- no title specified

The Magellanic Clouds are ideal laboratories for testing theories of massive star evolution: they are nearby, they span a range of metallicity from one-half solar (LMC) to one-third solar (SMC), and they are incredibly rich in massive stars. I will briefly review what we have learned about their massive star content, with an emphasis on their O-type star population. These unevolved massive stars present a special challenge in identification, with the result that only a minority of the most massive stars have been observed spectroscopically. Although photometry alone does not allow us to fully characterize these stars, it at least allows us to understand the limits of our current knowledge of the massive star population of our nearest galaxian neighbors.

The characteristics of infrared properties and mid-infrared (MIR) variability of red supergiant (RSG) stars in the Large Magellanic Cloud (LMC) are analyzed based on 12 bands of near-infrared (NIR) to MIR co-added data from 2MASS, Spitzer and WISE, and ∼6.6 years of MIR time-series data collected by the ALLWISE and NEOWISE-R projects. 773 RSGs candidates were compiled from the literature and verified by using the color-magnitude diagram (CMD), spectral energy distribution (SED) and MIR variability. About 15% of valid targets in the IRAC1-IRAC2/IRAC2-IRAC3 diagram may show polycyclic aromatic hydrocarbon (PAH) emission. We show that arbitrary dereddening Q parameters related to the IRAC4, S9W, WISE3, WISE4, and MIPS24 bands could be constructed based on a precise measurement of MIR interstellar extinction law. Several peculiar outliers in our sample are discussed, in which one outlier might be a RSG right before the explosion or an extreme asymptotic giant branch (AGB) star in the very late evolutionary stage based on the MIR spectrum and photometry. There are 744 identified RSGs in the final sample having both the WISE1- and WISE2-band time-series data. The results show that the MIR variability is increasing along with the increasing of brightness. There is a relatively tight correlation between the MIR variability, mass loss rate (MLR; in terms of Ks-WISE3 color), and the warm dust or continuum (in terms of WISE4 magnitude/flux), where the MIR variability is evident for the targets with Ks-WISE3>1.0 mag and WISE4<6.5 mag, while the rest of the targets show much smaller MIR variability. The MIR variability is also correlated with the MLR for which targets with larger variability also show larger MLR with an approximate upper limit of -6.1 M⊙/yr. Both the variability and the luminosity may be important for the MLR since the WISE4-band flux is increasing exponentially along with the degeneracy of luminosity and variability. The identified RSG sample has been compared with the theoretical evolutionary models and shown that the discrepancy between observation and evolutionary models can be mitigated by considering both variability and extinction.

Thousands of new Wolf-Rayet stars have been found since they were initially discovered in 1867 by Charles Wolf and Georges Rayet. Hundreds are known not only in our own galaxy, but also in the galaxies of the Local Group. Improvements in detection methods, such as the use of interference filters and CCDs, have brought us a long way since early objective prism surveys. Here I discuss what we've learned about the population of Wolf-Rayet stars within our neighboring galaxies, while emphasizing the larger importance of such studies. Obtaining a complete sample of Wolf-Rayet stars within a particular environment allows us to compare our results with stellar evolutionary theory, and I'll discuss where such comparisons can be made and where additional data is needed.

The Milky-Way contains a resolved and varied Wolf-Rayet population. Accurate distances are essential for determining their fundamental parameters, such as mass and mass loss rate. Constrained fits of these parameters are vital for understanding massive star evolution, as are indicators of their histories, such as runaway status from binary evolution. Past work relied upon distances to a subset of Wolf-Rayet stars, which are supposed members of clusters and associations. Precise parallax measurements remove the reliance on calibrations, and Gaia DR2 expands the Wolf-Rayet sample with parallaxes to hundreds of stars. This provides reliable distances to many field stars and increases the accuracy of critical parameters, including mass and luminosity. Combined with DR2 proper motions, these results also offer a better understanding of cluster and association membership and runaway stars. In this talk, I will present new distances from Gaia DR2 and the resulting insights into our closest Wolf-Rayet population. This includes identification and tracking of runaways, the fraction of Wolf-Rayet stars in clusters and associations and improved absolute magnitude calibrations. These results will also be connected to other massive star populations, such as LBVs. Finally, I will discuss future work building on DR2 and later Gaia releases.

Binary interaction is one of the important ingredients in the evolution of massive stars. Yet the physics of the interaction remains insufficiently understood. So far, massive star population studies have focused on the youngest star clusters (< 5-10 Myr), where most binaries did not have time to interact. These studies were important to constrain the initial multiplicity properties. We now take the next step by studying older clusters (10-30 Myr), for which population synthesis models predict a large fraction of post-binary interaction products. Using MUSE-WFAO science verification observations, we obtained unprecedented multi-epoch spectroscopic data of the whole population of massive stars in the dense core of NGC 330, revealing over 150 stars more massive than 8 Msun and over 2000 fainter objects. We present the multiplicity fraction and physical properties of the NGC 330 massive star population (Teff, log g, rotation rates), and we discuss the presence of a large Be star population. We search for observational constraints of post-binary interaction products and confront predictions of state-of-the-art single and binary evolution theories for a statistically significant sample.

Binary stars are generally assumed to behave and evolve as single stars unless they get in each other's way. According to standard evolutionary scenarios, the latter occurs when the Roche lobe overflow stage is reached and copious mass transfer takes place. In this talk I will describe the tidal interaction effects that occur on orbital timescales in eccentric binaries long before RLO occurs, and discuss the potential implications for their evolutionary trajectories. The ideas will be exemplified using the Wolf-Rayet/Luminous Blue Variable system HD 5980, which is located in the Small Magellanic Cloud and is a prime candidate progenitor for a gamma-ray burst or a pair instability supernova.

The formation of massive stars remains one of the most intriguing questions in astrophysics today. The main limitations result from the difficulty to obtain direct observational constraints on the formation process itself. Several formation theories have been proposed such as stellar collisions, merging, competitive accretion and monolithic collapse amongst others. In this context, the Carina High-contrast Imaging Project of massive Stars (CHIPS) aims to observe all 80+ O stars in the Carina nebula using the new VLT 2nd-generation extreme-AO instrument SPHERE. This instrument offers unprecedented imaging contrast allowing us to detect the faintest companions around massive stars. Here we present the first results of the CHIPS project, based on SPHERE observations of 1/3 of the sample. Finally, we discuss the multiplicity properties of massive stars at the highest contrast in the context of current formation scenarios.

The rate of apsidal motion, or orbital precession, in combination with evolutionary models, can provide an independent estimation of the masses for stars in binary systems. We aim at increasing our knowledge of masses for massive stars through the study of the apsidal motion in the orbits of massive binaries. To this purpose, we searched the OWN database, selecting 17 O-type binaries, for which non-negligible eccentricities had been previously reported. The OWN Survey has obtained around 900 high resolution and high quality spectra of these systems using the echelle spectrographs available at CASLEO, Las Campanas and ESO-La Silla observatories. The individual spectra of each binary component were obtained through a disentangling technique, then these data were used to determine spectral types, projected rotational velocities and radial velocities. With this information at hand we were able to compute new orbital solutions, including rates of apsidal motion, for 8 massive binary systems. For another 5 systems only preliminary rates were determined. We used the new apsidal motion rates in combination with evolutionary models to estimate absolute masses for the components of 7 massive systems. Among them, 3 are also eclipsing binaries for which absolute masses had previously been determined. A comparison of the masses obtained through both methods shows differences between 1% and 15%.

[1.9] FLAMing MiMeS: can we extend our investigations of massive-star magnetism to nearby galaxies?

