Probable Member Stars Research Articles

The Emerging Stellar Complex in Mon R2: Membership and Optical Variability Classification

Monoceros R2 (Mon R2) is one of the closest large active star-forming regions. This extremely young and partially embedded region provides an excellent laboratory for studying star formation and the early evolution of young stellar objects (YSOs). In this paper, we conduct an optical study of the greater Mon R2 region. Beginning with 1690 previously identified candidate YSOs, we used 496 sources with good proper motions and parallaxes from Gaia Data Release (DR) 3 to determine the astrometric properties for likely members of Mon R2. We then used both astrometric and photometric (isochronal and variability) criteria to determine that 308 of these stars are highly probable members. Using the same criteria, we considered a broad area search around Mon R2 in Gaia DR3 and separated candidate members from field stars. In total, we selected 651 likely new cluster members that had been missed in the previous X-ray and infrared excess selection techniques used in the past to establish cluster membership. Revised astrometric properties of the cluster were found using the combined sample of ∼959 highly probable member stars. For the literature plus the new candidate member list, optical light curves were compiled from the Zwicky Transient Facility. For 470 identified variable sources, we attempted classification based on the flux asymmetry (M) and quasiperiodicity (Q) metrics. We find that Mon R2 is dominated by quasiperiodic symmetric variables, with aperiodic sources also a significant population. A few tens of large-amplitude variables are identified that may be of interest for further study.

Astrophysical Parameters of the Open Cluster Berkeley 6

In this study, the structural and basic astrophysical parameters of poorly studied open cluster Berkeley 6 is calculated. Analyses of the cluster are carried out using the third photometric, spectroscopic and astrometric data release of Gaia (Gaia DR3). The membership probabilities of stars located through the cluster region are calculated by considering their astrometric data. Thus, we identified 119 physical members for Berkeley 6. The colour excess, distance and age of the cluster are determined simultaneously on the colour-magnitude diagram. We fitted solar metallicity PARSEC isochrones to the colour-magnitude diagram by considering the most probable member stars and obtained E(GBP-GRP) colour excess as 0.918±0.145 mag. Distance and age of the cluster are determined as d=2625±337 pc and t=350±50 Myr, respectively.

CCD UBV and Gaia DR3 based analysis of NGC 189, NGC 1758 and NGC 7762 open clusters

This paper presents photometric, astrometric, and kinematic analyses of the open clusters NGC 189, NGC 1758 and NGC 7762 based on CCD UBV photometric and Gaia Data Release 3 (DR3) data. According to membership analyses, we identified 32, 57 and 106 most probable member stars with membership probabilities P⩾0.5 in NGC 189, NGC 1758 and NGC 7762, respectively. The color excesses and photometric metallicities of each cluster were determined separately using UBV two-color diagrams. The color excess E(B-V) is 0.590±0.023 mag for NGC 189, 0.310±0.022 mag for NGC 1758 and 0.640±0.017 mag for NGC 7762. The photometric metallicity [Fe/H] is -0.08±0.03 dex for both NGC 189 and NGC 1758, and -0.12±0.02 dex for NGC 7762. Distance moduli and ages of the clusters were obtained by comparing PARSEC isochrones with the color-magnitude diagrams constructed from UBV and Gaia photometric data. During this process, we kept as constant color excess and metallicity for each cluster. The estimated isochrone distance is 1201±53 pc for NGC 189, 902±33 pc for NGC 1758 and 911±31 pc for NGC 7762. These are compatible with the values obtained from trigonometric parallax. Ages of the clusters are 500±50 Myr, 650±50 Myr and 2000±200 Myr for NGC 189, NGC 1758 and NGC 7762, respectively. Galactic orbit integration of the clusters showed that NGC 1758 completely orbits outside the solar circle, while NGC 189 and NGC 7762 enter the solar circle during their orbits.

