pinecone/core-2020-05-10-deduplication huggingface dataset:
The first stars: Where did they form?

Several emerging links between high-redshift observational cosmology and the
Galactic fossil evidence found in the kinematics, metallicities and ages of
Milky Way stars are discussed. In a flat Cold Dark Matter model with
$\Omega\simeq 0.3$ that agrees with present large-scale structure observations,
the oldest stars in the Milky Way should have formed in the first halos where
gas was able to cool, at $z\simeq 20$. These earliest, weakly bound dwarf
galaxies probably turned only a small fraction of their gas to stars, which
should be metal-poor. However, the merging rate in the early universe was much
faster than the present one, so massive halos with more efficient star
formation and metallicities up to the highest values present today in the bulge
could have formed less than $10^9$ years after the oldest stars. The mean
metallicity produced in the universe by a given redshift is related to the mean
surface brightness of star-forming galaxies above this redshift, and also to
the reionization epoch if galaxies were the dominant sources of ionizing
radiation. The biased distribution of the early dwarf galaxies where the first
stars formed should result in an age gradient with radius of the
low-metallicity stars in the Milky Way, with the oldest ones concentrated in
the bulge and the youngest in the outer halo.Comment: to appear in THE FIRST STARS, Proceedings of the Second MPA/ESO
  Workshop, eds. Weiss, Abel, Hill (Springer: Heidelberg), 200
First Structure Formation and the First Stars

We discuss the results of recent 3D simulations of first structure formation
in relationship to the formation of the first stars. On the basis of a new,
high-resolution AMR simulation (spatial dynamic range = 30,000,000), we
conclude that the first stars are likely to be massive.Comment: 11 pages, 4 figures (see
  http://logy.harvard.edu/tabel/Homepage/trans.html for color postscripts of
  Fig. 3.) to appear in "The First Stars", Eds. A. Weiss, T. Abel & V. Hill,
  Proceedings of the MPA/ESO Workshop, Garching, Germany 4-6 August 1999,
  (Springer Verlag, Heidelberg
Where are the First Stars now?

We use high-resolution simulations to show that the current standard paradigm
for the growth of structure in the Universe predicts the formation of a galaxy
like our own to differ substantially from the classic ELS and Searle/Zinn
pictures. On scales larger than the Local Group, the earliest star formation
was extremely inhomogeneous, suggesting that the high redshift intergalactic
medium should have large-scale abundance variations. The very oldest stars
should be found today in the central regions of rich galaxy clusters. In the
Milky Way's bulge and stellar halo little correlation is expected between age
and metallicity. Some of the lowest metallicity stars may be relatively young.
Many of the oldest stars may have high metallicity. Spheroid stars were formed
before and during halo assembly, the oldest now lying preferentially at small
radii, while low metallicity stars lie preferentially at large radii. The bulk
of the Milky Way's stellar spheroid came from a small number of progenitors. It
should show little spatial structure in the inner 5 to 15 kpc, but consist at
each point of a superposition of hundreds of `cold' streams. Such streams have
been detected in the Solar neighborhood.Comment: 9 pages, 3 figures. To appear in the proceedings of the 1999 MPA/ESO
  workshop "The First Stars" (eds A. Weiss, T. Abel and V. Hill
Probing distant galaxies with lensing clusters

Clusters of galaxies as gravitational lenses allow to study the stellar
content and properties of high-z galaxies much fainter than the usual
spectroscopic field surveys. We review the recent results obtained on the
identification and study of very distant galaxies seen through lensing
clusters. Using the gravitational amplification effect in lenses with well
known mass distributions, it is possible to build up and study a sample of
galaxies with 1 < z < 7. Source candidates are selected close to the critical
lines at high-z, through photometric redshifts computed on a large wavelength
interval, as well as lens-inversion criteria. This procedure allows to reduce
the selection biases in luminosity, and towards active star-forming objects,
provided that selection criteria include IR photometry. This is the method
presently used in our large collaborative program, aimimg to perform the
spectroscopic follow up with the VLT of high-z candidates selected from
suitable photometric campaigns.Comment: 7 pages, 5 figures, paper presented at the VLT Opening Symposium,
  Antofagasta (Chile), 1-4 March, 199
A Sunyaev-Zel'dovich Effect Survey for High Redshift Clusters