The past decade has witnessed remarkable advances in our understanding of the magnetic properties of massive stars, including the influence of magnetic fields on stellar mass loss and rotation (ud Doula 2002, 2008), and their ultimate impact on stellar evolution (Keszthelyi et al. 2018). Recently, examples of candidate magnetic O-type stars in the LMC and SMC have been identified (e.g. Nazé et al. 2015, Walborn et al. 2015), but first attempts to detect their magnetic fields have yielded negative results (Bagnulo et al. 2017). In this talk we will explore the realistic potential of current and forthcoming instrumentation to build on the successes of projects such as MiMeS and VFTS to survey populations of OB stars in the Magellanic Clouds for evidence of surface magnetic fields and magnetic field-stellar wind interactions. Extending our understanding of the magnetic and magnetospheric properties of massive stars to these environments of significantly lower metallicity will provide qualitatively new constraints on models of magnetic wind confinement and insights into the origins of the magnetic fields of hot stars.

Despite being detectable on the surface of only about 7% of Galactic OB stars, magnetic fields can play an extremely important role in the evolution of these stars and ultimately impact their end stages. Among all known magnetic O stars, NGC 1624-2 sticks out: it hosts a field that is roughly an order of magnitude stronger than that of any other star of its class. While the origin of its remarkable field remains unknown, multi-wavelength investigations of this puzzling object offer more and more insight into its properties, and in particular into the interaction between its magnetic field and its strong wind. In this talk, I will present new HST/COS observations of NGC 1624-2 that allow us to probe its dense magnetosphere. I will also discuss early efforts which leverage the recent wealth of knowledge we have accumulated on NGC 1624-2 to attempt to find other similar objects in our Galaxy. Finally, I will discuss some of the evolutionary implications of these searches and what they can allow us to learn about massive stars as they reach their end stages and beyond.

Since 2006 we are conducting a high resolution spectroscopic monitoring of Galactic O and WN stars. This project, known as the OWN Survey, has the main goal of characterizing the multiplicity of massive stars observing a sample of Galactic O- and WN-type stars. Twelve years after, we have collected about 7200 high resolution spectra of more than 200 stars. This huge database has allowed us to discover more than 100 new multiple systems, having derived orbital elements for half of them, while other targets exhibit either radial velocity variations beyond the uncertainties, or double lines, indicative of multiplicity. In this talk, I will review some highlights of the survey.

Massive stars are often found to be in pair. This configuration is both a blessing and a curse. From it, we can estimate their exact properties such as their masses but the interactions that result during their life considerably affect the way that the stars evolve. To characterize the massive binary population identified in 30 Dor by the VLT/FLAMES Tarantula Survey (VFTS), we go one step further with the Tarantula Massive Binary Monitoring (TMBM). 95 spectroscopic binaries were observed for 32 epochs sampled over 18 months with VLT/FLAMES and XSHOOTER. We combine these observations with several years of OGLE photometry. We use spectral disentangling and atmosphere modeling to determine the individual parameters of 32 double-lined and 51 single-lined spectroscopic binaries. We present the global analysis of these systems in order to test the theories of massive star evolution and to derive observational constraints of the binary interactions.

Super-AGB stars reside in the mass range ~6-12 Msun and bridge the divide between low/intermediate-mass and massive stars. They are characterised by off-centre carbon ignition prior to a thermally pulsing phase which can consist of many 10-1000s of thermal pulses. With their high luminosities and very large, cool, red stellar envelopes, these stars may appear seemingly identical to their slightly more massive red supergiant (RSG) counterparts and may act as massive star imposters in RSG surveys. Important for both of these classes of star is rotation, and in particular its impact to the surface composition relative to the process of second dredge up. The chemical surface enrichment may result in a clear nucleosynthetic signature to differentiate between super-AGB stars and (massive star) RSGs. The refining of this mass boundary has important implications for the energetics and chemical enrichment of galaxies. Here we present grids of rotating and non-rotating super-AGB star models along the entire TP phase and low-mass massive star models until the point of core collapse.

Multiplicity is a key factor to understand massive stellar evolution, since a large fraction of massive stars are expected to be born in binary or multiple systems. In this context, the OWN Survey has obtained more than 7500 multi-epoch high-resolution optical spectra of approximately 250 stars in the Milky Way aiming at measuring highly accurate radial velocities and determining orbital and stellar parameters in binary and multiple systems. We have initiated a campaign to characterize the orbital and physical properties of a set of presumably non-evolved OB stars in double-lined spectroscopic binaries (SB2) with wide orbits, with the final purpose of testing state-of-the-art theoretical models. Here we present our last results obtained from the quantitative study of a set of Galactic OB binary systems.

Here we present preliminary results of our aim to obtain the individual masses of each component of the binary system HM1 8 (O5 III + O9.7 V). To accomplish this, we used a set of 30 high-resolution spectra to measure radial velocities for some He I and He II lines, and adjusted a radial velocity curve which allowed us to determine the orbital parameters of HM1 8. Furthermore, since the primary eclipse could be detected in a set of photometric data secured at Las Campanas Observatory, we were able to determine the inclination of the system and its physical and photometric parameters (M1 = 37.5 ± 3.0 M , M2 = 18.8 ± 1.6 M , R1 = 12.67 ± 0.18 R , R2 = 8.00 ± 0.15 R , V1 = 12.75 ± 0.76, V2 = 14.7 ± 1.1). On the other hand, we reduced an observation in X-rays from XMM-Newton, extracted the spectrum and analysed it. In this way we were able to model the detected emission as that of a thermal gas, and calculate the X-ray luminosity from the adjusted model. By comparing it with the bolometric luminosity we obtained LX / Lbol = 0.14 × 10^−7. Taking into account typical values of this quotient found by previous authors, we estimated that the emission comes mainly from the stellar wind of the primary component of the system. It should be emphasised that until now, there was no measure of the mass of a giant star earlier than O7 by means of the eclipsing binary method.

Through their radiation, stellar winds, and supernova explosions, massive stars shape the evolution of their host galaxies. Wolf-Rayet (WR) are evolved, hydrogen depleted massive stars that exhibit strong mass-loss and dominate the stellar feedback on their environments. It is generally not known whether the majority of WR stars in the Magellanic Clouds originate via stripping in binary systems or via intrinsic mass-loss. We performed a complete spectral analysis of all known WR binaries in the Small and Large Magellanic Clouds (SMC, LMC), as well as additional orbital analyses, and constrained the evolutionary histories of these important stars. In my talk, I will summarize our study's findings regarding the origin of WR stars in the Magellanic Clouds and their feedback on their environments. I will further describe the our study's implications on stellar eruptions, gravitational wave progenitors, supernovae, and the initial mass function as at sub solar metallicities.

Stars more massive than 20−30 Msun are so luminous that the radiation force on the cooler, more opaque outer layers can balance or exceed the force of gravity. When exactly balanced, the star is said to be at the Eddington limit. These near or super-Eddington outer envelopes represent a long standing challenge for calculating the evolution of massive stars in one dimension, a situation that limits our understanding of the stellar progenitors of some of the most exciting and energetic explosions in the universe. In particular, the proximity to the Eddington limit has been the suspected cause for the variability, large mass loss rate and giant eruptions of an enigmatic class of massive stars: the luminous blue variables (LBVs). I will show that physically realistic three dimensional global radiation hydrodynamic simulations of radiation dominated massive stars naturally reproduce many observed properties of LBVs, specifically their location in the Hertzsprung-Russell (HR) diagram and their episodic mass loss. These calculations pave the way to a quantitative understanding of the structure, stability and the dominant mode of mass loss of massive stars.

