Wednesday Colloquium


"Asteroseismology in Close Binaries: Delta Scuti Stars and Tidally Induced Pulsations in Heartbeat Stars"

Zhao Guo (NCAC, Warsaw)

Great advancements have been made in understanding solar-like oscillators. However, this is not the case for variable stars of intermediate masses, such as Delta Scuti variables. By studying these stars in eclipsing binaries (EBs), model independent fundamental parameters such as mass and radius can be inferred. On one hand, this synergy constrains the parameter space and facilitates the asteroseismic modeling, and this is shown for the Delta Scuti type pulsating EB KIC 3858884 and KIC 9851944. On the other hand, studies of binary stars must address the complexities such as mass transfer. KIC 8262223 is such an example, which consists of a mass-gaining Delta Scuti primary and a pre-He white dwarf secondary. Some of the eccentric binary systems, the heartbeat stars, show tidally excited oscillations. After briefly reviewing the linear theory of tidally forced stellar oscillations, we study the tidal pulsating binary KIC 3230227 and demonstrate that both amplitude and phase can be used to identify the tidally excited pulsation modes.


"New forms of pulsation in classical pulsators"

Radosław Smolec (NCAC, Warsaw)


"MOCCA-SURVEY Database I Projects: Binary Black Holes and IMBHs in Globular Clusters"

Abbas Askar (NCAC, Warsaw)

Modeling the evolution of extremely dense stellar systems like globular clusters remains a challenging astrophysical problem. In this talk, I will briefly introduce the basic ideas behind the Monte Carlo method for simulating the long term evolution of star clusters and will describe the MOCCA (MOnte Carlo Cluster simulAtor) code and its features. My talk will focus on the results from two projects that utilized the results of the MOCCA-SURVEY Database I project in which about 2000 star cluster models were simulated using the MOCCA code. In the first project, we used the results from this database of star cluster models to determine the astrophysical properties and local merger rate densities for coalescing binary black holes. In the second project, we describe the dynamical evolution of a unique type of dark star cluster model in which the majority of the cluster mass at Hubble time is dominated by an intermediate mass black hole (IMBH). Taking one of these models, we apply the method of simulating realistic mock observations to obtain the photometric and kinematic observational properties of the dark star cluster model at 12 Gyr. We find that the perplexing Galactic globular cluster NGC 6535 closely matches the observational photometric and kinematic properties of the dark star cluster model and could potentially be harbouring an IMBH. I will also briefly mention other ongoing projects that are using results from the MOCCA-SURVEY Database I project and future plans to further improve and carry out more simulations.


"On Cataclysmic Variables in Globular Clusters"

Diogo Belloni (NCAC, Warsaw)

Cataclysmic variables are interacting binaries composed of a white dwarf undergoing stable mass transfer from (usually) a low-mass main sequence star and they are expected to exist in non-negligible numbers in globular clusters that are natural laboratories for testing theories of stellar dynamics and evolution. I will present the main aspects related to our understanding regarding the population of cataclysmic variables in globular clusters from two points of view: numerical simulation and observations. I will conclude by summarizing some key procedures associated with the fate of the research in such a field, including the role of our group in the process.