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
Astrochemistry
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).