858 research outputs found
ECCO: Edge-cloud chaining and orchestration framework for road context assessment
© 2020 IEEE. For road safety, detecting and reacting efficiently to road hazards is crucial and yet challenging due to practical restrictions such as limited data availability, which relies on network support. Moreover, from a system perspective we lack a computational model capable of providing to vehicles reliable and real-time assessment of the road context. As autonomous vehicles become widespread, the safety issues are further aggravated by the gap between cloud, roadside infrastructure and road users in terms of communication latency, software-hardware compatibility and data interoperability. To tackle this, we present ECCO: an orchestration framework that enables edge-cloud collaborative computing for road context assessment. ECCO can create on-demand task execution pipelines spanning multiple, potentially resource-constrained edge-nodes with the smart IoT infrastructure support. Our prototype lays the groundwork to support new services, which can use more efficiently the road infrastructure and deliver safety-critical applications for road users
New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection
It is still being debated whether the well-known metallicity - giant planet
correlation for dwarf stars is also valid for giant stars. For this reason,
having precise metallicities is very important. Different methods can provide
different results that lead to discrepancies in the analysis of planet hosts.
To study the impact of different analyses on the metallicity scale for evolved
stars, we compare different iron line lists to use in the atmospheric parameter
derivation of evolved stars. Therefore, we use a sample of 71 evolved stars
with planets. With these new homogeneous parameters, we revisit the metallicity
- giant planet connection for evolved stars. A spectroscopic analysis based on
Kurucz models in local thermodynamic equilibrium (LTE) was performed through
the MOOG code to derive the atmospheric parameters. Two different iron line
list sets were used, one built for cool FGK stars in general, and the other for
giant FGK stars. Masses were calculated through isochrone fitting, using the
Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the
metallicity distributions of various different samples of evolved stars and red
giants. All parameters compare well using a line list set, designed
specifically for cool and solar-like stars to provide more accurate
temperatures. All parameters derived with this line list set are preferred and
are thus adopted for future analysis. We find that evolved planet hosts are
more metal-poor than dwarf stars with giant planets. However, a bias in giant
stellar samples that are searched for planets is present. Because of a colour
cut-off, metal-rich low-gravity stars are left out of the samples, making it
hard to compare dwarf stars with giant stars. Furthermore, no metallicity
enhancement is found for red giants with planets (\,dex) with
respect to red giants without planets.Comment: 22 pages, 10 figures, 12 tables, accepted to A&
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
Due to the importance that the star-planet relation has to our understanding
of the planet formation process, the precise determination of stellar
parameters for the ever increasing number of discovered extra-solar planets is
of great relevance. Furthermore, precise stellar parameters are needed to fully
characterize the planet properties. It is thus important to continue the
efforts to determine, in the most uniform way possible, the parameters for
stars with planets as new discoveries are announced. In this paper we present
new precise atmospheric parameters for a sample of 48 stars with planets. We
then take the opportunity to present a new catalogue of stellar parameters for
FGK and M stars with planets detected by radial velocity, transit, and
astrometry programs. Stellar atmospheric parameters and masses for the 48 stars
were derived assuming LTE and using high resolution and high signal-to-noise
spectra. The methodology used is based on the measurement of equivalent widths
for a list of iron lines and making use of iron ionization and excitation
equilibrium principles. For the catalog, and whenever possible, we used
parameters derived in previous works published by our team, using well defined
methodologies for the derivation of stellar atmospheric parameters. This set of
parameters amounts to over 65% of all planet host stars known, including more
than 90% of all stars with planets discovered through radial velocity surveys.
For the remaining targets, stellar parameters were collected from the
literature.Comment: Astronomy & Astrophysics, accepted for publicatio
New and updated stellar parameters for 90 transit hosts. The effect of the surface gravity
Context. Precise stellar parameters are crucial in exoplanet research for
correctly determining of the planetary parameters. For stars hosting a
transiting planet, determining of the planetary mass and radius depends on the
stellar mass and radius, which in turn depend on the atmospheric stellar
parameters. Different methods can provide different results, which leads to
different planet characteristics.}%Spectroscopic surface gravities have shown
to be poorly constrained, but the photometry of the transiting planet can
provide an independent measurement of the surface gravity.
Aims. In this paper, we use a uniform method to spectroscopically derive
stellar atmospheric parameters, chemical abundances, stellar masses, and
stellar radii for a sample of 90 transit hosts. Surface gravities are also
derived photometrically using the stellar density as derived from the light
curve. We study the effect of using these different surface gravities on the
determination of the chemical abundances and the stellar mass and radius.
Methods. A spectroscopic analysis based on Kurucz models in LTE was performed
through the MOOG code to derive the atmospheric parameters and the chemical
abundances. The photometric surface gravity was determined through isochrone
fitting and the use of the stellar density, directly determined from the light
curve. Stellar masses and radii are determined through calibration formulae.
Results. Spectroscopic and photometric surface gravities differ, but this has
very little effect on the precise determination of the stellar mass in our
spectroscopic analysis. The stellar radius, and hence the planetary radius, is
most affected by the surface gravity discrepancies. For the chemical
abundances, the difference is, as expected, only noticable for the abundances
derived from analyzing of lines of ionized species.Comment: 12 pages, 6 figures, 5 tables, accepted to A&
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