Description
During the last decade, the increase in survey depth, cadence, and sky coverage has led to a significant increase in the number of discovered supernovae (SNe), and more importantly the number of SNe discovered soon after explosion. Discovering SNe within days of explosion enables investigation into the outer density profile of progenitor stars, and/or the presence of significant circumstellar material. Understanding the presence and diversity of this progenitor material can lead to strong constraints on the latter stages of stellar evolution. I will discuss the early time light-curves of both Hydrogen-rich SNe type II (SNe~II) and Hydrogen-poor SNe~IIb observed by the ATLAS survey. For SNe~II, we compare light-curve properties with the presence or absence of early-time 'flash' ionisation features, finding evidence that those SNe~II with/without such spectra features show distinct light curve properties. These results suggest a link between early-time interaction and later-phase transient properties of SNe~II.
In the case of SNe~IIb, we characterise the presence and frequency of early-excess in SNe~IIb light curves. We find a frequency of early-excess light curves of a sample of 63 SNe~IIb of between ~30 and 40%. In addition, we find that those SNe~IIb displaying an early-excess light curve appear to have longer-duration light curves, implying a link between the presence of an extended envelope and the bulk properties of the progenitor (i.e. the ejecta mass). I end this contribution with discussion of theimplications of these observational results on the progenitors, stellar evolution pathways, and mass-loss histories of SNe~II and SNe~IIb.
