Past Pizza Lunches

Número de entradas: 153

05
Abril 2019

White dwarfs in the Gaia era


Inicio: 12:15h
Ponente: Alberto Rebassa Mansergas (Universitat Politècnica de Catalunya)
Lugar: Sala Alberto Lobo

The vast majority of stars will end, or have ended, their lives in the form of a white dwarf. These objects have the average size of the Earth, however they can be more massive than the Sun. This makes white dwarfs to be extremely dense and to have exceptional properties. In this talk we will study the…
Inicio: 12:15h
Ponente: Alberto Rebassa Mansergas (Universitat Politècnica de Catalunya)
Lugar: Sala Alberto Lobo

The vast majority of stars will end, or have ended, their lives in the form of a white dwarf. These objects have the average size of the Earth, however they can be more massive than the Sun. This makes white dwarfs to be extremely dense and to have exceptional properties. In this talk we will study the physical characteristics of these exotic objects and we will see how the data provided by the Gaia satellite is helping us to significantly increase our understanding of white dwarfs.
 
22
Marzo 2019

Does the size matter?: The case of HH80-81 disk


Inicio: 12:15h
Ponente: Nacho Añez López (Institut de Ciències de l'Espai (CSIC-IEEC))
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)

Understanding how high-mass stars form and evolve is one of the hot topics in astrophysics, due to the high impact that these objects have in the life of a galaxy. It is well known that low-mass stars are formed through an accretion disk which transport gas and dust from the envelope of the system…
Inicio: 12:15h
Ponente: Nacho Añez López (Institut de Ciències de l'Espai (CSIC-IEEC))
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)

Understanding how high-mass stars form and evolve is one of the hot topics in astrophysics, due to the high impact that these objects have in the life of a galaxy. It is well known that low-mass stars are formed through an accretion disk which transport gas and dust from the envelope of the system to the protostar. HH80-81 seems to be very similar to the disk-jet systems found in low- and intermediate-mass protostars presenting a highly collimated and well-defined jet, a compact dust disk clearly perpendicular to the jet and possible rotating motions of the molecular gas around the massive protostar. The linear polarization of the dust emission is detected almost all along the disk, and its properties suggest that dust polarization is produced mainly by selfscattering. Polarization characteristic suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 microns. We applied disk models that have been successfully explained disks around low-mass prototstars as those developed by D'Alessio et al. (2001, 2006). These models satisfactorily explain the ALMA image at 1.14 mm with a massive central object (~20 Msun) and a massive disk (~7 Msun). The models shows that in first approximation the high-mass star formation process seems to be a scale up version of the low-mass star-formation scenario.
15
Marzo 2019

Chemical Complexity in Space and Earth Induced by Solid State Surfaces. Investigations by means of Quantum Chemistry


Inicio: 12:15h
Ponente: Albert Rimola (Chemistry Department, UAB)
Lugar: Sala Alberto Lobo

Our universe is molecularly rich [1-3], comprising from the most essential molecules (such as H2, H2O and NH3), passing through complex organic molecules (namely, COMs, molecules between 6 – 13 atoms where at least one is C rendering its organic character), reaching more evolved complex organic compounds,…
Inicio: 12:15h
Ponente: Albert Rimola (Chemistry Department, UAB)
Lugar: Sala Alberto Lobo

