Stephen Scott Lawrence

STIS spectral imaging of hot spots in SNR 1987A

We report on Space Telescope Imaging Spectrograph (STIS) 52X2 G750M spectra of SNR 1987A obtained in 2000 May, and compared with nearly-identical observations taken in 1997 April. Such carefully-matched observations allow for a clean subtraction of the inner equatorial ring (ER) emission and an improved measurement of the hot spot fluxes. We present Hα fluxes and line widths for the seven hot spots clearly detected in the 2000 May data. We also provide the first description of spatially-compact emission associated with HS 1-029 which spans wide wavelength ranges of the G140L, G230L, G430L and G750L spectra taken in 1999 September and October. We suggest that this apparent continuum most likely arises from free-bound, free-free, and two-photon decay transitions in H I.

New imaging results in the formation of SNR 1987A

We report HST imaging results of the equatorial circumstellar ring (ER) and its interaction with the ejecta (i.e. hot spots) of SN 1987A. Using archival and DD WFPC2 and STIS imaging, we study the ER morphology, produce multi-wavelength light curves of the first hot spot and spatially-resolved light curves for the ER in broad and narrow bands. The first hot spot grows with a power law t∼3 until late 1999, where it appears to be turning over. Spatially-resolved light curves for the ER reveal that the flux is brighter, and fades more rapidly to the North (nearer to Earth) than to the South, indicating a possible density gradient in the ring.

The structure of SN 1987A’s outer circumstellar envelope as probed by light echoes

We present ground-based and HST images processed by image subtraction to highlight transient reflection nebulae or “light echoes” of the maximum light pulse of the explosion of SN 1987A from surrounding material. Along with numerous structures already discussed elsewhere, we have found (in multiple epochs of data) a new feature opposite the SN from the mysterious “Napoleon’s Hat” which indicates a symmetric structure due to shocks internal to the SN’s red supergiant wind and probably caused by the pile-up of gas due to differential velocities within the outflow. We also show how echoes betray the ram pressure distribution of the progenitor mass loss flow.