Fatemeh Kayanikhoo (CAMK, Warsaw)
Fast radio burst (FRB) is a mysterious phenomenon ever discovered in deep space. On 28 April 2020, CHIME and STARE2, detected an FRB in our own galaxy. This is the brightest FRB ever detected with a known origin "SGR1935+2154" which is a magnetar. In this seminar, I will talk about FRBs, radio telescopes, and FRB200428.
Guilherme Limberg (University of São Paulo (IAG-USP))
We analyze the dynamical properties of ∼1500 very metal-poor (VMP; [Fe/H] ≲−2.0) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past thirty years, are supplemented by a number of calibration stars and other small samples, along with astrometric information from Gaia DR2. We apply a clustering algorithm to the 4-D energy-action space of the sample, and identify a set of 38 Dynamically Tagged Groups (DTGs), containing between 5 and 30 member stars. Many of these DTGs can be associated with previously known prominent substructures such as Gaia-Sausage/Enceladus (GSE), Sequoia, the Helmi Stream (HStr), and Thamnos. Others are associated with previously identified smaller dynamical groups of stars and streams. We identify 10 new DTGs as well, many of which have strongly retrograde orbits. We also investigate possible connections between our DTGs and ∼300 individual r-process-enhanced (RPE) stars \textbf{from a recent literature compilation}. We find that several of these objects have similar dynamical properties to GSE (5), the HStr (4), Sequoia (1), and Rg5 (1), indicating that their progenitors might have been important sources of RPE stars in the Galaxy. Additionally, a number of our newly identified DTGs are shown to be associated with at least two RPE stars each (DTG-2: 3, DTG-7: 2; DTG-27: 2). Taken as a whole, these results are consistent with ultra-faint and/or dwarf spheroidal galaxies as birth environments in which r-process nucleosynthesis took place, and then were disrupted by the Milky Way.
Greg Ashton (Monash University)
The first pulse-to-pulse observations of a neutron star glitch in the Vela pulsar identified a null pulse hinting at the sudden disruption of the neutron star’s magnetosphere. The only physical model connecting the glitch and the null pulse relies on a starquake either triggering, or being triggered by, the glitch itself . Until now, this was the only null pulse identified from over 50 years of observing the Vela pulsar. We identify five other null-like pulses, that we term quasi-nulls, before and after the glitch, separated by hundreds of seconds. We verify that such nulls are not found in data away from the glitch. We speculate that the quasi-nulls are associated with foreshocks and aftershocks preceding and following the main quake, analogously with terrestrial quakes. This implies the energy reservoir built up between glitches is not released suddenly, but over a period of minutes to hours around the time of the glitch.
Ebil Gügercinoğlu (Sabanci University)
The speaker will present an analysis of the timing solutions from the Fermi-LAT observations of gamma-ray pulsars PSR J0835−4510 (Vela), PSR J1023−5746, PSR J2111+4606 and PSR J2229+6114. In particular, PSR J1023−5746 is the most active pulsar and should be a target for frequently glitching Vela-like pulsars in future observations. By theoretical analysis of these glitches it is possible to obtain important information on the structure of neutron star, including moments of inertia of the superfluid regions participated in glitches and coupling time-scales between various stellar components.
Jean-Pierre Lasota-Hirszowicz (CAMK, Warsaw)
It is commonly accepted that the periods of superhumps can be satisfactorily explained within a model involving apsidal motion of the accretion disk provided the frequency of the apsidal motion in addition to the dynamical term includes also the pressure effects. Using a larger sample of systems with reliable mass ratios it is shown, however, that this view is not true and the model requires further modifications. The talk will be based on the work of J. Smak, https://arxiv.org/abs/2102.10599
Miljenko Cemeljic (NCAC, Warsaw)
The talk is based on: https://arxiv.org/abs/2012.08550
Fatemeh Kayanikhoo (CAMK, Warsaw)
Gravitational waves provide a powerful opportunity to constrain the dynamics in the interior of protoneutron stars during core collapse supernovae. Convective motions play an important role in generating neutron stars magnetic fields, which could explain magnetar formation in the presence of fast rotation. The gravitational wave emission from protoneutron star convection and its associated dynamo can be extracted from state of the art numerical simulations.The talk will be based on the recent work of Raphaël Raynaud, Pablo Cerdá-Durán and Jérôme Guilet, https://arxiv.org/abs/2103.12445
Gergeley Hajdu (CAMK, Warsaw)
The talk is based on: "Studies of RR Lyrae Variables in Binary Systems I.: Evidence of a Trimodal Companion Mass Distribution" by Gergely Hajdu, Grzegorz Pietrzyński, Johanna Jurcsik, Márcio Catelan, Paulina Karczmarek, Bogumił Pilecki, Igor Soszyński, Andrzej Udalski, Ian B. Thompson, https://arxiv.org/abs/2105.03750
Alessio Zicoschi (La Sapienza, Roma)
PSR J0537-6910 is a young energetic X-ray pulsar and is the most frequent glitcher known. The inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. The talk will be based on the recent analysis from the LIGO collaboration: "Constraints from LIGO O3 data on gravitational-wave emission due to r-modes in the glitching pulsar PSR J0537-6910" , see https://arxiv.org/abs/2104.14417
Vanessa Graber (ICE & IEEC, Barcelona)
The talk is based on the work "Analyzing the Galactic pulsar distribution with machine learning", arxiv preprint: https://arxiv.org/abs/2101.06145
Miljenko Cemeljic (CAMK, Warsaw)
The discussion will be inspired by the article: "Investigative Study on Preprint Journal Club as an Effective Method of Teaching Latest Knowledge in Astronomy" https://arxiv.org/abs/2106.01688
Yu Wang (ICRANet and INAF, Italy)
Rathish Previn (NCAC, Warsaw)
