STScI 2019 Spring Symposium Posters

Click on each entry to access the abstract and view the poster. [slideshow]

Mohammad Akashi, Technion

The Formation of Columns Crowns by Jets Interacting with a Circumstellar Dense Shell

"We conduct three-dimensional hydrodynamical simulations of two opposite jets that interact with a spherical slow wind that includes a denser shell embedded within it, and obtain a bipolar nebula where each of the two lobes is composed of two connected bubbles and Rayleigh-Taylor instability tongues that protrude from the outer bubble and form the _columns crown_. The jets are launched for a short time of 17 years and inflate a bipolar nebula inside a slow wind. When the bipolar structure encounters the dense shell, the interaction causes each of the two lobes to split to two connected bubbles. The interaction is prone to Rayleigh-Taylor instabilities that form tongues that protrude as columns from the outer bubble. The bases of the columns form a ring on the surface of the outer bubble, and the structure resemble a crown that we term the columns crown. This structure resembles, but is not identical to, the many filaments that protrude from the lobes of the bipolar planetary nebula Menzel 3. We discuss our results in comparison to the structure of Menzel 3 and the ways by which the discrepancies can be reconciled, and possibly turn our failure to reproduce the exact structure of Menzel 3 to a success with jets-shell interaction simulations that include more ingredients.",

Andrea Antoni, UC Berkeley

The Evolution of Binaries in a Gaseous Medium: Three-Dimensional Simulations of Binary Bondi-Hoyle-Lyttleton Accretion

"Binary systems in gaseous environments may evolve more quickly than via gravitational wave (GW) radiation alone. In these environments, the merger of binary black holes (BBHs) may be accompanied by electromagnetic emission. The disks of active galactic nuclei (AGN), in particular, readily trap and assemble stellar-mass BBHs. Drag forces and accretion rates dictate how these systems are transformed due to the gas. Here, we describe the results of three-dimensional hydrodynamic simulations of binaries embedded in Bondi-Hoyle-Lyttleton flows. The simulations indicate that a binary's center-of-mass motion is slowed over a shorter timescale than the pair inspirals or accretes and that the timescale for orbital inspiral is proportional to the semi-major axis to the 0.19 power. This positive scaling implies that gaseous drag forces can drive binaries either to coalescence or to the critical separation at which GW radiation dominates their further evolution. We provide the critical separation between gas- and GW- dominated inspiral and discuss the implications of these results for binaries in AGN disks and in common envelope phases.",

Igor Andreoni, Caltech

Probing the extragalactic fast transient sky at minute timescales with DECam

"We probed the fast transient sky with continuous 20s exposures with a field of view of 2.52 deg^2 at magnitude g < 23 for 26hr, searching for minute-timescale optical transients. Simultaneous multi-wavelength observations part of the Deeper, Wider, Faster program allowed us to search for fast radio burst and gamma-ray counterparts.",

Fiona Audcent-Ross, ICRAR-UWA

Radial Distribution of SNe vs Star Formation Tracers

"Given the limited availability of direct evidence (pre-explosion observations) for supernovae (SNe) progenitors, the location of SNe within their host galaxies can be used to set limits on one of their most fundamental characteristics, the initial mass of their progenitors. We present our constraints on the progenitors of Type Ia, Type II and stripped-envelope SNe (SE SNe), derived from comparing the radial distributions of 78 SNe in the SINGG and SUNGG surveys to the R-band, HAlpha, NUV and FUV fluxes of the 59 host galaxies. The strong correlation of SINGG Type Ia SNe with R-band fluxes is expected with progenitor models containing only low mass progenitors, such as the double degenerate model. SINGG Type Ia SNe do not trace FUV fluxes implying that the single degenerate model, which invokes a main sequence companion to the white dwarf progenitor, is an unlikely major progenitor stream for Type Ia SNe. Within smaller apertures containing 90 per cent of the total flux the radial distribution of the Type II SNe best traces FUV fluxes. This result is in line with the growing number of direct detections indicating that Type II SNe have moderately massive red supergiant progenitors. The 15 SE SNe have the strongest correlation with Halpha fluxes, consistent with very massive progenitors (Mstar gt 20solar). This result is in contradiction with a small, but growing, number of direct detections of SE SNe progenitors revealing a predominance of moderately massive binary systems but is consistent with a recent population analysis of SE SNe locations suggesting binary progenitor masses are regularly underestimated. The SE SNe are centralised with respect to Type II SNe and there are no SE SNe recorded in the outer third of the FUV apertures and none in the outer ~20 per cent of the R-band apertures. The observed deficit of SE SNe is consistent with reduced massive star formation efficiencies in the outskirts of the SINGG galaxies.",

Christopher Berry, Northwestern University

Revealing the Evolution of High-mass Binaries Using Gravitational-wave Observations

"The binary black holes observed by LIGO and Virgo provide a new source of information regarding the end-points of stellar evolution. Multiple potential formation channels have been suggested for these binaries, and each of these have associated physical uncertainties. The details of the formation channels leave imprints on the properties of the binary black holes, such as masses and spins. From these, we can infer how binary black holes form. With 1000 detections, we can use the chirp-mass distribution and merger rate to constrain population parameters for isolated binary evolution (such as common-envelope efficiency, natal kicks and mass-loss rates) to precision of a few percent. The merger rate is expected to evolve with redshift. This can be non-parametrically reconstructed, and used to further enhance constraints on binary evolution. Combining all the information from gravitational-wave observations will provide a tough test of our best models of binary evolution.",

William Blair, Johns Hopkins University

Results from Deep Multi-Wavelength Surveys of Nearby Galaxies to Study Supernova Remnants and Their Progenitors

"Supernova remnants (SNRs) are central to the overall cycle of star formation and evolution, depositing both energy and processed stellar ejecta back into the ISM of a galaxy. On the largest scales, the ensemble of SNRs in a galaxy thus becomes integral to the evolution of a galaxy as a whole. We will report key results from a multi-year, multi-wavelength campaign to identify and characterize the SNR populations in nearby galaxies, using observational techniques as diverse as ground-based imaging and spectroscopy, HST optical and near IR imaging in emission line and continuum bands, deep Chandra and XMM-Newton X-ray imaging surveys, and deep radio multi-frequency observations (to separate photoionized and non-thermal sources). We have focused our efforts especially on M33, M83, and NGC 6946, all relatively nearby and nearly face-on spiral galaxies. M33 is of course the closest of these (816 kpc), so the SNR morphologies and diameters are revealed even at ground-based resolution, but the large angular size of M33 makes surveys challenging. Some 220 optical SNRs have been located, 112 of which have X-ray counterparts. At radio wavelengths (White et al., this symposium) we detect 155 of the optical SNRs, and we show that the current generation of models for the radio emission are inadequate to explain the observations. No ejecta-dominated or Crab Nebula-like SNRs have been identified. M83 (4.6 Mpc) and NGC 6946 (6.7 Mpc) are both star-forming spiral galaxies that have hosted record numbers of historical SNe, and are close enough that HST resolution provides diameter estimates and morphology information for many of the SNRs. Despite the apparent frequency of SNe and numerous small-diameter (<10 pc) SNRs, only the remnant of SN 1957D in M83 shows evidence for ejecta in the form of broad lines exclusively from heavy elements. We have, however obtained spectra from the _old SNe_ SN1980K and SN2004et, (both in NGC 6946), plus the remnant of another SN that evidently exploded in M83 in the 20th century but was not observed. The spectra from all these indicate interaction of fast shocks with circumstellar shells. Thus, we find a paucity of young ejecta-dominated SNRs which may be due to very rapid evolution of most core-collapse SNe into an ISM-dominated state. We are using HST multi-band stellar photometry of stars adjacent to SNRs to constrain the progenitor masses of core collapse SNe. Recently, we have run this analysis on over 200 of the SNRs in M83 and compared the results with Local Group galaxies. Some progenitors are demonstrably above 20 Msol, and the progenitor mass distribution appears to be more top-heavy than found for SNRs M33 and M31.",

Azalee Bostroem, UC Davis

Using Supernovae to Understand Their Massive Star Progenitors

"Massive stars, the progenitors of core-collapse supernovae (CCSNe), are not well understood, especially as they near core-collapse. Modelling multi-wavelength observations that span the photometric and spectroscopic evolution of a supernova allows us to describe the progenitor star (e.g. mass, radius, mass-loss history), as well as the explosion parameters (e.g. explosion energy, explosion asymmetry, and nucleosynthesis yields). We will discuss the progenitor models of two CCSNe: ASASSN-15oz and DLT18aq (2018ivc) as well as future work to characterize the progenitors of a sample of CCSNe through light curve and nebular spectra modeling.",

