2,412 research outputs found
Spectrum Analysis of Bright Kepler late B- to early F- Stars
The Kepler satellite mission delivers single band-pass light curves of a huge
number of stars observed in the Cygnus-Lyra region opening a new window for
asteroseismology. In order to accomplish one of the preconditions for the
asteroseismic modelling of the stars, we aim to derive fundamental parameters
and individual abundances for a sample of 18 Gamma Dor (GD)/Delta Sct (DSct)
and 8 SPB/beta Cep candidate stars in the Kepler satellite field of view. We
use the spectral synthesis method to model newly obtained, high-resolution
spectra of 26 stars in order to derive their fundamental parameters and
individual abundances. The stars are then placed into the log(Teff)-log(g)
diagram and the obtained spectroscopic classification is compared to the
existing photometric one. For hot stars, the KIC temperatures appear to be
systematically underestimated, in agreement with previous findings. We also
find that the temperatures derived from our spectra agree reasonably well with
those derived from the SED fitting. According to their position in the
log(Teff)-log(g) diagram, two stars are expected GD stars, four stars are
expected DSct stars, and four stars are possibly DSct stars at the blue edge of
the instability strip. Two stars are confirmed SPB variables, and one star
falls into the SPB instability region but its parameters might be biased by
binarity. Two of the four stars that fall into the DSct instability region show
GD-type oscillation in their light curves implying that GD-like oscillations
are much more common among the DSct stars than is theoretically expected.
Moreover, one of the stars located at the hot border of the DSct instability
strip is classified as DSct-GD hybrid pulsator from its light curve analysis.
Given that these findings are fully consistent with recent investigations, we
conclude that a revision of the GD and DSct instability strips is essential.Comment: 14 pages, 14 figures, 6 tables; accepted for publication in MNRA
WASP-1: A lithium- and metal-rich star with an oversized planet
In this paper we present our results of a comprehensive spectroscopicanalysis
of WASP-1, the host star to the exoplanet WASP-1b. We derive T_eff = 6110 +/-
45 K, log g = 4.28 +/- 0.15, and [M/H] = 0.23 +/- 0.08, and also a high
abundance of lithium, log n(Li) = 2.91 +/- 0.05. These parameters suggests an
age for the system of 1-3 Gyr and a stellar mass of 1.25-1.35 M_sun. This means
that WASP-1 has properties very similar to those of HD 149026, the host star
for the highest density planet yet detected. Moreover, their planets orbit at
comparable distances and receive comparable irradiating fluxes from their host
stars. However, despite the similarity of WASP-1 with HD 149026, their planets
have strongly different densities. This suggests that gas-giant planet density
is not a simple function of host-star metallicity or of radiation environment
at ages of ~2 Gyr.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
Forecasting Design Day Demand Using Extremal Quantile Regression
Extreme events occur rarely, making them difficult to predict. Extreme cold events strain natural gas systems to their limits. Natural gas distribution companies need to be prepared to satisfy demand on any given day that is at or warmer than an extreme cold threshold. The hypothetical day with temperature at this threshold is called the Design Day. To guarantee Design Day demand is satisfied, distribution companies need to determine the demand that is unlikely to be exceeded on the Design Day.
We approach determining this demand as an extremal quantile regression problem. We review current methods for extremal quantile regression. We implement a quantile forecast to estimate the demand that has a minimal chance of being exceeded on the design day. We show extremal quantile regression to be more reliable than direct quantile estimation. We discuss the difficult task of evaluating a probabilistic forecast on rare events.
Probabilistic forecasting is a quickly growing research topic in the field of energy forecasting. Our paper contributes to this field in three ways. First, we forecast quantiles during extreme cold events where data is sparse. Second, we forecast extremely high quantiles that have a very low probability of being exceeded. Finally, we provide a real world scenario on which to apply these techniques
An Economic Evaluation of Cattle Supplies and Slaughter Plant Capacity in New York and the Northeast Region
A.E. Res. 82-1
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