It is well-known that some massive stars evolve to an end state which results in the collapse of the stellar core, as the hydrostatic pressure can no longer support gravity, leading to powerful explosions called supernovae (SNe). Even with over 6000 known SNe, we have only direct information about the progenitor star for a handful of explosions. Here, I summarise the observational constraints of the massive progenitor stars of several core-collapse supernovae.

A few core collapse supernovae progenitors have been found to be yellow or blue supergiants. Weshall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of corecollapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at theend of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristicsfor what concerns their surface compositions, rotational surface velocities and pulsational properties with respect toblue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weightedgravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solarmasses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well asthe small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massivestars and therefore on the end point of their evolution.

Type Ib/c supernovae (SNe Ib/c) are characterized by the lack of prominent hydrogen lines in thespectra, implying that their progenitors have lost most of their hydrogen envelopes by the time of the iron corecollapse. Binary interactions provide an important evolutionary chanel for SNe Ib/c, and recent observations indicatethat the inferred ejecta masses of SNe Ibc are more consistent with the prediction of the binary scenario than that ofthe single star scenario that invokes mass loss as the key evolutionary factor for SNe Ib/c progenitors. So far,theoretical predictions on the detailed properties of SNe Ib/c progenitors in binary systems have been made mostlywith models using solar metallicity. However, unlike the single star scenario, where SNe Ib/c are expected only forsufficiently high metallicity, hydrogen-deficent SN progenitors can be produced via binary interactions at anymetallicity. In this talk, I will discuss theoretical predictions on the metallicity dependence of the SNe Ib/c progenitorstructure, based on evolutionary models of massive binary stars. Sepefically, I will address how the ejecta masses ofSNe Ib and Ic and the ratio of SN Ib/c to SN IIb as well as SN Ib to SN Ic would systematically change as a function ofmetallicity, and which new types of SNe are expected in binary systems at low metallicity.

Core-collapse supernovae (SNe) are the final act in the evolution of stars more massive than about 8–9 solar masses. Determining the progenitors of these explosive events and how massive stars are linked to the different SN types are topics of major significance for several fields of astrophysics. Recent progress in observational techniques now allow for rapid-response spectroscopic observations of SNe within a day of detection Gal-Yam et al. (2014). This allows the study of early phases when the SN shock front has not yet reached spatial scales of 1014 cm. Depending on the progenitor's wind density and SN shock front velocity, these early-time SN observations may probe epochs early enough that the dense parts of the progenitor wind and circumstellar medium (CSM) have not yet been overrun by the SN shock front.

Massive stars at low metallicity are strong candidates for two of the most energetic explosions in the Universe: long duration gamma-ray bursts and superluminous supernovae. But what is the reason these explosions prefer low metallicity environments? To answer this question, we investigate how massive stellar evolution proceeds in low metallicity environments.

The evolution of massive stars after the main sequence is not very well known from a theoretical point of view. Recent studies have shown that the way internal mixing processes, such as rotation and convection, are implemented in stellar evolution codes lead to significant discrepancies between the predictions of these codes. Particularly, the end-points of stellar evolution can be considerably different, making hard to understand the evolutionary path the lead to the observed supernovae progenitors.

During a supernova explosion, fluid instabilities are generated because the star is in a hydrodynamically unstable situation, which is like the effects of stirring a fire or blowing air into a hot grill. The resulting mixing of the supernova ejecta may be observable. Here, we briefly discuss the multidimensional simulations of supernovae from very massive stars.

Recent searches for supernova II-P progenitors in external galaxies have led to the identification of red objects with magnitudes and colours indicative of red supergiants, in most cases implying quite low luminosities, and hence masses. Current results would suggest that all explosions come from objects less massive than ~ 18 M⊙ and that some explosions come from stars with masses well below 10 M⊙. Stellar models, on the other hand, can only produce explosions from objects more massive than > 9 M⊙. What does our knowledge of local red supergiants tell us about the expected properties of such objects? We present the results of complementary large spectroscopic surveys and detailed studies of open clusters that point to substantially different observational characteristics depending on metallicity.

