Intermediate-age Open Cluster Research Articles

Berkeley 76: An intermediate age open star cluster in Gaia Era

We studied the open star cluster Berkeley 76 using Gaia DR3 and 2MASS data sets. We obtained 314 most probable cluster members with a membership probability greater than 80%. We have found the cluster center as α = 106.67 ± 0.07 deg and δ=−11.75±0.07 deg. The mean PMs of cluster members in right ascension and declination are −0.60±0.22 and 1.35 ± 0.19 mas yr−1, respectively. The radial density profile estimates the cluster’s radius to be 4.5 arcmin. The cluster’s heliocentric distance is estimated as 4.27±0.91 kpc, and its age is determined as 1.60±0.35 Gyr. Using the most probable cluster members, we determined the mass function slope for Berkeley 76 as 1.57 ± 0.19. This value is close to Salpeter’s slope within the uncertainty. Berkeley 76 is a dynamically relaxed cluster with a relaxation time of 23.4 Myr.

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.

A Comprehensive Study of Five Intermediate-age Pismis (2, 3, 7, 12, 15) Clusters Using Photometric and Astrometric Data from Gaia EDR3

Open clusters are groups of stars that form simultaneously; hence, these are excellent probes to test theories of star formation, stellar evolution, and dynamics in the Milky Way disk. We carry out a detailed photometric and kinematic study of five poorly studied intermediate-age open clusters, Pismis 2 (Pi 2), Pismis 3 (Pi 3), Pismis 7 (Pi 7), Pismis 12 (Pi 12), and Pismis 15 (Pi 15), using the Gaia EDR3 database. By estimating the membership probabilities of stars, we recognized 635, 1488, 535, 368, and 494 most probable members for these clusters by using proper-motion and parallax data taken from Gaia EDR3. The radial density profiles of cluster members provide cluster radii of 4.′5–6.′5 for these clusters. Their ages range from 0.9 to 2.5 Gyr, and distances range, using parallax, from 2.15 to 5.10 kpc. The overall mass function slopes for main-sequence stars are found as 0.27 ± 0.16 (for 1.0–1.6 M ⊙ stars), 0.86 ± 0.27 (for 1.0–2.1 M ⊙ stars), 1.08 ± 0.32 (for 1.0–2.2 M ⊙ stars), 0.89 ± 0.38 (for 1.0–2.2 M ⊙ stars), and 1.07 ± 0.28 (for 1.0–2.1 M ⊙ stars) for clusters Pi 2, Pi 3, Pi 7, Pi 12, and Pi 15. Our obtained values of slopes are flatter in comparison with Salpeter’s value (x = 1.35) within uncertainty. The present study demonstrates that all these Pismis clusters are dynamically relaxed. We found that these objects follow a circular path around the Galactic center. We compute these clusters’ apex coordinates (A, D) and other kinematic parameters.

A Gaia based analysis of open cluster Berkeley 27

In this paper, we have used the Gaia’s Data Release-3 (DR3) data to study an intermediate-age open cluster Berkeley 27 (Be 27). A total of 131 most probable cluster members are picked within the cluster’s radius based on the membership probability (>80%). The cluster’s radius was estimated as 3.74 arcmin. The mean proper motion (PM) of Be 27 was determined to be (μαcosδ, μδ)= (−1.076±0.008, 0.152±0.007) mas yr−1. The blue straggler stars (BSS) of the cluster were found to be located in the central region. Theoretical isochrones of metallicity Zmetal = 0.008 were compared to the color-magnitude diagram (CMD) of Be 27. As a result, a heliocentric distance of 4.8 ± 0.2 kpc and log (age) = 9.36 ± 0.03 were determined for Be 27. The Galactic orbits are derived using the Galactic potential model which demonstrate that Be 27 follows a circular path around the Galactic center. The cluster does not seem to be affected much by the tidal forces from the Galactic thin disk.