Interferometric observations of the Sunyaev-Zel'dovich Effect (SZE) toward
clusters of galaxies provide sensitive cosmological probes. We present results
from 1 cm observations (at BIMA and OVRO) of a large, intermediate redshift
cluster sample. In addition, we describe a proposed, higher sensitivity array
which will enable us to survey large portions of the sky. Simulated
observations indicate that we will be able to survey one square degree of sky
per month to sufficient depth that we will detect all galaxy clusters more
massive than 2x10^{14} h^{-1}_{50}M_\odot, regardless of their redshift. We
describe the cluster yield and resulting cosmological constraints from such a
survey.Comment: 7 pages, 6 figures, latex, contribution to VLT Opening Symposiu
The connection between X-ray Clusters and Star Formation

The properties of X-ray clusters of galaxies can be well understood in terms
of a competition between shock heating and adiabatic compression. Strong shocks
are expected to be important for massive clusters, while adiabatic compression
is dominant for small clusters and groups. The scale of the shock/adiabatic
transition is marked by a change of slope of the L-T relation and in the global
properties of the emitting plasma. This scale is connected to star formation
processes. Two quantities are crucial: the average energy injected in the IGM
from stars and SNe, and the epoch of the energy injection. We show how these
quantities can be synthesized in terms of specific entropy, which ultimately
determines the X-ray emission from groups and clusters.Comment: 4 pages, including 2 figures, LaTex2e. To be published in the
  Proceedings of the ``VLT Opening Symposium'', Antofagasta (Chile), 1-4 March
  1999. Typos changed in eq. (3
Clustering at High Redshift

Together with the CMB, the three sources of information that astronomers have
at high redshift as probes of the formation and evolution of the LSS are QSOs,
galaxies and absorbers observed in the spectrum of distant background objects.
In this contribution I try to give a hint of historical perspective, following
how the technological advances have driven the emphasis from one class to
another, in order to show what are the likely forthcoming milestones.Comment: 8 pages Latex, with 3 PostScript figures. To appear in the
  Proceedings of the VLT Opening Symposium, Antofagasta, Chile 1-4 March 199
EIS - An Imaging Survey for VLT Science

The imaging data assembled by the recently completed ESO Imaging Survey (EIS)
are reviewed and their scientific value briefly assessed. Among the various
applications, the imaging data has been used to build a large sample of
candidate distant clusters of galaxies in the Southern Hemisphere to be used
for follow-up observations with the VLT as well as other space and ground-based
facilities. Preliminary results from ongoing work to confirm these candidates
are reported and the future prospects discussed.Comment: 6 pages, To be published in the Proceedings of the ``VLT Opening
  Symposium'', Antofagasta (Chile), 1-4 March 199
The Space Missions WAXS/WFXT and SWIFT: New Targets for the VLT

At OAB we were, during the year 1998, deeply involved in planning two
important space missions for which very large ground based telescopes, VLT in
particular, would play a very large and important role in the optical followup.
The study of the first mission, Wide Angle X-ray Survey using a Wide Field
X-ray Telescope, was coordinated by the Observatory of Brera, involved mainly
Italian industries and resulted in a proposal to the Italian Space Agency under
the Small Satellite Program. The second mission, SWIFT, has been coordinated
and directed by the Goddard Space Flight Center and resulted in the submission
of a proposal to NASA under the MIDEX program. The science goal of this mission
is the detection and study of the Gamma-ray bursts.Comment: 6 pages, including 1 figure, LaTex2e. To be published in the
  Proceedings of the ``VLT Opening Symposium'', Antofagasta (Chile), 1-4 March
  199
The Hubble Constant from the Fornax Cluster Distance

Type Ia supernovae are the best cosmological standard candles available. The
intrinsic scatter of their decline-rate- and colour-corrected peak brightnesses
in the Hubble diagram is within observational error limits, corresponding to an
uncertainty of only 3km/s/Mpc of the Hubble constant. Any additional
uncertainty, resulting from peak-brightness calibration, must be kept small by
measuring distances to nearby host galaxies most precisely.
  A number of different distance determinations of the Fornax cluster of
galaxies agree well on a distance modulus of 31.35+-0.04mag (18.6+-0.3Mpc).
This leads to accurate absolute magnitudes of the well-observed Fornax type Ia
SNe SN1980N, SN1981D, and SN1992A and finally to a Hubble constant of
H_0=72+-6km/s/Mpc.Comment: 5 pages, 1 figure, to be published in: Science in the VLT Era and
  Beyond. ESO VLT Opening Symposium, Springer, in press; typos remove
Studying the Stellar Populations of the Local Group with VLT

