Refining the true parameters of the open cluster NGC 4852

AbstractNGC 4852 is a moderately compact cluster centered at α2000 = 13 : 00 : 09; δ = −59 : 36 : 48, located near the center of an Hα superring. This cluster forms part of an extended region including young stellar aggregates inside a circle with a radius of 3 degrees, where many show an abundance of emission line stars. In the field of this cluster, two stars of known type exist: Wray 15–1039 (emission-line object) and CD −58:4845 (emission-line star). We do not yet know whether the Be phase is transient or whether it is just what randomly happens in some hot stars. It appears that Be star may be found even in clusters as old as 70 Myr with a high occurrence rate in clusters of 25–27 Myr old. A recent photometric survey in NGC 4852 down to V = 22 – 23 mag established that NGC 4852 is about 200 – 250 Myr old, located at 1.1 kpc from the Sun and with a mean E(B − V) = 0.45 mag. Since the presence of potential Be-type stars in the cluster area suggests it may be a very young object instead of moderately old, we decided to carry out spectroscopy for 33 selected stars and CCD UBVI photometry for the bright objects in the cluster area. This way, we attempt to clarify their evolutionary state and include them in the framework of emission-line stars and open clusters. From our analysis, we agree with the cluster distance and reddening determined by earlier studies, but we derive that the age of NGC 4852 is younger than 40 Myr.

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Radial-velocity search and statistical studies for short-period planets in the Pleiades open cluster

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa105 ◽

2020 ◽

Vol 72 (6) ◽

Author(s):

Takuya Takarada ◽

Bun’ei Sato ◽

Masashi Omiya ◽

Yasunori Hori ◽

Michiko S Fujii

Keyword(s):

Radial Velocity ◽

Open Cluster ◽

Open Clusters ◽

Occurrence Rate ◽

High Dispersion ◽

Echelle Spectrograph ◽

Upper Limit ◽

Stringent Constraint ◽

Short Period ◽

Statistical Studies

Abstract We report on a radial-velocity search for short-period planets in the Pleiades open cluster. We observed 30 Pleiades member stars at the Okayama Astrophysical Observatory with the High Dispersion Echelle Spectrograph. To evaluate and mitigate the effects of stellar activity on radial-velocity (RV) measurements, we computed four activity indicators (full width at half maximum, Vspan, Wspan, and SHα). Among our sample, no short-period planet candidates were detected. Stellar intrinsic RV jitter was estimated to be 52 m s−1, 128 m s−1, and 173 m s−1 for stars with $v$ sin i of 10 km s−1, 15 km s−1, and 20 km s−1, respectively. We determined the planet occurrence rate from our survey and set the upper limit to 11.4% for planets with masses 1–13 MJUP and period 1–10 d. To set a more stringent constraint on the planet occurrence rate, we combined the result of our survey with those of other surveys targeting open clusters with ages in the range 30–300 Myr. As a result, the planet occurrence rate in young open clusters was found to be less than 7.4%, 2.9%, and 1.9% for planets with an orbital period of 3 d and masses of 1–5, 5–13, and 13–80 MJUP, respectively.

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Open cluster study in LAMOST DR3

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317006676 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 391-393

Author(s):

Jing Zhong ◽

Li Chen ◽

Chaoli Zhang ◽

Zhengyi Shao ◽

Jinliang Hou

Keyword(s):

Radial Velocity ◽

Proper Motion ◽

Open Cluster ◽

Open Clusters ◽

Projection Area ◽

Distance Modulus ◽

Membership Probability ◽

Cluster Area ◽

Large Projection ◽

Cross Match

AbstractIn studying Galactic open clusters based on LAMOST DR3, we deliberately selected several nearby cluster, which have relatively large projection area and reliable proper motion measurements. For each cluster, we firstly determine the typical proper motion distribution profiles in the cluster-core and the outskirt region, respectively, and perform field-star decontamination on the cluster area. We then calculate kinematic membership probability for each star in the cluster area and cross-match the highly probable members with LAMOST DR3 spectral catalog. Based on enhanced signal of cluster-member radial velocity distribution emerging from the whole field, we have also obtained reliable radial velocity membership probability for each star. Finally, we perform isochrones fitting with MCMC technique to study basic properties of these cluster, including age, metallicity, and distance modulus.

