General Seminar (2022)
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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).
3 January 2022
“News about HIRES/ELT/ESO and the research infrastructure of the Piwnice optical and radio observatory”
Prof. Andrzej Niedzielski and Dr hab. Agnieszka Słowikowska (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
This seminar will be divided into two parts. First, we will summarize our recent contribution and future plans to the HIgh REsolution Spectrograph (HIRES) for the Extremely Large Telescope (ELT/ESO, prof. Andrzej Niedzielski). In the second part, we will give a general overview of updates of the research instrumentation in our Observatory in Piwnice (dr hab. Agnieszka Słowikowska).
10 January 2022
“Synchrotron emission of simulated galactic disks”
MSc Mateusz Ogrodnik (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Theoretical and numerical studies incorporating cosmic rays (CRs) into global modeling of magnetized interstellar medium demonstrate that CRs play an important role in the generation of large-scale galactic magnetic fields, and, at the same time, in driving galactic winds. CR-driven dynamos produce magnetic arms in galactic disks and large-scale helical magnetic fields in galactic halos. These models, however, often lack means to verify them via comparison with observable data.
A possible solution to this problem comes with the recently introduced and published ”Cosmic Ray Energy SPectrum” (CRESP) module of PIERNIK MHD code, being an implementation of energy-dependent propagation of CR electrons. In this model, CR electrons propagate using the energy-dependent diffusion-advection equation, including adiabatic cooling and synchrotron losses.
The algorithm is used in global galactic disk simulation to study propagation effects of CR electrons in edge-on disk galaxies and their imprint on resulting synchrotron radiation. Synchrotron radiation maps and slices are compared against observed radiation of NGC891 galaxy, allowing direct comparison of a used model.
In the course of the simulation galactic magnetic field is magnified, synthetic synchrotron radiation maps of simulated galaxies reproduce a number of features observable in physical edge-on galaxies, e.g. ‘X-shaped’ polarization patterns and similar spectral slope of total synchrotron emission. The disk, produces strong galactic wind is, with outflow velocity comparable to NGC891, however showing the conical shape and resulting in outflow-dominated emission, thus resembling starburst galaxy M82.
17 January 2022
“Hot and warm gas in star-forming regions in the outer galaxy”
MSc Ngan Le (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Star formation is ubiquitous in the Galaxy, but the physical and chemical conditions in star-forming sites might differ as a function of Galactocentric radius. For example, due to the negative metallicity gradient, the abundance of molecules and dust, and the efficiency of gas cooling is expected to decrease in the outer Galaxy. Recent infrared surveys revealed star formation sites in the Outer Galaxy in a wide range of environments. The CMa-l224 region in Canis Major at a distance of 1 kpc is a star-forming region hosting a few hundred low- to intermediate-mass young stellar object (YSO) candidates and showing evidence for the presence of outflows traced by the CO and the Spitzer 4.5 μm emission.
Here, I will present the results of the spectroscopic studies aimed at characterizing the gas accretion onto YSOs and the gas cooling from their surroundings in CMa-l224. By comparisons to other star-forming regions in the Galaxy as well as to YSOs in Magellanic Clouds, I will discuss the possible effects of metallicity on star formation as revealed in the outer Galaxy. Finally, I will also present some preliminary results concerning magnetic fields in a star-forming region in Ophiuchus-A, which will be later extended to the outer Galaxy.
21 February 2022
“Ultraluminous X-ray sources”
Prof. Jean-Pierre Lasota-Hirszowicz (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw and Institut d’Astrophysique de Paris)
Abstract:
Ultraluminous X-ray sources (ULXs) are off galactic-center objects whose X-ray luminosities surpass the 10M⦿ Eddington luminosity. It appears that most of the ULXs are massive binary systems containing accreting neutron stars; those observed directly are mainly identified through periodic pulsations (PULXs) indicating the presence of a magnetic field. After reviewing the ULX observations I will show that most of these very luminous objects contain usual X-ray pulsars during a short phase of the evolution of their binary systems. X-ray pulsars in Be/X-ray binaries become transient low-luminosity PULXs during so-called giant (Type II) outbursts of these systems. The PULX X-ray luminosity is beamed (collimated) explaining observed apparent luminosities surpassing even 1000 of neutron-star’s Eddington luminosities.