Christopher Britt, STScI

Finding Millisecond Pulsars to Explain the Fermi Gamma-ray Excess

"We have performed new 1.4 GHz and 5 GHz observations of the Local Group galaxy M33 with the Jansky Very Large Array. Our survey has a limiting sensitivity of 20 uJy (4-sigma) and a resolution of 5.9 arcsec (FWHM), corresponding to a spatial resolution of 24 pc at 817 kpc. Using a novel multi-resolution algorithm, we have created a catalog of 2875 sources, including 675 with well-determined spectral indices. Along with numerous H II regions, we detect 155 of the 217 optical supernova remnants included in the lists of Long et al. (2010) and Lee & Lee (2014). Current X-ray surveys have detected 98 of the radio-detected remnants, making this by far the largest sample of remnants at known distances with multiwavelength coverage. In M33 we can directly compare the X-ray, optical, and radio properties for a larger sample of supernova remnants at a common distance than for any other galaxy. The remnants show a large dispersion in the ratio of radio to X-ray luminosity at a given diameter, a result that challenges the current generation of models for synchrotron radiation evolution in supernova remnants. We will report the results of exploring the high-dimensional dataset using tools such as principal component analysis and t-SNE. This approach will be helpful for studies of the X-ray source population by distinguishing background AGNs from sources in M33.",

Peter Brown, Texas A&M

Ultraviolet Diversity of Standard Candles

"Ultraviolet spectroscopic observations with the Hubble Space Telescope are explaining some of the diversity seen in nearby Type Ia supernovae with the Neil Gehrels Swift Observatory. We will compare the UV-bright Super-Chandrasekhar SN2016ccj, UV-blue normal SNe 2011fe and 2011by, the intrinsically-red and dust-reddened SN2017erp. Understanding the diversity of these standard candles is important to accurately and confidently use them as cosmological distance indicators through the history of the universe.",

Jesse Bublitz, Rochester Institute of Technology

Irradiation Investigation: Exploring the Molecular Gas in Planetary Nebulae

"Planetary nebulae (PNe) represent the end stages of mass loss from low- to intermediate-mass stars. For some PNe, significant quantities of dense molecular gas and dust remain present in their stellar ejecta. Photodissociation and photoionization by UV and (in some objects) X-ray emission from the central stellar remnant then drive the chemical evolution. PNe with well-defined geometries and irradiation hence make ideal testbeds for models of radiation-driven heating and chemistry of molecular gas. We report the results of recent mm-wave molecular line surveys of nearby, well-studied PNe. We have obtained IRAM 30 m radio telescope observations of nine objects, and have targeted specific dense molecular knots in the Helix (NGC 7293) with the 30 m and ALMA. Among other results, these studies illustrate how the HNC/HCN abundance ratio serves as a diagnostic of UV irradiation of molecular gas. Meanwhile, our new IRAM/NOEMA maps of CO+ and HCO+ emission from the young PN NGC 7027 provide key insight into the mechanisms driving molecular ionization. These results demonstrate the potential applicability of molecule-rich PNe studies for other astrophysical environments in which molecular gas is irradiated by high-energy photons.",

Yssavo Camacho-Neves, Rutgers University

The Afterlife of Type Iax Supernovae

"Type Ia Supernovae (SN Ia) have been instrumental cosmological standard candles that led to the discovery of the accelerated expansion of the Universe. Yet, the progenitors and explosion mechanism of these important and powerful transient events remain elusive. Members of the recently categorized Type Iax (SN Iax) class may be able to constrain models and progenitor systems for exploding white dwarfs. SN Iax are the largest class of _peculiar_ white dwarf supernovae (>50 members). They have lower ejecta velocity, lower luminosities, and the only white dwarf supernova for which a pre-explosion progenitor system has been detected is a SN Iax. We aim to give an overview of the SN Iax class and present optical spectroscopy of SN 2014dt, a SN Iax in the nearby galaxy M61 that was the focus of extensive observations. We analyze the spectral evolution of SN 2014dt and compare it to the evolution of normal SN Ia, showing that SN 2014dt begins a _divergence phase_ from normal SN Ia around 100 days after peak brightness. We also use TARDIS to generate synthetic spectra of SN 2014dt to analyze the composition of the ejecta and to probe how the physical parameters of the explosion evolve with time. We argue that SN Iax may continue to have an ""afterlife"" beyond the supernova explosion, with a radioactively-powered bound remnant driving an optically-thick wind.",

Luke Chamandy, University Of Rochester

Global 3D Simulations of Common Envelope Evolution Using AMR

"Common envelope evolution (CEE) is key to understanding the fates of many binary stellar systems, including planetary nebulae and cataclysmic events involving the merger of two compact objects. We analyze four 3D high-resolution hydrodynamic simulations of CEE involving a $2\mathrm{M}_\odot$ red giant branch or asymptotic giant branch primary and a $0.25\mathrm{M}_\odot$, $0.5\mathrm{M}_\odot$ or $1\mathrm{M}_\odot$ secondary modeled as a point particle to understand the time evolution of energy transfer between various forms, the amount of unbinding of the envelope, and the influence of giant type and secondary mass. Although most of the envelope unbinding occurs during the initial plunge-in phase, most of the energy transferred to the tenuous outer envelope is compensated by tighter binding of the inner layers to the plunging secondary so that minimal net energy is transferred between the cores and envelope. Subsequently, energy is gradual transferred steadily from the cores to the envelope but not enough to unbind the remainder of the envelope. In analyzing the results, we assess the commonly used $\alpha_\mathrm{CE}$-energy formalism, and suggest an alternative that more cleanly separates core particles and gas. We discuss whether complete envelope ejection might be ",

Sihao Cheng, Johns Hopkins University

High-Mass White Dwarfs in Gaia DR2: the Q Branch and WD-WD Merger Rate

Studying highmass white dwarfs WDs can shed light on the progenitors of Type Ia supernovae. Recently the unprecedented power of Gaia data has revealed an unexpected enhancement of highmass WDs on the HR diagram called the Q branch. It indicates that some WDs are experiencing a delay in their cooling. To study their origin we analyze the velocity distribution of all WDs within 250 pc and estimate their kinematic ages. We find that 7 percent of WDs have an 8 Gyr cooling delay on the Q branch in addition to the delay caused by crystallization and mergers. We propose that such a long delay may be explained by the settling of 22Ne in WDWD merger products. Our velocity analysis also allows us to show that 12 to 25 percent of all high mass WDs result from mergers corresponding to a merger rate of 2.3 times 10 to minus 14th per solar mass per year in the mass range 1.09 to 1.27 solar masses. This is the most direct observational constraint on the rate of WDWD mergers a promising channel of Type Ia supernova explosions1,

Brian Davis, Penn State

An Empirical Limit on the Minimum Mass for Hot-Bottom Burning

"The [O III] 5007 planetary nebula luminosity function (PNLF) has been used as an extragalactic distance indicator for three decades. But the function is much more than a standard candle: it is also a way to probe the mass distribution of the brightest post-AGB stars in a stellar population. Such information is enormously important, as TP-AGB stars---the immediate progenitors of these post-AGB objects---are critical to our understanding of a galaxy_s near-IR energy budget and its integrated stellar mass. One issue that has prevented the PNLF from being used in this way is the unknown contribution of circumstellar extinction, as one generally only observes the emergent flux from a PN, not the total unattenuated flux. For the first time, we have determined the de-reddened PNLF of an old stellar population. By performing spectroscopy of the brightest PNe in M31_s bulge and measuring the objects_ Balmer decrements, we have removed the effects of circumstellar extinction and derived the true distribution of [O III] 5007 luminosities. We show that the bright PNe in the region are typically twice as luminous as what one would infer from their observed [O III] fluxes, and that even with accelerated-evolution post-AGB tracks, traditional population synthesis models cannot come close to producing the luminosities of their central stars. Since there are more than 10,000 AGB stars for every bright PN, our results show the necessity of including alternative channels of stellar evolution in population synthesis modeling.",

