Últimas charlas

Todas las charlas en el archivo, ordenadas por fecha.


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Thursday July 23, 2020
Dr. Mohammad Akhlaghi, Raúl Infante-Sainz
Instituto de Astrofísica de Canarias

Abstract

In the previous SMACKs, basic operations on the command-line were reviewed in interactive mode: where you enter one command, wait for it to finish and enter the next command. The shell's interactive mode is good for small/fast tests, but is not scalable. For example when you know the commands and parameters work and want to apply them to hundreds/thousands of targets. Shell scripts are simply plain-text files that store all the various commands that you want to be executed in sequence. They are designed precisely for the easier management of operations that are more complex than a simple command. In fact many of the commands in the Unix-like operating systems are actually shell scripts! Here will review some basic intricacies with designing robust shell scripts and avoiding common pitfalls. Also, since shell scripts are simple plain-text files, we will also do a short review of simple plain-text editors like GNU Nano and more advanced editors like Vim and GNU Emacs. Advanced editors have many useful features to simplify programming in many languages (including shell programming) and don't need complex graphic environments and can be run in the raw command-line (a major advantage when scaling your project up to supercomputers that don't have a graphic environment). For newcomers to data-intensive astronomical research, we encourage you to select an advanced editor, and master it early to greatly simply your research (in any language).

 

https://rediris.zoom.us/j/99353239065


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Tuesday July 21, 2020
Dr. Joris Vos
University of Potsdam

Abstract

Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation.
We have performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We have used a standard model for binary mass loss and a standard Galactic metallicity history.  We have achieved an excellent match to the observed period - mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a good match to the observed period - metallicity correlation.
We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.

Zoom link: https://rediris.zoom.us/j/98017007654


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Tuesday June 30, 2020
Luis Welbanks
Institute of Astronomy (University of Cambridge)

Abstract

Atmospheric compositions can provide powerful diagnostics of formation and migration histories of planetary systems. In this talk, I will present the results of our latest survey of atmospheric compositions focused on atmospheric abundances of H2O, Na, and K. We employ a sample of 19 exoplanets spanning from cool mini-Neptunes to hot Jupiters, with equilibrium temperatures between ~300 and 2700 K. We employ the latest transmission spectra, new H2 broadened opacities of Na and K, and homogeneous Bayesian retrievals. We confirm detections of H2O in 14 planets and detections of Na and K in 6 planets each. Among our sample, we find a mass-metallicity trend of increasing H2O abundances with decreasing mass, spanning generally substellar values for gas giants and stellar/superstellar for Neptunes and mini-Neptunes. However, the overall trend in H2O abundances, is significantly lower than the mass-metallicity relation for carbon in the solar system giant planets and similar predictions for exoplanets. On the other hand, the Na and K abundances for the gas giants are stellar or superstellar, consistent with each other, and generally consistent with the solar system metallicity trend. The H2O abundances in hot gas giants are likely due to low oxygen abundances relative to other elements rather than low overall metallicities, and provide new constraints on their formation mechanisms. Our results show that the differing trends in the abundances of species argue against the use of chemical equilibrium models with metallicity as one free parameter in atmospheric retrievals, as different elements can be differently enhanced.


Zoom link: https://rediris.zoom.us/j/92734027825


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Thursday June 25, 2020
Prof. Francesco Shankar
University of Southampton

Abstract

It has been claimed for decades that almost all galaxies in the local Universe host at their centre a supermassive black hole (SMBH) the mass of which appears to be tightly correlated with the stellar mass and the random motion ("velocity dispersion", sigma) of the stars in the host galaxy. In this talk I will first review the state of the art in this field. I will then highlight that significant biases affect local black hole-galaxy correlations.  I will specifically show that the majority of quiescent early-type galaxies with central black hole dynamical mass estimates have significantly higher velocity dispersions than local typical galaxies of similar stellar mass. Through aimed Monte Carlo simulations, residual analysis, and the comparison with latest AGN clustering measurements, I will then illustrate that present data sets of active and quiescent galaxies strongly favour on average lower SMBH masses than previously thought, and point to velocity dispersion as more ``fundamental'' than galaxy stellar mass, galaxy size or Sérsic index. I will then move on discussing the main implications of these findings, in particular: 1) The implied black hole radiative efficiencies and obscured fractions; 2) the consequences on feedback from active black holes and SMBH binary gravitational waves; 3) the connection to cosmological models that rely on velocity dispersion, rather than stellar mass, as main driver of black hole growth.