28 February 2022
“HD 133729 – a clue for understanding blue large-amplitude pulsators?”
Prof. dr hab. Andrzej Pigulski (Astronomical Institute, University of Wrocław)
Abstract:
Blue large-amplitude pulsators (BLAPs) form a small group of pulsating stars discovered less than a decade ago. These extremely rare and hot (effective temperatures of about 30 000 K) stars pulsate radially with the periods of the order of 30 minutes. Several alternative theories have been proposed to explain their origin. In general, they are believed to be evolved low-mass stars with masses ranging between 0.2 and 1 solar mass, depending on the evolutionary scenario. Using TESS data we found that HD 133729 is a binary consisting of a late B-type main-sequence star and a BLAP. This makes the star the first known binary BLAP. Its discovery opens an opportunity of a direct determination of the mass of a BLAP. In consequence, it should allow to verify evolutionary scenarios proposed for BLAPs.
7 March 2022, 11.00
“A Model of the Cosmos in the ancient Greek Antikythera Mechanism”
Prof. Tony Freeth and Dr Adam Wojcik (University College London, United Kingdom)
Abstract:
Our great guests are Professor Tony Freeth and Dr Adam Wojcik, members of the University College London Antikythera Research Team. The UCL team recently solved a major piece of the puzzle that makes up the ancient Greek astronomical calculator known as the Antikythera Mechanism, a hand-powered mechanical device, an analog computer, that was used to predict astronomical events.
Professor Tony Freeth is a mathematician and an award-winning filmmaker, he has conducted research on the Antikythera mechanism and promoted it through films and presentations since 2000. Dr Adam Wojcik’s research interests reside in the study of materials and in the development of techniques for materials testing, archeology and Classics.
The seminar will be conducted as a question and answer (Q&A) session. Prior to the seminar, please watch the professional video for an overview of the discovery and UCL team work presentation. We also recommend two recent papers published in the journal Nature Science Reports and in Scientific American.
14 March 2022
“Dynamical models to explain double debris belts systems and comparison with SPHERE observations”
Dr Cecilia Lazzoni (Physics and Astronomy, University of Exeter, United Kingdom)
Abstract:
Planets are the likely responsible for gaps inside disks. However, up to date, a very small number of them have been detected, even with very performing instrument such as SPHERE. For this reason we developed analytical tools to determine which planetary architectures can explain the presence of gaps. At the same time, we cross-checked the results (masses, semi-major axis, inclinations, etc.) with detection limits obtained with SPHERE. We thus obtained the most likely configurations that, at the same time, can match the width of the gap of a particular system and the (non) detectability of the planets.
21 March 2022
“The amazing old nova and symbiotic binary R Aquarii”
prof. dr hab. Joanna Mikołajewska (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw)
Abstract:
R Aqr is one of the closest symbiotic binaries composed of a white dwarf and Mira-type AGB star orbiting each other with ~44 yr period. It is one of the best studied symbiotic systems with the two binary components independently resolved by VLT and ALMA imaging. The binary is surrounded by very complex bipolar nebula with a spectacular jet outflow. I will review the properties of this system and present our results on ALMA imaging of the molecular CO lines and the continuum distributions as well as SiO maser monitoring.
28 March 2022
“Chaotic rotational dynamics of Hyperion”
Dr Mariusz Tarnopolski (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
Hyperion is an irregularly shaped satellite of Saturn that was predicted to remain in a chaotic rotational state. This was confirmed to some extent by Voyager 2 and Cassini series of images and time series analysis of ground-based photometric observations. The aim of this talk is to explore conditions for such observations to meet in order to estimate the maximal Lyapunov exponent, which is an indicator of chaos (i.e., measures sensitivity to initial conditions). Light curves existing in literature as well as 3D numerical simulations were examined using standard tools of theory of chaos and nonlinear time series analysis. It was found that observations from one site should be regularly performed over at least a year-long period to detect chaos, if present, in a reliable way. Moreover, using a simplified toy model the influence of Titan as a secondary source of gravity was found to be non-negligible in assessing the rotational state. Finally, a Hamiltonian-based chaos control method showed the chaotic rotation can be suppressed down to a strictly periodic behaviour, which while still futuristic, is crucial for future asteroid capture missions and mining attempts. The employed methodology is readily applied to other small bodies in the solar system as well.
