General Seminar (2023)

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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).

9 January 2023

Annual summary of the telescopes outcome in the Piwnice Observatory

dr hab. Agnieszka Słowikowska, prof. UMK, dr Paweł Zieliński, dr Karolina Bąkowska (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
During the last two years, the renovation of the 90-cm and 60-cm telescopes and recoating process of their mirrors took place. Additionally, the new instruments have been installed in the second dome and are ready for use. On the radio telescopes, the SPUB grant allowed the modernisation of the radio infrastructure. These challenging tasks ended with success, and the photometric and radio observations were resumed. We will present the outcome of the renovation, preliminary scientific results from the optical telescopes, ongoing projects and plans for these instruments in our institute. We encourage students and PhD students to participate in this seminar, as it will help you learn about a wide range of scientific collaboration opportunities.

16 January 2023

“Precise masses as fundamental parameter for planet structure, distributions and in-depth atmospheric studies”

dr Grzegorz Nowak (Instituto de Astrofísica de Canarias (IAC) Tenerife, Spain)

Abstract:
The basic characterisation of planets (internal structure, formation history and possible atmospheric composition) starts with a measurement of their masses and radii. The need to know both of these quantities is a motivation for a great development of the ground- and space-based transit surveys and for a continuous importance of the radial velocity (RV) technique, which together became a tandem of mutually supporting observing techniques. Having the three main planetary quantities, i.e. mass, radius and mean density, we are in a position to study the planets’ internal structure as well as their formation and evolution, by placing them within mass-radius and mass-density diagrams. Precise RV measurements from 3-4-metre class telescopes are fundamental in determining planetary masses, in filling these diagrams, and in explaining the large scatter in fundamental properties, especially for the smallest planets of 1-4 Earth radii.
In this talk I am going to present recent results of radial velocity follow-up of Kepler-K2 and TESS planet candidates with TNG/HARPS-N and CAHA/CARMENES instruments in a framework of KESPRINT and CARMENES consortia. These results include sub-Neptune planets around nearby M dwarfs LTT 3780 (TOI-732) and G 9-40 (K2-313, TOI-5097), an ultra-short-period, 1.7 R_Earth planet around a solar-type star HD 20329 (TOI-4524), sub-Saturn around G7V star K2-280, and a planetary system around G9V star HD 191939 (TOI-1339), including HD 191939 g – Uranus-mass planet in the habitable zone with an orbital period of ~300 days.

23 January 2023

“Cow, Camel and other explosive animals”

dr Mariusz Gromadzki (Astronomical Observatory, University of Warsaw)

Abstract:
An extensive development of all-sky surveys, in the last years, allowed discovery of fast, blue and very energetic extragalactic transients, which fade in a scale of a few weeks or shorter. In mid 2018, an enigmatic object was discovered AT 2018cow aka “Cow”, its untypicall evolution was systematically reported on Twitter and the nature of explosion for a long time remained a puzzle. Further, follow up observations solved the mystery and similar targets were discovered. “Cow” has become part of pop culture and the group of these transients got a nickname FBOTs (Fast Blue Optical Transients). In my talk I will present a brief review of this exciting topic.

30 January 2023

“Young open clusters asteroseismic potential”

dr Dawid Moździerski (Astronomical Institute, University of Wrocław)

Abstract:
Star clusters studies are known as a very good starting point for studies of stars themselves. I will briefly present the most interesting open clusters in terms of the asteroseismology of their members. Our latest results of the search for pulsating stars and their ensemble asteroseismology indicate, that young open clusters provide excellent conditions for asteroseismic studies of the parameters of stars and their interiors.

6 February 2023

“Progenitors of LGRBs: Are single stars enough”

MSc Rafia Sarwar (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
In recent years theoretical and observational stellar astrophysics strongly altered the paradigm of our current understanding of the life cycle of massive stars, from their birth in the dense interstellar medium to their final fate of collapsing into compact objects. If these compact objects are insufficiently close orbits, they start losing orbital energy via gravitational wave (GW) emission. Stellar evolutionary models are commonly used to infer the event rates of these gravitational waves statistically. Despite their significance, many if not all the evolutionary models of massive stars do not take in the final phase of the stellar explosion. The complexity of the problem is due to the intricate dependence of the explosion physics on the structure of the exploding star. Therefore, it is crucial to develop a new computer routine that associates stellar models with various types of supernovae in accordance with their explosion energies and ejecta mass. Here we present the preliminary results of Yoon et al. (2006), revised and expanded upon, including the new observational comparison for GRBs.

