Department seminars

August 29, 2023 at 2:15 PM

Precession of the orbital planes and rotational axes in transiting exoplanets

Dmytro Orikhovskyi

(Comenius University in Bratislava / Astronomický ústav SAV)

Orbital planes of numerous close-in exoplanets are not perpendicular to the host-star spin axis. This means that the current orbital plane of the exoplanet was probably altered after the system was formed. Projected spin-orbit misalignment can be measured in transiting exoplanets using so called Rossiter-McLaughlin effect affecting radial velocity of the host star during the transit. For fast-rotating host stars, where the radial velocities cannot be often measured with a sufficient precision, the planet signature can be found in the mean line profiles. Analysis of the profiles during the transit enables us to determine the projected spin axis-orbital plane misalignment. If the inclination angle of stellar spin axis is known from a high-precision photometry, the true misalignment (stellar obliquity) can be determined. Some misaligned objects (e.g. Kepler-13Ab) were found to show precession of the exoplanet orbit caused by the tides due to the rotationally-deformed parent star. The precession causes changes of the transit duration (TDV) due to the shift of the the transit chord across the stellar surface. Exoplanet’s orbit precession is always connected with precession of the parent’s star rotational axis due to the conservation of the total angular momentum but its amplitude is much smaller. Its analysis brings us information on the internal structure of the star. The primary goal of the diploma thesis was to find exoplanets with spin axis-orbital plane misalignment and to detect those which show transit duration variations (TDV) due to the orbital plane precession. This work used high-precision satellite photometry from TESS for objects selected from the ExoFOP website. The analysis of the light-curve asymmetries lead to detection of several objects where spin-orbit misalignment is plausible. One object significantly changing its transit depth was found. Light-curve modelling lead to improvement of transit ephemerides for 64 objects. Several objects were found to show interesting peculiarities and deserve future investigation.

August 29, 2023 at 1:30 PM

MWC 645: A Puzzling FS CMa-type Star

Andrea Torres

(Universidad Nacional de La Plata, Argentina)

The B[e] phenomenon encompasses a diverse group of stars encircled by gaseous and dusty envelopes, sharing similar physical characteristics. Among these stars, FS CMa-type objects are suspected binary systems that might be undergoing mass-transfer processes, potentially explaining their substantial surrounding material. Our study aims to contribute insights into a recently confirmed binary star system, MWC 645, which could be experiencing active mass transfer. Through spectroscopic analysis, we identify atomic and molecular features, derive quantitative properties of line profiles, and detect CO molecular bands in absorption at 1.62 μm and 2.3 μm for the first time. We set an upper limit of the effective temperature for the cooler binary component and find a correlation between enhanced Hα emission and decreased optical brightness, potentially linked to mass-ejection events or increased mass loss. Additionally, we outline the envelope’s global properties, which could cause brightness fluctuations due to variable extinction, and briefly discuss various hypothetical scenarios.

Previous seminars

June 29, 2023 at 1:30 PM

Modeling diatomic molecules in stellar disk

Rodolfo Vallverdú

(Universidad Nacional de La Plata, Argentina)

Stellar disks have temperatures low enough to allow for the formation of molecules. The presence of these molecules is detected through the observation of emission bands in the spectrum of the star and its disk. To identify which molecule corresponds to these bands, as well as determine some physical parameters of the disk, it is necessary to have synthetic spectra for comparison with observations. In this talk, I will discuss the code I have been developing to generate these synthetic spectra, its results, and its scope.

May 22, 2023 at 1:30 PM

Evolution of massive stars with new hydrodynamic wind models

Alex C. Gormaz-Matamala

(Centrum Astronomiczne im. Mikołaja Kopernika, Warsaw, Poland; Universidad Adolfo Ibáñez, Viña del Mar, Chile)

We present evolutionary models for a set of massive stars, introducing a new prescription for the mass loss rate obtained from hydrodynamic calculations in which the wind velocity profile and the line-acceleration are obtained in a self consistently way. Evolutionary models with the new recipe for mass loss retain more stellar mass through their evolution, which is expressed in larger radii and consequently more luminous tracks over the Hertzsprung-Russell diagram. Also, models with self-consistent winds predict a weaker braking in the rotational velocity and a more marked drift redwards of the evolutionary tracks across the HRD, as a direct consequence of the differences in the stellar angular momentum loss and in the rotational mixing. Together with the prediction of higher masses at the end of the main sequence, self-consistent tracks also predict a distribution of rotational velocities for Galactic O-type stars more in agreement with the diagnostics of recent surveys. Other hypothetical implications, such as the masses of Ofpe stars at the Galactic Centre or the contribution of the isotope Al-26 to the ISM, are open to discussion.

May 16, 2023 at 1:30 PM

Exploring the origin and evolution of hydrogen-deficient supergiants

Anirban Bhowmick

(VIT Bhopal University)

The peculiar characteristics of the enigmatic hydrogen(H) deficient supergiants suggest an evolutionary path very different from that of an H-normal star. Being extremely rare, these enigmatic objects are challenging to study, but a thorough knowledge of their chemical composition across their different samples can provide clues to their evolution. Broadly classified into four main categories- 1) the Extreme Helium stars (EHes), 2) the R Coronae Borealis Stars RCBs, 3) the Hydrogen-Deficient carbon stars HdCs, and the 4) DY Persei variables they span a wide range of temperature — from the coolest DY Persei variables (Teff~3500 K) to the hot Extreme Helium Stars (EHes) (Teff>14000 K). Based on their observed surface properties, two formation scenarios were proposed — 1) The Double Degenerate (DD) merger scenario involving the merger of two low-mass double-degenerate white dwarfs and 2) the FF scenario involving a late or final He shell flash in a post-AGB star. However, apart from H-deficiency, some of these stars share unique abundance anomalies, which tilt the balance towards the DD merger scenario and suggest a common evolutionary connection. While the cooler members — the cool RCBs and HdCs exhibit enhancement of 18O relative to 16O and depletion of 13C with respect to 12C, the hotter RCBs and the cool EHes showed enrichment of fluorine (F) with respect to iron (Fe) by 800-8000 times than solar, in their atmospheres. While the DD scenario can account for the observed abundance anomalies, these anomalies were not observed entirely across the sample, mainly in the cool DY Pers, and the hot EHes. In this talk, I explain my work investigating the evolutionary connection between the different members of H-deficient supergiants with a focus on the two extreme members of the group, the DY Persei variables and the hot EHes. Using multiwavelength (optical and NIR) spectroscopic observations obtained from 2m HCT, IAO India, as well as archival data (ESO-FEROS and UVES), I explore the status of the chemical peculiarities across the sample and investigate whether the proposed DD merger scenario can be accepted as the final formation scenario.

