pinecone/core-2020-05-10-deduplication huggingface dataset:
Shear-driven magnetic buoyancy oscillations

The effects of uniform horizontal shear on a stably stratified layer of gas
is studied. The system is initially destabilized by a magnetically buoyant flux
tube pointing in the cross-stream direction. The shear amplifies the initial
field to Lundquist numbers of about 200-400, but then its value drops to about
100-300, depending on the value of the sub-adiabatic gradient. The larger
values correspond to cases where the stratification is strongly stable and
nearly isothermal. At the end of the runs the magnetic field is nearly
axisymmetric, i.e. uniform in the streamwise direction. In view of Cowling's
theorem the sustainment of the field remains a puzzle and may be due to subtle
numerical effects that have not yet been identified in detail. In the final
state the strength of the magnetic field decreases with height in such a way
that the field is expected to be unstable. Low amplitude oscillations are seen
in the vertical velocity even at late times, suggesting that they might be
persistent.Comment: 10 pages, 16 figure
The open cluster Berkeley 53

We present a photometric study of the neglected open cluster Berkeley 53. We
derived its fundamental parameters, such as the age, the interstellar
reddening, and the distance from the Sun, based on BV photometry combined with
near-infrared JHK data. The structure and the mass function of the cluster were
also studied and the total number of members and the total mass were estimated.
The cluster was found to be a rich and massive stellar system, located in the
Perseus Arm of the Milky Way, 3.1+/-0.1 kpc from the Sun. Its age exceeds 1 Gy
but it seems to be very young in the context of its dynamical evolution. The
analysis of the two-color diagrams and color-magnitude diagrams indicates that
the cluster is significantly reddened. However, both methods resulted in
different values of E(B-V), i.e. 1.21+/-0.04 and 1.52+/-0.01, respectively.
This discrepancy suggests the presence of an abnormal interstellar extinction
law toward the cluster
Metal enrichment of the intracluster medium: SN-driven galactic winds

We investigate the role of supernova (SN)-driven galactic winds in the
chemical enrichment of the intracluster medium (ICM). Such outflows on galactic
scales have their origin in huge star forming regions and expel metal enriched
material out of the galaxies into their surroundings as observed, for example,
in the nearby starburst galaxy NGC 253. As massive stars in OB-associations
explode sequentially, shock waves are driven into the interstellar medium (ISM)
of a galaxy and merge, forming a superbubble (SB). These SBs expand in a
direction perpendicular to the disk plane following the density gradient of the
ISM. We use the 2D analytical approximation by Kompaneets (1960) to model the
expansion of SBs in an exponentially stratified ISM. This is modified in order
to describe the sequence of SN-explosions as a time-dependent process taking
into account the main-sequence life-time of the SN-progenitors and using an
initial mass function to get the number of massive stars per mass interval. The
evolution of the bubble in space and time is calculated analytically, from
which the onset of Rayleigh-Taylor instabilities in the shell can be
determined. In its further evolution, the shell will break up and
high-metallicity gas will be ejected into the halo of the galaxy and even into
the ICM. We derive the number of stars needed for blow-out depending on the
scale height and density of the ambient medium, as well as the fraction of
alpha- and iron peak elements contained in the hot gas. Finally, the amount of
metals injected by Milky Way-type galaxies to the ICM is calculated confirming
the importance of this enrichment process.Comment: 6 pages, 7 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
Cool gas accretion, thermal evaporation and quenching of star formation
  in elliptical galaxies

The most evident features of colour-magnitude diagrams of galaxies are the
red sequence of quiescent galaxies, extending up to the brightest elliptical
galaxies, and the blue cloud of star-forming galaxies, which is truncated at a
luminosity L~L*. The truncation of the blue cloud indicates that in the most
massive systems star formation must be quenched. For this to happen the
virial-temperature galactic gas must be kept hot and any accreted cold gas must
be heated. The elimination of accreted cold gas can be due to thermal
evaporation by the hot interstellar medium, which in turn is prevented from
cooling by feedback from active galactic nuclei.Comment: 2 pages, to appear in Astronomische Nachrichten (proceedings of
  Symposium 6 of the JENAM 2008, Vienna
The effect of clouds on the dynamical and chemical evolution of gas-rich
  dwarf galaxies