The Gaia-ESO Survey: Target selection of open cluster stars

Context. The Gaia-ESO Survey (GES) is a public, high-resolution spectroscopic survey, conducted with the multi-object spectrograph Fibre Large Array Multi Element Spectrograph (FLAMES) on the Very Large Telescope (European Southern Observatory, ESO, Cerro Paranal, Chile) from December 2011 to January 2018. Gaia-ESO has targeted all the main stellar components of the Milky Way, including thin and thick disc, bulge, and halo. In particular, a large sample of open clusters has been observed, from very young ones, just out of the embedded phase, to very old ones. Aims. The different kinds of clusters and stars targeted in them are useful to reach the main science goals of the open cluster part of GES, which are the study of the open cluster structure and dynamics, the use of open clusters to constrain and improve stellar evolution models, and the definition of Galactic disc properties (e.g., metallicity distribution). Methods. The Gaia-ESO Survey is organised in 19 working groups (WGs), each one being responsible for a task. We describe here the work of three of them, one in charge of the selection of the targets within each cluster or association (WG4), one responsible for defining the most probable candidate member stars (WG1), and another one in charge of the preparation of the observations (WG6). As the entire GES has been conducted before the second Gaia data release, we could not make use of the Gaia astrometry to define cluster member candidates. We made use of public and private photometry to select the stars to be observed with FLAMES, once brought on a common astrometric system (the one defined by 2MASS). Candidate target selection was based on ground-based proper motions, radial velocities, and X-ray properties when appropriate, for example, and it was mostly used to define the position of the clusters’ evolutionary sequences in the colour-magnitude diagrams. Targets for GIRAFFE were then selected near the sequences in an unbiased way. We used known information on membership, when available, only for the few stars to be observed with UVES. Results. We collected spectra for 62 confirmed clusters in the main observing campaign (and a few more clusters were taken from the ESO archive). Among them are very young clusters, where the main targets are pre-main sequence stars, clusters with very hot and massive stars currently on the main sequence, intermediate-age and old clusters where evolved stars are the main targets. Our strategy of making the selection of targets as inclusive and unbiased as possible and of observing a significant and representative fraction of all possible targets permitted us to collect the largest, most accurate, and most homogeneous spectroscopic data set on open star clusters ever achieved.

Herbig–Haro flows around the BBWo 192E (GM 1–23) nebula

ABSTRACT Looking for evidence of recent star formation, we have studied a small comet-shaped reflection nebula, known as BBWo 192E (GM 1–23), which is located in the dark cloud SL 4 in the Vela Molecular Ridge cloud C, and a young infrared cluster embedded into the nebula. We obtained the images of BBWo 192E in Hα and [S ii] lines and in a Sloan Digital Sky Survey i ′ filter with the Blanco telescope at the Cerro Tololo Inter-American Observatory in order to discover new Herbig–Haro (HH) flows. We used the Two-Micron All-Sky Survey and the Wide-field Infrared Survey Explorer to search for additional member stars of the cluster. We also studied the proper motions and parallaxes of the cluster members using GAIA Data Release 2. Five new groups containing at least nine HH objects, tracing several distinct outflows, were revealed. A previously unreported reflection nebula and a number of probable outflow sources were found in the infrared range. The proper motions allowed us to select eight probable member stars in the visual range. Their parallaxes correspond to a mean distance 800 ± 100 pc for this cluster. The bolometric luminosities of the brightest cluster members are 1010 L⊙ (IRAS 08513−4201, the strong source in the centre of the cluster) and 2–6 L⊙ for the five other stars. The existence of optical HH flows around the infrared cluster of young stellar objects suggests that star formation in this cloud is ongoing around the more massive Herbig Ae/Be star. Considering its morphology and other features, this star-forming region is similar to the zone of star formation near CPM 19.

Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey

Abstract We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238–4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630–0058), is identified as a resolved overdensity of stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

Member Stars of the GD-1 Tidal Stream from the SDSS, LAMOST, and Gaia Surveys

Abstract With the photometric data from the SDSS survey, the spectroscopic data from the SDSS/SEGUE and the LAMOST surveys, and the astrometric data from the Gaia DR2, we have identified 67 highly probable member stars of the GD-1 cold stellar stream spread along almost its entire length (i.e., from 126° to 203° in R.A.). With the accurate spectroscopic (i.e., metallicity and line-of-sight velocity) and astrometric (i.e., proper motions) information, the position–velocity diagrams, i.e., ϕ 1–μ α , ϕ 1–μ δ , and ϕ 1–v gsr, of the GD-1 stream are well mapped. The stream has an average metallicity [Fe/H] = −1.96. The rich information of member stars of the stream now available allow one not only to model its origin, but also to place strong constraints on the mass distribution and the gravitational potential of the Milky Way.

