Properties of the Optical Hot Spots in the Circumstellar Ring of SN 1987A

Abstract: The proximity of Supernova 1987A provides a great opportunity to study the aftermath of the impact of the ejecta with the dense clumps (observed as ”hot spots”) located in the equatorial circumstellar ring. This thesis examines the properties of the clumps by using Hubble Space Telescope optical imaging taken with the F625W and F675W broad filters between 1994 and 2022. The centroids and widths of the spots are measured by a 2-dimensional fitting of their intensities. These are subsequently used to determine the evolution of the spots. The analysis shows that the spots are radially expanding initially with velocities from 140 km s⁻¹ up to ∼ 1700 km s⁻¹. This wide range of velocities could imply a wide range of densities for the clumps. There is evidence that the spots are slowing down after ∼ 7000 days, which might be a consequence of the blast wave leaving the ring. The acceleration of the spots remains undetectable, indicating that it might be happening in faster times than the observational time scale of one year. Data further suggest that the brightest spots are spatially resolved with projected diameters of (3 − 5) × 10¹⁶ cm. It is hinted that the spots are increasing in size after the impact, suggesting that new gas is being swept up, though the dissolution of the spots might also be responsible for this effect. A rough mass estimate for the resolved spots of order 10⁻² M⊙ is inferred from the measured widths and an upper limit of 1.6 M⊙ on the mass of the shocked gas in the clumps in the whole ring. These estimates though depend on the geometry and composition idealizations used.