Julian Sitarek (Uniwersytet Łódzki)
Colloquium on-line. Join Zoom Meeting For details on the connection mail to bajtlik@camk.edu.pl. General information: https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/ During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
Colloquium on-line.
Join Zoom Meeting
For details on the connection mail to Stanisław Bajtlik.
General information:
https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/
During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
Agnieszka Janiuk (CFT PAN)
I will present the recent works of the relativistic astrophysics group in CTP PAS, related to modeling of cosmic sources containing accreting black holes. Numerical methods developed recently in the framework of the code HARM-COOL, have applications to the studies of gamma ray bursts, collapsars, and kilonovae.
Colloquium on-line.
Join Zoom Meeting
For details on the connection mail to bajtlik@camk.edu.pl.
General information:
https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/
During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
Jean-Pierre Lasota (IAP, Paris, CAMK, Warsaw)
Ultraluminous X–ray sources (ULXs) are objects with apparent (i.e assumed isotropic) luminosities Lapp > 1039 erg/s, exceeding the usual Eddington value for stellar– mass black holes, but which do not contain supermassive black holes. I will show that ultraluminous X-ray sources (ULXs) with coherent X-ray pulsing (PULXs) have normal (X-ray pulsar strength) magnetic fields and therefore their apparently super-Eddington luminosity must be geometrically beamed. I will present the model describing the physical properties od PULXs and show that they probably have neutron-star spin axes significantly misaligned from their central accretion discs. Scattering in the funnels collimating their emission and producing their apparent super-Eddington luminosities is the most likely origin of the observed correlation between pulse fraction and X-ray photon energy. Pulsing is suppressed in systems with the neutron-star spin closely aligned to the inner disc, explaining why some ULXs show cyclotron features indicating strong magnetic fields, but do not pulse. I will argue that alignment (or conceivably, field suppression through accretion) generally occurs within a fairly short fraction of the ULX lifetime, so that most neutron-star ULXs become unpulsed. This further suggest that almost all ULXs actually have neutron-star accretors, rather than black holes or white dwarfs, reflecting their progenitor high-mass X-ray binary and supersoft X-ray source populations.
Colloquium on-line.
Join Zoom Meeting
For details on the connection mail to bajtlik@camk.edu.pl.
General information:
https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/
During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
Cezary Gałan (CAMK, Warsaw)
Symbiotic stars are a type of evolved, long-period binary systems composed of a cool, giant donor and a hot, compact object - usually a white dwarf. The complex nature of interactions between the components of these systems makes them ideal for studying evolution in binary systems, especially at the final stages. Chemical composition, next to initial mass is among the major parameters determining stellar evolution. Until recently, knowledge of abundances in symbiotic red giants was limited to only a few cases. Our analyzes of the last several years, using high and low-resolution spectra in the optical and especially infrared domain not influenced significantly by the nebular continuum, increase statistics to well over one hundred objects. Our spectroscopic data and methods used will be presented. I will discuss what we can learn about the evolution of components of the long-period binary systems, the history of the mass transfer and evolution in Galactic stellar populations on the example of studies of chemical composition in symbiotic giants.
Colloquium on-line.
Join Zoom Meeting
For details on the connection mail to bajtlik@camk.edu.pl.
General information:
https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/
During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
Frederic H. Vincent (Observatoire de Paris)
The recent Event Horizon Telescope (EHT) millimeter image of the vicinity of the supermassive compact object M87* at the center of the galaxy M87 is a breakthrough. It is important to investigate what can and what cannot be inferred from such images. In this talk I will discuss a simple geometric model of the region of the accretion flow immediately surrounding M87*. I will use this model to discuss the highly-lensed features of EHT-like images, often loosely referred to as the "photon ring". I will discuss whether such features can be used as clean probes of the nature of the underlying spacetime. I will also discuss various EHT-like images of M87*, assuming this object is various kinds of compact alternatives to the standard black hole. This will allow discussing to what extent can EHT-like images help constrain the nature of the compact objects at the center of M87 or our Milky Way.
Colloquium on-line.
Join Zoom Meeting
For details on the connection mail to bajtlik@camk.edu.pl.
General information:
https://www.camk.edu.pl/en/camknet/audio-video/zoom-videoconferences/
During the Colloquium, please keep your cameras off and microphones mute (except for asking the question).
