List of all the talks in the archive, sorted by date.
A fully consistent picture of the SNe progenitor evolution can't be found yet. Such scenario increases in complexity as deep and wide surveys, using latest generation instruments, discover new types of transients with unprecedented observational characteristics. For example, the wide heterogeneity observed in interacting transients in the recent years. Still, the nature of these transients is largerly debated: Some are without doubt genuine core-collapse SNe, while others may be giant non-terminal outburst from luminous blue variables. The talk includes my contribution to this topic with data of the recent objects of study and the conclusions extracted from their analysis.
The Milky Way (MW) galaxy is not much different from its faraway cousins. However, our position within the MW allows us to study the properties of its stellar populations with exquisite detail in comparison to extragalactic sources. The bulge of the MW (i.e. the stellar population within ~3 kpc from the Galactic center) is the most massive stellar component of the MW hosting very old stars (>10 Gyr), therefore the study of its stellar population properties can shed light on the formation and evolution of the MW as a whole, and of other spiral galaxies at large.
So far, there is a general consensus on the global kinematic, chemical and structural properties of the bulge populations, however the age, or rather, the distribution of the ages of the stars in the bulge is yet to be completely understood.
We aimed at addressing the questions 'How old is the bulge?' and 'Is there a spatial age gradient in the bulge?' through the determination of the stellar ages in the different fields sparsely distributed within a region of 300 deg² centered on the bulge.
We use images from the VISTA Variables in the Vía Láctea (VVV) survey, based in near infrared passbands, to extract accurate magnitude and color of half a billion stars in the bulge area using point spread function fitting.
The newly derived photometric catalogs, used in addition to probe the extinction towards the bulge, will be made publicly available to the entire community.
The contribution of the intervening disk population along the bulge lines of sight has been detected and removed by using a statistical approach in order to obtain a final stars sample that is representative of the bulge population only.
The determination of the stellar ages in different fields is provided through the comparison between the observations and synthetic stellar population models, which have been carefully tailored to account for the observational effects (i.e. distance dispersion, differential reddening, photometric completeness, photometric and systematic uncertainties).
The simulations leading to the construction of synthetic populations have been carried out by using two different methods: i) a model that uses a spectroscopically derived metallicity distribution functions as prior, leaving the age as the only free parameter; ii) a genetic algorithm that finds the best solution within all possible combinations of age and metallicity (i.e. uniform prior in age and metallicity using IAC-POP/Minniac suite).
We ultimately find that the bulge itself appears to be on average old (>9.5 Gyr) throughout its extension (|l| < 10° and -10° < b < +5°), with a mild gradient of about 0.16 Gyr/deg towards the Galactic center.
The Exoplanet group in Ondrejov, CZ was founded in 2016. The astronomical Institute Ondrejov operates a 2-m telescope equipped with an Echellespectrograph. In the seminar an overview about the potential of our ground based support program for exoplanetary missions will be presented along with first results from 2017/2018 campaign. Furthermore, our institute in cooperation with Tautenburg Observatory and Universidad Catolica de Chile plans to design a new spectrograph for 1.52m telescope at ESO La Silla observatory, Chile which should contribute to candidate vetting process for PLATO in the future and most certainly also for TESS.
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.
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.
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 . 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 , 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,  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 , 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.
 Bentum M.J., Bonetti L., Spallicci A.D.A.M., 2017. Adv. Sp. Res., 59, 736. 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. Bonetti L., dos Santos Filho L.R., Helayël-Neto J.A., Spallicci A.D.A.M., 2017. Phys. Lett. B, 764, 203. Bonetti L., dos Santos Filho L.R., Helayël-Neto J.A., Spallicci A.D.A.M., 2017. arXiv:1709.04995 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. 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. 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. Retinò A., Spallicci A.D.A.M., Vaivads A., 2016. Astropart. Phys., 82, 49.
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.
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.
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.
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.
- Galactic thick disks in the Fornax ClusterDr. Francesca PinnaWednesday April 24, 2019 - 15:00 (OMEGA room)
- Investigating Galaxy Evolution with Deep Learning Dr. Marc Huertas CompanyThursday May 9, 2019 - 10:30 (Aula)