678 research outputs found
Orbital and physical properties of planets and their hosts: new insights on planet formation and evolution
We explore the relations between physical and orbital properties of planets
and properties of their host stars to identify the main observable signatures
of the formation and evolution processes of planetary systems. We use a large
sample of FGK dwarf planet hosts with stellar parameters derived in a
homogeneous way from the SWEET-Cat database to study the relation between
stellar metallicity and position of planets in the period-mass diagram. In the
second part we use all the RV-detected planets orbiting FGK stars to explore
the role of planet-disk and planet-planet interaction on the evolution of
orbital properties of planets with masses above 1MJup. We show that planets
orbiting metal-poor stars have longer periods than those in metal-rich systems.
This trend is valid for masses at least from 10MEarth to 4MJup. Earth-like
planets orbiting metal-rich stars always show shorter periods (fewer than 20
days) than those orbiting metal-poor stars. We also found statistically
significant evidence that very high mass giants have on average more eccentric
orbits than giant planets with lower mass.Finally, we show that the
eccentricity of planets with masses higher than 4MJup tends to be lower for
planets with shorter periods. Our results suggest that the planets in the P-MP
diagram are evolving differently because of a mechanism that operates over a
wide range of planetary masses. This mechanism is stronger or weaker depending
on the metallicity of the respective system. One possibility is that planets in
metal-poor disks form farther out from their central star and/or they form
later and do not have time to migrate as far as the planets in metal-rich
systems. The trends and dependencies obtained for very high mass planetary
systems suggest that planet-disk interaction is a very important and
orbit-shaping mechanism for planets in the high-mass domain. Shortened.Comment: 8 pages, 4 figures and 1 table. Accepted for publication in A&
FLICK: developing and running application-specific network services
Data centre networks are increasingly programmable, with application-specific network services proliferating, from custom load-balancers to middleboxes providing caching and aggregation. Developers must currently implement these services using traditional low-level APIs, which neither support natural operations on application data nor provide efficient performance isolation. We describe FLICK, a framework for the programming and execution of application-specific network services on multi-core CPUs. Developers write network services in the FLICK language, which offers high-level processing constructs and application-relevant data types. FLICK programs are translated automatically to efficient, parallel task graphs, implemented in C++ on top of a user-space TCP stack. Task graphs have bounded resource usage at runtime, which means that the graphs of multiple services can execute concurrently without interference using cooperative scheduling. We evaluate FLICK with several services (an HTTP load-balancer, a Memcached router and a Hadoop data aggregator), showing that it achieves good performance while reducing development effort
Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93
We explore the possibility that the stellar relative abundances of different
species can be used to constrain the bulk abundances of known transiting rocky
planets. We use high resolution spectra to derive stellar parameters and
chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass,
rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same
line along the mass-radius diagram, pointing toward a similar composition. The
derived abundance ratios are compared with the solar values. With a simple
stoichiometric model, we estimate the iron mass fraction in each planet,
assuming stellar composition. We show that in all cases, the iron mass fraction
inferred from the mass-radius relationship seems to be in good agreement with
the iron abundance derived from the host star's photospheric composition. The
results suggest that stellar abundances can be used to add constraints on the
composition of orbiting rocky planets.Comment: A&A Letters, in pres
Comparison of the spread of two different volumes of contrast medium when performing ultrasound-guided transversus abdominis plane injection in dog cadavers
ObjectivesTo compare, via CT imaging, the spread of different volumes of diluted iodinated contrast medium in the transversus abdominis muscle plane of dog cadavers.MethodsProspective, randomised study. An electro stimulation or a SonoTAP needle was inserted in plane with the ultrasound beam in the fascia between the internal oblique and transversus abdominis muscles. A test dose of 1âml of diluted contrast (30âmg/mL iohexol) was injected to confirm positioning, followed by 0 · 5âmL/kg (n=14) or 1âmL/kg (n=12) and the distribution of the fluid compared.ResultsContrast medium was identified exclusively in the transversus abdominis plane in 19 of 26 dogs. In one dog, the contrast lay between the external and internal oblique muscles and partially in three dogs. Intraperitoneal contrast was detected in 6 of 26 dogs (23%). No significant differences were found in the dorso-ventral or cranio-caudal spread or area of distribution but a significant difference was found in the transverse spread. There was an association between poor ultrasound visualisation of the tip of the needle and intraperitoneal injection.Clinical significanceInjection of 1âmL/kg of diluted contrast did not result in wider cranio-caudal spread in the transversus abdominis muscle plane of dog cadavers when compared with 0 · 5âmL/kg. Intraperitoneal injection is a risk and might be reduced with good needle visualisation
Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
[abridged]The aim of this work is to search for planets around evolved stars,
with a special focus on stars more massive than 2\,M in light of
previous findings that show a drop in planet occurrence around stars above this
mass. We used \texttt{kima} to find the Keplerian orbits most capable of
explaining the periodic signals observed in RV data. We also studied the
variation of stellar activity indicators and photometry in order to discard
stellar signals mimicking the presence of planets. We present a planet
candidate in the open cluster NGC3680 that orbits the 1.64\,M star No.