The evolutionary path of massive stars from the main-sequence all the way to their spectacular deaths as supernovae is still most uncertain. It comprises various extreme transition phases, in which the stars shed huge amounts of material into their environments, typically via episodic, sometimes even eruptive events. These objects are luminous super- or hypergiants populating the upper, luminous part of the Hertzsprung-Russell diagram and spreading from spectral type O to F or even later. As mass-loss is crucial for the fate of a star, understanding the mechanisms behind mass ejection phases and exploring the mass lost during such events is essential. On the cool side of the HR diagram pulsations are known to facilitate mass loss in red supergiants and to trigger outbursts in yellow hypergiants that attempt to pass through the yellow void. The situation is less clear for the hot counterparts. Blue supergiants display indication for time-variable mass loss, and some of these objects were recently discovered to pulsate in multiple modes. As not every mode is suitable to drive enhanced mass-loss or trigger eruptions, the search for the most ideal candidates, which is the subject of our research, remains challenging.

[2.5] Testing the evolution theory with accurate parameters for two early-type eclipsing binary systems in the LMC

Detached eclipsing binary systems are an important source of accurate and precise stellar parameters, letting us test the predictions of stellar evolution theory and our understanding of the related phenomena. This is particularly important for the massive stars for which not many good measurements of the fundamental parameters are available. Moreover, for these stars the observations often do not match the current evolutionary models, which results in the so-called "mass discrepancy" problem. In various cases, very high overshooting parameter values are also necessary to fit the measured properties. Here we will present our solution for two massive O and B-type well-detached SB2 systems in the Large Magellanic Cloud. Very accurate physical parameters (e.g. masses, radii) were measured using high-quality photometric and spectroscopic data. Precise temperatures, metallicities and reddening values were obtained from the spectral analysis. The masses of the components are about 20 Msun and 14 Msun, respectively. We have also compared our measurements with evolution theory models for different sets of parameters, and the presence of the systems in the LMC, let us probe the metallicity influence on the models.

Instituto de Astrofísica de La Plata, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata

The evolution of stars belonging to binary systems with short enough orbital periods is fundamentally different from the one the star would have if single. This is due to the existence of a maximum size, the Roche lobe, the star can have in hydrostatic equilibrium. If the most massive star of the pair swells enough to fill its lobe, it will behave as a donor star. Since then on, the binary system evolves in a way strongly dependent on the amount of mass the companion star is able to retain. We shall describe the main characteristics of the evolution of massive stars in close binary systems for different ranges of orbital periods. We shall address the case of systems in which the donor star undergoes Roche-lobe overflow (RLOF) while still burning hydrogen in its core (Class A mass transfer). Also, we discuss the case of systems with longer initial periods that undergo RLOF after core hydrogen exhaustion but prior to helium ignition (Class B mass transfer). At the final stages of presupernova, donors stars have structures that are plausible to account for the properties of some observed supernovae in a natural way. On the contrary, single stars require fine tuned physics to arrive to similar results. We shall apply this concept to few observed supernovae.

Although it is known that massive stars (Mstar > 8 Msun) have a key role in the evolution of the Universe, we still have a fragmented detailed knowledge in some evolutionary stages. Recent observational studies have demonstrated that at least 75% of O-type stars are part of binary or multiple systems, and at least 70% of them have strong interaction during their evolution (including 24% of mergers). This picture is achieved thanks to dedicated and thorough surveys of the O-type stars population in our Galaxy. The problem that arises now is that we know in detail the multiplicity status of O-type stars, but still is very fragmented the multiplicity status of the ZAMS massive stars, and advanced descendants in certain mass range, as is the case of early B-type supergiants and Wolf-Rayet stars. In this work, we present a glance into the multiplicity status of these type of stars based in the information collected from our finding, different surveys and databases, highlighting missing links in the evolution of massive binaries.

Massive stars are observed to rotate moderately fast early in their lives, and this rotation significantly affects their evolution, as well as their final fate. Multi-dimensional hydrodynamic simulations show the decisive effects of rapid rotation on the core-collapse dynamics, which might help explain the diversity of energetic transients accompanying the evolutionary end point of massive stars. Still, several uncertainties in modelling the evolution of massive stars make it difficult to predict the angular momentum profile within the star during its final stages leading to iron core collapse. The most notable uncertainties relevant for rotation are the effects of magnetic fields, and interactions with a companion, with most massive stars being members of high multiplicity systems. I discuss the angular momentum evolution in detailed models of massive binaries, including tidal interactions and mass transfer. These model represent progenitors of core-collapse supernovae, specifically types Ib/c and IIb where hydrogen has been removed, and can also be tested against observed systems with strong indications of mass transfer in their past.

University of Denver
Andrew G. Fullard (U. Denver), Jennifer L. Hoffman (U. Denver), Kenneth H. Nordsieck (U. Wisconsin), Anthony F. J. Moffat (U. Montréal), Nicole St-Louis (U. Montréal)

Like other massive stars, WR stars often occur in binaries, where interaction can affect their mass loss rates and provide the rapid rotation thought to be required for GRB production. The diagnostic tool of spectropolarimetry, along with the potentially eclipsing nature of a binary system, helps us to better characterize the CSM created by the stars’ colliding winds. Thus, we can constrain mass loss rates, probe wind interactions, and infer rapid rotation. We present spectropolarimetric results for a sample of WR+O binary systems, obtained with the Robert Stobie Spectrograph at the South African Large Telescope, between April 2017 and September 2018. The precisely phased observations we obtain with RSS/SALT allow us to map both continuum and emission line polarization variations over the binary cycle, and so reconstruct the shapes and locations of the emitting and scattering regions within the system. We discuss our initial findings and interpretations of the polarimetric variability in several of the sampled binary systems. We analyze one system in particular, the WN6+O5V binary WR 47 (CD Cru), using archival data and radiative transfer models of the scattering structures revealed by the new observations.

Star formation is an inefficient and slow process. Only a few percent of the available mass of a molecular cloud is converted into stars over the cloud lifetime. The low inefficiency can be attributed to the effects of internal processes of stellar feedback remains from massive stars. Massive stars shape their environment with their output of ionizing photons, powerful stellar winds, and cosmic rays. In this talk I will discuss the individual processes and use prototypical massive star-forming regions as observational templates: the Galactic star cluster Westerlund 2, 30 Doradus in the Large Magellanic Cloud, and the dominant Giant HII region in the dwarf galaxy II Zw 40.

[3.2] Over 100 massive stars in the Milky Way's central parsec: hydrodynamics, X-ray synthesis, and 360-degree videos

The Galactic center hosts a large collection of massive stars in the central parsec: ~30 Wolf-Rayet stars, ~100 O stars, and dozens of B stars. The interaction of all these stellar winds forms a complex structure in the vicinity of the ~4 million M_sun supermassive black hole (SMBH) Sgr A*, and so requires detailed modeling to determine the massive stars' influence in the region, particularly as a source of material accreting onto Sgr A*. We will first present our prior work of simulating the Wolf-Rayets and their winds under the gravitational influence of the SMBH, both in quiescent and outbursting states. We then synthesized the thermal X-ray mission from these hydrodynamic simulations to compare with Chandra observations. The model spectral shape from a ring around Sgr A* is well matched to the observations, while the flux level indicates that a moderate outburst from the SMBH is necessary to clear hot gas away from Sgr A*, even though this outburst ended ~100 yr ago. Current work involves incorporating the aforementioned O and B stars, about which we will provide an update, in particular about how the massive stars with the closest orbits, dubbed the 'S' stars, affect the flow of material towards Sgr A*. To dive into these simulations for both scientific and outreach purposes, we created 360-degree videos where you get to be Sgr A*, so the stars orbit you, and the rendered quantity – column density, thermal X-ray emission, etc. – appears over all 4pi sr. The most visually appealing aspect is the tidal stretching of inspiraling clumps, particularly since this stretching is perfectly seen from the SMBH's vantage point. We will present our 360-degree videos, in which the public's interest has been demonstrated since our Chandra/NASA press release propelled the column-density video on YouTube (https://youtu.be/YKzxmeABbkU) and Facebook to have over 1.2 million views.

