Daniel J. Patnaude’s research while affiliated with Center for Astrophysics Harvard & Smithsonian and other places

We report the results of deep H α and [O iii ] images of the bright WN6/WC4 Wolf–Rayet (WR) star WR 8 (HD 62910). These data show considerably more surrounding nebulosity than seen in prior imaging. The brighter portions of the nebula span ≃ 6 ′ in diameter and exhibit considerable fine-scale structure including numerous emission clumps and bright head-tail-like features, presumably due to the effects of the WR star’s stellar winds. Due to the overlap of a relatively bright band of unrelated foreground diffuse interstellar H α emission, WR 8’s nebula is best viewed via its [O iii ] emission. A faint 9 ′ × 1 3 ′ diffuse outer nebulosity is detected surrounding the nebula’s main ring of emission. Comparison of the nebula’s optical structure with that seen in Wide-field Infrared Survey Explorer 22 μ m data shows a similarly clumpy structure but within a better-defined emission shell of thermal continuum from dust. The infrared shell is coincident with the nebula’s southern [O iii ] emissions but is mainly seen in the fainter outer portions of the northern [O iii ] emission clumps. It is this greater radial distance of dust emission in the nebula’s northern areas that leads to a striking off-center position of the WR star from the IR shell.

We report the results of deep H-alpha and [O III] images of the bright WN7/WC4 Wolf-Rayet star WR 8 (HD 62910). These data show considerably more surrounding nebulosity than seen in prior imaging. The brighter portions of the nebula span 6' in diameter and exhibit considerable fine-scale structure including numerous emission clumps and bright head-tail like features presumably due to the effects of the WR star's stellar winds. Due to the overlap of a relatively bright band of unrelated foreground diffuse interstellar H-alpha emission, WR 8's nebula is best viewed via its [O III] emission. A faint 9' x 13' diffuse outer nebulosity is detected surrounding the nebula's main ring of emission. The nebula's optical structure is substantially different from that of its thermal continuum dust emission seen in WISE 22 micron infrared images which show a smaller and sharply defined emission shell.

When the ejecta of a supernova (SN) interact with the progenitor star's circumstellar environment, a strong shock is driven back into the ejecta, causing the material to become bright optically and in X-rays. Most notably, as the shock traverses the H-rich envelope, it begins to interact with metal-rich material. Thus, continued monitoring of bright and nearby SNe provides valuable clues about both the progenitor structure and its pre-SN evolution. Here we present late-time, multiepoch optical and Chandra X-ray spectra of the core-collapse SN, SN 1996cr. Magellan IMACS optical spectra taken in 2017 July and 2021 August show a very different spectrum from that seen in 2006 with broad, double-peaked optical emission lines of oxygen, argon, and sulfur with expansion velocities of ±4500 km s ⁻¹ . Redshifted emission components are considerably fainter compared to the blueshifted components, presumably due to internal extinction from dust in the SN ejecta. Broad ±2400 km s ⁻¹ H α is also seen, which we infer is shocked progenitor pre-SN, mass-loss, H-rich material. Chandra data indicate a slow but steady decline in the overall X-ray luminosity, suggesting that the forward shock has broken through any circumstellar shell or torus, which is inferred from prior deep Chandra ACIS-S/HETG observations. The X-ray properties are consistent with what is expected from a shock breaking out into a lower-density environment. Though originally identified as a Type IIn SN, based upon late-time optical emission-line spectra, we argue that the SN 1996cr progenitor was partially or highly stripped, suggesting a Type IIb/Ib SN.

Using optical and near-infrared images of the Cassiopeia A (Cas A) supernova remnant covering the time period 1951 to 2022, together with optical spectra of selected filaments, we present an investigation of Cas A's reverse shock velocity and the effects it has on the remnant's metal-rich ejecta. We find the sequence of optical ejecta brightening and the appearance of new optical ejecta indicating the advancement of the remnant's reverse shock in the remnant's main shell has velocities typically between 1000 and 2000 km/s, which is ~1000 km/s less than recent measurements made in X-rays. We further find the reverse shock appears to move much more slowly and is nearly even stationary in the sky frame along the remnant's western limb. However, we do not find the reverse shock to move inward at velocities as large as ~2000 km/s as has been reported. Optical ejecta in Cas A's main emission shell have proper motions indicating outward tangential motions ~3500 - 6000 km/s, with the smaller values preferentially along the remnant's southern regions which we speculate may be partially the cause of the remnant's faint and more slowly evolving southern sections. Following interaction with the reverse shock, ejecta knots exhibit extended mass ablated trails 0.2" - 0.5" in length leading to extended emission indicating reverse shock induced decelerated velocities as large as 1000 km/s. Such ablated material is most prominently seen in higher ionization line emissions, whereas denser parts of ejecta knots show surprisingly little deceleration.