41. The planet has a minimum mass of 5.13M\, and a period of 1155 days.
We also present periodic and large-amplitude RV signals of probable stellar
origin in two more massive stars (5.84 and 3.05\,M in the clusters
NGC2345 and NGC3532). Finally, using new data, we revise the RV signals of the
three stars analysed in our previous paper. We confirm the stellar origin of
the signals observed in NGC2423 No. 3 and NGC4349 No. 127. On the other hand,
the new data collected for IC4651 No. 9122 (1.79\,M) seem to support
the presence of a bona fide planet of 6.22M\, at a period of 744 days,
although more data will be needed to discard a possible correlation with the
CCF-FWHM. The targets presented in this work showcase the difficulties in
interpreting RV data for evolved massive stars. The use of several activity
indicators (CCF-FWHM, CCF-BIS, \ha), photometry, and long-term observations
(covering several orbital and stellar rotational periods) is required to
discern the true nature of the signals. However, in some cases, all this
information is insufficient, and the inclusion of additional data -- such as
the determination of magnetic field variability or RV points in the
near-infrared -- will be necessary to identify the nature of the discovered
signals.Comment: accepted in A&
Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
[abridged]The aim of this work is to search for planets around evolved stars,
with a special focus on stars more massive than 2\,M in light of
previous findings that show a drop in planet occurrence around stars above this
mass. We used \texttt{kima} to find the Keplerian orbits most capable of
explaining the periodic signals observed in RV data. We also studied the
variation of stellar activity indicators and photometry in order to discard
stellar signals mimicking the presence of planets. We present a planet
candidate in the open cluster NGC3680 that orbits the 1.64\,M star No.
