Latest talks

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


klaus_peter_schroder_180906s
Thursday September 6, 2018
Prof. Klaus-Peter Schroder
Universidad de Guanajuato

Abstract

Tigre is a 1.2m f:8 RC robotic telescope designed to do spectroscopic monitoring of dynamical processes, mainly in stellar astrophysics, for objects of less than 2" of size and brighter than magnitude 10...11. Its 2-channel (red/blue) echelle spectrograph HEROS has a resolution of 20,000 and covers simultaneously almost the whole range from the near IR to near UV (8800-3800A). It can also be used to determine the exact physical properties of stellar samples of interest, comparing high s/n (80-120) spectra with PHOENIX models and iSpec analysis. The large amount of spectroscopic data ideally serves a large variety of undergraduate and graduate thesis projects. This presentation gives a brief insight into this dedicated, yet economic international project of the universities of Hamburg, Guanajuato and Liege and the opportunities it has to offer to the international community.


alejandro_suarez_180905s
Wednesday September 5, 2018
Dr. Alejandro Suárez Mascareño
Observatoire Astronomique, Université de Genève

Abstract

The search of Earth-like extrasolar planets approaches a key moment in its history. With the arrival of ESPRESSO (observing already!), the possibility of detecting Earth-like planets around solar-type stars is at last a reality, and the opportunities to characterize earth-like planets and super-Earths are more numerous than ever. High precision radial velocity (RV) measurements (better than 1 m s−1 for instruments like HARPS and HARPS-N) have given astronomers the possibility of detecting and characterizing small exoplanets for a few years, down to the mass of the Earth, when orbiting M-dwarfs at short orbital periods, or a few Earth-masses at longer periods. The arrival of the new generation of instruments (ESPRESSO) brings a revolution in precision, to the level of 5-10 cm s-1, allowing for the detection or characterization of Earth-mass planets at longer orbital periods, in the habitable zone of Sun-like stars. At these levels of precision, signals induced by stellar activity in the RV curves become the most important limiting factor, even in the case of magnetically quiet stars. Stellar activity can induce apparent Doppler shifts of the stellar spectrum, which cause periodic signals that range from less than one to dozens of meters per second. The correct detection and characterization of the different star-induced signals and their effect in the RVs is one of the most important steps to detect and properly characterize low-mass exoplanets, and its importance will greatly increase with increased precision, as even in the case of the quietest stars, these signals will surface. Unveiling the population of small-mass planets in the range of super-Earths and smaller, especially at long orbital periods (close to the habitable zone of their stars and beyond), is a key step to understand the formation of planetary systems. To really paint the full picture of the systems, and accurately derive their parameters, we need to identify and model together the planetary companions and activity signals present in the data. I will present the current state of the field, the challenges and the techniques to overcome them, focusing on the efforts that I have made during the last years.


alessandro_spallicci_180904s
Tuesday September 4, 2018
Dr. Alessandro D.A.M. Spallicci
Université d’Orléans, Observatoire des Sciences de l’Univers en Région Centre,Centre Nationale de la Recherche Scientifique, Laboratoire de Physique et Chimie de l’Environnement et de l’Espace

Abstract

Inexplicable observations on the Universe prompt cosmologists to propose either ad hoc explanationsas dark matter and energy maintaining general relativity entirely valid, or to propose alternatives togeneral relativity, without evoking dark ingredients [7]. But for the former investigation track,experimental confirmations are missing, and for the latter general relativity continues to predictobservations with exactitude.Confronted with this dichotomy, and with a multi-parametrised cosmology, we consider legitimate alsoto investigate on the nature of the main messenger from the Universe, light, that we stick so far tointerpret as Maxwellian. But the photon in the Standard Model singles out as the only massless freeparticle, and the waves emerge from a linear theory of the XIX century. What if light were to bedescribed by a different theory?Results on testing non-Maxwellian electromagnetism (either massive initiated by de Broglie and Procaor non-linear by Born and Infeld, Heisenberg and Euler) include setting photon mass upper limits fromthe modified Ampère law in solar wind through the Cluster spacecraft [8], or from frequency dependentgroup velocities of photons from Fast Radio Bursts [2,5]. Future nanosatellite swarms operating in anew radio-astronomy window, 10 KHz - 10 MHz, [1] might provide a significant contribution.De Broglie formulated a photon mass already in 1922 and in the later year he estimated such mass to belower than 10 -53 kg, surprisingly close to the actual limits established by the Particle Data Group.Meanwhile, an effective photon mass emerges when Lorentz symmetry is broken in (possibly Super-Symmetrised) Standard Model Extensions, as well as bi-refringence and dissipation [3,4].Non-linear effects as polarisation dependent frequency shifts in strong magnetic field in Magnetars havebeen analysed too [6], but we are now progressing in modelling a general non-linear electromagnetismLagrangian and look whether wave dissipation in vacuum may occur, possibly in presence of abackground field. When wave dissipation is transferred into photon energy description, we cannot avoidconsidering, additional, non-cosmological redshifts.

