Investigating the properties of stripped-envelope supernovae; what are the implications for their progenitors?

We present observations and analysis of 18 stripped-envelope supernovae observed during 2013-2018. This sample consists of five H/He-rich SNe, six H-poor/He-rich SNe, three narrow lined SNe Ic, and four broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive ⁵⁶Ni and ejecta masses (M_Ni and M_ej). Additionally, the temperature evolution and spectral line velocity curves of each SN are examined. Analysis of the [O I] line in the nebular phase of eight SNe suggests their progenitors had initial masses <20 M_⊙. The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting data set gives the M_ej distribution for 80 SE-SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median M_ej, followed by narrow-lined SNe Ic, H/He-rich SNe, broad-lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of M_ej ranging from ∼1.2-11 M_⊙, considerably greater than any other subtype. For all SE-SNe <M_ej> = 2.8 ± 1.5 M_⊙ which further strengthens the evidence that SE-SNe arise from low-mass progenitors which are typically <5 M_⊙ at the time of explosion, again suggesting M_ZAMS <25 M_⊙. The low <M_ej> and lack of clear bimodality in the distribution implies <30 M_⊙ progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe.