- ID:
- ivo://CDS.VizieR/J/MNRAS/495/2882
- Title:
- Open cluster radii from Gaia proper motions
- Short Name:
- J/MNRAS/495/2882
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we improve a previously published method to calculate in a reliable way the radius of an open cluster (OC). The method is based on the behaviour of stars in the proper motion space as the sampling changes in the position space. Here, we describe the new version of the method and show its performance and robustness. Additionally, we apply it to a large number of OCs using data from Gaia second data release to generate a catalogue of 401 clusters with reliable radius estimations. The range of obtained apparent radii goes from Rc=1.4+/-0.1arcmin (for the cluster FSR 1651) to Rc=25.5+/-3.5arcmin (for NGC 2437). Cluster linear sizes follow very closely a lognormal distribution with a mean characteristic radius of Rc=3.7pc, and its high radius tail can be fitted by a power law as N{prop.to}Rc^-3.11+/-0.35^. Additionally, we find that number of members, cluster radius, and age follow the relationship Nc{prop.to}Rc^1.2+/-0.1^.Tc^-1.9+/-0.4^ where the younger and more extensive the cluster, the more members it presents. The proposed method is not sensitive to low density or irregular spatial distributions of stars and, therefore, is a good alternative or complementary procedure to calculate OC radii not having previous information on star memberships.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/655/A23
- Title:
- Open cluster red clump stars Lithium abundances
- Short Name:
- J/A+A/655/A23
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- It has recently been suggested that all giant stars with masses below 2M_{sun}_ suffer an episode of surface lithium enrichment between the tip of the red giant branch (RGB) and the red clump (RC). We test if the above result can be confirmed in a sample of RC and RGB stars that are members of open clusters. We discuss Li abundances in six open clusters with ages between 1.5 and 4.9Gyr (turn-off masses between 1.1 and 1.7M_{sun}_). We compare these observations with the predictions of different models that include rotation-induced mixing, thermohaline instability, mixing induced by the first He flash, and energy losses by neutrino magnetic moment. In six clusters, we find close to 35% of RC stars have Li abundances that are similar or higher than those of upper RGB stars. This can be a sign of fresh Li production. Because of the extra-mixing episode connected to the luminosity bump, the expectation has been for RC stars to have systematically lower surface Li abundances. However, we cannot confirm that this possible Li production is ubiquitous. For about 65% of RC giants, we can only determine upper limits in abundances that could be hiding very low Li content. Our results indicate the possibility that Li is being produced in the RC, at levels that would not typically permit the classification of these the stars as Li rich. The determination of their carbon isotopic ratio would help to confirm that the RC giants have suffered extra mixing followed by subsequent Li enrichment. The Li abundances of the RC stars can be qualitatively explained by the models by using an additional mixing episode close to the He flash.
- ID:
- ivo://CDS.VizieR/J/A+AS/146/251
- Title:
- Open clusters absolute proper motions. I.
- Short Name:
- J/A+AS/146/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mean proper motions and parallaxes of 205 open clusters were determined from their member stars found in the Hipparcos (<I/239>) Catalogue. 360 clusters were searched for possible members, excluding nearby clusters with distances D<200pc. Members were selected using ground based information (photometry, radial velocity, proper motion, distance from the cluster centre) and information provided by Hipparcos (proper motion, parallax). Altogether 630 certain and 100 possible members were found. A comparison of the Hipparcos parallaxes with photometric distances of open clusters shows good agreement. The Hipparcos data confirm or reject the membership of several Cepheids in the studied clusters.
- ID:
- ivo://CDS.VizieR/J/AJ/136/118
- Title:
- Open clusters as galactic disk tracers. I.
- Short Name:
- J/AJ/136/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have begun a survey of the chemical and dynamical properties of the Milky Way disk as traced by open star clusters. In this first contribution, the general goals of our survey are outlined and the strengths and limitations of using star clusters as a Galactic disk tracer sample are discussed. We also present medium-resolution (R~150000) spectroscopy of open cluster stars obtained with the Hydra multi-object spectrographs on the Cerro Tololo Inter-American Observatory 4m and WIYN 3.5m telescopes. Here we use these data to determine the radial velocities of 3436 stars in the fields of open clusters within about 3kpc, with specific attention to stars having proper motions in the Tycho-2 catalog. Additional radial velocity members (without Tycho-2 proper motions) that can be used for future studies of these clusters were also identified.
- ID:
- ivo://CDS.VizieR/J/A+AS/108/151
- Title:
- Open clusters CCD photometry. I.