February 16, 2023 at 1:00 PM

Resolving HD327083

Paula Marchiano

(Universidad Nacional de La Plata, Argentina)

B[e] stars are a massive peculiar star showing an important excess in the near infrared due to the presence of circumstellar dust around. Besides, due to their mass loss these objects deposit huge amounts of mass and energy into their environment and enrich it with chemically processed material. HD 327083 exhibits these and other characteristics of the B[e] phenomenon, but when we study this object with more detail…we ask : Is HD327083 a truly B[e] supergiant?

January 26, 2023 at 1:30 PM

Massive stars and their hydrodynamic wind regimes

Ignacio Araya

(Universidad Mayor, Chile)

The study of massive stars is significant in several fields of astrophysics. These objects play a dynamical and kinematic role in the interstellar medium, depositing a large amount of energy and momentum via their strong stellar winds. This talk will focus on these powerful winds, called line-driven winds. Based on the original “CAK” model, I will summarise the main hydrodynamic (stationary and time-dependent) wind solutions under varied conditions (e.g., due to rapid rotation) and their applications to different types of massive stars. Finally, I will present our undergoing work to derive the stellar and wind parameters from massive stars.

November 15, 2022 at 2:15 PM

Ray tracing modeling of radial velocity systematics

Marcelo Tala

(Universidad Adolfo Ibanez, Santiago de Chile, Chile)

We present moes, a ray tracing software that computes the path of rays through echelle spectrographs. Our algorithm is based on sequential direct tracing with Seidel aberration corrections applied at the detector plane. As a test case, we modeled the CARMENES VIS spectrograph. After subtracting the best model from the data, the residuals yield a rms of 0.042 pix, which is comparable to the precision of the wavelength solution of state-of-the-art radial velocity instruments. By including the influence of the changes of the environment in the ray propagation, we are able to predict instrumental radial velocity systematics at the 1 m/s level.

November 15, 2022 at 1:30 PM

The Zoo of emission line B-type stars. Attempts to derive fundamental parameters and understand their wind properties

Lydia Cidale

(Universidad Nacional de La Plata, Argentina)

B-type stars encompass distinct stellar groups with established evolutionary status: pre-main sequence (PMS) stars, main sequence stars, blue supergiants, and post-AGB stars. In some particular evolutionary stages, and even during the main sequence stage, some B-type stars exhibit emission lines in their spectra, mainly the Halpha and single ionized metals. Other stars show, in addition, forbidden emission lines and large IR excess due to the presence of a dusty ring-like structure. All these stars are deeply embedded in their circumstellar media, being extremely difficult to assign their fundamental parameters and classify them. During this seminar, we present the classification of the stars and discuss their IR properties and possible links. A second interesting group is the LBVs and blue supergiants. To understand their wind properties, we study their variability and mass-loss rates. We analyze the response of the line profiles to different hydrodynamical solutions and discuss the unicity of the solutions. Synthetic line profiles are computed by solving the radiative transfer equations in the co-moving frame for a multi-level atom in NLTE. The results are compared with optical and IR spectral lines.

November 3, 2022 at 1:30 PM

Resolving close binarity among classical Be stars with near-IR interferometry – a new set of binary orbits and dynamical masses

Robert Klement

(Georgia State University, CHARA)

Optical/IR interferometry has been instrumental in revealing the nature of classical Be stars, which are rapidly rotating B-type stars with self-ejected circumstellar disks. The near-critical rotation, which is a defining property of Be stars, was likely acquired by means of mass and angular momentum transfer in a close binary. The originally more massive component in this case loses a large fraction of its mass and becomes an evolved remnant stripped of its outer envelope. The present-day Be star, on the other hand, is rejuvenated and spun up, which can lead to the subsequent formation of the characteristic mass-loss disk. The observational test for this scenario is that Be stars should have evolved stripped (typically subdwarf O-type) companions. Detecting such faint companions to Be stars poses many difficulties, but near-IR interferometry is currently capable of directly detecting companions down to an angular separation of ~0.5 milliarcsec and up to a magnitude difference of ~6, which is sufficient for the detection of subdwarf companions of nearby Be stars. The possible prevalence of binarity among Be stars also offers a direct way of obtaining fundamental parameters and dynamical masses of both the Be stars and their companions, which are so far largely unavailable. Our efforts on interferometric mapping of Be star binary orbits have led to new sets of dynamical masses, which are crucially needed for the calibration of evolutionary models. These new results include binary orbits and first dynamical masses for at least eight Be binary systems, including the first characterization of a subdwarf B-type companion discovered around the B6e star kappa Dra.

October 18, 2022 at 1:30 PM

Follow-up spectroscopic in Be stars

Catalina Arcos

(Instituto de Fisica y Astronomia, Valparaiso, Chile)

Be stars are massive stars surrounded by a thin equatorial gas disk in quasi-Keplerian rotation. By studying the emission lines from their spectra, information about the features of the inner and outer parts of the disk can be obtained. Moreover, these stars are the only objects studied so far with the characteristic of forming, maintaining, and dissipating a disk, making them one of the most attractive stellar objects to be studied. The mechanism that transfers the mass and angular momentum from the star to the disk is still under debate, but once the material is placed in the circumstellar orbit, it is governed by viscosity. In this talk, I will present the follow-up variability of a sample of southern Be stars and our preliminary results of implementing new hydrodynamical solutions to form viscous decretion disks.

