10,462 research outputs found
The Binary White Dwarf LHS 3236
The white dwarf LHS 3236 (WD1639+153) is shown to be a double-degenerate
binary, with each component having a high mass. Astrometry at the U.S. Naval
Observatory gives a parallax and distance of 30.86 +/- 0.25 pc and a tangential
velocity of 98 km/s, and reveals binary orbital motion. The orbital parameters
are determined from astrometry of the photocenter over more than three orbits
of the 4.0-year period. High-resolution imaging at the Keck Observatory
resolves the pair with a separation of 31 and 124 mas at two epochs. Optical
and near-IR photometry give a set of possible binary components. Consistency of
all data indicates that the binary is a pair of DA stars with temperatures near
8000 and 7400 K and with masses of 0.93 and 0.91 M_solar; also possible, is a
DA primary and a helium DC secondary with temperatures near 8800 and 6000 K and
with masses of 0.98 and 0.69 M_solar. In either case, the cooling ages of the
stars are ~3 Gyr and the total ages are <4 Gyr. The combined mass of the binary
(1.66--1.84 M_solar) is well above the Chandrasekhar limit; however, the
timescale for coalescence is long.Comment: Accepted for the Astrophysical Journa
Beyond XSPEC: Towards Highly Configurable Analysis
We present a quantitative comparison between software features of the defacto
standard X-ray spectral analysis tool, XSPEC, and ISIS, the Interactive
Spectral Interpretation System. Our emphasis is on customized analysis, with
ISIS offered as a strong example of configurable software. While noting that
XSPEC has been of immense value to astronomers, and that its scientific core is
moderately extensible--most commonly via the inclusion of user contributed
"local models"--we identify a series of limitations with its use beyond
conventional spectral modeling. We argue that from the viewpoint of the
astronomical user, the XSPEC internal structure presents a Black Box Problem,
with many of its important features hidden from the top-level interface, thus
discouraging user customization. Drawing from examples in custom modeling,
numerical analysis, parallel computation, visualization, data management, and
automated code generation, we show how a numerically scriptable, modular, and
extensible analysis platform such as ISIS facilitates many forms of advanced
astrophysical inquiry.Comment: Accepted by PASP, for July 2008 (15 pages
On the origin of 140 GHz emission from the 4 July 2012 solar flare
The sub-THz event observed on the 4 July 2012 with the Bauman Moscow State
Technical University Radio Telescope RT-7.5 at 93 and 140~GHz as well as
Kislovodsk and Mets\"ahovi radio telescopes, Radio Solar Telescope Network
(RSTN), GOES, RHESSI, and SDO orbital stations is analyzed. The spectral flux
between 93 and 140 GHz has been observed increasing with frequency. On the
basis of the SDO/AIA data the differential emission measure has been
calculated. It is shown that the thermal coronal plasma with the temperature
above 0.5~MK cannot be responsible for the observed sub-THz flare emission. The
non-thermal gyrosynchrotron mechanism can be responsible for the microwave
emission near ~GHz but the observed millimeter spectral characteristics are
likely to be produced by the thermal bremsstrahlung emission from plasma with a
temperature of about 0.1~MK.Comment: 18 pages, 6 figure
The M33 Synoptic Stellar Survey. II. Mira Variables
We present the discovery of 1847 Mira candidates in the Local Group galaxy
M33 using a novel semi-parametric periodogram technique coupled with a Random
Forest classifier. The algorithms were applied to ~2.4x10^5 I-band light curves
previously obtained by the M33 Synoptic Stellar Survey. We derive preliminary
Period-Luminosity relations at optical, near- & mid-infrared wavelengths and
compare them to the corresponding relations in the Large Magellanic Cloud.Comment: Includes small corrections to match the published versio
Computing Preferred Answer Sets by Meta-Interpretation in Answer Set Programming
Most recently, Answer Set Programming (ASP) is attracting interest as a new
paradigm for problem solving. An important aspect which needs to be supported
is the handling of preferences between rules, for which several approaches have
been presented. In this paper, we consider the problem of implementing
preference handling approaches by means of meta-interpreters in Answer Set
Programming. In particular, we consider the preferred answer set approaches by
Brewka and Eiter, by Delgrande, Schaub and Tompits, and by Wang, Zhou and Lin.
We present suitable meta-interpreters for these semantics using DLV, which is
an efficient engine for ASP. Moreover, we also present a meta-interpreter for
the weakly preferred answer set approach by Brewka and Eiter, which uses the
weak constraint feature of DLV as a tool for expressing and solving an
underlying optimization problem. We also consider advanced meta-interpreters,
which make use of graph-based characterizations and often allow for more
efficient computations. Our approach shows the suitability of ASP in general
and of DLV in particular for fast prototyping. This can be fruitfully exploited
for experimenting with new languages and knowledge-representation formalisms.Comment: 34 pages, appeared as a Technical Report at KBS of the Vienna
University of Technology, see http://www.kr.tuwien.ac.at/research/reports
Community Schools Unfolded: A review of the literature.
Community schools are quickly increasing in number, but there is no evidence whether they are more effective than traditional schools. No study has empirically compared community schools to other schools. This study reviews the literature on the effectiveness of community schools. We focus on their three main components: cooperation with external organizations, parental involvement, and extracurricular activities. This review indicates that involving external organizations seems valuable in terms of social cohesion in neighborhoods. Parental involvement is particularly important for the educational development of lower socio-economic status families. Extracurricular activities positively relate to students? development in academic and social terms.
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