2,145 research outputs found
Stellar Activity and its Implications for Exoplanet Detection on GJ 176
We present an in-depth analysis of stellar activity and its effects on radial
velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 years from
the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are
supplemented with spectra from previous observations with the HIRES and HARPS
spectrographs, and V- and R-band photometry taken over 6 years at the Dyer and
Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth
exoplanet in an 8.8-day orbit. However, the velocities of this star are also
known to be contaminated by activity, particularly at the 39-day stellar
rotation period. We have examined the magnetic activity of GJ 176 using the
sodium I D lines, which have been shown to be a sensitive activity tracer in
cool stars. In addition to rotational modulation, we see evidence of a
long-term trend in our Na I D index, which may be part of a long-period
activity cycle. The sodium index is well correlated with our RVs, and we show
that this activity trend drives a corresponding slope in RV. Interestingly, the
rotation signal remains in phase in photometry, but not in the spectral
activity indicators. We interpret this phenomenon as the result of one or more
large spot complexes or active regions which dominate the photometric
variability, while the spectral indices are driven by the overall magnetic
activity across the stellar surface. In light of these results, we discuss the
potential for correcting activity signals in the RVs of M dwarfs.Comment: Accepted for publication in Ap
Data Mining to Uncover Heterogeneous Water Use Behaviors From Smart Meter Data
Knowledge on the determinants and patterns of water demand for different consumers supports the design of customized demand management strategies. Smart meters coupled with big data analytics tools create a unique opportunity to support such strategies. Yet, at present, the information content of smart meter data is not fully mined and usually needs to be complemented with water fixture inventory and survey data to achieve detailed customer segmentation based on end use water usage. In this paper, we developed a dataâdriven approach that extracts information on heterogeneous water end use routines, main end use components, and temporal characteristics, only via data mining existing smart meter readings at the scale of individual households. We tested our approach on data from 327 households in Australia, each monitored with smart meters logging water use readings every 5 s. As part of the approach, we first disaggregated the householdâlevel water use time series into different end uses via Autoflow. We then adapted a customer segmentation based on eigenbehavior analysis to discriminate among heterogeneous water end use routines and identify clusters of consumers presenting similar routines. Results revealed three main water end use profile clusters, each characterized by a primary end use: shower, clothes washing, and irrigation. Timeâofâuse and intensityâofâuse differences exist within each class, as well as different characteristics of regularity and periodicity over time. Our customer segmentation analysis approach provides utilities with a concise snapshot of recurrent water use routines from smart meter data and can be used to support customized demand management strategies.TU Berlin, Open-Access-Mittel - 201
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Predictive Value of Biomarkers for Normal and Pathological Ageing in a Rat Model
Sub-optimal diets are widely known to be associated with disease. This study investigated two questions: first, whether a Western affluent diet affects long-term health in the rat, and second, whether, and to what extent, early changes in blood biomarkers can predict specific pathologies. A rat model was used in which animals were fed from weaning either a control diet or a high fat, low protein, energy dense Western affluent diet. Rats were harvested at either 12 or 18 months, and at these time points blood samples were taken and various clinical biomarkers measured using a hospital analyser or by ELISA. Predictive biomarkers should show small changes at early time points and larger changes at later time-points, and be associated with disease(s). Tissues were examined for overt pathology, and data were mined to establish links between pathologies and specific blood markers that might be used predictively. Results showed that the Western affluent diet is associated with ill-health, with a relative risk of developing disease 4.5 times higher than for the control diet. Furthermore we conclude that triacylglycerol, HDL cholesterol, the ratio of total cholesterol to HDL cholesterol, creatinine and alanine aminotransferase were good predictors of disease as across the cohorts they showed altered levels before the clinical development of pathologies, in agreement with our hypothesis
Elemental Abundances of Solar Sibling Candidates
Dynamical information along with survey data on metallicity and in some cases
age have been used recently by some authors to search for candidates of stars
that were born in the cluster where the Sun formed. We have acquired high
resolution, high signal-to-noise ratio spectra for 30 of these objects to
determine, using detailed elemental abundance analysis, if they could be true
solar siblings. Only two of the candidates are found to have solar chemical
composition. Updated modeling of the stars' past orbits in a realistic Galactic
potential reveals that one of them, HD162826, satisfies both chemical and
dynamical conditions for being a sibling of the Sun. Measurements of
rare-element abundances for this star further confirm its solar composition,
with the only possible exception of Sm. Analysis of long-term high-precision
radial velocity data rules out the presence of hot Jupiters and confirms that
this star is not in a binary system. We find that chemical tagging does not
necessarily benefit from studying as many elements as possible, but instead
from identifying and carefully measuring the abundances of those elements which
show large star-to-star scatter at a given metallicity. Future searches
employing data products from ongoing massive astrometric and spectroscopic
surveys can be optimized by acknowledging this fact.Comment: ApJ, in press. Tables 2 and 4 are available in full in the "Other
formats: source" downloa
The Kepler Follow-up Observation Program
The Kepler Mission was launched on March 6, 2009 to perform a photometric
survey of more than 100,000 dwarf stars to search for terrestrial-size planets
with the transit technique. Follow-up observations of planetary candidates
identified by detection of transit-like events are needed both for
identification of astrophysical phenomena that mimic planetary transits and for
characterization of the true planets and planetary systems found by Kepler. We
have developed techniques and protocols for detection of false planetary
transits and are currently conducting observations on 177 Kepler targets that
have been selected for follow-up. A preliminary estimate indicates that between
24% and 62% of planetary candidates selected for follow-up will turn out to be
true planets.Comment: 12 pages, submitted to the Astrophysical Journal Letter
Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity
We investigate the nature of the long-period radial velocity variations in
Alpha Tau first reported over 20 years ago. We analyzed precise stellar radial
velocity measurements for Alpha Tau spanning over 30 years. An examination of
the Halpha and Ca II 8662 spectral lines, and Hipparcos photometry was also
done to help discern the nature of the long-period radial velocity variations.
