531 research outputs found
Global asteroseismic properties of solar-like oscillations observed by Kepler : A comparison of complementary analysis methods
We present the asteroseismic analysis of 1948 F-, G- and K-type main-sequence
and subgiant stars observed by the NASA {\em Kepler Mission}. We detect and
characterise solar-like oscillations in 642 of these stars. This represents the
largest cohort of main-sequence and subgiant solar-like oscillators observed to
date. The photometric observations are analysed using the methods developed by
nine independent research teams. The results are combined to validate the
determined global asteroseismic parameters and calculate the relative precision
by which the parameters can be obtained. We correlate the relative number of
detected solar-like oscillators with stellar parameters from the {\em Kepler
Input Catalog} and find a deficiency for stars with effective temperatures in
the range \,K and a drop-off in
detected oscillations in stars approaching the red edge of the classical
instability strip. We compare the power-law relationships between the frequency
of peak power, , the mean large frequency separation,
, and the maximum mode amplitude, , and show that
there are significant method-dependent differences in the results obtained.
This illustrates the need for multiple complementary analysis methods to be
used to assess the robustness and reproducibility of results derived from
global asteroseismic parameters.Comment: 14 pages, 9 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Mode identification in rapidly rotating stars
Context: Recent calculations of pulsation modes in rapidly rotating polytropic models and models based on the Self-Consistent Field method have shown that the frequency spectrum of low degree pulsation modes can be described by an empirical formula similar to Tassoul's asymptotic formula, provided that the underlying rotation profile is not too differential.
Aims: Given the simplicity of this asymptotic formula, we investigate whether it can provide a means by which to identify pulsation modes in rapidly rotating stars.
Methods: We develop a new mode identification scheme which consists in scanning a multidimensional parameter space for the formula coefficients which yield the best-fitting asymptotic spectra. This mode identification scheme is then tested on artificial spectra based on the asymptotic formula, on random frequencies and on spectra based on full numerical eigenmode calculations for which the mode identification is known beforehand. We also investigate the effects of adding random frequencies to mimic the effects of chaotic modes which are also expected to show up in such stars.
Results: In the absence of chaotic modes, it is possible to accurately find a correct mode identification for most of the observed frequencies provided these frequencies are sufficiently close to their asymptotic values. The addition of random frequencies can very quickly become problematic and hinder correct mode identification. Modifying the mode identification scheme to reject the worst fitting modes can bring some improvement but the results still remain poorer than in the case without chaotic modes
Verification of the Kepler Input Catalog from Asteroseismology of Solar-type Stars
We calculate precise stellar radii and surface gravities from the
asteroseismic analysis of over 500 solar-type pulsating stars observed by the
Kepler space telescope. These physical stellar properties are compared with
those given in the Kepler Input Catalog (KIC), determined from ground-based
multi-color photometry. For the stars in our sample, we find general agreement
but we detect an average overestimation bias of 0.23 dex in the KIC
determination of log (g) for stars with log (g)_KIC > 4.0 dex, and a resultant
underestimation bias of up to 50% in the KIC radii estimates for stars with
R_KIC < 2 R sun. Part of the difference may arise from selection bias in the
asteroseismic sample; nevertheless, this result implies there may be fewer
stars characterized in the KIC with R ~ 1 R sun than is suggested by the
physical properties in the KIC. Furthermore, if the radius estimates are taken
from the KIC for these affected stars and then used to calculate the size of
transiting planets, a similar underestimation bias may be applied to the
planetary radii.Comment: Published in The Astrophysical Journal Letter
Cancer and systemic inflammation: treat the tumour and treat the host
Determinants of cancer progression and survival are multifactorial and host responses are increasingly appreciated to have a major role. Indeed, the development and maintenance of a systemic inflammatory response has been consistently observed to confer poorer outcome, in both early and advanced stage disease. For patients, cancer-associated symptoms are of particular importance resulting in a marked impact on day-to-day quality of life and are also associated with poorer outcome. These symptoms are now recognised to cluster with one another with anorexia, weight loss and physical function forming a recognised cluster whereas fatigue, pain and depression forming another. Importantly, it has become apparent that these symptom clusters are associated with presence of a systemic inflammatory response in the patient with cancer. Given the understanding of the above, there is now a need to intervene to moderate systemic inflammatory responses, where present. In this context the rationale for therapeutic intervention using nonselective anti-inflammatory agents is clear and compelling and likely to become a part of routine clinical practice in the near future. The published literature on therapeutic intervention using anti-inflammatory agents for cancer-associated symptoms was reviewed. There are important parallels with the development of useful treatments for the systemic inflammatory response in patients with rheumatological disease and cardiovascular disease