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Be Star Surveys in Open Clusters with Balmer-line Photometry

International Astronomical Union Colloquium ◽

10.1017/s0252921100055603 ◽

2000 ◽

Vol 175 ◽

pp. 63-66

Author(s):

Gemma Capilla ◽

Juan Fabregat ◽

Deborah Baines

Keyword(s):

Emission Line ◽

Main Sequence ◽

Open Clusters ◽

Balmer Line ◽

Be Stars ◽

Late Type ◽

Efficient Tool ◽

Be Star ◽

Almost All ◽

Evolutionary Interpretation

AbstractWe present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.

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Evolution and appearance of Be stars in SMC clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991724 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 470-473

Author(s):

C. Martayan ◽

D. Baade ◽

Y. Frémat ◽

J. Zorec

Keyword(s):

Main Sequence ◽

Milky Way ◽

Open Cluster ◽

Central Star ◽

Open Clusters ◽

Be Stars ◽

Ob Stars ◽

Be Star ◽

The Impact ◽

Key Parameter

AbstractStar clusters are privileged laboratories for studying the evolution of massive stars (OB stars). One particularly interesting question concerns the phases during which the classical Be stars occur, which—unlike HAe/Be stars—are not pre-main-sequence objects, nor supergiants. Rather, they are extremely rapidly rotating B-type stars with a circumstellar decretion disk formed by episodic ejections of matter from the central star. To study the impact of mass, metallicity, and age on the Be phase, we observed Small Magellanic Cloud (SMC) open clusters with two different techniques: (i) with the ESO–WFI in slitless mode, which allowed us to find the brighter Be and other emission-line stars in 84 SMC open clusters, and (ii) with the VLT–FLAMES multifiber spectrograph to determine accurately the evolutionary phases of Be stars in the Be-star-rich SMC open cluster NGC 330. Based on a comparison to the Milky Way, a model of Be stellar evolution, appearance as a function of metallicity and mass, and spectral type is developed, involving the fractional critical rotation rate as a key parameter.

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Formation rate of LB-1-like systems through dynamical interactions

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa021 ◽

2020 ◽

Vol 72 (3) ◽

Cited By ~ 3

Author(s):

Ataru Tanikawa ◽

Tomoya Kinugawa ◽

Jun Kumamoto ◽

Michiko S Fujii

Keyword(s):

Open Cluster ◽

Formation Rate ◽

Open Clusters ◽

Type Star ◽

Dynamical Mechanism ◽

Milky Way Galaxy ◽

Triple Systems ◽

Stellar Collisions ◽

Solar Metallicity ◽

Helium Star

Abstract We estimate formation rates of LB-1-like systems through dynamical interactions in the framework of the theory of stellar evolution before the discovery of the LB-1 system. The LB-1 system contains a ∼70 ${M_{\odot}}$ black hole (BH), a so-called pair instability (PI) gap BH, and a B-type star with solar metallicity, and has nearly zero eccentricity. The most efficient formation mechanism is as follows. In an open cluster, a naked helium star (with ∼20 ${M_{\odot}}$) collides with a heavy main sequence star (with ∼50 ${M_{\odot}}$) which has a B-type companion. The collision results in a binary consisting of the collision product and the B-type star with a high eccentricity. The binary can be circularized through the dynamical tide with radiative damping of the collision product envelope. Finally, the collision product collapses to a PI-gap BH, avoiding pulsational pair instability and pair instability supernovae because its He core is as massive as the pre-colliding naked He star. We find that the number of LB-1-like systems in the Milky Way galaxy is ∼0.01(ρoc/104 ${M_{\odot}}$ pc−3), where ρoc is the initial mass densities of open clusters. If we take into account LB-1-like systems with O-type companion stars, the number increases to ∼0.03(ρoc/104 ${M_{\odot}}$ pc−3). This mechanism can form LB-1-like systems at least ten times more efficiently than the other mechanisms: captures of B-type stars by PI-gap BHs, stellar collisions between other types of stars, and stellar mergers in hierarchical triple systems. We conclude that no dynamical mechanism can explain the presence of the LB-1 system.