UOCS –VIII. UV study of the open cluster NGC 2506 using ASTROSAT★

ABSTRACT We study an intermediate-age open cluster (OC) NGC 2506 using the ASTROSAT/UVIT data and other archival data. We identified 2175 cluster members using a machine learning-based algorithm, ML–MOC, on Gaia EDR3 data. Among the cluster members detected in UVIT filters, F148W, F154W, and F169M, we detect nine blue straggler stars (BSS), three yellow straggler stars (YSS), and three red clump (RC) stars. We construct multiwavelength spectral energy distributions (SEDs) of these objects to characterize them and to estimate their parameters. We discovered hot companions to three BSS, two YSS, and three RC candidates and estimated their properties. The hot companions with estimated temperatures, Teff ∼ 13250–31 000 K, are WDs of extremely low mass (ELM, ∼ 0.20 M⊙), low mass (LM, ∼ 0.20–0.40 M⊙), normal mass (∼ 0.40–0.60 M⊙), and high mass (∼ 0.8 M⊙). We suggest that systems with ELM and LM WDs as companions are formed via Case-A/Case-B mass transfer mechanism. A BSS is the likely progenitor of the high-mass WD, as a star with more than the turn-off mass of the cluster is needed to form a high-mass WD. Thus, systems with a high-mass WD are likely to be formed through merger in triple systems. We conclude that mass transfer as well as merger pathways of BSS formation are present in this cluster.

FSR 1776: A new globular cluster in the Galactic bulge?

Context. Recent near-IR surveys have uncovered a plethora of new globular cluster (GC) candidates towards the Milky Way bulge. These new candidates need to be confirmed as real GCs and properly characterised. Aims. We investigate the physical nature of FSR 1776, a very interesting star cluster projected towards the Galactic bulge. This object was originally classified as an intermediate-age open cluster, and has recently been re-discovered independently and classified as a GC candidate (Minni 23). Firstly, our aim is to confirm its GC nature; secondly, we determine its physical parameters. Methods. The confirmation of the cluster existence is checked using the radial velocity (RV) distribution of a MUSE data cube centred at FSR 1776. The cluster parameters are derived from isochrone fitting to the RV-cleaned colour-magnitude diagrams (CMDs) from visible and near-IR photometry taken from VVV, 2MASS, DECAPS, and Gaia all together. Results. The predicted RV distribution for the FSR 1776 coordinates, considering only contributions from the bulge and disc field stars, is not enough to explain the observed MUSE RV distribution. The extra population (12% of the sample) is FSR 1776 with an average RV of −103.7 ± 0.4 km s−1. The CMDs reveal that it is 10 ± 1 Gyr metal-rich population with [Fe/H]phot ≈ +0.2 ± 0.2, [Fe/H]spec = +0.02 ± 0.01(σ = 0.14 dex), located at the bulge distance of 7.24 ± 0.5 kpc with AV ≈ 1.1 mag. The mean cluster proper motions are (⟨μα⟩,⟨μδ⟩) = (−2.3 ± 1.1, −2.6 ± 0.8) mas yr−1. Conclusions. FSR 1776 is an old GC located in the Galactic bulge with a super-solar metallicity, among the highest for a Galactic GC. This is consistent with predictions for the age–metallicity relation of the bulge, being FSR 1776 the probable missing link between typical GCs and the metal-rich bulge field. High-resolution spectroscopy of a larger field of view and deeper CMDs are now required for a full characterisation.

A Deep Study of an Intermediate-age Open Cluster SAI 35 (Juchert 20) Using Ground-based Imaging and Gaia EDR3 Astrometry

Abstract We present a CCD UBVI photometric study of poorly studied intermediate-age open cluster SAI 35 (Juchert 20) for the first time. To accomplish this study, we also used LAMOST DR5, Two Micron All Sky Survey, and Gaia EDR3 databases. We identified 214 most probable cluster members with membership probability higher than 50%. The mean proper motion of the cluster is found as and μ δ = −1.66 ± 0.01 mas yr−1. We find the normal interstellar extinction law using the various two-color diagrams. The age, distance, reddening, and radial velocity of the cluster are estimated to be 360 ± 40 Myr, 2.9 ± 0.15 kpc, 0.72 ± 0.05 mag, and −91.62 ± 6.39 km s−1, respectively. The overall mass function slope for main-sequence stars is found to be 1.49 ± 0.16 within the mass range 1.1–3.1 M ⊙, which is in agreement with Salpeter’s value within uncertainty. The present study demonstrates that SAI 35 is dynamically relaxed. Galactic orbital parameters are determined using Galactic potential models. We found that this object follows a circular path around the Galactic center.

