Asteroseismology of the young open cluster NGC 2516 I: Photometric and spectroscopic observations
Astronomy & Astrophysics(2023)
Abstract
Asteroseismic modelling of isolated star presents significant challenges due
to the difficulty in accurately determining stellar parameters, particularly
the stellar age. These challenges can be overcomed by observing stars in open
clusters, whose coeval members share an initial chemical composition. The light
curves by TESS allow us to investigate and analyse stellar variations in
clusters with an unprecedented level. We aim to detect gravity-mode
oscillations in the early-type main-sequence members of the young open cluster
NGC 2516. We selected the 301 member stars as our sample and analysed the TESS
FFI light curves. We also collected high-resolution spectra using the FEROS for
the g-mode pulsators. By fitting the theoretical isochrones to the
colour-magnitude diagram (CMD) of a cluster, we determined an age of 102 ±
15 Myr and inferred the extinction at 550 nm (A_0) is 0.53 ± 0.04 mag. We
identified 147 stars with surface brightness modulations, 24 with g-mode
pulsations (γ Doradus or Slowly Pulsating B stars), and 35 with p-mode
pulsations (δ Sct stars). When sorted by colour index, the amplitude
spectra of the δ Sct stars show a distinct ordering and reveal a
discernible frequency-temperature relationship. The near-core rotation rates,
measured from period spacing patterns in two SPB and nine γ Dor stars,
reach up to 3/d . This is at the high end of the values found from Kepler data
of field stars of similar variability type. The γ Dor stars have
internal rotation rates as high as 50
stars exhibit rotation rates close to their critical rate. We did not find
long-term brightness and colour variations in the mid-infrared, which suggests
that there are no disk or shell formation events in our sample. We also
discussed the results of our spectroscopic observations for the g-mode
pulsators.
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