Mariangelly Diaz-Rodriguez, Florida State University

Progenitor Mass Distribution for Core Collapse Supernova Remnants

"We infer the progenitor mass distribution for 100 core-collapse supernovae. In particular, we infer the age of stellar populations surrounding 94 supernova remnants (SNRs) in M31 and M33. From these ages, we infer the progenitor mass distribution. Assuming each progenitor evolved as a single star, we find that the minimum mass is $M_{min} = 7.33^{+0.02}_{-0.16} msun$, the slope of the progenitor distribution is $\alpha = -2.96^{+0.45}_{-0.25}$, and the maximum mass is greater than $M_{max} > 38 msun$. The accuracy on the minimum mass may provide tight constraints on stellar evolution. The steep distribution suggests that the most massive stars are either not exploding with the same frequency as the stars near the minimum mass, or SNR catalogs are biased against the youngest SF regions. If there is a bias on the SNR catalogs, it will most likely only affect the slope. This bias will not affect the minimum mass or the lower limit on the maximum mass. In the future, we will infer the progenitor ages and masses for thousands of SNRs, placing unique and robust constraints on which stars explode as CCSNe.",

Francisco Forster, Millennium Institute Of Astrophysics

Shock Breakout Delayed by Circumstellar Material Detected in Most Type II Supernovae

"Type II supernovae (SNe) originate from the explosion of hydrogen_rich supergiant massive stars. Their first electromagnetic signature is the shock breakout (SBO), 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 SBOs in a dense circumstellar matter (CSM) consistent with a mass loss rate _ > 10 _4 M 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 CSM SBOs in most Type II SNe.",

Ori Fox, STScI

Signatures of Circumstellar Interaction in the Unusual Transient AT2018cow

"AT2018cow is a unique transient that stands out due to its relatively fast light-curve, high peak bolometric luminosity, and blue color. These properties distinguish it from typical radioactively powered core-collapse supernovae (SNe). Instead, the characteristics are more similar to a growing sample of Fast Blue Optical Transients (FBOTs). Mostly discovered at hundreds of Mpc, FBOT follow-up is usually limited to several photometry points and low signal-to-noise spectra. At only ~60 Mpc, AT2018cow offers an opportunity for detailed followup. Studies of this object published to date invoke a number of exotic interpretations for AT2018cow, including Tidal Disruption Events and Magnetars. I will present a new, recently submitted study that suggests that AT2018cow may be better described as SN undergoing significant, early-time interaction with a dense, nearby Hydrogen poor CSM shell, similar to some SNe Ibn. I show that while the spectra were dominated by a featureless blue continuum at early times, narrow lines on order of ~1000 km/s begin to emerge by day ~50. I go on to compare AT2018cow to interacting SNe Ibn and transitional IIn, finding a number of noteworthy similarities, including light-curve rise and fall times, peak magnitude, X-ray light-curves, and spectroscopic properties.",

Andrew Fullard, University Of Denver

Spectropolarimetric Analysis of WR + O Binaries with SALT

"Massive stars often occur in binaries, and WR stars are no exception. Interaction in binaries can affect their mass loss rates, and possibly provide the rapid rotation thought to be required for GRB production. Spectropolarimetry can help us to better characterize the CSM created by the stars_ colliding winds, and thus constrain mass loss and probe wind interaction. 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. 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 WC8d+O8-9IV binary WR 113 (SV Ser), using archival data and radiative transfer models of the scattering structures revealed by the new observations.",late

Monica Gallegos Garcia, Northwestern University

Revisiting the Treatment of Common-envelope Evolution in Population Synthesis Codes

"Rapid binary population synthesis codes have been used for decades to investigate the complex evolution of compact binaries. Although these codes are widely used, they typically lack thorough calculations and prescriptions of physical processes (e.g., common-envelope, Roche lobe overflow, post main-sequence evolution) that are crucial to accurately predict the fate of these binary systems. Many of these processes, however, have been more carefully implemented in stellar evolution codes such as MESA (Modules for Experiments in Stellar Astrophysics). Motivated by this, we perform binary evolution simulations to compare results between a rapid binary synthesis code, Binary Star Evolution (BSE), and MESA. Our simulations focus on binary systems that undergo common-envelope evolution before merging. We find discrepancies between models that affect merging rates of compact binaries.",

Avishai Gilkis, University Of Cambridge

Leftover Hydrogen in Stripped Massive Stars

"Most massive stars evolve in interacting binary systems before exploding as core-collapse supernovae (CCSNe). Uncertainties in the efficiency of mass transfer by Roche-lobe overflow (RLOF) and the subsequent mass loss through stellar winds make it difficult to predict the material and angular momentum content in the system at its final stages. I will present binary stellar evolution simulations with decisively different assumptions for these key processes and discuss the implications for CCSNe, with special focus on the post-RLOF mass loss by stellar winds and supernovae of types IIb and Ib, for which little or no hydrogen is left in the stellar envelope. I will underscore the significant sensitivity of the stellar evolution models to the assumed mass-loss rates and the need to develop a better theoretical understanding of stellar winds.",

Roni Gofman, Technion Institute Of Technology

The Strongly Interacting Binary Scenarios of the Enigmatic Supernova iPTF14hls

"I will present our comparison of several binary scenarios proposed for the enigmatic core-collapse supernova (CCSN) iPTF14hls. We examine in depth the magnetar scenario and the shocked circumstellar material (CSM) scenario and explore the required properties of these scenarios for them to account for the extra radiation of iPTF14hls. We calculate the associated timescales and the required angular momentum for these scenarios. We conclude that both scenarios require a strong binary interaction. Together with the common envelope jets supernova (CEJSN) scenario, these three scenarios predict the supernova remnant to be bipolar due to jets before and/or during the explosion. Our results can serve the construction of models for future enigmatic super-luminous CCSNe.",

Sebastian Gomez, Harvard University

SN 2016iet: A Type I Pulsational Pair-Instability Supernova Candidate With Signatures of Hydrogen and Helium Free Circumstellar Interaction

"SN 2016iet is a Type I supernova (SN) at a redshift of z = 0.0676 which shows a number of peculiar features that make it a candidate pair-instability supernovae (PISN). We present optical photometry and spectroscopy of the source obtained over a period of 2 years. The most striking features of the light curve are two distinct peaks of comparable brightness and a long separation of about 100 days, and an overall long duration, taking more than 700 days to decline by 4 magnitudes from the first peak. We interpret the long, double-peaked, light curve as being powered by interaction with a circumstellar medium (CSM). But interestingly, the spectra of the source show no evidence for the presence of hydrogen nor helium at any point during its evolution. We present a series of possible models to explain the nature of SN 2016iet. A model in which the envelope of the progenitor was ejected through episodic mass loss events, eventually leading to a SN that breaks out of a dense CSM, producing the first light curve peak, than then proceeds to interact with a CSM, powering the long lasting light curve, provides a good explanation for the SN. Our best models give an estimate of ~20 solar masses of ejecta interacting with ~30 solar masses of CSM. Another interesting feature of SN 2016iet is the fact that it is very far removed from its host, a low mass dwarf galaxy with one of the lowest metallicities observed for either Type Ic or superluminous SN. Further modeling will be required to understand the true nature of this usual SN.",

Ben Gompertz, University of Warwick

The Environments of the Most Energetic GRBs

"Long gamma-ray bursts (GRBs) are explosive transients associated with the deaths of massive stars. Stellar core-collapse launches highly relativistic bipolar jets that can emit more than 1052 ergs in gamma-rays over a few minutes. As the relativistic ejecta interacts with the surrounding medium, it decelerates and forms shocks that emit a broad-band synchrotron afterglow.",

John Graham, Kavli Institute For Astronomy And Astrophysics

A Constant LGRB Host Metallicity Distribution Across Redshifts z < 2.5

"Recent improvements in the population of Long-duration Gamma Ray Burst (LGRB) host galaxies with measured metallicities and host masses allows us to investigate how the distributions of both these properties change with redshift. First we exclude, out to z < 2.5, strong redshift dependent populations biases in mass and metallicity measurements. We then find a surprising lack of evolution in the metallicity distribution of the LGRB host galaxy population. This is at odds with the general evolution in the mass metallicity relation, which becomes progressively more metal poor with increasing redshift. We further find that the LGRB host galaxy mass distribution increase with redshift is consistent with that needed to preserve the LGRB metallicity distribution as the mass metallicity relation decreases with redshift therefore the expected metallicities of the LGRB host population (given their mass and redshift) also does not evolve. However, the metallicities estimated from mass and redshift are about twice as metal rich as the population with actually measured metallicity values which resolves much of the difference between the LGRB formation metallicity cutoff of about a third solar in Graham & Fruchter 2015 with the cutoff value of solar claimed in Perley et al. 2016 in favor of the former.",