Our universe is molecularly rich [1-3], comprising from the most essential molecules (such as H2, H2O and NH3), passing through complex organic molecules (namely, COMs, molecules between 6 – 13 atoms where at least one is C rendering its organic character), reaching more evolved complex organic compounds, in which in some cases are of biological relevance, such as amino acids, nucleobases and sugars. Formation of early Solar-type systems involves successive steps, mainly represented by the prestellar, protostellar, protoplanetary disk, and planetesimal and planet formation phases. This evolution goes hand-in-hand with an increase of the molecular complexity, in which more complex molecules form at each step [4]. The usual interpretation of the complex scenario of molecular reactions occurring in space is through a cascade of gas-phase reactions [5]. Nevertheless, it has since long recognized, with kinetic models, that gas-phase process alone cannot justify the abundance in the universe of even the simplest molecule, H2, but resort to reactions occurring on cosmic grain surfaces is mandatory to reconcile prediction with observation [6]. Accordingly, a key role of the chemical complexity is also played by cosmic solid state materials, as their surfaces provide catalytic sites that favor pivotal chemical reactions. A possible fate of the cosmic biomolecules is to reach Earth through meteorites or comets to become one of the building blocks for the formation of the pristine biopolymers. Biopolymer formation is very difficult, as these reactions are thermodynamically disfavoured in water with high kinetic barriers [7]. However, it has been long proposed that naturally-occurring minerals could have played a key role favouring these reactions, as they present specific surface sites that can adsorb and concentrate prebiotic organic compounds [8,9]. Computational quantum chemical methods may help in clarifying possible reactive channels towards molecule formations using proper atomistic structural models of the systems (including the extended surfaces), as they allow us to characterize chemical paths along the potential energy surfaces.In the talk, we discuss few examples from our own work for simulating essential molecules and COMs on interstellar grains as well as formation of polypeptides via condensation reaction of amino acids on mineral surfaces.
08
Marzo 2019

Pulsations in (few, exotic) hot subdwarf stars


Inicio: 12:15h
Ponente: Marcelo Miller Bertolami (Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata)
Lugar: Sala Alberto Lobo

Most hot subdwarf stars (spectral types sdBs, sdOs) are core helium-burning stars at the blue end of the horizontal branch with masses slightly below half a solar mass. They are found in all Galactic stellar populations and are sufficiently common to account for the UV-upturn of early-type galaxies.…
Inicio: 12:15h
Ponente: Marcelo Miller Bertolami (Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata)
Lugar: Sala Alberto Lobo


Most hot subdwarf stars (spectral types sdBs, sdOs) are core helium-burning stars at the blue end of the horizontal branch
with masses slightly below half a solar mass. They are found in all Galactic stellar populations and are sufficiently common to
account for the UV-upturn of early-type galaxies. Yet, the evolutionary channel leading to them does not seem to be the same
in all stellar populations. While in the Galactic Field half of the sdBs reside in close binaries, most hot subdwarfs in galactic
clusters seem to be the outcome of single stellar evolution. 
Thanks to the discovery of  multi-periodic brightness variations in a significant fraction of these stars, asteroseismology has become a 
useful tool to constrain the internal structure of these stars and consequently their evolutionary histories.
Two main families of sdB pulsators exist, the hot rapid pulsators (sdBVr, pressure modes, with periods 80–400 s) and the
cold slow pulsators (sdBVs, gravity modes with periods 2500-7000s). Pulsations in both groups of stars of can be
explained by the action of the kappa mechanism acting on the opacity bump due to M-shell ionizations of iron group
elements.  While the vast majority of pulsating sdB stars belong to these two families there exists a small group of He-rich hot
subdwarfs that display anomalous pulsation properties that cannot be explained by this mechanism.
In this talk I will first review properties of hot subdwarf stars as well as the evolutionary channels proposed for their
formation. Then I will describe the main properties of hot subdwarf pulsators as well as the driving mechanism behind their
pulsations.  Finally, I will discuss recent work we have been doing to explain the pulsations in He-rich hot subdwarfs and to
test possible evolutionary channels for the formation of He-rich hot subdwarfs.
 
01
Marzo 2019

On the history of the Universe expansion: Edwin Hubble, Georges Lemaitre and Vesto Slipher


Inicio: 12:15h
Ponente: Emilio Elizalde
Lugar: Sala Alberto Lobo

In this talk, a follow up of previous ones, I will present my final conclusions about the role of each of the contributors to the discovery of the Universe expansion, concentrating in particular on the seminal role of Vesto Slipher, and on the ideas that led to the even more important finding that…
Inicio: 12:15h
Ponente: Emilio Elizalde
Lugar: Sala Alberto Lobo


In this talk, a follow up of previous ones, I will present my final conclusions about the role of each of the contributors to the discovery of the Universe expansion, concentrating in particular on the seminal role of Vesto Slipher, and on the ideas that led to the even more important finding that our Universe had an origin.
 
