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.