6 March 2023

“Catching unusual phenomena with extensive maser monitoring”

MSc Michał Durjasz (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
6.7 GHz methanol masers are located in the vicinity of the massive protostars. Due to their sensitivity to the physical conditions of the matter they originate from, they are a decent marker of the protostellar activity. Toruń 32 m radio telescope has been monitoring about 140 methanol maser sources since 2009 – such amount of monitored sources allowed us to discover 13 new periodic sources and anticorrelated variability of the 6.7 GHz and 22 GHz H2O masers in G107.29+5.64. We also observed accretion bursts in G192.600-0.048 and G358.93-0.03. An apparent correlation between the far-IR photometry (WISE telescope) and the methanol masers’ integrated flux density for several sources was also discovered. Our monitoring is not only useful as a way for early detection of the maser bursts but also allows to extend the scientific output of the VLBI observations.

“Simultaneous observations of exited OH and methanol maser -coincidence and magnetic field”

MSc Agnieszka Kobak (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
We present the results of simultaneous observations of the 6.035 GHz exited OH and 6.7 GHz methanol masers toward a sample of 10 high-mass young stellar objects (HMYSOs), observed using eMERLIN in 2020 and 2022. Searching for the coincidence and avoidance of these two maser transitions, we estimate physical conditions around central protostars. We identify Zeeman-splittings of the OH emission and determine the strength of the magnetic field. Combining it with linear polarization, we derive the magnetic field structure in these high-mass star-forming regions.

13 March 2023

“Gravitational entropy in Szekeres class I models”

MSc Fernando A. Pizaña (Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México)

Abstract:
Developing a self-consistent notion of gravitational entropy in the context of cosmological structure formation has been so far an elusive task. Various theoretical proposals have been presented, initially based on Penrose’s Weyl curvature hypothesis, and variations of it. A more recent proposal by Clifton, Ellis, and Tavakol (CET) considered a novel approach by defining such entropy from a Gibbs equation constructed from an effective stress–energy tensor that emerges from the ‘square root’ algebraic decomposition of the Bel–Robinson tensor, the simplest divergence-less tensor related to the Weyl tensor. Since, so far all gravitational entropy proposals have been applied to highly restrictive and symmetric spacetimes, we probe in this paper the CET proposal for a class of much less idealized spacetimes (the Szekeres class I models) capable of describing the joint evolution of arrays of arbitrary number of structures: overdensities and voids, all placed on selected spatial locations in an asymptotic ΛCDM background. By using suitable covariant variables and their fluctuations, we find the necessary and sufficient conditions for a positive CET entropy production to be a negative sign of the product of the density and Hubble expansion fluctuations. To examine the viability of this theoretical result we examine numerically the CET entropy production for two elongated over dense regions surrounding a central spheroidal void, all evolving jointly from initial linear perturbations at the last scattering era into present day Mpc-size CDM structures. We show that CET entropy production is positive for all times after last scattering at the precise spatial locations where structure growth occurs and where the exact density growing mode is dominant. The present paper provides the least idealized (and most physically robust) probe of a gravitational entropy proposal in the context of structure formation.

20 March 2023

“Follow-up observations of Gaia alerted eruptive young star candidates”

dr Zsofia Nagy (Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Budapest, Hungary)

