72 research outputs found
Roughness in Fuzzy Cayley Graphs
Rough set theory is a worth noticing approach for inexact and uncertain system modelling. When rough set theory accompanies with fuzzy set theory, which both are a complementary generalization of set theory, they will be attended by potency in theoretical discussions. In this paper a definition for fuzzy Cayley subsets is put forward as well as fuzzy Cayley graphs of fuzzy subsets on groups inspired from the definition of Cayley graphs. We introduce rough approximation of a Cayley graph with respect to a fuzzy normal subgroup. We introduce the approximation rough fuzzy Cayley graphs and fuzzy rough fuzzy Cayley graphs. The last approximation is the mixture of the other approximations. Some theorems and properties are investigated and proved
A new bow-shock source with bipolar morphology in the vicinity of Sgr A*
Here we present a new bowshock blue-shifted source in the close vicinity of
Sgr A* that we name X8. We use data-sets that are based on SINFONI observations
with the Very Large Telescope. We can trace the source between 2006 and 2016 in
the blue-shifted line maps and it shows not only positional similarities to X7
but also the same spectral footprint. The symmetry axis of both extended
sources points towards Sgr A* and exhibits [Fe III] emission lines that arise
due to wind-wind shocks. In particular, the source X8 has a bipolar morphology,
which makes it the closest bipolar source in the vicinity of Sgr A*. In
addition, we can trace a K-band continuum counterpart of X8. This points
towards a stellar counterpart to the line-map emission. Overall, the source X8
can be interpreted as either a Young Stellar Object or a young planetary
nebula, which makes this source unique among so-far detected main-sequence OB
stars in this region.Comment: Accepted for publication by A&A, 15 pages, 13 figure
The pro-nilpotent group topology on a free group
In this paper, we study the pro-nilpotent group topology on a free group. First we describe the closure of the product of finitely many finitely generated subgroups of a free group in the pro-nilpotent group topology and then present an algorithm to compute it. We deduce that the nil-closure of a rational subset of a free group is an effectively constructible rational subset and hence has decidable membership. We also prove that the G(nil)-kernel of a finite monoid is computable and hence pseudovarieties of the form V (sic) G(nil) have decidable membership problem, for every decidable pseudovariety of monoids V. Finally, we prove that the semidirect product J * G(nil) has a decidable membership problem
First results from a large-scale proper motion study of the Galactic Centre
Proper motion studies of stars in the centre of the Milky Way have been
typically limited to the Arches and Quintuplet clusters and to the central
parsec. Here, we present the first results of a large-scale proper motion study
of stars within several tens of parsecs of Sagittarius A* based on our
angular resolution GALACTICNUCLEUS survey (epoch 2015) combined with NICMOS/HST
data from the Paschen- survey (epoch 2008). This study will be the
first extensive proper motion study of the central of the
Galaxy, which is not covered adequately by any of the existing astronomical
surveys such as Gaia because of its extreme interstellar extinction ( mag). Proper motions can help us to disentangle the different
stellar populations along the line-of-sight and interpret their properties in
combination with multi-wavelength photometry from GALACTICNUCLEUS and other
sources. It also allows us to infer the dynamics and interrelationship between
the different stellar components of the Galactic Centre (GC). In particular, we
use proper motions to detect co-moving groups of stars which can trace low mass
or partially dissolved young clusters in the GC that can hardly be discovered
by any other means. Our pilot study in this work is on a field in the nuclear
bulge associated by HII regions that show the presence of young stars. We
detect the first group of co-moving stars coincident with an HII region. Using
colour-magnitude diagrams, we infer that the co-moving stars are consistent
with being the post-main sequence stars with ages of few Myrs. Simulations show
that this group of stars is a real group that can indicate the existence of a
dissolving or low to intermediate mass young cluster. A census of these
undiscovered clusters will ultimately help us to constrain star formation at
the GC in the past few ten Myrs.Comment: Accepted for publication in A&A. 13 pages, 17 figure
Nuclear Activity and the Conditions of Star-formation at the Galactic Center
The Galactic Center is the closest galactic nucleus that can be studied with
unprecedented angular resolution and sensitivity. We summarize recent basic
observational results on Sagittarius A* and the conditions for star formation
in the central stellar cluster. We cover results from the radio, infrared, and
X-ray domain and include results from simulation as well. From (sub-)mm and
near-infrared variability and near-infrared polarization data we find that the
SgrA* system (supermassive black hole spin, a potential temporary accretion
disk and/or outflow) is well ordered in its geometrical orientation and in its
emission process that we assume to reflect the accretion process onto the
supermassive black hole (SMBH).Comment: 11 pages, 4 figures, 1 table; published in PoS-SISSA Proceedings of
the: Frontier Research in Astrophysics - II, 23-28 May 2016, Mondello
(Palermo), Ital
Experimental Indicators of Accretion Processes in Active Galactic Nuclei
Bright Active Galactic Nuclei are powered by accretion of mass onto the super
massive black holes at the centers of the host galaxies. For fainter objects
star formation may significantly contribute to the luminosity. We summarize
experimental indicators of the accretion processes in Active Galactic Nuclei
(AGN), i.e., observable activity indicators that allow us to conclude on the
nature of accretion. The Galactic Center is the closest galactic nucleus that
can be studied with unprecedented angular resolution and sensitivity.
Therefore, here we also include the presentation of recent observational
results on Sagittarius A* and the conditions for star formation in the central
stellar cluster. We cover results across the electromagnetic spectrum and find
that the Sagittarius A* (SgrA*) system is well ordered with respect to its
geometrical orientation and its emission processes of which we assume to
reflect the accretion process onto the super massive black hole.Comment: 16 pages, 4 figures, conference proceeding: Accretion Processes in
Cosmic Sources - APCS2016 - 5-10 September 2016, Saint Petersburg, Russi
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