Calculating Asteroseismic Diagrams for Solar-Like Oscillations

Mon. Not. R. Astron. Soc.

Chaplin

Brogaard

et al. 2016

116

Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens of thousands of field stars. Tests against independent estimates of these properties are however scarce, especially in the metal-poor regime. Here, we report the detection of solar-like oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular cluster M4. The detections were made in photometric observations from the K2 Mission during its Campaign 2. Making use of independent constraints on the distance, we estimate masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs. When introducing a correction to the ∆ν scaling relation as suggested by stellar models, for RGB stars we find excellent agreement with the expected masses from isochrone fitting, and with a distance modulus derived using independent methods. The offset with respect to independent masses is lower, or comparable with, the uncertainties on the average RGB mass (4 − 10%, depending on the combination of constraints used). Our results lend confidence to asteroseismic masses in the metal poor regime. We note that a larger sample will be needed to allow more stringent tests to be made of systematic uncertainties in all the observables (both seismic and non-seismic), and to explore the properties of RHB stars, and of different populations in the cluster.

Section: Massesmentioning

confidence: 99%

Detection of solar-like oscillations in relics of the Milky Way: asteroseismology of K giants in M4 using data from the NASA K2 mission

Mon. Not. R. Astron. Soc.

Chaplin

Brogaard

et al. 2016

116

“…Section 2.3), is 0.8 per cent larger than the observed one ( ∆ν ⊙,obs = 135.0 µHz). We then follow the approach by White et al (2011) and adopt as a solar reference value that of our calibrated solar model ( ∆ν ⊙ = ∆ν mod,⊙ = 136.1µHz).…”

Section: Surface Effectsmentioning

confidence: 99%

“…First, there are significant evidences of corrections of a few percent being necessary (see White et al 2011;Miglio 2012;Miglio et al 2013;Brogaard et al 2016;Miglio et al 2016;Guggenberger et al 2016;Sharma et al 2016;Handberg et al 2016) in the ∆ν scaling relation. Although such corrections are expected to have little impact on the stellar radii (and hence on the distances), they are expected to reduce the errors in the derived stellar masses, hence on the derived ages for giants.…”

Section: Introductionmentioning

confidence: 99%

Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations

Rodrigues

Bossini

Mon. Not. R. Astron. Soc.

et al. 2017

117

Asteroseismic parameters allow us to measure the basic stellar properties of field giants observed far across the Galaxy. Most of such determinations are, up to now, based on simple scaling relations involving the large frequency separation, ∆ν, and the frequency of maximum power, ν max . In this work, we implement ∆ν and the period spacing, ∆P , computed along detailed grids of stellar evolutionary tracks, into stellar isochrones and hence in a Bayesian method of parameter estimation. Tests with synthetic data reveal that masses and ages can be determined with typical precision of 5 and 19 per cent, respectively, provided precise seismic parameters are available. Adding independent information on the stellar luminosity, these values can decrease down to 3 and 10 per cent respectively. The application of these methods to NGC 6819 giants produces a mean age in agreement with those derived from isochrone fitting, and no evidence of systematic differences between RGB and RC stars. The age dispersion of NGC 6819 stars, however, is larger than expected, with at least part of the spread ascribable to stars that underwent mass-transfer events.

“…An example of possible systematic biases concerning the mass determination are departures from a simple scaling of ∆ν with the square root of the stellar mean density (see, e.g., Belkacem et al 2013;Miglio et al 2012Miglio et al , 2013aWhite et al 2011). Suggested corrections to the ∆ν scaling are likely to depend (to a level of few percent) on the the stellar structure itself.…”

Section: From Precise To Accurate Stellar Propertiesmentioning

confidence: 99%

Asteroseismology of red giants: From analysing light curves to estimating ages

Davies

2016

Astron Nachr

Asteroseismology has started to provide constraints on stellar properties that will be essential to accurately reconstruct the history of the Milky Way. Here we look at the information content in data sets representing current and future space missions (CoRoT, Kepler, K2, TESS, and PLATO) for red giant stars. We describe techniques for extracting the information in the frequency power spectrum and apply these techniques to Kepler data sets of different observing length to represent the different space missions. We demonstrate that for KIC 12008916, a low-luminosity red giant branch star, we can extract useful information from all data sets, and for all but the shortest data set we obtain good constraint on the g-mode period spacing and core rotation rates. We discuss how the high precision in these parameters will constrain the stellar properties of stellar radius, distance, mass and age. We show that high precision can be achieved in mass and hence age when values of the g-mode period spacing are available. We caution that tests to establish the accuracy of asteroseismic masses and ages are still "work in progress".