SN 1987A in its third decade imaged by the Hubble Space Telescope: Evolution of the ejecta and equatorial ring
Sophie Rosu (KTH Royal Institute of Technology, Stockholm, Sweden)

The spatially resolved view of the transition into a young supernova (SN) remnant offered by SN 1987A makes it the most thoroughly studied SN so far, from ground to space, at all wavelengths. Its evolution has notably been followed by the Hubble Space Telescope (HST) since its launch in 1990 with an excellent spatial resolution.

We present the recently (2022) acquired HST imaging observations of SN 1987A. For the first time since 2009, the observations cover the entire optical domain between 200 and 1100 nm. We make use of these and earlier observations to study the recent evolution of the spectral energy distribution (SED) and morphology of all parts of the system. We also use the annual imaging in the blue and red filters to provide lightcurves for the different parts of the system.

The recent imaging provides us with a spatially resolved view of both the freely expanding ejecta and the interaction of this latter with the circumstellar medium, revealing the asymmetric ejecta structure in increasingly greater detail.

We observe a decay in the lightcurve of the equatorial ring (ER), explained by the continuous fading of the hotspots that started ∼8000 days after the explosion. A noticeable increase in the ejecta flux is observed until day ∼ 11000, after which the flux seems to flatten around a constant value, owing to the X-ray input coming from the ER.

We do not observe any clear evidence for a point source at the center of the ejecta that would be associated with the direct detection of a compact object. We discuss the implication of our findings in terms of both the energy sources contributing to the ejecta emission and limits on the compact object.

Physics opportunities of CEvNS experiments
Diego Aristizabal Sierra (Santa Maria U., Valparaiso)

Experimental facilities that study coherent elastic neutrino-nucleus scattering, or CEvNS (pronounced sevens), provide a rich environment for precise measurements of Standard Model parameters and searches of new physics. In this talk, I will discuss a few aspects of this program involving solar neutrinos and third-generation dark-matter detectors as well as directional detectors in the Fermilab neutrino beamlines.

Future "firsts" in gravitational-wave observations
David Keitel (IEB, Mallorque)

Beyond the highly successful detection efforts for compact binary coalescences (CBCs), gravitational-wave astronomy also comprises other long-standing search efforts, such as those for continuous waves (CWs) from individual spinning neutron stars. Furthermore, the field is diversifying with new searches for additional astrophysical effects and source types.

I will summarise some recent progress towards three such potential "next first detections":

• . The search for signatures of gravitational lensing on CBC signals, where heavy masses along the signals' long voyage to Earth can magnify, multiply or deform them. Here I will focus in particular on recent work regarding the effects of waveform systematics and Bayesian sampler choices, which are crucial to understand for making robust detections.
• . A wide range of searches pursued within the LVK collaboration for known or unknown neutron stars as CW emitters, or even for more exotic sources involving dark matter.
• . Searches for long-duration transient CW-like signals from newborn or perturbed neutron stars, such as binary neutron star remnants or glitching pulsars.

Searching for Evidence of Life Beyond the Solar System with the Giant Magellan Telescope (GMT) and the GMT-Consortium Large Earth Finder (G-CLEF)
Andrew Szentgyorgyi (Harvard-Smithsonian Center for Astrophysics)

Two of the highest priority programs in astrophysics are the discovery and characterization of Earth 2.0 – rocky, Earth-mass exoplanets orbiting Solar-type stars in their habitable zone and the search for biomarkers in the atmospheres of exoplanets in general, The first program is enabled by precision radial velocity (PRV) measurements of the line-of-sight reflex motion of host stars in response to the gravitational influence of low-mass exoplanets that orbit those stars. The search for biomarkers and the characterization of the molecular composition of exoplanets requires extremely high spectral resolution spectrographs on large aperture telescopes. The G-CLEF spectrograph has been designed to provide these capabilities. Before deployment at the GMT, G-CLEF will be delivered to the Magellan telescopes in 2027, to do several pathfinder observational programs that will allow observers to optimize G-CLEF for its delivery to the GMT in 2032. A key project for G@M+MagAO-X will be to resolve and search for O2 in the atmosphere of a habitable zone planet orbiting the star nearest to the Sun – Proxima Cen b. The talk will discuss several aspects of habitability, habitability searches and several technical innovations we will deploy to optimize the Proxima Cen b habitability search.

