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 (https://git.io/JqJhf) 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.