We study the effects of clouds on the dynamical and chemical evolution of
gas-rich dwarf galaxies, in particular focusing on two model galaxies similar
to IZw18 and NGC1569. We consider both scenarios, clouds put at the beginning
of the simulation and continuously created infalling ones. Due to dynamical
processes and thermal evaporation, the clouds survive only a few tens of Myr,
but during this time they act as an additional cooling agent and the internal
energy of cloudy models is typically reduced by 20 - 40% in comparison with
models without clouds. The clouds delay the development of large-scale
outflows, therefore helping to retain a larger amount of gas inside the galaxy.
However, especially in models with continuous creation of infalling clouds,
their bullet effect can pierce the expanding supershell and create holes
through which the superbubble can vent freshly produced metals. Moreover,
assuming a pristine chemical composition for the clouds, their interaction with
the superbubble dilutes the gas, reducing the metallicity (by up to ~ 0.4 dex)
with respect to the one attained by diffuse models.Comment: 3 pages, 3 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
The Evolution of Cluster Early-Type Galaxies over the Past 8 Gyr

We present the Fundamental Plane (FP) of early-type galaxies in the clusters
of galaxies RXJ1415.1+3612 at z=1.013. This is the first detailed FP
investigation of cluster early-type galaxies at redshift z=1. The distant
cluster galaxies follow a steeper FP relation compared to the local FP. The
change in the slope of the FP can be interpreted as a mass-dependent evolution.
To analyse in more detail the galaxy population in high redshift galaxy
clusters at 0.8<z<1, we combine our sample with a previous detailed
spectroscopic study of 38 early-type galaxies in two distant galaxy clusters,
RXJ0152.7-1357 at z=0.83 and RXJ1226.9+3332 at z=0.89. For all clusters
Gemini/GMOS spectroscopy with high signal-to-noise and intermediate-resolution
has been acquired to measure the internal kinematics and stellar populations of
the galaxies. From HST/ACS imaging, surface brightness profiles, morphologies
and structural parameters were derived for the galaxy sample. The least massive
galaxies (M=2x10^{10}M_{\sun}) in our sample have experienced their most recent
major star formation burst at z_{form}~1.1. For massive galaxies
(M>2x10^{11}M_{\sun}) the bulk of their stellar populations have been formed
earlier z_{form}>~1.6. Our results confirm previous findings by Jorgensen et
al. This suggests that the less massive galaxies in the distant clusters have
much younger stellar populations than their more massive counterparts. One
explanation is that low-mass cluster galaxies have experienced more extended
star formation histories with more frequent bursts of star formation with
shorter duration compared to the formation history of high-mass cluster
galaxies.Comment: 6 pages, 2 figures, Talk for "Matter Cycles of Galaxies in Clusters",
  presented at JENAM 2008, Vienna, to be published in Astronomische Nachrichten
  in Nov 2009 (proceedings of Symposium 6 of the JENAM 2008, Vienna
A continuum of structure and stellar content from Virgo cluster
  early-type dwarfs to giants?

Based on the wealth of multiwavelength imaging data from the SDSS, we
investigate whether dwarf and giant early-type galaxies in the Virgo cluster
follow a continuum in their structural parameters and their stellar population
characteristics. More specifically we study the relation between size and
brightness for the galaxies and their color magnitude relation. In both cases,
we find noticeable deviations from a simple joint behavior of dwarfs and
giants. We discuss these findings in the light of the different formation
mechanisms commonly assumed for dwarf and giant early types, thereby taking
into account the existence of several distinct early-type dwarf subclasses. By
comparing our results to a semianalytic model of galaxy formation, we argue
that the analyzed relations might be reproduced by processes that form dwarfs
and giants altogether. The work presented here is based on Janz & Lisker 2008,
2009.Comment: 7 pages, 3 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
A composite K-band Luminosity Function for Cluster Galaxies