Our Line-of-Sight to Eta Carinae is Changing

"The study of Eta Carina is an effort that keeps on giving answers, yet raises still more questions. As we probe deeper and deeper into this massive binary and its complex ejecta using successive generations of new observatories and instruments, we gain insight on how massive stars may evolve, especially in the environment of other massive companions. Specifically, the studies of Eta Carina have impact on our understanding of the many pseudosupernovae, thought to originate from massive stars in distant galaxies. Today we know that a binary system (~100 Mo and 40 Mo) survived a major event in the 1840s even though possibly greater than 40 solar masses of material was ejected. Based upon Herschel/SPIRE measures of 12C/13C~4, that material came from a star (or stars) that initially exceeded 60 solar masses. Which companion ejected that material? Massive amounts of dust exist in the ejecta. Yet carbon and oxygen, thought to be integral to dust formation, is greatly depleted. Many metals, such as strontium, scandium that are not seen in the ISM, are present, in addition to large amounts of iron, titanium. Is this due to complete consumption of carbon and oxygen, or is this due to a very different dust being formed in the massive eruptions? Eta Carina has been thought to be very unstable. Yet studies of fossil winds and now of long term photometry indicate that over the past few decades, the binary and its winds are very stable. Is this an interim phase, or indicative, that Eta Carina has entered a lengthy period of relative stability before that ultimate supernova(s) event(s).",

Matthew Hankins, Caltech

Uncovering Infrared Transients with Palomar Gattini-IR

"Palomar Gattini-IR is a new survey designed to undertake a ground-based wide-field search for infrared transients. We recently began full survey operations and are covering ~9,000 square degrees in J-band from Mount Palomar to a depth of 16.0 mag (AB) every night. Gattini-IR science goals include finding obscured supernovae, stellar mergers, and potential new classes of near-IR transients. We plan to present results from the first six months of survey data and discuss synergies with other ongoing transient surveys",

Marianne Heida, Caltech

The Donor Star of NGC 300 ULX-1/SN2010da

"SN2010da was a bright transient event in the nearby galaxy NGC 300. Discovered in 2010, it was initially classified as a supernova but quickly identified as a supernova impostor. After the 2010 outburst the system showed up as an increasingly bright X-ray source (Binder+2011), and it has been in the ULX regime for the past few years. The origin of the 2010 outburst is still unclear; the dusty progenitor has been identified as a luminous blue variable (Chornock+2010, Elias-Rosa+2010), a yellow supergiant transitioning onto a blue loop (Villar+2016) or a supergiant B[e] star (Lau+2016). X-ray observations with XMM-Newton, NuSTAR and Swift revealed that the accretor is a rapidly up-spinning neutron star (Carpano+2018, Walton+2018, Binder+2018). We have obtained deep optical through near-infrared spectra of SN2010da with X-shooter in 2018 that for the first time reveal the massive star in this system to be a red supergiant. I will discuss the implications of this discovery for the origin of the 2010 outburst and the resulting X-ray binary.",

Kenneth Hinkle, NOAO

SyXB NS Afterlife Powered By an Evolving Low Mass Star

X-ray symbiotic binaries (SyXB) are a rare class consisting of a neutron star (NS) with an M III companion. We have observed seven members of this class using high-resolution infrared spectroscopy. For two systems we have derived orbits. The systems are detached with orbital periods of order a decade. The best formation scenario creates the NS from a core collapse SN with the SyXB representing the few surviving high mass - low mass binary systems. For the two well studied systems the M giant has a mass in the 1 - 2 solar mass range implying an age of gigayears for the NS. NS activity is fueled by mass loss from the M III. We will review the observational material for the known members of this class and comment on the evolution of the binaries as the low mass star reaches the AGB.,

Alec Hirschauer, STScI

Asymptotic Giant Branch Stars in the Low-Metallicity Galaxy NGC 6822

"The high-redshift systems in which the earliest generations of stars were formed, produced heavy elements and dust, and subsequently ended their life cycles were vastly different from the Milky Way. Nearby galaxies with low metal abundances provide important laboratories for observationally accessing the physical conditions equivalent to what had been ubiquitous throughout the early Universe. In order to more fully understand the role of dust in metal-poor environments, it is critically important to robustly identify their evolved, dust-producing asymptotic giant branch (AGB) stars. The local (~500 kpc) metal-poor ([Fe/H] _ -1.2; Z _ 30% Z_) star-forming galaxy NGC 6822 is thought to be analogous to higher-redshift systems at the epoch of peak star formation. We present color-magnitude diagrams (CMDs) utilizing archival photometry from the Spitzer Space Telescope (Khan et al. 2015; IRAC 3.6, 4.5, 5.8, and 8.0 _m and MIPS 24 _m) and the United Kingdom Infrared Telescope (Sibbons et al. 2012; UKIRT J-, H-, and K-band) of NGC 6822. Isolating red-excess objects and carefully employing color cuts, we identify oxygen- and carbon-rich AGB star candidates. Subsequent work will entail spectral energy distribution (SED) fitting of these sources to quantify the dust mass and dust mass loss rate of this galaxy. This project was completed in anticipation of a James Webb Space Telescope (JWST) guaranteed time observation (GTO) program for this galaxy, which will probe NGC 6822 to a depth comparable to the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution; Meixner et al. 2006) surveys of the Large and Small Magellanic Clouds.",

Anna Hornschemeier, NASA GSFC

Stellar-origin Black Holes and Neutron Stars in the 2020s and Beyond: The Post Chandra and XMM-Newton Era

"We present prospects for studying black hole (BH) and neutron star (NS) populations in nearby galaxies, focusing on science topics that will require next generation X-ray telescopes. Higher-throughput X-ray telescopes in the future will open up parameter space for time-domain studies of accreting stellar origin BH and NS populations. The topics are wide-ranging, from understanding gravitational wave merger progenitor populations such as Wolf-Rayet X-ray binaries to unraveling the complicated physics that allows for a population of _ultraluminous_ pulsars which currently appear to defy our picture of how accretion works. We can also understand the birth of compact objects via supernova events through constraint of SN kicks in the dynamical evolution of X-ray binaries. Capabilities such as a large field of view, improved angular resolution, increased sensitivity/effective area, and timing resolution are required to answer such questions and expand our understanding of accreting BH and NS systems. We will summarize the prospects for answering these questions based on our current knowledge and simulations of Athena Wide Field Imager observations of galaxies. Athena is an ESA mission planned for launch in ~2031 and the Wide Field Imager is an example of a next generation instrument that will be excellent for studies of BH and NS populations.",

Matthew Hosek, University of California Los Angeles

Young Massive Clusters at the Galactic Center: Top Heavy Initial Mass Function and the Increased Population of Compact Objects

"The discovery of gravitational waves has renewed interest in the production rate and locations of stellar mass black holes. One important aspect of this problem is the stellar initial mass function (IMF), which sets the mass of the progenitor stars and hence the number of compact remnants in star clusters. We discuss the IMFs of three young clusters at the Galactic Center: The Young Nuclear Cluster, Arches Cluster, and the Quintuplet cluster. We forward model observations of these clusters to simultaneously constrain the cluster IMF and other properties (such as age and total mass) while accounting for observational uncertainties, completeness, mass segregation, and stellar multiplicity. We find that the IMFs of these clusters are either top-heavy (an overabundance of high-mass stars) or bottom-light (an under abundance of low-mass stars) relative to the standard IMF observed in local star forming regions. We investigate whether these unusual IMFs can be attributed to the Galactic Center environment or are a general property of young massive clusters, and discuss implications for the populations of compact objects that will be generated by these clusters.",

Griffin Hosseinzadeh, CfA

Type Ibn Supernovae May Not All Come from Massive Stars

"Type Ibn supernovae are a rare class of transients whose spectra show signatures of interaction with hydrogen-poor circumstellar material. Compared to other interacting supernovae, their light curves relatively homogeneous and fast-evolving. The leading theory has been that these are the explosions of very massive Wolf_Rayet stars in which material ejected by the supernova collides with mass lost from the progenitor through winds or eruptions. These stars should have short lifetimes and thus only be found in areas with active star formation. However, one of the ~30 Type Ibn supernovae occurred in a galaxy cluster environment with no detectable star formation. I will present new HST observations of this environment, which strengthen the star formation limit below the levels of almost all known core-collapse supernovae. In light of this limit, I will discuss whether all Type Ibn supernovae can come from massive stars.",

