Seminars and Colloquia at ESO/Santiago

For ESO and ESO-related Conferences and Workshops in Europe and Chile please check the main Conferences and Workshops page.


Broadcast of the ESO talks is available upon request.  If anyone is interested, kindly contact us via email
at least 60 min prior  to the beginning of the talk.


May 2015

26.05.15 (Tuesday)
12:00
"The stable decretion disk around a late-type Be star beta CMi"
Robert KLEMENT (Charles University, Prague, Czech Republic)
Abstract
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"Multi-The stable decretion disk around a late-type Be star beta CMi"

Robert KLEMENT (Charles University, Prague, Czech Republic)

Abstract

Be stars are the most rapidly rotating non-degenerate stars and their characteristic observables, emission lines and IR and radio excess, originate in purely gaseous, outflowing disks, whose evolution is governed by viscosity. We applied the viscous decretion disk (VDD) model, which currently explains most of observable properties of Be stars, to the case of a stable, tenuous disk surrounding the late type (B8Ve) beta CMi by the means of Monte Carlo radiative transfer modeling using the HDUST code (Carciofi & Bjorkman 2006, ApJ, 639,1081). The physical properties of the disk and the central star were determined by fitting the model observables to a large set of multi-wavelength (UV to radio) and multi-technique (photometry, spectroscopy, linear polarimetry, interferometry) observations. The results revealed a more complex density structure than expected for an isolated, steady-state decretion disk, which represents evidence for either non-steady decretion or the presence of an undetected binary companion tidally influencing the primary's disk. The binary hypothesis is supported by the modeling of radio flux measurements, which showed evidence for truncation of the disk, by several unexpected spectral features, and by an overall good agreement with the outcomes of smooth particle hydrodynamics (SPH) simulation of the influence of the possible binary orbit on the Be disk. Finally, we report on the diagnostic potential of the almost purely photospheric UV spectrum to constrain the polar radius and luminosity of the central star (2.8 R_sun and 185 L_sun), the linear polarimetry to constrain its rotation rate (W >~ 0.98, i.e., almost critical), and the interferometric shape extracted from VLTI/AMBER observations to constrain the inclination angle (43 degrees).

27.05.15 (Wednesday)
15:30
"Multi-dataset modelling of close eclipsing binaries with Roche"
Theo PRIBULLA (Slovak Academy of Sciences)
Abstract
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"Multi-dataset modelling of close eclipsing binaries with Roche"

Theo PRIBULLA (Slovak Academy of Sciences)

Abstract

Code ROCHE enables robust modeling of multi-dataset observations of close eclipsing binaries such as radial velocities, multi-wavelength light curves, broadening functions, interferometric visibilities or apparent positions in the case of resolved binaries. The code includes starspots, eccentric orbits, asynchronous rotation, and third light. The program makes use of synthetic spectra to compute apparent UBVRIJHK magnitudes from the surface model and the object parallax. The surface grid is derived from a regular icosahedron/octahedron to secure more-or-less equal elements with observed intensities computed from synthetic spectra for supplied passband transmission curves. All proximity effects (tidal deformation, reflection effect, gravity darkening) are taken into account. Integration of synthetic curves is improved by adaptive phase step. The code capabilities are documented on a few systems included interferometrically resolved binary V923 Sco.

28.05.15 (Thursday)
12:00
"A review in mixed chemistry of low mass evolved stars"
Lizette GUZMAN (ESO,Chile)
Abstract
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"A review in mixed chemistry of low mass evolved stars"

Lizette GUZMAN (ESO,Chile)

Abstract

During the late stages of their evolution, Sun-like stars bring products of nuclear burning to the surface. Most of the Carbon in the Universe is believed to originate from stars with mass up to a few solar masses. Although there is a chemical dichotomy between oxygen-rich and carbon-rich evolved stars, in the last three decades, a few stars have been shown to display both carbon and oxygen-rich material in their circumstellar envelopes. I will present observations and results of these mixed-chemistry objects using Spitzer, HST, UVES, VISIR, and SOFIA.


June 2015

2.06.15 (Tuesday)
12:00
"Exoplanetary systems imaging with Subwavelength Grating Vortex (SGV) coronagraphs: first on-sky results and next generation devices"
Christian DELACROIX (University of Lyon)
Abstract
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"Exoplanetary systems imaging with Subwavelength Grating Vortex (SGV) coronagraphs: first on-sky results and next generation devices"

