26 research outputs found
Asteroseismic fundamental properties of solar-type stars observed by the NASA Kepler Mission
We use asteroseismic data obtained by the NASA Kepler Mission to estimate the
fundamental properties of more than 500 main-sequence and sub-giant stars. Data
obtained during the first 10 months of Kepler science operations were used for
this work, when these solar-type targets were observed for one month each in a
survey mode. Stellar properties have been estimated using two global
asteroseismic parameters and complementary photometric and spectroscopic data.
Homogeneous sets of effective temperatures were available for the entire
ensemble from complementary photometry; spectroscopic estimates of T_eff and
[Fe/H] were available from a homogeneous analysis of ground-based data on a
subset of 87 stars. [Abbreviated version... see paper for full abstract.]Comment: Accepted for publication in ApJS; 90 pages, 22 figures, 6 tables.
Units on rho in tables now listed correctly as rho(Sun
Properties of 42 Solar-type Kepler Targets from the Asteroseismic Modeling Portal
Recently the number of main-sequence and subgiant stars exhibiting solar-like
oscillations that are resolved into individual mode frequencies has increased
dramatically. While only a few such data sets were available for detailed
modeling just a decade ago, the Kepler mission has produced suitable
observations for hundreds of new targets. This rapid expansion in observational
capacity has been accompanied by a shift in analysis and modeling strategies to
yield uniform sets of derived stellar properties more quickly and easily. We
use previously published asteroseismic and spectroscopic data sets to provide a
uniform analysis of 42 solar-type Kepler targets from the Asteroseismic
Modeling Portal (AMP). We find that fitting the individual frequencies
typically doubles the precision of the asteroseismic radius, mass and age
compared to grid-based modeling of the global oscillation properties, and
improves the precision of the radius and mass by about a factor of three over
empirical scaling relations. We demonstrate the utility of the derived
properties with several applications.Comment: 12 emulateapj pages, 9 figures, 1 online-only extended figure, 1
table, ApJS accepted (typo corrected in Eq.8
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
Kepler observations of variability in B-type stars
The analysis of the light curves of 48 B-type stars observed by Kepler is
presented. Among these are 15 pulsating stars, all of which show low
frequencies characteristic of SPB stars. Seven of these stars also show a few
weak, isolated high frequencies and they could be considered as SPB/beta Cep
hybrids. In all cases the frequency spectra are quite different from what is
seen from ground-based observations. We suggest that this is because most of
the low frequencies are modes of high degree which are predicted to be unstable
in models of mid-B stars. We find that there are non-pulsating stars within the
beta Cep and SPB instability strips. Apart from the pulsating stars, we can
identify stars with frequency groupings similar to what is seen in Be stars but
which are not Be stars. The origin of the groupings is not clear, but may be
related to rotation. We find periodic variations in other stars which we
attribute to proximity effects in binary systems or possibly rotational
modulation. We find no evidence for pulsating stars between the cool edge of
the SPB and the hot edge of the delta Sct instability strips. None of the stars
show the broad features which can be attributed to stochastically-excited modes
as recently proposed. Among our sample of B stars are two chemically peculiar
stars, one of which is a HgMn star showing rotational modulation in the light
curve.Comment: 19 pages, 11 figures, 4 table
Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission
In addition to its search for extra-solar planets, the NASA Kepler Mission
provides exquisite data on stellar oscillations. We report the detections of
oscillations in 500 solartype stars in the Kepler field of view, an ensemble
that is large enough to allow statistical studies of intrinsic stellar
properties (such as mass, radius and age) and to test theories of stellar
evolution. We find that the distribution of observed masses of these stars
shows intriguing differences to predictions from models of synthetic stellar
populations in the Galaxy.Comment: 20 pages, including on-line supporting materia
PLATO as it is: a legacy mission for Galactic archaeology
Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial-mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red-giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental pre-requisite to then reach the more ambitious goal of a similar level of accuracy, which will only be possible if we have to hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal which conveniently falls within the main aims of PLATO's core science
Luminosity variation in the extended one-zone RR Lyrae model
The Stellingwerf one-zone stellar model is extended by assuming, a slow and uniform rotation that leads to a very small oblateness of the star. The matter in the core-surrounding shell is supposed to consists of a mixture of ideal gas and radiation. This one-zone stellar pulsation model is proposed as a tool to investigate the factors affecting luminosity variations of pulsating stars. Linear and nonlinear analyses of the resulting equations are described. The results are in very good agreement with the observed RR Lyrae light curves.
Evidence for a source of H chondrites in the outer main asteroid belt
Aims. In this paper we report near-infrared spectroscopic observations of one of the largest potentially hazardous asteroids, (214869) 2007 PA