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Munich Joint Astronomy Colloquia |
February 2001
1 - R. Laing
TBD
8 - Aake Nordlund (Copenhagen Astronomical Observatory)
"Star Formation and the Initial Mass Function"
ABSTRACT:
Super-sonic turbulence fragments molecular clouds in the
interstellar medium into dense sheets, filaments, cores and
large low density "voids", via the action of highly radiative
shocks. The distribution of core masses depends primarily on the
power spectrum of the turbulent flow, and on the jump conditions
for isothermal shocks in a magnetized gas. For a power spectrum
index beta=-1.8, consistent with results of numerical experiments
of super-sonic turbulence as well as with Larson's velocity-size
relation, we obtain a power law mass distribution of dense cores
with a slope equal to 3/(4-beta) = 1.36, consistent with the
slope of the Salpeter stellar IMF. We conclude that turbulent
fragmentation is the most important process at the origin of the
stellar IMF.
If the magnetic field is so weak that the magnetic pressure in the
postshock gas is smaller than the thermal pressure the IMF is much
steeper, with a power slope 3/(5-2 beta) = 2.1, which may be
relevant for star formation at high redshift.
For further details, see astro-ph/0011465.
15 - Marek Abramowicz (ITP Goeteborg University and Chalmers
University of Technology)
"Convection in black hole accretion disks"
ABSTRACT:
It was found recently that for realistic (alpha ~0.1) viscosity,
the dominant cooling mechanism in radiatively inefficient accretion flows
is provided by convection. Thus, the popular ADAF model for black hole
accretion disks should be revised. There are no strong outflows of purely
hydrodynamical origin from accretion disks. Such outflows should be
explained by other effects: probably those rooted in magnetohydrodynamics
or radiative transfer instabilities.
22 - Peter Schneider (Bonn)
"Cosmological parameters from cosmic shear"
ABSTRACT:
March 2001
1 - Andrzej Zdziarski (Copernicus Astronomical Center, Warsaw)
"Observational constraints on high-energy processes and geometry of
Seyferts and black-hole binaries"
ABSTRACT:High-quality observations of X-ray/soft gamma-ray spectra and variability
of accreting black holes obtained during the last decade impose severe
constraints on their theoretical models. The spectra and variability of
Seyferts is consistent with predominantly thermal Comptonization in a hot
plasma with kT of about 100 keV, and reprocessing of the Comptonized
radiation both close to the central black hole and in a remote torus. The
reprocessing region supplies also seed photons for Compton
upscattering. Correlations between various spectral components (the X-ray
power law, high-energy cutoff, Compton reflection, Fe K alpha
line) constrain the geometry, e.g., ruling out a static corona above a
cold disk. Very similar results are obtained for the hard state of
persistent and transient black-hole binaries. Consideration of synchrotron
emission of the hot plasma leads to constraints on any non-thermal tail in
the electron distribution and on the magnetic field. On the other hand,
studies of the soft state of black hole binaries (e.g., Cyg X-1, GRS
1915+105) lead to a picture with predominant non-thermal Comptonization in
flares above the surface of an accretion disk.
8 - K. Danzmann
"Listening to the Sound of the Universe:
Gravitational Wave Detectors on the Ground and in Deep Space"
ABSTRACT:
15 - Juergen Schmitt
"X-ray Astronomy of Stars"
ABSTRACT:
The last two decades have seen the emergence of a new field
in stellar astrophysics: Stellar X-ray astronomy. With soft X-ray
imagery X-ray emission was found from many thousands of solar-like stars.
I argue that these stars belong to a generic class of astrophysically
interesting sources, i.e., magnetically active systems.
I will summarize the most important findings of X-ray surveys of
late type stars and put those into the context of the solar-stellar
connection. Similarities and differences between solar and stellar X-ray
emission will be discussed. Recent results of CHANDRA
X-ray spectroscopy of stellar coronae will also presented.
22 - Francois-Xavier Desert (Grenoble)
"Archeops: a balloon experiment for measuring the cosmic microwave
background anisotropies"
ABSTRACT:
The Cosmic Microwave Background Radiation was emitted by the Universe
when it was 300,000 years old just after the Big Bang. Because this
ancient light has travelled through most of the observable Universe
and has been ``bent'' by its gravitation, its pattern can also yield
an indirect measurement of the density, age and curvature of the
Universe. There have been many experiments, like TOCO, Boomerang, and
Maxima that have measured these anisotropies.
The Archeops experiment aims at mapping the anisotropies from small to
large scales at the same time. For this purpose, a beam of at most 8
arcminutes is swept through the sky by spinning a 1.5 m telescope
pointing at 41 degree elevation around its vertical axis. A large
fraction of the sky is covered when the Earth rotation makes the swept
circle drift across the celestial sphere. A test flight of the
experiment containing only 6 bolometers was done in Sicily in
1999. The full experiment has just been flown from Kiruna (Sweden) to
Russia. It contained 21 bolometers with four frequency bands (143,
217, 353, 545 GHz) and covered 22 percent of the sky with a beam of 6
to 8 arcminutes. This experiment is unique not only for the large
fraction of the sky covered, but also because, for the first time,
polarisers were used for the analysis of the polarisation of the
interstellar dust emission.
