428 research outputs found
Formation of Short-Period Binary Pulsars in Globular Clusters
We present a new dynamical scenario for the formation of short-period binary
millisecond pulsars in globular clusters. Our work is motivated by the recent
observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc,
most neutron stars acquire binary companions through exchange interactions with
primordial binaries. The resulting systems have semimajor axes in the range
\~0.1-1 AU and neutron star companion masses ~1-3 Msun. For many of these
systems we find that, when the companion evolves off the main sequence and
fills its Roche lobe, the subsequent mass transfer is dynamically unstable.
This leads to a common envelope phase and the formation of short-period neutron
star - white dwarf binaries. For a significant fraction of these binaries, the
decay of the orbit due to gravitational radiation will be followed by a period
of stable mass transfer driven by a combination of gravitational radiation and
tidal heating of the companion. The properties of the resulting short-period
binaries match well those of observed binary pulsars in 47 Tuc.Comment: To appear in ApJ Letters, slightly abbreviated version with only
minor change
What are Hybrid Development Methods Made Of?
Regardless of company size or industry sector, a majority of project teams and companies use customized processes that combine different development methods-so-called hybrid development methods. Even though such hybrid development methods are highly individualized, a common understanding of how to systematically construct synergetic practices is missing. Based on 1,467 data points from a large-scale online survey among practitioners, we study the current state of practice in process use to answer the question: What are hybrid development methods made of? Our findings reveal that only eight methods and few practices build the core of modern software development. This small set allows for statistically constructing hybrid development methods
Exploring the Nature of Weak Chandra Sources near the Galactic Centre
We present results from the first near-IR imaging of the weak X-ray sources
discovered in the Chandra/ACIS-I survey (Wang et al. 2002) towards the Galactic
Centre (GC). These ~800 discrete sources, which contribute significantly to the
GC X-ray emission, represent an important and previously unknown population
within the Galaxy. From our VLT observations we will identify likely IR
counterparts to a sample of the hardest sources, which are most likely X-ray
binaries. With these data we can place constraints on the nature of the
discrete weak X-ray source population of the GC.Comment: In Proc. of ``Interacting Binaries: Accretion, Evolution, and
Outcomes'', eds. L. A. Antonelli et al., AIP, Cefalu, Sicily, 200
From climatological to small-scale applications: simulating water isotopologues with ICON-ART-Iso (version 2.3)
We present the new isotope-enabled model ICON-ART-Iso. The physics package of the global ICOsahedral Nonhydrostatic (ICON) modeling framework has been extended to simulate passive moisture tracers and the stable isotopologues HDO and H182O. The extension builds on the infrastructure provided by ICON-ART, which allows for high flexibility with respect to the number of related water tracers that are simulated. The physics of isotopologue fractionation follow the model COSMOiso. We first present a detailed description of the physics of fractionation that have been implemented in the model. The model is then evaluated on a range of temporal scales by comparing with measurements of precipitation and vapor.
A multi-annual simulation is compared to observations of the isotopologues in precipitation taken from the station network GNIP (Global Network for Isotopes in Precipitation). ICON-ART-Iso is able to simulate the main features of the seasonal cycles in δD and δ18O as observed at the GNIP stations. In a comparison with IASI satellite retrievals, the seasonal and daily cycles in the isotopologue content of vapor are examined for different regions in the free troposphere. On a small spatial and temporal scale, ICON-ART-Iso is used to simulate the period of two flights of the IAGOS-CARIBIC aircraft in September 2010, which sampled air in the tropopause region influenced by Hurricane Igor. The general features of this sample as well as those of all tropical data available from IAGOS-CARIBIC are captured by the model.