We present a composite K-band luminosity function for 10 clusters at low
redshift, where member galaxies are identified from an existing spectroscopic
survey (the 2dF galaxy redshift survey). Our kinematically selected K-band
luminosity function is well fitted by a Schechter function with $M^*_K=-24.50 +
5\log h$ and $\alpha=-0.98$ over $-27 < <M_K -5\log h < -22$. This is very
similar to the 2dF field value and suggests that the integrated mass accretion
history of galaxies does not vary strongly with environmentComment: 3 pages, 1 figure, Astronomische Nachrichten (JENAM 2008 Symposium 6
The evolution of cluster dwarfs

We summarize the results from analyzing six clusters of galaxies at 0.14 < z
< 0.40 observed with the Hubble Space Telescope Advanced Camera for Surveys. We
derive deep composite luminosity functions in B,g,V,r,i and z down to an
absolute magnitude of -14 +5 log h mag. The luminosity functions are fitted by
a single Schechter function with M^*=-19.8,-20.9,-21.9, -22.0,-21.7 and -22.3 i
B,g,V.r,i,z respectively and alpha=-1.3 for all bands. The data suggest that
the red sequence dominates the luminosity function down to more than 6 mag.
below L*, the dwarf spheroidal regime. Hence, at least at z=0.3 the red
sequence is well established and galaxies down to dwarf spheroidals are fully
assembled within these clusters. We do not detect the faint-end upturn (M >
-16) that is observed in lower redshift clusters. If this is real, the
faint-end population has originated since z = 0.3.Comment: To be published in Astronomische Nachrichten, proceeding of JENAM
  2008 Symposium 6. Includes an.cls classfil
Metallicity Gradients - Mass Dependency in Dwarf Elliptical Galaxies

The formation and evolution of galaxies is imprinted on their stellar
population radial gradients. Two recent articles present conflicting results
concerning the mass dependence of the metallicity gradients for early-type
dwarf galaxies. On one side, Spolaor et al. show a tight positive correlation
between the total metallicity, Z/H and the mass. On the other side, in a
distinct sample, we do not find any trend involving Fe/H (Koleva et al.). In
order to investigate the origin of the discrepancy, we examine various factors
that may affect the determination of the gradients: namely the sky subtraction
and the signal-to-noise ratio. We conclude that our detection of gradients are
well above the possible analysis biases. Then, we measured the Mg/Fe relative
abundance profile and found moderate gradients. The derived Z/H gradients
scatter around -0.4 dex/r_e. The two samples contain the same types of objects
and the reason of the disagreement is still not understood.
  Based on observations made with ESO telescopes at La Silla Paranal
observatory under program ID076.B-0196.Comment: 6 pages, 4 figures, Talk for "Matter Cycles of Galaxies in Clusters",
  JENAM 2008, Vienna, to be published in Astronomische Nachrichten; (1) IAC,
  Spain (2) Observatoire de Lyon, France (3) Ghent University, Belgium (4)
  University of Vienna, Austri
The Properties of Fossil Groups of Galaxies

Numerical simulations as well as optical and X-ray observations over the last
few years have shown that poor groups of galaxies can evolve to what is called
a fossil group. Dynamical friction as the driving process leads to the
coalescence of individual galaxies in ordinary poor groups leaving behind
nothing more than a central, massive elliptical galaxy supposed to contain the
merger history of the whole group. Due to merging timescales for less-massive
galaxies and gas cooling timescales of the X-ray intragroup medium exceeding a
Hubble time, a surrounding faint-galaxy population having survived this
galactic cannibalism as well as an extended X-ray halo similar to that found in
ordinary groups, is expected. Recent studies suggest that fossil groups are
very abundant and could be the progenitors of brightest cluster galaxies (BCGs)
in the centers of rich galaxy clusters. However, only a few objects are known
to the literature. This article aims to summarize the results of observational
fossil group research over the last few years and presents ongoing work by the
authors. Complementary to previous research, the SDSS and RASS surveys have
been cross-correlated to identify new fossil structures yielding 34 newly
detected fossil group candidates. Observations with ISIS at the 4.2m William
Herschel Telescope on La Palma have been carried out to study the stellar
populations of the central ellipticals of 6 fossil groups. In addition
multi-object spectroscopy with VLTs VIMOS has been performed to study the shape
of the OLF of one fossil system.Comment: 10 pages, 5 figures, 4 tables, to be published in Astronomische
  Nachrichten (proceedings of Symposium 6 of the JENAM 2008, Vienna
Transport of cosmic rays in the nearby starburst galaxy NGC 253