Photometric study of the open cluster NGC 381

We present UBVRcIc photometry of stars, down to the 20th magnitude, in the region of the intermediate-age open cluster NGC 381. The core and the cluster radii are estimated to be 2.99 ± 0.93 and 5.6 ± 0.1 arcmin, respectively. A total of 350 probable cluster member stars are identified by using proper motion from GAIA as the criterion of membership. The mean proper motion of the cluster is ūx = 1.55 ± 0.38 mas yr-1, ūy = -2.19 ± 0.39 mas yr-1. We notice an anomalous reddening as the optical total-to-selective extinction ratio in the direction of the cluster Rcluster = 3.7 ± 0.1. The reddening E(BV) = 0.35 ± 0.04 mag is found in the direction of the cluster NGC 381. The distance to the cluster is 957 ± 93 pc and the cluster has an estimated age of log(Age)=8.50 ± 0.05 years.

Candidate star clusters toward the inner Milky Way discovered on deep-stackedKS-band images from the VVV Survey

The census of star clusters in the inner Milky Way is incomplete because of extinction and crowding. We embarked on a program to expand the star cluster list in the direction of the inner Milky Way using deep stacks of Ks-band images from the VISTA Variables in Via Lactea (VVV) Survey. We applied an automated two-step procedure to the point-source catalog derived from the deep Ks images: first, we identified overdensities of stars, and then we selected only candidate clusters with probable member stars that match an isochrone with a certain age, distance, and extinction on the color-magnitude diagram. This pilot project only investigates the cluster population in part of one VVV tile, that is, b201. We identified nine cluster candidates and estimated their parameters. The new candidates are compact with a typical radius on the sky of ~0.2--0.4 arcmin (~0.4-1.6 pc at their estimated distances). They are located at distances of ~5-14 kpc from the Sun and are subject to moderate extinction of E(B-V)=0.4-1.0 mag. They are sparse, probably evolved, with typical ages log(t/1 yr)~9. Based on the locations of the objects inside the Milky Way, we conclude that one of these objects is probably associated with the disk or halo and the remaining objects are associated with the bulge or the halo. The cluster candidates reported here push the VVV Survey cluster detection to the limit. These new objects demonstrate that the VVV survey has the potential to identify thousands of additional cluster candidates. The sub-arcsec angular resolution nd the near-infrared wavelength regimen give it a critical advantage over other surveys.

Proper motions of stars in the globular clusters using WFI@2.2 m telescope

AbstractWe present results of our studies for a sample of Galactic globular star clusters with the aim of deriving relative proper motions. We used CCD archival data observed with Wide Field Imager (WFI) mounted on ESO 2.2 m telescope at La Silla, Chile. Astrometric software designed by Anderson et al. is used to derive relative proper motions. The vector point diagrams show clear separation of field stars from the cluster stars. We used proper motions to determine membership probabilities and to produce color-magnitude diagrams with most probable cluster member stars. Our membership catalogue can be used to study the membership status of the peculiar stars including various variables reported in the literature.

SPENDING TOO MUCH TIME AT THE GALACTIC BAR: CHAOTIC FANNING OF THE OPHIUCHUS STREAM

ABSTRACT The Ophiuchus stellar stream is peculiar: (1) its length is short given the age of its constituent stars, and (2) several probable member stars have dispersions in sky position and velocity that far exceed those seen within the stream. The stream’s proximity to the Galactic center suggests that its dynamical history is significantly influenced by the Galactic bar. We explore this hypothesis with models of stream formation along orbits consistent with Ophiuchus’ properties in a Milky Way potential model that includes a rotating bar. In all choices for the rotation parameters of the bar, orbits fit to the stream are strongly chaotic. Mock streams generated along these orbits qualitatively match the observed properties of the stream: because of chaos, stars stripped early generally form low-density, high-dispersion “fans” leaving only the most recently disrupted material detectable as a strong over-density. Our models predict that there should be a significant amount of low-surface-brightness tidal debris around the stream with a complex phase-space morphology. The existence of or lack of these features could provide interesting constraints on the Milky Way bar and would rule out formation scenarios for the stream. This is the first time that chaos has been used to explain the properties of a stellar stream and is the first demonstration of the dynamical importance of chaos in the Galactic halo. The existence of long, thin streams around the Milky Way, presumably formed along non- or weakly chaotic orbits, may represent only a subset of the total population of disrupted satellites.