This experiment results from an international collaboration including
USA (detectors and telescope), UK (cold optics), Italy (gondola, pivot
and star sensor) and France (cryogenics, electronics, instrument
integration and operation). It is a precursor for the Planck satellite
in many respects (open cycle dilution refrigerator that provides the
0.1 K temperature, scanning strategy...) and prepares the scientific
community working in Cosmology for the large Planck datasets.
I will present some conclusions from the Trapani flight and early
results from the January Swedish flight.
29 - F. Aharonian
"Ground-based Gamma-ray Astronomy: present status and
future perspectives"
ABSTRACT:The recent exciting observational results and theoretical predictions
supply a strong rationale for the systematic study of cosmic gamma
radiation in the very high energy domain. The new generation of imaging
atmospheric Cherenkov telescope arrays with energy threshold 100 GeV,
angular resolution of a few arc minutes, energy resolution better than
15%, and energy flux sensitivity of about 10**{-13} erg/cm^2 s will
provide crucial insight into a number of fundamental problems of modern
astrophysics and cosmology. I will describe the current status of the
ground-based gamma-ray astronomy and discuss the prospects of the field
with an emphasis on the concept and the performance of a future powerful
instrument - 5@5 (a 5 GeV energy threshold stereoscopic array of several
large imaging atmospheric Cherenkov telescopes installed at very high
mountain elevation of about 5 km a.s.l.) for the study of the gamma-ray
sky at energies from approximately 5 GeV to 100 GeV, where the
capabilities of both the current space-based and ground-based gamma-ray
projects are quite limited. With its potential to detect the ``standard''
EGRET gamma-ray sources with spectra extending beyond several GeV in
exposure times from 1 to 100 seconds, such a detector may serve as an
ideal "Gamma-Ray Timing Explorer" for the study of transient non-thermal
phenomena like gamma-radiation from AGN jets, synchrotron flares of
microquasars, the high energy (GeV) counterparts of Gamma Ray Bursts. 5@5
would also allow detailed gamma-ray spectroscopy of persistent nonthermal
sources like pulsars, supernova remnants, plerions, radiogalaxies, with
unprecedented for gamma-ray astronomy photon statistics.
April 2001
5 - Melissa McGrath
"Hubble Space Telescope Observations of Jupiter and its Galilean
Satellites"
ABSTRACT:
12 - no colloqium
19 - Gerda Horneck
"Origin and evolution of life in a cosmological context"
ABSTRACT:This is an attempt to consider life and the processes that lead to its
appearance, evolution and distribution not as a single shot that happened
on Earth once, but as a planetary phenomenon, embedded in the evolution of
the universe. To do this, a concerted action of many disciplines is
required, involving astrophysics, planetary sciences, organic chemistry,
paleontology in addition to the various sub disciplines of biology. The
talk will cover the different evolutionary steps towards the emergence of
life, such as the formation and occurrence of the biogenic elements, the
chemical evolution of complex organic molecules as precursors of life, the
history of life on Earth including the strategies of life to adapt to
extreme environments, potential habitats beyond the Earth
and possible modes of transport of life within our solar system. The
ultimate goal is to reach a more universal definition of life.
26 - Martin Elvis
"Banishing Quasar Confusion:
Unifying all the Emission, Absorption and Reflection Regions"
ABSTRACT:
For well over 30 years quasars and AGN have presented an ever
growing list of diverse and confusing phenomenology from optical to
X-ray wavelengths: Broad emission lines, narrow absorption lines,
broad absorption lines, `warm' soft X-ray absorbers, fluorescent
X-ray Fe-K emission, and Compton scattering 'humps'. Progress has been
slow, with each of these phenomena treated more or less in isolation.
Dr. Elvis has proposed a simple geometric and kinematic model that allows
all of these diverse phenomena to be understood as part of a single
structure. Once in place, this structure suggests a natural physical
interpretation, and constrains models. One consequence is that
the broad X-ray Fe-K line may not originate in the GR dominated
part of an accretion disk.
With minor extensions the model also suggests explanations for the
Baldwin effect (and its relatives), the "ionization" cones in AGN, and
the lack of high luminosity obscured AGN. The need for a "molecular
torus" in AGN is also much weaker, if this model is correct.
The model may also have surprising consequences for star formation
in the early universe.
May 2001
3 - Wyn Evans (Oxford)
"No Need for Dark Matter in Galaxies ?"
ABSTRACT:
10 - TBD
17 - D. Zaritsky
"Recovering the History of the Magellanic Clouds"
ABSTRACT:
24 - Holiday
31 - Evgeny Mazets
"20 years of Gamma-Ray Bursts with Konus experiments"
ABSTRACT:
June 2001
7 - M. Fall
"Formation and Disruption of Globular Star Clusters"
ABSTRACT:
14 - Holiday
21 - M. Strauss (Princeton)
"SDSS"
ABSTRACT:
28 - TBD
July 2001
5 - Tim Heckman (Johns Hopkins University)
"Starburst-driven winds: physics, phenomenology and implications"
ABSTRACT:
| Last update: May 25, 2001 | K.M. Górski | Send Comments |
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