Recent Talks

List of all the talks in the archive, sorted by date.

Tuesday June 14, 2022
Dr. Klaus-Peter Schroder
Universidad de Guanajuato (Mexico)



X-ray observations and non-detections of cool giants suggested a picture of a division
of warm solar-like giants with Coronae and cool inactive giants with cool winds instead,
first suggested by Linsky and Haish 1979. But in the meantime, photospheric magnetic field
has been detected in cool giants, and their chromospheric emission mostly surpasses the
"basal" flux, which is a minimum emission found in entirely inactive stars. Hence, the absence
of coronae in cool giants is not caused by a lack of magnetic activity! The real reason lies in
fundamental chromospheric physics, as we will show. Mayor evidence is provided by the 
Wilson Bappu effect: with lower gravity, density scale-heights increase. At the same time, 
chromospheric heating decreases and the "Athay point", at which the solar corona begins,
because chromospheric radiative cooling collapses by reaching full Hydrogen ionization, 
is not passed in giant chromospheres. A few case studies of eclipsing binaries with cool 
giants, providing a direct account of their chromospheric extent and density profiles, 
are presented to illustrate this explanation.  

Friday June 10, 2022
Dr. Enrique Joven Álvarez
Instituto de Astrofísica de Canarias


El uso de campos magnéticos no es habitual en la instrumentación desarrollada por el IAC. Sin embargo, en la actualidad dos proyectos hacen uso de los mismos con propósitos bien distintos. Por un parte DALI (PoP), un prototipo de haloscopio que busca los hipotéticos axiones (¿materia oscura?) a altas frecuencias. Y, por otra, la nueva infraestructura criogénica del laboratorio de detectores (LISA) que, para caracterizar los novedosos mKIDs, hace uso de un criostato de tipo ADR (Adiabatic Demagnetization Refrigerator), una tecnología que permite alcanzar temperaturas inferiores a 0.1 K. Y para ambas cosas necesitamos campos magnéticos intensos.


Tuesday June 7, 2022
Sepideh Eskandarlou, Dr. Mohammad Akhlaghi


LaTeX is a professional typesetting system to create a ready-to-print or publish (usually PDF!) document (usually papers!). LaTeX is the format used by arXiv, and many journals, when you want to submit your scientific papers. With LaTeX, you "program" the final document: text, figures, tables, bibliography and etc, through a plain-text (source)  file. When you run LaTeX on your source, it will parse your LaTeX source and find the best way to blend everything in a nice and professionally design PDF document. Therefore LaTeX allows you to focus on the actual content of your text, tables, plots, and not have to worry about the final design (the "style" file provided by the journal will do all of this for you automatically). This is in contrast to "What-You-See-Is-What-You-Get" (or WYSIWYG) editors, like Microsoft Word or LibreOffice Writer, which force you to worry about style in the middle of content writing (which is very frustrating). Since the source of a LaTeX document is plain-text, you can use version-control systems like Git to keep track of your changes and updates (Git was introduced in SMACK 5, SMACK 6 and SMACK 8). This feature of LaTeX allows easy collaboration with your co-authors, and is the basis of systems like Overleaf. Previously (in SMACK 11), some advanced tips and tricks were given on the usage of LaTeX. This SMACK session is aimed to complement that with a hands-on introduction for those who are just starting to use LaTeX. It is followed by SMACK 17 on other basic features that are necessary to get comfortable with LaTeX.

Lecture notes:

Tuesday May 31, 2022
Dr. Orlagh Creevey
Observatoire Cote d'Azur (France)


Gaia Data Release 3 (13 June 2022) contains astrophysical parameters for up to 1.5 billion sources derived from the low resolution BP and RP prism spectra, the high resolution RVS spectra, photometry and astrometry.

These include object classifications (star, galaxy, stellar spectral type,...), unresolved galaxies and quasar redshifts (~6 million), outlier objects, interstellar medium characterisation (extinction and DIBs), and spectroscopic and evolutionary parameters (~470 million) for a large variety of stellar types from ultra-cool dwarfs to hot OB stars.

In this talk, I will present an overview of the astrophysical parameter content of Gaia DR3 that was derived using the Astrophysical Parameters Inference System (Apsis) software. I will first give a brief description of the data, models and methods that were employed, and then I will focus on describing what type of parameters you can find in the archive and where to find them among the 30+ new tables. I will then describe the overall performance and present some pre-Gaia DR3 highlights.

Friday May 27, 2022
Dr. José Miguel Delgao Hernández
Instituto de Astrofísica de Canarias


La óptica adaptativa de GTC está en su fase final de integración y verificación. El primer instrumento que se tiene previsto utilizar es FRIDA que puede tener un retraso en su entrega, por lo que el IAC ha decidido desarrollar una cámara de infrarrojo  denominada incialmente GRANCAIN, basada en el detector de infrarojo Hawaii-2 (H2). La presente charla presenta el diseño inical del instrumento y el estado actual en el que se encuentra su desarrollo.