Abstract:
Young stellar objects (YSOs) are still accreting material from their disc via magnetic field lines. About half of YSOs show photometric variations on daily-weekly timescales, with an amplitude of a few times 0.1 mag. Some young stars show brightness variations on even longer time-scales: months, years, centuries. These variations are related to different physical processes, such as changes in the circumstellar extinction or the accretion rate. Eruptive young stars show brightness variations with an amplitude of a few magnitudes and remain bright on longer timescales. These outbursts of eruptive YSOs are caused by a sudden increase of the mass accretion rate by a few orders of magnitude. Eruptive YSOs are commonly divided into two main classes: EX Lupi-type stars (EXors) and FU Orionis-type stars (FUors). The former show brightenings of 2-4 mag, last for less than a year and are recurrent, the latter brighten by up to 5 magnitudes and last for several decades. So far the number of confirmed FUors is limited to no more than a dozen while the number of known EXors is limited to less than 25, including candidates.
The Gaia Photometric Science Alerts System with its large sky coverage and approximately monthly cadence, provides a highly efficient tool to identify new eruptive YSOs. The literature contains several young eruptive stars discovered by Gaia. Our group has recently published the discovery of a new FUor, Gaia18dvy, the EXors, Gaia20eae and Gaia19fct, and another young star, Gaia17afn, where the follow-up observations suggested an extinction event rather than an accretion burst. We also found two other Gaia-alerted YSOs, which show accretion-related brightening on a time-scale similar to EXors, but with lower accretion rates.
We are currently analyzing the follow-up photometry and spectroscopy of several Gaia alerted young eruptive star candidates. Our follow-up observations include photometry using 1-m class telescopes in Hungary, Poland, and Chile, and spectroscopy using the Telescopio Nazionale Galileo, the Nordic Optical Telescope, the Liverpool Telescope, the New Technology Telescope, the Gran Telescopio CANARIAS, the Large Binocular Telescope, and the Very Large Telescope.
I will summarize our latest results on follow-up observations of young eruptive star candidates found from Gaia alerts, and demonstrate that the Gaia Science Alerts System has proven to be an efficient tool for the research of young stars and episodic accretion.

27 March 2023

“Symbiotic binaries in the era of Gaia and other surveys”

dr Jaroslav Merc (Astronomical Institute of Charles University, Prague, Czech Republic)

Abstract:
In this talk, I will introduce symbiotic stars, interacting binaries consisting of a cool red giant and a hot component, typically a white dwarf but systems with neutron stars are known as well. Although the first symbiotic stars were discovered more than a century ago, many questions regarding these astrophysical laboratories remain open, even in the era of massive ground- and space-based surveys such as the groundbreaking Gaia, as well as modern machine-learning techniques. My focus will be on our ongoing projects, which aim to provide a ‘clean’ sample of symbiotic stars, discover new objects of this class, better characterize their parameters, and ultimately help us to understand the symbiotic population as a whole.

3 April 2023

“Advanced modeling of Microlensing events”

MSc Paolo Rota (Università degli Studi di Salerno, Italy)

Abstract:
The search for exoplanets is one of the most exciting challenges. From the first exoplanets discovered around the pulsar PSR B1 257+12 back in 1992 until today there are over 5200 exoplanets discovered. And the number will continue to rise in the coming years with the advent of the latest generation telescopes.
There are various techniques for finding exoplanets such as transit, radial velocity, pulsar timing, direct imaging etc. But among these, gravitational microlensing is one of the most fascinating. Gravitational microlensing is a particular technique to detect exoplanets otherwise unavailable with other techniques such as transits or radial velocity. We have a microlensing event when the light from a distant source is deflected by a lens passing through the source and the observer. The result, in the simplest case, is a bell-shaped peak in the light curve. Planets can be detected studying the anomalies in the lightcurve (additional peaks or dips, longer distortions, etc.). But microlensing is not important only for exoplanets. The fact that with this technique it is possible to reach distances of the order of the galactic center allows us to discover objects ranging from the disk to the bulge allowing us to have a much more complete overview of the study of the stellar populations of our galaxy.
And in particular with the study of binary systems we can detect faint objects that are impossible to reveal with other techniques, such as brown dwarfs, mysterious objects of which little is known yet and which are presumed to populate our galaxy in great abundance. Microlensing is undoubtedly the best method to discover these objects, since having extremely low luminosities they are difficult to see with telescopes except when they play the role of lens. Moreover, in some cases the orbital motions of the system can also be detected, allowing us to study their dynamics in more detail. The typology of microlensing events is enormous and this allows us to explore our Milky Way providing us with information on the distribution of the various stellar populations that inhabit our galaxy and giving us details on its formation and dynamics.