I will also give a brief overview of my other scientific endeavours, particularly in the fields of gamma-ray bursts and active galactic nuclei.
4 April 2022
“Chemical ingredients of stellar nurseries. ALMA interferometer paves the way for James Webb Space Telescope”
Dr Łukasz Tychoniec (European Southern Observatory, Garching)
Abstract:
The physical and chemical conditions in the earliest stages of formation of Solar-system analogues are fundamental in unveiling the chemical composition of protostars and its impact on planet formation. Simple molecules and more complex organic and prebiotic species are found in the ice and gas as they are being transferred from the molecular clouds into the planet-forming disks and planetary cores and atmospheres. Therefore, to understand how life originates around Solar-like stars, it is essential to trace the chemical evolution during the first few hundred thousand years of star and planet formation.
I will present recent work in which we use a suite of Atacama Large Millimeter/submillimeter Array (ALMA) datasets in Band 6 (1 mm), Band 5 (1.8 mm) and Band 3 (3 mm) at spatial resolutions 0.5 – 3 arcsec for 16 protostellar sources. This is an effort to pinpoint chemical tracers to the physical components of the young protostellar systems at the Solar System scales (50 au). I will put our results in the context of the recently launched James Webb Space Telescope (JWST) and our Cycle 1 observing program. From protostars targeted in our work, 12 will be observed by JWST with MIRI and NIRSpec observations. ALMA provides a kinematic map of components for which JWST will deliver the sub-arcsecond observations in near- and mid-infrared for the first time.
11 April 2022
“The Atmospheres of Extrasolar Planets”
Dr Monika Stangret (Instituto de Astrofísica de Canarias, IAC)
Abstract:
The study of exoplanetary atmospheres is still in its infancy, with only a handful of reliable detections of atmospheric features. The main reason behind this is the intrinsic difficulty of such observations. But the situation is quickly changing, with the arrival of ultra-stable high dispersion spectrographs (HDS) mounted on 4-m-class telescopes. Observations with HDS allows not only for the detection of chemical species, but also for the determination of the temperature profile of upper atmospheric layers and even search for high-altitude winds.
During my presentation I will introduce you to the techniques of detections of exoplanetary atmospheres, focusing on observations of hot and ultra-hot Jupiters, gas-giant planets with short orbital period, and hot, extended atmospheres. HJs and UHJs are most suitable objects in order to study the chemical composition of the atmospheres using emission and transmission spectroscopy. Their tidally-locked nature leads to big differences between night and day side temperatures, and in consequence differences in the atmospheric chemical composition on both
sides.
25 April 2022
“Differentiated planetesimals in the Solar System as revealed from observations of V-type asteroids”
Dr Dagmara Oszkiewicz (Institute Astronomical Observatory, Adam Mickiewicz University, Poznań)
Abstract:
Basaltic V-type asteroids are considered parts of mantles and crusts of theoretically plentiful differentiated planetesimals that existed in the Solar System billion years ago. Some Solar System theories suggest that those objects formed in the terrestrial planet region and were then implanted to the Main Asteroid Belt. In consequence we should observe a large number of fragments of multiple differentiated planetesimals in the inner Main Belt. Through physical and dynamical characterization of V-type asteroids we verify those theories and put constraints on the formation location of the differentiated planetesimals.
9 May 2022
“Transformative advances in post-main-sequence planetary system science”
Dr Dimitri Veras (University of Warwick, UK)
Abstract:
Connecting planetary systems at different stages of stellar evolution helps us understand their formation, evolution, and fate, and provides us with exclusive and crucial insights about their dynamics and chemistry. Post-main-sequence white dwarf and giant branch stars host planetary systems which include a variety of observed objects and phenomena, such as planetary debris discs, disintegrating and embedded asteroids, exo-comets, photospheric metal pollution, and planets themselves. Here, I provide a review of both our current knowledge of these systems and models which have been used to explain them. I also highlight the transformative advances expected in upcoming years with the current and next generation of ground-based and space-based initiatives.