Dominika Hubova, Charles University

Kinematics of Mass Loss from the Outer Lagrange Point L2

"We investigate the mass loss from the vicinity of the outer Lagrange point L2 of binary stars, a phenomenon that is associated with the common envelope evolutionary phase. This evolutionary stage can result in stellar merger or in formation of close binary systems. The circumstellar medium of the remnant might be significantly affected by the mass loss from the L2 point. We evaluate trajectories of test particles ejected from the proximity of the L2 point with arbitrary initial velocity and we compute the amount of energy and angular momentum these particles carry away from the system.",

Tiara Hung, UC Santa Cruz

Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in Tidal Disruption Event AT2018zr

"Discovery of Highly Blueshifted Broad Balmer Absorption Lines in a Tidal Disruption EventRecent progress in the observations of tidal disruption events (TDEs; when stars pass too close to a black hole and is torn apart by tidal stress) have revealed an unexpected enhancement in their UV and optical emission, making the underlying emission mechanism (circularization v.s. reprocessing) a hot debate. Spectroscopy plays an important role in disentangling these scenarios as line formation is governed by the underlying physical state of the emitting gas. In this talk, I will present the discovery of a transient high-velocity outflow (~0.05c) in the TDE AT2018zr based on prominent absorption features in the UV and optical spectra in rest wavelength range of 1100-9000 angstrom. The detection of both high- and low-ionization absorption lines makes its spectrum resemble a low-ionization broad absorption line (LoBAL) QSO. Furthermore, rare hydrogen Balmer and the metastable HeI absorption lines are also detected. We conclude that these transient absorption features are likely to arise in an outflow environment, which rules in favor of the reprocessing mechanism and suggests that outflow may be ubiquitous amongst TDEs.",

Elizabeth Jeffery, California Polytechnic State University

Gaia White Dwarfs and the Age of the Galaxy

"The Milky Way is composed of four major stellar populations: the thin disk, thick disk, bulge, and halo. At present, we do not know the age of any of these populations to better than one or two billion years. This lack of knowledge keeps us from answering fundamental questions about the Galaxy: When did the thin disk, thick disk, and halo form? Did they form over an extended period, and if so, how long? Was star formation continuous across these populations or instead occur in distinct episodes? The Gaia satellite is providing precise trigonometric parallaxes for a plethora of white dwarfs in each of these populations. We combine these parallaxes (and hence, distances) with photometry and analyze them using a modeling technique that relies on Bayesian statistics. This allows us to derive precise ages for individual white dwarfs and determine the age distribution and star formation history for each of the constituents of our Galaxy. We will present current progress in this endeavor, with emphasis on the ages of individual white dwarfs in two star clusters: the Hyades and Praesepe. Measuring the ages of individual white dwarfs in these well-studied clusters provides proof of concept for our technique, as well as exploration of any systematic offsets caused by timescales from main sequence models or the initial-final mass relation.",

Noa Kaplan, Technion Institute Of Technology

The Influence of Jets on the Light Curve of Supernovae

"I will present results of our study of the light curve of core collapse supernovae (CCSNe) where late jets deposit energy to the ejecta. We assume that each jet deposits its kinetic energy within a small region and during a short time. The energy that each jet deposits in the ejecta is modelled to diffuse outwards through the ejecta, while the shocked jet's material expands and cools. We build a toy model where the interaction of each jet with the ejecta is modeled as a `small local explosion'. In our model the total luminosity of the CCSN is the combination of the CCSN explosion and the contributions of the late jets. Comparison of the composite light curve with observations of some CCSNe can reveal some properties of late jets in rare CCSNe.",

Maria Kopsacheili, University Of Crete

Study of Extragalactic Supernova Remnants

"Studies of populations of supernova remnants (SNRs) in different galaxies provide a more representative picture of their importance for feedback and metal enrichment in a wide variety of galactic environments. We present our results on the SNRs populations in a sample of nearby spiral galaxies (NGC 7793, NGC 55, NGC 45, NGC 1313), based on deep narrow-band H_ and [S II] images. We find a total of 194 candidate SNRs. We derive the H_ and excitation distributions of the SNRs, both of which are proxies of the energy deposition on the galactic interstellar medium (ISM). In our analysis we develop methods to account for selection effects that allow us to directly compare results between different galaxies. We compare our results with similar studies in irregular galaxies and we discuss the effects of recent star-forming activity and the morphology and physical conditions in the ISM on the SNR populations and their physical properties. We also present a new, efficient, diagnostic tool for identifying SNRs and measuring their shock velocities based on narrow-band imaging. Through the effective differentiation from HII regions this diagnostic provides more complete samples of SNRs including those in later evolutionary phases with slower shocks.",

Kathleen Kraemer, Boston College

Mid-Infrared Spectra of Carbon-Rich Post-AGB Stars Across the Decades

"Many phases of stellar evolution occur on slow timescales of millions or billions of years. The post-asymptotic giant branch (post-AGB) phase, though, when a star rapidly transitions from a cool, dust-enshrouded object to a hot white dwarf illuminating a planetary nebula (PN), lasts only 1,000-10,000 years. We have obtained 5-37 micron spectra with SOFIA's FORCAST instrument of several carbon-rich post-AGB objects in the Milky Way. We compare the new spectra to the mid-infrared spectra of the same objects that were observed at roughly 10-15 year intervals over the past 35 years with IRAS, ISO, and Spitzer. Secular changes on these timescales have already been detected in optical photometry and spectra, tracing changes in the central star. We are now in a position to investigate the corresponding changes in the circumstellar material, as it is being processed from forms found around AGB stars to those seen in PNe. These observations potentially probe the real-time evolution of circumstellar shells and the processes that occur during one of the most fleeting stages in a star's life.",

Kelsie Krafton, Louisiana State University

Disentangling Dust Components in SN 2010jl: The First 1400 Days

"Our original motivation for studying dust formation in core collapse supernovae (CCSNe) was the exciting discovery that some high redshift (z > 6) galaxies were dust rich. These galaxies are less than 1 Gyr old, and so a significant fraction of the observed dust must be coming from massive stars, which evolve quickly and return their material back to the interstellar medium through supernovae (SNe). Even still, the amount of dust required per star or SN is high, with theoretical models predicting that 0.1 - 1 solar masses of dust would be needed per CCSN. Many studies by our group and others found that only about 0.0001 - 0.01 solar masses of dust have formed two or three years after the explosion. How is it that CCSNe have formed only a small amount of dust after three years, but SN 1987A has a dust mass that is several orders of magnitude larger after 25 years? To investigate the suggestion of continuous dust formation, we used two Monte Carlo Radiative transfer codes to model dust in the circumstellar medium (CSM) and ejecta of SN 2010jl. MOCASSIN fits visible and IR SEDs, while DAMOCLES fits optical emission lines. Dust located in the ejecta will preferentially extinguish emission from the far-side, red-shifted gas and result in a shift of the emission line profiles to the blue. The presence of dust also causes an infrared excess. Combining these signatures by using both models allows us to estimate the mass of dust produced by SN 2010jl. I present estimates of both new and preexisting dust masses at each epoch for SN 2010jl, over the first 1400 days of its evolution. The mass of new dust is increasing and may reach levels similar to that of SN 1987A, given enough time.",

Petr Kurfurst, Charles University

Interactions between Supernova Ejecta and Asymmetric Circumstellar Material

Progenitors of core-collapse supernovae (SN) may experience enhanced mass loss by stellar winds or outburst episodes shortly before the SN explosion. We study the hydrodynamics of spherical SN explosion into a dense circumstellar medium (CSM) with various non-spherical geometries. We calculate the evolution of thermodynamic quantities in the interaction zone with the ultimate goal of synthesizing supernova light curves and other observables.,

Ryan Lau, Isas/jaxa

WR DustERS: JWST-ERS Program to Resolve the Nature of Dust in Wolf-Rayet Winds

"Thermal infrared (IR) emission from dust is a key probe of the evolution and death of short-lived, massive stars. Dust itself is a key component of the interstellar medium; however, the dominant channels of dust production throughout cosmic time are uncertain. In this talk, I will discuss our JWST Director's Discretionary Early Release Science (DD ERS) program, where we will investigate the formation mechanism and chemical composition of dust formed in the colliding winds of a Carbon-rich Wolf-Rayet (WC) binary. With dust production rates ranging from 10^-8 - 10^-6 Msun/yr, such massive stellar binaries may have a significant influence on the dust abundance galaxies in both the local and early Universe. Dust abundances, composition and formation pathways in the hostile and luminous environment around WC+OB binaries are, however, uncertain due to observational challenges in achieving both high spatial resolution and sensitivity in the mid-IR. Our planned JWST/MIRI+MRS and NIRISS+AMI observations of the archetypal periodic dust forming Wolf-Rayet binary system WR140 will address these uncertainties and also demonstrate the utility of these observing modes for IR bright targets with faint extended emission.",

