Open Clusters Research Articles

Stellar clustering and the kinematics of stars around Collinder 121 using Gaia DR3

ABSTRACT We study the region around Collinder 121 (Cr 121) using newly available 6D data from the Gaia DR3 catalogue. Situated in the third quadrant, near the Galactic plane, Collinder 121 lies in the region of Canis Major centred around (l, b) ≈(236°, −10°). Previous studies have suggested that the stellar associations in this region comprise an OB association (CMa OB2) lying at about 740 pc with a more distant open cluster (Cr 121) at approximately 1170 pc. Despite these studies, the precise nature of Collinder 121 remains uncertain. This study investigates the region bounded by the box (l, b) = (225°–245°, 0.00° to −20.00°) to a depth of 700 pc from 500 to 1200 pc which fully encompasses the region discussed in the literature. Using Gaia DR3 data, we do not find associations at the distances given in the literature. Instead, using the hdbscan machine learning algorithm, we find a major association of OB stars centred around 803 pc. Within this association we find four smaller subgroups that may be indicative of a larger association and which are located at a mean distance of 827 pc. Proper motion studies find coherence between these four subgroups and show a distinctive east-to-west increase in the size of the velocity vectors which supports contemporary studies that show similar trends in OB populations in Cygnus and within the Carina spiral Arm. Therefore, we hypothesize that Cr 121 and CMa OB2 are the same cluster, consistent with the 1977 study by Hoogerwerf.

Exploring the origin of the extended main-sequence turn-off in M37 through the white dwarf cooling sequence

ABSTRACT We use new observations from the Canada–France–Hawaii Telescope to study the white dwarf cooling sequence of the open cluster M37, a cluster that displays an extended main-sequence turn-off and, according to a recent photometric analysis, also a spread of initial chemical composition. By taking advantage of a first epoch collected in 1999 with the same telescope, we have been able to calculate proper motions for sources as faint as g ∼ 26 (about ∼ 6 mag fainter than the Gaia limit), allowing us to separate cluster members from field stars. This has enabled us to isolate a sample of the white dwarf population of M37, reaching the end of the cooling sequence (at g ∼ 23.5). Here, the derived atlas and calibrated catalogue of the sources in the field of view is publicly released as supplementary online material. Finally, we present an exhaustive comparison of the white dwarf luminosity function with theoretical models, which has allowed us to exclude the age-spread scenario as the main responsible for the extended turn-off seen in the cluster colour–magnitude diagram.

Unveiling the Initial Conditions of Open Star Cluster Formation

Open clusters (OCs) are infrequent survivors of embedded clusters gestated in molecular clouds. Up to now, little is known about the initial conditions for the formation of OCs. Here, we studied this issue using high-precision astrometric parameters provided by Gaia data release 3. The statistics show that the peculiar motion velocities of OCs vary slightly from infancy to old age, providing a remarkable opportunity to use OCs to trace their progenitors. Adopting a dynamical method, we derived the masses of the progenitor clumps where OCs were born, which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy. Moreover, the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars. In fact, after inspecting the observed OCs and O-type stars, we found that there are many O-type stars in OCs. The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters, and only those sufficiently dense ones can survive as OCs.

The broadening of the main sequence in the open cluster M38

Abstract Our recent multi-band photometric study of the colour width of the lower main sequence of the open cluster M37 has revealed the presence of a sizeable initial chemical composition spread in the cluster. If initial chemical composition spreads are common amongst open clusters, this would have major implications for cluster formation models and the foundation of the chemical tagging technique. Here we present a study of the unevolved main sequence of the open cluster M38, employing Gaia DR3 photometry and astrometry, together with newly acquired Sloan photometry. We have analysed the distribution of the cluster’s lower main sequence stars with a differential colour-colour diagram made of combinations of Gaia and Sloan magnitudes, like in the study of M37. We employed synthetic stellar populations to reproduce the observed trend of M38 stars in this diagram, and found that the observed colour spreads can be explained simply by the combined effect of differential reddening across the face of the cluster and the presence of unresolved binaries. There is no need to include in the synthetic sample a spread of initial chemical composition as instead necessary to explain the main sequence of M37. Further photometric investigations like ours, as well as accurate differential spectroscopic analyses on large samples of open clusters, are necessary to understand whether chemical abundance spreads are common among the open cluster population.