16 May 2022
“The depth and the vertical extent of the energy deposition layer in medium-class solar flares and recent progress in preparations of the ESA’s ROSIE project”
prof. dr hab. Paweł Rudawy (Astronomical Institute, University of Wrocław)
Abstract:
1. The position and the vertical extent of the energy deposition layer (EDL) of the solar flares can not be observed. I will present the results of numerical modeling of the EDL in a typical solar flare, based on X-ray data collected with the RHESSI satellite and validated with high-time resolution spectra-imaging observations collected with the MSDP-type spectrograph in the Bialkow Observatory of the University of Wroclaw. Some information about the new generation of the MSDP spectrographs will be also given.
2. I will present also short information about a recent stage of the ESA’s ROSIE program of a high-time resolution observations of the F10.7 cm (2850 MHz) and F30 cm (1000 MHz) solar indexes and spectra.
23 May 2022
“Massive stars from various simulations: different, but why?”
dr Dorottya Szécsi (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
The evolution of massive stars is the basis of several astrophysical investigations, from predicting gravitational-wave event rates to studying star-formation and stellar populations in clusters. However, 1D simulations of massive stars, especially those above 40 M☉, are subject to serious uncertainties. I present a comparison between five published sets of stellar models from the PARSEC, MIST/MESA, Geneva, BPASS and BoOST/Bonn simulations at near-solar composition. The different methods adopted by the stellar evolution codes when the Eddington-limit is exceeded inside massive stars can result in up to 18% difference in terms of ionizing radiation coming from stellar populations. For the same reason, the mass of the remaining black-hole can vary up to 20 M☉ between various sets of models. These differences are important, as they can lead to strikingly different results in explaining observations of stellar populations such as gravitational-wave event rate predictions. Any set of massive star models should be applied with caution, keeping in mind that evolutionary predictions for very massive stars have not yet reached a scientific consensus.
30 May 2022
“Search for black holes using gravitational microlensig events observed by Gaia”
mgr Katarzyna Kruszyńska (Astronomical Observatory, University of Warsaw)
Abstract:
On the 19th of December 2013 Gaia Space Satellite was launched by the European Space Agency. Its main goal is to measure proper motions and parallaxes of over 1 billion stars in the Milky Way. However, ever since the first data was acquired in 2014, Gaia has observed much more than that. Up to this day its alerting system of sudden change in brightness of observed sources AlertPipe has detected around 18’000 transients. More than 300 of them have been classified as microlensing candidates from all over the sky, with Gaia16aye, Gaia18cbf, Gaia19bld, Gaia19dke and Gaia20fnr as spectacular examples among them.
Gravitational microlensing is an effect of General Relativity that allows us to see the invisible. A white dwarf, neutron star or a black hole, which normally we would not be able to observe, can pass in front of a star within the Galaxy and magnify its light in a characteristic manner. By searching for such events, we can learn more about the origins of the dark remnants of stellar evolution, their distribution and abundance in the Milky Way and their properties, like mass or velocity.
Microlensing events detected and observed by Gaia offer a possibility for registering not only photometric effect, but also its astrometric counterpart. This will provide additional data that will help break degeneracies for single source-single lens events, which might lead to mass measurements of lenses and, in particular, to discovering lensing black holes.
I will present the most interesting events discovered by the Gaia Alerts, in particular the analysis of one of the longest events ever found, Gaia18cbf with its time-scale of nearly 500 days. The lens properties derived based on Gaia and follow-up data suggest it is a dark remnant at about 4 Solar masses.