17 April 2023

“The art of recovery: best practices for handling observational gaps”

dr Javier Pascual-Granado (Stellar Physics Department, Instituto de Astrofísica de Andalucía, Granada, Spain)

Abstract:
Astronomical data sets rarely come as an uninterrupted series with a regular sampling interval. Even in the case of space satellites or ground-based networks observing continuously without the interruptions of the day-night cycle, there are always observational gaps due to instrumental effects, the impact of cosmic rays, operational issues, etc. Without lack of generality, here we consider the case of regularly sampled time series gathered by ultra-precise space missions and how to deal with their gaps.
Estimation of statistical properties of the signal require proper treatment of the observational gaps. Frequency domain approaches, e.g. in radioastronomy, include the CLEAN method which is based on a spectral deconvolution of the power spectrum. This method is used to avoid the effects of the spectral window (i.e. the Fourier transform of the observational window) in the determination of the frequency components of the signal. On the other hand, time-domain approaches, e.g. in asteroseismology, include the so-called pre-whitening procedure as the usual solution. This consists in performing a non-linear least squares of harmonic components and extract them until only white noise is left as residuals. A more general approach is filling the gaps using a suitable interpolation once the optimal models are fitted to the data.
In this talk I will show several recent examples of data sets gathered by photometric space missions such as CoRoT, Kepler, TESS, etc. which are designed to detect tiny brightness variations of stars. Issues with the different methodologies to handle observational gaps will be discussed in the context of the ESA M3 space mission, PLAnetary Transits and Oscillations of stars (PLATO), which will be dedicated to detect and characterize transiting exoplanets including information from the seismic properties of their stellar hosts. I will conclude with an outline of what I consider best practices for handling observational gaps in astronomical data. The aim is minimizing ignorance while preserving the original information contained in the time series.

24 April 2023

“ARGOS: a Next-Generation Radio Telescope for Multi-Messenger Astrophysics “

PhD John Antoniadis (FORTH Institute of Astrophysics, Greece)

Abstract:
Astronomy is being transformed by multi-messenger surveys performed with instruments capable of searching the sky with high speed and sensitivity, while delivering science-ready datasets to the community. While radio astronomy is not yet fully participating in this revolution, it is clear that an instrument following the same philosophy is not only urgent but inevitable. ARGOS is a concept for a leading-edge, low-cost, sustainable European astronomical facility that will finally realise this ambition, directly addressing multiple fundamental scientific questions, from the nature of dark matter and dark energy to the origin of fast radio bursts and the properties of extreme gravity, thereby satisfying urgent needs of the community. ARGOS will enable, for the first time, continuous wide-field monitoring of the sky at centimetre wavelengths, while publicly distributing science-ready data and alerts in real time.
ARGOS recently entered a three-year detailed design phase, which will prepare the subsequent rapid implementation of this leading-edge public radio facility on European grounds, and ensure its optimal integration into the network of existing and future international astronomical infrastructures. This will be achieved following a systems-engineering approach that will integrate technical studies, community groundwork, and prototyping, as well as quantitative cost-to-benefit analysis, and assess socioeconomic impact, sustainability, technological readiness, and innovation needs.
In this talk, I will describe the project and its main science and engineering objectives, as well as ARGOS-pathfinder, a 16-dish prototype that will be installed at Skinanas as part of the project.

8 May 2023

“Multiple stellar populations in globular clusters from winds of massive stars”

PhD Richard Wunsch (Astronomical Institute of the Czech Academy of Sciences)

Abstract:
It has been found by both spectroscopic and photometric observations that globular clusters (GCs) include two or more populations of stars differing in their chemical composition. Specifically, stars show variability in abundances of light chemical elements and the observed patterns can be understood by assuming that some stars have been formed out of the gas enriched by products of high-temperature hydrogen burning.
We develop a model of Rapidly Cooling Shocked Stellar Winds in which the subsequent stellar populations in GCs are formed out of winds of massive stars of the first population. In dense and massive young star clusters, the hot gas originating from wind-wind collisions becomes thermally unstable and forms dense warm gaseous structures that sink into the cluster centre where they accummulate, cool further due to self shielding of the ionising radiation of stars, and form new stars.
We use two numerical implementations of the model: fast 1D semi-analytic code and 3D radiation hydrodynamic simulations based on the FLASH code. The former allows exploration of the full parameter space and identification of regions where the secondary star formation occurs. We use it to estimate initial parameters of Galactic globular clusters, consistent with current observed ratios of population masses. The latter allows much more detail studies of the formation of thermally unstable clumps and secondary star formation, which helps us to verify the semi-analytic code. The radiation is calculated by our novel algorithm TreeRay which I will also introduce.

