1,006 research outputs found
Asteroseismic modeling of 16 Cyg A & B using the complete Kepler data set
Asteroseismology of bright stars with well-determined properties from
parallax measurements and interferometry can yield precise stellar ages and
meaningful constraints on the composition. We substantiate this claim with an
updated asteroseismic analysis of the solar-analog binary system 16 Cyg A & B
using the complete 30-month data sets from the Kepler space telescope. An
analysis with the Asteroseismic Modeling Portal (AMP), using all of the
available constraints to model each star independently, yields the same age
( Gyr) and composition (, ) for both stars, as expected for a binary system. We quantify the
accuracy of the derived stellar properties by conducting a similar analysis of
a Kepler-like data set for the Sun, and we investigate how the reliability of
asteroseismic inference changes when fewer observational constraints are
available or when different fitting methods are employed. We find that our
estimates of the initial helium mass fraction are probably biased low by
0.02-0.03 from neglecting diffusion and settling of heavy elements, and we
identify changes to our fitting method as the likely source of small shifts
from our initial results in 2012. We conclude that in the best cases reliable
stellar properties can be determined from asteroseismic analysis even without
independent constraints on the radius and luminosity.Comment: 5 emulateapj pages, 1 table, 1 figure. ApJ Letters, accepte
Empirical relations for the accurate estimation of stellar masses and radii
In this work, we have taken advantage of the most recent accurate stellar
characterizations carried out using asteroseismology, eclipsing binaries and
interferometry to evaluate a comprehensive set of empirical relations for the
estimation of stellar masses and radii. We have gathered a total of 934 stars
-- of which around two-thirds are on the Main Sequence -- that are
characterized with different levels of precision, most of them having estimates
of M, R, Teff, L, g, density, and [Fe/H]. We have deliberately used a
heterogeneous sample (in terms of characterizing techniques and spectroscopic
types) to reduce the influence of possible biases coming from the observation,
reduction, and analysis methods used to obtain the stellar parameters. We have
studied a total of 576 linear combinations of Teff, L, g, density, and [Fe/H]
(and their logarithms) to be used as independent variables to estimate M or R.
We have used an error-in-variables linear regression algorithm to extract the
relations and to ensure the fair treatment of the uncertainties. We present a
total of 38 new or revised relations that have an adj-R2 regression statistic
higher than 0.85, and a relative accuracy and precision better than 10% for
almost all the cases. The relations cover almost all the possible combinations
of observables, ensuring that, whatever list of observables is available, there
is at least one relation for estimating the stellar mass and radius.Comment: 49 Pages, 17 figures, 11 tables, accepted for publication in ApJ
Asteroseismology of KIC 8263801:Is it a member of NGC 6866 and a red clump star?
We present an asteroseismic analysis of the Kepler light curve of KIC
8263801, a red-giant star in the open cluster NGC 6866 that has previously been
reported to be a helium-burning red-clump star. We extracted the frequencies of
the radial and quadrupole modes from its frequency power spectrum and
determined its properties using a grid of evolutionary models constructed with
MESA. The oscillation frequencies were calculated using the GYRE code and the
surface term was corrected using the Ball & Gizon(2014) prescription. We find
that the star has a mass of , age Gyr and radius . By analyzing the internal
structure of the best-fitting model, we infer the evolutionary status of the
star KIC 8263801 as being on the ascending part of the red giant branch, and
not on the red clump. This result is verified using a purely asteroseismic
diagnostic, the diagram which can distinguish red
giant branch stars from red clump stars. Finally, by comparing its age with NGC
6866 ( Gyr) we conclude that KIC 8263801 is not a member of
this open cluster
The installation of a digital autoguider and tiger counters in Narrabri in 2013 April
A digital autoguider (the \mount controller") was installed. New \Tiger" counters replaced the existing, broken, scaler system
Changing the Scaling Relation: The Need For a Mean Molecular Weight Term
The scaling relations that relate the average asteroseismic parameters
and to the global properties of stars are used quite
extensively to determine stellar properties. While the scaling
relation has been examined carefully and the deviations from the relation have
been well documented, the scaling relation has not been examined
as extensively. In this paper we examine the scaling relation
using a set of stellar models constructed to have a wide range of mass,
metallicity, and age. We find that as with , does not
follow the simple scaling relation. The most visible deviation is because of a
mean molecular weight term and a term that are commonly ignored. The
remaining deviation is more difficult to address. We find that the influence of
the scaling relation errors on asteroseismically derived values of are
well within uncertainties. The influence of the errors on mass and radius
estimates is small for main sequence and subgiants, but can be quite large for
red giants.Comment: 15 pages, 14 figures, accepted for publication in Ap
K2P A photometry pipeline for the K2 mission
With the loss of a second reaction wheel, resulting in the inability to point
continuously and stably at the same field of view, the NASA Kepler satellite
recently entered a new mode of observation known as the K2 mission. The data
from this redesigned mission present a specific challenge; the targets
systematically drift in position on a ~6 hour time scale, inducing a
significant instrumental signal in the photometric time series --- this greatly
impacts the ability to detect planetary signals and perform asteroseismic
analysis. Here we detail our version of a reduction pipeline for K2 target
pixel data, which automatically: defines masks for all targets in a given
frame; extracts the target's flux- and position time series; corrects the time
series based on the apparent movement on the CCD (either in 1D or 2D) combined
with the correction of instrumental and/or planetary signals via the KASOC
filter (Handberg & Lund 2014), thus rendering the time series ready for
asteroseismic analysis; computes power spectra for all targets, and identifies
potential contaminations between targets. From a test of our pipeline on a
sample of targets from the K2 campaign 0, the recovery of data for multiple
targets increases the amount of potential light curves by a factor .