6 June 2022
“PRECISEly localising and timing FRBs — hunting cosmic flashes with VLBI”
dr Franz Kirsten (ASTRON | Onsala Space Observatory)
Abstract:
Fast radio bursts (FRB) are millisecond duration, extremely bright bursts of extragalactic origin. Despite a known population of ~1000 sources, we still do not know their progenitors, let alone the emission mechanism generating these flashes in the radio band. Most FRBs have only been seen once while some FRBs burst repeatedly, the so-called repeating FRBs. One key aspect needed to understand the nature of fast radio bursts (FRB) is their precise location. Simply knowing what type of host galaxies they are emitted from is not quite sufficient — it is the local environment, e.g. star forming or not; association with a persistent counterpart or not — that can give us insights on the type of objects that we can expect to emit FRBs. The astrometric precision required for such environmental studies is of order milliarcseconds, a resolution that can only be achieved with VLBI. In this talk I will discuss the latest results of our ad-hoc VLBI campaign called PRECISE. As of late, we doubled the number of repeating FRBs with a milliarcsecond-localisation. One of our targets, FRB20200120E, proved to be in a globluar cluster, challenging models that invoke a young magnetar formed via a core-collapse supernova as FRB progenitors. On the other hand, this source’s bursts exhibit microstructure that is similar to what is seen in giant pulses from the Crab pulsar, tightening the link between extragalactic FRBs and young Galactic pulsars.
13 June 2022
“Gaia Data Release 3 Day: Press Conference and Lecture”
prof. dr hab. Łukasz Wyrzykowski (Astronomical Observatory, University of Warsaw)
Abstract:
In agreement with the speaker, Prof. Łukasz Wyrzykowski of the Warsaw Astronomical Observatory, the last IA seminar of the semester will be held as part of the unusual ceremonial opening event of the third, largest to date, archive of data from the European Space Agency’s Gaia space mission (https://sci.esa.int/web/gaia, Gaia DR3). Gaia is an outstanding survey of approx. 2 billion of stars in which Polish astronomers actively participate, and Prof. Wyrzykowski is the leader of the Polish Gaia team.
A webcast of the event and accompanying lecture will be available at https://bit.ly/gaiadr3pl. The meeting will take place on June 13, 2022, from 9:55 a.m. to 12:15 p.m. at the Warsaw University Astronomical Observatory, 4 Ujazdowskie Avenue, lecture hall of the Warsaw Botanical Garden.
See the event program received from the organizers, copied in the attachment below.
10 October 2022
Evolution of short-period massive binary stars in the Magellanic Clouds
dr Koushik Sen (Argelander-Institut für Astronomie, Universität Bonn, Bonn, Germany)
Abstract:
Massive stars tend to form in close binaries that will interact during their lifetime. Up to one-third of them are so close that they undergo mass transfer during hydrogen burning and yield most of the observable post-interaction binaries. As rapid binary evolution codes cannot provide accurate predictions for these systems, we study them using large grids of detailed binary evolution models that include internal differential rotation and magnetic angular momentum transport, time-dependent tidal coupling, and a self-consistently derived mass and angular momentum transfer prescription. Through follow-up population synthesis, we derive the observable properties of massive semi-detached binaries, Wolf-Rayet/helium star binaries, black hole/neutron star binaries, pre-supernova stars and their companions, for constant star formation as well as for coeval star cluster populations. We find that our tide and spin dependant mass transfer efficiency model can reproduce most properties of the observed massive Algol population, while a purely conservative or non conservative model does not. We also show that Bondi-Hoyle wind accretion during the BH+O star phase is expected to lead to observable X-ray emission only in exceptionally favourable cases such as high angular momentum accretion efficiency onto the black hole, very low wind speed from the O star companion, and high spin of the black hole. This creates a strong bias towards observing high mass black hole X-ray binaries with rapidly spinning BHs, as is seen in observations (Cyg X-1, LMC X-1 and M33 X-7). Our results provide important constraints for the evolution of massive binaries towards detectable gravitational wave sources.
17 October 2022
The chirp mean — a new normalization for the chirp mass
dr Áron Szabó (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
The chirp mass is a type of effective mass of a double compact object that governs the inspiral phase of a binary merger leading to a gravitational wave emission. With recent breakthroughs of gravitational wave detection, the chirp mass has become experimentally measurable. However, the standard normalization for the chirp mass can be improved upon. In this talk, I propose a new normalization and argue that it makes the mathematical properties of the chirp mass more transparent. I show that the chirp mass with the new normalization has the properties of a mathematical mean, hence the name ‘chirp mean’. Then I study the properties of this mean and show the exact relation between it and the standard mathematical means called the power means.
