Wednesday Colloquium


"Complex evolutionary and asteroseismic modelling of pulsating components in eclipsing binary systems"

Amadeusz Miszuda (CAMK, Warsaw)

Eclipsing binary systems are well-proven benchmarks in testing stellar evolution theory. Precise stellar parameters that can come from their analysis aid systems' age determination along with tracing back their evolution history. Eclipsing binaries that contain pulsating components are a special subclass of binaries that combine information coming from orbital and pulsational analyses. Whereas the single-star pulsators are rather well understood, the precise effect that binarity and possible mass transfer have on the pulsational characteristics of components has yet to be determined. In my talk, I will highlight some of the most important results from my studies of pulsating components in binary systems. In particular I will discuss the effect that accumulation of He in outer layers of accretor caused by mass transfer has on excitation of the high radial-order g modes in models of delta Scuti stars and the evolution of radial mode frequencies during the main sequence evolutionary phase.


"Magnetic white dwarfs in close binaries: origin, evolution, surfeit, and dearth"

Diogo Belloni (Departamento de Física, Universidad Técnica Federico Santa María)

Since the 1940s, understanding why some white dwarfs become strongly magnetized while others do not has been one of the fundamental unsolved issues of stellar evolution. Several models have been suggested for the magnetic field generation in white dwarfs, but they all fail when confronted with the observed incidence of magnetism in single white dwarfs and white dwarfs in binaries. We recently suggested that a rotation- and crystallization-driven dynamo, similar to those operating in planets and low-mass stars, is responsible for a large fraction of the observed strongly magnetized white dwarfs. During this talk, I will show that this new scenario can explain the existence of pulsar-like white dwarfs, the absence of bright X-ray accreting white dwarfs in globular clusters, the accumulation of magnetic white dwarfs among metal-polluted white dwarfs, the occurrence rate of strong magnetic fields in double white dwarf binaries, the paucity of white dwarfs accreting from brown dwarfs, and why a large fraction of accreting white dwarfs but only a small part of their detached progenitors contain a strongly magnetized white dwarf. That implies a rotation- and crystallization-driven dynamo most likely plays an unprecedentedly important role in the magnetic field generation in white dwarfs.


"Dynamical evolution of the Milky Way globular clusters in cosmological timescale"

Marina Ishchenko (Main Astronomical Observatory, National Academy of Sciences of Ukraine)

The main idea of the work is to perform the dynamic evolution of the orbits of Globular Cluster subsystems (GCs) with a look-back time up to 10 Gyr. This will allow us to estimate the possible interaction of GCs with the Galactic Center (GalC) region, including the influence of the super-massive black hole (SMBH), which has dynamically changed in the past and collisional rates with each other’s (GC with GC). To reproduce the structure of the Galaxy in time, we used external potentials selected from the large-scale cosmological database IllustrisTNG-100, whose properties (mass and size of the disk and halo) are similar to the physical values of the Milky Way at present. In these potentials, we have reproduced the orbits of 159 GCs in 10 Gyr lookback time using our own high-order N-body parallel dynamical code, the phi-GPU code. For the initial proper motions, radial velocity and heliocentric distance of each GC, we take prom from the Baumgardt & Vasiliev (2021) catalog based on Gaia Data Release 3. To identify clusters that have interaction with the GalC we used the criteria that the relative distance between the SMBH and the GC is at least four times the sums of the GCs half-mass radii. Using these simple criteria, we obtained statistically significant rates of close passages of the GCs with the Galactic Center. During our investigation, we analyzed the GC orbital evolution to find a GC that has such a close passage and prepare the statistical probability of such events. For the selected GCs, we generated an initial mass function and performed a full N-body modeling to find out the potential influence on the GCs stellar populations due to the SMBH influence in the Galactic Center region. Also, we present a statistical analysis of the cumulative close passages rate: about ten close passages with relative distances shorter than 50 pc for every billion years for each of the five external potentials. We present the 22 most reliable collision pairs with a good probability. As an example: Terzan 4 versus Terzan 2, Terzan 4 versus NGC 6624, Terzan 4 versus Terzan 5, Terzan 4 versus NGC 6440, and Terzan 4 versus Liller 1. The most active globular cluster in the collision sense is Terzan 4, which has 5.65 collision events on average. Most collisions are located inside the Galactic disk and form two ring-like structures. The first ring-like structure has the highest collision number density at 1 kpc, and the second structure has a maximum at 2 kpc.


"Surveying the skies at high sensitivity: The anticipated science with the Rubin Observatory / LSST"

Greg Madejski (Kavli Institute for Particle Astrophysics and Cosmology, SLAC and Stanford University)

Vera Rubin Observatory is under construction at the Cero Pachon mountain summit in Chile. The observatory will feature a mirror with 8 meter diameter, and the largest CCD camera in its focal plane, with 3.2 gigapixels. The large field of view of the telescope - 9.6 square degrees - will allow for efficient surveys of large fraction of the sky. During the 10-year the "Legacy Survey of Space and Time" - LSST - the observatory will study a wide range of celestial phenomena. This includes making a sensitive measurement of the evolution of dark energy as a function of cosmic time, study of transient celestial sources such as supernovae, and taking census of small bodies in the Solar System. This presentation will describe those scientific goals in some detail, and will present the current status of the project.