Bibcode
Kallinger, T.; Beck, P. G.; Hekker, S.; Huber, D.; Kuschnig, R.; Rockenbauer, M.; Winter, P. M.; Weiss, W. W.; Handler, G.; Moffat, A. F. J.; Pigulski, A.; Popowicz, A.; Wade, G. A.; Zwintz, K.
Bibliographical reference
Astronomy and Astrophysics, Volume 624, id.A35, 17 pp.
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4
2019
Journal
Citations
12
Refereed citations
9
Description
Context. The study of stellar structure and evolution depends crucially
on accurate stellar parameters. The photometry from space telescopes has
provided superb data that enabled the asteroseismic characterisation of
thousands of stars. However, typical targets of space telescopes are
rather faint and complementary measurements are difficult to obtain. On
the other hand, the brightest, otherwise well-studied stars, are lacking
seismic characterization. Aims: Our goal is to use the
granulation and/or oscillation timescales measured from photometric time
series of bright red giants (1.6 ≤ V mag ≤ 5.3) observed with
BRITE-Constellation to determine stellar surface gravities and masses.
Methods: We used probabilistic methods to characterise the
granulation and/or oscillation signal in the power density spectra and
the autocorrelation function of the BRITE-Constellation time series. Results: We detect a clear granulation and/or oscillation signal in
23 red giant stars and extract the corresponding timescales from the
power density spectra as well as the autocorrelation function of the
BRITE-Constellation time series. To account for the recently discovered
non-linearity of the classical seismic scaling relations, we used
parameters from a large sample of Kepler stars to re-calibrate the
scalings of the high- and low-frequency components of the granulation
signal. We developed a method to identify which component is measured if
only one granulation component is statistically significant in the data.
We then used the new scalings to determine the surface gravity of our
sample stars, finding them to be consistent with those determined from
the autocorrelation signal of the time series. We further used radius
estimates from the literature to determine the stellar masses of our
sample stars from the measured surface gravities. We also defined a
statistical measure for the evolutionary stage of the stars.
Conclusions: Our sample of stars covers low-mass stars on the lower
giant branch to evolved massive supergiants and even though we cannot
verify our mass estimates with independent measurements from the
literature, they appear to be at least good enough to separate high-mass
from low-mass stars. Given the large known but usually not considered
systematic uncertainties in the previous model-based mass estimates, we
prefer our model-independent measurements.
Based on data collected by the BRITE Constellation satellite mission,
designed, built, launched, operated, and supported by the Austrian
Research Promotion Agency (FFG), the University of Vienna, the Technical
University of Graz, the University of Innsbruck, the Canadian Space
Agency (CSA), the University of Toronto Institute for Aerospace Studies
(UTIAS), the Foundation for Polish Science & Technology (FNiTP
MNiSW), and National Science Centre (NCN).