15 May 2023

“The Important Role of Cosmic Ray Transport in Galaxy Evolution”

PhD Philipp Kempski (Princeton University, Department of Astrophysical Sciences)

Abstract:
Although negligible by number density, relativistic cosmic rays (CRs) are an energetically important component of the plasmas filling galaxies and galaxy clusters. As a result, these particles may play an important role in shaping large-scale galactic (thermo)dynamics, for example by driving galactic winds and/or heating diffuse gas in galaxy halos. For this reason, “CR feedback” has become a key ingredient in galaxy evolution models. However, a fundamental limitation of these models is that the nature of CR feedback is a very strong function of the assumed CR transport, which remains uncertain. In this talk, I will give an overview of CR feedback in galaxies, discuss theoretical uncertainties in CR propagation and how CR spectra measured at Earth help us constrain the physics of their transport. I will argue that popular existing transport models are full of theoretical uncertainties and are generally not in good agreement with observations. This suggests that we may need a new theory of CR transport.

22 May 2023

“Energy reconstruction method for MAGIC telescopes system”

PhD Kazuma Ishio (University of Łódź, Faculty of physics and applied computer science)

Abstract:
MAGIC is a system of two 17-m diameter imaging atmospheric Cherenkov telescopes, located at an altitude of 2200 m in the Observatorio Roque de los Muchachos on the Canary island of La Palma. MAGIC detects gamma rays from 50 GeV and up to 100 TeV. The minimum energy can be further lowered to 15 GeV with the Sum-Trigger-II system, which was specially optimised for low energies. The maximum energy can be extended by benefitting from the higher collection area during a high Zd observation. This talk gives an overview of the energy reconstruction capability of MAGIC, focusing on the new official energy reconstruction method.
A gamma ray from an astronomical source initiates an air shower in the atmosphere, and its Cherenkov radiation can be seen by a Cherenkov telescope as a shower image. Since the air shower can be regarded as the energy deposition of the primary gamma ray, the brightness of the shower image can tell its primary energy. However, the image brightness is dependent not only on the energy, but also on the distance to the shower from the telescope, the lateral distance to the shower axis from the telescope, the relative difference between the incoming direction and telescope pointing direction, and so forth. On the basis of these corrections, the energy of an observed gamma ray is estimated by an energy estimator, which is constructed from MC simulation events, since it is impossible to give a real calibration event.
The talk will introduce such basis of the energy reconstruction in general, and the new energy estimator. The performance will be reviewed from the general aspect such as resolution and bias, as well as systematic effects and uncertainty. In addition, the talk will feature the effect of outliers, which is the rare events with very large estimation error. The risk of outlier events in an energy spectrum will also be introduced together with its reduction in the new energy estimator.

29 May 2023

“OB stars in the observations of SMEI instrument”

MSc Przemek Mikołajczyk (Astronomical Institute, University of Wrocław, Astronomical Observatory, University of Warsaw)

Abstract:
The Solar Mass Ejection Imager (SMEI) instrument mounted aboard the Coriolis satellite was designed for investigations of the solar wind by means of measuring light scattering on free electrons. In order to increase the contrast between the low-signal sky background and the bright stars visible in its three cameras and achieve desired photometric accuracy, Point-Spread-Function photometry has been performed on all images gathered by SMEI.
A time series for about 5700 stars have been obtained as a by-product. SMEI photometric data contains low-quality light curves for the brightest stars (V ≥ 6 mag) and additional parameters describing PSF fit. These parameters serve as a starting point for decorrelating the light curves, which may transform the data from initially useless to a high-quality set of photometric observations. SMEI data spans over 8 years, which makes it perfect for investigating long-period variables, looking for changes in period and amplitudes of pulsating stars as well as searching for long-period exoplanets.
I will present an extended review of the SMEI instrument’s capabilities, the methods behind improving data quality, examples of data already published by third parties and the most interesting cases of OB stars observed by SMEI.