From heartbeat to heartbreak: the story about eccentric binary systems, tidally excited oscillations and collapsing tidal waves
Piotr Kolaczek-Szymanski (STAR - ULiège)

Currently, no one is surprised by the information that most stars in the Universe reside in binary or even multiple systems. Furthermore, in the case of massive stars (with initial masses >8Msun), we can be almost certain that they have at least one companion, which is most likely also a high- or intermediate-mass star. This means that the evolution of massive stars cannot be studied without taking into account their common binarity. Due to the relatively young age of these systems, many of them still have eccentric orbits. However, significant non-zero orbital eccentricity is not restricted only to young massive stars, but it is also observed in evolved systems, containing red giant(s). The tidal forces acting within them determine the further fate of the system, which under favorable conditions can lead to the stellar merger at very different stages of evolution. Periodically varying tidal potential leads to a series of interesting and significant phenomena from an evolutionary point of view. Among them, so-called heartbeat stars are the prominent ones, due to their characteristic light curves resembling an electrocardiogram. In eccentric binary systems, we can also observe tidally induced oscillations, which directly participate in the evolution of the system's orbit, leading to its accelerated tightening. In some systems, the components pass so close to each other at periastron that the resulting huge tidal deformation cannot return to equilibrium and spectacularly collapses onto the star's surface. During my seminar, I will discuss all these processes, primarily considering the effects of my recently defended PhD thesis and outlining certain research plans for the future.

Linking stellar compositions and planet formation: implications for solar models and stellar surface abundances
Masanobu Kunitomo (Kurume University)

Stars grow by accretion from the protoplanetary disk where planets are formed. Planet formation theory predicts that the composition of the disk gas, and thus of the gas accreted by protostars, must have been variable: the growth and inward drift of dust in the disk leads to the generation of a temporal "pebble wave" of increased metallicity, followed by a phase in which the exhaustion of the pebbles and the formation of planets leads to the accretion of metal-poor gas. How does accretion affect stellar composition? First I will show our solar models with the accretion in the early Solar System which can have a larger central metallicity by up to 5% and thus higher neutrino fluxes, demonstrating that the formation history of the Solar System constitutes a key element in resolving the "solar modeling problem". I will also discuss the implications for chemical peculiarities in other stars: the surface compositions of refractory-poor solar twins, binary systems, and lambda Boo stars.

A Few Topics in Nonlinear and Binary Asteroseismology
Zhao Guo (KULeuven)

Stellar oscillations are not necessarily linear. Some oscillation modes can be weakly nonlinear and may produce daughter modes via parametric instability. This process is a potential amplitude limitation mechanism that determines the final observed oscillation amplitude, as demonstrated in Delta Scuti stars and Slowly Pulsating B stars. Observational signatures of nonlinear mode coupling include periodic amplitude and phase modulations. The behavior of a coupled-mode system can be rich and complex, including period doubling, intermittency, and various pathways to chaos. In some binary star systems with elliptical orbits, tidal forces can directly induce stellar gravity modes, manifesting as luminosity variations at orbital harmonic frequencies. These tidally excited oscillations (TEOs) can mostly be understood within the framework of linear theory. However, nonlinearity can induce non-orbital harmonic TEOs, and we can use these secondary modes to pioneer a new approach to asteroseismology. Finally, I will present another aspect of the nonlinear effect: wave-mean flow interactions. The quadratic terms in the wave equations can modify the background mean flow, and vice versa. We employ a quasi-linear approximation to study the spin-up of the solar core by the ingoing gravity waves induced by a planet, comparing it with direct numerical simulations.

A multimessenger GW-GRB study of the sGRB population and its future developments
Matteo Pracchia (Université de Liège)

The unambiguous joint detection of GRB 170817A and GW170817 has been the long-awaited smoking gun for the association between short gamma-ray bursts (sGRBs) and the merger of binary neutron stars (BNS) systems. The aforementioned sGRB, however, was extremely close and had an unexpectedly low measured luminosity when compared to the other observed sGRBs, suggesting that there is a sub-luminous fraction of the GRB population which is undetected at the usually measured distances.

This work aims to characterize the low-luminosity part of the sGRB population through a multi-messenger GW-GRB Bayesian study. The sGRB population is described via its luminosity probability distribution, modelled through an extension of a broken power law whose parameters have already been constrained through mid-high luminosity sGRB observations. The parameters of this power-law extension, i.e. the low luminosity power index and the low-luminosity cutoff, are constrained through a Bayesian analysis which exploits the results from the modelled GW follow-up analysis of the short GRBs detected during the first three observing runs of the International Gravitational-Wave observatory Network (IGWN).

The results obtained allow us to define the luminosity distribution at lower values for the sGRB population and to give an estimate of the value found for the astrophysical sGRB rate and the joint GW-GRB detection rate for the next IGWN observing runs. There are, nonetheless, some upgrades to the method used for this study that could give a more precise and complete outline of the astrophysical sGRB population.

