Strömgren Survey for Asteroseismology and Galactic Archaeology: Let the Saga Begin

Abstract

Asteroseismology has the capability of precisely determining stellar properties which would otherwise be inaccessible, such as radii, masses and thus ages of stars. When coupling this information with classical determinations of stellar parameters, such as metallicities, effective temperatures and angular diameters, powerful new diagnostics for Galactic studies can be obtained. The ongoing Strömgren survey for Asteroseismology and Galactic Archaeology (SAGA) has the goal of transforming the Kepler field into a new benchmark for Galactic studies, similarly to the solar neighborhood. Here we present first results from a stripe centred at Galactic longitude 74 • and covering latitude from about 8 • to 20 • , which includes almost 1000 K-giants with seismic information and the benchmark open cluster NGC 6819. We describe the coupling of classical and seismic parameters, the accuracy as well as the caveats of the derived effective temperatures, metallicities, distances, surface gravities, masses, and radii. Confidence in the achieved precision is corroborated by the detection of the first and secondary clump in a population of field stars with a ratio of 2 to 1, and by the negligible scatter in the seismic distances among NGC 6819 member stars. An assessment of the reliability of stellar parameters in the Kepler Input Catalogue is also performed, and the impact of our results for population studies in the Milky Way is discussed, along with the importance of an all-sky Strömgren survey.

Synthetic stellar photometry – I. General considerations and new transformations for broad-band systems

“…To accomplish this, filter systems are tailored to select regions in stellar spectra where the variations of the atmospheric parameters leave their characteristic traces with enough prominence to be detected in photometric data. Beginning with the influential papers by Johnson (1966) and Strömgren (1966), which describe the basis of broad-and et al 2012), intermediate-and narrow-band photometry is more limited in this respect, although still very informative (e.g., Mould & Bessell 1982;Bonnell & Bell 1982;Yong et al 2008;Árnadóttir et al 2010;Casagrande et al 2014a).…”

Modelling of Red Giant Stars: The state-of-the-art

“…The MLT contains four free parameters, whose values affect the predicted T eff of the stellar models. Three parameters are fixed a priori 2 (and define what it is denoted as the MLT flavour), and the only one left to be calibrated is α MLT , the ratio of the mixing length to the local pressure scale height H P , that provides the scale length of the convective motions. As a general rule, an increase of α MLT corresponds to an increase of the convective transport efficiency and an increase of the stellar model T eff .…”

“…Before closing this section, we wish to emphasise that an accurate determination of the RGB ML efficiency is a crucial issue also in the context of using stellar models and seismic measurements for Galactic archaelogy ( [2]). Indeed, one has to bear in mind that the computation of ages for red giant stars (both RGB stars and RC ones) heavily relies on the knowledge of their masses.…”

Asteroseismic Properties of Solar-type Stars Observed with the NASAK2Mission: Results from Campaigns 1–3 and Prospects for Future Observations

“…Two sets of atmospheric parameters were obtained, one from spectroscopy and one from the InfraRed Flux Method (IRFM; see Casagrande et al 2014). Below we go through these in turn.…”