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ana_chies_santos_190214s
Thursday February 14, 2019
Dr. Ana Chies Santos
UFRGS, Porto Alegre, Brasil

Abstract

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.


Hans_Zinnecker_190212s
Tuesday February 12, 2019
Dr. Hans Zinnecker
Univ. Autónoma de Chile, Severo Ochoa senior researcher

Abstract

 

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.

Friday February 8, 2019
Prof. George Djorgovski
Caltech, Division of Physics, Mathematics and Astronomy

Abstract


Ondrej_Pejcha_190207s
Thursday February 7, 2019
Dr. Ondrej Pejcha
Charles University (Czech Republic)

Abstract

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.


Matthew_Shetrone_190205s
Tuesday February 5, 2019
Dr. Matthew Shetrone
McDonald Observatory

Abstract

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].


Roland_Bacon_190129s
Tuesday January 29, 2019
Prof. Roland Bacon
CRAL - Observatoire de Lyon

Abstract

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.


cristina_ramos_almeida_190124s
Thursday January 24, 2019
Dr. Cristina Ramos Almeida
IAC

Abstract

In the past 10-15 years our view of AGN has significantly evolved thanks to the combination of new observations and models. X-ray, infrared and sub-mm data have been crucial to peer into the inner region of AGN and study the properties of the tori, circum-nuclear disks and nuclear outflows. In this talk I will summarize our current view of nuclear obscuration in AGN, focusing on the variations of the torus properties with gas phase. I will also present preliminary results from a new project aimed to characterize nuclear outflows in a sample of nearby quasars and study their impact in the stellar populations, on-going star formation and molecular gas reservoirs of the galaxies.


martinez_lombilla_cristina_190117s
Thursday January 17, 2019
Dr. Cristina Martínez Lombilla, Dr. Felipe Jiménez Ibarra
IAC

Abstract

A young just married couple of Astrophysicist decided going to Kenya for they honeymoon. There, they meet Dr. Dismas Simiyu at Meru University, in Meru town, 240 km north from Nairobi. All of them together organised an Astrophysics Workshop in order to introduce both students and staff, into the Astrophysics and Computer Programming word. Follow the adventures in Kenya of this two young Astrophysicists next Thursday in the IAC seminar!


carlos_allende_190116s
Wednesday January 16, 2019
Dr. Carlos Allende
IAC

Abstract

The High Optical Resolution Spectrograph (HORuS), is now ready for operation on Gran Telescopio Canarias (GTC). HORuS is mainly a recyled instrument, largely based on components from UES, which was available at the WHT in the 90's. HORuS offers single-object R=25,000 spectroscopy with broad spectral coverage (380-700 nm, with gaps in the red). A 3x3 integral field unit (IFU) covering 4.4 arcsec2 gathers the light on the focal plane into optical fibers that later align to form a pseudo-slit at the entrance of the spectrograph.
The science fibers can be illuminated with light from calibration lamps. On the detector, with the IFU acting as an image slicer, monochromatic light spreads over hundreds of pixels, enabling the possibility of achieving, for very bright targets, signal-to-noise ratios per resolution element of several thousand in a single exposure. For fainter targets (12<V<16), readout noise is minimized by on-chip binning 8 (spatial) x 2 (spectral). From direct comparison of spectra of the same targets, the combined efficiency of HORuS+GTC is about 40% lower than UVES+VLT. For a V=7 star, the signal-to-noise per resolution element in a 900-seconds integration is about 1500 at 525 nm.


jose_fernandez-trincado_190115s
Tuesday January 15, 2019
Dr. J. G. Fernández-Trincado
Universidad de Atacama, Copiapó, Chile

Abstract

APOGEE contains more than hundred thousands new giant stars. This enabled
us to collected an unprecedented and homogeneous sample of giant stars with
light-element abundance variations similar to observed in “
*second-generation*” globular cluster stars. If they are really former
members of dissolved globular clusters, stars in these groups should show
some of the basic SG-like chemical patterns known for stars currently
belonging to the Milky Way globular clusters, such as depletion in C and O
together with N and Al enrichments. Here, I will present the results of an
updated census of *SG-like* stars from a near-infrared manual analysis
using the Brussels Automatic Stellar Parameter (BACCHUS) code to provide
the abundances of C, N, O, Mg, Si, Al, Fe, Ce and Nd for every line of
possible cluster member stars, which they migrate to the disk, halo and
bulge as unbound stars, and become part of the general stellar population
of the Milky Way. By combining wide-field time-series photometry with
APOGEE-2S spectroscopy data, we are in a good position to put the big
picture together. The VVV survey have produced a large variability dataset
towards the Milky Way bulge and disk, including data in the near-IR (J and
Ks). These data will allow us to place constraints on the “polluters" that
are responsible for the chemical peculiarities, with candidates including
TP-AGB stars, binary mass transfer, accretion of material from the winds of
AGB stars, etc.  A cross match between VVV sources and APOGEE targets is
ongoing.



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