Open cluster membership probability based on K-means clustering algorithm

In the field of galaxies images, the relative coordinate positions of each star with respect to all the other stars are adapted. Therefore the membership of star cluster will be adapted by two basic criterions, one for geometric membership and other for physical (photometric) membership. So in this paper, we presented a new method for the determination of open cluster membership based on K-means clustering algorithm. This algorithm allows us to efficiently discriminate the cluster membership from the field stars. To validate the method we applied it on NGC 188 and NGC 2266, membership stars in these clusters have been obtained. The color-magnitude diagram of the membership stars is significantly clearer and shows a well-defined main sequence and a red giant branch in NGC 188, which allows us to better constrain the cluster members and estimate their physical parameters. The membership probabilities have been calculated and compared to those obtained by the other methods. The results show that the K-means clustering algorithm can effectively select probable member stars in space without any assumption about the spatial distribution of stars in cluster or field. The similarity of our results is in a good agreement with results derived by previous works.

Membership determination of open cluster NGC 188 based on the DBSCAN clustering algorithm

High-precision proper motions and radial velocities of 1046 stars are used to determine member stars using three-dimensional (3D) kinematics for open cluster NGC 188 based on the density-based spatial clustering of applications with noise (DBSCAN) clustering algorithm. By implementing this algorithm, 472 member stars in the cluster are obtained with 3D kinematics. The color-magnitude diagram (CMD) of the 472 member stars using 3D kinematics shows a well-defined main sequence and a red giant branch, which indicate that the DBSCAN clustering algorithm is very effective for membership determination. The DBSCAN clustering algorithm can effectively select probable member stars in 3D kinematic space without any assumption about the distribution of the cluster or field stars. Analysis results show that the CMD of member stars is significantly clearer than the one based on 2D kinematics, which allows us to better constrain the cluster members and estimate their physical parameters. Using the 472 member stars, the average absolute proper motion and radial velocity are determined to be (PMα, PMδ) = (−2.58 ± 0.22, +0.17 ± 0.18) mas yr−1 and Vr = −42.35 ± 0.05 km s−1, respectively. Our values are in good agreement with values derived by other authors.

B-TYPE VARIABLES IN THE YOUNG OPEN CLUSTER NGC 457

We have performed long-term, two-color time-series CCD photometry of the young open cluster NGC 457 to search for B-type variables. The light variations of about 400 stars located in a 165 × 165 field of the cluster were examined. It resulted in the detection of 13 periodic variables, including 8 B-type variables. With the two-color photometric data, we have constructed a color-magnitude diagram for the cluster. A brief isochrone fitting yields a reddening of E(B – V) = 0.46 ± 0.05 and a distance modulus of (m – M) V = 13.30 ± 0.10 with an age of log(Age) = 7.30. With the above results, we identified three probable member stars in addition to six certain ones from the new variable sample. Through a preliminary photometric analysis with the obtained B- and V-band light curves, we have determined the amplitude and period of light variations for each of the variables. Based on this, the physical properties and classification of the detected variables are discussed. As a conclusion, we have identified one β Cep, five candidate SPB stars, and three δ Scuti-type pulsating stars plus three EA-type eclipsing binaries and one EW-type one in NGC 457.

A KINEMATIC AND PHOTOMETRIC STUDY OF THE GALACTIC YOUNG STAR CLUSTER NGC 7380

We present proper motions, radial velocities, and a photometric study of the Galactic open cluster NGC?7380, which is associated with prominent emission nebulosity and dark molecular clouds. On the basis of the sample of highly probable member stars, the star cluster is found to be at a distance of 2.6 ? 0.4?kpc, has an age of around 4?Myr, and a physical size of ~6?pc across with a tidal structure. The binary O-type star DH?Cep is a member of the cluster in its late stage of clearing the surrounding material, and may have triggered the ongoing star formation in neighboring molecular clouds which harbor young stars that are coeval and comoving with, but not gravitationally bound by, the star cluster.

Probable member stars of the gravitational theory-testing globular clusters AM 1, Pal 3 and Pal 14

Some of the Galactic outer halo globular clusters are excellent tools to probe gravitational theories in the regime of weak accelerations. The measurement of the line-of-sight velocity dispersion among stars in these clusters will differentiate between the validity of Newtonian dynamics (low velocity dispersion) and the possiblity of modified Newtonian dynamics (MOND) or dark matter dominated globular clusters (high velocity dispersion). In this paper, the properties of probable member stars of the three best-case gravitational theory-testing clusters AM 1, Pal 3 and Pal 14 are presented. The member selection is based on VLT photometry in Johnson $\it BV$. The positions of the stars were determined with an accuracy of the order of ≤ $0\farcs2$, allowing their direct use for follow-up spectroscopy. The distance, reddening, age and metallicities of the clusters were estimated from isochrone fitting. Furthermore, improved structural parameters, like central coordinates, ellipticity, half-light radius, King model core and tidal radius, are presented.

