Constraining the initial conditions of NGC 2264 using ejected stars found in <i>Gaia</i> DR2

Schoettler, Christina; Parker, R. J.; Bruijne, J. H. J. de

doi:10.1093/mnras/stab3529

Cited by 17 publications

(18 citation statements)

References 169 publications

(175 reference statements)

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“…The idea is that both types of high-velocity stars have been ejected from their star-forming regions, and backtracking will allow us to determine their origins and characterise their parent star cluster (e.g. Olczak et al 2008;Farias et al 2020;Schoettler et al 2022). Schoettler et al (2022) search for runaway and walkaway stars within 100 pc of the 3-5 Myr old cluster NGC 2264 using Gaia DR2.…”

Section: Backtrackingmentioning

confidence: 99%

“…Olczak et al 2008;Farias et al 2020;Schoettler et al 2022). Schoettler et al (2022) search for runaway and walkaway stars within 100 pc of the 3-5 Myr old cluster NGC 2264 using Gaia DR2. They compare the number of the runaway and walkaway stars (17) to a range of Nbody simulations with different initial conditions and find consistency with initial conditions with a high initial stellar density (≈ 10 000 M pc −3 ) and a high initial amount of spatial substructure.…”

Section: Backtrackingmentioning

confidence: 99%

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Unbound stars hold the key to young star cluster history

Arunima¹,

Pfalzner²,

Govind³

2023

Preprint

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Aims. GAIA delivers the positions and velocities of stars at an unprecedented precision. Therefore, for star clusters, there exists much higher confidence in whether a specific star is a member of a particular cluster or not. However, membership determination is still especially challenging for young star clusters. At ages 2-10 Myr, the gas is expelled, ending the star formation process and leading to their expansion, while at the same time, many former members become unbound. As a first step, we aim to assess the accuracy of the methods commonly used to distinguish between bound and unbound cluster members; after identifying the most suitable technique for this task, we wish to understand which of the two populations is more suited to provide insights into the initial configuration and the dynamical history of a cluster starting from its currently observed properties. Methods. Here, we perform N-body simulations of the dynamics of such young star clusters. We investigate how cluster dynamics and observational limitations affect the recovered information about the cluster from a theoretical perspective. Results. We find that the much-used method of distance and velocity cutoffs for membership determination often leads to false negatives and positives alike. Often observational studies focus on the stars remaining bound. However, bound stars quickly lose the memory of the pre-gas expulsion phase due to their ongoing interaction with their fellow cluster members. Our study shows that it is the unbound stars that hold the key to charting a cluster's dynamic history. Backtracking unbound stars can provide the original cluster size and determine the time of gas expulsion -two parameters that are currently still poorly constrained. This information is lost in the bound population. In addition, former members are often better indicators for disc lifetimes or initial binary fractions. We apply the backtracking analysis, with varying success, to the clusters: Upper Scorpius and NGC 6530. For highly substructured clusters such as Upper Scorpius, backtracking to the individual subcluster centres will provide better results in future.

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Section: Backtrackingmentioning

confidence: 99%

Section: Backtrackingmentioning

confidence: 99%

Unbound stars hold the key to young star cluster history

Arunima¹,

Pfalzner²,

Govind³

2023

Preprint

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“…When calculating Moran's I all stars at distances greater than two half-mass radii from the centre of mass of the cluster are excluded. This is because in reality not all original members of a star forming region are likely to be observed; stars that have been ejected from a region and have traveled a large distance away are significantly less likely to be positively identified as members by observers (Schoettler et al 2020(Schoettler et al , 2022. Given the low likelihood that such outliers would be identified as members in observational data sets their exclusion from the calculation of Moran's I statistic is justified.…”

Section: Quantifying Kinematic Substructurementioning

confidence: 99%

Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation

Arnold¹,

Wright²,

Parker³

2022

Preprint

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We investigate whether spatial-kinematic substructure in young star-forming regions can be quantified using Moran's I statistic. Its presence in young star clusters would provide an indication that the system formed from initially substructured conditions, as expected by the hierarchical model of star cluster formation, even if the cluster were spatially smooth and centrally concentrated. Its absence, on the other hand, would be evidence that star clusters form monolithically. The Moran's I statistic is applied to N-body simulations of star clusters with different primordial spatial-velocity structures, and its evolution over time is studied. It is found that this statistic can be used to reliably quantify spatial-kinematic substructure, and can be used to provide evidence as to whether the spatial-kinematic structure of regions with ages 6 Myr is best reproduced by the hierarchical or monolithic models of star formation. Moran's I statistic is also able to conclusively say whether the data are not consistent with initial conditions that lack kinematic substructure, such as the monolithic model, in regions with ages up to, and potentially beyond, 10 Myrs. This can therefore provide a kinematic signature of the star cluster formation process that is observable for many Myr after any initial spatial structure has been erased.

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“…Gaia will also continue to enable the discovery of previously unknown star clusters [254]. The current Gaia optical mission has enabled us to assess the kinematics of exposed (gas-free) clusters and also quantified the numbers of runaway (> 30 km s −1 ) and walkaway (> 5 km s −1 ) stars on the outskirts of star-forming regions [255,256]. In the future, a near-IR version of Gaia would facilitate studies of the kinematics of star-forming regions at much earlier ages.…”

Section: Future Directions and Future Facilitiesmentioning

confidence: 99%

Dynamics of young stellar clusters as planet-forming environments

Reiter

Parker

2022

Eur. Phys. J. Plus

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Most stars and thus most planetary systems do not form in isolation. The larger star-forming environment affects protoplanetary disks in multiple ways: Gravitational interactions with other stars truncate disks and alter the architectures of exoplanet systems; external irradiation from nearby high-mass stars truncates disks and shortens their lifetimes; and the remaining gas and dust in the environment affect dynamical evolution (if removed by feedback processes) and provide some shielding for disks from external irradiation. The dynamical evolution of the region regulates when and how long various feedback mechanisms impact protoplanetary disks. Density is a key parameter that regulates the intensity and duration of UV irradiation and the frequency of dynamical encounters. The evolution of larger star-forming complexes may also play an important role by mixing populations. Observations suggest that clusters are not a single-age population but multiple populations with small age differences, which may be key to resolving several timescale issues (i.e., proplyd lifetimes, enrichment). In this review, we consider stellar clusters as the ecosystems in which most stars and therefore most planets form. We review recent observational and theoretical results and highlight upcoming contributions from facilities expected to begin observations in the next 5 years. Looking further ahead, we argue that the next frontier is large-scale surveys of low-mass stars in more distant high-mass star-forming regions. The future of ecosystem studies is bright as faint low-mass stars in more distant high-mass star-forming regions will be routinely observable in the era of extremely large telescopes.

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Constraining the initial conditions of NGC 2264 using ejected stars found in Gaia DR2

Cited by 17 publications

References 169 publications

Unbound stars hold the key to young star cluster history

Unbound stars hold the key to young star cluster history

Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation

Dynamics of young stellar clusters as planet-forming environments

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