ESO Santiago Science Colloquia and Seminars 2014

April 2014

16.4.14 (Wednesday)
15:30
"IP Eri and the formation of long-period eccentric binaries with a helium white dwarf"
Lionel SIESS (Universite Libre de Bruxelles, Belgium)
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"IP Eri and the formation of long-period eccentric binaries with a helium white dwarf"

Lionel SIESS (Universite Libre de Bruxelles, Belgium)

Abstract

The recent discovery of long-period eccentric binaries hosting a He-WD or a sdB star has been challenging binary-star modelling. Based on accurate determinations of the stellar and orbital parameters for IP Eri, a K0 + He-WD system, we propose an evolutionary path that is able to explain the observational properties of this system and, in particular, to account for its high eccentricity (0.25). Our scenario invokes an enhanced-wind mass loss on the first red giant branch (RGB) in order to avoid mass transfer by Roche-lobe overflow, where tides systematically circularize the orbit. We explore how the evolution of the orbital parameters depends on the initial conditions and show that eccentricity can be preserved and even increased if the initial separation is large enough. The low spin velocity of the K0 giant implies that accretion of angular momentum from a (tidally-enhanced) RGB wind should not be efficient.

March 2014

5.3.14 (Wednesday)
15:30
"Large scale correlations of quasar polarization vectors: hints of extreme scale structures or evidence for axion-like particles?"
Damien HUTSEMÉKERS (Astrophysics Institute, University of Liege, Belgium)
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"Large scale correlations of quasar polarization vectors: hints of extreme scale structures or evidence for axion-like particles?"

Damien HUTSEMÉKERS (Astrophysics Institute, University of Liege, Belgium)

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Based on a sample of 355 quasars with significant optical linear polarization and using various statistical methods, we show that quasar polarization vectors are not randomly oriented over the sky with a probability often in excess of 99.9%. The polarization vectors appear coherently aligned over huge regions of the sky (~1 Gpc), located at both low (z ~0.5) and high (z ~1.5) redshifts and characterized by different preferred directions of the polarization. These characteristics make the alignment effect difficult to explain in terms of contamination by instrumental or interstellar polarization in our Galaxy. We notice that the region of the sky where the alignments are prominent is not far from preferred directions tentatively identified in the Cosmic Microwave Background. Polarization alignments may thus reveal structures at scales beyond the homogeneity scale of concordance cosmology. Several interpretations are discussed. In particular, we show that the dichroism and birefringence predicted by photon pseudo-scalar oscillation along the line of sight cannot reproduce the observed properties of the alignments. Besides, accurate measurements of quasar circular polarization allow us to strongly constrain the parameter space of axion-like particles.
11.3.14 (Tuesday)
12:00
"A dynamical study of the open star cluster NGC 2287"
Anna SIPPEL (ESO, Chile)
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"A dynamical study of the open star cluster NGC 2287"

Anna SIPPEL (ESO, Chile)

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Estimating open cluster masses using photometry can lead to different results depending on the method used. To understand which approach leads to more accuarate results, we use multi-epoch FLAMES spectroscopy to calculate the dynamical mass -- an independent mass estimate. With the ultimate goal of understanding if open clusters have a chance to survive or are born to disperse, I will present the preliminary results of this pilot study and my project here at ESO.
20.3.14 (Thursday)
12:00
"Probing the inner structure of quasar using gravitational microlensing"
Lorraine BRAIBANT (Universite de Liege, Belgium)
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"Probing the inner structure of quasar using gravitational microlensing"

Lorraine BRAIBANT (Universite de Liege, Belgium)

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Gravitational microlensing is a powerful tool which allows astronomers to study the most inner parts of QSO that can’t be spatially resolved by current telescopes. Indeed, stellar-mass objects contained in the lensing galaxy can typically substantially magnify regions of the source plane on scales of a few nano- or micro-arcseconds, which interestingly correspond to the size of QSO unresolved inner regions. Among other things, microlensing can give rise to spectral differences between the multiple images of a same background quasar which constitute a cosmic mirage. A lot of information about the physical properties of the accretion disk and the geometry of the broad line region can be retrieved from these spectral differences. (e.g., Hutsemékers et al., 2010, Sluse et al., 2012). Using the decomposition method described in Sluse et al. (2007) and Hutsemékers et al. (2010), which allows to disentangle the part of the quasar spectrum affected by microlensing, we have studied three quadruple gravitational lenses which are known or suspected to be affected by microlensing: H1413+117, HE0435-1223 and PG1115+080.
27.3.14 (Thursday)
12:00
"As the Dust Settles: using time-domain observations to reveal cloud structure in substellar atmospheres"
Jackie RADIGAN (STScI,USA)
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"As the Dust Settles: using time-domain observations to reveal cloud structure in substellar atmospheres"

