The Temperature and Ionization of Unshocked Ejecta in Cas A

Abstract

The supernova remnant Cassiopeia A (Cas A) is one of the few remnants in which it is possible to observe unshocked ejecta. A deep 1.64 micron image of Cas A shows a patch of diffuse emission from unshocked ejecta, as well as brighter emission from Fast-Moving Knots and Quasi-Stationary Flocculi. Emission at 1.64 micron is usually interpreted as [Fe II] emission, and spectra of the bright knots confirm this by showing the expected emission in other [Fe II] lines. We performed NIR spectroscopy on the diffuse emission region and found that the unshocked ejecta emission does not show those lines, but rather the [Si I] 1.607 micron line. This means that the 1.64 micron line from the unshocked ejecta may be the [Si I] 1.645 line from the same upper level, rather than [Fe II]. We find that the [Si I] line is formed by recombination, and we use the [Si I] to [Si II] ratio to infer a temperature about 100 K, close to the value assumed for analysis of low frequency radio absorption and that inferred from emission by cool dust. Our results constrain estimates of Cas A's total mass of unshocked ejecta that are extremely sensitive to temperature assumptions, but they do not resolve the ambiguity due to clumping.

arXiv comment16 pages, 1 table, 4 figures

References in corpus (35)

• Explosion Mechanisms of Core-Collapse Supernovae
• Scattering by Interstellar Dust Grains: Optical and Ultraviolet
• CHIANTI - An atomic database for Emission Lines. Version 8
• On the magnetic fields and particle acceleration in Cas A
• The Cassiopeia A Supernova was of Type IIB
• Nucleosynthesis and Mixing in Cassiopeia A
• The Expansion Center and Dynamical Age of the Galactic Supernova Remnant Cassiopeia A
• A Chandra X-ray Survey of Ejecta in the Cassiopeia A Supernova Remnant
• The Three-Dimensional Structure of Cassiopeia A
• X-ray spectral imaging and Doppler mapping of Cassiopeia A
• Production and Distribution of ${}^{44}$Ti and ${}^{56}$Ni in a Three-dimensional Supernova Model Resembling Cassiopeia A
• The dust mass in Cassiopeia A from a spatially resolved Herschel analysis
• A Detailed Kinematic Map of Cassiopeia A's Optical Main Shell and Outer High-Velocity Ejecta
• Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta
• The Bubble-like Interior of the Core-Collapse Supernova Remnant Cassiopeia A
• Phosphorus in the Young Supernova Remnant Cassiopeia A
• Spitzer Spectral Mapping of Supernova Remnant Cassiopeia A
• The 3-D Structure of SN 1987A's inner Ejecta
• MMT & Magellan Infrared Spectrograph
• Dust masses for SN 1980K, SN1993J and Cassiopeia A from red-blue emission line asymmetries
• The Three-Dimensional Structure of Interior Ejecta in Cassiopeia A at High Spectral Resolution
• The Density and Mass of Unshocked Ejecta in Cassiopeia A through Low Frequency Radio Absorption
• MARCS-Model Stellar Atmospheres, and Their Application to the Photometric Calibration of the Spitzer-IRS
• An HST Survey of the Highest-Velocity Ejecta in Cassiopeia A
• The Reddening Towards Cassiopeia A's Supernova: Constraining the 56Ni Yield
• Infrared [Fe II] Emission Lines from Radiative Atomic Shocks
• Low-Frequency Radio Absorption in Cassiopeia A
• iPTF15eqv: Multi-wavelength Exposé of a Peculiar Calcium-rich Transient
• Fine-structure infrared lines from the Cassiopeia A knots
• Data Reduction Pipeline for the MMT and Magellan Infrared Spectrograph
• Matter mixing in aspherical core-collapse supernovae: a search for possible conditions for conveying ${}^{56}$Ni into high velocity regions
• Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A
• Interaction between Cassiopeia A and Nearby Molecular Clouds
• Near-Infrared Knots and Dense Fe Ejecta in the Cassiopeia A Supernova Remnant
• On the continuum radio-spectrum of Cas A: possible evidence of the non-linear particle acceleration

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• The mass, location and heating of the dust in the Cassiopeia A supernova remnant
• Element Abundances in the Unshocked Ejecta of Cassiopeia A
• Dust survival rates in clumps passing through the Cas A reverse shock -- II. The impact of magnetic fields
• Dust destruction and survival in the Cassiopeia A reverse shock
• A Sub-Solar Metallicity Progenitor for Cassiopeia A, the remnant of a Type IIb Supernova
• Low-frequency radio absorption in Tycho's supernova remnant
• Free-free absorption parameters of Cassiopeia A from low-frequency interferometric observations
• He abundance of Dense Circumstellar Clumps in the Cassiopeia A Supernova Remnant
• Near-Infrared Spectroscopy of Dense Ejecta Knots in the Outer Eastern Area of the Cassiopeia A Supernova Remnant
• Multi-antenna probing of absorbing regions inside and outside Cassiopeia A