22
Febrero 2019

Asteroseismology of Red-Giant and Solar-Analogue stars in the golden age of space photometry and ground-based spectroscopy


Inicio: 12:15h
Ponente: Paul Beck (Instituto de Astrofisica de Canarias)
Lugar: Sala Alberto Lobo

Asteroseismology is a powerful tool to study structure and dynamics of the stellar interior as well as their evolution. Such analysis can be done for thousands of stars in differing evolutionary stages from data of unprecedented photometric quality, provided by the NASA Kepler space telescope. In particular,…
Inicio: 12:15h
Ponente: Paul Beck (Instituto de Astrofisica de Canarias)
Lugar: Sala Alberto Lobo

Asteroseismology is a powerful tool to study structure and dynamics of the stellar interior as well as their evolution. Such analysis can be done for thousands of stars in differing evolutionary stages from data of unprecedented photometric quality, provided by the NASA Kepler space telescope. In particular, the study of stochastic, solar-like oscillators in combination with high-resolution ground-based spectroscopy has led to numerous breakthroughs in our understanding of the stellar structure and evolution of solar-like stars and is an important tool to characterize the host stars of exoplanets.

In this talk, the principles of asteroseismology of solar-like oscillators will be discussed on the basis of case studies. We first view the best studied case, the Sun. On the main sequence, solar-analogue stars provide a treasure trove of high-quality oscillation spectra which provide besides mass and radius also information on age, activity cycles, etc. Combined with complimentary data, such as activity proxies, surface rotation rate or lithium abundances allow to draw a comprehensive picture of stars like our Sun. Solar-like oscillations are also found further away from the main sequence, in the more advanced evolutionary phases of the sub- and red-giant branch. Due to a characteristic in the oscillation properties, we can use seismology to look even deeper into the stars and ultimately study the properties of the core with seismic techniques.

Finally, an outlook to the forthcoming space missions, such as NASA TESS and ESA PLATO will be given and how they will influence the future of asteroseismology and the search for exoplanets.
15
Febrero 2019

Too fast, too furious: rapid planet formation by gravitational instability


Inicio: 12:15h
Ponente: Dimitris Stamatellos (University of Central Lancashire)
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)

Stars are born with discs that during their initial stages of formation are relatively massive, asymmetric and they are being fed with material from their parent clouds. ALMA observations have revealed young discs with multiple gaps and discs with spiral structures. Such features may be due to forming…
Inicio: 12:15h
Ponente: Dimitris Stamatellos (University of Central Lancashire)
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)

Stars are born with discs that during their initial stages of formation are relatively massive, asymmetric and they are being fed with material from their parent clouds. ALMA observations have revealed young discs with multiple gaps and discs with spiral structures. Such features may be due to forming planets, raising the exciting possibility that planets and planetary systems may form much faster than it has been previously thought. I will discuss whether gravitational instabilities may be responsible for the fast formation of planet-seeds in early-phase protostellar discs. I will also discuss how young planet-seeds evolve when they form within relatively massive discs, and I will argue that their fate is quite diverse, depending on the detailed physics of their interactions with their parent discs.
08
Febrero 2019

Cosmic acceleration and type Ia supernovae luminosity-redshift dependence


Inicio: 12:15h
Ponente: Isaac Tutusaus Lleixa (Institute of Space Sciences (ICE, CSIC and IEEC))
Lugar: Alberto Lobo Seminar Room (ICE, UAB Campus)

The ΛCDM model is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has recently been…
Inicio: 12:15h
Ponente: Isaac Tutusaus Lleixa (Institute of Space Sciences (ICE, CSIC and IEEC))
Lugar: Alberto Lobo Seminar Room (ICE, UAB Campus)


The ΛCDM model is the current standard model in cosmology thanks to its ability to reproduce the observations. The first observational evidence for this model appeared roughly 20 years ago from the type Ia supernovae (SNIa) Hubble diagram from two different groups. However, there has recently been some debate in the literature concerning the statistical treatment of SNIa, and their ability to prove the cosmic acceleration. In this talk I will focus on the standard assumption that SNIa intrinsic luminosity is independent of the redshift. After briefly motivating the relaxation of this assumption, I will first present the conclusions that we can draw on the accelerated nature of the expansion of the Universe if we only consider low-redshift cosmological probes and an expanding universe with constant velocity: the Rh=ct model. In the second part of the talk, I will further test this exotic model by including high-redshift information coming from the cosmic microwave background. Finally, I will generalize the previous two parts and present the role of SNIa on the accelerated nature of the expansion of the Universe when we account for the main background cosmological probes in a model-independent way.
01
Febrero 2019