We present results from the LCOGT Supernova Key Project, a three year program to obtain lightcurves and spectra of 600 supernovae. The Las Cumbres Observatory Global Telescope Network is a network of eleven robotic 1m and 2m telescopes located at 5 sites around the world. With this facility long term monitoring of transient phenomena is possible, as are nearly instantaneous observations. We report on both core-collapse and thermonuclear supernovae observed within days of explosion, allowing insight into their progenitor stars.

We have aggregated together data available in the literature, or analysed by us, to compute the lightcurves of most young supernovae (SNe) that have been detected in X-rays. Currently the database contains about 60 SNe spanning all the various types, but it is expanding rapidly. We use this library of lightcurves and spectra to explore the diversity of SNe, the characteristics of the environment into which they are expanding, and the implications for their progenitors. X-ray spectra can provide insight into the density structure, composition and metallicity of the surrounding medium, and the ionization level, through the spectra themselves as well as the X-ray absorption. Since core-collapse SNe expand mainly in environments created by the progenitor star mass-loss, this can provide crucial information about the nature of the progenitor star, and its mass-loss parameters in the decades or centuries before its death. In a few cases, via detailed modelling, we can distinguish the composition of the SN ejecta from that of the environment. X-ray observations therefore provide an invaluable probe into the stellar environments of core-collapse SNe, complementing data available at other wavelengths. We provide an overview of the X-ray lightcurves of various SN types, the implications for their environment, and clues to their progenitor stars.

Theory and observation strongly favor the notion that asymmetric explosions drive core-collapse supernovae, but where and how this asymmetry becomes introduced is uncertain. The most likely places of origin are in the explosion mechanism itself or the interior structure of the star into which the explosion proceeds. Investigating the recently uncovered bubble-like interiors of young, nearby supernova remnants may provide a way to unravel which of these competing processes dominate.

Do cycles of violent, intense, but short-lived bursts constitute a significant mode of global starformation in present-day galaxies? Such events can have a profound effect on galaxies, particularly those with shallowpotential wells, and observational measures of their prevalence inform our understanding of a wide range of issues ingalaxy evolution. I will highlight what we have learned about starbursts from multi-wavelength observations of galaxiesin the local volume on both galactic and smaller scales, and explore how connections with the study of the deaths ofmassive stars may further our understanding of open issues in galaxy evolution.

I review the recent observational progresses of star-forming galaxies at a redshift up to z~10. Inconjunction with gravitational lensing magnifications, deep HST observations obtain first density estimates of UV continuum radiation given by young massive stars, and reveal that the star-formation rate density (SFRD)continuously decreases from z~2-3 to z~10. This SFRD decrease towards high-z should be explained by thecombination of the cosmic structure formation and radiative cooling+feedback effects in a halo. To decouple thecontribution of the cosmic structure formation from the SFRD decrease, the stellar-to-halo mass ratios (SHMR) ofhigh-z galaxies are derived by intensive clustering analyses with HST and Subaru survey data. The SHMR-halo massrelation shows a clear evolution from z~0 to 6, suggesting that the cooling and feedback effects are different betweenthe present and early epochs of the cosmic history. By deep imaging and spectroscopic observations, feedbacksignatures are found in 10-100 kpc-scale outflow of ionized oxgen gas identified around star-forming galaxies with andwithout an AGN heating. There are similarly-large hydrogen Lyα halos and blobs associated with high-z star-forminggalaxies, but the physical origin of these Lyα halos and blobs is an open question. At z≳6, UV radiation of ionizingphotons produced by star-forming galaxies contribute to the cosmic reionization, while it is thought that the UVradiation prevent formation of next generation stars in dwarf galaxies at the early cosmic epoch, which works as acosmological feedback effect. I discuss this reionizations cosmological feedback effect with the up-to-date resultsfrom the HST and Planck data.

Gamma-ray burst host galaxies are deficient in molecular gas, and show anomalous metal-poor regions close to GRB positions. Using recent Australia Telescope Compact Array (ATCA) Hi observations we show that they have substantial atomic gas reservoirs. This suggests that star formation in these galaxies may be fuelled by recent inflow of metal-poor atomic gas. While this process is debated, it can happen in low-metallicity gas near the onset of star formation because gas cooling (necessary for star formation) is faster than the Hi-to-H2 conversion.