567-P: Impact of Diabetes Prevention Education Program on Diabetes Knowledge among Adults with Prediabetes—A Cluster Randomized Controlled Trial in Nepal

Background: Diabetes knowledge is important for diabetes prevention but has been less studied among people with prediabetes. This study aimed to assess the impact of a community-based lifestyle intervention program called Diabetes Prevention Education Program (DiPEP) on diabetes knowledge among adults with prediabetes in Nepal. Method: This study is a part of a two-arm open cluster randomized controlled trial conducted from October 2019-September 2021 in two urban areas of Nepal. Participants of the intervention arm received four 1-hour weekly education sessions, follow-up for the next 5 months, diabetes prevention education brochure, exercise calendar and daily food logbook. The control arm received an education brochure at baseline and 1-hour education session after endline data collection. The change in diabetes knowledge was assessed using Nepali validated 24-items Diabetes Knowledge Questionnaire (DKQ), with higher score representing better disease knowledge. Linear mixed model was used to analyze the impact of the DiPEP on diabetes knowledge score with intent-to-treat approach. Results: A total of 291 participants were recruited in the trial with mean age of 50.3±7.6 years and 67% were female. Only 290 participants had baseline DKQ (158 intervention, 132 control), out of these 258 completed the endline DKQ (139 intervention, 119 control). At baseline, mean DKQ score was 9.2 (SD 5.2) in intervention and 10.6 (SD 4.8) in control arm. After the intervention, mean change in the score between intervention and control group was 0.4 (95% CI -1.0-1.7) among those with good compliance to DiPEP. The results did not change from main analysis for those who attended ≥3 of all 4 sessions. Conclusion: Diabetes knowledge did not improve significantly after the intervention among the participants. Regular and frequent engagement of participants might help to improve diabetes knowledge among the individuals. Disclosure P.Shakya: None. A.Shrestha: None. B.M.Karmacharya: None. A.Shrestha: None. M.Bajracharya: None. B.E.Kulseng: None. E.Skovlund: None. A.Sen: None. Funding Norwegian University of Science and Technology, Department of Public Health and Nursing (81850087)

Photometric and kinematic studies of open cluster NGC 1027

Photometric and kinematic studies of open cluster NGC 1027

Search for the least massive objects in the Hyades open cluster with the help of a wide stellar view

Search for the least massive objects in the Hyades open cluster with the help of a wide stellar view

Oort cloud (exo)planets

ABSTRACT Dynamical instabilities among giant planets are thought to be nearly ubiquitous and culminate in the ejection of one or more planets into interstellar space. Here, we perform N-body simulations of dynamical instabilities while accounting for torques from the galactic tidal field. We find that a fraction of planets that would otherwise have been ejected are instead trapped on very wide orbits analogous to those of Oort cloud comets. The fraction of ejected planets that are trapped ranges from 1 to 10 per cent, depending on the initial planetary mass distribution. The local galactic density has a modest effect on the trapping efficiency and the orbital radii of trapped planets. The majority of Oort cloud planets survive for Gyr time-scales. Taking into account the demographics of exoplanets, we estimate that one in every 200–3000 stars could host an Oort cloud planet. This value is likely an overestimate, as we do not account for instabilities that take place at early enough times to be affected by their host stars’ birth cluster or planet stripping from passing stars. If the Solar system’s dynamical instability happened after birth cluster dissolution, there is a ∼7 per cent chance that an ice giant was captured in the Sun’s Oort cloud.

Stellar Rotation and Structure of the α Persei Complex: When Does Gyrochronology Start to Work?

On the pre-main sequence, the rotation rates of Sun-like stars are dictated by the interplay between the protostellar disk and the star’s contraction. At ages exceeding 100 Myr, magnetic spindown erases the initial stellar spin rate and enables rotation-based age dating (gyrochronology). The exact time at which the transition between these two regimes occurs depends on stellar mass, and has been challenging to empirically resolve due to a lack of viable calibration clusters. The α Persei open cluster (t ≈ 80 Myr, d ≈ 170 pc) may provide the needed calibrator, but recent analyses of the Gaia data have provided wildly varying views of its age and spatial extent. As such, we analyze a combination of TESS, Gaia, and LAMOST data to calibrate gyrochronology at the age of α Per and to uncover the cluster’s true morphology. By assembling a list of rotationally confirmed α Per members, we provide strong evidence that α Per is part of a larger complex of similarly aged stars. Through kinematic back-integration, we show that the most diffuse components of α Per were five times closer together 50 Myr ago. Finally, we use our stellar rotation periods to derive a relative gyrochronology age for α Per of 67% ± 12% the age of the Pleiades, which yields 86 ± 16 Myr given current knowledge. We show that by this age, stars more massive than ≈0.8 M ⊙ have converged to form a well-defined slow sequence.