- Short Name:
- J/A+AS/108/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+A/616/A10
- Title:
- 46 open clusters GaiaDR2 HR diagrams
- Short Name:
- J/A+A/616/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A80
- Title:
- Open clusters in APOGEE and GALAH surveys
- Short Name:
- J/A+A/623/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are ideal laboratories to investigate a variety of astrophysical topics, from the properties of the Galactic disk to stellar evolutionary models. Knowing their metallicity and possibly detailed chemical abundances is therefore important. However, the number of systems with chemical abundances determined from high resolution spectroscopy is still small. To increase the number of open clusters with radial velocities and chemical abundances determined from high resolution spectroscopy we used publicly available catalogues of surveys in combination with Gaia data. Open cluster stars have been identified in the APOGEE and GALAH spectroscopic surveys by cross-matching their latest data releases with stars for which high-probability astrometric membership has been derived in many clusters on the basis of the Gaia second data release. Radial velocities have been determined for 131 and 14 clusters from APOGEE and GALAH data, respectively. This is the first radial velocity determination from high resolution spectra for 16 systems. Iron abundances have been obtained for 90 and 14 systems from APOGEE and GALAH samples, respectively. To our knowledge 66 of these clusters (57 in APOGEE and 9 in GALAH) do not have previous determinations in the literature. For 90 and 7 clusters in the APOGEE and GALAH samples, respectively, we have also determined average abundances for Na, Mg, Al, Si, Ca, Cr, Mn, and Ni.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/880
- Title:
- Open clusters in Auriga OB2
- Short Name:
- J/MNRAS/459/880
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the area around the HII region Sh 2-234, including the young open cluster Stock 8, to investigate the extent and definition of the association Aur OB2 and the possible role of triggering in massive cluster formation. We obtained Stromgren and J, H, Ks photometry for Stock 8 and Stromgren photometry for two other cluster candidates in the area, which we confirm as young open clusters and name Alicante 11 and Alicante 12. We took spectroscopy of ~33 early-type stars in the area, including the brightest cluster members. We calculate a common distance of 2.80+0.27-0.24kpc for the three open clusters and surrounding association. We derive an age 4-6Ma for Stock 8, and do not find a significantly different age for the other clusters or the association. The star LS V +34 23, with spectral type O8 II(f), is likely the main source of ionization of Sh 2-234. We observe an important population of pre-main-sequence stars, some of them with discs, associated with the B-type members lying on the main sequence. We interpret the region as an area of recent star formation with some residual and very localized ongoing star formation. We do not find evidence for sequential star formation on a large scale. The classical definition of Aur OB2 has to be reconsidered, because its two main open clusters, Stock 8 and NGC 1893, are not at the same distance. Stock 8 is probably located in the Perseus arm, but other nearby HII regions whose distances also place them in this arm show quite different distances and radial velocities and, therefore, are not connected.
- ID:
- ivo://CDS.VizieR/J/ApJ/912/162
- Title:
- Open clusters in solar neighborhood
- Short Name:
- J/ApJ/912/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located within 500pc of the Sun, using Gaia} EDR3 and kinematic data from literature. Members of OCs are identified using the unsupervised machine learning method StarGO, using 5D parameters (X, Y, Z, {mu}_{alpha}cos{delta}, {mu}_{delta}). The OC sample covers an age range of 25Myr-2.65Gyr. We correct the asymmetric distance distribution due to the parallax error using Bayesian inversion. The uncertainty in the corrected distance for a cluster at 500pc is 3.0-6.3pc, depending on the intrinsic spatial distribution of its members. We determine the 3D morphology of the OCs in our sample and fit the spatial distribution of stars within the tidal radius in each cluster with an ellipsoid model. The shapes of the OCs are well-described with oblate spheroids (NGC 2547, NGC 2516, NGC 2451A, NGC 2451B, NGC 2232), prolate spheroids (IC 2602, IC 4665, NGC 2422, Blanco 1, Coma Berenices), or triaxial ellipsoids (IC 2391, NGC 6633, NGC 6774). The semi-major axis of the fitted ellipsoid is parallel to the Galactic plane for most clusters. Elongated filament-like substructures are detected in three young clusters (NGC 2232, NGC 2547, NGC 2451B), while tidal-tail-like substructures (tidal tails) are found in older clusters (NGC 2516, NGC 6633, NGC 6774, Blanco 1, Coma Berenices). Most clusters may be super-virial and expanding. N-body models of rapid gas expulsion with an SFE of ~1/3 are consistent with clusters more massive than 250M_{sun}_, while clusters less massive than 250M_{sun}_ tend to agree with adiabatic gas expulsion models. Only six OCs (NGC 2422, NGC 6633, and NGC 6774, NGC 2232, Blanco 1, Coma Berenices) show clear signs of mass segregation.
- ID:
- ivo://CDS.VizieR/J/A+A/511/A38
- Title:
- Open clusters in third galactic quadrant
- Short Name:
- J/A+A/511/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine accurate distances and ages of eight open clusters in order to: (1) assess their possible binarity (2) provide probes to trace the structure of the Third Galactic Quadrant. Cluster reddenings, distances, ages and metallicities are derived from ZAMS and isochrone fits in UBVRI photometric diagrams. Field contamination is reduced by restricting analysis to stars within the cluster limits derived from star counts. Further membership control is done by requiring that stars have consistent positions in several diagrams and by using published spectral types.
