Spitzer's final Infrared Array Camera observations of SN 1987A show the 3.6 and 4.5 m emission from the equatorial ring (ER) continues a period of steady decline. Deconvolution of the images reveals ...that the emission is dominated by the ring, not the ejecta, and is brightest on the west side. Decomposition of the marginally resolved emission also confirms this, and shows that the west side of the ER has been brightening relative to the other portions of the ER. The infrared morphological changes resemble those seen in both the soft X-ray emission and the optical emission. The integrated ER light curves at 3.6 and 4.5 m are more similar to the optical light curves than the soft X-ray light curve, though differences would be expected if dust is responsible for this emission and its destruction is rapid. Future observations with the James Webb Space Telescope will continue to monitor the ER evolution, and will reveal the true spectrum and nature of the material responsible for the broadband emission at 3.6 and 4.5 m. The present observations also serendipitously reveal a nearby variable source, subsequently identified as a Be star, that has gone through a multiyear outburst during the course of these observations.
We present infrared photometry of the WC8 Wolf-Rayet system WR 48a observed with telescopes at the European Southern Observatory, the South African Astronomical Observatory and the Anglo Australian ...Telescope between 1982 and 2011, which show a slow decline in dust emission from the previously reported outburst in 1978-79 until about 1997, when significant dust emission was still evident. This was followed by a slow rise, accelerating to reach and overtake the first (1978) photometry, demonstrating that the outburst observed in 1978-79 was not an isolated event, but that they recur at intervals of 32+ years. This suggests that WR 48a is a long-period dust maker and colliding-wind binary. The locus of WR 48a in the (H−L), K colour-magnitude diagram implies that the rate of dust formation fell between 1979 and about 1997 and then increased steadily until 2011. Superimposed on the long-term variation are secondary ('mini') eruptions in (at least) 1990, 1994, 1997, 1999 and 2004, characteristic of relatively brief episodes of additional dust formation. Spectra show evidence for an Oe or Be companion to the WC8 star, supporting the suggestion that WR 48a is a binary system and indicating a system luminosity consistent with the association of WR 48a and the young star clusters Danks 1 and Danks 2. The range of dust formation suggests that these stars are in an elliptical orbit having e∼ 0.6. The size of the orbit implied by the minimum period, together with the WC wind velocity and likely mass-loss rate, implies that the post-shock WC wind is adiabatic throughout the orbit - at odds with the observed dust formation. A similar conflict is observed in the 'pinwheel' dust-maker WR 112.
We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a five year period spanning the epochs between days {approx}6000 and 8000 since the explosion. The supernova (SN) ...has evolved into a supernova remnant and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from {approx}180 K silicate dust, collisionally heated by the hot X-ray emitting gas with a temperature and density of {approx}5 x 10{sup 6} K and {approx}3 x 10{sup 4} cm{sup -3}, respectively. The mass of the radiating dust is {approx}1.2 x 10{sup -6} M{sub sun} on day 7554 and scales linearly with IR flux. Comparison of the IR data with the soft X-ray flux derived from Chandra observations shows that the IR-to-X-ray flux ratio, IRX, is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of IRX is most consistent with the scenario that very little grain processing or gas cooling has occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased by a factor of {approx}5 with a time dependence of t'{sup 0.87{+-}0.20}, t' being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER, as also suggested by X-ray observations. The constant spectral shape of the IR emission provides strong constraints on the density and temperature of the shocked gas in which the interaction takes place. Silicate grains, with radii of {approx}0.2 {mu}m and temperature of T {approx} 180 K, best fit the spectral and temporal evolution of the {approx}8-30 {mu}m data. The IR spectra also show the presence of a secondary population of very small, hot (T {approx}> 350 K), featureless dust. If these grains spatially coexist with the silicates, then they must have shorter lifetimes. The data show slightly different rates of increase of their respective fluxes, lending some support to this hypothesis. However, the origin of this emission component and the exact nature of its relation to the silicate emission is still a major unsolved puzzle.
We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow ( Delta *Dv ~ 300 ...km s--1) emission lines from the circumstellar ring, broad ( Delta *Dv ~ 10-20 X 103 km s--1) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise ratio (>40 per resolution element) broad Ly Delta *a emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at Delta *l > 1350 A can be explained by H I two-photon (2s 2 S 1/2-1s 2 S 1/2) emission from the same region. We confirm our earlier, tentative detection of N V Delta *l1240 emission from the reverse shock and present the first detections of broad He II Delta *l1640, C IV Delta *l1550, and N IV Delta *l1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ? 0.06. The N V/H Delta *a line ratio requires partial ion-electron equilibration (Te /Tp 0.14-0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring.
Multiwavelength observations of supernova remnant 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared (IR), and radio wavelengths as the blast wave from the ...explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed IR radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray-emitting plasma component of the shocked gas. Spitzer Infrared Spectrograph spectra at 5-30 mum taken on day 6190 since the explosion show that the emission arises from image of silicate grains radiating at a temperature of image K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard Large Magellanic Cloud dust abundances. IRX has decreased by a factor of image2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding supernova blast wave on dynamic timescales. Detailed models consistent with the observed dust temperature, the ionization timescale of the soft X-ray emission component, and the evolution of IRX suggest that the radiating silicate grains are immersed in a image K plasma with a density of image cm super(-3) and have a size distribution that is confined to a narrow range of radii between 0.023 and 0.22 mum. Smaller grains may have been evaporated by the initial UV flash from the supernova.
The equatorial ring of Supernova (SN) 1987A has been exposed to forward shocks from the SN blast wave, and it has been suggested that these forward shocks have been causing ongoing destruction of ...dust in the ring. We obtained Stratospheric Observatory For Infrared Astronomy The Faint Object InfraRed CAmera for the SOFIA Telescope (FORCAST) 11.1, 19.7, and 31.5 |$\mu \rm m$| photometry of SN 1987A in 2016. Compared with Spitzer measurements 10 yr earlier, the 31.5 |$\mu \rm m$| flux has significantly increased. The excess at 31.5 |$\mu \rm m$| appears to be related to the Herschel 70 |$\mu \rm m$| excess, which was detected 5 yr earlier. The dust mass needed to account for the 31.5–70 |$\mu \rm m$| excess is 3–7 × 10^−4 M_⊙, more than 10 times larger than the ring dust mass (∼1 × 10^−5 M_⊙) estimate from the data 10 yr earlier. We argue that dust grains are re-formed or grown in the post-shock regions in the ring after forward shocks have destroyed pre-existing dust grains in the ring and released refractory elements into gas. In the post-shock region, atoms can stick to surviving dust grains, and the dust mass may have increased (grain growth), or dust grains might have condensed directly from the gas. An alternative possibility is that the outer part of the expanding ejecta dust might have been heated by X-ray emission from the circumstellar ring. The future development of this excess could reveal whether grains are reformed in the post-shocked region of the ring or eject dust is heated by X-ray.
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