Radio halos require the coexistence of extra-planar cosmic rays and magnetic
fields. Because cosmic rays are injected and accelerated by processes related
to star formation in the disk, they have to be transported from the disk into
the halo. A vertical large-scale magnetic field can significantly enhance this
transport. We observed NGC 253 using radio continuum polarimetry with the
Effelsberg and VLA telescopes. The radio halo of NGC 253 has a dumbbell shape
with the smallest vertical extension near the center. With an estimate for the
electron lifetime, we measured the cosmic-ray bulk speed as 300+/-30 km/s which
is constant over the extent of the disk. This shows the presence of a "disk
wind" in NGC 253. We propose that the large-scale magnetic field is the
superposition of a disk (r,phi) and a halo (r,z) component. The disk field is
an inward-pointing spiral with even parity. The conical (even) halo field
appears in projection as an X-shaped structure, as observed in other edge-on
galaxies. Interaction by compression in the walls of the superbubbles may
explain the observed alignment between the halo field and the lobes of hot
Halpha- and soft X-ray emitting gas. The disk wind is a good candidate for the
transport of small-scale helical fields, required for efficient dynamo action,
and as a source for the neutral hydrogen observed in the halo.Comment: 6 pages, 9 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
A study of major mergers using a multi-phase ISM code

Galaxy interactions are a common phenomenon in clusters of galaxies.
Especially major mergers are of particular importance, because they can change
the morphological type of galaxies. They have an impact on the mass function of
galaxies and they trigger star formation - the main driver of the Galactic
Matter Cycle. Therefore, we conducted a study of major mergers by means of a
multi-phase ISM code. This code is based on a TREE-SPH-code combined with a
sticky particle method allowing for star formation controlled by the properties
of a multi-phase ISM. This is in contrast to the usually implemented Schmidt
law depending mainly on the gas density. Previously, this code was used on
isolated galaxies. Since our star formation recipe is not restricted to a
special type of galaxy, it is interesting to apply it to interacting galaxies,
too. Our study on major mergers includes a research of global properties of the
interacting system, namely the star formation rate and the star formation
efficiency, the evaporation and condensation rates, as well as the mass
exchange of distinct components, namely stars, diffuse ISM, and clouds.
Investigating these properties provides insight to interrelations between
various physical processes. The results indicate that the star formation
efficiency as well as the evaporation and condensation rates are influenced by
the interaction.Comment: 6 pages, 7 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
The Evolution of Spheroidal Galaxies in Different Environments

We analyse the kinematic and chemical evolution of 203 distant spheroidal
(elliptical and S0) galaxies at 0.2<z<0.8 which are located in different
environments (rich clusters, low-mass clusters and in the field). VLT/FORS and
CAHA/MOSCA spectra with intermediate-resolution have been acquired to measure
the internal kinematics and stellar populations of the galaxies. From HST/ACS
and WFPC2 imaging, surface brightness profiles and structural parameters were
derived for half of the galaxy sample. The scaling relations of the
Faber-Jackson relation and Kormendy relation as well as the Fundamental Plane
indicate a moderate evolution for the whole galaxy population in each density
regime. In all environments, S0 galaxies show a faster evolution than
elliptical galaxies. For the cluster galaxies a slight radial dependence of the
evolution out to one virial radius is found. Dividing the samples with respect
to their mass, a mass dependent evolution with a stronger evolution of
lower-mass galaxies (M<2x10^{11} M_{\sun}) is detected. Evidence for recent
star formation is provided by blue colours and weak OII emission or strong
H\delta absorption features in the spectra. The results are consistent with a
down-sizing formation scenario which is independent from the environment of the
galaxies.Comment: 4 pages, 2 figures, to be published in Astronomische Nachrichten
  (proceedings of Symposium 6 of the JENAM 2008, Vienna
Early-type dwarf galaxies in clusters: a mixed bag with various origins?