5 June 2023

“Modeling primary and secondary cosmic ray propagation in the interstellar medium”

MSc Antoine Baldacchino-Jordan (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Cosmic Rays (CR), relativistic charged subatomic particles traveling through the (inter)galactic medium, represents an important component that acts on galactic evolution, as well as high energy processes like gamma ray production or synchrotron radiation. The question of their propagation involves issues for experiment, theory and numerical simulation, and many codes (e.g GALPROP) were built to investigate CR physics in galaxies. One important clue to the understanding of CR is to model their behavior in a magneto-hydrodynamical environment, which is nowadays the most faithful way to reproduce galactic dynamics with magnetic field structure. For this purpose, the PIERNIK MHD code and its CRESP (Cosmic Ray Energy SPectrum) algorithm was designed.
I will introduce the main ideas on galactic CR physics. Then I will present my attempts to model propagation of primary and secondary nuclei in a dynamical environment. I will show results on the primary to secondary (Boron to Carbon) ratio, which indicates this quantity is strongly dependent on the local environment and therefore is crucial for CR parameters determination.

12 June 2023

“Measuring star positions from space: Hipparcos and Gaia”

prof. Michael Perryman (University College Dublin, Ireland)

Abstract:
The Hipparcos satellite project of the European Space Agency was dedicated to measuring the accurate positions of more than 100,000 stars. Doing so from space represented a fundamentally new discipline in space science. After the publication of the scientific results from the Hipparcos mission in 1997, ESA adopted the Gaia mission, a follow-on and vastly more advanced star-mapping satellite, in 2000. Gaia was launched in 2013 and continues to operate from its advantageous location at the Sun-Earth Lagrange point, L2. Gaia is measuring the positions of more than two billion stars in our Galaxy with extreme accuracy, and is revolutionising many areas of astronomy. The talk will explain why the measurement of star positions is of such scientific importance, recall its history, and present some of the many areas of astronomy that are being impacted by these latest state-of-the-art measurements.

19 June 2023

“FRB adventures in Undergrounds”

dr Marcin Gawroński (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Fast radio bursts (FRBs) are one of the hottest topics in modern astrophysics. Despite the fast growth of the observational database, there are no answers to the most fundamental questions: what objects and what physical processes are responsible for this phenomenon? The 32-m Toruń radio telescope is strongly involved in FRB observations, more than a third of the total observation time is allocated for global and local FRB experiments.
During my talk, I will summarize the current state of our project, and present some of the latest results related to the localization and monitoring of selected active FRB sources. I will also discuss and describe the prospects for the future.

26 June 2023

“Probing planet-star tidal interactions with precise transit timing of hot Jupiters”

MSc Jan Golonka (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Hot Jupiters are gas giants on tight orbits around their host stars. Due to their high mass and close proximity, it is thoerised that they could induce tidal interactions with their host stars. An observational proof of these interactions could be a shift in transit times of the planet, caused by transfer of orbital angular momentum from the planet to the star. In this talk I will present my preliminary results from transit timing analysis of select objects, with the goal of putting observational constraints on theoretical predictions of tidal interactions.

9 October 2023

“How can we find galaxy mergers and what even are they?”

dr William Pearson (National Centre for Nuclear Research)

Abstract:
Galaxy mergers underpin our current understanding of how galaxies grow and evolve over cosmic time. In our current dark matter cosmology, the dark matter halos grow hierarchically. As a result, the baryonic component that the halos host, the galaxies, also collide. These mergers can radically change the morphologies of the interacting galaxies, throwing dust, gas and stars around and creating and destroying fainter and finer structures. The merging galaxies can also undergo massively increased star-formation rates or highly enhanced active galactic nuclei activity. But when these powerful events occur, and indeed how powerful they can be, is hotly contested. Thus we need large, statistical samples to better understand what happens.

There is a wide range of methods to identify galaxy mergers, spanning simply looking at the images to cutting edge, machine learning methods. Throughout this seminar we will discuss the range of techniques that can be used to identify galaxy mergers and see their strengths and weaknesses. We will discover how advanced techniques allow us to explore often overlooked parameter space and find galaxy mergers in surprising ways.

This all assumes, of course, that we know what a galaxy merger is. Perhaps surprisingly the answer is not as simple as it seems. So we will also look to better understand what exactly a galaxy merger is. We will also look to the future and explore the kinds of science that we will be able to study over the next few years.

16 October 2023

“Astrophysical masers – recent studies.”

dr hab Anna Bartkiewicz, prof UMK (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Cosmic masers are broadly used in research on star formation and evolved stars, astrometric measurements of the Milky Way galaxy, as well as studies of extragalactic environments.
I will present recent studies that have been carried out and presented by international teams during the International Astronomical Union Symposium 380 in Kagoshima, Japan.