October 11, 2022 at 1:30 PM

Galactic archaeology with Gaia and old population pulsators

Zdenek Prudil

(Astronomisches Rechen-Institut, Heidelberg, Germany)

Galactic archaeology uses stars as fossils to study the evolutionary history of galaxies like our own Milky Way (MW). In my work, I investigate the MW formation history using RR Lyrae stars. The RR Lyrae stars are pulsating variable stars associated with the old stellar populations in our Galaxy and are often used as distance and metallicity indicators within the Local Group. In my talk, I will summarize several projects focusing on various MW substructures, particularly the MW halo, bulge, and disk, where RR Lyrae pulsators played a crucial role. I will show how the synergy between RR Lyrae variables and astrometric data from the Gaia space mission expands our understanding of the MW formation history.

September 27, 2022 at 1:30 PM

Research activities in the frame of the POEMS and PhD projects

Lorena Verónica Mercanti

(Universidad Nacional de La Plata, Argentina)

Two lines of research will be presented, which contribute to the Physics of Extreme Massive Stars (POEMS) project. The first part is dedicated to the modelling of different tracers of circumstellar envelopes of B[e] supergiants. In order to reproduce the line profiles typically observed in B-type stars with radiation-driven winds, a stellar atmospheric model to generate the line spectrum of Ca II and Mg II in NLTE is to be developed. In the second part of the talk the spectroscopic analysis of the chemically peculiar star HD 142301 is presented. Observed spectra of the star are used to shed light on the surface heterogeneities of chemical abundances and some processes that potentially control the abundance patterns of different chemical elements.

September 8, 2022 at 11:00 AM

S-Process Nucleosynthesis in and from AGB Stars: Observations

Alexander Dimoff

(Max Planck Institute for Astronomy, Heidelberg, Germany)

Around half the heavy elements are formed through slow neutron captures taking place in evolved asymptotic giant branch (AGB) stars in the mass range ~1-6M. Depending on the temperature the neutrons are produced through different reactions – via the 13C(a,n) reaction or at higher temperatures via 22Ne(a,n). The nucleosynthetic imprint can be studied by looking at the s-process material in the surface of the AGB star that has been dredged up. The surface chemical composition therefore provides insight into the internal s-process production (of, e.g., Rb, Sr, Y, Zr, Nb, Mo, Tc, Ba, La, Ce, Nd, Pb). These elements can be studied by directly observing the AGB star, or indirectly by studying the companions of binary systems that have been polluted by mass transfer from an AGB star that has faded away. Thus, we need accurate radial velocities, stellar parameters, and abundances of single and binary AGB stars to understand the s-process as well as mass loss or mass transfer in binaries.

June 28, 2022 at 2:30 PM

Researches of stars in ShAO: observations, results

Nariman Ismayilov and Aynur Abdulkerimova

(Shamakhy Astrophysical Observatory, Azerbaijan)

We are planning to talk about observational devices, telescopes and the night sky condition of ShAO. We will describe some details on the technical condition of our 2-m telescope and the methods and objects of spectral observations. Then we will briefly describe the main scientific fields that are carried out at our observatory. We will tell you about the research of stars, especially about the early stage of the evolution of low and intermediate mass stars. We will present some new results obtained by our team.

May 26, 2022 at 1:30 PM

V838 Mon: A slow waking up of a Sleeping Beauty?

Tiina Liimets

(Astronomical Institute of the Czech Academy of Sciences)

V838 Monocerotis is a peculiar binary that underwent an immense stellar explosion in 2002, leaving behind an expanding cool supergiant and a hot B3V companion. Five years after the outburst, the B3V companion disappeared from view, and it has been obscured ever since. In this presentation I will present our long-term photometric and spectral monitoring of this intriguing star during the past 13 years. Our analysis imply that the system is slowly recovering from the eclipse.

April 26, 2022 at 1:30 PM

Eccentric binaries with long, but too short, orbital periods

Henri Boffin

(European Southern Observatory, Garching)

The majority of stars are in binary systems and a non-negligible fraction of these will interact in some way, leading to various phenomena and types of stars. For solar-like stars, the interactions are more likely to take place when the primary star ascends the first red giant or the asymptotic giant branch (AGB). In some cases, this will then lead to a common envelope, with the orbit dramatically shrinking from several years to less than a few days. However, in many other cases, if a mass transfer does take place, such common envelope evolution is avoided. The outcome is then sometimes a binary system containing a (pre-)white dwarf, but with orbital periods of hundreds to thousands of days and significant eccentricities. Such long periods are however too small for current models to explain them. Moreover, the fact that these systems show a non-zero eccentricity is also very puzzling. This is the case for many important binary classes: post-AGB binaries, symbiotic stars, blue straggler stars, barium, CH and S stars, CEMP-s stars, etc. I will review these systems and show why they are important to understand mass transfer in binary systems, what we have learned so far, and what remains to be understood.

February 10, 2022 at 1:30 PM

Recent discoveries and observations of GRB optical afterglows from Ondřejov

Martin Jelinek

(Astronomical Institute of the Czech Academy of Sciences )

I will show a selection of recently observed GRB optical afterglows. Two of them were even discovered from Ondrejov observatory, which is a rare thing, comparable to a victory in a race. One – GRB 210312B – was found with the 2m Perek telescope. I will pass through the particularities of these particular events and try to get a little deeper into the understanding of what processes are responsible for these features.

