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We re-examine the classifications of supernovae (SNe) presented in the Lick Observatory Supernova Search (LOSS) volume-limited sample with a focus on the stripped-envelope SNe. The LOSS volume-limited sample, presented by Leaman et al. and Li et al., was calibrated to provide meaningful measurements of SN rates in the local universe; the results presented therein continue to be used for comparisons to theoretical and modeling efforts. Many of the objects from the LOSS sample were originally classified based upon only a small subset of the data now available, however, and recent studies have both updated some subtype distinctions and improved our ability to perform robust classifications, especially for stripped-envelope SNe. We re-examine the spectroscopic classifications of all events in the LOSS volume-limited sample (180 SNe and SN impostors) and update them if necessary. We discuss the populations of rare objects in our sample including broad-lined SNe Ic, Ca-rich SNe, SN 1987A-like events (we identify SN 2005io as SN 1987A-like here for the first time), and peculiar subtypes. The relative fractions of SNe Ia, SNe II, and stripped-envelope SNe in the local universe are not affected, but those of some subtypes are. Most significantly, after discussing the often unclear boundary between SNe Ib and Ic when only noisy spectra are available, we find a higher SN Ib fraction and a lower SN Ic fraction than calculated by Li et al.: spectroscopically normal SNe Ib occur in the local universe 1.7 0.9 times more often than do normal SNe Ic.

Kilonovae produced by the coalescence of compact binaries with at least one neutron star are promising standard sirens for an independent measurement of the Hubble constant ( H 0 ). Through their detection via follow-up of gravitational-wave (GW), short gamma-ray bursts (sGRBs) or optical surveys, a large sample of kilonovae (even without GW data) can be used for H 0 contraints. Here, we show measurement of H 0 using light curves associated with four sGRBs, assuming these are attributable to kilonovae, combined with GW170817. Including a systematic uncertainty on the models that is as large as the statistical ones, we find H 0 = 73 . 8 − 5.8 + 6.3 km s − 1 Mpc − 1 and H 0 = 71 . 2 − 3.1 + 3.2 km s − 1 Mpc − 1 for two different kilonova models that are consistent with the local and inverse-distance ladder measurements. For a given model, this measurement is about a factor of 2-3 more precise than the standard-siren measurement for GW170817 using only GWs. Kilonovae observations can be used to out constraints on the Hubble constant (H0). Here, the authors show H0 measurements by combining light curves of four short gamma-ray burts with GW170817 are about a factor of 2-3 more precise than the standard-siren measurements using only gravitational-waves.

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion 1 , 2 , 3 . Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova 4 , 5 is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0–G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.

How supernovae shape up Supernovae have been subjected to extensive study over the years, particularly since the discovery of their involvement with γ-ray bursts. But there are still some basic questions about them that remain unanswered, for instance, what shape are they? Explosion geometry has been a difficult subject to tackle because supernovae in other galaxies are so distant that they remain point-like in our night sky. Now observations of SN 2004dj, the closest normal Type II-P supernova ever observed, show that the innermost regions of the expanding ejecta are severely distorted, the result of an explosion mechanism that is strongly nonspherical. This property may be inherent to the core-collapse process in all types of supernovae. Multi-epoch spectropolarimetry of a supernova reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta — roughly 90 days after explosion. An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities 1 , associations of supernovae with long-soft γ-ray bursts 2 , 3 , and asymmetries in late-time emission-line profiles 4 . Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry 5 , 6 . Large polarizations have been measured for ‘stripped-envelope’ (that is, type Ic; ref. 7 ) supernovae, which confirms their non-spherical morphology 8 , 9 ; but the explosions of massive stars with intact hydrogen envelopes 7 , 10 (type II-P supernovae) have shown only weak polarizations at the early times observed 11 , 12 . Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (∼90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.

We present Keck spectropolarimetry of the unusual Type Ia supernova (SN Ia) 2005hk several days before maximum light. An analysis of the high signal‐to‐noise ratio total‐flux spectrum shows the object’s extreme similarity to the peculiar SN 2002cx. SN 2005hk has an optical spectrum dominated by Feiiilines and only weak lines of intermediate‐mass elements, unlike a normal SN Ia at this epoch. The photospheric velocity measured from the minima of strong absorption lines is very low for an SN Ia (∼6000 km s−1), solidifying the connection to SN 2002cx. The spectrum‐synthesis code SYNOW was used to identify the presence of iron‐peak elements, intermediate‐mass elements, and possibly unburned carbon at similar velocities in the outer ejecta of SN 2005hk. Many weak spectral features remain unidentified. The spectropolarimetry shows a low level of continuum polarization (∼0.4%) after correction for the interstellar component, and only a weak Feiiiline feature is detected. The level of continuum polarization is normal for an SN Ia, implying that the unusual features of SN 2005hk cannot be readily explained by large asymmetries.