Shaping the initial-final mass relation of white dwarfs with AGB outflows

AbstractA recent analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way (MW) identified a kink in the initial-final mass relation (IFMR), located over a range of initial masses, 1.65 ≲ Mi/M⊙ ≲ 2.10, which unexpectedly interrupts the commonly assumed monotonic trend. The proposed interpretation links this observational fact to the formation of carbon stars and the modest outflows (with mass loss rate < 10−7M⊙/yr) that are expected as long as the carbon excess remains too low to produce dust grains in sufficient amount. Under these conditions the mass of the carbon-oxygen core can grow more than is generally predicted by stellar models. We discuss these new findings also in light of a new systematic follow-up investigation, based on Gaia EDR3, of evolved giants (13 carbon stars, 3 S stars and 4 M stars) belonging to intermediate-age open clusters.

Variable stars in the field of intermediate-age open cluster NGC 559

ABSTRACT This work presents the first long-term photometric variability survey of the intermediate-age open cluster NGC 559. Time series V-band photometric observations on 40 nights taken over more than 3 yr with three different telescopes are analysed to search for variable stars in the cluster. We investigate the data for the periodicity analysis and reveal 70 variable stars including 67 periodic variables in the target field, all of them are newly discovered. The membership analysis of the periodic variables reveals that 30 of them belong to the cluster and remaining 37 are identified as field variables. Out of the 67 periodic variables, 48 are short-period (P < 1 d) variables and 19 are long-period (P > 1 d) variables. The variable stars have periodicity between 3 h to 41 d and their brightness ranges from V  = 10.9 to 19.3 mag. The periodic variables belonging to the cluster are then classified into different variability types on the basis of observational properties such as shape of the light curves, periods, amplitudes, as well as their positions in the Hertzsprung–Russell (H–R) diagram. As a result, we identify 1 Algol type eclipsing binary, 1 possible blue straggler star, 3 slowly pulsating B type stars, 5 rotational variables, 11 non-pulsating variables, 2 FKCOM variables, and remaining 7 are characterized as miscellaneous variables. We also identify three eclipsing binary stars (EBs) belonging to the field star population. The phoebe package is used to analyse the light curve of all four EBs in order to determine the parameters of the binary systems such as masses, temperatures, and radii.

Long-term Periodicities in Kepler Photometry of Open Cluster NGC 6811

Abstract Long-term photometric variability can sometimes be related to the emergence of starspots in the photosphere following a quasi-periodic magnetic activity cycle. In order to investigate the existence and properties of magnetic cycles in a narrow range of fundamental parameters, we focused on solar-type stars in the intermediate-age open cluster NGC 6811 (1 Gyr). The cluster membership was analyzed both in terms of stellar kinematics and Gaia photometry. Rotation periods and photometric variability were analyzed for 138 stars from Kepler light curves and we discuss the existing trends and relationships. We also searched a sample of 11 solar-type stars for cycle-like periodicities and in each case classified the variability as either cyclic, multicyclic, flat, or acyclic. The results suggest a significant scatter, possibly due to sensitive nonlinearities in the dynamo process. This raises theoretical questions on whether these periodicities can be associated to activity cycles and what determines the stellar cycle presence or its period. Also, the lack of solar-twin flat activity stars in NGC 6811 combined with other recent results, suggests that the presence of magnetic grand minima in the Sun is a relatively recent phenomenon.

