448 research outputs found
The spectroscopic orbit and the geometry of R Aqr
R Aqr is one of the closest symbiotic binaries and the only D-type system
with radial velocity data suitable for orbital parameters estimation. The aims
of our study are to derive a reliable spectroscopic orbit of the Mira
component, and to establish connections between the orbital motion and other
phenomena shown by R Aqr. We reanalize velocity data recently published by
McIntosh & Rustan complemented by additional velocities. We find an eccentric
orbit (e=0.25) with a period 43.6 yr. This solution is in agreement with a
resolved VLA observation of this system. We demonstrate that the last 1974-1981
increase of extinction towards the Mira occured during its superior
spectroscopic conjunction, and can be due to obscuration by a neutral material
in the accreting stream. We also show that jet ejection is not connected with
the orbital position.Comment: 7 pages, 4 figures, accepted for publication in A&
On the uniqueness of -gonal automorphisms of Riemann surfaces
Let be a compact Riemann surface of genus . A cyclic subgroup of
prime order of is called properly -gonal if it has a fixed
point and the quotient surface has genus . We show that if , then a
properly -gonal subgroup of is unique. We also discuss some
related results.Comment: final version, 9 pages, minor improvements, added 2 reference
Automated novelty detection in the WISE survey with one-class support vector machines
Wide-angle photometric surveys of previously uncharted sky areas or
wavelength regimes will always bring in unexpected sources whose existence and
properties cannot be easily predicted from earlier observations: novelties or
even anomalies. Such objects can be efficiently sought for with novelty
detection algorithms. Here we present an application of such a method, called
one-class support vector machines (OCSVM), to search for anomalous patterns
among sources preselected from the mid-infrared AllWISE catalogue covering the
whole sky. To create a model of expected data we train the algorithm on a set
of objects with spectroscopic identifications from the SDSS DR13 database,
present also in AllWISE. OCSVM detects as anomalous those sources whose
patterns - WISE photometric measurements in this case - are inconsistent with
the model. Among the detected anomalies we find artefacts, such as objects with
spurious photometry due to blending, but most importantly also real sources of
genuine astrophysical interest. Among the latter, OCSVM has identified a sample
of heavily reddened AGN/quasar candidates distributed uniformly over the sky
and in a large part absent from other WISE-based AGN catalogues. It also
allowed us to find a specific group of sources of mixed types, mostly stars and
compact galaxies. By combining the semi-supervised OCSVM algorithm with
standard classification methods it will be possible to improve the latter by
accounting for sources which are not present in the training sample but are
otherwise well-represented in the target set. Anomaly detection adds
flexibility to automated source separation procedures and helps verify the
reliability and representativeness of the training samples. It should be thus
considered as an essential step in supervised classification schemes to ensure
completeness and purity of produced catalogues.Comment: 14 pages, 15 figure
Identifying the ejected population from disintegrating multiple systems
Kinematic studies of the Hipparcos catalogue have revealed associations that
are best explained as disintegrating multiple systems, presumably resulting
from a dynamical encounter between single/multiple systems in the field (Li et
al. 2009). In this work we explore the possibility that known ultra-cool dwarfs
may be components of disintegrating multiple systems, and consider the
implications for the properties of these objects. We will present here the
methods/techniques that can be used to search for and identify disintegrating
benchmark systems in three database/catalogues: Dwarf Archive, the Hipparcos
Main Catalogue, and the Gliese-Jahrei{\ss} Catalogue. Placing distance
constraints on objects with parallax or colour-magnitude information from
spectrophotometry allowed us to identify common distance associations. Proper
motion measurements allowed us to separate common proper motion multiples from
our sample of disintegrating candidates. Moreover, proper motion and positional
information allowed us to select candidate systems based on relative component
positions that were tracked back and projected forward through time. Using this
method we identified one candidate disintegrating quadruple association, and
two candidate disintegrating binaries, all of them containing one ultra-cool
dwarf.Comment: 5 pages, 1 figure, proceeding of The 19th Cambridge Workshop on Cool
Stars, Stellar Systems, and the Su
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