1,489 research outputs found
BVR photometry of the resolved dwarf galaxy Ho IX
We present BVR CCD photometry down to limiting magnitude B=23.5 mag for 232
starlike objects and 11 diffuse objects in a 5.4' x 5.4' field of Ho IX. The
galaxy is a gas-rich irregular dwarf galaxy possibly very close to M 81, which
makes it especially interesting in the context of the evolution of satellite
galaxies and the accretion of dwarf galaxies. Investigations of Ho IX were
hampered by relatively large contradictions in the magnitude scale between
earlier studies. With our new photometry we resolved these discrepancies. The
color magnitude diagram (CMD) of Ho IX is fairly typical of a star-forming
dwarf irregular, consistent with earlier results. Distance estimates from our
new CMD are consistent with Ho IX being very close to M 81 and therefore being
a definite member of the M 81 group, apparently in very close physical
proximity to M 81.Comment: 9 pages, 8 figures, uses aa.cls, A&A in pres
Chemo-dynamical evolution of Globular Cluster Systems
We studied the relation between the ratio of rotational velocity to velocity
dispersion and the metallicity (/\sigma_{v}-metallicity relation) of
globular cluster systems (GCS) of disk galaxies by comparing the relation
predicted from simple chemo-dynamical models for the formation and evolution of
disk galaxies with the observed kinematical and chemical properties of their
GCSs. We conclude that proto disk galaxies underwent a slow initial collapse
that was followed by a rapid contraction and derive that the ratio of the
initial collapse time scale to the active star formation time scale is \sim 6
for our Galaxy and \sim 15 for M31. The fundamental formation process of disk
galaxies was simulated based on simple chemo-dynamical models assuming the
conservation of their angular momentum. We suggest that there is a typical
universal pattern in the /\sigma_{v}-metallicity relation of the GCS
of disk galaxies. This picture is supported by the observed properties of GCSs
in the Galaxy and in M31. This relation would deviate from the universal
pattern, however, if large-scale merging events took major role in
chemo-dynamical evolution of galaxies and will reflect the epoch of such
merging events. We discuss the properties of the GCS of M81 and suggest the
presence of past major merging event.Comment: 25 pages, 8 figures, Accepted for publication in the Astrophysical
Journa
Anomalous nucleation far from equilibrium
We present precision Monte Carlo data and analytic arguments for an
asymmetric exclusion process, involving two species of particles driven in
opposite directions on a lattice. We propose a scenario which
resolves a stark discrepancy between earlier simulation data, suggesting the
existence of an ordered phase, and an analytic conjecture according to which
the system should revert to a disordered state in the thermodynamic limit. By
analyzing the finite size effects in detail, we argue that the presence of a
single, seemingly macroscopic, cluster is an intermediate stage of a complex
nucleation process: In smaller systems, this cluster is destabilized while
larger systems allow the formation of multiple clusters. Both limits lead to
exponential cluster size distributions which are, however, controlled by very
different length scales.Comment: 5 pages, 3 figures, one colum
A Position-Space Renormalization-Group Approach for Driven Diffusive Systems Applied to the Asymmetric Exclusion Model
This paper introduces a position-space renormalization-group approach for
nonequilibrium systems and applies the method to a driven stochastic
one-dimensional gas with open boundaries. The dynamics are characterized by
three parameters: the probability that a particle will flow into the
chain to the leftmost site, the probability that a particle will flow
out from the rightmost site, and the probability that a particle will jump
to the right if the site to the right is empty. The renormalization-group
procedure is conducted within the space of these transition probabilities,
which are relevant to the system's dynamics. The method yields a critical point
at ,in agreement with the exact values, and the critical
exponent , as compared with the exact value .Comment: 14 pages, 4 figure
Quasi Periodic Oscillations and Strongly Comptonized X-ray emission from Holmberg IX X-1
We report the discovery of a 200mHz quasi-periodic oscillation (QPO) in the
X-ray emission from a bright ultra-luminous X-ray source (ULX) Holmberg IX X-1
using a long XMM-Newton observation. The QPO has a centroid at
202.5_{-3.8}^{+4.9}mHz, a coherence Q ~9.3 and an amplitude (rms) of 6% in the
0.2-10keV band. This is only the second detection of a QPO from an ULX, after
M82 X-1, and provides strong evidence against beaming. The power spectrum is
well fitted by a power law with an index of ~0.7. The total integrated power
(rms) is ~9.4% in the 0.001-1Hz range. The X-ray spectrum shows clear evidence
for a soft X-ray excess component that is well described by a multicolor disk
blackbody (kT_in ~ 0.3keV) and a high energy curvature that can be modeled
either by a cut-off power law (Gamma ~ 1; E_cutoff ~9keV) or as a strongly
Comptonized continuum in an optically thick (tau ~7.3) and cool (kT_e ~3keV)
plasma. Both the presence of the QPO and the shape of the X-ray spectrum
strongly suggest that the ULX is not in the high/soft or thermally dominated
state. A truncated disk and inner optically thick corona may explain the
observed X-ray spectrum and the presence of the QPO.Comment: Submitted to ApJ Letter
Menarcheal timing is accelerated by favorable nutrition but unrelated to developmental cues of mortality or familial instability in Cebu, Philippines
High H2 Sorption Energetics in Zeolitic Imidazolate Frameworks
A combined experimental and theoretical study of H2 sorption was carried out on two isostructural zeolitic imidazolate frameworks ZIFs , namely ZIF 68 and ZIF 69. The former consists of Zn2 ions that are coordinated to two 2 nitroimidazolate and two benzimidazolate linkers in a tetrahedral fashion, while 5 chlorobenzimidazolate is used in place of benzimidazolate in the latter compound. H2 sorption measurements showed that the two ZIFs display similar isotherms and isosteric heats of adsorption Qst . The experimental initial H2 Qst value for both ZIFs was determined to be 8.1 kJ mol 1, which is quite high for materials that do not contain exposed metal centers. Molecular simulations of H2 sorption in ZIF 68 and ZIF 69 confirmed the similar H2 sorption properties between the two ZIFs, but also suggest that H2 sorption is slightly favored in ZIF 68 with regards to uptake at 77 K 1.0 atm. This work also presents inelastic neutron scattering INS spectra for H2 sorbed in ZIFs for the first time. The spectra for ZIF 68 and ZIF 69 show a broad range of intensities starting from about 4 meV. The most favorable H2 sorption site in both ZIFs corresponds to a confined region between two adjacent 2 nitroimidazolate linkers. Two dimensional quantum rotation calculations for H2 sorbed at this site in ZIF 68 and ZIF 69 produced rotational transitions that are in accord with the lowest energy peak observed in the INS spectrum for the respective ZIFs. We found that the primary binding site for H2 in the two ZIFs generates high barriers to rotation for the adsorbed H2, which are greater than those in several metal organic frameworks MOFs which possess open metal sites. H2 sorption was also observed for both ZIFs in the vicinity of the nitro groups of the 2 nitroimidazolate linkers. This study highlights the constructive interplay of experiment and theory to elucidate critical details of the H2 sorption mechanism in these two isostructural ZIF
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