Our pipeline could be applied to the upcoming TESS (Ricker et al. 2014) and
PLATO 2.0 (Rauer et al. 2013) missions.Comment: 14 pages, 20 figures, Accepted for publication in The Astrophysical
Journal (Apj
Spatial incoherence of solar granulation: a global analysis using BiSON 2B data
A poor understanding of the impact of convective turbulence in the outer
layers of the Sun and Sun-like stars challenges the advance towards an improved
understanding of their internal structure and dynamics. Assessing and
calibrating these effects is therefore of great importance. Here we study the
spatial coherence of granulation noise and oscillation modes in the Sun, with
the aim of exploiting any incoherence to beat-down observed granulation noise,
hence improving the detection of low-frequency p-modes. Using data from the
BiSON 2B instrument, we assess the coherence between different atmospheric
heights and between different surface regions. We find that granulation noise
from the different atmospheric heights probed is largely incoherent; frequency
regions dominated by oscillations are almost fully coherent. We find a
randomised phase difference for the granulation noise, and a near zero
difference for the evanescent oscillations. A reduction of the incoherent
granulation noise is shown by application of the cross-spectrum.Comment: 8 pages, 7 figures, MNRAS in pres
A synthetic sample of short-cadence solar-like oscillators for TESS
NASA's Transiting Exoplanet Survey Satellite (TESS) has begun a two-year
survey of most of the sky, which will include lightcurves for thousands of
solar-like oscillators sampled at a cadence of two minutes. To prepare for this
steady stream of data, we present a mock catalogue of lightcurves, designed to
realistically mimic the properties of the TESS sample. In the process, we also
present the first public release of the asteroFLAG Artificial Dataset
Generator, which simulates lightcurves of solar-like oscillators based on input
mode properties. The targets are drawn from a simulation of the Milky Way's
populations and are selected in the same way as TESS's true Asteroseismic
Target List. The lightcurves are produced by combining stellar models,
pulsation calculations and semi-empirical models of solar-like oscillators. We
describe the details of the catalogue and provide several examples. We provide
pristine lightcurves to which noise can be added easily. This mock catalogue
will be valuable in testing asteroseismology pipelines for TESS and our methods
can be applied in preparation and planning for other observatories and
observing campaigns.Comment: 14 pages, 6 figures, accepted for publication in ApJS. Archives
containing the mock catalogue are available at
https://doi.org/10.5281/zenodo.1470155 and the pipeline to produce it at
https://github.com/warrickball/s4tess . The first public release of the
asteroFLAG Artificial Dataset Generator v3 (AADG3) is described at
https://warrickball.github.io/AADG3
Galactic Archaeology with TESS: Prospects for Testing the Star Formation History in the Solar Neighbourhood
A period of quenching between the formation of the thick and thin disks of
the Milky Way has been recently proposed to explain the observed
age-[{\alpha}/Fe] distribution of stars in the solar neighbourhood. However,
robust constraints on stellar ages are currently available for only a limited
number of stars. The all-sky survey TESS (Transiting Exoplanet Survey
Satellite) will observe the brightest stars in the sky and thus can be used to
investigate the age distributions of stars in these components of the Galaxy
via asteroseismology, where previously this has been difficult using other
techniques. The aim of this preliminary study was to determine whether TESS
will be able to provide evidence for quenching periods during the star
formation history of the Milky Way. Using a population synthesis code, we
produced populations based on various stellar formation history models and
limited the analysis to red-giant-branch stars. We investigated the
mass-Galactic-disk-height distributions, where stellar mass was used as an age
proxy, to test for whether periods of quenching can be observed by TESS. We
found that even with the addition of 15% noise to the inferred masses, it will
be possible for TESS to find evidence for/against quenching periods suggested
in the literature (e.g. between 7 and 9 Gyr ago), therefore providing stringent
constraints on the formation and evolution of the Milky Way.Comment: 4 pages, 3 figures, proceedings of "Seismology of the Sun and the
Distant Stars 2016", Mario J. P. F. G. Monteiro, Margarida S. Cunha, Joao
Miguel T. Ferreira editor
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