University of Lyon

Abstract

The subwavelength grating vortex (SGV) coronagraph is a focal-plane spiral-like phase mask whose key benefit is to allow high contrast imaging at small angles. Directly etched onto a CVD diamond substrate, it is well suited to perform in the mid-infrared domain. It provides a continuous helical phase ramp with a dark singularity in its center, and is characterized by its number of phase revolutions, called the topological charge. Over the past two years, we have manufactured several charge-2 SGVs (a.k.a. annular groove phase masks) and successfully demonstrated their performances on 10-m class telescopes (LBT, VLT/NaCo, VLT/VISIR). To prevent stellar leakage on future 30-m class telescopes (E-ELT, TMT, GMT), a broader off-axis extinction is required, which can be achieved by increasing the topological charge. We have recently proposed an original design for a charge-4 SGV allowing less starlight to leak through the coronagraph, at the cost of a degraded inner working angle. In this talk, we report on our latest development of higher charge SGVs. From 3D rigorous numerical simulations using a finite-difference time-domain (FDTD) algorithm, we have derived a family of coronagraphs with higher topological charge (SGV4/6/8). Our new optimization method addresses the principal limitation of such space-variant polarization state manipulation, i.e., the inconvenient discontinuities in the discrete grating pattern. The resulting gratings offer improved precision to the phase modulation compared to previous designs. Finally, we present our preliminary manufacturing and metrology results for infrared components down to the K-band.

3.06.15 (Wednesday)
12:00
"The massive stars nursery R136"
Zeinab KHORRAMI (Laboratoire Lagrange – Observatoire de la Cote d’Azur)
Abstract
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"The massive stars nursery R136 "

Zeinab KHORRAMI (Laboratoire Lagrange – Observatoire de la Cote d’Azur)

Abstract

As most stars are born in a clustered mode, young massive star clusters are the best places to find and study the formation and evolution of massive stars. R136 is one of the most massive nearby clusters in the LMC, which contains at least until now 72 known O and Wolf-Rayet stars. These young objects are usually embedded in dust and gas so that correcting the local extinction plays an important role for estimating the mass of stars. The extinction is derived for 26 O-stars in different HST filters using TLUSTY[3] atmosphere model for O-stars. Then we derived the mass and hence the Mass Function (MF) by multicolour photometry from HST data. We also simulated series of R136-like clusters using the Nbody6 code to test the segregation scenario for R136. thus we checked if massive stars tend to be formed locally at the center of a cloud or homogeniously. By comparing the surface brightness profiles (SBP) of simulated clusters mimicking R136’s SBP from HST data, we could determine which scenario is simulated the best R136. the results of these studies bring a new homogenious insight to the understanding of R136 and similar clusters in the light of future VLT and E-ELT high dynamic imaging observations at the diffraction limit in visible and IR wavelengths.

4.06.15 (Thursday)
12:00
"Twenty years of discoveries in Exoplanets: from the first planet to future instrumentation"
Pedro FIGUEIRA (Porto University)
Abstract
Close
"Twenty years of discoveries in Exoplanets: from the first planet to future instrumentation"

Pedro FIGUEIRA (Porto University)

Abstract

As most stars are born in a clustered mode, young massive star clusters are the best places to find and study the formation and evolution of massive stars. R136 is one of the most massive nearby clusters in the LMC, which contains at least until now 72 known O and Wolf-Rayet stars. These young objects are usually embedded in dust and gas so that correcting the local extinction plays an important role for estimating the mass of stars. The extinction is derived for 26 O-stars in different HST filters using TLUSTY[3] atmosphere model for O-stars. Then we derived the mass and hence the Mass Function (MF) by multicolour photometry from HST data. We also simulated series of R136-like clusters using the Nbody6 code to test the segregation scenario for R136. thus we checked if massive stars tend to be formed locally at the center of a cloud or homogeniously. By comparing the surface brightness profiles (SBP) of simulated clusters mimicking R136’s SBP from HST data, we could determine which scenario is simulated the best R136. the results of these studies bring a new homogenious insight to the understanding of R136 and similar clusters in the light of future VLT and E-ELT high dynamic imaging observations at the diffraction limit in visible and IR wavelengths.

11.06.15 (Thursday)
12:00
"Unveiling the Massive Stars in the Galactic Centre"
Hui DONG (Instituto de Astrofísica de Andalucía, Spain)
Abstract
Close
"Unveiling the Massive Stars in the Galactic Centre"

Hui DONG (Instituto de Astrofísica de Andalucía, Spain)

Abstract

Because of the proximity, the Galactic Centre is a unique lab for studies of the interplay between stars, ISM and super massive black holes in galactic nuclei. The central 200 pc of the Galactic Centre includes 4x10^7 molecular clouds and has a star formation rate of ~0.03 M/yr. Three young, massive and compact star clusters were found and includes around 100 massive stars, which strongly shape the nearby ISM. However, the massive stars beyond the clusters are still unknown. A complete census of these `field' massive stars have an important impact on our understanding of several fundamental astrophysical questions, such as 1) how molecular clouds form stars in this extreme environments, 2) initial massive function and 3) the stellar evolution models for massive stars in high metallicity environment. I will present our effort during these years to identify massive stars in the Galactic Centre and study their properties and origin. Our results show that massive stars pervade the Galactic Centre and they partly formed in situ and partly were ejected from the three clusters.


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