November 25, 2021 at 1:30 PM

B Supergiants: Atmospheres and Physical Properties

Matheus Peron

(Emmy Noether research group on stellar atmospheres and mass loss, Astronomisches Rechen-Institut, Heidelberg)

High-mass stars are very important to many areas of Astronomy. These objects deeply impact their surroundings through their powerful winds and their deaths as supernovae. Therefore, understanding the behavior of such stars is essential to understand their impacts on their host galaxies’ properties and history.
The aim of this research project is to analyze the atmospheres of B supergiants (BSGs, evolved massive stars) using the CMFGEN (Hillier & Miller 1998), a 1D, non-LTE atmosphere code — which is one of the state-of-the art tools used to analyze hot stars. The focus of the project is to investigate whether more recent models (e.g., the inclusion of x-rays, clumping, more recent atomic data) can better explain the optical and UV observed spectra of these stars, since previous studies failed to model several important UV lines (Crowther et al. 2006; Searle et al. 2008).
As results we obtained (i) an overall improved agreement between BSGs observed and model spectra at the UV considering the effects of clumping and x-rays in the wind. Also we noticed (ii) important differences in their properties between hot (B1 – B0) and warm (B2 – B5) BSGs were also found, and it is in agreement with recent hydrodynamical simulations, such as Driessen et al. (2019). Beyond that, (iii), we have found a general trend of the CNO abundances for BSGs compatible with previous works in the literature and to the current high-mass stellar evolution predictions. However, (iv) despite a decrease in terminal velocity at the Bi-Stability Jump, we found no increase in mass-loss, instead, we have found a slightly decreasing trend towards later spectral types.

November 18, 2021 at 1:30 PM

Parallelized model atmospheres via LXC-based virtualization

Gabriel Szász

(Masaryk University)

Our science case requires a calculation of as many model atmospheres as possible in a short amount of time. After the initial investigation, we opted to run Atlas12_ada code (Stift, 2017) within an LXC-based multi-node environment running on top of a modern computing cluster. Even though we still do not use the platform’s full potential, the versatility and scalability of the solution can already be demonstrated.

September 16, 2021 at 1:30 PM

The EREBOS project: Investigating the influence of very low-mass companions on stellar evolution

Veronika Schaffenroth

(Institute for Physics and Astronomy of the University of Potsdam)

Planets, brown dwarfs and very low mass stars in close orbits will interact with their host stars, as soon as they evolve to become red giants. However, the outcome of those interactions is still unclear. Hot subdwarf stars are He-core burning stars found on the extreme horizontal branch. For their formation a huge mass-loss on the RGB is required, which is mainly explained by close binary evolution. Recently, several brown dwarfs have been discovered orbiting hot subdwarf stars in very short orbital periods of 0.065 – 0.096 d. More than 8% of those stars might have close substellar companions. This shows that such companions can significantly affect late stellar evolution and that sdB binaries are ideal objects to study this influence.
Eclipsing binaries consisting of a hot subdwarf stars and low-mass companions are of special importance, as they allow the determination of absolute parameters as masses and radii, which are important to understand the previous interaction. Only about 20 of such systems have been analysed so far. In course of the EREBOS project, we increased the number of known systems to 200. The main goal of the EREBOS project is photometric and spectroscopic follow up of as many objects as possible. We are using different telescopes to do this including the 65 cm telescope in Ondrejov.
Here, I will give an overview of the current status of the project including some first results.

August 26, 2021 at 1:30 PM

SUPPNet: neural network for stellar spectrum normalisation

Tomasz Różański

(Astronomical Institute of Wrocław University)

High resolution spectra of stars are a very abundant source of information about stellar atmospheres. However, analysis of stellar spectra often requires normalisation which involves element-wise division of observed flux by modelled pseudo-continuum.
Pseudo-continuum modelling is a non-trivial task. Its shape is due to several factors: the spectrum of the observed star, interstellar absorption, absorption in the Earth’s atmosphere, the response function of the spectrograph and the reduction pipeline. All these factors introduce numerous low- and high-frequency distortions that are difficult to model automatically, which in turn leads to time-consuming manual normalisation. The most important limitation of automatic methods is the assumption that the local flux maximum is a good approximation of the pseudo-continuum. This is obviously false in case of spectra with emission features and in wavelength ranges where spectral lines heavily blend.
I would like to present a method for stellar spectrum normalisation based on deep convolutional neural network called SUPPNet. The algorithm is available on-line ( and as standalone Python code.

June 17, 2021 at 1:30 PM

ReSpefo: a powerful tool for one-dimensional spectra analysis

Adam Harmanec

(Faculty of Mathematics and Physics, Charles University) 

The original program SPEFO for processing stellar spectra has been refreshed and updated with new modern controls and user interface. I will introduce the updated program reSpefo and do a short demonstration of its new internal file format and new functionality including the equivalent width and other spectrophotometric measurements and interactive rectification of spectra from echelle spectrometers.

June 10, 2021 at 1:30 PM

XSL: a new generation empirical stellar library and stellar population models

Kristiina Verro

(Kapteyn Astronomical Institute, University of Groningen) 

With the next generation wide-field spectroscopic facilities, such as the upcoming WEAVE for the William Herschel Telescope, and recent advances in the infrared instruments on large telescopes, such as X-shooter and KMOS, spectroscopic information of different types of galaxies in various environments will increase in quantity and in quality. Stellar spectral libraries and associated stellar population models need to keep up with the times. We are presenting a new generation empirical stellar library – the X-shooter Spectral Library (XSL), and stellar population models. With 830 stellar spectra, this moderate-resolution near-UV to near-IR (R ~ 10 000, 300 – 2480 nm) spectral library will cover the entire HR diagram, with an emphasis on M giants. The extended wavelength coverage, and high resolution of the new XSL-based stellar populations models will help us to bridge the optical and the near-IR studies of intermediate and old stellar population, and clarify the role of evolved cool stars in stellar population synthesis.

May 20, 2021 at 1:30 PM

A-F variables from the TESS continuous viewing zone

Marek Skarka

(Astronomical Institute of the Czech Academy of Sciences ) 

The region of the main sequence where A and F stars are located is a transition region of various physical phenomena. This is the reason why we can observe stars showing signs of rotation, pulsation, chemical peculiarity, binarity, etc. often at the same time. To our current knowledge, some of the observed phenomena should not co-exist. I will discuss the identification and classification of the A-F variable stars near the ecliptic pole gathered by the TESS satellite and show some intriguing cases.