Our radial velocity data show that the long-period, low amplitude radial
velocity variations are long-lived and coherent. Furthermore, Halpha equivalent
width measurements and Hipparcos photometry show no significant variations with
this period. Another investigation of this star established that there was no
variability in the spectral line shapes with the radial velocity period. An
orbital solution results in a period of P = 628.96 +/- 0.90 d, eccentricity, e
= 0.10 +/- 0.05, and a radial velocity amplitude, K = 142.1 +/- 7.2 m/s.
Evolutionary tracks yield a stellar mass of 1.13 +/- 0.11 M_sun, which
corresponds to a minimum companion mass of 6.47 +/- 0.53 M_Jup with an orbital
semi-major axis of a = 1.46 +/- 0.27 AU. After removing the orbital motion of
the companion, an additional period of ~ 520 d is found in the radial velocity
data, but only in some time spans. A similar period is found in the variations
in the equivalent width of Halpha and Ca II. Variations at one-third of this
period are also found in the spectral line bisector measurements. The 520 d
period is interpreted as the rotation modulation by stellar surface structure.
Its presence, however, may not be long-lived, and it only appears in epochs of
the radial velocity data separated by 10 years. This might be due to an
activity cycle. The data presented here provide further evidence of a planetary
companion to Alpha Tau, as well as activity-related radial velocity variations.Comment: 18 pages, 14 figures. Accepted for publication in Astronomy and
Astrophysic
Energy transfer in pendant perylene diimide copolymers
We report the synthesis, characterisation and polymerisation of two novel asymmetric perylene diimide acrylate monomers. The novel monomers form a sensitiserâacceptor pair capable of undergoing Förster resonance energy transfer, and were incorporated as copolymers with tert-butyl acrylate. The tert-butyl acrylate units act as spacers along the polymer chain allowing high concentrations of dye while mitigating aggregate quenching, leading to persistent fluorescence in the solid state at high concentrations of up to 0.3 M. Analysis of fluorescence kinetics showed efficient energy transfer between the optically dense sensitiser and the lower concentration acceptor luminophores within the polymer. This reduced reabsorption within the material demonstrates that the copolymer-scaffold energy transfer system has potential for use in luminescent solar concentrators
Revised Stellar Properties of Kepler Targets for the Q1-17 (DR25) Transit Detection Run
The determination of exoplanet properties and occurrence rates using Kepler
data critically depends on our knowledge of the fundamental properties (such as
temperature, radius and mass) of the observed stars. We present revised stellar
properties for 197,096 Kepler targets observed between Quarters 1-17 (Q1-17),
which were used for the final transiting planet search run by the Kepler
Mission (Data Release 25, DR25). Similar to the Q1--16 catalog by Huber et al.
the classifications are based on conditioning published atmospheric parameters
on a grid of Dartmouth isochrones, with significant improvements in the adopted
methodology and over 29,000 new sources for temperatures, surface gravities or
metallicities. In addition to fundamental stellar properties the new catalog
also includes distances and extinctions, and we provide posterior samples for
each stellar parameter of each star. Typical uncertainties are ~27% in radius,
~17% in mass, and ~51% in density, which is somewhat smaller than previous
catalogs due to the larger number of improved logg constraints and the
inclusion of isochrone weighting when deriving stellar posterior distributions.
On average, the catalog includes a significantly larger number of evolved
solar-type stars, with an increase of 43.5% in the number of subgiants. We
discuss the overall changes of radii and masses of Kepler targets as a function
of spectral type, with particular focus on exoplanet host stars.Comment: 19 pages, 13 figures. ApJS in pres
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