41. The planet has a minimum mass of 5.13M\, and a period of 1155 days.
We also present periodic and large-amplitude RV signals of probable stellar
origin in two more massive stars (5.84 and 3.05\,M in the clusters
NGC2345 and NGC3532). Finally, using new data, we revise the RV signals of the
three stars analysed in our previous paper. We confirm the stellar origin of
the signals observed in NGC2423 No. 3 and NGC4349 No. 127. On the other hand,
the new data collected for IC4651 No. 9122 (1.79\,M) seem to support
the presence of a bona fide planet of 6.22M\, at a period of 744 days,
although more data will be needed to discard a possible correlation with the
CCF-FWHM. The targets presented in this work showcase the difficulties in
interpreting RV data for evolved massive stars. The use of several activity
indicators (CCF-FWHM, CCF-BIS, \ha), photometry, and long-term observations
(covering several orbital and stellar rotational periods) is required to
discern the true nature of the signals. However, in some cases, all this
information is insufficient, and the inclusion of additional data -- such as
the determination of magnetic field variability or RV points in the
near-infrared -- will be necessary to identify the nature of the discovered
signals.Comment: accepted in A&
Li abundances in F stars: planets, rotation and galactic evolution
We find that hot jupiter host stars within the T range
5900-6300K show lower Li abundances, by 0.14 dex, than stars without detected
planets. This offset has a significance at the level 7, pointing to a
stronger effect of planet formation on Li abundances when the planets are more
massive and migrate close to the star. However, we also find that the average v
\textit{sin}i of (a fraction of) stars with hot jupiters is higher on average
than for single stars in the same T region, suggesting that
rotationally-induced mixing (and not the presence of planets) might be the
cause for a greater depletion of Li. We confirm that the mass-metallicity
dependence of the Li dip is extended towards [Fe/H] 0.4 dex (beginning
at [Fe/H] -0.4 dex for our stars) and that probably reflects the
mass-metallicity correlation of stars of the same T on the Main
Sequence. We find that for the youngest stars ( 1.5 Gyr) around the Li dip,
the depletion of Li increases with v \textit{sin}i values, as proposed by
rotationally-induced depletion models. This suggests that the Li dip consists
of fast rotators at young ages whereas the most Li-depleted old stars show
lower rotation rates (probably caused by the spin-down during their long
lifes). We have also explored the Li evolution with [Fe/H] taking advantage of
the metal-rich stars included in our sample. We find that Li abundance reaches
its maximum around solar metallicity but decreases in the most metal-rich
stars, as predicted by some models of Li Galactic production.Comment: 10 pages, accepted to A&
The role of the LIRG and ULIRG phases in the evolution of Ks-selected galaxies
We investigate the role of the luminous infrared galaxy (LIRG) and
ultra-luminous infrared galaxy (ULIRG) phases in the evolution of Ks-selected
galaxies and, in particular, Extremely Red Galaxies (ERGs). With this aim, we
compare the properties of a sample of 2905 Ks<21.5 (Vega mag) galaxies in the
GOODS/CDFS with the sub-sample of those 696 sources which are detected at 24
microns. We find that LIRGs constitute 30% of the galaxies with stellar mass
M>1x10^{11} Msun assembled at redshift z=0.5. A minimum of 65% of the galaxies
with M>2.5x10^{11} Msun at z~2-3 are ULIRGs at those redshifts. 60% of the
ULIRGs in our sample have the characteristic colours of ERGs. Conversely, 40%
of the ERGs with stellar mass M>1.3x10^{11} Msun at 1.5<z<2.0 and a minimum of
52% of those with the same mass cut at 2.0<z<3.0 are ULIRGs. The average
optical/near-IR properties of the massive ERGs at similar redshifts that are
identified with ULIRGs and that are not have basically no difference,
suggesting that both populations contain the same kind of objects in different
phases of their lives.
LIRGs and ULIRGs have an important role in galaxy evolution and mass
assembly, and, although they are only able to trace a fraction of the massive
(M>1x10^{11} Msun) galaxies present in the Universe at a given time, this
fraction becomes very significant (>50%) at redshifts z>~2.Comment: Accepted for publication in A&A. 9 pages, 6 figure
FLICK: Developing and running application-specific network services
Data centre networks are increasingly programmable, with network services proliferating, from custom load-balancers to middleboxes providing caching and aggregation. Developers must currently implement these services using traditional low-level APIs, which neither support natural operations on application data nor provide efficient performance isolation.
We describe FLICK, a framework for the programming and execution of application-specific network services on multi-core CPUs. Developers write network services in the FLICK , which offers high-level processing constructs and application-relevant data types. FLICK programs are translated automatically to efficient, parallel , implemented in C++ on top of a user-space TCP stack. Task graphs have bounded resource usage at runtime, which means that the graphs of multiple services can execute concurrently without interference using cooperative scheduling. We evaluate FLICK with several services (an HTTP load-balancer, a Memcached router and a Hadoop data aggregator), showing that it achieves good performance while reducing development effort.Engineering and Physical Sciences Research CouncilThis is the author accepted manuscript. The final version is available from USENIX via https://www.usenix.org/conference/atc16/technical-sessions/presentation/ali
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