We have calculated using Nbody simulations (EMACSS) the evolution over a Hubble time of absolute blue magnitude, velocity dispersion and size (M_B,sigma,R) of young Super Star Clusters (SSC, Giant HII regions and HII galaxies), taking into account the effects of both dynamic and stellar evolution. We found that, after 12 Gyr, the SSC fall into the region of the M_B,sigma plane occupied by globular clusters and Ultra Compact Dwarf galaxies, suggesting a possible parentage line.

Massive stars live in HII regions and are the source of ionizing photons. Emission line ratios from HII regions therefore serve as a diagnostic of massive star content in young stars clusters. With optical spectra of nearly 30,000 HII regions from 667 galaxies, the CALIFA survey enables a unique, systematic study of the properties of HII regions in nearby galaxies. Besides the usual strong emission lines in the spectral region from 3650 to 7501 A, some HII region show weak emission lines such as the [ArIII], [NeIII] and HeII lines. Additionally, some HII regions show WR features around HeII4686 and a few also around CIV5808. We find that some of those WR regions show nebular HeII emissions and some do not. We also find HII regions that show nebular HeII emissions without the presence of WR features. From the flux of the recombination lines of hydrogen and helium we calculated the number of ionizing photons per HII region at different energies and compared them to the number of ionizing photons from stellar atmosphere models for different spectral type stars. We find that hard ionizing radiation sources are needed to explain the measured HeII emission. We assess the likelihood that stripped binary stars or X-ray binaries contribute the required HeII ionizing flux.

Direct radio imaging at the sub-arcsecond scale constitutes certainly the best tool to probe wind collision regions (WCR) in massive binary stellar systems. However, systems observable within a reasonable amount of time or with a sufficient angular separation are scarce. We briefly review here other approaches to investigate CWR. In particular, how radio interferometric observations can provide different pieces of information in studies of colliding wind binaries and the associated phenomena. As examples, we present the latest results of multi-frequency observations of WR 11 (gamma Velorum) taken with the Giant Metrewave Radio Telescope, and of a monitoring campaign using the Very Large Array dedicated to WR 133.

Instituto de Astrofísica de La Plata, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata

I will review the current understanding of the nature of stripped-envelope SN progenitors from an observer’s standpoint. I will focus on the efforts that are being made to understand how some massive stars lose their envelopes and how that determines the SN properties.

Authors: Laplace, de Mink, Piro, Dodds, Farmer, Gotberg, Justham, Renzo, Zapartas.

Stripped-envelope supernovae mark the death of massive stars that have lost their H-rich envelope and are related to exotic events such as long gamma-ray burst progenitors and to the formation of gravitational wave progenitors. The progenitors can result from binaries that experience one or more phases of mass transfer and lead to very fast and faint events. Current transient surveys are still highly incomplete, but the rise of fast cadence and deep surveys is expected to dramatically improve our understanding of these events. At present, theoretical predictions for their light curves based on self consistent binary evolutionary models are still scarce. We present a new grid of binary evolutionary models and a library of the resulting light curves. We discuss their properties and compare with existing observations. We evaluate the accuracy of Arnett-like fits for estimating the explosion parameters (nickel mass, explosion energy) and the physical parameters of the progenitor (ejecta mass, radius of the progenitor). We will publicly release our models for comparison with newly detected events by robmotic transient surveys (e.g. ZTF, Pan-STARRS, LSST).

Most massive stars are known to be members of binary systems. Therefore, many of the core-collapse supernovae should be occurring in binaries. When a supernova ejecta collides with its binary companion, the ejecta can alter the appearance of the companion significantly. We have carried out a large number of hydrodynamical simulations of ejecta-companion interaction over a wide parameter range. From these simulations we now have a better understanding of how much energy of the ejecta is transferred to the companion envelope and where it is deposited. This allows us to estimate the appearance of a companion star after supernova in a binary in any binary configuration, which may be useful for companion searches after supernovae.

[4.4] Light echoes of Eta Carinae, LBV eruptions, and pre-supernova mass loss [INVITED]

I will present recent results of spectroscopy of Eta Carinae's 19th century eruption obtained by observing light echoes from the historical event. Spectroscopy of echo light has revealed a number of new intriguing properties of the eruption, such as the existence of extremely fast ejecta expanding at 10,000 km/s. Light echoes have provided critical new information about the physics of the event, and have raised important questions about the fundamental nature of Eta Car and LBVs in general. Many lines of evidence point toward LBVs as being the products of interacting binary evolution, including mergers and mass transfer, rather than a brief unstable stage in single-star evolution, and recent distance estimates from Gaia point to a more diverse range of properties for LBVs than previously recognized. These clues have implications not only for their evolutionary state, but the cause of their irregular variability and outbursts. There are also a number of implications for a subset of supernovae that suffer extreme mass loss shortly before exploding, and new clues contribute to our evolving understanding o the LBV/SN connection.

Red supergiants (RSGs) are the helium-fusing descendants of moderately massive (10-25Mo) stars. As the coldest and largest (in physical size) members of the massive star population, these evolved stars serve as ideal "magnifying glasses" for scrutinizing our current understanding of massive stars and their role as supernova progenitors. RSGs are the observationally-confirmed progenitors of Type II-P, an intermediate evolutionary phase in the lifetimes of some stripped-envelope SN progenitors, and a crucial step in the formation and population statistics of massive interacting binaries (including those that will ultimately produce compact object binaries and gravitational waves). This talk will provide an overview of our field's current knowledge of RSGs, identify some of the most pressing open questions about these stars and their role as supernova progenitors, and consider the importance of RSGs in the coming decade as the next generation of observatories comes online.

I will present some recent results on the direct imaging identification and characterization of the progenitors of Type II-P supernovae. It is now well established that these progenitors are massive stars in the red supergiant phase. There have been statistical analyses which have led to inference of both lower and upper limits on the initial masses for these stars, which has resulted in discussion of a so-called “red supergiant problem,” and I will address this problem in light of our results, which will include the progenitors of SN 2017eaw and SN 2018aoq.

I will present the analysis of a select group of hydrogen-rich supernovae (SNe) for which there is a good photometric and spectroscopic monitoring, as well as pre-explosion images with direct information from the putative progenitor star and post-explosion images confirming the disappearance of the progenitor star. Physical parameters of the progenitor (mass and radius) and the explosion (energy and amount of nickel) were determined for this group of objects through their light curves modeling. We find the agreement between the masses derived from our hydrodynamical modeling and those derived from the pre-explosion information available in the literature, better than achieved in previous works.

We investigate a progenitor mass distribution of core-collapse supernova remnants (CCSNRs) in our Galaxy and the Large and Small Magellanic Clouds, for the first time. We count the number of CCSNRs in three mass ranges divided by the zero-age main-sequence mass, M_ZAMS; A: M_ZAMS < 15 Msun, B: 15 Msun < M_ZAMS < 22.5 Msun, C: 22.5 Msun < M_ZAMS. Simple compilation of progenitor masses in the literature yields a progenitor mass distribution of f_A: f_B: f_C = 0.24 : 0.28 : 0.48, where f is the number fraction of the progenitors. The distribution is inconsistent with any standard initial mass functions. We notice, however, that previous mass estimates are subject to large systematic uncertainties because most of the relative abundances (X/Si) are not really good probe for the progenitor masses. Instead, we propose to rely only on the Fe/Si ratio which is sensitive to the CO core mass M_COcore) and M_ZAMS. Comparing Fe/Si ratios in SNRs in the literature with the newest theoretical model, we estimate 33 M_COcore and M_ZAMS, leading to a revised progenitor mass distribution of f_A: f_B: f_C = 0.47 : 0.32 : 0.21. This is consistent with the standard Salpeter initial mass function. However, the relation between M_COcore and M_ZAMS} could be affected by binary evolution, which is not taken into account in this study and should be considered in the future work to derive a better progenitor mass distribution estimate.

