Past Talks @ ICE

Number of entries: 42

31
March 2020

ALL SEMINARS ARE CANCELLED UNTILL FURTHER NOTICE


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27
February 2020

Radio emission from neutron star high-mass X-ray binaries: new jet physics and predictions for future surveys


Start: 14:30h
Speaker: Jakob van den Eijnden (University of Amsterdam)
Place: alberto lobo

X-ray binaries, wherein a compact object accretes from an orbiting companion star, are prime targets to study accretion, ejection, and their connection. With their large range in easily measurable spin and magnetic field strengths, neutron star systems are particularly interesting to understand the effect…
Start: 14:30h
Speaker: Jakob van den Eijnden (University of Amsterdam)
Place: alberto lobo

X-ray binaries, wherein a compact object accretes from an orbiting companion star, are prime targets to study accretion, ejection, and their connection. With their large range in easily measurable spin and magnetic field strengths, neutron star systems are particularly interesting to understand the effect of the compact object on the presence, power, and properties of jets. For decades, no jets were observed from accreting neutron star systems with magnetic fields exceeding ~10^12 Gauss, creating the paradigm that such strong fields disrupt the commonly-invoked Blandford-Payne jet launching mechanism. In this talk, I will describe our surprising discovery of jets from such strongly-magnetized neutron stars and its implication for our understand of jet formation. Since these strongly-magnetized neutron stars dominate the known sample of Galactic high-mass X-ray binaries, and therefore constitute about half of all X-ray binaries, I will also discuss expectations for the detectability of these systems and their jets in future radio surveys. 
11
February 2020

NoiseChisel and Gnuastro: non-parametric detection and analysis of astronomical targets


Start: 10:00h
Speaker: Mohammad Akhlaghi ((IAC) )
Place: Alberto Lobo Conference Room

Astronomical instrumentation has greatly advanced over the last 40 years: with digital detectors, space telescopes and +8m class ground-based telescopes for example. However, the signal-based detection paradigm (for example from Petrosian or Kron in the 1970s, mostly used as implemented in SExtractor…
Start: 10:00h
Speaker: Mohammad Akhlaghi ((IAC) )
Place: Alberto Lobo Conference Room


Astronomical instrumentation has greatly advanced over the last 40 years: with digital detectors, space telescopes and +8m class ground-based telescopes for example. However, the signal-based detection paradigm (for example from Petrosian or Kron in the 1970s, mostly used as implemented in SExtractor from the mid-1990s) is still the dominant method of low-level data analysis: detection, segmentation and measurements or catalog production. In this talk, after reviewing the major systematic biases regarding astronomical object detection that is inherent to the signal-based paradigm, I will introduce a fundamentally new noise-based detection paradigm for detecting signal that may have extremely low signal-to-noise ratios. With thresholds that are far below the Sky value, and non-parametric expansion into noise, it is successfully able to detect very diffuse and irregularly shaped signal in noise (e.g., galaxies, comets and etc). The software implementation is called NoiseChisel. The talk will continue with an introduction to NoiseChisel’s parent software: GNU Astronomy Utilities (or Gnuastro). It is a large package of useful programs and libraries for astronomical data analysis directly on the command-line without the need to use mini-environments like IRAF or Python. It fully conforms with the GNU Coding Standards for easy integration into all Unix-like operating systems (GNU/Linux distros and MacOS for example) with familiar installation, usage and documentation.

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08
January 2020

Global Hydrogen Cosmology Data Analysis for Rigorously Separating the Signal from Systematics


Start: 11:00h
Speaker: Dr. David Rapetti Visiting Scientist / NASA Ames Research Center - Universities Space Research Association and University of Colorado Boulder. (Director adjunto de NESS (Network for Exploration and Space Science) https://www.colorado.edu/ness/.)
Place: Alberto Lobo room