Jackie RADIGAN (STScI,USA)

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The combination of condensate clouds and rapid rotation has long motivated searches for weather phenomena in ultracool (late-M, L and T) dwarf (UCD) atmospheres. Pioneering work in this field dating back as early as 1999 suggested that variability is quite common for UCDs. Yet these early studies were ambiguous: detections were often low-amplitude and/or lacking periodicity, and the mechanisms responsible remained unclear. Observations made in the past 5 years, utilizing continuous monitoring strategies, better instruments, and larger telescopes have demonstrated conclusive and surprisingly large near-infrared variability for a subset of brown dwarfs at the transition between L and T spectral types, suggesting a patchy distribution of silicate clouds in their atmospheres. Brightness variations as large as 25% on readily observable rotational timescales allow light curves of exquisite precision, worthy of detailed analysis, to be obtained from both ground and space based facilities. While the L/T transition is the realm of spectacular variability, recent space-based efforts have confirmed lower levels of variability for a substantial fraction of UCDs at all spectral types. I will describe how such multi-wavelength, multi-epoch observations are contributing to an emerging picture of cloud structure in brown dwarf and exoplanet atmospheres.
31.3.14 (Monday)
12:00
"Systemic mass loss in interacting binaries: Can we reconcile binary star models with observations?"
Romain DESCHAMPS (ESO, Chile)
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"Systemic mass loss in interacting binaries: Can we reconcile binary star models with observations?"

Romain DESCHAMPS (ESO, Chile)

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Systemic mass loss in interacting binaries such as of the Algol-type has been inferred since the 50s. There is indeed gathering indirect evidence indicating that some Algols follow non-conservative evolutions but still no direct detection of large mass outflows. As a result, little is known about the eventual ejection mechanism. In order to reconcile stellar models with observations, we compute typical Algol models with the state-of-the-art binary star evolution code Binstar. We investigate systemic mass losses within the hotspot paradigm where large outflows of material forms from the accretion impact during the mass transfer phase. We then study the impact of this outflow on the spectral emission distribution of the system with the radiative transfer codes Cloudy and Skirt.

February 2014

6.2.14 (Thursday)
15:30
"Physics of Star Formation"
Thomas HENNING (Max Planck Institute for Astronomy, Heidelberg)
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"Physics of Star Formation"

Thomas HENNING (Max Planck Institute for Astronomy, Heidelberg)

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Star formation is a fundamental process in the universe, shaping the structure of our and other galaxies. The birth of stars is triggered by the gravitational collapse and fragmentation of cold molecular clouds. The talk will summarize the general physical principles of the star formation process. It will discuss global properties such as the star formation efficiency and the initial mass function. In addition, it will also demonstrate the power of adaptive optics in revealing the structure of star-forming regions and will show new exciting results obtained with the Herschel Space Observatory.
27.2.14 (Thursday)
12:00
"The metallicity of the z~2.5 circumgalactic medium"
Neil CRIGHTON (Swinburne University of Technology)
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"The metallicity of the z~2.5 circumgalactic medium"

Neil CRIGHTON (Swinburne University of Technology)

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Observations of the gaseous halos of galaxies (the circumgalactic medium or CGM) are able to constrain important but poorly-understood mechanisms that govern galaxy formation, such as supernovae-driven outflows and gas inflowing along cold-accretion streams. I will present the first results from our group's survey of cool gas in the CGM of galaxies at z~2.5, near the peak of the cosmic star formation rate. By comparing the gas absorption features seen towards a background QSO sightline nearby a foreground galaxy to photo-ionization models we measure the metallicity of the CGM gas, which is crucial to determine its origin. We introduce a new method of measuring the gas metallicity that incorporates variations in the shape of the UV radiation field illuminating the gas, resulting in robust metallicity uncertainties. We apply this method to a galaxy-absorber pair discovered by our survey, and show that metal-enriched gas exists in the galaxy's halo out to a minimum radius of ~50 kpc.