The analysis of supernovae light curves and spectra provides insights into the SN progenitor, the nature of the explosion, and provides constraints on nucleosynthetic yields. Using the 1D non-LTE time dependent radiative transfer code cmfgen, we have been exploring different classes of SN – Types Ia, IIP, IIn, IIpec, Ibc, and pair instability. These studies have provided important insights and raised new questions. In this presentation we highlight some key results, and discuss important issues that have arisen as a consequence of our modeling, and the modeling of others. As input, cmfgen uses the SN structure generally derived from 1D explosion models, although 1D models extracted from 2D or 3D explosion models can also be used. Apart from some smoothing, which can also induce mixing, we make no major changes to the hydrodynamical models. For a model sequence we typically use a 10% time step, and model the SN ejecta into the nebula stage. As there are no free parameters in the simulations once a model sequence begins, the resulting spectra and light curves depend only on the accuracy of the adopted initial hydrodynamical model and the cmfgen calculations. Our results are sensitive to the progenitor properties, and hence are subject to the uncertainties of stellar evolution. For example, different convection and mixing prescriptions can influence spectra at late times, while uncertainties in the mass-loss history make it difficult to relate SN properties to the initial progenitor mass. For Type IIP SNe we obtain excellent qualitative agreement with observed light curves and spectra. For Type Iipec, Type Ibc, and especially broad-lined Type Ic SNe, the assumption of spherical symmetry is likely a limiting factor in our simulations. To take advantage of the extensive SN data sets that are becoming available, enhancements in existing tools, together with the development of additional techniques, are needed. In some cases the accuracy of the atomic data used in the calculations may be a limiting factor in the accuracy of the models, and this should be addressed. Given the complexity of the existing codes, and the atomic data, consistency checks between different codes are needed. At the present time, for example, independent groups find different results for the ejecta masses of Type IIP SNe. As part of our work on Ia SNe, we are involved in a benchmark study in which several groups are currently running comparison calculations using the same initial models. A similar exercise should be undertaken for core-collapse SNe.

The evidence is now ubiquitous that a significant fraction of stars show mass loss in the last months of their life. I'll present several examples from the Global Supernova Project, a multi-year program to monitor hundreds of supernovae with lightcurves and spectra using the Las Cumbres observatory global robotic network of 21 telescopes. These include a large sample of Type II-P and II-L lightcurves that are best modeled with interaction, examples of interaction both with and without narrow features in spectra, stripped envelope interaction (Ibn), and flash spectroscopy illuminating circumstellar material.

There is now substantial evidence that the progenitors of some core-collapse supernovae undergo enhanced or extreme mass loss prior to explosion. The imprint of this mass loss is observed in the spectra and dynamics of the expanding blast wave on timescales of days to years after core collapse, and the effects on the spectral and dynamical evolution may linger long after the supernova has evolved into the remnant stage. I will present recent results which highlight how mass loss, either isotropic or enhanced during some late stage of the progenitor's evolution, can profoundly impact the dynamics and spectral qualities of the supernova remnant, centuries after core collapse.

Despite more than 30 years of searches, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. We also investigate the total energy budget by comparing the expected input from radioactive 44Ti and the observed bolometric luminosity of the remnant, which can be used to put a limit on the bolometric luminosity of the compact object. These limits can be used to constrain the effective temperature of a neutron star, accretion rate, surface magnetic field strength, and spin period. Most theories predict the formation of a neutron star in SN 1987A. Observations rule out many scenarios for a neutron star, but a few low-luminosity scenarios are still allowed. For the analysis of SN 1987A, we have modeled ejecta X-ray absorption using three-dimensional neutrino-driven SN explosion models. These results are general and apply to CCSNe from ~100 days to ~300 years after the explosion.

Light echoes (LEs) give us a rare opportunity in astronomy: the direct observation of the cause (the explosion/eruption) and the effect (the remnant) of the same historic astronomical event. Here we present a new application: the distance measurement to these historic transients. We use the recently available E(B-V) 3D map of Green et al. (2015), derived from PS1 data, to determine the distance to the scattering dust. With that in hand, we can geometrically derive the distance to the historic transient. Using the brightest Tycho light echo, we derive a distance of 10450 ly, with a statistical uncertainty of 3.5%. The systematic uncertainties are dominated by the systematics in the dust 3D map, which by now have an upper limit of approximately 10%. We show how we plan to decrease this systematic uncertainty in the future.

The gravitational wave event following a binary neutron star merger and detected by the Ligo-Virgo interferometers on 17 August 2017 was a watershed for multi-messenger astronomy. As predicted by theory, the optical/infrared electromagnetic counterpart of the compact binary merger is a radioactive source produced by isotopes of elements heavier than iron, nucleosynthesized during the coalescence via rapid neutron capture process. This detection opens up not only a new perspective for multi-messenger exploration, but also a pathway into the history of cosmic chemical enrichment.

iPTF14hls is a transient which displays the most common supernova spectra (i.e. Type IIP) but: The spectra evolve ~10 times slower than a normal IIP, staying photospheric and with velocities of several thousand km/s over 600 days after explosion; The light curve displays at least five peaks; and there is evidence of a strong eruption at the SN position in images from 1954. While iPTF14hls might constitute the first pulsational pair instability SN ever observed, it still violates some principles of that model. In fact, the properties of iPTF14hls are difficult to explain in the framework of any single SN model. I will present new late-time ground-based and HST data that might provide some more clues as to the origin of this very peculiar and unique massive star explosion.

We present the spectroscopic and photometric analysis of DES16C3cje. Discovered in late 2016, DES16C3cje was classified as a type II supernova (SN II), however, its evolution over time has many peculiar properties, never seen before in the SN II class. Its light curve shows an atypical behaviour. On the one hand, it is a sub-luminous and very low energy event with long rise time reminiscent of SN 1987A (but in a longer scale). On the other hand, DES16C3cje showed a temporary drop in the light curve followed by a sudden increase. Its spectra show very narrow lines, implying very low expansion velocities (~1200 km/s). The spectrum at ~400 days is dominated by prominent Halpha and Ca II NIR triplet in emission, but there is no evidence of forbidden lines. Taking into account all these properties, we suggest DES16C3cje is a fall-back SN. In addition, we will discuss alternative scenarios.

The properties of the broad-lined Type Ic Supernovae that are typically discovered in coincidence with long-duration Gamma-ray Bursts will be reviewed, and compared to those of other Supernovae for which GRBs are not observed. The SNe associated with GRBs are of Type Ic. They are brighter than the norm, and show very broad absorption lines in their spectra, indicative of high expansion velocities and hence of large explosion kinetic energies. There is strong evidence for gross asymmetries in the SN ejecta. SNe associated with X-ray flashes are significantly less luminous, massive and energetic. They also appear to be less aspherical. This evidence suggests that GRB/SNe come from more massive stars. For GRB/SNe the collapsar model is traditionally favoured, while XRF/SNe may host magnetars. While the properties of the associated GRB can vary widely, those of the SNe seem to be almost constant. Possible implications of this will be discussed. Finally, the recent extension of the SN-GRB connection to ultra-long GRBs and a subclass of Superluminous SNe will be presented, and its implications discussed.