23 October 2023

“ANDES, the high resolution spectrograph for ELT.”

prof dr hab Andrzej Niedzielski (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
I will briefly present the concept, current status, key science cases and the planned Polish involvement in the ESO ELT high resolution spectrograph ANDES.

30 October 2023

“The ARIEL space mission, and the pre-launch preparations by the Stellar Characterisation Working Group.”

dr hab. Krzysztof Hełminiak (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Torun)

Abstract:
ARIEL is the European Space Agency’s next-generation mission to observe the chemical make-up of distant extrasolar planets. It is scheduled to be launched in 2029, and operate for at least four years. It will obtain spectra of ~1000 exoplanets, transiting stars of different spectral types, chemical compositions, and ages. The mission’s goal is mainly to study the planet formation scenarios and evolution in various environments. This will not, however, be possible to achieve without a prior information about the host stars, including their precise masses, radii, effective temperatures, activity indices, ages, and abundances of a number of elements that are the key to understand planetary formation mechanisms. For this purpose the ARIEL Stellar Characterization Working Group (SCWG) started in 2019 a large-scale observational campaign of spectroscopic and multi-band photometric observations of the ARIEL target sample. In my talk I will present a short overview of the mission, its current status, and present various scientific activities and results of the SCWG.

06 November 2023

“Polish contribution to the research of the Universe at radio waves.”

dr hab. Krzysztof Katarzyński, prof. UMK (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
During the seminar, the history of Polish radio astronomy will be presented. This history is closely related to different antennas and radio telescopes built in our country. We will recall the first antennas and the beginnings of Polish radio astronomy from the 1950s, as well as most of the telescopes built in later years. The most important and interesting scientific results obtained using the above-mentioned instruments will also be discussed. It will be a kind of short summary of the rich history of Polish radio astronomy, which will celebrate its seventieth anniversary next year.

13 November 2023

“Modeling the structure and variability of magnetized jets from accreting black holes.”

dr Bestin James (Center for Theoretical Physics of the Polish Academy of Sciences)

Abstract:
Astrophysical black hole sources usually show variable outflows. These sources are found at different mass scales of the black hole from the cores of active galactic nuclei in the supermassive regime to gamma-ray bursts in the stellar mass regime. Both gamma-ray bursts and blazars have a relativistic jet pointing towards our line of sight. In such sources, the variability of the inflow can be transmitted to the properties of outflows. It is also possible that these two kinds of sources share similar jet physics. Observational studies have shown correlations between the observed jet variability time scales and the Lorentz factor of the jets emitted. Motivated by these observational properties, we investigated the time variability and the jet structure in such sources with GRMHD simulations. We modeled the central engine of blazars and gamma-ray bursts starting from analytic equilibrium solutions embedded in a poloidal magnetic field that initiated the accretion of matter onto the black hole. We performed axisymmetric simulations of a family of models and investigated the correlations between the jet Lorentz factor and variability timescales. We then focused on the GRB central engines and investigated the dependence of the jet structure and time variability on the formation of a magnetically arrested disk state (MAD).

20 November 2023

“High-mass stars in the Milky Way and in external galaxies.”

dr Miguel Figueira (National Centre for Nuclear Research)

Abstract:
High-mass stars emit ultraviolet radiation which ionized the surrounding medium and create ionized (HII) regions. These structures further expand, sweep-up the surrounding dust and gas, and form a circular layer of neutral material which fragments to form a new generation of stars. It was proposed that this mechanism, called the Collect and Collapse (C&C), could favor the formation of high-mass stars. This hypothesis was later strengthened by the fact that 30% of high-mass Galactic sources are found at the edges of HII regions. However, the true impact of such expansion on the next generation of stars in the layer might not be as clear as initially proposed, as found in simulations.
In this talk, I will focus on the widely-studied HII region RCW120, relatively close to us (1.34kpc) and slightly above the Galactic plane (b=0.5º), which shows a nice ovoid shape. Towards the ring of neutral material enclosing the HII region, we observed stars in their earliest stages of formation, which may have been induced thanks to the expansion of the region.
In the extragalactic domain, the (direct or indirect) emission from high-mass stars allow us to reliably estimate the Star Formation Rate (SFR) of galaxies. However, a majority of existing SFR calibrations is based on local galaxy samples, the largest of them being the SDSS (z<0.3), with Ha that cannot be observed at z>0.5. I will discuss the validity of these calibrations at higher redshift (VIPERS; 0.5<z<0.9) using the CIGALE code in order to quantify the accuracy of each indicator.
I will conclude with my future projects, in particular concerning the Outer Galaxy High Resolution Survey (OGHReS), an APEX CO survey towards the third quadrant of the Galaxy.