A Photometric Hα Survey of the Open Cluster King 16

Photometric Hα observations of the young open cluster King 16 have been used to search for emission-line stars. Seven cluster members with enhanced Hα emission are identified, of which five are new discoveries. Three of these newly found objects have a near-infrared excess, which suggests they may be Herbig AeBe stars. Hα emission is also present in three field stars, of which two are new detections.

A rotational age for the open cluster NGC 2281

Context.Cool star rotation periods have become an important tool in determining ages of open clusters.Aims.We aim to estimate the age of the open cluster NGC 2281 based on the rotational properties of its low-mass members. Previous age estimates for this open cluster range from 275 Myr to 630 Myr.Methods.Based on an eight month-long photometric time series obtained at the 1.2 m robotic STELLA telescope in Tenerife, we measured rotation periods for 126 cool star members (70% of the observed members) of NGC 2281.Results.The large set of rotation periods allows us to construct a rich colour-period diagram for NGC 2281 with very few outliers above the slow rotator sequence. We identify an evolved fast rotator sequence which can be used to accurately age date the open cluster relative to other open clusters. Comparisons with M 37 and M 48 show that all three open clusters are roughly coeval, and we estimate the age of NGC 2281 to be 435 ± 50 Myr. Through comparisons with the younger NGC 3532 and the older Praesepe, we determine the spin down rates of mid-K and early-M fast rotators to be significantly lower than for early-K stars. We suspect that the spin down of early-K fast rotators might be governed by an additional mass dependence.Conclusions.Finally, we show the path towards an empirical description of the evolved fast rotator sequences in open clusters.

Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy

Context. Lithium-rich giant stars are rare and their existence poses a challenge to our understanding of stellar structure and evolution. In particular, open clusters aptly constrain the mass and age of their members, offering a unique opportunity to understand the evolutionary stage where Li enrichment occurs. Aims. We take advantage of the high-quality sample gathered for the search for planets in open clusters with HARPS and UVES to look for Li-rich giants and to identify the Li enrichment mechanisms responsible. Methods. We derived stellar parameters for 247 stars belonging to 32 open clusters, with 0.07 Ga < ages < 3.6 Ga. We employed the spectral synthesis technique code FASMA for the abundance analysis of 228 stars from our sample. We also determined the ages, distances, and extinction using astrometry and photometry from Gaia and PARSEC isochrones to constrain their evolutionary stage. Our sample covers a wide range of stellar masses from 1 to more than 6 M⊙ where the majority of the masses are above 2 M⊙. Results. We find 14 canonical Li-rich giant stars that have experienced the first dredge-up. This corresponds to 6% of our total sample, higher than what is typically found for field stars. The majority of the stars (11/14) are located at the red clump, two lie on the red giant branch, and we could not conclude on its evolutionary stage for one. Apart from the canonical limit, we used the maximum Li abundance of the progenitor stars as a criterion for Li enrichment and found 12 Li enriched stars (five appearing in the red clump, five at the upper red giant branch, and two that are inconclusive). We find Li enhancement also among eight stars that have passed the first dredge-up and show strong Li lines based on the fact that stars at the same evolutionary stage in the same cluster have significantly different Li abundances. We confirm that giants with higher Li abundances correspond to a higher fraction of fast-rotating giants, suggesting a connection between Li enhancement and stellar rotation, as predicted by stellar models. Conclusions. Our Li-rich giants are found in various evolutionary stages, implying that no unique Li production mechanism is responsible for Li enrichment. Instead, there are different intrinsic or external mechanisms that are simultaneously at play.