GRB 171205A was one of the closest long GRBs ever detected at only 163 Mpc and the first one ever located in a grand-design spiral galaxy. The GRB-SN was the faintest ever detected together with a very weak afterglow component. However, its proximity allows us to study the event as well as its host and the close environment of the GRB in unprecedented detail. We collected optical IFU spectra from MUSE, CO emission with ALMA and HST images at a resolution of <100 pc as well

as HI observations. This is the first time that data of the resolution of individual HII regions are available for a GRB host and the first time we can compare the current and future star-formation of the galaxy. We study the spatially resolved metallicities and abundances, star formation rate, kinematics and various other properties. The GRB site has relatively high metallicity for a GRB site of 12+log(O/H)~8.5, but also high ionization, high star-formation but little CO emission. The galaxy shows a negative metallicity gradient as expected for a grand-design spiral with an inside-out star-formation evolution. This fits well to the fact that the GRB location is in one of the outer, somewhat more metal poor, star-forming and ionized spiral arms and similar to properties of the more „usual“ dwarf starburst galaxies hosting GRBs. This galaxy confirms the idea that the local properties are crucial for the creation of a long GRB, which can occur in different kinds of (star-forming) galaxies.

ATLAS18qqn/AT2018cow/SN2018cow was discovered by the ATLAS survey as a very fast rise transient coincident with the galaxy CGCG137-068 at a redshift of 0.014. UV/optical/NIR observations revealed dominant very hot black body emission with superposed undulations that, during the first days, resembled the features of a broad-lined type Ic SN. The event was also accompanied by bright X-ray, millimetre and radio emission, which indicated an additional relativistic component. Both the relativistic emission and the possible broad-lined supernova components are typically associated with gamma-ray bursts. Here I will review the observations performed for this very peculiar event and will give our view on its nature based on the broadband observations collected by our team, including NOEMA and ALMA mm/submm data and optical spectroscopy with the 10.4m Gran Telescopio Canarias.

I will review the current understanding of superluminous supernovae and its issues with a focus on their power sources and progenitors.

Stars are expected to undergo a pair instability supernovae (PISN) if they have helium cores larger than ~60Msun. These stars are expected to be fully disrupted due to encountering the pair instability region. Here, gamma rays are converted to electron-positrons and reduce the pressure support inside the star leading to a collapse followed by a shock which disrupts the entire star. However, stars of slightly lower mass will undergo a series of pulses, rather than complete disruption when they encounter this instability, and produce a black hole remnant. Thus the boundary between these two outcomes, complete disruption or a black hole, determines the lower edge of the second black hole mass gap, a black hole mass region explorable by LIGO/VIRGO. Even more massive stars may also not be fully disrupted by the PISN, and thus potentially form ~140Msun black holes at the upper edge of the second black hole mass gap. Those objects undergoing pulses may eject up to a few solar masses of CSM, potentially proving a observational signal when the shock from the star, undergoing a core collapse, collides with this material. Here, I will discuss what conditions are necessary for a star to undergo a PISN, and what sets both the lower and upper boundaries of the second black hole mass gap. I will also discuss how robust the boundary between the different potential fates is, given uncertainties in the physics of stellar modelling and what this might entail for LIGO/VIRGO detections.

Superluminous supernovae (SLSNe) and long Gamma-Ray Bursts (LGRBs) are believed to result from the deaths of very massive stars. I will present 8m-class spectroscopic and HST imaging evidence for an unusually high fraction of high redshift SLSN and LGRB host galaxies undergoing recent galaxy interaction via their tidal tails, disturbed morphology, close companions, and/or pair absorption (two sets of galaxy absorption features very close in velocity space) in LGRB afterglow spectra. The observed fraction is ~50%, to the limiting depths and resolution of the observations. Using basic geometric arguments and the physical nature of the systems, I show that the interacting fraction is very likely ~50-100%. This investigation provides important requirements on the environment and metallicities necessary to form the massive stars that result in SLSNe and LGRBs.

Contrary to H-poor superluminous supernovae (SLSNe I), the study of H-rich SLSNe II has hitherto been restricted to a small number of individual objects, such as the exceptional SN 2006gy. Here I present a sample of SLSNe II from the Palomar Transient Factory and, for the first time, study their properties in a statistical manner, as well as their relation to other SN classes. The sample is dominated by luminous SNe IIn and has a wide distribution of absolute magnitudes from -20.6 to -22.5 mag. The decline times of SLSNe II are significantly longer than those of SLSNe I even for similar rise times. Simple CSM model fits and a short discussion of their spectroscopic properties will also be presented.

In this talk, I present a historical review of supernova discovery programs in Chile, beginning with the pioneering work of José Maza's group in 1979, and extending to the expectation of millions of supernova discoveries by the LSST. I will also briefly highlight the work of the Carnegie Supernova Project, in which Nidia Morrell has played a fundamental role during the last 15 years.

[6.2] Early supernova discoveries: what can the observers contribute to our understanding of the final breaths of massive stars, progenitors of core-collapse supernovae

Ofer Yaron

ofer.yaron AT weizmann.ac.il

Weizmann Institute for Science

We have finally entered the era of Day-1 supernova (SN) observations, enabling us to systematically probe temporal regimes that were previously accessible only by chance. Discovering a SN in its infancy, several hours from explosion, and utilizing quick and efficient follow-up capabilities allows us to directly probe the immediate surrounding of the star that has just exploded, before the whole region is “destroyed” by the several solar masses of the SN ejecta. A sample of “Flash-Spectroscopy” events from the last several years revealed strong evidence for the existence of nearby circumstellar distribution of material (CSM) that is likely ejected from the progenitor star at an elevated, maybe eruptive, manner, shortly (months to several years) before the final demise of the massive star. Accumulated observational evidence points to the understanding that this phenomenon is possibly more widespread than previously anticipated. These realizations have already began providing additional boost for theoretical studies that aim at improving our understanding of the very final stages in the evolution of massive stars. Constraining (by direct prompt observations) the mass-loss history, surface composition and profiles of various thermodynamic properties of the progenitor star at the onset of explosion also provides meaningful initial conditions for the explosion calculations themselves. I will also briefly mention near-future prospects of both ground and space-based transient-hunting facilities; all of which have the potential to further shorten our discovery and follow-up capabilities to within the 1-hour(!) timespan from explosion.

[6.3] Shock breakout delay due to circumstellar material seen in most Type II supernovae

Förster Francisco

francisco.forster AT gmail.com

Center for Mathematical Modeling - U. Chile / Millennium Institute for Astrophysics

Type II supernovae (SNe) originate from the explosion of hydrogen–rich supergiant massivestars. Their first electromagnetic signature is the shock breakout, a short–lived phenomenon which can last from hours to days depending on the density at shock emergence. We present 26 rising optical light curves of SN II candidates discovered shortly after explosion by the High cadence Transient Survey (HiTS) and derive physical parameters based on hydrodynamical models using a Bayesian approach. We observe a steep rise of a few days in 24 out of 26 SN II candidates, indicating the systematic detection of shock breakouts in a dense circumstellar matter consistent with a mass loss rate Ṁ > 10 −4 Msun yr −1 or a dense atmosphere. This implies that the characteristic hour timescale signature of stellar envelope SBOs may be rare in nature and could be delayed into longer–lived circumstellar material shock breakouts in most Type II SNe.

[6.4] High-cadence light curves of transients from the Kepler Telescope

Rest Armin

arest AT stsci.edu

Space Telescope Science Institute

Despite the expanding set of SNe discovered in recent surveys like PS1, ATLAS, PTF, and ASAS-SN, several fundamental questions remain of the nature of these explosions and their progenitor systems. The early light curves of SNe contain the critical information to understanding the nature of the progenitors and explosion physics: detonation, deflagration, and inwards-moving diffusion waves and much more. However, it has been difficult to obtain early light curve data with sufficient cadence and accuracy from the ground. With K2, and in the future TESS, we are now able to obtain high-cadence early light curves with exquisite photometric accuracy for thermonuclear and core-collapse SNe. I will discuss our growing and diverse sample of transients with high cadence light curves, ranging from SN Ia and IIPs to more exotic events like IIb's, fast transients, and TDEs.