We present optical photometric and spectral data of the peculiar Type Ic supernova SN 2002ap. Photometric coverage includesUBVRIbands from 2002 January 30, the day after discovery, through 2002 December 12. There are five early‐time spectra and eight in the nebular phase. We determine that SN 2002ap is similar to SN 1997ef and the gamma‐ray burst–associated SN 1998bw with respect to spectral and photometric characteristics. The nebular spectra of SN 2002ap present the largest Mgi] λ4571 to [Oi] λλ6300, 6364 ratio of any supernova spectra yet published, suggesting that the progenitor of SN 2002ap was a highly stripped star. Comparing the nebular spectra of SN 1985F and SN 2002ap, we notice several similar features, casting the classification of SN 1985F as a normal Type Ib supernova in doubt. We also present nebular modeling of SN 2002ap and find that the object ejected ≳1.5M ⊙of material within the outer velocity shell of the nebula (∼5500 km s−1) and synthesized ∼0.09M ⊙of56Ni.

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.

The detection of the luminous, blue progenitor system of the type Iax supernova 2012Z suggests that this supernova was the explosion of a white dwarf accreting material from a helium-star companion. A type Iax supernova progenitor SN 2012Z, discovered in the Lick Observatory Supernova Search on 29 January 2012, is a type Iax supernova. Sometimes referred to as 'mini supernovae', these are initially spectroscopically similar to some type-Ia supernovae but diverge with time and are much less energetic and fainter. It is not clear what triggers a type Iax explosion. This paper reports the detection of a progenitor in deep observations of NGC 1309, the host galaxy of SN 2012Z, obtained with the Hubble Space Telescope and including the location of the supernova before its explosion. Its optical properties and similarity to the progenitor of the helium nova V445 Puppis suggest that SN 2012Z was probably an explosion of a white dwarf accreting from a helium-star companion. Type Iax supernovae are stellar explosions that are spectroscopically similar to some type Ia supernovae at the time of maximum light emission, except with lower ejecta velocities 1 , 2 . They are also distinguished by lower luminosities. At late times, their spectroscopic properties diverge from those of other supernovae 3 , 4 , 5 , 6 , but their composition (dominated by iron-group and intermediate-mass elements 1 , 7 ) suggests a physical connection to normal type Ia supernovae. Supernovae of type Iax are not rare; they occur at a rate between 5 and 30 per cent of the normal type Ia rate 1 . The leading models for type Iax supernovae are thermonuclear explosions of accreting carbon–oxygen white dwarfs that do not completely unbind the star 8 , 9 , 10 , implying that they are ‘less successful’ versions of normal type Ia supernovae, where complete stellar disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type Iax SN 2012Z in deep pre-explosion imaging. The progenitor system's luminosity, colours, environment and similarity to the progenitor of the Galactic helium nova V445 Puppis 11 , 12 , 13 suggest that SN 2012Z was the explosion of a white dwarf accreting material from a helium-star companion. Observations over the next few years, after SN 2012Z has faded, will either confirm this hypothesis or perhaps show that this supernova was actually the explosive death of a massive star 14 , 15 .

Here we present previously unpublished optical spectra of supernova (SN) 2001ig, a Type IIb SN, from about a week after explosion until nearly one year later. The earliest spectrum consists of only a few broad absorption features, but soon more common Type II SN features including hydrogen P Cygni profiles and helium absorption become apparent. At later times, as the H features fade and the Heiabsorption becomes more prominent, we observe the SN to transition from a Type II to a Type Ib. Finally, observations after 250 days past explosion show a nebular-phase SN spectrum with one of the largest magnesium to oxygen intensity ratios ever seen. Additionally, we present models of the late-time spectra which indicate that the inner ejecta consist of∼1.15 M ⊙ ∼ 1.15     M ⊙ of material, most of which (by mass) is in the form of oxygen, with∼0.13 M ⊙ ∼ 0.13     M ⊙ of 56Ni Ni 56 and essentially no hydrogen.

Located on the campus of the Thacher School in Southern California, the Thacher Observatory has a legacy of astronomy research and education that dates back to the late 1950s. In 2016, the observatory was fully renovated with upgrades including a new 0.7 m telescope, a research grade camera, and a slit dome with full automation capabilities. The low-elevation site is bordered by the Los Padres National Forest and therefore affords dark to very dark skies allowing for accurate and precise photometric observations. We present a characterization of the site including sky brightness, weather, and seeing, and we demonstrate the on-sky performance of the facility. Our primary research programs are based around our multi-band photometric capabilities and include photometric monitoring of variable sources, a nearby supernova search and followup program, a quick response transient followup effort, and exoplanet and eclipsing binary light curves. Select results from these programs are included in this work which highlight the broad range of science available to an automated observatory with a moderately sized telescope.