SPITZER SPECTROSCOPY OF THE GALACTIC SUPERNOVA REMNANT G292.0+1.8: STRUCTURE AND COMPOSITION OF THE OXYGEN-RICH EJECTA
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States)
- Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States)
We present mid-infrared (mid-IR; 5-40 {mu}m) spectra of shocked ejecta in the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8, acquired with the Infrared Spectrograph onboard the Spitzer Space Telescope. The observations targeted two positions within the brightest oxygen-rich feature in G292.0+1.8. Emission lines of [Ne II] {lambda}12.8, [Ne III] {lambda}{lambda}15.5,36.0, [Ne V] {lambda}24.3, and [O IV] {lambda}25.9 {mu}m are detected from the shocked ejecta. In marked contrast to what is observed in Cassiopeia A, no discernible mid-IR emission from heavier species such as Mg, Si, S, Ar, or Fe is detected in G292.0+1.8. We also detect a broad emission bump between 15 and 28 {mu}m in spectra of the radiatively shocked O-rich ejecta in G292.0+1.8. We suggest that this feature arises from either shock-heated Mg{sub 2}SiO{sub 4} (forsterite) dust in the radiatively shocked O-rich ejecta or collisional excitation of polycyclic aromatic hydrocarbons in the blast wave of the SNR. If the former interpretation is correct, this would be the first mid-IR detection of ejecta dust in G292.0+1.8. A featureless dust continuum is also detected from nonradiative shocks in the circumstellar medium around G292.0+1.8. The mid-IR continuum from these structures, which lack mid-IR line emission, is seen in Chandra images as bright X-ray filaments, is well described by a two-component silicate dust model. The temperature of the hot dust component (M {sub d} {approx} 2 x 10{sup -3} M {sub sun}) is {approx}115 K, while that of the cold component (roughly constrained to be {approx}<3 M {sub sun}) is {approx}35 K. We attribute the hot component to collisionally heated dust in the circumstellar shocks in G292.0+1.8, and attribute the cold component to dust heated by the hard FUV radiation from the circumstellar shocks. Using average O/Ne and O/Si mass ratios measured for a sample of ejecta knots in the X-rays, our models yield line strengths consistent with mass ratios M {sub O}/M {sub Ne} {approx} 3, M {sub O}/M {sub Si} {approx}> 61, and M {sub O}/M {sub S} {approx} 50. These ratios (especially the large O/Ne mass ratio) are difficult to reproduce with standard nucleosynthesis models of well-mixed supernova ejecta. This reinforces the conclusions of existing X-ray studies that the reverse shock in G292.0+1.8 is currently propagating into the hydrostatic nucleosynthetic layers of the progenitor star, and has not yet penetrated the layers dominated by explosive nucleosynthetic products.
- OSTI ID:
- 21300699
- Journal Information:
- Astrophysical Journal, Vol. 696, Issue 2; Other Information: DOI: 10.1088/0004-637X/696/2/1307; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
COSMIC RADIATION
DUSTS
EMISSION
EXPLOSIONS
MASS
NUCLEOSYNTHESIS
OXYGEN
POLYCYCLIC AROMATIC HYDROCARBONS
SHOCK WAVES
SILICATES
SPECTRA
SPECTROSCOPY
STARS
SUPERNOVA REMNANTS
TELESCOPES