New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach

We have calculated proper motions and re-evaluated the membership probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC 1807. We have obtained absolute proper motions from 25 plates in the reference system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of 81 years; and they were taken with the double astrograph at Zô-Sè station of Shanghai Observatory, which has an aperture of 40 cm and a plate scale of 30´´ mm-1. The average proper motion precision is 1.55 mas yr-1. These proper motions are used to determine the membership probabilities of stars in the region, based on there being only one very extended physical cluster: NGC 1817. With that aim, we have applied and compared parametric and non-parametric approaches to cluster/field segregation. We have obtained a list of 169 probable member stars.

Photometric and Spectroscopic Study of Stars in the Field of the Young Open Cluster Roslund 4

We present photometric and spectroscopic observations performed in the field of the Galactic open cluster Roslund 4, which contains the two cataloged nebulae IC 4954 and IC 4955. UBVRI photometry was carried out in a field of 11' × 6' around the cluster center. Medium-resolution optical spectroscopy has been obtained for 41 stars, including previously selected main-sequence and pre–main-sequence candidate cluster members. Narrowband Hα, [S II], and continuum images have been secured. The observations allow us the measurement of different physical parameters for the cluster. Assuming an absorption coefficient AV/E(B - V) = 3.1 and a reddening slope E(U - B)/E(B - V) = 0.72, we obtain a color excess E(B - V) = 1.1 ± 0.2 and a distance modulus DM0 = 11.7 ± 0.5. Fitting of isochrones to the color-magnitude diagrams gives log age(yr) = 7.2 ± 0.2, and the spectroscopic measurements provide the value VR = -15.7 ± 5.2 km s-1 for the heliocentric radial velocity. Among the 41 stars with spectroscopic data, 11 stars are probable cluster members on the basis of their radial velocity, and another 10 are considered as possible members. Two probable member stars of spectral types A5 and G1 show hints of absorption in the Li I 6708 A line, with respective equivalent widths of 0.10 and 0.28 A, and 22 stars of spectral types from B2 to G0 show different degrees of emission in Hα, [N II], and [S II] lines. With the exception of three stars of spectral type earlier than A0, the emission of which is mainly photospheric, all other emissions seen in Hα and forbidden lines have a nebular origin. They arise in an ionized cloud that surrounds the cluster and is causing diffuse emission and, possibly, local variations in the extinction law from star to star. In addition to the stars, spectra of several nebular condensations with relatively higher excitation have been analyzed. Two of them have been suggested to be Herbig-Haro (HH) objects. Our spectra indicate that only one of these condensations could be considered as an HH object.

A multiwavelength study of star formation in the very young open cluster NGC 6530

The distance and formation history of the very young open cluster NGC 6530 were investigated by study- ing a total of 132 probable member stars of this open cluster. It was concluded that the distance to NGC 6530 is 1:8 0:2 kpc, and its interstellar reddening E(B V ) is 0: m 30. Furthermore, we conclude that the extinction law of the intracluster material is normal (i.e. RV =3 :1), but anomalous extinction laws were found for several more embedded stars in the cluster. Of the 132 stars included in this study, 11 are suspected to be variable, ve show H in emission and nine show an infrared excess. Among the member stars of NGC 6530, three were found to be part of the Herbig Ae/Be stellar class, whereas two others are possible members of this stellar group as well. Also, one cluster member is probably a new massive post-AGB star, whereas the same could possibly apply to another member star. Finally, from the distribution of post- and pre-main sequence stars in the cluster's HR-diagram, it was concluded that the process of star formation in NGC 6530 must have started a few times 10 7 years ago and, for the less massive stars, is probably still going on today.

A New Photometric Investigation of the Young Open Cluster NGC 663

The investigation of the open cluster NGC 663, based on the application of the method of UBV three colour photometry and the use of new photographic material, lead to a new distance to the cluster of 2550pc, E(B-V) & E(U-B) colour excesses of 0.74 & 0.53 mag and consequently a total visual absorption AV of 2.22 mag. An age of 3.9 × 107 y and a spectral type B2-B3 can be estimated for it; accordingly, it fits well the Perseus Arm (+1) near the outer edge and lies below the galactic plane at a distance of 47 pc.From the distribution of 476 stars investigated, around both the ZAMS and the apparent centre of the cluster, 270 probable physical member stars could be separated from the field stars and neither late type giants nor a giant branch are in existence.