Margaret Lazzarini, University Of Washington

Young Accreting Compact Objects in M31: The Combined the Power of NuSTAR Chandra and Hubble

"Combining NuSTAR, Chandra, and the Hubble Space Telescope (HST) imaging of nearby galaxies, we are able to study both the compact object and donor star in high mass X-ray binaries (HMXBs) in the context of their local star forming environments. We infer compact object type, spectral type of the donor star, and age using multiwavelength observations from NuSTAR, Chandra, and HST. The hard X-ray colors and luminosities from NuSTAR permit the classification of accreting X-ray binary systems by compact object type, distinguishing black hole from neutron star systems. We identify UV-bright optical counterparts spatially associated with X-ray sources using high quality HST imaging. We perform spectral energy distribution (SED) fitting for the most likely optical counterparts to the HMXB candidates to infer the most likely stellar mass and temperature for the companion stars. We can also obtain high quality age estimates using spatially resolved star formation histories (SFHs). In M31, we find 15 HMXB candidates: X-ray sources spatially associated with UV-bright point source optical counterparts. To determine the quality of HMXB candidates we evaluate the SED fitting to determine if a massive, young star appears to be the donor, age estimation using spatially resolved SFHs, and compact object classification using NuSTAR hard X-ray colors and luminosities.",

Richard Miller, Johns Hopkins University Applied Physics Laboratory

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"Ex Luna Scientia: The Lunar Occultation Explorer (LOX)

Brenna Mockler, UC Santa Cruz

Weighing BHs with Tidal Disruption Events

"While once rare, observations of tidal disruption events are quickly becoming commonplace. To continue to learn from these events it is necessary to robustly and systematically compare our growing number of observations with theory. Here I present a tidal disruption model (as part of the transient fitting code MOSFiT) and the results from fitting 14 TDEs. Our model uses hydrodynamical simulations to generate accretion rates and passes these accretion rates through viscosity and light reprocessing modules to create multi-wavelength light curves. It then uses an MCMC fitting routine to compare these theoretical light curves with observations. This procedure provides a robust method for measuring the masses of supermassive black holes because the shape of a TDE light curve depends strongly on the black hole_s mass. In addition to describing this new black hole mass measurement method, I will discuss the implications these fits have for understanding the physics of TDEs, particularly for accretion under these extreme conditions.",

Daniel Muthukrishna, University Of Cambridge

RAPID: Early Classification of Explosive Transients using Deep Learning

"We present RAPID (Real-time Automated Photometric IDentification), a novel time-series classification tool capable of automatically identifying transients from within a day of the initial alert, to the full lifetime of a light curve. Using a deep recurrent neural network with Gated Recurrent Units (GRUs), we present the first method specifically designed to provide early classifications of astronomical time-series data, typing 12 different transient classes. Our classifier can process light curves with any phase coverage, and it does not rely on deriving computationally expensive features from the data, making RAPID well-suited for processing the millions of alerts that ongoing and upcoming wide-field surveys such as the Zwicky Transient Facility (ZTF), and the Large Synoptic Survey Telescope (LSST) will produce. The classification accuracy improves over the lifetime of the transient as more photometric data becomes available, and across the 12 transient classes, we obtain an average area under the receiver operating characteristic curve of 0.95 and 0.98 at early and late epochs, respectively. We have made RAPID available as a software package for machine learning-based alert-brokers to use for the autonomous and quick classification of several thousand light curves within a few seconds.",

Anna Ogrady, University Of Toronto

Identifying Candidate Thorne-Zytkow Objects: The Role of Variability

"The thermally-pulsing asymptotic giant branch (TP-AGB) experienced by low- and intermediate-mass stars is one of the most uncertain phases of stellar evolution. Despite the theoretical and observational efforts made so far, the impact of TP-AGB stars on some key aspects of galaxy evolution is still debated, i.e. their contribution to the integrated light of galaxies and to the interstellar dust budget.",

Giada Pastorelli, University Of Padova

Constraining the TP-AGB phase with resolved stellar populations in the Small Magellanic Cloud

"The thermally-pulsing asymptotic giant branch (TP-AGB) experienced by low- and intermediate-mass stars is one of the most uncertain phases of stellar evolution. Despite the theoretical and observational efforts made so far, the impact of TP-AGB stars on some key aspects of galaxy evolution is still debated, i.e. their contribution to the integrated light of galaxies and to the interstellar dust budget. In this work, we put quantitative constraints on the parameters that control the third dredge-up and the mass loss in TP-AGB stars by coupling high-quality observations of resolved stars in the Small Magellanic Cloud (SMC) with detailed stellar population synthesis simulations. The strength of our approach relies on the detailed spatially-resolved star formation history of the SMC, derived from the deep near-infrared photometry of the VISTA survey of the Magellanic Clouds, as well as on the capability to quickly and accurately explore a wide variety of parameters and effects with the COLIBRI code for the TP-AGB evolution. Our work led to identify two best-fitting models that reproduce the observed star counts and luminosity functions, but differ in the efficiencies of the third dredge-up and mass loss in TP-AGB stars with initial masses larger than about 3 solar masses. We fully characterize the TP-AGB stellar population of the SMC in terms of stellar parameters (initial masses, C/O ratios, carbon excess, mass-loss rates) and we provide extensive tables of isochrones including these improved models. ",

Ondrej Pejcha, Charles University

Mass Loss Transients and Dust from Catastrophically Interacting Binary Stars

"We investigate the mass loss from the vicinity of the outer Lagrange point L2 of binary stars, a phenomenon that is associated with the common envelope evolutionary phase. This evolutionary stage can result in stellar merger or in formation of close binary systems. The circumstellar medium of the remnant might be significantly affected by the mass loss from the L2 point. We evaluate trajectories of test particles ejected from the proximity of the L2 point with arbitrary initial velocity and we compute the amount of energy and angular momentum these particles carry away from the system.",

Abigail Polin, UC Berkeley

Observational Signatures of sub-Chandrasekhar Mass Type Ias

"Carbon-Oxygen white dwarfs accreting a Helium shell have the potential to explode in the sub-Chandrasekhar mass regime. Previous studies have shown how the ignition of a Helium shell can either directly ignite the white dwarf at the core-shell interface or propagate a shock wave into the center of the core causing a central ignition. I will discuss recent hydrodynamics simulations of these explosions, which exhibit an inherent relationship between SiII velocity and luminosity. This, for the first time, identifies a sub-class of Type Ia supernovae that likely result from these sub-Chandrasekhar mass progenitors.",

Peter Roming, Southwest Research Insitute

Shock Break Out Mission

"The death of massive stars, manifested as core-collapse supernovae, critically influence how the universe evolves. Despite their fundamental importance, our understanding of these enigmatic objects is severely limited. We have performed a concept study of a space-based transient observatory that will rapidly facilitate an expansion of our understanding of these objects. By combining a very wide-field X-ray telescope with an ultraviolet telescope, and a rapidly slewing spacecraft we can constrain the poorly understood explosion mechanism of massive stars. This goal is met by observing the shock breakout of core-collapse supernovae to measure the outer envelope parameters of massive stars. A description of the observatory, mission simulation, and technology used will be provided.",

Stuart Ryder, Macquarie University

Four Decades of the Type IIn Supernova 1978K

"Supernova 1978K in NGC 1313 is the oldest, and one of the closest of the class of Type IIn supernovae that explode into an unusually dense circumstellar medium. Since discovering it serendipitously in 1992 we have been following it at X-ray, optical, and radio wavelengths. Recent VLBI measurements confirm significant deceleration of the ejecta. SN 1978K is only the third evolved extragalactic supernova to be detected with ALMA, yielding important clues about dust formation in core-collapse supernovae.",