15 April, 2021 at 1:30 PM

Large grids of model atmospheres for a rapid analysis of stellar spectra

Janos Zsargó

(Instituto Politécnico Nacional, Mexico) 

We present a database of 43 340 atmospheric models for stars with stellar masses between 9 and 120 M☉, covering the region of the OB main-sequence and Wolf-Rayet stars in the Hertzsprung-Russell diagram. The models were calculated using the stellar atmosphere code CMFGEN. The parameter space has six dimensions: the effective temperature, the luminosity, the metallicity, and three stellar wind parameters: velocity law, the terminal velocity, and the volume filling factor. For each model, we also calculate synthetic spectra in the UV, optical, and near-IR regions. We also present the results of the reanalysis of ∊ Ori using our grid to demonstrate the benefits of databases of precalculated models. Our analysis succeeded in reproducing the best-fit parameter ranges of the original study, although our results favor the higher end of the mass-loss range and a lower level of clumping. Our results indirectly suggest that the resonance lines in the UV range are strongly affected by the velocity-space porosity, as has been suggested by recent theoretical calculations and numerical simulations.

26 March, 2021 at 1:30 PM

Moving-mesh radiation hydrodynamics and an application to wind-reprocessed transients

Diego Calderón

(Charles University, Prague) 

The development of surveys with high cadence on large fields has improved significantly in the last decades. This has made possible conducting detailed studies of many transient phenomena such as tidal disruption events, supernovae, luminous red novae among others. However, such improvements have posed a major challenge for explaining their nature, specifically on understanding how these sources are being powered. Numerical simulations of such processes are very challenging mainly due to the need of coupling radiation with hydrodynamics while, at the same time, covering a wide dynamic range spatially and temporarily. In order to overcome this problem, we developed a new module for coupling radiation into the moving-mesh hydrodynamics code JET. The moving-mesh nature of the code allows us to perform simulations with a wide dynamic range of more than five orders of magnitude spatially as well as temporarily. We present the code and its first applications for modelling wind-reprocessed transients.

11 February, 2021 at 1:30 PM

PLATOSpec, new spectrograph for La Silla

Petr Kabáth

(Astronomical Institute of the Czech Academy of Sciences

I will present the new spectrograph PLATOSpec planned for ESO La Silla observatory, Chile. PLATOSpec will be a modern echelle spectrograph sensitive in blue wavelengths with resolving power of R=70000 which will be mounted at E152 telescope (former ESO telescope). Main goal of the project is the support of the upcoming PLATO space mission. Scientific topics covered with PLATOSpec will range from exoplanets till stellar physics and beyond. Currently, the project is in the telescope upgrade stage and the spectrograph is undergoing the Design Review phase. Full operations are planned for the end of 2023. The project is led by the AsU in partnership with Pontifica Universidad Catolica de Chile, Chile and Thueringer Landessternwarte Tautenburg, Germany. I will describe the current status of the project, its time line and planned operations scheme. PLATOSpec and OES spectrographs will be compared and the accuracies will be described and put into context with other instruments.

10 December, 2020 at 1:30 PM

Symbiotic binaries: the mystery of cool giants and hot dwarfs

Jaroslav Merc

(Charles University, Prague; P. J. Šafárik University, Košice, Slovakia) 

Symbiotic stars are interacting binaries consisting of an evolved, cool giant transferring mass to a hot companion – a white dwarf or rarely a neutron star. The presence of both ionized and neutral regions in their surroundings, interacting winds, jets, accretion disks, or dust forming regions make them extraordinary astrophysical laboratories for studying various aspects of the interaction and evolution in binary systems. Although some of the symbiotic systems are studied for more than a hundred years, there are still several open questions concerning the mechanisms of activity, individual components, and their evolution. We will briefly review the important information on symbiotic stars and present the results connected with the New Online Database of Symbiotic Variables and long-term monitoring of selected objects.

12 November, 2020 at 1:30 PM

Constraining the Rapid Neutron-Capture Process with Meteoritic I-129 and Cm-247

Andrés Yagüe López

(Konkoly Observatory, Budapest, Hungary) 

Among all radioactive isotopes produced in the Galaxy, a small number of them have relatively short mean lives between 0.1 and 100 Myr. Early Solar System abundances of these radioisotopes can be determined through meteoritic analysis and, due to their short half lives, give us insight into the sites and processes that produced them. In this talk, I discuss the ratio of two of these short-lived radioisotopes, I-129 and Cm-247. I also show how, due to their remarkably similar half lives, they give us a unique opportunity to constrain the physical conditions of the last rapid neutron-capture process event that contributed to the enrichment of the pre-solar nebula.

15 October, 2020 at 1:30 PM

ALMA and the Cool Universe

Abhijeet Borkar

(Astronomical Institute of the Czech Academy of Sciences

The Atacama Large Millimeter/submillimeter Array (ALMA) is currently the largest radio telescope in the world, a complete imaging and spectroscopic instrument operating in the high frequency radio regime. It is located in northern Chile as a partnership between Europe (ESO), North America (NRAO, USA and NRC, Canada) and East Asia (NAOJ, Japan, ASIAA, Taiwan, and KASI, South Korea). ALMA provides an extensive breadth and depth of science, from cosmology & high redshift Universe, planet & star formation, to solar system objects, and offers capabilities which are unique and complimentary to major terrestrial and space telescope of the modern era. In this talk, I will provide an overview of ALMA telescope, operations, science capabilities & highlights and how you can use ALMA for your favourite science. I will also review the role of the Czech ALMA Regional Center node and preparations for the proposal Cycle.

24 September, 2020 at 1:30 PM

Nebulosities of the symbiotic binary R Aquarii

Tiina Liimets

(Astronomical Institute of the Czech Academy of Sciences

I will give an overview of the fascinating nebulae around one of the closest known symbiotic star R Aquarii. Together with historic and more recent observational data I will present results of our own long-term monitoring of these intriguing nebulosities: an ancient arcs, hour-glass nebula and puzzling, still active jet.