Zoom link:  https://rediris.zoom.us/j/97154760685


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Tuesday June 23, 2020
Javier de Miguel Hernández
Instituto de Astrofísica de Canarias

Abstract

Axion detection would be one of the most exciting moments in the entire history of science. This hypothetical particle can simultaneously explain two fundamental problems in Modern Physics: the mystery of dark matter and the CP problem of the strong interaction. In this talk, I will provide an overview of the status for the search for axions and I will explain how the DALI experiment can go beyond these frontiers.

 

https://rediris.zoom.us/j/98051612614



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Tuesday June 9, 2020
Prof. Mariangela Bernardi
University of Pennsylvania

Abstract

Stellar populations vary across the galaxy population. However, even within a single galaxy, there are stellar population gradients which spatially resolved spectroscopic studies are beginning to reveal. The MaNGA survey permits a study of gradients in a sample of early-type galaxies which is nearly two orders of magnitude larger than previous work. This allows us to quantify the effects of gradients on estimates of the stellar and dynamical masses of these galaxies, and to study how age and abundance gradients, and thus star formation and assembly histories, vary across the population. In this talk I will present results from our recent analysis.

 

zoom link: https://rediris.zoom.us/j/97614680345


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Tuesday June 2, 2020
Prof. Manuela Temmer
Institute of Physics, University of Graz

Abstract

The Sun is an active star that influences the Earth as well as the entire solar system. Most dynamic phenomena on the Sun are observed as coronal mass ejections (CMEs) and flares. CMEs present massive clouds of magnetized plasma having speeds up to a few thousand km/s, that may propagate over Sun-Earth distance within less than a day and may cause strong geomagnetic disturbances at Earth (Space Weather). As CMEs are optically thin, using remote sensing data measurements of intrinsic properties such as speed, width, propagation direction, density etc. are severely affected by projection effects. By combining image data with in-situ measurements, valuable information is provided enabling CME 3D analyzes, and with that facilitate a better quantification of the uncertainties in the observational measurements that are used to feed CME propagation models. With that, a much better understanding of CMEs as they propagate in interplanetary space could be gained.

The talk will cover the physisc about CME-flare phenomena, the interplanetary propagation behavior of CMEs related to the background solar wind, and Space Weather forecasting.

Zoom link: https://rediris.zoom.us/j/92170419398


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Thursday May 28, 2020
Prof. Avishai Dekel
Hebrew University of Jerusalem

Abstract

This talk will address the preferred mass and time for galaxy formation, in dark-matter haloes similar to that of the Milky way but when the Universe was a few Gigayears old. It is proposed that this is due to the interplay between two mechanisms, first *supernova* feedback that removes gas from the galaxy, and second *hot gas* in the deep potential well of massive haloes that suppresses cold gas supply to the galaxy, the two being effective in galaxies of lower and higher masses respectively. Cosmological simulations reveal that the same mechanisms are responsible for a robust sequence of events were galaxies undergo a dramatic gaseous *compaction*, sometimes caused by mergers, into a compact star-forming “blue nugget”. This triggers inside-out *quenching* of star formation, which is maintained by a hot massive halo aided by black-hole feedback, leading to todays passive elliptical galaxies. The blue-nugget phase is responsible for drastic transitions in the main galaxy structural, kinematic and compositional properties. In particular, the growth of the *black hole* in the galaxy center, first suppressed by supernova feedback when below the critical mass, is boosted by the compaction event and keeps growing once the halo is massive enough to lock the supernova ejecta by its deep potential well and the hot halo. The compaction events also trigger the formation of extended rings in high-z massive galaxies. These events all occur near the same characteristic halo mass, giving rise to the highest efficiency of galaxy formation and black-hole growth at this magic mass and time.