The power of high quality imaging combined with the large collecting area of
each VLT telescope is impressive, and there are clearly many exciting
discoveries waiting to be made. The study of resolved stellar populations will
certainly benefit greatly from this new observatory, as with Palomar before. We
will now be able to probe a much large range of star forming environment within
the Local Group, and specifically very low metallicity regions in nearby dwarf
irregular galaxies. The study of individual stars and star-formation regions in
the nearby universe is the only way we will understand the observations of
galaxy populations at high redshift. We present some initial results from the
BVI imaging of the Local Group galaxy Antlia made during FORS1 science
verification in January 1999.Comment: To appear in the proceedings of the VLT Opening Symposium, held in
  Antofagasta, Chile in March 199
Fine structure of the red clump in Local Group galaxies

Some fine structures can nowadays be identified in the high-quality
colour-magnitude diagrams (CMD) of Local Group galaxies. The clump of red
giants, for instance, may present a significant colour spread, and extensions
to both brighter and fainter luminosities. Such features are predicted by
population synthesis models which consider stars in the complete relevant
ranges of ages and metallicities, and are potentially useful for constraining
the star formation histories of the parent galaxies over scales of gigayears.
We briefly comment the cases of fields in the Magellanic Clouds, M31, and the
local CMD from Hipparcos.Comment: To appear in Proc. of the VLT Opening Symposium (Parallel Workshop 2:
  Star-Way to the Universe
Abundances in Sagittarius: present state and perspectives for the use of
  VLT

Sagittarius, the nearest external galaxy, will be amenable to detailed
abundance studies with VLT and other 8m class telescopes. Such data, in
conjuction with the similar data of our own galaxy, will allow a deeper
understanding of chemical evolution. Our study conducted with NTT shows the
presence of metal-rich stars with radial velocities compatible with Sagittarius
membership and of stars as metal-poor as [Fe/H]=-1.5. In this talk I shall
address the way in which VLT instruments will allow to clarify this intricate
situation.Comment: Invited talk at the ESO VLT Opening Symposium, Antofagasta, March 1-4
  199
Tidal Tails around 20 Galactic Globular Clusters

We present our study of the 2-D structures of the tidal tails associated with
20 galactic globular clusters, structures obtained by using the wavelet
transform to detect weak structures at large scale and filter the strong
background noise for the low galactic latitude clusters (Leon, Meylan & Combes
2000). We also present N-body simulations of globular clusters, in orbits
around the Galaxy, in order to study quantitatively and geometrically the tidal
effects they encounter (Combes, Leon & Meylan 2000).Comment: 6 pages, 2 figures, to be published in ``Star-Way to the Universe'',
  Proceedings of the VLT Opening Workshop, eds. L. Pasquini and R.P. Kudritzki,
  (Berlin: Springer
Cosmic Star Formation History and the Brightness of the Night Sky

I review the constraints imposed by the observed extragalactic background
light (EBL) on the history of the stellar birthrate in galaxies. At faint
magnitudes, the logarithmic slope of the galaxy counts is flatter than 0.4 in
all seven UBVIJHK optical bandpasses of the Hubble Deep Field-South imaging
survey. The integration of the number counts provides a lower limit to the
surface brightness of the optical extragalactic sky of 15 nW/m2/sr, comparable
to the intensity of the far-IR background from COBE data. If the initial mass
function has a Salpeter slope with a lower mass cutoff consistent with
observations of M subdwarf disk stars, a lower limit of Omega_*>0.005 (at
Hubble constant 50 km/s/Mpc) is derived for the visible (processed gas + stars)
mass density needed to generate an extragalactic background light (EBL) at a
level of 50 nW/m2/sr. The current `best-guess' estimate to Omega_* is 0.012,
about 16% of the nucleosynthetic baryon density. The contribution of quasar
activity to the observed EBL is unlikely to exceed 20%.Comment: LaTeX, 9 pages, 4 figures, invited review at the VLT Opening
  Symposium, Antofagasta, Chile 1-4 March 199
Planetary Microlensing: Present Status and Long-term Goals

