The Effects of the Overshooting of the Convective Core on Main-sequence Turnoffs of Young- and Intermediate-age Star Clusters

Yang, Wuming; Tian, Zhijia

doi:10.3847/1538-4357/aa5b9d

Cited by 18 publications

(23 citation statements)

References 61 publications

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“…An overlooked role possibly related to the presence of eMSTO regions is convective overshooting. Yang & Tian (2017) calculated the impact of convective overshooting on the MSTO of clusters as young as 100 Myr. They found that adoption of varying overshooting parameters(δ ov ) for individual stars-with δ ov varying from 0.0 to 0.7-can potentially explain the observed eMSTOs in young and intermediate-age clusters.…”

Section: Resultsmentioning

confidence: 99%

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Extended Main-sequence Turnoffs in the Double Cluster h and χ Persei: The Complex Role of Stellar Rotation

Sun

Grijs

et al. 2019

ApJ

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Using Gaia Data Release 2 photometry, we report the detection of extended main-sequence turnoff (eMSTO) regions in the color-magnitude diagrams (CMDs) of the ∼ 14 Myr-old double clusters h and χ Persei (NGC 869 and NGC 884). We find that stars with masses below ∼1.3 M in both h and χ Persei populate narrow main sequences (MSs), while more massive stars define the eMSTO, closely mimicking observations of young Galactic and Magellanic Cloud clusters (with ages older than ∼30 Myr). Previous studies based on clusters older than ∼30 Myr find that rapidly rotating MS stars are redder than slow rotators of similar luminosity, suggesting that stellar rotation may be the main driver of the eMSTO. By combining photometry and projected rotational velocities from the literature of stars in h and χ Persei, we find no obvious relation between the rotational velocities and colors of non-emission-line eMSTO stars, in contrast with what is observed in older clusters. Similarly to what is observed in Magellanic Cloud clusters, most of the extremely rapidly rotating stars, identified by their strong Hα emission lines, are located in the red part of the eMSTOs. This indicates that stellar rotation plays a role in the color and magnitude distribution of MSTO stars. By comparing the observations with simulated CMDs, we find that a simple population composed of coeval stars that span a wide range of rotation rates is unable to reproduce the color spread of the clusters' MSs. We suggest that variable stars, binary interactions, and stellar rotation affect the eMSTO morphology of these very young clusters.

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Section: Resultsmentioning

confidence: 99%

“…Such a nitrogen abundance dispersion cannot be produced by any combination of rotating models with moderate overshooting, δ ov = 0.2, and non-rotating models. This may then be used to differentiate convective core overshooting models from rotation models (Yang & Tian 2017).…”

Section: Resultsmentioning

confidence: 99%

Extended Main-sequence Turnoffs in the Double Cluster h and χ Persei: The Complex Role of Stellar Rotation

Sun

Grijs

et al. 2019

ApJ

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“…As such, we investigate if the asteroseismically calibrated mixing mechanisms discussed above, and particularly their consequence in terms of increased core mass, play a role in the formation of the eMSTO of young open clusters. Yang & Tian (2017) already considered the case of allowing for different levels of convective penetration as the mechanism for CBM for non-rotating stellar models of a coeval population and showed that this can explain the eMSTO to some extent. We generalise this approach to investigate to what level the mixing profiles calibrated by asteroseismology of stars with a convective core can explain the eMSTOs of young clusters.…”

Section: Introductionmentioning

confidence: 99%

“…These areas naturally form an extended TAMS region. Unlike Yang & Tian (2017), who only considered penetrative convection with un-calibrated large values of the penetration distance up to 0.7 times the local pressure scale height, we consider the general case of both CBM and REM and limit the overall amount of CBM and REM to measured levels calibrated by asteroseismology of intermediate-and high-mass field stars as achieved by the MfA studies. We fit isochrone-clouds to CMDs of two prototypical clusters with observed eMSTOs to illustrate the capacity and limitations of isochrone clouds in explaining this observed phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Isochrone-cloud fitting of the extended main-sequence turn-off of young clusters

Johnston

Aerts

Pedersen

et al. 2019

A&A

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Context. Extended main-sequence turn-offs (eMSTO) are a commonly observed property of young clusters. A global theoretical interpretation for the eMSTOs is still lacking, but stellar rotation is considered a necessary ingredient to explain the eMSTO. Aims. We aim to assess the importance of core-boundary and envelope mixing in stellar interiors for the interpretation of eMSTOs in terms of one coeval population. Methods. We construct isochrone-clouds based on interior mixing profiles of stars with a convective core calibrated from asteroseismology of isolated galactic field stars. We fit these isochrone-clouds to the measured eMSTO to estimate the age and core mass of the stars in the two young clusters NGC1850 and NGC884, assuming one coeval population and fixing the metallicity to the one measured from spectroscopy. We assess the correlations between the interior mixing properties of the cluster members and their rotational and pulsational properties. Results. We find that stellar models based on asteroseismically-calibrated interior mixing profiles lead to enhanced core masses of eMSTO stars and can explain a good fraction of the observed eMSTOs of the two considered clusters in terms of one coeval population of stars, with similar ages to those in the literature, given the large uncertainties. The rotational and pulsational properties of the stars in NGC 884 are not sufficiently well known to perform asteroseismic modelling, as it is achieved for field stars from space photometry. The stars in NGC 884 for which we have v sin i and a few pulsation frequencies show no correlation between these properties and the core masses of the stars that set the cluster age. Conclusions. Future cluster space asteroseismology may allow to interpret the values of the core masses in terms of the physical processes that cause them, based on the modelling of the interior mixing profiles for the individual member stars with suitable identified modes.

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“…Multiple scenarios have been proposed to explain the observational results, including an extended star formation history (Goudfrooij et al 2011), variable stars (Salinas et al 2016), stellar rotation, and convective overshooting (Yang & Tian 2017). Thus far, the stellar rotation interpretation is most favored by a range of observations, including the 2 W. Sun et al…”

Section: Introductionmentioning

confidence: 99%

Stellar rotation bifurcation caused by tidal locking in the open cluster NGC 2287?

Sun

Deng

et al. 2019

Proc. IAU

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We present a detailed analysis of the projected stellar rotational velocities of the well-separated double main sequence (MS) in the young, ∼ 200 Myr-old Milky Way open cluster NGC 2287 and suggest that stellar rotation may drive the split MSs in NGC 2287. We find that the observed distribution of projected stellar rotation velocities could result from a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster's member stars in stellar binary systems. The slow rotators are likely stars that initially rotated rapidly but subsequently slowed down through tidal locking induced by low-mass-ratio binary systems. However, the cluster may have a much larger population of short-period binaries than is usually seen in the literature, with relatively low secondary masses.

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The Effects of the Overshooting of the Convective Core on Main-sequence Turnoffs of Young- and Intermediate-age Star Clusters

Cited by 18 publications

References 61 publications

Extended Main-sequence Turnoffs in the Double Cluster h and χ Persei: The Complex Role of Stellar Rotation

Extended Main-sequence Turnoffs in the Double Cluster h and χ Persei: The Complex Role of Stellar Rotation

Isochrone-cloud fitting of the extended main-sequence turn-off of young clusters

Stellar rotation bifurcation caused by tidal locking in the open cluster NGC 2287?

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