Seismic/Newtonian noise challenges for third generation gravitational wave detector
Dixeena Lopez (Université de Liège)

The mitigation of various sources of noise that mimic the effect of gravitational waves or constrain the detector's sensitivity is the main challenge for ground-based GW searches. The seismic noises which are active at the low-frequency range below 10 Hz are usually filtered away using seismic attenuation chains and new design implementation. However, the presence of Newtonian noise by the subtler effect of seismic waves and atmospheric effects causes fluctuations in test masses, which mimic the passing of GWs in frequencies below 30Hz.

The Einstein Telescope (ET) is a ground-based underground detector planned to be built in Europe, and observation is likely to start in 2035. The proposed design of ET is a triangular shape interferometer with an arm length of 10 km, which increases the low-frequency sensitivity to almost 1 Hz by the reduction in displacement noise. There will be a ten times improvement in overall strain sensitivity for ET than the current generation gravitational wave ground-based detectors. However, the ET sensitivity is limited by Newtonian noise at low frequencies, and there is no efficient way to shield this effect. In order to improve the low-frequency ET sensitivity to sources like GW memory, one needs to reduce the effect of Newtonian noise using advanced instrumental and data analysis techniques. The accurate models of Newtonian noise, which depends on the complex seismic fields, geology and topography near the site, are required for noise cancellation. In this presentation, we delve into the seismic/Newtonian noise challenges encountered in the ET operation and explore machine-learning approaches to address them. By understanding the sources and characteristics of seismic noise, we aim to devise effective strategies that could significantly enhance ET's detection capabilities. Leveraging the power of artificial intelligence, we explore how machine learning algorithms can enhance our ability to distinguish gravitational wave signals from background noise, even in the presence of seismic disturbances.

Charge-breaking opportunities for the early Universe
Igor Ivanov (Zhongshan U., Zhuhai, China)

The hot early Universe must have evolved through one or several phase transitions around the electroweak epoch, but the details of this evolution are not known. Multi-Higgs models often possess scalar potentials which, at finite temperatures, exhibit several competing minima and may lead to phase transitions of peculiar nature. In this talk, I will show that there exists a regime in the two-Higgs-doublet model in which thermal evolution of the early Universe passes through an intermediate phase with a charge-breaking vacuum. This regime leads to a sequence of phase transitions and can be tested at colliders. In addition, I will show that multi-Higgs-doublet models can support phase transitions in which two neutral minima are separated by a charge-breaking bubble wall, with remarkable and yet unexplored cosmological consequences.

Searching For Transiting Planets around Red Clump Stars: Constraining the Occurrence Rate of Close-In Jovian Planets
Victoria Bonidie (Pittsburgh University)

The fate of close-in planets as their host stars evolve past the main sequence is not well understood. To address this question, we perform a transit survey in the Kepler light curves of red clump (RC) stars, the post-RGB core-helium burning phase for low-mass stars. Our search yields no evidence for transiting Jupiter-sized planets in our sample, allowing us to place the first upper limits on the occurrence rate of exoplanets around RC stars. We find a 1-σ upper limit occurrence range between 0.1%< f<0.7% for Hot Jupiters, with a mean upper limit of 0.3%. This mean becomes 0.5% when considering all Jupiter-sized planets with orbital periods <20 days. In this talk, I will discuss our current understanding of the effects stellar evolution has on planetary survival, the techniques and outcome of my search, and the implications of finding no evidence of Hot Jupiters around RC stars.

Companion-Disc Interactions: From Planet Formation to Gravitational Wave Sources
Josh Calcino (Tsinghua University)

Accretion discs are ubiquitous in astrophysics. Around protostars, they are responsible for the formation of planetary systems and are known as protoplanetary discs. Around supermassive black holes, they produce the brightest electromagnetic phenomena in the Universe, active galactic nuclei (AGN). Spatially resolved observations of protoplanetary discs have revealed a multitude of substructures. From gaps and cavities, to spiral arms and perturbed kinematics, these observations are highly suggestive of companion-disc interactions. Protoplanetary disc kinematics in particular are becoming a valuable method for uncovering hidden companions. While there exists a substantial amount of literature on the understanding of planet-disc interactions and their observational implications, little attention has been made towards circumbinary discs. Using 3D hydrodynamical simulations post-processed with Monte Carlo radiative transfer, I found several kinematic and morphological features that can identify circumbinary discs. I will show that Doppler flips, spiral arms, eccentric gas motion, and vortex-like kinematic signatures are commonly seen. These complex kinematic structures may explain some of the observed, and potentially misinterpreted, kinematic signatures seen in the literature. I will finish the seminar by providing a brief summary of recent promising results that suggest stellar mass binary black holes embedded in AGN discs can be the progenitors to gravitational wave sources.