10 December, 2020 at 1:30 PM
Symbiotic binaries: the mystery of cool giants and hot dwarfs
Jaroslav Merc
(Charles University, Prague; P. J. Šafárik University, Košice, Slovakia)
Symbiotic stars are interacting binaries consisting of an evolved, cool giant transferring mass to a hot companion – a white dwarf or rarely a neutron star. The presence of both ionized and neutral regions in their surroundings, interacting winds, jets, accretion disks, or dust forming regions make them extraordinary astrophysical laboratories for studying various aspects of the interaction and evolution in binary systems. Although some of the symbiotic systems are studied for more than a hundred years, there are still several open questions concerning the mechanisms of activity, individual components, and their evolution. We will briefly review the important information on symbiotic stars and present the results connected with the New Online Database of Symbiotic Variables and long-term monitoring of selected objects.
12 November, 2020 at 1:30 PM
Constraining the Rapid Neutron-Capture Process with Meteoritic I-129 and Cm-247
Andrés Yagüe López
(Konkoly Observatory, Budapest, Hungary)
Among all radioactive isotopes produced in the Galaxy, a small number of them have relatively short mean lives between 0.1 and 100 Myr. Early Solar System abundances of these radioisotopes can be determined through meteoritic analysis and, due to their short half lives, give us insight into the sites and processes that produced them. In this talk, I discuss the ratio of two of these short-lived radioisotopes, I-129 and Cm-247. I also show how, due to their remarkably similar half lives, they give us a unique opportunity to constrain the physical conditions of the last rapid neutron-capture process event that contributed to the enrichment of the pre-solar nebula.
15 October, 2020 at 1:30 PM
ALMA and the Cool Universe
Abhijeet Borkar
(Astronomical Institute of the Czech Academy of Sciences)
The Atacama Large Millimeter/submillimeter Array (ALMA) is currently the largest radio telescope in the world, a complete imaging and spectroscopic instrument operating in the high frequency radio regime. It is located in northern Chile as a partnership between Europe (ESO), North America (NRAO, USA and NRC, Canada) and East Asia (NAOJ, Japan, ASIAA, Taiwan, and KASI, South Korea). ALMA provides an extensive breadth and depth of science, from cosmology & high redshift Universe, planet & star formation, to solar system objects, and offers capabilities which are unique and complimentary to major terrestrial and space telescope of the modern era. In this talk, I will provide an overview of ALMA telescope, operations, science capabilities & highlights and how you can use ALMA for your favourite science. I will also review the role of the Czech ALMA Regional Center node and preparations for the proposal Cycle.
24 September, 2020 at 1:30 PM
Nebulosities of the symbiotic binary R Aquarii
Tiina Liimets
(Astronomical Institute of the Czech Academy of Sciences)
I will give an overview of the fascinating nebulae around one of the closest known symbiotic star R Aquarii. Together with historic and more recent observational data I will present results of our own long-term monitoring of these intriguing nebulosities: an ancient arcs, hour-glass nebula and puzzling, still active jet.
14 July, 2020 at 1:30 PM
Wray 15-906: a post-red supergiant luminous blue variable discovered with WISE, Herschel and SALT
Olga Maryeva
(Astronomical Institute of the Czech Academy of Sciences)
Presently we know two evolutionary paths leading massive stars to Wolf-Rayet (WR) stage. Stars witn M>40Msun after the end of hydrogen burning in the core come to WR through the phase of Luminous blue variables (LBV). On the other hand, stars with lower mass (~30Msun) before LBV phase cross the stage of red supergiant (RSG). Theory predicts what the latters may explode as supernova (SN) directly after LBV phase showing before explosion the spectrum of WN11 type. However in practice in our Galaxy there are only three stars of WN11 type and all of them have higher initial masses, and therefore they did not pass through RSG phase. In my talk I will present results of study of recently discovered Galactic candidate luminous blue variable Wray 15-906. I will show how spectral classification was performed, and how stellar parameters were calculated. Estimated location on Hertzsprung-Russell diagram shows that Wray 15-906 is a post-red supergiant star. Collected spectral data together with results of modelling show that properties of Wray 15-906 are very similar to predicted ones for a star with initial mass of ≈25Msun, which will pass through WN11h stage right before exploding as a supernova.
11 June, 2020 at 1:30 PM
Asteroseismology
Julieta Sanchez Arias
(Astronomical Institute of the Czech Academy of Sciences)
Variable stars offer a great opportunity to study their interiors through asteroseismology. This powerful astrophysics tool allows us to derive stellar parameters such as the mass, the radius, the metallicity and the age by the comparison between theoretical models and the frequency spectrum derived from observations. In this opportunity, I will present the challenges in the modelling of hybrids delta Stc-gamma Dor stars and the analysis of the light curve of one particular hybrid star with surface activity. In addition, I will introduce asteroseismic tools to distinguish two different kinds of variable stars, which usually lie in the same region of the seismic HR diagram: delta Sct stars and the precursors of the so-called extremely low mass white dwarf stars. Finally, I will present a brief overview of the potential of asteroseismology in massive stars.
30 January, 2020 at 1:30 PM
Self-consistent solutions for line-driven winds using Lambert W-function
Alex C. Gormaz-Matamala
(Universidad de Valparaíso, Chile)
Hot massive stars present strong stellar winds which are driven by absorption, scattering and reemission of photons by the ions of the atmosphere (line-driven winds). A better comprehension of this phenomenon and a more accurate calculation of hydrodynamics and radiative acceleration is required to determine accurate mass-loss rates, and hence constrain evolutionary tracks of hot massive stars. The equation of motion for the stellar winds of a hot massive star is solved analytically by using the Lambert W-function. To solve radiative transfer equation in the stellar atmosphere and to calculate the radiative acceleration g_line(r) we use the non-LTE code CMFGEN. Since the acceleration depends now only on radial coordinate, it can be used to solve analytically the equation of motion by means of the Lambert W-function. An iterative procedure between the solution of the radiative transfer and the equation of motion is executed in order to obtain a consistent result.