Latest talks

List of all the talks in the archive, sorted by date.

Thursday March 21, 2019
Dr. A. M. Varela
Starlight Foundation, IAC


Starlight principles and recommendations are brought together in the “Declaration in Defence of the Night Sky and the Right to Starlight” (“La Palma Declaration.” 2007), in which, in addition to the IAC, representatives of UNESCO, UNWTO, IAU, UNEP-CMS, CE, SCBD, COE, MAB and the Ramsar Convention all participated and launched Starlight as an international movement in defence of the sky by night and day and to treat it as a source of knowledge and culture that should be shared with society as a whole, promoting the dissemination of astronomy and sustainable, high-quality tourism in those places where the night sky is cared.  The Starlight Reserves, Tourist Destinations and other modalities are scenarios that incorporate the observation of the sky as part of the natural, scenic, cultural and scientific heritage and encourage “Star Tourism”, promoting infrastructure, products, activities and training of specialized guides in the field of sustainable tourism. The Starlight Foundation has been selected to lead the UNWTO Affiliate Member Working Group on Scientific Tourism. Updated Starlight certifications and current projects will be summarized in this presentation.

Thursday March 14, 2019
Prof. Jon Holtzman
Fundacion Jesus Serra


The SDSS Apache Point Observatory Galactic Evolution 
Experiment (APOGEE) has
collected high resolution near-IR spectra of several hundred thousand stars
across the Milky Way. I'll describe some observational results about the
spatial variation of chemical abundances as a function of Galactocentric
radius and distance from the midplane, discussing mean abundances, 
distribution function, and the variation of abundance ratios of multiple
elements. Additional information related to stellar ages can be obtained
from [C/N] for red giant stars. Several lines of evidence suggest that 
migration has had a significant impact on the Galactic disk. The 
observed patterns of
abundance ratios may provide observational constraints on 
nucleosynthetic yields.

Thursday February 28, 2019
Prof. Alex Fullerton
Space Telescope Science Institute


The growth of astrophysical understanding typically results fromthe constructive interplay between theoretical ideas andobservational insights, with each mode of exploration drivingprogress at different times. The result is invariably a morecomplicated but richer picture of the phenomenon than initiallyenvisaged, as well as deeper appreciation of the behavior ofcomplex systems.In this talk, I will use the development of our understanding ofthe structure of outflows from massive O- and B-type stars toillustrate this collaborative “dance”. Starting from the smooth,spherically symmetric models for radiatively driven windsdeveloped in the late 1960s, our view of these outflows hasevolved to include the growth of inhomogeneities on a variety ofspatial scales. Explanations for the origin of this structure havein turn prompted the realization that non-radiative processesmust also shape the emergence of the wind from the stellarphotosphere. Consequently, O- and B-type stars are morecomplicated – and interesting! – objects than often thought.While many fruitful avenues of research remain to be explored,the current paradigm provides a (mostly) self-consistent pictureof massive stars and their outflows.

Thursday February 21, 2019
Dr. Hans Zinnecker
Severo Ochoa senior researcher



Tuesday February 19, 2019
Dr. Hans Zinnecker
Deutsches SOFIA Institut, Univ. of Stuttgart, Germany (retired)



SOFIA, short for Stratospheric Observatory for Infrared Astronomy,
is a 2.7m telescope flying on a Boeing 747SP at altitudes of 12-14km,
to detect and study mid- and far-infrared radiation that is blocked
by water vapor in the earth's atmosphere and cannot reach the
ground. It is the successor to the Kuiper Airborne Observatory (1974-1995)
and currently the only access to and platform for astronomical observations
in the far-infrared (30-300 microns), except for balloon-borne telescopes.
SOFIA normally flies out of California, but once a year also
deploys to the Southern Hemisphere (usually to Christchurch,
New Zealand), benefitting from the excellent wintertime
stratospheric conditions to study the rich southern skies.
Although a bilateral project (80:20)
between USA (NASA/USRA) and Germany (DLR/DSI), it is open for
proposals from the world-wide astronomical community at large.
It addresses many science questions that ESA's successful but
now extinct Herschel Observatory has left unanswered and
offers observational opportunities similar to and beyond Herschel.
SOFIA also has many synergies with ALMA and APEX, as well as IRAM
and other submm and radio telescopes.

In part I of this SOFIA lecture, I will introduce the observatory 
in general, the plane, the telescope, the mode of operation, and 
in particular the current and future instrumentation.

In part II (later this week),  I will present a glimpse of SOFIA science
highlights and discoveries in its first 6 years of operation
(since 2012), including the most recent astrophysical and astrochemical 
results. I will also address its future ISM and star formation potential.  

SOFIA is a unique observatory, different from ground-based and
space platforms, which will serve the mid- and far-infrared 
astronomical community for many years to come.
It is a fascinating experience to fly on SOFIA! 