The formation of early-type dwarf (dE) galaxies, the most numerous objects in
clusters, is believed to be closely connected to the physical processes that
drive galaxy cluster evolution, like galaxy harassment and ram-pressure
stripping. However, the actual significance of each mechanism for building the
observed cluster dE population is yet unknown. Several distinct dE subclasses
were identified, which show significant differences in their shape, stellar
content, and distribution within the cluster. Does this diversity imply that
dEs originate from various formation channels? Does "cosmological" formation
play a role as well? I try to touch on these questions in this brief overview
of dEs in galaxy clusters.Comment: 10 pages, 7 figures, Review for "Matter Cycles of Galaxies in
  Clusters", JENAM 2008, Vienna, to be published in Astronomische Nachrichte
Orbital eccentricity of the symbiotic star MWC 560

We present projected rotational velocity measurements of the red giant in the
symbiotic star MWC 560 (V694 Mon), using the high-resolution spectroscopic
observations with the FEROS spectrograph. We find that the projected rotational
velocity of the red giant is vsini = 8.2 +/- 1.5 km/s, and estimate its
rotational period to be P_rot = 144-306 days. Using the theoretical predictions
of tidal interaction and pseudosynchronization, we estimate the orbital
eccentricity e=0.68-0.82. We briefly discuss the connection of our results with
the photometric variability of the object.Comment: AN, accepte
Fluctuation dynamo based on magnetic reconnections

We develop a new model of the fluctuation dynamo in which the magnetic field
is confined to thin flux ropes advected by a multi-scale flow which models
turbulence. Magnetic dissipation occurs only via reconnections of flux ropes.
The model is particularly suitable for rarefied plasma, such as the Solar
corona or galactic halos. We investigate the kinetic energy release into heat,
mediated by dynamo action, both in our model and by solving the induction
equation with the same flow. We find that the flux rope dynamo is more than an
order of magnitude more efficient at converting mechanical energy into heat.
The probability density of the magnetic energy released during reconnections
has a power-law form with the slope -3, consistent with the Solar corona
heating by nanoflares. We also present a nonlinear extension of the model. This
shows that a plausible saturation mechanism of the fluctuation dynamo is the
suppression of turbulent magnetic diffusivity, due to suppression of random
stretching at the location of the flux ropes. We confirm that the probability
distribution function of the magnetic line curvature has a power-law form
suggested by (Schekochihin et al., 2002). We argue, however, using our results
that this does not imply a persistent folded structure of magnetic field, at
least in the nonlinear stage.Comment: 17 page
New photometry and astrometry of the isolated neutron star RX J0720-3125
  using recent VLT/FORS observations

Since the first optical detection of RXJ0720.4-3125 various observations have
been performed to determine astrometric and photometric data. We present the
first detection of the isolated neutron star in the V Bessel filter to study
the spectral energy distribution and derive a new astrometric position. At ESO
Paranal we obtained very deep images with FORS 1 (three hours exposure time) of
RXJ0720.4-3125 in V Bessel filter in January 2008. We derive the visual
magnitude by standard star aperture photometry.Using sophisticated resampling
software we correct the images for field distortions. Then we derive an updated
position and proper motion value by comparing its position with FORS 1
observations of December 2000. We calculate a visual magnitude of V = 26.81 +-
0.09mag, which is seven times in excess of what is expected from X-ray data,
but consistent with the extant U, B and R data. Over about a seven year epoch
difference we measured a proper motion of mu = 105.1 +- 7.4mas/yr towards theta
= 296.951 deg +- 0.0063 deg (NW), consistent with previous data.Comment: 7 pages, 9 figure
The evolution of chaos in active galaxy models with an oblate or a
  prolate dark halo component

The evolution of chaotic motion in a galactic dynamical model with a disk, a
dense nucleus and a flat biaxial dark halo component is investigated. Two cases
are studied: (i) the case where the halo component is oblate and (ii) the case
where a prolate halo is present. In both cases, numerical calculations show
that the extent of the chaotic regions decreases exponentially as the
scale-length of the dark halo increases. On the other hand, a linear
relationship exists between the extent of the chaotic regions and the flatness
parameter of the halo component. A linear relationship between the critical
value of the angular momentum and the flatness parameter is also found. Some
theoretical arguments to support the numerical outcomes are presented. An
estimation of the degree of chaos is made by computing the Lyapunov
Characteristic Exponents. Comparison with earlier work is also made.Comment: Published in Astronomische Nachrichten journa