A sample of Type II-L supernovae

Abstract

What are Type II-Linear supernovae (SNe II-L)? This class, which has been ill\ndefined for decades, now receives significant attention -- both theoretically,\nin order to understand what happens to stars in the ~15-25Mo range, and\nobservationally, with two independent studies suggesting that they cannot be\ncleanly separated photometrically from the regular hydrogen-rich SNe II-P\ncharacterised by a marked plateau in their light curve. Here, we analyze the\nmulti-band light curves and extensive spectroscopic coverage of a sample of 35\nSNe II and find that 11 of them could be SNe II-L. The spectra of these SNe are\nhydrogen deficient, typically have shallow Halpha absorption, may show indirect\nsigns of helium via strong OI 7774 absorption, and have faster line velocities\nconsistent with a thin hydrogen shell. The light curves can be mostly\ndifferentiated from those of the regular, hydrogen-rich SNe II-P by their\nsteeper decline rates and higher luminosity, and we propose as a defining\nphotometric characteristic the decline in the V band: SNe II-L seem to decline\nby more than 0.5 mag from peak brightness by day 50 after explosion. Using our\nsample we provide template light curves for SNe II-L and II-P in 4 photometric\nbands.\n