I will discuss our data analysis for sky-averaged 21-cm observations and the status of the experiments for which we are currently developing specific applications of this pipeline, the ground-based Cosmic Twilight Polarimeter (CTP) and the space-based Dark Ages Polarimeter PathfindER (DAPPER). The first…
Start: 11:00h
Speaker: Dr. David Rapetti Visiting Scientist / NASA Ames Research Center - Universities Space Research Association and University of Colorado Boulder. (Director adjunto de NESS (Network for Exploration and Space Science) https://www.colorado.edu/ness/.)
Place: Alberto Lobo room

I will discuss our data analysis for sky-averaged 21-cm observations and the status of the experiments for which we are currently developing specific applications of this pipeline, the ground-based Cosmic Twilight Polarimeter (CTP) and the space-based Dark Ages Polarimeter PathfindER (DAPPER). The first aims at independently validating the recent EDGES results, and the second at precision measurements of the Cosmic Dawn absorption trough plus the first detection of the purely cosmological Dark Ages trough at lower frequencies. For this, I will present how we self-consistently separate the signal from large systematics using a pattern recognition method based on training sets. We then use the analytically calculated, spectral signal fit to start a Markov Chain Monte Carlo (MCMC) exploration of a nonlinear signal parameter space of choice. Efficiently, at each MCMC step we marginalize over the weights of all linear beam-weighted foreground modes, allowing the complexity of the foreground model to be greatly increased without requiring additional MCMC parameters. We demonstrate the success of this methodology by recovering the input parameters from multiple randomly simulated signals (10-200 MHz), while rigorously accounting for realistically modeled foregrounds. Time permitting, I will also describe ongoing studies in which we benefit from our pipeline to both model foregrounds and implement two key experimental designs into our analysis, a time-series drift scan and induced polarization.
07
October 2019

Inflationary universe in 𝐹(𝑅) gravity with antisymmetric tensor fields and their suppression during its evolution


Start: 11:00h
Speaker: Tanmoy Paul
Place: Alberto Lobo Room

The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four-…
Start: 11:00h
Speaker: Tanmoy Paul
Place: Alberto Lobo Room

The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four- and in five-dimensional spacetime. The results here obtained reveal that the amplitude of the Kalb-Ramond field may be actually large and playa  significant role during the early universe, while the presence of higher-order gravity suppresses this field during the cosmological evolution, so that it eventually becomes negligible in the current universe. Besides the suppression of the Kalb-Ramond field, the extra degree of freedom in F(R) gravity, usually known as scalaron, also turns out to be responsible for inflation. Such F(R) gravity with Kalb-Ramond fields may govern the early universe to undergo an inflationary stage at early times (with the subsequent graceful exit) for a wider range of F(R) gravity than without antisymmetric fields. Furthermore, the models—in four-and five-dimensional spacetimes—are linked to observational constraints, with the conclusion that the corresponding values of the spectral index and tensor-to-scalar ratio closely match the values provided by the Planck survey 2018 data.
07
October 2019

Dark Matter and Dark Energy from a New Nonlocal Modified Gravity


Start: 12:00h
Speaker: Branko Dragovich (Institute of Physics, University of Belgrade, Belgrade, Serbia)
Place: Alberto Lobo Room

I will present some exact cosmological solutions for modified gravity based on a nonlocal operator acting between two factors of the square root of R – 2 Lambda. One of these solutions imitates properties similar to an interplay of the dark matter and the dark energy. For this solution, we computed…
Start: 12:00h
Speaker: Branko Dragovich (Institute of Physics, University of Belgrade, Belgrade, Serbia)
Place: Alberto Lobo Room

I will present some exact cosmological solutions for modified gravity based on a nonlocal operator acting between two factors of the square root of R – 2 Lambda. One of these solutions imitates properties similar to an interplay of the dark matter and the dark energy. For this solution, we computed some cosmological parameters which are in a good agreement with observations. This talk is based on a recent paper published in Phys. Lett. B.
13
September 2019

Studying the Expansion of the Universe with quasar spectra


Start: 12:00h
Speaker: Andreu Font Ribera (University College London)
Place: Sala Alberto Lobo

From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift…
Start: 12:00h
Speaker: Andreu Font Ribera (University College London)
Place: Sala Alberto Lobo

From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF).