Efrat Sabach, Technion Institute Of Technology

SN IIb Progenitors by Fatal Common Envelope Evolution

"Stars that do not gain angular momentum (J) by a companion along their post-main sequence evolution are termed J-isolated stars, hereafter Jsolated stars. We argue that the mass-loss rate of Jsolated stars is poorly determined because the mass-loss rate expressions on the giant branches are empirically based on samples containing stars that experience strong binary interaction, with stellar or sub-stellar companions. We follow the evolution of several observed exoplanetary systems under the Jsolated framework and show that by lowering the mass loss rate of single solar-like stars during their giant branches these stars will engulf their planets at the tip of their asymptotic giant branch phase. Under the traditional mass loss rate such stars will not engulf their planets and will not form detectable planetary nebulae (PNe), yet under the Jsolated scheme the planets will have a major role in shaping the PNe and most likely lead the stars to form elliptical PNe. We apply our scheme to several systems including a recently discovered planet detected around a subgiant star of ~ 0.97Mo for which we find that future interaction between the star and the planet might result in an observed PN.",

Beth Sargent, STScI

Infrared Studies of the Variability of a Sample of Dusty Asymptotic Giant Branch Stars in the Magellanic Clouds

"The asymptotic giant branch (AGB) stars with the reddest colors have the largest amounts of circumstellar dust, which in turn suggests extremely high mass-loss rates. AGB stars vary in their brightness, and studies show that the reddest AGB stars tend to have longer periods than other AGB stars and are more likely to be fundamental mode pulsators. Such dusty AGB stars are difficult to study, as their colors are so red due to their copious amounts of circumstellar dust that they are often not detected at optical wavelengths. Therefore, they must be observed at infrared wavelengths to explore their variability. Using the Spitzer Space Telescope, my team and I have observed a sample of very dusty AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) during the Warm Spitzer mission. For each cycle, we typically observed a set of AGB stars at both 3.6 and 4.5 microns wavelength approximately monthly for most of a year. These observations reveal a wide range of variability properties. We present results from our analysis of the data obtained from these Spitzer variability programs, including light curve analyses and comparison to period-luminosity diagrams. Potentially the most interesting set of stars we observed is the sample of 13 stars from the LMC included in the set of so-called Extremely Red Objects (EROs) that were studied by Gruendl et al (2008, ApJ, 688, L9), who determined these carbon stars to have among the highest mass-loss rates of the LMC_s carbon-rich AGB star population. Paradoxically, we found most of these stars to have little to no variability, perhaps suggesting these stars are reaching or have just reached the end of the AGB phase of their lives. We are also exploring the possibility of supplementing the light curves of all of our sample stars with multi-epoch photometry from the WISE mission.",

Ivo Seitenzahl, University Of New South Wales Canberra

Non-radiative Coronal Lines in the Shocked Ejecta of Type Ia Supernova Remnants

"We report on our discovery of optical, broad coronal line emission from the shocked iron-rich ejecta in young Type Ia supernova (SN Ia) remnants. Deep MUSE observations reveal broad and spatially resolved coronal lines of Fe and S, most prominently [Fe XIV]5303. This indicates the progression of the reverse shock into the Fe rich layers of ejecta, allowing Fe masses to be estimated. The width of the broad lines gives us for the first time a direct determination of the reverse shock speed and hence a new observational measurement to constrain the masses and explosion energies of the progenitors.",

Sagiv Shiber, Technion Institute Of Technology

Envelope Removal by Jets in the Common Envelope Evolution

"I conduct three-dimensional hydrodynamical simulations, and show that when a secondary star launches jets while interacting with a primary giant star in a close orbit, the jets facilitate the removal of the giant envelope. I assume that the secondary star accretes mass via an accretion disk and that the accretion disk launches the jets. The results indicate that the jets eject most of the envelope gas and unbind a part of it. The jets produce high velocity outflow in the polar directions that can be as massive as the equatorial outflow. When comparing simulations with and without jets, the final orbital separation is larger and the orbit is more eccentric when jets are included. These results show that jets might solve some puzzles in the theory of common envelope evolution, namely the ejection of the envelope and the shaping of the outflow.",

Erin Smith, NASA/GSFC

SOFIA 3-Micron Observations of PAHs in Planetary Nebulae

"Although they are less dramatic than their explosive supernova counterparts, planetary nebulae are important contributors to the chemistry of the ISM. This is especially true in the role they are believed to play in the generation of Polycyclic Aromatic Hydrocarbons (PAHs)_assemblies of benzene-like rings of carbon dust which, when excited by UV photons, relax through emission in broad bands throughout the infrared. PAHs are observed in multiple astronomical phenomena, most notably in star forming regions, which has led to their use as a marker for estimating star formation rates in distant galaxies. Understanding the formation environments of PAHs is therefore essential to multiple aspects of Astrophysics. Using ground-based (Lick) and stratospheric (SOFIA) observations of the ~3-5 micron spectra of young planetary nebulae obtained by the SOFIA instrument FLITECAM, we investigate the spatial distribution and spectral variation of the 3.3 micron PAH feature, its associated aliphatic features and set limits on the theoretical contribution of the 4.4-4.8 micron deuterated-PAH features. ",

Noam Soker, Technion Institute Of Technology

The Role of Jets in the Death of Stars: Review of the Most Recent Results

"I will describe recent results on the role of jets in the common envelope evolution of all types of evolved stars and in exploding massive stars, and will compare the results with the most recent observations and with other theoretical studies. I will discuss new ideas of processes that become possible by jets, such as the grazing envelope evolution, common envelope jets supernovae, and the jittering jets explosion mechanism of massive stars aided by neutrino heating. I will compare these to the most recent observations of similarities between supernova remnants and planetary nebulae, and to the most recent theoretical studies that do not include jets.",

Amy Steele, University of Maryland

Modeling Circumstellar Gas around Polluted White Dwarfs

"At least 30% of white dwarfs (WDs) show heavy elements in their atmospheres. This ""pollution"" likely arises from the accretion of planetesimals that were perturbed by outer planet(s) into the white dwarf's tidal radius. A small fraction of these WDs show either emission or absorption from circumstellar (CS) gas. The CS component arises from a gas disk produced through the sublimation of a transiting, disintegrating planetesimal. For WD1145+017, the photospheric abundances have been measured and are similar to the bulk composition of the Earth.",

Samaporn Tinyanont, Caltech

Supernova 2017eaw: The Progenitor Circumstellar Material and Chemical Evolution

"The Type II-P SN 2017eaw in NGC 6946 is the most nearby core-collapse supernova (CCSN) in the recent years, providing us with an opportunity for detailed and long-term observations. We present 3 results from our infrared (IR) photometric and spectroscopic observations. First, progenitor observations in the Ks band in 4 epochs from 1 year to 1 day before the explosion reveal no significant variability in the progenitor star greater than 6% that last longer than 200 days, indicating no significant mass loss event in this period. Second, spectroscopic monitoring during the plateau phase reveals a high-velocity He I 1.083 micron absorption line, which may be results of a shock interaction with circumstellar medium or a time dependent excitation effect. Lastly, IR photometry and spectroscopy show condensation and cooling of carbon monoxide (CO), and consequently dust, in the ejecta of SN 2017eaw. The CO shows similar line profile and temporal evolution to that of SN 1987A, suggesting a common formation pathway. Spitzer photometry showed that dust started to form at ~200 days post explosion. For SN 2017eaw, we found that the evolution of dust mass is consistent with a scenario in which a large amount of ejecta dust formed early (few hundred days) but was self obscured. Such a scenario will explain the discrepancy between the small dust mass (10-4 - 10-3 solar mass) inferred from near to mid-IR observations of extragalactic SNe and the large dust mass (0.1 - 1 solar mass) inferred from far-IR and sub-millimeter observations of the nearby SN 1987A and Galactic SN remnants.",

Yisheng Tu, University Of Rochester

Energy Budget Unbound Mass in Common Enbvelope Evolution

"Common envelope evolution (CEE) is the key to understand the formation of many planetary nebulae (such as the Hourglass Nebula). A 3D simulation is necessary to explore the full evolution of the system in enough detail, yet simulations have not ejected the envelope without adding new uncertain energy sources. We map out the energy and mass structure of CEE in space and time. We find that the asymmetry of the mass ejection leads to relative motion between the center of mass of the disrupted envelope and that of the cores. We propose this process as a mechanism to explain the offsets between the geometric centers of certain planetary nebulae and their binary central stars. Further, we explore the parameter space of the secondary mass and of the evolutionary stage of the primary (red giant branch and asymptotic giant branch).",