January 2014

7.1.14 (Tuesday)
12:00
"The origin of hot subdwarf stars"
Roy ØSTENSEN (Leuven University, Belgium)
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"The origin of hot subdwarf stars"

Roy ØSTENSEN (Leuven University, Belgium)

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Hot subdwarf stars are the remnants of stars that have somehow lost their hydrogen envelope during the red giant phase, and are now core-helium burning without a hydrogen burning shell. In order to reach this peculiar configuration they must have lost almost all their remaining hydrogen in some kind of binary interaction. The majority of such subdwarfs are found in binary systems, but a significant number appears to be devoid of any companions that can have caused such significant mass loss. I discuss the latest results with respect to the binary connections and the asteroseismic results revealed by data from the Kepler spacecraft, and outline the tentative connections for giant planets to be involved in the envelope ejection.
10.1.14 (Friday)
12:00
"Is Mars Alive?"
Geronimo VILLANUEVA (NASA-GSFC/CUA, Greenbelt, MD)
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"Is Mars Alive?"

Geronimo VILLANUEVA (NASA-GSFC/CUA, Greenbelt, MD)

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Is there any biological or geological activity currently on Mars? Is Mars currently habitable or has ever been so? We are much closer to answer these fundamental questions than ever before, thanks to the astronomical power of telescopes such as VLT, Keck and NASA-IRTF. We have obtained extremely detailed spectra of Mars for the last 10 years using these three observatories, leading to the most comprehensive spectral database targeting trace species on Mars ever acquired. Our measurements include the search for methane, a biomarker on Earth, and of water, including several of its isotopes.These astronomical results will be contrasted with the measurements obtained by NASA’s Curiosity rover, which is now exploring the Gale Crater with the most powerful suite of instruments ever to reach the surface of Mars.
13.1.14 (Monday)
15:30
"The GRBs Afterglow: ESO Key Role"
Guido CHINCARINI (Università degli Studi di Milano)
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"The GRBs Afterglow: ESO Key Role"

Guido CHINCARINI (Università degli Studi di Milano)

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After a brief introduction I review some of the highlights of the GRBs afterglow evidencing the observations obtained using the ESO facilities. With the discovery that also short GRBs are extragalactic we got a reasonable understanding of the energy and the likely progenitor identified as a NS+NS merging. This leads to the need of demonstrating it via gravitational waves detection. Long GRBs show evidence of early (prompt emission) variability all over the electromagnetic spectrum and the effect the radiation has on the Interstellar Medium. This call for high speed pointing capability telescopes. One of the strongest clue for modeling the collapse is the connection GRBs ­ SNe. ESO did an excellent work observing all events with z <0.2. Long GRBs have been detected at high redshifts so that GRBs may be a way to better understand the Cosmic Star Formation Rate (CSFR) that is poorly understood at high z. One of the main tasks for the future will be the understanding of GRBs magnetic fields, their formation and related particle acceleration.
15.1.14 (Wednesday)
15:30
"The Venus Transit of 2012 & other Transits"
Paolo MOLARO (Osservatorio Astronomico di Trieste)
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"The Venus Transit of 2012 & other Transits"

Paolo MOLARO (Osservatorio Astronomico di Trieste)

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Since antiquity the transit of planets, or their absence, have been important in the construction of the Heavens. The Transit of Venus foreseen by Kepler provided an important argument in favor of the Copernican model and allowed a precise measurement of the dimensions of the solar system. The study of the transit of exoplanets is an important technique in the study of their physical properties and therefore we exploited scientifically the Venus Transit of 6th June 2012. By using the Moon as a reflector of the solar light we have detected the Rossiter MacLaughlin effect produced by Venus transiting the solar disk. With this detection we showed that it is possible to detect a very small RM effect against the stellar jitter. This technique showed also that it is possible to measure small variations of the photospheric solar lines at the m/s level. A novel solar atlas based on Laser Frequency Comb will be presented along with some possible applications. The recent observations of the Earth transit in front of the solar disk as seen from Jupiter on the 5th January 2014 will be also mentioned.
16.1.14 (Thursday)
12:00
"The Multi Unit Spectroscopic Explorer MUSE for the VLT"
Roland BACON (Observatoire de Lyon, France)
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"The Multi Unit Spectroscopic Explorer MUSE for the VLT"

