Found 2 talks width keyword Orion Nebulae

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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.

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Thursday October 20, 2011
Dr. Adal Mesa
University of Hawaii, USA

Abstract

The spectral analysis of HII regions allows one to determine the chemical composition of the ionized gas phase of the interstellar medium (ISM) from the solar neighborhood to the high-redshift galaxies. Therefore, it stands as an essential tool for our knowledge of the chemical evolution of the Universe. However, it turns out that chemical abundances of heavy-element ions determined from the bright collisionally excited lines (CELs) are systematically lower than the abundances derived from the faint recombination lines (RLs) emitted by the same ions. Today, this controversial issue is known as abundance discrepancy problem and it is far from negligible. In the analysis of Galactic and extragalactic HII regions the O2+/H+ ratio calculated from the OII RLs is between 0.10 and 0.35 dex higher than that obtained from the [OIII] CELs. In this talk, we will face this problem in the benchmark object of the solar vicinity, the Orion Nebula. Due to its high surface brightness and proximity, the Orion Nebula is an ideal lab, which allows us to study in detail the possible role of its rich and well-resolved internal structure (such as Herbig-Haro objects, protoplanetary disks or bars) on the abundance discrepancy.


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    Donaji Esparza Arredondo
    Tuesday September 17, 2019 - 12:30  (Aula)
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    Prof. Michael Kramer
    Thursday October 3, 2019 - 10:30  (Aula)

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