Cluster CMD Research Articles

High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681* †

Abstract We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5 ± 3.7 km s−1 and find a mean [Fe/H] = −1.63 ± 0.07 dex and [α/Fe] = 0.42 ± 0.11 dex. Additionally, we confirm the existence of a Na–O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini et al. and Piotto et al. we are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.

Multiple stellar populations in the globular cluster M3 (NGC 5272): a Strömgren perspective

We present Str\"omgren photometry of the Galactic Globular Cluster M3 to study its multiple generations phenomenon. The use of different colour-magnitude diagrams and especially of the notoriously efficient c_y index allowed us to detect a double Red Giant Branch in the cluster CMD. After decontamination from fore- and background sources, the two sequences turned out to be equally populated. The two components also show a bimodal radial distribution well corresponding to that predicted by numerical simulations for clusters living in an intermediate dynamical evolutive state and with a population with modified chemical composition that was born more centrally concentrated than the primordial. The analysis of high-resolution spectra quantitatively demonstrates that the two detected sequences correspond to the first (Na-poor) generation and the second (Na-rich) generation, thus confirming the importance of synergy between photometry and spectroscopy.

Globular cluster ages from main sequence fitting and detached, eclipsing binaries: The case of 47 Tuc

AbstractAge constraints are most often placed on globular clusters by comparing their CMDs with theoretical isochrones. The recent discoveries of detached, eclipsing binaries in such systems by the Cluster AgeS Experiment (CASE) provide new insights into their ages and, at the same time, provide much-needed tests of stellar evolution models. We describe efforts to model the properties of the detached, eclipsing binary V69 in 47 Tuc and compare age constraints derived from stellar evolution models of V69A and B with ages obtained from fitting isochrones to the cluster CMD. We determine whether or not, under reasonable assumptions of distance, reddening, and metallicity, it is possible to simultaneously constrain the age and He content of 47 Tuc.

The embedded cluster DBSB 48 in the nebula Hoffleit 18: Comparison with Trumpler 14

We derive fundamental parameters of the embedded cluster DBSB 48 in the southern nebula Hoffleit 18 and the very young open cluster Trumpler 14, by means of deep JHK s infrared photometry. We build colour–magnitude and colour–colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from K-excess fractions. A prominent pre-main sequence population is present in DBSB 48, and the K-excess fraction f K = 55 ± 6% gives an age of 1.1 ± 0.5 Myr. A mean reddening of A K s = 0.9 ± 0.03 was found, corresponding to A V = 8.2 ± 0.3. The cluster CMD is consistent with the far kinematic distance of 5 kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of 1.7 ± 0.7 Myr. The fraction of stars with infrared excess in Trumpler 14 is f K = 28 ± 4%. Despite the young ages, both clusters are described by a King profile with core radii R core = 0.46 ± 0.05 pc and R core = 0.35 ± 0.04 pc, respectively, for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is Δ K s ≈ 2 mag, while in Trumpler 14 it is Δ K s ≈ 5 mag, consistent with the estimated ages.

WIYN Open Cluster Study. XV. Photometric Monitoring of Open Clusters: New Variables in NGC 188

Photometric monitoring of the central 17' × 17' of the old open cluster NGC 188 with the WIYN 3.5 m telescope has resulted in the discovery of a number of new variable stars, down to 21.5 mag in V, 35 of which have well-determined periods. The variability types of the fainter stars of the sample (18–21.5 mag) remain uncertain. However, most of the brighter stars (15–18 mag) probably make up the low-luminosity extension of the already known W UMa population of NGC 188. We also report the discovery of two longer period variables on the subgiant branch of the cluster CMD, most likely FK Comae stars, which suggests that the cluster may provide significant insight on the formation and evolution of contact binary systems. Alternatively, these objects may represent a new kind of pulsation variables.

The White Dwarf Cooling Age of the Open Cluster NGC 2420

We have used deep HST WFPC2 observations of two fields in NGC 2420 to produce a cluster CMD down to V = 27. After imposing morphological selection criteria we find eight candidate white dwarfs in NGC 2420. Our completeness estimates indicate that we have found the terminus of the WD cooling sequence. We argue that the cluster distance modulus is likely to be close to 12.10 with E(B-V) = 0.04. With these parameters we find a white dwarf cooling age for NGC 2420 of 2.0 +- 0.20 (1 sigma) Gyrs. The 0.20 Gyr uncertainty includes errors in the photometry, sequence fitting, precursor time scales, and theoretical white dwarf cooling time scales. Comparing the cluster white dwarf cooling age to ages derived from stellar isochrone fitting we find a preference for ages derived from models incorporating convective overshoot.