 

[1] Bentum M.J., Bonetti L., Spallicci A.D.A.M., 2017. Adv. Sp. Res., 59, 736.[2] Bonetti L., Ellis J., Mavromatos N.E., Sakharov A.S., Sarkisyan-Grinbaum E.K.G., Spallicci A.D.A.M., 2016. Phys. Lett.B, 757, 548.[3] Bonetti L., dos Santos Filho L.R., Helayël-Neto J.A., Spallicci A.D.A.M., 2017. Phys. Lett. B, 764, 203.[4] Bonetti L., dos Santos Filho L.R., Helayël-Neto J.A., Spallicci A.D.A.M., 2017. arXiv:1709.04995[5] Bonetti L., Ellis J., Mavromatos N.E., Sakharov A.S., Sarkisyan-Grinbaum E.K.G., Spallicci A.D.A.M., 2017. Phys. Lett.B, 768, 326.[6] Bonetti L., Perez Bergliaffa S.E., Spallicci A.D.A.M., 2017, 14 th Marcel Grossmann Meeting, 12-18 July 2015 Roma, M.Bianchi, R.T. Jantzen, R. Ruffini Eds., World Scientific, 3531.[7] Capozziello S., Prokopec T., Spallicci A.D.A.M., 2017. Aims and Scopes of the Special Issue: Foundations of Astrophysicsand Cosmology, Volume 47, Issue 6.[8] Retinò A., Spallicci A.D.A.M., Vaivads A., 2016. Astropart. Phys., 82, 49.


Natalia_shagatova_180726s
Thursday July 26, 2018
Dr. Natalia Shagatova
stronomical Institute Slovak Academy of Sciences (Slovakia)

Abstract

In symbiotic stars, two different physical regimes of circumstellar
material exist side by side. Around the donor red giant star, there is a
cool and dense conical region of neutral wind. During quiescent phases,
the rest of the wind from the donor is ionized by its companion, in most
cases, a very hot and luminous white dwarf powered by accretion from the
giant's wind. Mass outflow from the majority of cool components in
symbiotic binaries is still not understood well. Some information about
the distribution of circumstellar matter can be obtained by measuring the
neutral hydrogen column densities from Rayleigh scattering along the
multiple lines of sight. I will present the wind velocity profiles derived
from the measured column densities of neutral hydrogen for two quiet
high-inclination symbiotic systems, EG And and SY Mus. The column density
models indicate the wind focusing towards the orbital plane and allow to
investigate the origin of the asymmetric UV continuum light curve profiles
of symbiotic stars.


sugata_kaviraj_180725s
Wednesday July 25, 2018
Dr. Sugata Kaviraj
University of Hertfordshire

Abstract

A new era of observational surveys that are both deep and wide is poised to revolutionise our understanding of galaxy evolution, by enabling, for the first time, statistical studies of the low-surface-brightness (LSB) Universe. While largely inaccessible in past wide-area surveys like the SDSS (due to their lack of depth), the uncharted LSB regime holds the key to a complete understanding of galaxy evolution. While small, deep surveys and new instruments have long hinted at the existence of a rich population of LSB galaxies below the surface-brightness limits of surveys like the SDSS, the mechanisms that create these galaxies remain unexplored. We use, Horizon-AGN, a cosmological hydrodynamical simulation to study how and why low-surface-brightness galaxies (LSBGs;  mu > 23 mag arcsec^-2), and in particular, the recently studied population of ultra-diffuse galaxies, form and evolve over time. For stellar masses greater than 10^7  MSun, LSBGs contribute 85, 10 and 11 per cent of the local number, mass and luminosity densities respectively. When controlled for stellar mass, today's LSBGs have similar dark-matter fractions and angular momenta to their high-surface-brightness (HSB) counterparts but larger (x 2.5) effective radii and lower (< 5% vs 30%) star-forming gas fractions. Interestingly, LSBGs originate from the same progenitors as HSB systems at high redshift (z~3). However, LSBG progenitors form stars more rapidly at early epochs. The higher resultant supernova energy injection flattens their gas-density profiles which, in turn, creates shallow stellar profiles that are more susceptible to tidal processes. After z~1, harassment and tidal heating steadily expand LSBG stellar distributions and quench star formation by heating cold gas, creating the population of diffuse, gas-poor LSB systems seen today. In clusters, ram-pressure stripping provides an additional mechanism that assists in gas removal in LSBG progenitors. The study of LSBGs will be one of most exciting advances in galaxy evolution in the coming years. This study offers insights into the demographics and properties of a population of galaxies that will have a transformational impact on our understanding of galaxy evolution.