Tuesday May 24, 2022
Michael Himes, Dr. Matti Dorsch
Univ. of Central Florida, USA
Friedrich-Alexander University


Accelerating Computational Modeling via Neural Networks: Application to Exoplanet Atmospheric Retrieval

IIn physics and astronomy, computationally expensive forward models are often an integral part of preparing experiments/observations, analyzing data, and/or planning future instrumentation/telescopes.  In many of these cases, machine learning (ML) models, such as neural networks (NNs), can offer a significant reduction in compute time with minimal loss in accuracy.  We demonstrate this approach on the problem of exoplanet atmospheric retrieval, which involves on the order of 10^5 -- 10^6 radiative transfer (RT) model evaluations.  We find that the ML RT approach yields the same scientific conclusions as the traditional method, while requiring ~1000x less compute cost for typical setups.  We present our open-source software packages that implement this technique, and we discuss broader applications of this NN surrogate modeling approach.


The first magnetic Helium-sdOs: which mergers are magnetic?

Magnetic fields play an important role throughout stellar evolution, and among white dwarfs, the end stage of 95% of all stars, the fraction of strongly magnetic systems is larger than 20%. The origins of magnetic white dwarfs are still under discussion, but it is likely that a significant fraction of them are formed by stellar mergers.

Several types of merger remnants are thought to ignite helium fusion, such as the merger of a helium-WD (He-WD) with a second He-WD, a He/C/O hybrid WD, or a low-mass main sequence star, thus forming a hot subdwarf star. The majority of hot subdwarf stars are helium burning stars with very thin or no hydrogen envelopes. In particular, most of the hot and helium-poor He-sdO stars are thought to be formed by mergers. However, out of hundreds of hot subdwarfs studied over several decades, none showed detectable magnetic fields.
This changed recently, when four almost identical magnetic He-sdO stars were discovered, with mean field strengths between 300 and 500kG.

Why are these stars magnetic while vast majority of other He-sdOs are non-magnetic? This question is still open. In this talk I will give a short introduction to He-sdO stars and their formation and then try to highlight the differences between the four magnetic stars and their non-magnetic cousins.

Tuesday May 24, 2022
Prof. Kfir Blum
Weizmann Institute


Gravitational dynamical friction affecting the orbits of globular clusters (GCs) was studied extensively as a possible formation mechanism for nuclear star clusters in galaxies. In well-known examples that showcase this phenomenon, like the Milky Way and M31 galaxies, the medium which affects the dynamical friction is dominated by bulge stars. In comparison, the case for dynamical friction in dark matter-dominated systems is much less clear. A puzzling example is the Fornax dwarf galaxy, where the observed positions of GCs have long been suspected to pose a challenge for dark matter, dynamical friction theory, or both. We search for additional systems that are dark matter-dominated and contain a rich population of GCs, offering a test of the mechanism. A possible example is the ultra diffuse galaxy NGC5846-UDG1: we show that GC photometry in this galaxy provide evidence for the imprint of dynamical friction, visible via mass segregation. If confirmed by future analyses of more GC-rich UDG systems, these observations could provide a novel perspective on the nature of dark matter.

Friday May 20, 2022
Noelia Feijoo Amoedo
Instituto de Astrofísica de Canarias


El banco de pruebas de Óptica Adaptativa Multi-Conjugada (MCAO) para el Telescopio Solar Europeo (EST), con el que se pretende estudiar diferentes soluciones de óptica adaptativa (AO), está siendo montado e integrado en el laboratorio de AIV. El banco de pruebas emula un telescopio de 4 m con un campo de visión (FoV) de 70 arcsec y actualmente opera con una configuración SCAO. En este seminario se explicará la integración y alineado de cada subsistema que constituye el banco.


Thursday May 19, 2022
Dr. Ignacio Martin-Navarro


Black hole feedback is central to our theoretical understanding of galaxies. The energy and momentum radiated by growing supermassive black holes is expected to regulate the baryonic cycle, in particular, within massive dark matter halos, modulating gas cooling and thus star formation. Observational evidence of the role of black hole feedback remains, however, scarce, casting serious doubt on our current galaxy formation modelling. In this talk I will summarize our recent efforts trying to empirically characterize the effect of black hole feedback on galactic scales. I will describe how the combination of detailed stellar population analysis and well-known scaling relations can be used to actually constrain the physical processes behind black hole feedback. Moreover, I will also present evidence of black hole feedback acting beyond the host galaxy, further supporting the importance of black hole feedback in regulating the evolution of galaxies.

Tuesday May 17, 2022
Prof. Gastón Giribet
Universidad de Buenos Aires


In this talk, I will review the recently discovered infinite-dimensional symmetries that emerge in the near horizon region of black hole horizons. I will explain how the conserved charges associated with those symmetries carry information of the black hole, and, in particular, about its thermodynamic properties. I will focus on the case of magnetized black holes; namely, black holes that are embedded in strong magnetic fields.

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Recent Talks