[6.5] Wide-Field supernova surveys: probing new regimes of transient science [INVITED]

Drout Maria

mdrout AT carnegiescience.edu

Carnegie Observatories

The astronomical community quickly progressed from discovering a few dozen supernova in the early 1990s to more than 10,000 supernova and other transients in 2018. In this talk I will give a broad overview of how modern wide-field time domain surveys are facilitating new types of scientific discoveries. I will focus on three main pillars: (a) the identification of large samples of known classes of supernovae (b) the discovery of intrinsically rare transients and (c) opening new regimes of transient science. For each pillar I will highlight recent scientific results, emphasizing how survey design impacts the types of discoveries the can be made, and giving prospects for future and upcoming missions.

[6.6] Observational differences and similarities between SNe II and stripped-envelope events

Anderson Joseph

janderso AT eso.org

ESO

Core-collapse supernovae (CCSNe) can be broadly separated into those events showing long-lasting

hydrogen in their spectra; SNeII, and those that don't; stripped-envelope SNe (SE-SNe: IIb, Ib and Ic). This difference implies that the latter have been stripped of the majority (or all) of their outer hydrogen-dominated envelopes before explosion. Mass can be lost through various channels: steady winds; eruptive winds; mass transfer to a binary companion. Which of these processes dominate is still unknown as is the fraction of SE-SNe produced through single or binary-star channels. Here, I will first summarise the range of observational constraints on the explosions and progenitors of SNeII and SE-SNe and discuss how these imply differences and also similarity in their progenitor properties. Then, I will focus on two specific constraints. 1) I will discuss the nature of the environments of CCSNe and argue that they imply statistical differences in the progenitors of different events. 2) I will present a meta analysis of estimated CCSN Ni56 masses. The latter distributions shows clear, significant differences between SNeII and SE-SNe. In addition, SE-SN Ni56 masses appear - in general - to be too large to be explained through standard explosion models using progenitors with standard density profiles. Finally, I will summarise the implications of these results for our overall understanding of the diversity in CCSN progentiors and explosions.

[6.7] Comparison of optical light curves of hydrogen-rich and hydrogen poor type II supernovae

Pessi Priscila J.

pjpessi AT gmail.com

Facultad de Ciencias Astronómicas y Geofísicas (FCAG), Instituto de Astrofísica de La Plata (IALP)

P. J. Pessi, G. Folatelli and J. P. Anderson

We present a comparative study of the light-curve morphology between hydrogen-rich (Type II) and hydrogen-poor (Type IIb) supernovae (SNe). The ultimate goal of this study is to tackle the question of whether these two types of events have a common origin. It is assumed that Type II SNe arise from massive stars that retained a large fraction of their outer envelopes, and that Type IIb SNe exhibit less hydrogen because their progenitors lost most, although not all, of their envelopes. If both Types share a common progenitor nature, then it is expected that the SN properties should show a continuum. The opposite is expected if they arise from different evolutionary channels (e.g., one Type coming from single stars and the other from binaries). In this work we explore a set of self-defined parameters related to the light-curve shapes, such as rise times and decline rates, based on a sample of 73 Type II SNe and 23 Type IIb SNe. We find evidence against the existence of a continuum of properties between both Types, which suggests a different origin of their progenitors.

[6.8] Connecting supernova rates with the host galaxies parameters: results from the SUDARE survey

Pignata Giuliano

pignago AT gmail.com

Universidad Andres Bello

Supernova (SN) rates as a function of cosmic time and their link with the properties of the galaxy parent population is a powerful tool to investigate the nature of progenitor stars and to shed light on the origin of SN diversity. I will present supernova rates per unit volume and per unit of mass computed from the data collected by the Supernova Diversity and Rate Evolution (SUDARE) experiment. I will show the correlation between the rates of SNe of different type and the main parameters of the host galaxies. SUDARE monitored the Cosmic Evolution Survey (COSMOS) and Chandra Deep Field South (CDFS) fields in the g; r; i filters with the VLT Survey Telescope (VST) between 2011 and 2015. At the same epochs COSMOS and CDFS have been also observed by the VISTA public surveys UltraVISTA and VIDEO, providing the opportunity to compare optical and NIR SN rates in the same galaxy sample. I will present preliminary results on this comparison.

[6.9] Using the environment to infer supernova progenitor properties

Galbany Lluís

lluisgalbany AT gmail.com

U. Pittsburgh

Integral Field Spectroscopy (IFS) applied to supernova (SN) environmental studies have shown the potential of this technique to directly characterize the galactic environmental parameters at SN locations, compare them to those at different locations of the galaxy, and put constraints on progenitor stars for different SN types. Here, I will summarize current efforts from the PISCO compilation, Hi-KIDS, and the AMUSING survey, that have put together more than 500 SN hosts observed with IFS, and give details about published results from these 3 datasets.

[6.10] Host environments of long GRBs, SLSNe and SNe Ic-BL: implications for progenitors

Vergani Susanna

s usanna.vergani AT obspm.fr

CNRS - Paris Observatory

A robust understanding on which are the key properties (e.g. mass, binarity, metallicity, rotation rate, mass-loss and probably magnetic fields) of massive stars that lead to the different types of core-collapse SNe is still to be achieved. I will present the results of the series of studies carried out by our group over the last years on the host galaxies of long gamma-ray bursts (LGRBs), super-luminous supernovae (SLSNe) and broad-line Ic supernovae (Ic-BL Sne). Lacking the direct evidence of their progenitors because of their distances, we obtain indirect information from the study and comparison of the properties of the host galaxies of these explosions. We confirm that metallicity is an important driver of the different explosions, though the trend we find is different from past studies. In general we find similar properties for GRBs and type-I SLSN host galaxies. The differences we highlight for those of Ic-BL SNe allow us to conclude that there is a genuine Ic-BL SN population not associated with GRB explosions.

Session 7: Cosmology with supernovae

[7.1] Measuring the Hubble constant: it takes a village [INVITED]

Burns Christopher

cburns AT carnegiescience.edu

Carnegie Observatories

Ever since it was first measured in 1927, the value of the Hubble constant has been contentious. Despite a general convergence over the past 90 years, there has always seemed to be a “high camp” and “low camp”. That continues to this day, where Cosmic Microwave Background (CMB) measurements find a low value (~67 km/s/Mpc) and local measurements find a high value (~73 km/s/Mpc). This “tension” could herald new physics or indicate some unknown systematic. In this talk, I will describe the local measurement using type Ia supernovae. But these are just the last rung in a complex network of distance indicators, which I will discuss. Lastly, I will present the latest measurement of the Hubble constant from the Carnegie Supernova Project.

[7.2] Near-IR Hubble diagrams of SNe II

Rodríguez Ósmar

olrodrig AT gmail.com

Universidad Andres Bello / MAS

In a previous work we show that, at near-IR wavelengths, SNe II have the potential to become standardizable candles as good as SNe Ia. This promising result is limited by the small SN sample we use for the analysis, which makes results not fully statistically robust. In this talk I will present the results of the SN II follow-up campaign we carried out during 2015-2018. These data were used to compute near-IR distances to SNe II using the Photosphere Magnitude Method. With around 60 SNe II at z=0.01-0.03 we construct near-IR Hubble diagrams, which allow to constrain more robustly the precision of SNe II distances at near-IR wavelengths.

[7.3] Optimizing spectroscopic follow-up strategies for supernova photometric classification with active learning

González-Gaitán Santiago

gongsale AT gmail.com

Instituto Superior Tecnico, Universidade de Lisboa

We report a framework for spectroscopic follow-up design for optimizing supernova photometric classification for cosmology in coming large wide-field surveys like LSST. The strategy accounts for the unavoidable mismatch between spectroscopic and photometric samples, and can be used even in the beginning of a new survey – without any initial training set. The framework uses so called Active Learning to minimize the number of spectroscopic objects needed in a training set. Using the Supernova Photometric Classification Challenge (SNPCC) and a random forest classifier, we show that using only 12% of the spectroscopic training sample, this approach is able to double the purity. Such results were obtained using the same amount of spectroscopic time necessary to observe the original SNPCC spectroscopic sample, showing that this type of strategy is feasible with current available spectroscopic resources.