24 October 2022
Quantum communication with optical satellite links
dr hab. Piotr Kolenderski prof. UMK (Institute of Physics, Nicolaus Copernicus University)
Abstract:
There is a wide range of applications where methods of single photon generation, control and detection are useful. Quantum communication benefits from the ability to generate single wave packets and entanglement. In order to make this protocols useful their range and efficiency must be improved. During my talk I will present the main results and goals related to implementation of satellite quantum communication at Nicoalus Copernicus University.
7 November 2022
Volume limited sample of low mass red giant stars, the progenitors of hot subdwarf stars
dr Murat Uzundag (Instituto de Fisica y Astronomia, Universidad de Valparaiso, European Southern Observatory, Santiago, Chile)
Abstract:
Hot subdwarf stars of spectral class B (sdB) are low mass core helium-burning stars with an extremely thin hydrogen-rich envelope.
The current theory predicts that sdB binaries are produced from evolved low-mass binaries that have undergone mass transfer and drastic mass loss during either a common envelope (CE) phase or a phase of stable Roche lobe overflow (RLOF) while on the red giant branch (RGB).
In this talk, I will concentrate on the progenitor systems of wide orbit hot sdB + main sequence (MS) binaries that are the product of a stable RLOF mechanism.
Orbital parameters of wide sdB binaries have been solved for 26 systems with orbital periods ranging from 500 to 1500 days. The observed systems present striking correlations between orbital elements such as period-mass ratio and period-eccentricity. Recently, Vos et al. (2020) performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA in order to explain these correlations. The authors modelled progenitors of wide sdB + MS binaries at the moment before they start the mass transfer phase. In order to observationally complement their findings we performed a spectroscopic volume-limited survey searching for low-mass RG binaries with orbital periods in the range of 100-800 d within 200 pc aiming at analyzing the observed characteristics of progenitors of the wide sdB binaries.
The observed volume-limited samples composed of pre- and post-mass transfer binaries will allow us to study the binary interaction and the angular momentum loss mechanisms during the mass loss on the RGB.
14 November 2022
Old/new problems with Active Galactic Nuclei and AGN application to cosmology
prof. dr hab. Bożena Czerny (Center for Theoretical Physics of the Polish Academy of Sciences, Warsaw, Poland)
Abstract:
After several decades of studies the basic nature of nuclear activity of galaxies is well understood. However, unexpected behaviour of AGN was already noted in the past, and with the rise of the amount of data we see numerous evidence of phenomena which still require explanation, line Quasi-Periodic Ejection sources, and Changing-Look AGN. Also it is now time to address in more detail the physical nature of the simple AGN components like Broad Line Region and Dusty/Molecular torus. Despite these problems, the various correlations between the AGN parameters opens a way to use them also as tools in cosmology, although systematic errors in this case are likely underestimated.
21 November 2022
The quality of the night sky in Polish astronomical observatories
dr Sylwester Kołomański (Astronomical Institute, University of Wrocław, Poland)
Abstract:
Poland is a country with high and increasing light pollution. For astronomy, the quality of the night sky, which can be significantly affected by light pollution, is crucial for conducting scientific research.
ALPS is a network of automatic stations designed for continuous monitoring of the sky. The stations record images of the entire sky and measure its brightness. At present, they are located mainly in astronomical observatories. The main goal of the project is to study the brightness of the night sky, taking into account meteorological conditions, and to track changes and sources of light pollution. Based on the ALPS data the degree of night sky degradation in the astronomical observatories in Białków, Piwnice, Ostrowik and Sopotnia Wielka was determined. The obtained results show that urgent measures are needed to protect the night sky over astronomical observatories in Poland.
28 November 2022
Observing hot spots orbiting Sagittarius A* with ALMA
dr Maciej Wielgus (Max Planck Institute for Radio Astronomy, Bonn, Germany)
Abstract:
I will present a first detection of an orbiting hot spot in ALMA millimeter light curves of Sagittarius A*, the supermassive black hole in the Galactic Center. The orbital motion manifests in the loop-like patterns on the linear polarization Q-U plane, following the X-ray flare detected by Chandra. The observed hot spot period corresponds to about 70 minutes, and the implied orbital radius corresponds to about 5 Schwarzschild radii. These new observations constrain the magnetic field to be predominantly vertical and the viewing angle of the hot spot orbit to be close to face-on, which is broadly consistent with the infrared constraints provided by the VLTI observations with GRAVITY. Presented results support theoretical interpretation of the accretion system in Sagittarius A* as a magnetically arrested disk, and flaring activity as related to the magnetic reconnection.
