays with NICER Open
The 2021 outburst of the symbiotic recurrent nova RS Oph was monitored with the Neutron Star Interior Composition Explorer Mission (NICER) in the 0.2–12 keV range from day one after the optical maximum, until day 88, producing an unprecede…
View article: Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra
Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra Open
Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds…
View article: Survey of X-rays from Massive Stars Observed at High Spectral Resolution with Chandra
Survey of X-rays from Massive Stars Observed at High Spectral Resolution with Chandra Open
Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds…
View article: The RS Oph outburst of 2021 monitored in X-rays with NICER
The RS Oph outburst of 2021 monitored in X-rays with NICER Open
The 2021 outburst of the symbiotic recurrent nova RS Oph was monitored with the Neutron Star Interior Composition Explorer Mission (NICER) in the 0.2-12 keV range from day one after the optical maximum, until day 88, producing an unprecede…
View article: A multiyear photopolarimetric study of the semi-regular variable V CVn and identification of analog sources
A multiyear photopolarimetric study of the semi-regular variable V CVn and identification of analog sources Open
The semi-regular variable star V Canum Venaticorum (V CVn) is well known for its unusual linear polarization position angle (PA). Decades of observing V CVn reveal a nearly constant PA spanning hundreds of pulsation cycles. This phenomenon…
View article: A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources
A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources Open
The semi-regular variable star V Canum Venaticorum (V CVn) is well-known for its unusual linear polarization position angle (PA). Decades of observing V CVn reveal a nearly constant PA spanning hundreds of pulsation cycles. This phenomenon…
View article: Data Files of "A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources"
Data Files of "A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources" Open
The semi-regular variable star V Canum Venaticorum (V CVn) is well-known for its unusual linear polarization position angle (PA). Decades of observing V CVn reveal a nearly constant PA spanning hundreds of pulsation cycles. This phenomenon…
View article: Data Files of "A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources"
Data Files of "A Multi-Year Photopolarimetric Study of the Semi-Regular Variable V CVn and Identification of Analogue Sources" Open
The semi-regular variable star V Canum Venaticorum (V CVn) is well-known for its unusual linear polarization position angle (PA). Decades of observing V CVn reveal a nearly constant PA spanning hundreds of pulsation cycles. This phenomenon…
View article: X-Shooting ULLYSES: Massive stars at low metallicity
X-Shooting ULLYSES: Massive stars at low metallicity Open
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 ow…
View article: UV spectropolarimetry with Polstar: massive star binary colliding winds
UV spectropolarimetry with Polstar: massive star binary colliding winds Open