GaiaData Release 3

Context.GaiaData Release 3 (GaiaDR3) contains the second release of the combined radial velocities. It is based on the spectra collected during the first 34 months of the nominal mission. The longer time baseline and the improvements of the pipeline made it possible to push the processing limit fromGRVS = 12 inGaiaDR2 toGRVS = 14 mag.Aims.We describe the new functionalities implemented forGaiaDR3, the quality filters applied during processing and post-processing, and the properties and performance of the published velocities.Methods.ForGaiaDR3, several functionalities were upgraded or added to the spectroscopic pipeline. The calibrations were improved in order to better model the temporal evolution of the straylight and of the instrumental point spread function (PSF). The overlapped spectra, which were mostly discarded inGaiaDR2, are now handled by a dedicated module. The hot star template mismatch, which prevented publication of hot stars inGaiaDR2, is largely mitigated now, down toGRVS = 12 mag. The combined radial velocity of stars brighter than or equal toGRVS = 12 mag is calculated in the same way as inGaiaDR2, that is, as the median of the epoch radial velocity time series. The combined radial velocity of the fainter stars is measured from the average of the cross-correlation functions.Results.GaiaDR3 contains the combined radial velocities of 33 812 183 stars. With respect toGaiaDR2, the temperature interval has been expanded fromTeff ∈ [3600, 6750] K toTeff ∈ [3100, 14 500] K for the bright stars (GRVS ≤ 12 mag) and [3100, 6750] K for the fainter stars. The radial velocities sample a significant part of the Milky Way: they reach a few kiloparsecs beyond the Galactic centre in the disc and up to about 10−15 kpc vertically into the inner halo. The median formal precision of the velocities is 1.3 km s−1atGRVS = 12 and 6.4 km s−1atGRVS = 14 mag. The velocity zeropoint exhibits a small systematic trend with magnitude that starts aroundGRVS = 11 mag and reaches about 400 m s−1atGRVS = 14 mag. A correction formula is provided that can be applied to the published data. TheGaiaDR3 velocity scale agrees satisfactorily with APOGEE, GALAH, GES, and RAVE; the systematic differences mostly remain below a few hundred m s−1. The properties of the radial velocities are also illustrated with specific objects: open clusters, globular clusters, and the Large Magellanic Cloud. For example, the precision of the data allows mapping the line-of-sight rotational velocities of the globular cluster 47 Tuc and of the Large Magellanic Cloud.

Magnetic Braking with MESA Evolutionary Models in the Single Star and Low-mass X-Ray Binary Regimes

Magnetic braking has a prominent role in driving the evolution of close low-mass binary systems and heavily influences the rotation rates of low-mass F- and later-type stars with convective envelopes. Several possible prescriptions that describe magnetic braking in the context of 1D stellar evolution models currently exist. We test four magnetic braking prescriptions against both low-mass X-ray binary orbital periods from the Milky Way and single-star rotation periods observed in open clusters. We find that the data favor a magnetic braking prescription that follows a rapid transition from fast to slow rotation rates, exhibits saturated (inefficient) magnetic braking below a critical Rossby number, and that is sufficiently strong to reproduce ultra-compact X-ray binary systems. Of the four prescriptions tested, these conditions are satisfied by a braking prescription that incorporates the effect of high-order magnetic field topology on angular momentum loss. None of the braking prescriptions tested are able to replicate the stalled spin down observed in open cluster stars aged 700–1000 Myr or so, with masses ≲0.8 M ⊙.

Blind Search of the Solar Neighborhood Galactic Disk within 5 kpc: 1179 New Star Clusters Found in Gaia DR3

Studying open clusters (OCs) may help to provide a comprehensive understanding of the structure and evolution of the Milky Way. Many previous studies have systematically searched for OCs near the solar system within 1.2 kpc or 20° of Galactic latitude. However, few studies have searched for OCs at higher Galactic latitudes and deeper distances. In this study, based on a hybrid unsupervised clustering algorithm (friends-of-friends and pyUPMASK) and a binary classification algorithm (random forest), we extended the search region (i.e., Galactic latitude and performed a fine-grained blind search for Galactic clusters in Gaia DR3. After crossmatching, the newly discovered cluster candidates are fitted using isochrone fitting to estimate the main physical parameters (i.e., age and metallicity) of these clusters. These cluster candidates were then checked using manual visual inspection. Their statistical properties were also compared with previously exposed cluster catalogs. We found 1179 new clusters with considerable confidence within 5 kpc.