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Defining the Binary Star Population in the Young Open Cluster M35 (NGC 2168)

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308015391 ◽

2007 ◽

Vol 3 (S246) ◽

pp. 105-106

Author(s):

Ella K. Braden ◽

Robert D. Mathieu ◽

Sören Meibom

Keyword(s):

Binary Systems ◽

Initial Conditions ◽

Binary Star ◽

Open Cluster ◽

Open Clusters ◽

Spatial Period ◽

Large Sample Size ◽

Long Baseline ◽

Dynamical Simulations ◽

Young Open Cluster

AbstractWe present current results from the ongoing WIYN Open Cluster Study radial-velocity survey for 1410 stars in the young (150 Myr) open cluster M35 (NGC 2168) and establish a benchmark for initial conditions in young open clusters. We find for periods ≲ 1000 days a minimum binary frequency of 0.36 – 0.51. We also analyze the spatial, period and eccentricity distributions of the binary systems and find that the period and eccentricity distributions are well approximated by scaled field distributions from Duquennoy & Mayor (1991). With our large sample size and long baseline, we have a unique understanding of the binary population in this young cluster, making it ideal for defining initial conditions for dynamical simulations.

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Reanalysis of nearby open clusters using Gaia DR1/TGAS and HSOY

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731905 ◽

2018 ◽

Vol 615 ◽

pp. A12 ◽

Cited By ~ 12

Author(s):

Steffi X. Yen ◽

Sabine Reffert ◽

Elena Schilbach ◽

Siegfried Röser ◽

Nina V. Kharchenko ◽

...

Keyword(s):

Milky Way ◽

Open Cluster ◽

Star Clusters ◽

Open Clusters ◽

Parameter Estimates ◽

Cluster Membership ◽

Fitting Procedure ◽

Cluster Data ◽

The Galaxy ◽

Automatic Tool

Context. Open clusters have long been used to gain insights into the structure, composition, and evolution of the Galaxy. With the large amount of stellar data available for many clusters in the Gaia era, new techniques must be developed for analyzing open clusters, as visual inspection of cluster color-magnitude diagrams is no longer feasible. An automatic tool will be required to analyze large samples of open clusters. Aims. We seek to develop an automatic isochrone-fitting procedure to consistently determine cluster membership and the fundamental cluster parameters. Methods. Our cluster characterization pipeline first determined cluster membership with precise astrometry, primarily from TGAS and HSOY. With initial cluster members established, isochrones were fitted, using a χ2 minimization, to the cluster photometry in order to determine cluster mean distances, ages, and reddening. Cluster membership was also refined based on the stellar photometry. We used multiband photometry, which includes ASCC-2.5 BV, 2MASS JHKs, and Gaia G band. Results. We present parameter estimates for all 24 clusters closer than 333 pc as determined by the Catalogue of Open Cluster Data and the Milky Way Star Clusters catalog. We find that our parameters are consistent to those in the Milky Way Star Clusters catalog. Conclusions. We demonstrate that it is feasible to develop an automated pipeline that determines cluster parameters and membership reliably. After additional modifications, our pipeline will be able to use Gaia DR2 as input, leading to better cluster memberships and more accurate cluster parameters for a much larger number of clusters.

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A Gaia DR2 view of the open cluster population in the Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833476 ◽

2018 ◽

Vol 618 ◽

pp. A93 ◽

Cited By ~ 180

Author(s):

T. Cantat-Gaudin ◽

C. Jordi ◽

A. Vallenari ◽

A. Bragaglia ◽

L. Balaguer-Núñez ◽

...

Keyword(s):

Stellar Evolution ◽

Milky Way ◽

Galactic Plane ◽

Galactic Disk ◽

Open Cluster ◽

Open Clusters ◽

Number Of Clusters ◽

History Of ◽

Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

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The Bologna Open Cluster Chemical Evolution project: a large, homogeneous sample of Galactic open clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031809 ◽

2008 ◽

Vol 4 (S258) ◽

pp. 153-160

Author(s):

Angela Bragaglia

Keyword(s):

Chemical Evolution ◽

Galactic Disk ◽

Open Cluster ◽

Open Clusters ◽

Photometric Data ◽

Homogeneous Sample ◽

Metallicity Distribution

AbstractThe Bologna Open Cluster Chemical Evolution (BOCCE) project is a photometric and spectroscopic survey of open clusters, to be used as tracers of the Galactic disk properties and evolution. The clusters parameters (age, distance, reddening, metallicity, and detailed abundances) are derived in a precise and homogeneous way. This will contribute to a solid, reliable description of the disk: the clusters parameters will be used, for instance, to determine the metallicity distribution in the Galactic disk and how it has evolved with time. We have concentrated on old open clusters and we have presently in our hands data for about 40 open clusters; we have fully analyzed the photometric data for about one half of them and the spectra for one quarter of them.

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