Blue straggler populations of seven open clusters with Gaia DR2

ABSTRACT Blue straggler stars (BSS) are well studied in globular clusters but their systematic study with secure membership determination is lacking in open clusters. We use Gaia DR2 data to determine accurate stellar membership for four intermediate-age open clusters, namely Melotte 66, NGC 2158, NGC 2506, and NGC 6819, and three old open clusters, namely, Berkeley 39, NGC 188, and NGC 6791, to subsequently study their BSS populations. The BSS radial distributions of five clusters, namely Melotte 66, NGC 188, NGC 2158, NGC 2506, and NGC 6791, show bimodal distributions, placing them with Family II globular clusters that are of intermediate dynamical ages. The location of minima, rmin, in the bimodal BSS radial distributions, varies from 1.5rc to 4.0rc, where rc is the core radius of the clusters. We find a positive correlation between rmin and Nrelax, the ratio of cluster age to the current central relaxation time of the cluster. We further report that this correlation is consistent in its slope, within the errors, with the slope of the globular cluster correlation between the same quantities, but with a slightly higher intercept. This is the first example in open clusters that shows BSS radial distributions as efficient probes of dynamical age. The BSS radial distributions of the remaining two clusters, Berkeley 39 and NGC 6819, are flat. The estimated Nrelax values of these two clusters, however, indicate that they are dynamically evolved. Berkeley 39 especially has its entire BSS population completely segregated to the inner regions of the cluster.

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

ABSTRACT We present UBVRcIc photometric study of three intermediate age open star clusters NGC 381, NGC 2360, and Berkeley 68 (Be 68). We examine the cluster membership of stars using recently released Gaia DR2 proper motions and obtain a total of 116, 332, and 264 member stars in these three clusters. The mean reddening of E(B − V) = 0.36 ± 0.04, 0.08 ± 0.03, and 0.52 ± 0.04 mag is found in the direction of these clusters where we observe an anomalous reddening towards NGC 381. We fitted the solar metallicity isochrones to determine age and distance of the clusters which are found to be log(Age) = 8.65 ± 0.05, 8.95 ± 0.05, and 9.25 ± 0.05 yr with the respective distance of 957 ± 152, 982 ± 132, and 2554 ± 387 pc for the clusters NGC 381, NGC 2360, and Be 68. A two-stage power law in the mass function (MF) slope is observed in the cluster NGC 381, however, we observe only a single MF slope in the clusters NGC 2360 and Be68. To study a possible spatial variation in the slope of MF, we estimate slopes separately in the inner and the outer regions of these clusters and notice a steeper slope in outer region. The dynamic study of these clusters reveals deficiency of low-mass stars in their inner regions suggesting the mass segregation process in all these clusters. The relaxation times of 48.5, 78.9, and 87.6 Myr are obtained for the clusters NGC 381, NGC 2360, and Be 68, respectively, which are well below to their respective ages. This suggests that all the clusters are dynamically relaxed.

High-resolution spectroscopy of red giants and ‘yellow stragglers’ in the southern open cluster NGC 2539

ABSTRACT We present a detailed high-resolution spectroscopic analysis of 12 red giant stars, in single and binaries or multiples systems, classified as members of the intermediate-age (631 Myr) open cluster NGC 2539. We used FEROS echelle spectra and the standard LTE analysis to derive the atmospheric parameters for the stars and the abundance ratios of light elements (Li, C, N), light odd-Z elements (Na, Al), α-elements (Mg, Si, Ca, Ti), Fe-group elements (Cr, Fe, Ni), and n-capture elements (Y, Zr, Ce, Nd, Eu). Our results show that the sample star of NGC 2539 has low projected rotational velocities and an almost solar metallicity, with a mean of [Fe/H] = −0.03 ± 0.07 dex. The abundance pattern displays for the analyzed stars are, in general, similar to those presented by solar neighborhood stars, including giant members of others open clusters. In particular, light elements and Na abundance pattern shows anomalies resulting from the appearance of enriched material on the stellar surface, produced by mechanisms like the first dredge-up and/or thermohaline and rotation-induced mixing. We also identified two of the spectroscopic binaries of our sample as ‘yellow stragglers’ and we determined the nature of their companions.

Variability in the Massive Open Cluster NGC 1817 from K2: A Rich Population of Asteroseismic Red Clump, Eclipsing Binary, and Main-sequence Pulsating Stars.