27 November 2023

“Neutron star physics in the multi-messenger era.”

dr hab. Brynmor Haskell (Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences)

Abstract:
Neutron stars are spectacular laboratories in which we can study fundamental physics in conditions that are impossible to replicate with terrestrial experiments. Fortunately a growing number of multi-messenger observations of astrophysical phenomena related to neutron stars is becoming available, and allows us to constrain our models. In this talk I will discuss both the theoretical models that are being developed, and the observations that are being used to constrain them, with a specific focus on gravitational wave observations during the recent third observational run (O3) of the LIGO-Virgo-KAGRA collaboration. In particular I will focus not only on compact binary inspires, but mainly on continuous wave signals. These signals have not yet been detected, but I will show that the detectors can now start exploring realistic physical models for their origin.

4 December 2023

“Explaining globular cluster abundance anomalies with expanded BoOST stellar model grids.”

MSc. Hanno Stinshoff (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Globular clusters consist of old low-mass stars today. However, back when they formed, there also existed massive stars in them that by now died. The anti-correlation of elements like Sodium and Oxygen in their stars is a topic of current research. Stars that are not hot enough to undergo the needed processes to produce certain abundance patterns still display them regardless, puzzling the scientific community (Szécsi & Wünsch, 2019).

Massive stars could be the missing piece. A first generation of (massive) stars could have produced said patterns and the second generation of low-mass stars could have inherited them despite not being able to produce them themselves. This means that investigating the properties of massive stars and creating appropriate models is essential for globular cluster research.

In this talk I will present my newly-created, wide range of state-of-the-art models, computed with the Bonn Code. I explain why and how I filter the data before it can be applied to globular cluster research (the so-called BoOST format, see: Szécsi et al., 2022) and also show how some of the models exhibit the phenomenon called Chemically Homogeneous Evolution.

The models indicate that the stellar evolution is highly dependent on the three free initial parameters, mass, metallicity and rotational velocity, which makes these grids a useful resource not only in globular cluster research but beyond.

11 December 2023

“Evolution of very massive binary stars and their observable counterparts.”

dr Koushik Sen (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Our study focuses on very massive stars, which are commonly born in close binary systems. We analyse detailed binary evolution models (30…90 Msun) and identify four effects that challenge the current knowledge in binary evolution. All these effects are related to the proximity of the models to the Eddington limit. We find that most models undergo mass transfer during core hydrogen burning. During the following nuclear timescale evolution, many mass donors remain more massive than their companions (”reverse Algols”). For the highest masses, nuclear timescale mass transfer may be interrupted or absent completely due to an increased wind mass-loss rate from the donor that widens the binary. Due to the elevated luminosity-to-mass ratio, many core-hydrogen-burning donors may develop Wolf-Rayet-type winds at luminosities where single stars would not. We identify observed massive semi-detached binaries and hydrogen-rich Wolf-Rayet stars that are undergoing/have undergone the reverse Algol evolution channel. We argue that understanding very massive Algol systems is essential in predicting the advanced evolution of very massive binaries, including their potential to become observable gravitational wave sources.

18 December 2023

“Search for low-mass planets in hot Jupiter systems.”

dr hab. Gracjan Maciejewski, prof. UMK (Institute of Astronomy, Nicolaus Copernicus University)

Abstract:
Hot Jupiters, giant planets on tight orbits, have been perceived as loners devoid of planetary companions in close orbital proximity. However, recent discoveries based on space-borne precise photometry have revealed that at least some fraction of giant planets coexist with low-mass planets in compact orbital architectures. The origin of hot Jupiters is a long-lasting question in the planetary formation and evolution theory. Three main pathways are proposed to explain the formation of those planets: in situ formation, disk migration, and high eccentricity tidal migration. The question of what the dominant path is still needs clarification. The answer is hidden in the architectures of those systems, which is only partially understood. In my talk, I will share the results of an ongoing project aimed at searching for nearby transiting planetary companions to hot Jupiters, including a tale on the WASP-84 system.