 

Zoom link:  https://rediris.zoom.us/j/98813487304


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Tuesday May 26, 2020
Dr. Mohammad Akhlaghi, Raúl Infante-Sainz, Joseph Putko
Instituto de Astrofísica de Canarias

Abstract

 

Gnuastro is an official GNU package that is currently maintained at the IAC. It is a large collection of programs to enable easy, robust, fast and efficient data analysis directly on the command-line. For example it can perform arithmetic operations on image pixels or table columns/rows without having to write programs, visualize FITS images as JPG or PDF, convolve an image with a given kernel or matching of kernels, perform cosmological calculations, crop parts of large images (possibly in multiple files), manipulate FITS extensions and keywords, and perform statistical operations. In addition, it contains programs to make catalogs from detection maps, add noise, make mock profiles with a variety of radial functions using monte-carlo integration for their centers, match catalogs, and detect objects in an image among many other operations. Gnuastro is written to comply fully with the GNU coding standards and integrates well with all Unix-like operating systems. This enables astronomers to expect a fully familiar experience in the building, installing and command-line user interaction that they have seen in all the other GNU software that they use (core components in many Unix-like/POSIX operating systems). In this SMACK, we will introduce Gnuastro and demonstrate a selection of its commonly used features. Relevant links are as follows. Lecture-notes: in https://gitlab.com/makhlaghi/smack-talks-iac/-/blob/master/smack-3-gnuastro.md, Gnuastro's main webpage: https://www.gnu.org/s/gnuastro, Gnuastro documentation: https://www.gnu.org/s/gnuastro/manual, Gnuastro tutorials: https://www.gnu.org/s/gnuastro/manual/html_node/Tutorials.html

 

Zoom link https://rediris.zoom.us/j/94454701469


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Thursday May 21, 2020
Dr. Ana Escorza Santos
KU Leuven

Abstract

About half of the stars in our Galaxy are born in binary systems meaning that their evolution might be affected by the presence of a companion. Many aspects of binary interaction are still unknown so understanding the products that result from interacting systems is crucial to unravel the physical mechanisms involved. A prototypical example of such post-interaction binary systems in the low- and intermediate-mass regime are Barium (Ba) stars. Ba stars are main-sequence or giant stars which show an enhancement of chemical elements that should not yet be overabundant at these evolutionary stages. Currently, it is widely accepted that these chemicals were transferred from a more evolved companion during a phase of mass transfer and that this companion evolved into a cool white dwarf. Understanding the orbital properties of these systems, as well as the stellar properties of the Ba star and its polluter, is the key to the system’s interaction history.

In the last years, the synergy between Gaia data, of unprecedented quality, high-resolution spectroscopy, long-term radial-velocity monitoring programmes, and state-of-the-art stellar and binary evolution models has contributed to a better understanding of the properties of Ba stars and provided new observational constraints to theoretical studies. The new Hertzsprung-Russell diagrams of Ba stars allowed us to accurately determine their evolutionary status and their masses. Additionally, we have recently determined the orbital properties of many main-sequence Ba stars, much less studied until now than their giant counterparts, which led to a thorough comparison of the properties of the two samples. The comparison between the distributions of masses, periods and eccentricities that resulted from this analysis allowed us to investigate the evolution of Ba-star systems between these two phases. Our models show that a second stage of binary interaction, this time between the main-sequence Ba star and its white-dwarf companion, also takes place in some systems, affecting the distribution of orbits observed among Ba giants.

Zoom link:   https://rediris.zoom.us/j/96557655189



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