14 July, 2020 at 1:30 PM

Wray 15-906: a post-red supergiant luminous blue variable discovered with WISE, Herschel and SALT

Olga Maryeva

(Astronomical Institute of the Czech Academy of Sciences

Presently we know two evolutionary paths leading massive stars to Wolf-Rayet (WR) stage. Stars witn M>40Msun after the end of hydrogen burning in the core come to WR through the phase of Luminous blue variables (LBV). On the other hand, stars with lower mass (~30Msun) before LBV phase cross the stage of red supergiant (RSG). Theory predicts what the latters may explode as supernova (SN) directly after LBV phase showing before explosion the spectrum of WN11 type. However in practice in our Galaxy there are only three stars of WN11 type and all of them have higher initial masses, and therefore they did not pass through RSG phase. In my talk I will present results of study of recently discovered Galactic candidate luminous blue variable Wray 15-906. I will show how spectral classification was performed, and how stellar parameters were calculated. Estimated location on Hertzsprung-Russell diagram shows that Wray 15-906 is a post-red supergiant star. Collected spectral data together with results of modelling show that properties of Wray 15-906 are very similar to predicted ones for a star with initial mass of ≈25Msun, which will pass through WN11h stage right before exploding as a supernova.

11 June, 2020 at 1:30 PM


Julieta Sanchez Arias

(Astronomical Institute of the Czech Academy of Sciences

Variable stars offer a great opportunity to study their interiors through asteroseismology. This powerful astrophysics tool allows us to derive stellar parameters such as the mass, the radius, the metallicity and the age by the comparison between theoretical models and the frequency spectrum derived from observations. In this opportunity, I will present the challenges in the modelling of hybrids delta Stc-gamma Dor stars and the analysis of the light curve of one particular hybrid star with surface activity. In addition, I will introduce asteroseismic tools to distinguish two different kinds of variable stars, which usually lie in the same region of the seismic HR diagram: delta Sct stars and the precursors of the so-called extremely low mass white dwarf stars. Finally, I will present a brief overview of the potential of asteroseismology in massive stars.

30 January, 2020 at 1:30 PM

Self-consistent solutions for line-driven winds using Lambert W-function

Alex C. Gormaz-Matamala

(Universidad de Valparaíso, Chile) 

Hot massive stars present strong stellar winds which are driven by absorption, scattering and reemission of photons by the ions of the atmosphere (line-driven winds). A better comprehension of this phenomenon and a more accurate calculation of hydrodynamics and radiative acceleration is required to determine accurate mass-loss rates, and hence constrain evolutionary tracks of hot massive stars. The equation of motion for the stellar winds of a hot massive star is solved analytically by using the Lambert W-function. To solve radiative transfer equation in the stellar atmosphere and to calculate the radiative acceleration g_line(r) we use the non-LTE code CMFGEN. Since the acceleration depends now only on radial coordinate, it can be used to solve analytically the equation of motion by means of the Lambert W-function. An iterative procedure between the solution of the radiative transfer and the equation of motion is executed in order to obtain a consistent result.

29 October, 2019 at 1:30 PM

Common envelope transients: buried in infrared

Nadia Blagorodnova

(Radboud University Nijmegen, Nederlands) 

Most stars in our Universe live in binaries.  Unstable mass transfer from one star to another can lead to the formation of a shared gaseous non co-rotating shell where both stars orbit: the common envelope. The end of this phase is marked by the quick spiral-in of the secondary star towards its companion, leading to violent interactions between the components. The whole, or part of the binary’s common envelope gets ejected, and the pair may even completely merge. This last phase has been serendipitously witnessed as astrophysical transients called luminous red novae (LRNe), allowing us to study the progenitor stars, the energetics of the outburst and the properties of the ejected material. In my talk, I will provide an overview of LRNe, their progenitor systems and their main formation scenarios, explored by recent theoretical models. Observations of these common-envelope transients show that the previous mass loss from the system is crucial to extract the angular momentum from the system. At later times, as the emission quickly fades in the optical bands, the infrared signature remains bright, revealing the formation of cold dust shells reprocessing the light of the newly coalesced star.

17 October, 2019 at 1:30 PM

A Planet Search among Kepler Giant Stars

Marie Karjalainen

(IAC/The MAGIC Telescopes, La Palma, Spain) 

Planet searches around intermediate mass K giant stars may provide us with important clues on a dependence of planet formation on stellar mass. To date over 120 exoplanets (3 % of the total) have been discovered orbiting giant stars. Unlike for a main-sequence star it is more problematic to determine the stellar mass of a giant star. Evolutionary tracks for stars covering a wide range of masses all converge to the similar region of the H-R diagram. Fortunately, the stellar mass can be derived from solar-like oscillations. The Kepler space mission was monitoring a sample of over 13,000 red-giant stars which can be used for asteroseismic studies. This represents a unique sample for planet searches as a planetary detection would mean that we can determine reliable stellar properties via asteroseismic analysis, characteristics not well known for many other planet-hosting giant stars. For this reason, in 2010 we started a planet-search program among 95 Kepler asteroseismic-giant stars, and we would like to give an overview of the roject with actual results here.

27 September, 2019 at 1:30 PM

Simultaneous J, H, K and L band spectroscopic observations of galactic Be stars

Yanina Cochetti

(Universidad Nacional de La Plata, Argentina) 

Be stars are rapidly rotating non-supergiant B-type stars whose spectra show or have shown Hα line in emission. Their infrared region is characterized by moderate flux excess and the presence of hydrogen recombination lines. Because of the small contribution of the photospheric absorption to hydrogen infrared lines, the near-infrared spectral region provides a powerful tool to infer physical properties, morphology, and dynamics of the circumstellar envelopes, which cannot easily be acquired from other spectral regions. In this talk, I will present near-infrared medium-resolution spectroscopic observations of a sample of 22 Galactic Be stars, with different spectral subtypes and luminosity classes. I will describe the main characteristics observed in the J, H, K and L bands (especially the hydrogen recombination lines from Paschen, Brackett, Pfund and Humphreys series) and the properties of the circumstellar environment derived from the shape and intensity of the line profiles.