In this talk I will overview the final results from the LyaF working group in BOSS, and I will present updated results obtained with the extended BOSS survey (eBOSS, 2014-2019). This include the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Sainte Agathe et al. 2019), and from its cross-correlation with quasars (Blomqvist et al. 2019). From the combination of these studies we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.


Starting in 2020, the Dark Energy Spectroscopic Instrument (DESI) will increase this data set by an order of magnitude. DESI will provide an exquisite measurement of the expansion over cosmic time, while at the same time addressing other interesting questions: the sum of the mass of the neutrino species, properties of dark matter particles, tests of general relativity and the shape of the primordial power spectrum of density fluctuations.
30
July 2019

After the Habitable Zone


Start: 12:30h
Speaker: Prof. Rory Barnes (University of Washington Department of Astronomy, Virtual Planetary Lab )
Place: Alberto Lobo Seminar Room (ICE, UAB Campus)

The habitable zone (HZ), that region around a star in which the Earth could retain surface water, has served scientists well as they began to idnetify exoplanets that could support liquid water. However, as we move into the era of targeting exoplanets for biosignature detection, the simplifications…
Start: 12:30h
Speaker: Prof. Rory Barnes (University of Washington Department of Astronomy, Virtual Planetary Lab )
Place: Alberto Lobo Seminar Room (ICE, UAB Campus)

The habitable zone (HZ), that region around a star in which the Earth could retain surface water, has served scientists well as they began to idnetify exoplanets that could support liquid water. However, as we move into the era of targeting exoplanets for biosignature detection, the simplifications inherent to the HZ are being exposed. Stellar evolution, internal properties, flares, ocean behavior, tidal effects, galactic perturbations, and orbital oscillations all affect the habitability of exoplanets. As astrobiologists and astronomers begin the first remote sensing campaigns of potential habitable worlds in the next decade, a new paradigm must emerge in which models of planetary system formation and evolution are compared to observational data, both spectral and photometric. This new approach will require a massive and collaborative effort between scientists across a range of disciplines, including leveraging new insights from data scientists to analyze the large and high-dimensional data sets that must be generated and compared. Ultimately the discovery of active biology requires that all possible histories of a planet are simulated and compared to observations to find that only those case that include a biosphere are consistent with data. Developing a framweork to build these formation and evolutionary models is a grand scientific challenge of the 21st century, but the successful discovery of life beyond the Solar System depends on its creation and implementation.
08
July 2019

PBHs-as-CDM scenario and Gravitational Waves


Start: 12:00h
Speaker: Dr. Misao Sasaki (IPMU, Tokyo, Japan)
Place: Alberto Lobo room

We argue that primordial black holes (PBHs) with mass of an asteroid can be CDM of the Universe. In this scenario, the associated curvature perturbations will produce secondary gravitational waves with a unique spectral feature, and the amount produced will be large enough to be detected by the future…
Start: 12:00h
Speaker: Dr. Misao Sasaki (IPMU, Tokyo, Japan)
Place: Alberto Lobo room

We argue that primordial black holes (PBHs) with mass of an asteroid can be CDM of the Universe. In this scenario, the associated curvature perturbations will produce secondary gravitational waves with a unique spectral feature, and the amount produced will be large enough to be detected by the future space gravitational wave antenna, LISA.
01
July 2019

Bouncing solutions in modified gravity


Start: 12:00h
Speaker: Dr. Gauranga Samanta
Place: L3-03 workshop room.

In this talk I would like to discuss about the modification of general relativity and why we need the modification. Subsequently, I will discuss about the bouncing solutions in modified gravity. Bouncing problem is one of the fascinating parts of the study of cosmological dynamics in  modified gravity,…
Start: 12:00h
Speaker: Dr. Gauranga Samanta
Place: L3-03 workshop room.

In this talk I would like to discuss about the modification of general relativity and why we need the modification. Subsequently, I will discuss about the bouncing solutions in modified gravity. Bouncing problem is one of the fascinating parts of the study of cosmological dynamics in  modified gravity, because the big bang singularity could be avoided by a big bounce.The indication of the bouncing universe is: the size of the scale factor contracted to a finite volume.
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