Massive gravitational microlensing programs were begun about a decade ago as
a means to search for compact baryonic dark matter in the Galaxy, but before
the first events were detected the technique was also proposed as a means of
detecting extra-solar planets in our Galaxy. Current microlensing planet
searches, which have been underway for four years, are sensitive to jovian-mass
planets orbiting a few to several AU from their parent Galactic stars. Within
two years, sufficient data should be in hand to characterize or meaningfully
constrain the frequency of massive planets in this range of parameter space,
nicely complementing information about planets at smaller orbital radii now
being provided by radial velocity searches. In principle, the technique could
be pushed to smaller planetary masses, but only if a larger number of faint
microlensed sources can be monitored with higher precision and temporal
sampling. The VST on Paranal, with spectroscopic follow-up with the VLT, may be
the ideal instrument for such an ambitious program.Comment: Invited Review at VLT Opening Symposium, Antofagasta, Chile, March
  1999. To appear in the Springer-Verlag series ``ESO Astrophysics Symposia'
Why Do Black--Hole X-ray Binaries Tend to Be Transient?

Black hole X-ray binaries are transient probably because their discs are
subject to the same thermal-viscous instability which is present in dwarf nova
binary systems. I discuss applications of the dwarf-nova instability model to
transient, low-mass, X-ray binary systems. When disc truncation and X-ray
irradiation are taken into account this model is capable of reproducing the
basic properties of X-ray binary outbursts (Dubus et al. 2000).Comment: 6 pages, 2 figures; Proceedings of the ESO Workshop on "Black Holes
  in Binaries and Galactic Nuclei: Diagnostics, Demography and Formation", in
  honour of Prof. R. Giacconi, in pres
Supermassive Black Holes Can Hardly Be "Silent"

There is now ample evidence that most - perhaps all - galactic spheroids host
a supermassive BH at their center. This has been assessed using a variety of
observational techniques, from stellar and/or gas dynamics to megamasers. Yet
another promising technique is offered by the case of the Virgo elliptical NGC
4552, in which early HST/FOC observations revealed a central low-luminosity
flare. Subsequent HST/FOS observations with a 0.21 arcsec aperture have
revealed a rich emission-line spectrum with broad and narrow components with
FWHM of 3000 and 700 km/s, respectively. This variable, mini-AGN at the center
of NGC 4552 is most naturally the result of a sporadic accretion event on a
central BH. It has a H$\alpha$ luminosity of only $\sim 10,000 \lsun$, making
it the likely, intrinsically faintest AGN known today. Only thanks to the
superior resolution of HST such a faint object has been discovered and studied
in detail, but adaptive optics systems on large ground-based telescopes may
reveal in the future that a low level of accretion onto central massive BHs is
an ubiquitous phenomenon among galactic spheroids. FOC/FOS observations of a
central spike in NGC 2681 reveal several analogies with the case of NGC 4552,
while yet another example is offered by a recent exciting finding with STIS by
R.W. O'Connell in NGC 1399, the third galaxy in our original program.
garchingbhComment: 7 pages, Latex, lamuphys.sty, to appear in ``Black Holes in Binaries
  and Galactic Nuclei'', ed. L. Kaper, E.P.J. van den Heuvel, P.A. Woudt
  (Berlin: Springer
Jets from black hole binaries and Galactic Nuclei

Relativistic outflows are a common phenomenon in accreting black holes.
Despite the enormous differences in scale, stellar-mass black holes in binaries
and supermassive black holes in Galactic Nuclei produce jets with analogous
properties. In both are observed two types of relativistic outflows: 1) steady
compact jets with flat-spectrum, and 2) sporadic extended jets with
steep-spectrum and apparent superluminal motions. Besides, the most common
class of gamma-ray bursts are afterglows from ultra-relativistic jets
associated to the formation of black holes at cosmological distances.Comment: 6 pages, 3 figures. To be published at the Proceedings of the ESO
  Workshop on Black holes in binaries and galactic nuclei. September 6-8, 1999,
  Garching, German
Neutron Star Mass Determinations

