Recent Talks

Until the advent in the late 1990’s of sensitive submillimetre arrays such as SCUBA, it was generally thought that the main sources for the interstellar dust found in galaxies were the dusty outflows from evolved AGB stars and M supergiants, although a dust contribution from supernovae had long been predicted on theoretical grounds. The detection at submillimetre wavelengths of very large dust masses in some high redshift galaxies emitting less than a billion years after the Big Bang led to a more serious consideration of core-collapse supernovae (CCSNe) from massive stars as major dust contributors. KAO and Spitzer mid-infrared observations confirmed that CCSN ejecta could form dust but it was not until the Herschel mission and subsequent ALMA observations that direct evidence has been obtained for the presence of significantly large masses of cold dust in young CCSN remnants. As well as using infrared spectral energy distributions to measure the amounts of dust forming in CCSN ejecta, dust masses can also be quantified from the analysis of red-blue asymmetries in their late-time optical emission line profiles. I will describe current results from these methods for estimating ejecta dust masses, and their implications.

The existence of apparently isolated massive stars has been recognized for some time, and various explanations have been proposed to explain these ranging from isolated star formation to variouscluster ejection mechanisms. In this talk I will present recent results from Gaia and Hubble on stellar dynamics within the Tarantula Nebula/30 Doradus region of the Large Magellanic Cloud. I will discuss how these complementary datasets have improved our knowledge of this nearby mini-starburst. The first results indicate the existence of a few stars in the region with masses ~100 solar masses that have been ejected from the central dense cluster R136. Ejection velocities appear torange from a few 10s of km/s to ~100 km/s. Given the extreme youth of R136 it is therefore likely that the mechanism of ejection was via the dynamical interaction channel rather than the binary supernova ejection scenario.

Nature Astronomy, launched in January 2017, is a new research journal published by Springer Nature. Sitting alongside our sister journal Nature, we aim to publish high impact research in the fields of astronomy, astrophysics and planetary science. In this talk I will cover the motivation and scope of the journal, the types of manuscripts we publish, the editorial process and what we look for in papers. I will also cover common pitfalls of writing and submitting papers and I will share hints and tips on how to maximize the impact of your paper, from writing an engaging but informative title and a properly contextualized but concise abstract, to structuring your paper in a way that your results are communicated succinctly.

We propose to use convolutional neural networks to detect contaminants in astronomical images. Once trained, our networks are able to detect various contaminants such as cosmic rays, hot and bad pixels, persistence effects, satellite or plane trails, residual fringe patterns, nebulosity, saturated pixels, diffraction spikes and tracking errors in images, encompassing a broad range of ambient conditions (seeing), PSF sampling, detectors, optics and stellar density. MaxiMask is performing semantic segmentation: it can output a probability map for each contaminant, assigning to each pixel its probability to belong to the given contaminant class, except for tracking errors where another convolutional neural network can assign the probability that the entire focal plane is affected. Training and testing data have been gathered from real data originating from various modern CCD and near-infrared cameras or simulated data. We show that MaxiMask achieves good performance on test data and propose a prior modification technique based on Bayesian statistics to optimize its behaviour to any expected class proportion in real data.

The Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia (FMPI CU) operates its own Astronomical and Geophysical Observatory in Modra, Slovakia (AGO). AGO consists of several optical systems, from which some were developed by FMPI. One of the mentioned systems is a 70-cm Newton telescope (AGO70) with primary focus on the space debris research, space surveillance and tracking (SST) to support the European attempts for autonomous SST operations.

AGO70 has several parallel scientific programs with primary focus on space debris characterization. In the last two years we created our own space debris light curve catalogue which is available for scientific community. The light curve catalogue is further used for the BVRI photometry where the shape of the phase-diagram and the synodic rotation period define the strategy for the data acquisition and processing once acquired with multi-band filters. Astrometric measurements are used for three goals. To validate and calibrate the AGO70 system’s data, to support the cataloguing efforts which requires orbit determination and improvement, and to improve the tracking efficiency of Satellite Laser Ranging stations.

Part of the improvement of AGO70 system is also hardware and software modifications. There have been efforts given to the improvement of the image processing software responsible for the real-time processing of acquired FITS frames. This so-called Image Processing Elements (IPE) pipeline is based on the modular design to make it more flexible for modifications and implementation to other systems. Currently, there are nine IPEs in total responsible for many different tasks like image segmentation, astrometric reduction, tracklet building or object correlation.

In our work we will present the AGO70 system’s technical characteristics and observation programs. We will introduce the overall design of the system and its functionalities. The planning, acquisition and processing of light curves, BVRI photometric data, and astrometric measurements will be discussed in detail. We will present the image processing pipeline which improves the obtained data’s quality and latency.

Brightness variations due to dark spots on the stellar surface encode information about stellar surface rotation and magnetic activity. As stars slow down and become less active, the rotation rate is observed to decrease, thus rotation is often used as a diagnostic for age. Rotation and magnetic fields affect stellar evolution and the mode frequencies used to infer fundamental properties of stars. Furthermore, rotation itself is an important ingredient for dynamo mechanisms. Therefore, it is of extreme importance to constrain surface rotation and magnetic properties of stars. In this work, we analyze the spot modulation in light-curves for main-sequence and subgiant stars observed by Kepler main-mission. We analyze four data sets: KADACS time-series obtained for 20-, 55-, and 80-day filters; and PDC-MAP time-series. The rotation estimates are retrieved through a combination of wavelet analysis and the autocorrelation function of light-curves. Reliable rotation periods are determined by comparing the rotation estimates obtained from the different diagnostics and for the different time-series. We recover rotation periods for more than 60% of the targets. For those, we also study the photometric activity level and lifetime of active regions. We find the rotation rate to increase with effective temperature and mass, while the photometric activity proxy increases towards fast rotators. Active region lifetimes are found to be longer with increasing rotation rate and photometric activity. In this analysis we also identify potential polluters, such as mis-classified Red Giants, classical pulsator candidates, and photometric pollution of light-curves.