When the ejecta of supernovae interact with the progenitor star's circumstellar environment, a strong shock is driven back into the ejecta, causing the material to become bright optically and in X-rays. Most notably, as the shock traverses the H-rich envelope, it begins to interact with metal rich material. Thus, continued monitoring of bright and nearby supernovae provides valuable clues about both the progenitor structure and its pre-supernova evolution. Here we present late-time, multi-epoch optical and Chandra} X-ray spectra of the core-collapse supernova SN 1996cr. Magellan IMACS optical spectra taken in July 2017 and August 2021 show a very different spectrum from that seen in 2006 with broad, double-peaked optical emission lines of oxygen, argon, and sulfur with expansion velocities of $\pm 4500$ km s$^{-1}$. Red-shifted emission components are considerably fainter compared to the blue-shifted components, presumably due to internal extinction from dust in the supernova ejecta. Broad $\pm 2400$ km s$^{-1}$ H$\alpha$ is also seen which we infer is shocked progenitor pre-SN mass-loss, H-rich material. Chandra data indicate a slow but steady decline in overall X-ray luminosity, suggesting that the forward shock has broken through any circumstellar shell or torus which is inferred from prior deep Chandra ACIS-S/HETG observations. The X-ray properties are consistent with what is expected from a shock breaking out into a lower density environment. Though originally identified as a SN IIn, based upon late time optical emission line spectra, we argue that the SN 1996cr progenitor was partially or highly stripped, suggesting a SN IIb/Ib.

The degree to which Type Ia Supernova (SN Ia) progenitors modify their surroundings remains an open question. In this work, we explore the parameter space for circumstellar interaction in Type Ia Supernova Remnant (SNR) 0519−69.0 by comparing observed archival Chandra spectra with model SNR spectra calculated assuming different SN Ia explosion scenarios and ambient medium (AM) structures. We compared SNR models expanding into a uniform AM with those expanding into a post-common envelope cocoon generated from a planetary nebula model. We conclude that the X-ray spectra and bulk dynamics of SNR 0519−69.0 are best explained by an interaction with a planetary nebula cocoon, implying that the progenitor of this SN Ia went through a common envelope episode shortly (~10,000 yr) before the SN explosion.

We investigate SN 2014C using three-dimensional (3D) hydrodynamic modeling, focusing on its early interaction with a dense circumstellar medium (CSM). Our objective is to uncover the pre-supernova (SN) CSM structure and constrain the progenitor star’s mass-loss history prior to core collapse. Our comprehensive model traces the evolution from the progenitor star through the SN event and into the SN remnant phase. We simulate the remnant’s expansion over approximately 15 yr, incorporating a CSM derived from the progenitor star’s outflows through dedicated hydrodynamic simulations. Analysis reveals that the remnant interacted with a dense toroidal nebula extending from 4.3 × 10 ¹⁶ to 1.5 × 10 ¹⁷ cm in the equatorial plane, with a thickness of approximately 1.2 × 10 ¹⁷ cm. The nebula’s density peaks at approximately 3 × 10 ⁶ cm ⁻³ at the inner boundary, gradually decreasing as ≈ r ⁻² at greater distances. This nebula formed due to intense mass loss from the progenitor star between approximately 5000 and 1000 yr before collapse. During this period, the maximum mass-loss rate reached about 8 × 10 ⁻⁴ M ⊙ yr ⁻¹ , ejecting ≈2.5 M ⊙ of stellar material into the CSM. Our model accurately reproduces Chandra and NuSTAR spectra, including the iron (Fe) K line, throughout the remnant’s evolution. Notably, the Fe line is self-consistently reproduced, originating from shocked ejecta, with ≈0.05 M ⊙ of pure-Fe ejecta shocked during the remnant–nebula interaction. These findings suggest that the 3D geometry and density distribution of the CSM, as well as the progenitor star’s mass-loss history, align with a scenario where the star was stripped through binary interaction, specifically common-envelope evolution.

(Abridged) Core-collapse supernova remnants (SNRs) display complex morphologies and asymmetries, reflecting anisotropies from the explosion and early interactions with the circumstellar medium (CSM). Spectral analysis of these remnants can provide critical insights into supernova (SN) engine dynamics, the nature of progenitor stars, and the final stages of stellar evolution, including mass-loss mechanisms in the millennia leading up to the SN. This white paper evaluates the potential of the Line Emission Mapper (LEM), an advanced X-ray probe concept proposed in response to NASA 2023 APEX call, to deliver high-resolution spectra of SNRs. Such capabilities would allow detailed analysis of parent SNe and progenitor stars, currently beyond our possibilities. We employed a hydrodynamic model that simulates the evolution of a neutrino-driven SN from core-collapse to a 2000-year-old mature remnant. This model successfully replicates the large-scale properties of Cassiopeia A at an age of about 350 years. Using this model, we synthesized mock LEM spectra from different regions of the SNR, considering factors like line shifts and broadening due to plasma bulk motion and thermal ion motion, deviations from ionization and temperature equilibrium, and interstellar medium absorption. Analyzing these mock spectra with standard tools revealed LEM impressive capabilities. We demonstrated that fitting these spectra with plasma models accurately recovers the line-of-sight velocity of the ejecta, enabling 3D structure exploration of shocked ejecta, similar to optical methods. LEM also distinguishes between Doppler and thermal broadening of ion lines and measures ion temperatures near the limb of SNRs, providing insights into ion heating at shock fronts and cooling in post-shock flows. This study highlights LEM potential to advance our understanding of core-collapse SN dynamics and related processes.