knut_olsen_180724s
Tuesday July 24, 2018
Dr. Knut Olsen
NOAO

Abstract

I will present a story of how a chance observing run kicked off more than a decade of exploration of the dynamics of the Magellanic Clouds, leading to the discovery, from line-of-sight velocities and Ca triplet abundances, that ~5% of the stars in the inner LMC actually appear to belong to the SMC. The existence of this debris agrees well with a scenario in which the Clouds collided directly with each other, and provides a natural explanation for the star formation activity in 30 Doradus and the LMC microlensing signal, and may be linked with star clusters with multiple populations.  I will show how Gaia DR2 resolves the ambiguity present in our line-of-sight velocity data and allows us to consider the geometry of the debris.  These results were motivation for the SMASH survey, with which we are mapping the debris from the LMC/SMC interaction, exploring their star formation histories, and have discovered new structures around the Clouds and potential companion dwarf galaxies.


vanessa_hill_180718s
Wednesday July 18, 2018
Vanessa Hill

Abstract

Understanding formation and evolution of galaxies on the galactic and sub-galactic scales is a key question to modern astrophysics. The L-CDM concordant cosmology paradygm, sucessful in predicting many large scale observables of the Universe, starts to fail at the galactic or sub-galactic scales (e.g., missing satellites problems, planes of satellites, central dark matter density profiles of galaxies, etc.). The Milky Way, with its system of dwarf galaxy satelites, is the environment in which we can hope to constrain in most details the physical processes that play a role in the formation and evolution of galaxies, encoded in the location, kinematics and chemistry of individual stars, a field often referred to as Galactic Archaeology. Taking the example of the Sculptor dwarf galaxy, for which a wealth of complementary data are available, from wide field photometry to sizeable spectroscopic samples, and now also astrometric Gaia data, I will discuss our current observational understanding of how chemical enrichment proceeds at the smalest scales. 

In the context of the Gaia space mission and ground based large spectroscopic surveys such as WEAVE@WHT,  Galactic Archaeology, is living a revolution. I will review some of the most prominent science cases for a Galactic Archaeology survey with the WEAVE wide field multi-object facility for the WHT, and highlight how this complements the Gaia astrometric mission. 


elena_donghia_180717s
Tuesday July 17, 2018
Dr. Elena D'Onghia
Universidad Wisconsin-Madison

Abstract

By providing information on distances and proper motions for one billion stars, the Gaia satellite allows us to investigate the major unsolved challenges in galaxy formation: the nature of dark matter, the origin of Galactic spiral activity and its relation to the bar, and more generally the history of the Milky Way. 
My research aims to develop a theoretical approach to modeling and exploiting the big data and address problems at the forefront of Galactic Dynamics at various scales. What is the origin of the spiral activity in the Milky Way? How are all of these perturbations to the structure of the Galaxy coupled to each other directly and through the dark-matter halo?  I will also present my ongoing work on statistical techniques of big-data analysis and advanced numerical simulations used to interpret the evolution of star clusters and discover streams in the stellar disk of the Milky Way.


Manuel_Vazquez_Jorge_Sanchez_180705s
Thursday July 5, 2018
Manuel Vazquez Abeledo, Jorge Sanchez Almeida
IAC

Abstract

Principios del siglo XXI, en una fecha por determinar. Una desconocida deja en la biblioteca del IAC siete cuadernos de observaciones astronómicas realizadas más de cien años antes (1886 – 1891), en Madrid y Santa Cruz de Tenerife, por un tal Juan Valderrama y Aguilar (JVyA). Los cuadernos duermen en la biblioteca otros diez años hasta que los descubrimos por casualidad. Nos sorprende la calidad y meticulosidad de los dibujos que ilustran los cuadernos, el hecho de que trabajos de Juan Valderrama son citados en el ADS (Astrophysics Data System) y, sobre todo, el que siendo nosotros astrónomos profesionales del IAC, jamás hubiéramos oído hablar de él. ¿Podría haber vivido en Santa Cruz un astrónomo del que la historia oficial de la astronomía Canaria no tuviera noticia alguna? La respuesta a la pregunta anterior es "sí". JVyA es un completo desconocido para la historia oficial, pero tiene una biografía científica digna de ser recordada. Fuera de los ambientes universitarios y de la ciencia oficial, JVyA estaba, sin embargo, bien conectado con el mundo de la astronomía moderna de la época. Suyo es el que puede ser considerado el primer artículo de astronomía publicado por un canario en una revista internacional (Valderrama, 1886, L’Astronomie, Vol. 5, Pág. 388), y lo hace cuando tiene sólo 17 años. Hemos escrito una breve biografía de JVyA que reivindica su figura de astrónomo, y que será publicado por el Cabildo de Tenerife. En la charla queremos presentar a JVyA así como alguna de sus contribuciones astronómicas.


mauro_donofrio_180703s
Tuesday July 3, 2018
Prof. Mauro D'Onofrio
Dept. of Physics and Astronomy, University of Padova

Abstract

I will review the properties of nearby early-type galaxies and galaxy clusters showing the most interesting observed parallelisms, such as the Sersic behavior of the light profiles, the color-magnitude diagram and the main scaling relations. I will show a comparison with the data extracted from the ILLUSTRIS simulation and present the constraints to the star formation history that are necessary to obtain a reliable distribution of galaxies in the color-magnitude diagram.



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