We present a survey of variable stars detected in K2 Campaign 13 within the massive intermediate-age (~1 Gyr) open cluster NGC 1817. We identify a complete sample of 44 red clump stars in the cluster, and have measured asteroseismic quantities (ν max and/or Δν) for 29 of them. Five stars showed suppressed dipole modes, and the occurrence rates indicate that mode suppression is unaffected by evolution through core helium burning. A subset of the giants in NGC 1817 (and in the similarly aged cluster NGC 6811) have ν max and Δν values at or near the maximum observed for core helium-burning stars, indicating they have core masses near the minimum for fully nondegenerate helium ignition. Further asteroseismic study of these stars can constrain the minimum helium core mass in red clump stars and the physics that determines this limit. Two giant stars show photometric variations on timescales similar to previously measured spectroscopic orbits. Thirteen systems in the field show eclipses, but only five are probable cluster members. We identify 32 δ Sct pulsators, 27 γ Dor candidates, and 7 hybrids that are probable cluster members, with most being new detections. We used the ensemble properties of the δ Sct stars to identify stars with possible radial pulsation modes. Among the oddities we have uncovered are: an eccentric orbit for a short-period binary containing a δ Sct pulsating star; a rare subgiant within the Hertzsprung gap showing δ Sct pulsations; and two hot γ Dor pulsating star candidates.

DS Andromedae: A Detached Eclipsing Double-lined Spectroscopic Binary in the Galactic Cluster NGC 752*

Abstract The Wilson–Devinney program has been used to analyze well-calibrated photometric and new radial velocity data to determine the properties and distance of DS Andromedae, a 1.01 day period, double-lined, totally eclipsing binary system of early-F spectral type and a likely member of the intermediate-age open cluster NGC 752. The determinations of many of the system elements including the distance are robust against modest changes in model assumptions. Third light is present in all passbands at the 10% level. The weighted means of the best-fitting model yield a distance of 477 ± 4 ±12 pc, equivalent to (m – M)0 = 8.390 ± 0.018 ± 0.060 mag, and masses of 1.655 ± 0.003 ± 0.030 M Sun and 1.087 ±0.005 ± 0.040 M Sun, radii of 2.086 ± 0.003 ± 0.013 and 1.255 ± 0.005 ± 0.012 R Sun, and effective temperatures 7056 ± 21 ± 140 R Sun and 5971 ± 33 ± 130 K, for components 1 and 2, respectively, where the formal internal uncertainties are followed by conservatively estimated systematic errors. Possible but less satisfactory semidetached models produce more parameter variations and larger mean residuals. The primary star is seen to be at or very close to the main-sequence turnoff at an age of 1.55 ± 0.05 Gyr but appears to be too small for its mass, whereas the secondary appears to be too luminous for its temperature and too large for its mass compared to models of single stars.

The Gaia-ESO Survey: The inner disc, intermediate-age open cluster Pismis 18

Context. Pismis 18 is a moderately populated, intermediate-age open cluster located within the solar circle at a Galactocentric distance of about seven kpc. Few open clusters have been studied in detail in the inner disc region before the Gaia-ESO Survey. Aims. New data from the Gaia-ESO Survey allowed us to conduct an extended radial velocity membership study as well as spectroscopic metallicity and detailed chemical abundance measurements for this cluster. Methods. Gaia-ESO Survey data for 142 potential members, lying on the upper main sequence and on the red clump, yielded radial velocity measurements, which, together with proper motion measurements from the Gaia Second Data Release (Gaia DR2), were used to determine the systemic velocity of the cluster and membership of individual stars. Photometry from Gaia DR2 was used to re-determine cluster parameters based on high confidence member stars only. Cluster abundance measurements of six radial-velocity member stars with UVES high-resolution spectroscopy are presented for 23 elements. Results. The average radial velocity of 26 high confidence members is −27.5 ± 2.5 (std) km s−1 with an average proper motion of pmra = −5.65 ± 0.08 (std) mas yr−1 and pmdec = −2.29 ± 0.11 (std) mas yr−1. According to the new estimates, based on high confidence members, Pismis 18 has an age of τ = 700+40−50 Myr, interstellar reddening of E(B − V) = 0.562+0.012−0.026 mag and a de-reddened distance modulus of DM0 = 11.96+0.10−0.24 mag. The median metallicity of the cluster (using the six UVES stars) is [Fe/H] = +0.23 ± 0.05 dex, with [α/Fe] = 0.07 ± 0.13 and a slight enhancement of s- and r-neutron-capture elements. Conclusions. With the present work, we fully characterized the open cluster Pismis 18. We confirmed its present location in the inner disc. We estimated a younger age than the previous literature values and we gave, for the first time, its metallicity and its detailed abundances. Its [α/Fe] and [s-process/Fe], both slightly super-solar, are in agreement with other inner-disc open clusters observed by the Gaia-ESO survey.