Asteroseismology of solar-type stars with K2
We present the first detections by the NASA K2 Mission of oscillations in
solar-type stars, using short-cadence data collected during K2 Campaign\,1
(C1). We understand the asteroseismic detection thresholds for C1-like levels
of photometric performance, and we can detect oscillations in subgiants having
dominant oscillation frequencies around . Changes to the
operation of the fine-guidance sensors are expected to give significant
improvements in the high-frequency performance from C3 onwards. A reduction in
the excess high-frequency noise by a factor of two-and-a-half in amplitude
would bring main-sequence stars with dominant oscillation frequencies as high
as into play as potential asteroseismic targets for
K2.Comment: Accepted for publication in PASP; 16 pages, 2 figure
Solar-like oscillations in cluster stars
We present a brief overview of the history of attempts to obtain a clear
detection of solar-like oscillations in cluster stars, and discuss the results
on the first clear detection, which was made by the Kepler Asteroseismic
Science Consortium (KASC) Working Group 2.Comment: 4 pages, 7 figures, accepted by Astronomische Nachrichte
A comparison of the prognostic value of composite ratios and cumulative scores in patients with operable rectal cancer
The aim of this study was to directly compare the prognostic value of cumulative scores and composite ratios in patients with operable rectal cancer. Within a single surgical unit preoperative differential blood cell results including neutrophil (N), lymphocyte (L), monocyte (M) and platelet (P) counts, as well as CRP (C) and albumin (A) levels were recorded. These results were used to construct a series of composite ratios (NLR, PLR, LMR, CAR) and cumulative scores (NLS, PLS, LMS, NPS, mGPS). The relationship between composite ratios and the cumulative scores and clinicopathological characteristics, cancer specific survival (CSS) and overall survival (OS) were examined. A total of 413 patients were included. When adjusted for TNM stage, surgical approach, time of surgery and margin involvement mGPS (p < 0.05) was associated with CSS. In addition, most composite ratios/scores showed correlations with neoadjuvant therapy (p < 0.001). When a direct comparison between NPS (myeloid) and mGPS (liver) was carried out they showed similar associations with both CSS and OS. Therefore, both composite ratios and cumulative scores have been shown to be prognostic in patients with operable rectal cancer
Prospects for asteroseismology
The observational basis for asteroseismology is being dramatically
strengthened, through more than two years of data from the CoRoT satellite, the
flood of data coming from the Kepler mission and, in the slightly longer term,
from dedicated ground-based facilities. Our ability to utilize these data
depends on further development of techniques for basic data analysis, as well
as on an improved understanding of the relation between the observed
frequencies and the underlying properties of the stars. Also, stellar modelling
must be further developed, to match the increasing diagnostic potential of the
data. Here we discuss some aspects of data interpretation and modelling,
focussing on the important case of stars with solar-like oscillations.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar
modelling', eds M. Marconi, D. Cardini & M. P. Di Mauro, Astrophys. Space
Sci., in the press Revision: correcting abscissa labels on Figs 1 and
Predicting the detectability of oscillations in solar-type stars observed by Kepler
Asteroseismology of solar-type stars has an important part to play in the
exoplanet program of the NASA Kepler Mission. Precise and accurate inferences
on the stellar properties that are made possible by the seismic data allow very
tight constraints to be placed on the exoplanetary systems. Here, we outline
how to make an estimate of the detectability of solar-like oscillations in any
given Kepler target, using rough estimates of the temperature and radius, and
the Kepler apparent magnitude.Comment: 21 pages, 6 figures, accepted for publication Astrophysical Journa
Asteroseismology of Solar-type Stars with Kepler I: Data Analysis
We report on the first asteroseismic analysis of solar-type stars observed by
Kepler. Observations of three G-type stars, made at one-minute cadence during
the first 33.5d of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: About 20 modes of oscillation can
clearly be distinguished in each star. We discuss the appearance of the
oscillation spectra, including the presence of a possible signature of faculae,
and the presence of mixed modes in one of the three stars.Comment: 5 pages, 4 figure, submitted to Astronomische Nachrichte
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