Determination of the Spiral Pattern Speed in the Milky Way from Young Open Star Clusters

Determination of the Spiral Pattern Speed in the Milky Way from Young Open Star Clusters

A New Revision of the Stellar Content and Physical Properties of the Young Open Cluster vdB 130 in the Region of the Stellar Association Cyg OB1 Based on Gaia DR3 Data

A New Revision of the Stellar Content and Physical Properties of the Young Open Cluster vdB 130 in the Region of the Stellar Association Cyg OB1 Based on Gaia DR3 Data

Asteroseismic age constraints on the open cluster NGC 2477 using oscillating stars identified with TESS FFI

Context. Asteroseismology is one of the few methods to derive ages of individual stars due to the high precision of their observations. Isochrone fitting is a powerful alternative method for deriving ages by studying clusters of stars. Pulsating stars in clusters should therefore allow for detailed studies of the stellar models. Aims. Our objectives are to exploit the NASA TESS data along with ESA Gaia data to search for and detect oscillations in cluster member stars. We analyse the intermediate-age open cluster NGC 2477, known to suffer from differential extinction, to explore if asteroseismology and cluster characteristics can help us understand the metallicity and extinction, as well as result in better age determinations than isochrone-fitting alone. Methods. We combined a multitude of recent observations from Gaia, high-resolution spectroscopy, and extinction maps to analyse the cluster and then search for and detect variability in the member stars using TESS full frame images (FFIs) data. To interpret all of these data, we used stellar structure, evolution and oscillation codes. Results. We conducted an in-depth analysis of the extinction and metallicity of NGC 2477, using the most recent spectroscopic, photometric, and extinction observations for the cluster. Analysis of dust and extinction maps confirmed that the differential extinction in the direction of the cluster is not due to the background. The cluster’s metallicity from high-resolution spectroscopy varies from 0.06 to 0.16 dex. We performed an isochrone fitting to the cluster using publically available isochrones (BASTI, MIST, and PARSEC), which provides a cluster age of between 0.6 to 1.1 Ga. Then using TESS FFI, we analysed the time dimension of the members of this cluster. We created optimised pixel light curves using the tessipack package which allows us to consider possible contamination by nearby stars. Using these light curves, we identified many interesting levels of variability of stars in this cluster, including binaries and oscillating stars. For the asteroseismic analysis, we selected a few uncontaminated A–F type oscillating stars and used the MESA and GYRE codes to interpret the frequency signals. By comparing the theoretical and the observed spectra, we identified frequency separations, Δν, for four stars. Then using the identified Δν and imposing that the best matched theoretical models have the same age, metallicity, and background extinction, we constrained the cluster’s age to 1.0 ± 0.1 Ga. Conclusions. We conclude that using the TESS FFI data, we can identify oscillating stars in clusters and constrain the age of the cluster using asteroseismology.

Gaia Data Release 3

Context. With the most recent Gaia data release, the number of sources with complete 6D phase space information (position and velocity) has increased to well over 33 million stars, while stellar astrophysical parameters are provided for more than 470 million sources, and more than 11 million variable stars are identified. Aims. Using the astrophysical parameters and variability classifications provided in Gaia DR3, we selected various stellar populations to explore and identify non-axisymmetric features in the disc of the Milky Way in configuration and velocity space. Methods. Using more about 580 000 sources identified as hot OB stars, together with 988 known open clusters younger than 100 Myr, we mapped the spiral structure associated with star formation 4−5 kpc from the Sun. We selected over 2800 Classical Cepheids younger than 200 Myr that show spiral features extending as far as 10 kpc from the Sun in the outer disc. We also identified more than 8.7 million sources on the red giant branch (RGB), of which 5.7 million have line-of-sight velocities. This later sample allows the velocity field of the Milky Way to be mapped as far as 8 kpc from the Sun, including the inner disc. Results. The spiral structure revealed by the young populations is consistent with recent results using Gaia EDR3 astrometry and source lists based on near-infrared photometry, showing the Local (Orion) Arm to be at least 8 kpc long, and an outer arm consistent with what is seen in HI surveys, which seems to be a continuation of the Perseus arm into the third quadrant. The subset of RGB stars with velocities clearly reveals the large-scale kinematic signature of the bar in the inner disc, as well as evidence of streaming motions in the outer disc that might be associated with spiral arms or bar resonances. A local comparison of the velocity field of the OB stars reveals similarities and differences with the RGB sample. Conclusions. This cursory study of Gaia DR3 data shows there is a rich bounty of kinematic information to be explored more deeply, which will undoubtedly lead us to a clearer understanding of the dynamical nature of the non-axisymmetric structures of the Milky Way.

Kinematics of the Galactic Disk Based on Open Cluster Data

Kinematics of the Galactic Disk Based on Open Cluster Data