I review attempts made to determine the properties of neutron stars. The
focus is on the maximum mass that a neutron star can have, or, conversely, the
minimum mass required for the formation of a black hole. There appears to be
only one neutron star for which there is strong evidence that its mass is above
the canonical 1.4 solar masses, viz., Vela X-1, for which a mass close to 1.9
solar masses is found. Prospects for progress appear brightest for studies of
systems in which the neutron star should have accreted substantial amounts of
matter.Comment: 6 pages, 3 figures, to appear in Proc. ESO Workshop on "Black Holes
  in Binaries and Galactic Nuclei", Garching (Sept. 1999), L. Kaper, E.P.J. van
  den Heuvel, P.A. Woudt eds., Springer-Verla
On the Formation of Jets

The phenomenology of jets associated with a variety of black hole systems is
summarized, emphasizing the constraints imposed on their origin. Models of jet
formation are reviewed, focusing in particular on recent ideas concerning MHD
models. Finally, the potential for advancing our understanding of jets both
through future observations - especially forthcoming X-ray missions - and for
elucidating some crucial theoretical questions is highlighted.Comment: 10 pages, Springer-Verlag LaTex style. To appear in Proc. ESO
  Workshop on "Black Holes in Binaries and Galactic Nuclei", Garching (Sept.
  1999), L. Kaper, E.P.J. van den Heuvel, P.A. Woudt eds., Springer-Verla
Structure of the globular cluster M15 and constraints on a massive
  central black hole

Globular clusters could harbor massive central black holes (BHs), just as
galaxies do. So far, no unambiguous detection of a massive BH has been reported
for any globular cluster. However, the dense core-collapsed cluster M15 seems
to be a good candidate. I review the available photometric and kinematic data
for this cluster. Both are consistent with a BH of approximately 2000 solar
masses, although such a BH is not unambiguously required by the data. I discuss
some ongoing studies with Keck and HST which should shed more light on this
issue in the coming years.Comment: To appear in `Black Holes in Binaries and Galactic Nuclei',
  Proceedings of an ESO Workshop in September 1999, Kaper L., van den Heuvel E.
  P. J., Woudt P. A., eds., Springer-Verlag, 2000. 6 pages LaTeX with 1
  PostScript figur
Counting points on hyperelliptic curves over finite fields

International audienceWe describe some algorithms for computing the cardinality of hyperelliptic curves and their Jacobians over finite fields. They include several methods for obtaining the result modulo small primes and prime powers, in particular an algorithm à la Schoof for genus 2 using Cantor's division polynomials. These are combined with a birthday paradox algorithm to calculate the cardinality. Our methods are practical and we give actual results computed using our current implementation. The Jacobian groups we handle are larger than those previously reported in the literature
Experiences building a service execution node for distributed IN systems

We describe a Distributed Intelligent Network architecture. By laying a distributed processing environment a more flexible mapping between functional and physical entities is afforded. Mobile code can in turn be employed to cater for performance or load balancing considerations as well as to increase the overall flexibility and manageability of the system. Changes in the physical locations of the endpoints of a control relationship can be abstracted to higher layer software by virtue of the location transparency properties of the environment. We report on the development of an experimental implementation and we demonstrate how the aforesaid technologies improved its characteristics
Analysing Time Dependent Security Properties in CSP Using PVS.

This paper details an approach to verifying time dependent authentication properties of security protocols. We discuss the introduction of time into the Communicating Sequential Processes (CSP) protocol verification framework of [11]. The embedding of CSP in the theorem prover PVS (Prototype Verification System) is extended to incorporate event-based time, retaining the use of the existing rank function approach to verify such properties. An example analysis is demonstrated using the Wide-Mouthed Frog protocol
Analysis of human motion using snakes and neural networks

The original publication is available at www.springerlink.comA novel technique is described for analysing human movement in outdoor scenes. Following initial detection of the humans using active contour models, the contours are then re-represented as normalised axis crossover vectors. These vectors are then fed into a neural network which determines the typicality of a given human shape, allowing for a given human???s motion deformation to be analysed. Experiments are described which investigate the success of the technique being presented