5 December 2022
Light propagation beyond the standard model of cosmology
mgr Matteo Cinus (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
In a little more than 100 years from its birth physical cosmology has made enormous progress. Most of its many successes can be attributed to the LCDM model, also called the standard model of cosmology. However, as more and more precise measurements become available, the standard model of cosmology seems to fall shorter and shorter of explaining them. The Hubble tension is the most known but not the only challenge for the LCDM model.
In order to reconcile theory and observations, many alternative models have been proposed that loosen the assumptions of the LCDM model, e.g. allowing for anisotropies or inhomogeneities, or extend Einstein’s theory of General Relativity (GR) on which the standard model of cosmology is based. In my talk, I will consider geometrical extensions of GR, i.e. those theories that are obtained by considering more general spacetimes than Riemann spaces. I will discuss some of the cosmological signatures that can be expected from models that allow for non-null torsion. Finally, I will show the results of my recent work on how inhomogeneities in the form of voids can affect light propagation and possibly our understanding of the Universe.
12 December 2022
Formation, evolution and detection of rocky planets around very low mass stars
dr Mariana Sanchez (Leiden Observatory, Leiden University)
Abstract:
Rocky planets located in the habitable zones around M-dwarfs are ideal targets for the search of life outside our Solar System. On the one hand, in order to better understand their formation and evolution, N-body simulations were developed. The central object was assumed to be a star close to the substellar mass limit. The simulations included tidal and general relativistic effects that incorporate the contraction and evolution of the rotational period of the central object during 100 Myr, as well as gas-disk interactions with a sample of protoplanetary embryos during the gas-disk lifetime. A very relevant result is that just one of the prescriptions used to treat the interactions between the gas-disk and the sample of embryos allows the survival of a close-in compact planet population of interest, located in the habitable zone of the systems with a wide range of masses from Mars-like planets up to Earth-like planets and close to commensurabilities. Moreover, the resulting planets with semi-major axis a < 0.1 au are in agreement with the cumulative distribution of period ratio of adjacent terrestrial-like exoplanets around stars with masses M < 0.14 Msun (Sanchez et el 2022, https://arxiv.org/pdf/2203.13389.pdf).
On the other hand, in order to estimate the probability of detection of planetary systems around very low mass stars, a numerical tool in python was developed. This new tool calculates the changes in stellar flux, radial velocity and proper motion of a sample of stars due to the interaction with their planetary systems, and estimates the probability of detection of planetary systems regarding different samplings and errors associated with a given instrument or survey. A significant result is that the radial velocity method allows a high probability of planetary detection around very low mass stars, with the current and future technology (Sanchez et al, in prep).
19 December 2022
Investigating comsic voids in cosmological simulations
mgr Marius Peper (Institute of Astronomy, Nicolaus Copernicus University)
Abstract:
In this talk I will investigate the large underdense regions that are dominating our Universe, known as cosmic voids. In the first part of the talk I will investigate the influence of voids on galaxy formation. In contrast to the dense environment of galaxy clusters, the underdense environment is less favourable for galaxies to form and should even counteract the formation. The analysis will be carried out using a fully reproducible approach to generate galaxies in cosmological N-body simulations by starting from primordial density fluctuations, extracting dark matter halo merger history trees, and using semi-analytical recipes for conversion of baryons to stars. I will present our analysis of properties of galaxies including the matter infall rate, the size of galaxy disks, the spin parameter and the formation epoch. The second part will investigate if geometrical optics parameters, i.e. parameters that describe light propagation, can be used to trace voids. I will present a simplified approach to detect voids utilising projected quantities: the optical scalars, the weak lensing shear and the projected surface mass density. These photometric voids will be connected to the 3D voids identified in the 3D density distribution.