Roland BACON (Observatoire de Lyon, France)

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The 2nd generation VLT instrument MUSE is now in Paranal and commissioning will start in a few days. I will present this innovative instrument, its expected performances and its science prospect, with an emphasis on the field of galaxy formation and evolution.
21.1.14 (Tuesday)
12:00
"230 years of AGN monitoring: Frequency of cloud occultation events in AGN & constraints for clumpy torus models"
Mirko KRUMPE (ESO, Garching)
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"230 years of AGN monitoring: Frequency of cloud occultation events in AGN & constraints for clumpy torus models"

Mirko KRUMPE (ESO, Garching)

Abstract

We systematically search for discrete absorption events in the vast archive of the Rossi X-ray Timing Explorer. This includes dozens of nearby type I and Compton-thin type II AGN and covers timescales from days to over a decade for individual objects. We are sensitive to discrete absorption events due to clouds of full-covering, neutral or mildly-ionized gas with columns 1022-25 cm-2 transiting the line of sight. We detect 13 eclipse events in 8 objects, roughly tripling the number of previously published events from this archive. Despite sensitivity to events with NH up to 1024-25 cm-2, we measured no Compton-thick eclipses in our sample. Peak column densities span 2.5 - 19 x 1022 cm-2. Event durations span hours to months. We infer the clouds’ distances from the black hole, assuming Keplerian motion, to span 0. 2 - 80 x 104 Schwarzschild radii. We find no statistically significant difference between the individual cloud properties of type I and II objects. The presence of eclipses in both type Is and IIs argues against sharp-edged cloud distributions. The type II AGN show a level of “base-line” X-ray absorption that is consistent with being constant over timescales from 0.6 to 8.4 yr. This can either be explained by a homogeneous medium, or by X-ray-absorbing clouds that each have NH << 1022 cm-2. Considering the "selection function" of the monitoring, we derive the probability of cloud occultation events. Finally, we derive the first X-ray statistical constraints for clumpy-torus models.
27.1.14 (Monday)
12:00
"What can stellar magnetic field tell us about exoplanetary systems?"
Rim FARES (University of St Andrews, School of Physics & Astronomy)
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"What can stellar magnetic field tell us about exoplanetary systems?"

Rim FARES (University of St Andrews, School of Physics & Astronomy)

Abstract

Extrasolar planets at small orbital distances (hot Jupiters) interact with their hosting star in several ways: irradiation, gravitation, flow of particles and magnetic fields. The planet, embedded in the large-scale stellar magnetic field throughout its orbit, can influence the star in the form of induced photospheric activity, or by influencing the stellar magnetic field via tidal interactions. Studying the stellar magnetic field can give us insights on the interactions in these systems.
I will present my work on the study of the magnetic field of a sample of hot-Jupiter hosting stars and show how the properties of their magnetic field compare to cool stars with no hot-Jupiter. We observed the first large-scale magnetic cycle for a star other than the Sun. The magnetic field flips polarity every year. I will discuss the possible role of star-planet interactions on such a short cycle.
In addition to this observational aspect, I will discuss the effect the stellar magnetic field on the planet, planetary environment and planetary radio emission.
29.1.14 (Wednesday)
15:30
"New results on galaxy evolution from SpARCS, the Spitzer Adaptation of the Red-sequence Cluster Survey"
Chris LIDMAN (AAO, Australia)
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"New results on galaxy evolution from SpARCS, the Spitzer Adaptation of the Red-sequence Cluster Survey"

Chris LIDMAN (AAO, Australia)

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Covering the 50 square degrees of Spitzer SWIRE Legacy Fields, the Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is one of the largest surveys of its kind. It has detected hundreds of galaxy clusters up to z=1.7. Over the past few years, the SpARCS team has been examining the properties of galaxies in these clusters though multi-wavelength imaging and multi-object spectroscopy. In this talk, I will discuss what we are learning about galaxy evolution in these the densest of environments. I will also discuss our plans to push these studies to even higher redshifts where it seems that drastic changes to the galaxy population in the cores of clusters is occurring.