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We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within 1 day of explosion…

I present an overview of optical observations (mostly spectra) of Type II supernovae. SNe II are defined by the presence of hydrogen, and exhibit a very wide variety of properties. SNe II-L tend to show evidence of late-time interaction…

Over-luminous type Ia supernovae (SNe Ia) show peculiar observational features, for which an explosion of a super-massive white dwarf (WD) beyond the classical Chandrasekhar-limiting mass has been suggested, largely based on their high…

We set sensitive upper limits to the X-ray emission of four Type Ia supernovae (SNe Ia) using the Chandra X-ray Observatory. SN 2002bo, a normal, although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an absorbed, high…

It has been widely accepted that Type Ia supernovae (SNe Ia) are thermonuclear explosions of a CO white dwarf. However, the natures of the progenitor system(s) and explosion mechanism(s) are still unclarified. Thanks to the recent…

We present very early, high-cadence photometric observations of the nearby Type Ia SN 2017cbv. The light curve is unique in that it has a blue bump during the first five days of observations in the U, B, and g bands, which is clearly…

We present late-time spectra of eight Type Ia supernovae (SNe Ia) obtained at $>200$ days after peak brightness using the Gemini South and Keck telescopes. All of the SNe Ia in our sample were nearby, well separated from their host galaxy's…

Variable NaI absorption lines have been reported in a number of type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a giant donor star may be the progenitors of these SNeIa…

Type Ia supernovae (SNe Ia) are important cosmological tools, probes of binary star evolution, and contributors to cosmic metal enrichment; yet, a definitive understanding of the binary star systems that produce them remains elusive. In…

I present an overview of optical observations (mostly spectra) of Type II, Ib, and Ic supernovae (SNe). SNe II are defined by the presence of hydrogen, and exhibit a very wide variety of properties. SNe II-L tend to show evidence of…

The Type Ia supernova (SN Ia) 2013dy in NGC 7250 (d ~ 13.7 Mpc) was discovered by the Lick Observatory Supernova Search. Combined with a prediscovery detection by the Italian Supernova Search Project, we are able to constrain the…

We present a study of the continuum polarization over the 400--600 nm range of 19 Type Ia SNe obtained with FORS at the VLT. We separate them in those that show Na I D lines at the velocity of their hosts and those that do not. Continuum…

In this paper, we present extensive optical and ultraviolet (UV) observations of the type Ia supernova (SN Ia) 2013gs discovered during the Tsinghua-NAOC Transient Survey. The photometric observations in the optical show that the light…

We present photometric and spectroscopic observations of the nearby Type Ia SN 2019yvq, from its discovery $\sim$1 day after explosion to $\sim$100 days after its peak brightness. This SN exhibits several unusual features, most notably an…

As part of the European Supernova Collaboration we obtained extensive photometry and spectroscopy of the type Ia SN 2002dj covering epochs from 11 days before to nearly two years after maximum. Detailed optical and near-infrared…

We present the spectral evolution, light curve, and corresponding interpretation for the "normal-bright" Type Ia Supernova 2005cg discovered by ROTSE-IIIc. The host is a low-luminosity (M_r = -16.75), blue galaxy with strong indications of…

SN 2013dy is a Type Ia supernova for which we have compiled an extraordinary dataset spanning from 0.1 to ~ 500 days after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with HST/STIS, 47 epochs of…

While O is often seen in spectra of Type Ia supernovae (SNe Ia) as both unburned fuel and a product of C burning, C is only occasionally seen at the earliest times, and it represents the most direct way of investigating primordial white…

The properties of the highest velocity ejecta of normal Type Ia supernovae (SNe Ia) are studied via models of very early optical spectra of 6 SNe. At epochs earlier than 1 week before maximum, SNe with a rapidly evolving Si II 6355 line…

There is a wide consensus that type Ia supernovae (SN Ia) originate from the thermonuclear explosion of CO white dwarfs (WD), with the lack of hydrogen in the observed spectra as a distinctive feature. Here, we present SN 2016jae, which was…