Variable stars in the globular cluster NGC 6362

ABSTRA C T We report the results of a CCD search for short-period variables in the field of a southern globular cluster NGC 6362. We identified 19 new candidate variables, five of which are cluster RR Lyraes, four are probable SX Phe-type stars and eight are eclipsing binaries. Of the discovered binaries, three are EA-type systems, two of which are located on the cluster CMD in the turn-off region and the third 1 mag above the turn-off point, in the yellow straggler region. Five other systems are of W UMa type, three of which are foreground objects and two are likely cluster members. The remaining two candidates exhibit a modulation of the brightness level with an amplitude of 0.1‐0.2 mag; further observations are needed to reveal the nature of their variability. Phased VI light curves for 20 variables (18 RR Lyrae stars and two blue stragglers) located in the central region of the cluster are presented.

Observations of Cepheid Variables in Two LMC Clusters Using EROS 2 Data

It is well known that Cepheid variables are very important distance indicators because of their PL and PLC relations. The distances derived through the quoted relations are affected by well known systematic effects, since, in general, we have a poor knowledge of both reddening and metallicity of the Cepheid sample. Good estimates of the quoted parameters can be achieved if the observed Cepheids are cluster members since, by comparison between cluster CMD and theoretical isochrones we can estimate the cluster reddening, metallicity and age, i.e., the evolving masses for each evolutionary phase. The ideal objects to be searched for Cepheid membership are Magellanic Cloud clusters since they are well populated in the relevant evolutionary phases.

Observations of Cepheid Variables in Two LMC Clusters Using EROS 2 Data

It is well known that Cepheid variables are very important distance indicators because of their PL and PLC relations. The distances derived through the quoted relations are affected by well known systematic effects, since, in general, we have a poor knowledge of both reddening and metallicity of the Cepheid sample. Good estimates of the quoted parameters can be achieved if the observed Cepheids are cluster members since, by comparison between cluster CMD and theoretical isochrones we can estimate the cluster reddening, metallicity and age, i.e., the evolving masses for each evolutionary phase. The ideal objects to be searched for Cepheid membership are Magellanic Cloud clusters since they are well populated in the relevant evolutionary phases.

Variable Stars in Magellanic Cloud Clusters. II. NGC 1850

view Abstract Citations (26) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Variable Stars in Magellanic Cloud Clusters. II. NGC 1850 Sebo, K. M. ; Wood, P. R. Abstract We present the results of a study aimed at identifying variable stars in the rich LMC cluster NGC 1850. V and I band CCD imaging spanning more than 5 years in a 10' x 10' field surrounding the cluster has allowed us to identify more than 30 variable stars, including seven classical Cepheids, one anomalous Cepheid, two RR Lyrae variables, 19 long-period variables (LPVs), one blue eclipsing binary, one possible pair of eclipsing giants, and several peculiar variables. The only likely cluster member is a Cepheid. Isochrone fitting to the cluster CMD yields an age of 80 Myr if an LMC distance modulus of 18.5 is adopted. A comparison of pulsation and evolution masses for the Cepheids still yields a ratio of evolution to pulsation mass of ∼1.2 for evolution models computed with core overshoot parameter Λ = 0.5, where Λ = 2dovHp ,dov is the distance that convection overshoots beyond the Schwarzschild boundary and Hp is the pressure scale height. An overshoot parameter Λ ∼ 1.0 would be required to bring the evolution and pulsation masses into agreement. One of the Cepheids in the field is a bump Cepheid. A calculation of the bump mass yields a value in reasonable agreement with the pulsation mass. We show that detailed modelling of individual bump Cepheids is capable of providing very tight constraints on the LMC distance modulus. The Cepheid period-luminosity-color relation compared to the theoretical relation yields a LMC distance modulus of 18.60. Finally, arguments are presented which suggest that the LPVs are a mixture of fundamental mode pulsators and small-amplitude overtone pulsators. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/176042 Bibcode: 1995ApJ...449..164S Keywords: GALAXIES: MAGELLANIC CLOUDS; GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL NGC NUMBER: NGC 1850; STARS: CEPHEIDS; STARS: EVOLUTION full text sources ADS | data products SIMBAD (37) NED (1) CDS (1)