The cosmological constant and the size of our Universe


Inicio: 12:15h
Ponente: Enrique Gaztañaga (Institut de Ciències de l'Espai)
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)

We consider the cosmological constant 𝚲 to be a free parameter of the symmetries of gravity that can fixed by a boundary condition: the particles should be free when outside causal contact (traditionally at infinity). Under this conditions we show that constant vacuum does not contribute to gravity.…
Inicio: 12:15h
Ponente: Enrique Gaztañaga (Institut de Ciències de l'Espai)
Lugar: Sala Alberto Lobo (ICE building, Campus UAB)


We consider the cosmological constant 𝚲 to be a free parameter of the symmetries of gravity that can fixed by a boundary condition: the particles should be free when outside causal contact (traditionally at infinity). Under this conditions we show that constant vacuum does not contribute to gravity. Moreover we find that there is no cosmic acceleration for an infinitely large and uniform Universe, no matter what the values are for the cosmological constant 𝚲 or vacuum energy rho_{vac}. Cosmic acceleration at present time requires either a finite Physical Universe (causal boundary) or significant evolution in the late time vacuum energy (i.e. equation of state w>-1). If we assume that vacuum has not evolved strongly in recent times (or that w = -1 as favored by observations), then the measured cosmic acceleration \rho_ 𝚲 = (2.23 ± 0.03) rho_m just tell us that the Physical Universe (or causal boundary) has a co-moving radius of chi= (3.137 ± 0.004) c/H_0, where H_0 is the present expansion rate. This result predicts the lack of structure seem in our CMB sky on scales larger than 60 degrees and gives new constraints for inflation. We conclude that there is no need for a mysterious Dark Energy to explain the observed cosmic acceleration.
 
25
Enero 2019

Feeding and feedback from little monsters: black holes in dwarf galaxies


Inicio: 12:15h
Ponente: Mar Mezcua Pallerola
Lugar: Sala Alberto Lobo

Supermassive black holes of 10^10 solar masses already existed when the Universe was ~1 Gyr old and are also found in local brightest cluster galaxies. To reach this mass, they should have started as seed intermediate-mass black holes (IMBHs) of 100-10^6 solar masses at z~10 and grow very fast via accretion…
Inicio: 12:15h
Ponente: Mar Mezcua Pallerola
Lugar: Sala Alberto Lobo

Supermassive black holes of 10^10 solar masses already existed when the Universe was ~1 Gyr old and are also found in local brightest cluster galaxies. To reach this mass, they should have started as seed intermediate-mass black holes (IMBHs) of 100-10^6 solar masses at z~10 and grow very fast via accretion and mergers. Detecting such IMBHs in the early Universe is extremely challenging; however, those seed black holes that did not become supermassive should be found in local dwarf galaxies resembling the first galaxies formed at early epochs. 
I will show that a population of actively accreting IMBHs exists in local dwarf galaxies and that they can be detected out to z~3 with the use of deep multiwavelength surveys like COSMOS. The black hole occupation fraction of these dwarf galaxies suggests that the early Universe seed black holes formed from direct collapse of pre-galactic gas disk, which is reinforced by the finding that the scaling relations between supermassive black hole mass and host galaxy properties flatten at the low-mass end. This scenario is however challenged by the recent suggestion that dwarf galaxy mergers and black hole feedback can yield significant growth of the primordial seeds. In this case, IMBHs in local dwarf galaxies should not be treated as the fossils of the early Universe seed black holes. 
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An institute of the Consejo Superior de Investigaciones Científicas

An institute of the Consejo Superior de Investigaciones Científicas
Affiliated with the Institut d'Estudis Espacials de Catalunya

Affiliated with the Institut d'Estudis Espacials de Catalunya