The study demonstrates that ICON-ART-Iso is a flexible tool to analyze the water cycle of ICON. It is capable of simulating tagged water as well as the isotopologues HDO and H182
A High-Frequency Search for Pulsars Within the Central Parsec of SgrA*
We report results from a deep high-frequency search for pulsars within the
central parsec of Sgr A* using the Green Bank Telescope. The observing
frequency of 15 GHz was chosen to maximize the likelihood of detecting normal
pulsars (i.e. with periods of \,ms and spectral indices of ) close to Sgr A*, that might be used as probes of gravity in the
strong-field regime; this is the highest frequency used for such pulsar
searches of the Galactic Center to date. No convincing candidate was detected
in the survey, with a detection threshold of Jy
achieved in two separate observing sessions. This survey represents a
significant improvement over previous searches for pulsars at the Galactic
Center and would have detected a significant fraction ($\gtrsim 5%) of the
pulsars around Sgr A*, if they had properties similar to those of the known
population. Using our best current knowledge of the properties of the Galactic
pulsar population and the scattering material toward Sgr A*, we estimate an
upper limit of 90 normal pulsars in orbit within the central parsec of Sgr A*.Comment: 10 pages, 7 figures, accepted for publication in the ApJ
The future of midlatitude cyclones
This is the final version. Available from the publisher via the DOI in this record.Purpose of Review This review brings together recent research on the structure, characteristics, dynamics, and impacts of
extratropical cyclones in the future. It draws on research using idealized models and complex climate simulations, to evaluate
what is known and unknown about these future changes.
Recent Findings There are interacting processes that contribute to the uncertainties in future extratropical cyclone changes, e.g.,
changes in the horizontal and vertical structure of the atmosphere and increasing moisture content due to rising temperatures.
Summary While precipitation intensity will most likely increase, along with associated increased latent heating, it is unclear to
what extent and for which particular climate conditions this will feedback to increase the intensity of the cyclones. Future research
could focus on bridging the gap between idealized models and complex climate models, as well as better understanding of the
regional impacts of future changes in extratropical cyclones.Natural Environment Research Council (NERC
Green Bank Telescope Measurement of the Systemic Velocity of the Double Pulsar Binary J0737-3039 and Implications for its Formation
We report on the measurement at 820- and 1400-MHz of orbital modulation of
the diffractive scintillation timescale from pulsar A in the double-pulsar
system J0737-3039 using the Green Bank Telescope. Fits to this modulation
determine the systemic velocity in the plane of the sky to be V_iss ~ 140.9 +/-
6.2 km/s. The parallel and perpendicular components of this velocity with
respect to the line of nodes of the pulsar's orbit are V_plane ~ 96.0 +/- 3.7
km/s and V_perp ~ 103.1 +/- 7.7 km/s respectively. The large V_perp implies
that pulsar B was born with a kick speed of >~ 100 km/s. Future VLBA
determination of the angular proper motion in conjunction with improved V_iss
measurements should provide a precise distance to the system. Using
high-precision timing data and the V_iss model, we estimate a best-fit orbital
inclination of i = 88.7 +/- 0.9 deg.Comment: 5 pages, 3 figures. To be submitted to ApJ Letters. A version with
higher resolution figures is available upon request from S. Ranso
Is our Sun a Singleton?
Most stars are formed in a cluster or association, where the number density
of stars can be high. This means that a large fraction of initially-single
stars will undergo close encounters with other stars and/or exchange into
binaries. We describe how such close encounters and exchange encounters can
affect the properties of a planetary system around a single star. We define a
singleton as a single star which has never suffered close encounters with other
stars or spent time within a binary system. It may be that planetary systems
similar to our own solar system can only survive around singletons. Close
encounters or the presence of a stellar companion will perturb the planetary
system, often leaving planets on tighter and more eccentric orbits. Thus
planetary systems which initially resembled our own solar system may later more
closely resemble some of the observed exoplanet systems.Comment: 2 pages, 1 figure. To be published in the proceedings of IAUS246
"Dynamical Evolution of Dense Stellar Systems". Editors: E. Vesperini (Chief
Editor), M. Giersz, A. Sill
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