The mass and structural assembly of galaxies is still a matter of intense debate. Current theoretical models predict the existence of a linear relationship between galaxy effective radius (R_e ) and the host dark matter halo virial radius (R_h ).

By making use of accurate and transparent semi-empirical models compared to the size distributions of central galaxies from the Sloan Digital Sky Survey, I will provide robust constraints on the normalization and scatter of the Re − Rh relation in the framework of Halo Abundance Matching. Specifically, I will explore the parameter space
of models in which the relation between galaxy size and halo radius is mediated by the dynamical or structural properties of the dark matter halo. Within the same framework, I will also discuss the size evolution of Ultra Massive Galaxies, which is still poorly understood.

I will show that the data require extremely tight relations for both early-type and late type galaxies, especially for more massive galaxies. These constraints challenge models based on angular momentum conservation, which predict significantly wider distributions of galaxy sizes and no trend with stellar mass. I will also show that a constant Re-Rh relation is able to reproduce the size evolution of Ultra Massive Galaxies and provide a framework to the size evolution of galaxies with any mass.

I will conclude showing that the normalization and scatter of the size-halo radius relation of both early- and late-type galaxies might be consistent with pure merger models, though a complete picture for the structural evolution of galaxies remains elusive.

For the beginning of my presentation, I would like to briefly present the astronomy program at the Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava, Slovakia.

Continuing, the main results of my diploma thesis will be presented during which I simulated the propagation of ultra-high energy cosmic rays throught the Universe using the simulation code SimProp v2r4 modelling the characteristics of possible sources. The results were compared with the observations from the Pierre Auger Observatory which is situed in Argentina. Thesis has been made with the cooperation of the Institute of Physics of Czech Academy of Sciences in Prague. Ultra-high energy cosmic rays (UHECRs) represent the subatomic particles, mainly protons and nuclei of different elements, which can attain energies up to 10²⁰ eV. Colliding with the Earth´s atmosphere they create the shower of secondary particles which can be detected by specific detectors on the ground. Origin of these particles with the highest energies is still a problem which haven´t been solved to these days.

Besides the corpuscular particles, the Earth is permanetly bombarded also by high energy photons or gamma rays. These are formed in the vicinity of exotic objects like active galactic nuclei (AGN) or supernova remnants (SNRs) or as a product of UHECRs. Colliding with the atmosphere, they also create a shower of secondary particles which is narrower than in the case of UHECRs. To observe this shower the Imaging Atmospheric Cherenkov Telescopes (IACTs) have been developed observing the Cherenkov light formed as a product of the cascade. Such telescopes are for example the MAGIC telescopes situed at Observatorio del Roque de los Muchacos (ORM) on La Palma or the future Cherenkov Telescope Array (CTA) which northern part will be also situed at ORM.

Study of gamma rays represents currently the main topic of my PhD project. For this reason I am glad to had an opportunity to participate on ERASMUS+ mobility at IAC for 3 months and to cooperate with the astroparticle physics group. During this period I have been analyzing archival data taken by MAGIC telescopes of the active region around SNR G24.7+0.6. Specifically we are interested in a source labeled as 2FHL J1839.5-0705. Preliminary results of my study will be presented.

Although the name 'fundamental metallicity relation' (FMR) may sound a bit bombastic, it really represents a fundamental relation in the sense of revealing a fundamental process in galaxy formation. Numerical simulations predict that accretion of cosmic web gas feeds star formation in star-forming galaxies. However, this solid theoretical prediction has been extremely elusive to confirm. The FMR, i.e., the fact that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity (Zg), is one of the best observational supports available yet. The talk will introduce the FMR and then present recent results of our group showing how the FMR emerges from a local anti-correlation between SFR and Zg existing in the disks of galaxies. Thus, understanding the FMR is equivalent to understanding why active star-forming regions tend to have low relative metallicity. The existence of the local anti-correlation SFR-vs-Zg is found by Sanchez-Menguiano+19 ApJ  and Sanchez Almeida+18 MNRAS, whereas the equivalence between local and global laws is in Sanchez Almeida & Sanchez-Menguiano 19 ApJL.

Supernova SN1987A in the Large Magellanic Cloud offers an unprecedented opportunity to tackle fundamental issues of supernova explosions: dust and molecule formation, interaction with the circumstellar medium, particle acceleration, pulsar formation, etc. Since 2011, instruments like ALMA have been fundamental for such endeavor. Tomographic techniques have recently permitted to obtain 3D-images of the molecular emission. High-resolution images of dust emission have recently been obtained. All those results, compared with predictions from hydro-dynamical simulations, are paving the way to a better understanding of supernovae explosions. In the talk, the main results will be highlighted with emphasis on the advances produced since 2017 in the understanding of the structure of the inner ejecta or debris.