The majority of young massive stars are found in close binary systems. Recently, dedicated observing campaigns have provided strong constraints on the binary fraction as well as the distribution of the parameters that characterize the binary systems: the masses of both components, the orbital period and eccentricities. Most strikingly these findings imply that the majority of massive stars experience strong interaction (roche lobe overflow, a common envelope phase and or a merger) with a binary companion before their final explosion. I will discuss recent results from detailed binary star models and population synthesis models.

High surface density, rapidly star-forming galaxies are observed to have ≈ 50 - 100 km s−1 line-of-sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae.

We find that such motions lead to strong global outflows in the highly-compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds -35 km s−1, as occurs in the dense disks that have star formation rate densities above ≈ 0.1 M⊙ yr−1 kpc−2. These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the star-formation rate density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from stellar explosions.

These results are explained in more detailed in Sur, Scannapieco, & Ostriker (2015).

We present multi-epoch millarcsecond resolution images of the most compact supernova remnants in the nearby starburst galaxy M82, spanning 25 years of evolution. In particular, we will briefly discuss the new transient source first detected in 2009 as well as the unusual object 41.95+57.5 and its potential as a GRB afterglow.

Superluminous supernovae (SLSNe) were discovered during the last decade by wide-field surveys. Despite their importance for stellar evolution and mass loss, especially at low metallicities, and their utility as high-redshift probes and possible distance indicators, their nature remains poorly understood. I present here new exciting observations of SLSNe and their host galaxies that offer new clues in the hunt for their progenitors and explosion mechanism. These include constraints on the ages and the metallicities at the SN environments, double peaks revealed by early observations, the presence of H in nebular spectra, and the first evidence on the explosion geometry, through polarimetry.

A rare subclass of Type Ia supernovae (SNe Ia) shows evidence of strong interaction with a hydrogen-rich circumstellar medium (CSM); these objects are referred to as SNe Ia-CSM. PTF11kx began life as a SN Ia, but after a month it began to show indications of significant interaction with its CSM. This well-studied object solidified the connection between SNe Ia-CSM and more typical SNe Ia, despite their spectral similarity to Type IIn SNe (which likely come from massive star progenitors, as opposed to the white dwarf progenitors for the SNe Ia-CSM). The spectra of all ~20 known SNe Ia-CSM are dominated by Hα emission (with widths of ~2000 km s−1) and exhibit large Hα/Hβ intensity ratios; moreover, they have an almost complete lack of He I emission (see left panel of Figure 1). They also show possible evidence of dust formation through a decrease in the red wing of Hα 75–100 days past maximum brightness. The absolute magnitudes of SNe Ia-CSM are found to be -21.3 mag ≤ MR ≤ −19 mag (see right panel of Figure 1), and they also show ultraviolet emission at early times and strong infrared emission at late times (but no detected radio or X-ray emission). Finally, the host galaxies of SNe Ia-CSM imply that these objects come from a relatively young stellar population.

Supernova (SN) rates serve as an important probe of star formation models and initial mass functions, particularly at high redshifts due to the SN intrinsic luminosity. Ground-based optical surveys, however, typically discover nearly ten times fewer SNe than predicted, challenging our understanding of massive star formation and evolution. These results are generally attributed to the high dust extinction associated with the nuclei of star forming galaxies, such as Ultra Luminous InfraRed Galaxies (ULIRGs). Near-infrared surveys have been unsuccessful due to extinction values exceeding AV > 25 mag, and even on an 8-m AO system, subtraction algorithms used to find the SNe inevitably leave large residuals associated with the inner 2” of the galactic nucleus, which is where a majority of the SNe occur. A successful survey must be conducted at longer wavelengths and with a space-based telescope, which has stable seeing that reduces the necessity for any subtraction algorithms and, therefore, residuals. Here we present ongoing work from our 300 hour Spitzer 3.6 micron survey for dust-extinguished SNe in the nuclear regions of ULIRGs within 200 Mpc. The direct product of this study will be an improved understanding of the connection between the far-IR luminosity of ULIRGs and massive star formation.