Membership and fundamental parameters of the intermediate-age open clusters NGC 2281 and NGC 2539 based on Gaia-DR2

Abstract This paper presents an investigation on the two intermediate-age open clusters NGC 2281 and NGC 2539 based on Gaia Data Release 2 (Gaia-DR2). A combined machine-learning method is used to identify likely cluster members of the two clusters, taking into account the astrometric and photometric data of Gaia-DR2. It is found that NGC 2281 and NGC 2539 each have more than 600 likely cluster members, which are highly suitable for further investigation of the fundamental parameters of the two clusters. Robust estimates of the distances, proper motions, and radial velocities for the two clusters are obtained via a Monte Carlo simulation technique. NGC 2281 is found to have a distance of 522$\, \pm \,$12 pc, a proper motion of (〈μαcos δ〉, 〈μδ〉) = ($-2.947\, \pm \,$0.014, $-8.344\, \pm \,$0.014) mas yr−1, and a radial velocity of $+20.0\, \pm \,$0.7 km s−1. The distance, proper motion, and radial velocity of NGC 2539 are determined to be 1271$\, \pm \,$70 pc, (〈μαcos δ〉, 〈μδ〉) = ($-2.335\, \pm \,$0.007, $-0.583\, \pm \,$0.006) mas yr−1, and $+29.6\, \pm \,$0.4 km s−1, respectively. We find that NGC 2281 has a core radius of ${8{^{\prime}_{.}}89}$$\, \pm \,$${0{^{\prime}_{.}}27}$ (1.3 pc) and a limiting radius of ${79{^{\prime}_{.}}26}$$\, \pm \,$${2{^{\prime}_{.}}86}$ (12.0 pc). The core and limiting radius of NGC 2539 are determined to be ${5{^{\prime}_{.}}62}$$\, \pm \,$${0{^{\prime}_{.}}28}$ (2.1 pc) and ${33{^{\prime}_{.}}65}$$\, \pm \,$${1{^{\prime}_{.}}96}$ (12.4 pc), respectively. In addition, we find strong evidence for the existence of mass segregation in the two clusters.

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.

A Chemical and Kinematical Analysis of the Intermediate-age Open Cluster IC 166 from APOGEE and Gaia DR2

Abstract IC 166 is an intermediate-age open cluster (OC) (∼1 Gyr) that lies in the transition zone of the metallicity gradient in the outer disk. Its location, combined with our very limited knowledge of its salient features, make it an interesting object of study. We present the first high-resolution spectroscopic and precise kinematical analysis of IC 166, which lies in the outer disk with R GC ∼ 12.7 kpc. High-resolution H-band spectra were analyzed using observations from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment survey. We made use of the Brussels Automatic Stellar Parameter code to provide chemical abundances based on a line-by-line approach for up to eight chemical elements (Mg, Si, Ca, Ti, Al, K, Mn, and Fe). The α-element (Mg, Si, Ca, and whenever available Ti) abundances, and their trends with Fe abundances have been analyzed for a total of 13 high-likelihood cluster members. No significant abundance scatter was found in any of the chemical species studied. Combining the positional, heliocentric distance, and kinematic information, we derive, for the first time, the probable orbit of IC 166 within a Galactic model including a rotating boxy bar, and found that it is likely that IC 166 formed in the Galactic disk, supporting its nature as an unremarkable Galactic OC with an orbit bound to the Galactic plane.

Photometric study and search for variable stars in the intermediate-age open cluster NGC 2126

Photometric study and search for variable stars in the intermediate-age open cluster NGC 2126