325 research outputs found
The Kepler Smear Campaign: Light curves for 102 Very Bright Stars
We present the first data release of the Kepler Smear Campaign, using
collateral 'smear' data obtained in the Kepler four-year mission to reconstruct
light curves of 102 stars too bright to have been otherwise targeted. We
describe the pipeline developed to extract and calibrate these light curves,
and show that we attain photometric precision comparable to stars analyzed by
the standard pipeline in the nominal Kepler mission. In this paper, aside from
publishing the light curves of these stars, we focus on 66 red giants for which
we detect solar-like oscillations, characterizing 33 of these in detail with
spectroscopic chemical abundances and asteroseismic masses as benchmark stars.
We also classify the whole sample, finding nearly all to be variable, with
classical pulsations and binary effects. All source code, light curves, TRES
spectra, and asteroseismic and stellar parameters are publicly available as a
Kepler legacy sample.Comment: 35 pages, accepted ApJ
An asteroseismic age estimate of the open cluster NGC 6866 using Kepler and Gaia
Asteroseismology of solar-like oscillations in giant stars allow the
derivation of their masses and radii. For members of open clusters this allows
an age estimate of the cluster which should be identical to the age estimate
from the colour-magnitude diagram, but independent of the uncertainties that
are present for that type of analysis. Thus, a more precise and accurate age
estimate can be obtained. We aim to measure asteroseismic properties of
oscillating giant members of the open cluster NGC 6866 and utilise these for a
cluster age estimate. Model comparisons allow constraints on the stellar
physics, and here we investigate the efficiency of convective-core overshoot
and effects of rotation during the main-sequence, which has a significant
influence on the age for these relatively massive giants. We identify six giant
members of NGC 6866 and derive asteroseismic measurements for five of them.
This constrains the convective-core overshoot and enables a more precise and
accurate age estimate than previously possible. Asteroseismology establishes
the helium-core burning evolutionary phase for the giants, which have a mean
mass of 2.8 . Their radii are significantly smaller than predicted
by current 1D stellar models unless the amount of convective-core overshoot on
the main sequence is reduced to in the
step-overshoot description. Our measurements also suggest that rotation has
affected the evolution of the stars in NGC 6866 in a way that is consistent
with 3D simulations but not with current 1D stellar models. The cluster age is
estimated to be 0.43 0.05 Gyr, significantly younger and more precise
than most previous estimates. We derive a precise cluster age while
constraining convective-core overshooting and effects of rotation in the
models. We uncover potential biases for automated age estimates of helium-core
burning stars.Comment: Accepted on 21/08/2023 for publication in Section 7. Stellar
structure and evolution of Astronomy & Astrophysics. 20 Pages, 11 Figures +
appendi
K2 results for "young" -rich stars in the Galaxy
The origin of apparently young -rich stars in the Galaxy is still a
matter of debate in Galactic archaeology, whether they are genuinely young or
might be products of binary evolution and merger/mass accretion. We aim to shed
light on the nature of young -rich stars in the Milky Way by studying
their distribution in the Galaxy thanks to an unprecedented sample of giant
stars that cover different Galactic regions and have precise asteroseismic
ages, chemical, and kinematic measurements. We analyze a new sample of
6000 stars with precise ages coming from asteroseismology. Our sample combines
the global asteroseismic parameters measured from light curves obtained by the
K2 mission with stellar parameters and chemical abundances obtained from APOGEE
DR17 and GALAH DR3, then cross-matched with Gaia DR3. We define our sample of
young -rich stars and study their chemical, kinematic, and age
properties. We investigate young -rich stars in different parts of the
Galaxy and we find that the fraction of young -rich stars remains
constant with respect to the number of high- stars at 10%.
Furthermore, young -rich stars have kinematic and chemical properties
similar to high- stars, except for [C/N] ratios. This suggests that
these stars are not genuinely young, but products of binary evolution and
merger/mass accretion. Under that assumption, we find the fraction of these
stars in the field to be similar to that found recently in clusters. This fact
suggests that 10% of the low- field stars could also have their
ages underestimated by asteroseismology. This should be kept in mind when using
asteroseismic ages to interpret results in Galactic archaeology.Comment: 13 pages, 7 figures. Accepted by A&
K2 results for “young” α-rich stars in the Galaxy
Context. The origin of apparently young α-rich stars in the Galaxy is still a matter of debate in Galactic archaeology, whether they are genuinely young or might be products of binary evolution, and mergers or mass accretion.Aims: Our aim is to shed light on the nature of young α-rich stars in the Milky Way by studying their distribution in the Galaxy thanks to an unprecedented sample of giant stars that cover different Galactic regions and have precise asteroseismic ages, and chemical and kinematic measurements.Methods: We analyzed a new sample of ∼6000 stars with precise ages coming from asteroseismology. Our sample combines the global asteroseismic parameters measured from light curves obtained by the K2 mission with stellar parameters and chemical abundances obtained from APOGEE DR17 and GALAH DR3, then cross-matched with Gaia DR3. We define our sample of young α-rich stars and study their chemical, kinematic, and age properties.Results: We investigated young α-rich stars in different parts of the Galaxy and we find that the fraction of young α-rich stars remains constant with respect to the number of high-α stars at ∼10%. Furthermore, young α-rich stars have kinematic and chemical properties similar to high-α stars, except for [C/N] ratios.Conclusions: Thanks to our new K2 sample, we conclude that young α-rich stars have similar occurrence rates in different parts of the Galaxy, and that they share properties similar to the normal high-α population, except for [C/N] ratios. This suggests that these stars are not genuinely young, but are products of binary evolution, and mergers or mass accretion. Under that assumption, we find the fraction of these stars in the field to be similar to that found recently in clusters. This suggests that ∼10% of the low-α field stars could also have their ages underestimated by asteroseismology. This should be kept in mind when using asteroseismic ages to interpret results in Galactic archaeology
- …