Thursday February 14, 2019
Dr. Ana Chies Santos
UFRGS, Porto Alegre, Brasil


The bimodal distribution of red and blue galaxies can often be linked through a quenching mechanism that can attenuate the active star forming galaxies into passive ones. Both environment and the stellar mass play an important role in this transition. The ram pressure stripping (RPS) is an important environmental mechanism in dense environments that can severely change the properties and morphology of galaxies. The most extreme cases of galaxies undergoing RPS are known as jellyfish galaxies. Studying this transitioning piece is crucial to improve our understanding of the evolutionary path of galaxies and how quenching succeeds in galaxy clusters. However, jellyfish galaxies are not well characterised morphologically and finding them is still a complex task based mainly on visual inspection. We present the results of a comprehensive study on the properties of a large sample of jellyfish candidates in the multi-cluster system A901/2. We find evidence that the multi-cluster is triggering the effects of RPS in preferential regions in the system and that these galaxies show an enhancement in their star formation rates. We also use the software Morfometryka in order to analyse the unique morphometric features in jellyfish galaxies providing a better comprehension of their physical state and future. This can help unravel the physical processes behind such extreme morphologies as well as helping to automatise the search for jellyfish galaxy candidates in large surveys.

Tuesday February 12, 2019
Dr. Hans Zinnecker
Univ. Autónoma de Chile, Severo Ochoa senior researcher



In this talk, I will review some highlights of my
studies of star formation in the past 35 years.

I started my PhD thesis on the theory of the stellar IMF
in 1977 at MPE in Garching and completed it in 1981.
I studied two different models: (a) hierarchical
cloud fragmentation (star formation as a random
multiplicative process) and (b) competitive accretion
in a protostellar cluster. The first model predicted a
log-normal stellar mass distribution (down to substellar
masses) while the second model produced a power law
(with a slope x = -1, close to the Salpeter slope). 
I will outline both models and discuss how they stood 
the test of time. 
Later, as a postdoc at ROE in Scotland (1983-87), I became 
an observer (mostly at UKIRT) and turned to near-infrared 
(J,H,K) observations of young embedded star clusters, 
such as the Orion Trapezium Cluster, using infrared arrays. 
We observed near-infrared stellar luminosity functions
and derived the corresponding stellar mass spectrum,
using time-dependent mass-luminosity relations based
on pre-Main Sequence evolutionary tracks (without accretion).
A key cluster we studied (with HST) in the near-IR was 
R136/30Dor in the LMC, and we proved the existence of a 
low-mass pre-Main Sequence population in this starburst cluster.
In the 1990s, we carried out the first direct imaging studies
of young low-mass pre-Main Sequence binary stars and also the
multiplicity of massive stars, using 2D speckle interferometry
and adaptive optics observations.
We also discovered the first molecular hydrogen (H2) jets
from deeply embedded low-mass protostars (HH211, HH212).  
Finally, time permitting, I will describe how I turned from a
near-infrared stellar astronomer to an interstellar
far-infrared astronomer, working with the B747SP
air-borne Stratospheric Observatory for Infrared
Astronomy (SOFIA) at NASA-Ames for the last 6 years.

Thursday February 7, 2019
Dr. Ondrej Pejcha
Charles University (Czech Republic)


The collapse of the core and the associated supernova explosion mark the end of life of most massive stars, but the mechanism of explosion is poorly understood and perhaps even unknown. Some of its puzzling features were recently observed in the statistics of supernova progenitors, explosion energies, nickel yields, and in the remnant neutron star and black hole mass functions. I will describe my theoretical studies of the supernova explosion mechanism, its dependence on the progenitor star structure, and the connection with observables. I will argue that successful explosions are intertwined with failures in a complex but well-defined pattern that is tied to the pre-collapse structure of the progenitor star. I will also present a new method to extract the supernova parameters from light curves and expansion velocities, and illustrate how to constrain the explosion mechanism in the future.

Tuesday February 5, 2019
Dr. Matthew Shetrone
McDonald Observatory


Despite being some of the most abundant elements in the  Universe the determination and understanding of the chemical evolution  of C and N is still very uncertain.  One of the main limitations in understanding chemical evolution of C and N is the fact that C and N are altered as during the first dredge-up on the red giant branch.   We present old red giants at various metallicities and luminosities in a sample that is more than 100 times larger than the seminal work of Gratton et al. 2000. Using this we can see the impact of the first dredge-up as well as the on set of "extra" mixing at the bump in the luminosity function for giants more metal-poor than [Fe/H] < -0.4. These observations can be used to constrain future models of mixing.    At a fixed metallicity younger stars have a stronger mixing response during dredge-up.   This fact allows up to infer ages from the first dredge-up [C/N] ratio.   We demonstrate that we are able to interpret the DR14 [C/N]-[Fe/H] abundance distributions as trends in age-[Fe/H] space. Our results show that an anti-correlation between age and metallicity, which is predicted by simple chemical evolution models, is not present at any Galactic zone. Stars far from the plane (|Z| > 1 kpc) exhibit a radial gradient in [C/N]. The [C/N] dispersion increases toward the plane.  We measure a disk metallicity gradient for the youngest stars from 6 kpc to 12 kpc, which is in agreement with the gradient found from other surveys.  Older stars exhibit a flatter gradient, which is predicted by simulations in which stars migrate from their birth radii. We also find that radial migration is a plausible explanation for the observed upturn of the [C/N]-[Fe/H] abundance trends in the outer Galaxy, where the metal-rich stars are relatively enhanced in [C/N].

Tuesday January 29, 2019
Prof. Roland Bacon
CRAL - Observatoire de Lyon


Thanks to its unique capabilities, the MUSE integral field spectrograph at ESO VLT has given us new insight of the Universe at high redshift. In this talk I will review some breakthrough in the observation of the Hubble Ultra Deep field with MUSE including the discovery of a new population of faint galaxies without HST counterpart in the UDF and the ubiquitous presence of extended Lyman-alpha haloes around galaxies.

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