24 September, 2019 at 1:30 PM


Despina Panoglou

(Observatorio Nacional, Rio de Janeiro, Brazil) 

Both the atmosphere and interior of Earth are largely molecular. Atoms do not exist free in the terrestrial atmosphere and whatever knowledge regarding atoms observed in space has to be acquired under laboratory conditions. On the contrary, out of Earth atoms are the norm. Whenever molecules are observed, an investigation of their existence plays a key role on the study of the ambiance where they are found. As chemistry studies the formation and destruction of bonds between atoms, astrochemistry is the study of synthesis of molecules in extraterrestrial environments. In this talk I give a short review on the reactions that involve the most common species, including ionizing agents, carbon chemistry, gas-dust interactions and photochemistry.

5 September, 2019 at 1:30 PM

Radiation Line-driven wind theory vs observations

Lydia Cidale

(Universidad Nacional de La Plata, Argentina) 

The classical theory of radiatively driven stellar winds often fairly represents the observed stellar wind conditions of massive stars. However, some discrepancies are still found between the parameters predicted by the theory and those observed in mid-B, late-B, and A-type supergiants. Inclusion of rotation and ionization in the models brought a remarkable progress in the development of the theory of stellar winds. Three types of stationary wind regimes are currently known: the classical fast solution, the $\Omega$–slow solution that arises for fast rotators, and the $\delta$–slow solution that takes place in highly ionized winds. I discuss these hydrodynamical solutions in the context of the observed wind properties of B and Be stars.

23 July, 2019 at 1:30 PM

Spectral and photometric properties of UX Ori type star WW Vul

Sabina Mammadova

(Shamakhy Astrophysical Observatory, Azerbaijan)

1 July, 2019 at 1:30 PM

First results of tunable-filter observations with MaNGaL

Alexei Moiseev

(Special Astrophysical Observatory, Nizhnij Arkhyz, Russia)

The Mapper of Narrow Galaxy Lines (MaNGaL) was developed in the Special Astrophysical Observatory of the Russian Academy of Sciences at the 1-m SAO RAS telescope and 2.5-m telescope of the Caucasus Observatory of the Sternberg Astronomical Institute of the Lomonosov Moscow State University. The instrument is based on the  low-order scanning Fapry-Perot interferometer (FPI) working as a narrow (bandwidth ~1.5 nm) filter precisely positioned at the selected emission lines. We present  the results of the first observations with MaNGaL of various Galactic nebulae and emission-line galaxies: star-formation regions and planetary nebulae, ionized cones around active galactic nuclei and galactic wings. The benefits and disadvantages of the tunable-filter observations as compared with other 3D-spectroscopy methods are considered.

21 June, 2019 at 1:30 PM

Modeling molecules in stellar environments

Rodolfo Vallverdú

(Universidad Nacional de La Plata, Argentina)

30 May, 2019 at 1:30 PM

All you ever wanted to know about hot subdwarfs

Maja Vuckovic

(Instituto de Física y Astronomía, Facultad de Ciencias,  Universidad de Valparaíso, Chile)

Hot subdwarfs stars of spectral type B (sdB) are associated with the so-called Extended Horizontal Branch forming a blue extension to the Horizontal Branch (HB). These stars correspond to the low-mass (about 0.47 Msun) objects burning He in their cores. However, they differ from HB stars mainly at the level of their residual H-rich envelope, which has been strongly reduced during the prior evolution phase, leaving only a tiny layer less massive than 0.02 Msun. As a consequence, sdB stars remain hot and compact (Teff ~ 22 000-40 000 K, log g ~ 5.2-6.2) throughout their He-burning lifetime, and never ascend the Asymptotic Giant Branch before reaching the white dwarf cooling tracks. They play an important role in our understanding of binary evolution, stellar atmospheres and interiors, and of the Galaxy itself. They are also known to pulsate and their asteroseismic properties are allowing us to probe their interiors and measure the sizes of their convective cores. In this talk I will present the current NASA Transiting Exoplanet Survey Satellite (TESS) mission and its’ contribution to the field of hot subdwarfs. I will show our fresh asteroseismic results from the TESS — we have analyzed a total of 615 hot subdwarfs and candidates that have been observed in the first 8 sectors of the TESS space mission with a cadence of 2-min and found periodicities in about 50 out of which 34 are new pulsators.

16 May, 2019 at 1:30 PM

A 5D map of the nearest open clusters from high-mass stars down to the substellar regime

Nicolas Lodieu

(Instituto de Astrofisica de Canarias, Spain)

We present a 5D map of four of the nearest clusters to the Sun: Alpha Persei (d~178 pc, 85 Myr), the Pleiades (d~135 pc; 125 Myr), the Hyades (d~46 pc; 650 Myr; Lodieu et al. 2019), and Praesepe (d~187 pc; 590 Myr). We identified bona-fide kinematic members from high-mass stars down to the hydrogen-burning limit and below (depending on the distance and age of the cluster) in the second data release of Gaia. We revised the physical sizes of the clusters, and inferred updated mean distances and velocities. We derive the luminosity and mass functions and compare them to the log-normal form of the Chabrier field mass function. We also looked at the 3D spatial distribution of members and produced movies of the new members in 3D space. We find that high-mass stars tend to be located in the central regions of the clusters while low-mass stars are more frequent beyond the half-mass radii. We clearly confirm the presence of a stream in the Hyades and the Pleiades. We also compare the age of these clusters, from the literature, with the ages that we obtain from a few white dwarfs belonging to the clusters (Lodieu et al. 2019a,b).

17 December, 2018 at 1:00 PM

On the rotation period of the O giant ξ Persei: a magnetic star?