Gregory Vance, Arizona State University

Titanium and Iron in the Cassiopeia A Supernova Remnant

"Since the observations of SN 1987A three decades ago, theorists have worked towards a model of the supernova engine in which convective motions above the proto-neutron star are essential for driving the explosion. Geometric asymmetries and unexplained mixing of ejecta in 1987A motivated the original development of these models, and newer observations have continued to push them forwards. As simulations have grown in sophistication, so too has the body of data available for comparison to results from computer models. Estimates of stellar progenitor masses, observations of the remnant mass gap, details of remnant morphologies, and spatially mapped yield data have become important for constraining and improving the latest supernova models. Cassiopeia A, one of the best-studied supernova remnants to date, continues to serve as a gold mine for observational data that can be used to this end. This includes detailed spatial yields from NuStar, Chandra, and XMM-Newton for titanium-44 and iron, which can constrain the explosion energy and isolate low-mode asymmetries caused by convective flows. We present a 3D supernova model based on the convective engine and compare its spatially resolved yields to the iron and titanium observations from Cassiopeia A. A series of smaller nucleosynthetic calculations with varying thermodynamic evolutions are included to analyze the production of titanium-44 and other isotopes in the explosion simulation. The simulations are able to reproduce the type of strongly anisotropic distributions and the titanium-to-iron ratios observed in Cassiopeia A.",

Laura Vega, Vanderbilt University / Nasa - GSFC

X-ray & Submillimeter Observations of the Pulsating RV Tau Variable U Mon

"RV Tauri variables are post-Asymptotic Giant Branch (post-AGB) supergiants that may be a crucial stage in the evolution of low-to-intermediate mass stars with a stellar companion. The presence of a circumbinary disk also has an important impact on the orbital evolution of these systems, which is still not well understood. The association between disk, binarity, and the RV Tau variability phenomenon had remained elusive until the Kepler spacecraft's observation of the RV Tau star, DF Cyg (Vega et al. 2017). Based on modeling of the Kepler light curve, a literature radial-velocity period, and the spectral energy distribution (SED) for RV Tau variable, DF Cyg, we argued that the long-term RV Tau phenomenon (RVb) is likely to be fundamentally connected to the circumbinary disk, revealed by infrared excess, obscuring the binary system. However, as with most RV Tau variables, the lack of flux measurements long-ward of 20 microns restricts modeling of the SED and disk parameters. It is only at long wavelengths such as 800--1000 microns that the optically thin emission of the disk can be sampled and used to constrain key properties such as overall disk mass and total size for these systems. We have obtained flux measurements at 230 GHz and at 345 GHz for an RVb variable, U Mon, with the Smithsonian Submillimeter Array (SMA). The SMA fluxes will add to U Mon's SED, while the SMA images may provide direct measurements of the size of the circumbinary disk. Additionally, we have obtained XMM-Newton measurements for U Mon, which may be the first RV Tau variable to be detected in X-rays. Our XMM-Newton observations reveal hard X-ray emission which may be consistent with a close companion possibly accreting material via an accretion disk.",

Neven Vulic, Nasa Gsfc / Umcp / Cresst Ii

Black Holes & Neutron Stars in Nearby Galaxies: Insigns from NuSTAR

"During the thermally pulsing asymptotic giant branch (TP-AGB) phase, low- and intermediate-mass stars lose mass at high rates, enriching the interstellar medium of galaxies with metals and dust. The dense environment of the circumstellar envelopes of TP-AGB stars represents the ideal site for dust condensation. Stellar pulsation triggers shock waves that lift the gas above the stellar surface where the temperature is low enough to allow solid particles to form and to accelerate the outflow if sufficient momentum is transferred. Despite the importance of TP-AGB stars as dust factories, many questions related to the dust production process and the dust properties, as well as the mass-loss mechanism, remain unanswered. In this talk I will review what we learned from observations of TP-AGB stars, as well as the most recent advancements in",

Rick White, STScI

A New Deep JVLA Radio Survey of Supernova Remnants in M33

"We have performed new 1.4 GHz and 5 GHz observations of the Local Group galaxy M33 with the Jansky Very Large Array. Our survey has a limiting sensitivity of 20 Jy (4-sigma) and a resolution of 5.9 arcsec (FWHM), corresponding to a spatial resolution of 24 pc at 817 kpc. Using a novel multi-resolution algorithm, we have created a catalog of 2875 sources, including 675 with well-determined spectral indices.",

Marc Williamson, New York University

Optimal Classification and Outlier Detection for Stripped-Envelope Core-Collapse Supernovae

"The core collapse supernovae (SNe) of massive stars offer valuable insight into one of the most active areas of supernova research: stellar progenitors. By studying the composition of the supernova ejecta, we can learn about the composition of the progenitor before the supernova. A particularly interesting subset of all core collapse supernovae are the stripped-envelope supernovae (SESNe). The spectra of these explosions indicate that the stellar progenitors were stripped of parts or all of their outer Hydrogen and Helium envelopes. In this talk, we present a novel method for classifying SESNe that is both quantitative and continuous to better reflect the physical properties of the SESNe stellar progenitors prior to explosion. We apply our method, which combines principal component analysis (PCA) with a support vector machine (SVM), to a dataset of over 150 SNe, each with spectra taken at multiple times during the SN evolution. We find that our classification method can recreate the standard class labels and naturally handles ""transition SNe,"" in addition to yielding insight into the relationship between different SESNe types.",

Emily Wilson, Rochester Institute Of Technology

The Role of Convection in Determining the Ejection Efficiency of Common Envelope Interactions

"A widely used method for parameterizing the outcomes of common envelopes (CEs) involves defining an ejection efficiency, alpha, that represents the fraction of orbital energy used to unbind the envelope as the orbit decays. Given alpha, a prediction for the post-CE orbital separation is then possible with knowledge of the energy required to unbind the primary's envelope from its core. Unfortunately, placing observational constraints on alpha is challenging as it requires knowledge of the primary's structure at the onset of the common envelope phase. Numerical simulations have also had difficulties reproducing post-CE orbital configurations as they leave extended, but still bound, envelopes. Using detailed stellar interior profiles, we calculate alpha values for a matrix of primary-companion mass pairs when the primary is likely to incur a CE, i.e. at maximal extent in its evolution. We find that the ejection efficiency is most sensitive to the properties of the surface-contact convective region (SCCR). In this region, the convective transport times are often short compared to orbital decay timescales, thereby allowing the star to effectively radiate orbital energy and thus lower alpha. The inclusion of convection in numerical simulations of CEs may resolve the ejection problem without the need for additional energy sources as the orbit must shrink substantially further before the requisite energy can be tapped to drive ejection, or convection will transport energy throughout the envelope's mass. Additionally, convection leads to predicted post-CE orbital periods of less than a day in many cases, an observational result that has been difficult to reproduce in population studies where alpha is taken to be constant. Finally, we provide a simple method to calculate alpha if the properties of the SCCR are known.",

Emily Witt, CU Boulder

A Comparison Between Infrared and Ultraviolet Observations of Photodissociation Regions

"Photodissociation regions (PDRs) are regions in the interstellar medium (ISM) where energetic photons, usually far ultraviolet (FUV), are actively dissociating molecules. These regions feature intense molecular line activity in both IR traced rotational-vibrational H$_2$ emission and the FUV traced electronic H$_2$ absorption. While much work has been done in the IR and UV regimes separately, it is not clear how these different wavelength regimes compare. Especially problematic is the lack of imaging resolution in the Lyman UV (1000 \AA) where the majority of H$_2$ features reside and where the powerful O VI $\lambda$1038 feature is. PDRs inform much of our understanding of how material is processed in the ISM, a mechanism that greatly influences the life cycle of stars and galaxies. This work combines archival spectroscopic measurements from the \textit{Spitzer Space Telescope} and the Far Ultraviolet Spectroscopic Explorer (\textit{FUSE}) to probe the molecular activity within these important regions. This poster presents preliminary results of a comparison between H$_{2}$ features, PAHs and other PDR diagnostics calculated from common IR and FUV relations. This archival \textit{Spitzer}/\textit{FUSE} project sets the groundwork for a future flight demonstration of the Integral Field Ultraviolet Spectroscopic Experiment (INFUSE), the first FUV integral field spectrograph (IFS), which will map energetic regions of PDRs and supernova remnants to 2"" scales over a field of view of 5' x 4.3' at moderate resolving power (R $\sim$ 5000) over a 1000 - 1600 \AA\ bandpass. INFUSE is a sounding rocket borne instrument under development at the University of Colorado (CU) with a projected launch date of 2022.",