[7.4] Young super stellar clusters: precision cosmology and the universality of the initial mass function

Terlevich Roberto

rjt AT inaoep.mx

Instituto Nacional de Astrofísica, Óptica y Electrónica, Puebla

I will report results of our study of the properties of the young Super Stellar Clusters that power Giant HII regions and HII galaxies. I will discuss the tight relation between ionized gas velocity dispersions and Balmer emission line luminosities in these systems, its implications and its use as distance indicator to trace the expansion of the Universe up to z ~ 3 with present ground based instrumentation and up to z ~ 9 with JWST. This approach yields tight independent constraints on H0, Ωm and the Dark Energy equation of state parameter w. The combined analysis of HIIG and SNIa results provides strong cosmology independent constrains. The concordance between our determinations of H0, Ωm and w with those from SNIa, BAO and Planck strongly support a universal IMF in these young and massive Super Stellar Clusters.

Session 8: SN Ia progenitors and explosion mechanisms

[8.1] Constraining the explosions and progenitor systems of Type Ia supernovae [INVITED]

Maguire Kate

kate.maguire AT qub.ac.uk

Queen's University Belfast

The stellar systems that explode as Type Ia supernovae remain elusive. Despite extensive theoretical and observational work, the subtle signatures that would allow us to distinguish between progenitor scenarios have not been identified. In this talk, I will review the main models for producing Type Ia supernovae and their predicted observational signatures, as well as give an overview of current surveys and studies that aim to test these predictions. In particular, I will describe how very early observations of Type Ia supernovae very soon after explosion are a very promising method for understanding how they explode. I will also describe future prospects for improving their use as cosmological distance indicators by better understanding what the stellar systems that produce them.

[8.2] Red vs blue: early observations of thermonuclear supernovae reveal two distinct populations?

Stritzinger Maximilian

max AT phys.au.dk

Aarhus University

I will present an examination of the early phase intrinsic B-V color evolution of a dozen Type Ia supernovae discovered within three days of inferred time of first light and that have B-V color information beginning within 5 days of the time of first light. Inspection of the current sample indicates two distinct early populations. The first is a population exhibiting blue colors that slowly evolve, and the second population exhibits red colors and evolves more rapidly. Placing the first sample on the Branch diagram indicates all blue objects are of the Branch Shallow Silicon (SS) spectral type, while all early-red events – except for the peculiar SN 2012fr – are of the Branch Core-Normal (CN) or CooL (CL) type. Inspection of their light curves indicate early-blue events are typically more luminous with slower declining light curves than those exhibiting early-red colors. A number of potential processes contributing to the early emission will be briefly mentioned, and I conclude that great care must be taken when interpreting early-phase light curves of Type Ia supernovae.

[8.3] Multiple origins of early-excess Type Ia supernovae and their implications

Jiang Ji-an

yuzhoujiang AT ioa.s.u-tokyo.ac.jp

The University of Tokyo

Photometric information within a few days of type Ia supernova (SN Ia) explosion plays an important role in understanding the progenitor system and explosion mechanism of SNe Ia. Here, we will present SNe Ia which show additional luminosity enhancement in the early phase ("early-excess SNe Ia"), and further discuss possible origins of these peculiar early-phase light curves. Then, we will introduce our on going survey projects which are optimized for hunting SNe in the early phase with the new-generation wide-field survey facilities.

[8.4] NIR spectroscopy of Type Ia supernovae

Hsiao Eric

ehsiao AT fsu.edu

Florida State University

Shifting Type Ia supernova (SNIa) cosmology to the near-infrared (NIR) is a promising way to significantly reduce the systematic errors, as the strategy minimizes our reliance on the empirical width-luminosity relation and unknown dust laws. Any future experiments in the rest-frame NIR would require knowledge of the SNIa NIR spectroscopic evolution, which is currently based on a small sample of observed spectra. We introduce the unique four-year NIR spectroscopy program, part of the Carnegie Supernova Project-II (CSP-II). We obtained 624 NIR spectra of 151 SNe Ia. Within this sample, 513 NIR spectra of 114 SNe Ia have CSP-II follow-up light curves. Such a sample will allow detailed studies of the NIR spectroscopic properties of SNe Ia, as well as, open up the wavelength window to improve our understanding of the physics and origins of SNe Ia.

[8.5] SN Ia progenitors and explosion mechanisms [INVITED]

Maeda Keiichi

keiichi.maeda AT kusastro.kyoto-u.ac.jp

Kyoto University

I will provide a review on the current status of observational constraints on the progenitor systems and explosion mechanisms of type Ia Supernovae (SNe Ia). Recent development in the field is highlighted by accumulating observational discoveries of diversities found for SNe Ia. An idea is emerging that SNe Ia are perhaps not at all a uniform system as previously believed for many years, and thermonuclear explosions may lead to various outcomes which could correspond to various types of transients. In this talk, I will summarize different observational constraints placed for different sub-types of SNe Ia and related phenomena, and connect these findings to different types of progenitors and modes of explosions which have been theoretically predicted.

[8.6] Progenitor signatures of Type Ia supernovae

Hoeflich Peter

phoefich77 AT gmail.com

Florida State University

We discuss new signatures of the progenitors of SN Ia in light of recent observations and the upcoming JWST.

[8.7] Fast declining SNe Ia in the NIR

Ashall Chris

chris.ashall24 AT gmail.com

Florida State University

The exact nature of the explosion mechanism and progenitors of Type Ia Supernova (SNe Ia) is still unknown. It is under debate whether SNe Ia come from one of multiple populations (i.e. Ch-mass vs sub-Ch mass explosion, delayed denotations vs. pulsation delayed detonations). Fast declining and normal SNe Ia have been theorized to be both from the same population and different populations. Spectroscopically, in the NIR SNe Ia show alot more diversity than in the optical. Therefore probing these wavelengths provides more clues about the physics of these explosions. I will present a subset of the CSP-II SNe Ia dataset. ~80 NIR spectra of 24 fast declining (ΔM15>1.4 mag) SNe Ia will be shown. I will present a comparison to explosion models and specifically show: how the location of the 56Ni changes for different objects, how metallicity affects the spectra, and how the distribution of unburnt material varies. Finally I explore the possibility that sub-luminous objects could be distinct from normal ones.

[8.8] NIR nickel emission features in SN Ia spectra

Kumar Sahana

sahanak AT gmail.com

Florida State University / CSP2

Near Infrared (NIR) spectra of Type Ia supernovae (SN Ia) can yield constraints on their progenitor systems and explosion mechanisms. The presence of NIR nickel features at late times may constrain the likelihood of sub-Chandrasekhar-mass explosions. Since radioactive Nickel-56 synthesized in the explosion decays to Cobalt by late times, these nickel emission features may be attributed to stable Nickel-58 in the central region of the supernova, thus indicating higher central densities that require a progenitor mass near the Chandrasekhar mass. Recent models (Friesen et al. 2014, Blondin et al. 2015, Wilk et al. 2017) predict a [Ni II] 1.939 micron emission feature during the transitional phase that begins approximately +30 days past peak brightness. However there is significant disagreement on the strength, identification, and temporal evolution of this emission feature. High quality NIR spectra obtained using the high-throughput FIRE spectrometer provide the opportunity to investigate these spectral features and compare observations to various models. Our sample includes 143 NIR FIRE spectra of nearby SNe Ia at phases spanning from +30 days past peak brightness through +150 days past peak.