Natallia Sudnik

(The Maxim Tank Belarusian State Pedagogical University)

Many spectral lines in OB stars show unexplained variability on a rotational timescale. This occurs for example in the so-called discrete absorption components (DACs) in UV wind-line profiles and in many wind-sensitive optical lines. This variability is generally considered to be cyclical (like sunspots), rather than periodic. The absence of strict periodicity is in accordance with the lack of evidence for a permanent magnetic field, with typical upper limits of ∼ 300 G. We aim to identify regions in spectra of the O7.5III(n)((f)) star ξ Persei that are formed very close to the star and which suffer a minimum of contamination with disturbing features like doublet overlap or irregular surface phenomena which may prevent the detection of a periodic signal. We present strong evidence for a rotation period of 2.0406 d of the ξ Per, derived from the N IV λ1718 wind line in 12 yr of IUE data. Since this period can be ruled out as due to nonradial pulsations, we predict that ξ Per has a (corotating) magnetic dipole field. We calculate the most favorable phase to attempt new magnetic measurements. In contrast to earlier work, we can exclude ∼ 4 d as the rotation period, since this is constrained by the stellar parameters. The sinusoidal behavior implies that only one magnetic pole is visible, which gives i ∼ 56, and hence β should be near 90− i = 34. We propose that the azimuthal distribution of strong DACs corresponds to the location of a magnetic pole on the surface. The crucial observational test consists of detecting a magnetic field.

5 December 2018at 2:00 PM

Using hot subdwarf binaries to constrain RLOF models

Joris Vos

(The Institute of Physic and Astronomy, University of Potsdam, Germany)

Hot subdwarf B (sdB) stars are evolved core helium burning stars that have lost most of their hydrogen envelope due to binary interaction on the red giant branch. As sdB stars in wide binary systems can only be created by stable Roche lobe overflow, they are a great test sample to constrain the theoretical models for stable mass loss on the red giant branch. We have setup a long term monitoring program using high resolution spectrographs on different telescopes to create a sample of solved long period sdB binaries. An important advantage of using wide sdB binaries in these studies is that all of them are double lined binaries, and the GAIA data shows that it is a uniform population of canonical sdB stars. This way the sdB+MS binaries provide much stronger constraints on theoretical models than many other systems. The first results of our observing program are now available. We found two main features in the orbital parameters. The majority of the systems has eccentric orbits with systems on longer orbital period having a higher eccentricity. As these systems have undergone mass loss near the tip of the RGB, circularisation theory predicts them to be circularized. Our observations suggest that efficient eccentricity pumping mechanisms are active during the mass loss phase. A second finding is a strong correlation between the mass ratio and the orbital period. Using binary evolution models, this relation is used to derive an upper limit on the critical mass ratio for stable RLOF which depends on the orbital period of the system. Furthermore a split in the P-q relation seems to indicate two different groups with somewhat different formation histories.

28 November, 2018 at 1:30 PM

HDUST and SHELLSPEC codes – two tools for modelling the stellar observables

Mohammad Ghoreyshi

(Tartu Observatory, Estonia)

31 October, 2018 at 11:00 AM

Binary stars as the key to understand planetary nebulae

Henri Boffin

(ESO Garching, Germany)

Binarity and mass transfer appear to play a key role in the shaping and, most likely, in the formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a dramatic increase in the number of post-common envelope binary central stars of PNe, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer – and accretion – prior to the common envelope phase.

14 August, 2018 at 11:00 AM

Spectral research of young stars at Shamakhy Astrophycial Observatory

Gunel Bahaddinova

(Shamakhy Astrophycial Observatory, Azerbaijan)

7 February, 2018 at 2:00 PM

OPERA tool for reduction of echelle spectra from OES

Roaman Grossova

(Masaryk University, Brno, Czech Republic)

OPERA is an open-source software package developed by a CFHT scientific group in Hawaii for reducing echelle data from ESPaDOnS. Later on, it was adapted to several other instruments, including OES. In comparison with the reduction software IRAF, OPERA was able to solve a long-standing problem of tilted lines in the OES spectra. A user-friendly GUI framework was developed for the fast routine reduction of your scientific data.

27 September 2017, at 1:00 PM

Binary stars with RR Lyrae component – why so rare?

Marek Skarka

(Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Science)

Large portion of stars of all spectral types is bound in binary systems. However, there is one spectacular exception. Among 100 000 catalogized stars of RR Lyrae type only several tens of binary candidates are known and none of them has been unambiguously confirmed yet. Could this lack of binaries be real? Why it is so difficult to discover RR Lyrae star in binary system? Are there any observational limitations? What methods are suitable for the search for such binaries? I will discuss all these questions, give an overview about the progress in last three years, and will show why many of the candidates could actually be false positives.

23 August, 2017 at 10:30 AM

Instrumentation at Astronomical Institute in the High Tatras-Slovakia

Martin Vanko

(Astronomical Institute of Slovak Academy of Sciences)

Astronomical Institute of the Slovak Academy of Sciences (AI SAS) runes several observatories located at different places in the High Tatras. Our telescopes are equipped with new high-end post-focus instruments producing valuable data in the field of the stellar and exoplanetary astronomy. First results will be presented in my talk. Finally, I will present existing and future projects between our Institutes.

18 May, 2017 at 11:00 AM

Blue atmosphere or stellar activity – is the blue atmosphere of the exoplanet GJ 3470 b real?

Silvia Kunz

(Thueringer Landessternwarte Tautenburg, Germany)

One of the big challenges in the field of exoplanet atmospheres is to distinguish the influence of stellar activity on transit measurements from real effects that can be seen in photometric measurements in different bands. Oshagh et al. (2014) assumed that an increase of planetary radii in the blue part of the spectrum can be explained with the presence of a hot plage region on the stellar surface. In particular they stated that the measured blue atmosphere of the sub-Uranus-mass low-density planet GJ 3470b could be mimicked by a plage region that covers only 2.56% of the star’s surface. We have developed a method to exclude the influence of plage regions on transit measurements. The Ca II H,K lines are tracers of stellar activity – especially of plage regions. If plage regions were occulted those lines should vary during transit. We therefore have observed one transit of GJ 3470 b with the high-resolution UVES spectrograph at the 8.2 m Very Large Telescope. We have found that the difference of the Ca II H,K lines in- and out-of-transit is only 0.67 ± 0.22% and have determined a magnetic filling factor of about 10–15%. In order to confirm the Rayleigh scattering slope we have analyzed the planet‘s lightcurve by observing three transits with the low-resolution OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias. With those almost simultaneous measurements of GJ3470b‘s transit we  were able to confirm its Rayleigh scattering slope towards the blue.”