Variability in the Massive Open Cluster NGC 1817 from K2: A Rich Population of Asteroseismic Red Clump, Eclipsing Binary, and Main-sequence Pulsating Stars

Sandquist, Eric L.; Stello, Dennis; Arentoft, T.; Brogaard, K.; Grundahl, F.; Vanderburg, Andrew; Hedlund, Anne; DeWitt, R.; Ackerman, Taylor R.; Aguilar, Miguel; Buckner, Andrew J.; Juarez, Christian; Ortiz, Arturo J.; Richarte, David; Rivera, Daniel Ivan; Schlapfer, Levi

doi:10.3847/1538-3881/ab68df

Cited by 11 publications

(7 citation statements)

References 84 publications

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“…Furthermore, star 765ʼs membership may also be in question due to it is relatively low parallax (Table 2), but its proper motions are consistent with NGC 7789 membership. The dereddened CMD presented in Figure of Sandquist et al (2020) for multiple open clusters shows that the approximate red clump center is at…”

Section: The Stellar Samplementioning

confidence: 98%

Chemical Compositions Of Red Giant Stars in the Old Open Cluster NGC 7789

Neel

Sneden

Afşar

et al. 2023

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We have gathered optical-region spectra, derived model atmosphere parameters, and computed elemental abundances for 15 red giant stars in the open cluster NGC 7789. We focus on the light element group CNOLi that provides clues to evolutionary changes associated with internal fusion events and chemical mixing. We confirm and extend an early report that NGC 7789 stars 193 and 301 have anomalously large Li abundances, and that these values are apparently unconnected to any other elements’ abundances in these stars. A companion study of He i λ10830 lines in both field stars and cluster members shows that star 301 has a strong He feature while star 193 does not. Possible explanations for the large Li abundances of these stars include helium flash-induced mixing events and binary interactions at some past or present times. In either case an internal eruption of energy could cause fresh synthesis of lithium via the Cameron-Fowler Berillyum transport mechanism. Rapid transport of lithium to the outer layers may have created significant chromospheric transient disturbances, producing enough helium ionization to allow for the strong λ10830 absorption in star 301.

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Section: The Stellar Samplementioning

confidence: 98%

Chemical Compositions Of Red Giant Stars in the Old Open Cluster NGC 7789

Neel

Sneden

Afşar

et al. 2023

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“…Open clusters are known to host a rich variety of variable stars (Xue et al 2019;Joshi et al 2020a;Sandquist et al 2020). These stars play a crucial role in our understanding of stars' intrinsic properties such as pulsation, rotation, and emission.…”

Section: Introductionmentioning

confidence: 99%

Investigating Stellar Variability in the Open Cluster Region NGC 381

Maurya¹,

Joshi²,

Panchal³

et al. 2023

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We study variable stars in the field of the open cluster NGC 381 using photometric data observed over 27 nights and identify a total of 57 variable stars, six of which are member stars. The variable stars are classified based on their periods, amplitudes, light-curve shapes, and locations in the H-R diagram. We found a rich variety of variable stars in the cluster. We identified a total of 10 eclipsing binaries, of which two are of Algol type while eight are of W UMa type (EW). The estimated ages of these EW binaries are greater than 0.6 Gyr, which is in agreement with the formation time constraint of ≥0.6 Gyr on short-period eclipsing binaries. The physical parameters of the two EW-type binaries are estimated using PHOEBE model-fitting software. The pulsating variable stars include one each from the δ Scuti and γ Dor variability classes. We determined the pulsation modes of pulsating variables with the help of the FAMIAS package. We obtained 15 rotational variable stars comprising four dwarf stars identified on the basis of their log(g) versus log(T eff) diagram. These dwarf stars are found to have generally longer periods than the remaining rotational variables.

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“…Asteroseismology of solar-like oscillators is a strong tool for further improving such studies (e.g. Miglio et al 2012Miglio et al , 2016Handberg et al 2017;Arentoft et al 2019;Sandquist et al 2020;Tailo et al 2022;Howell et al 2022), however, it requires long and uninterrupted high-precision observations. This currently limits detailed asteroseismic cluster studies to those observed by CoRoT (Baglin et al 2006), Kepler (Borucki et al 2010) or K2 (Howell et al 2014), with a few exceptions (e.g.…”

Section: Introductionmentioning

confidence: 99%

Asteroseismic age estimate of the open cluster NGC 6866 using Kepler and Gaia

Brogaard,

Arentoft,

Miglio

et al. 2023

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Context. Asteroseismic investigations of solar-like oscillations in giant stars allow for the derivation of their masses and radii. For members of open clusters, this allows us to obtain an age estimate of the cluster that is expected to be identical to the age estimate given by 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. Aims. We aim to identify and measure the asteroseismic properties of oscillating giant members of the open cluster NGC 6866 and utilise them for a cluster age estimate. Model comparisons also allow constraints to be placed on the stellar physics. Here, we investigate the efficiency of convective-core overshoot during the main sequence evolution, which has a significant influence on the age estimations for these relatively massive giants. The effects of rotation and core overshoot are similar, but not identical, and so, we also investigated the potential of our measurements to distinguish between these effects. Methods. We identified six giant members of NGC 6866 via photometry, proper motions, and parallaxes from Gaia, and spectroscopic literature measurements. These were combined with asteroseismic measurements, which we derived using photometric data from the Kepler mission for five of the stars. Comparisons to stellar-model isochrones constrained the convective-core overshoot and enable a more precise and accurate age estimate than previously possible. Results. A significant amount of differential reddening is found for NGC 6866. Asteroseismology establishes the helium-core burning evolutionary phase for the giants, which have a mean mass of 2.8 M⊙. 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 αov ≤ 0.1 ⋅ Hp 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 age of NGC 6866 is estimated to be 0.43 ± 0.05 Gyr, which is significantly younger and more precise than most previous estimates. Conclusions. We derive a precise cluster age while constraining convective-core overshooting and the effects of rotation in the stellar models. A comparison to age estimates from machine learning methods of the same and similar giant stars uncovers potential biases for automated asteroseismic and non-asteroseismic age estimates of helium-core burning stars.

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Variability in the Massive Open Cluster NGC 1817 from K2: A Rich Population of Asteroseismic Red Clump, Eclipsing Binary, and Main-sequence Pulsating Stars

Cited by 11 publications

References 84 publications

Chemical Compositions Of Red Giant Stars in the Old Open Cluster NGC 7789

Chemical Compositions Of Red Giant Stars in the Old Open Cluster NGC 7789

Investigating Stellar Variability in the Open Cluster Region NGC 381

Asteroseismic age estimate of the open cluster NGC 6866 using Kepler and Gaia

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