Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe extended Main-Sequence Turnoff of the Milky Way open cluster Collinder 347
84
0
0.0
(
0
)
Added by
Andr\\'es E. Piatti
Publication date
2019
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We made use of the Gaia DR2 archive to comprehensively study the Milky Way open cluster Collinder 347, known until now as a very young object of solar metal-content. However, the G versus G_BP-G_RP colour-magnitude diagram (CMD) of bonafide probable cluster members, selected on the basis of individual stellar proper motions, their spatial distribution and placement in the CMD, reveals the existence of a Hyades-like age open cluster (log(t /yr) = 8.8) of moderately metal-poor chemical content ([Fe/H] = -0.4 dex), with a present-day mass of 3.3x10^3 Mo. The cluster exhibits an extended Main-Sequence turnoff (eMSTO) of nearly 500 Myr, while that computed assuming Gaussian distributions from photometric errors, stellar binarity, rotation and metallicity spread yields an eMSTO of ~340 Myr. Such an age difference points to the existence within the cluster of stellar populations with different ages.
rate research
Read More
We present photometric analysis of twelve Galactic open clusters and show that the same multiple-population phenomenon observed in Magellanic Clouds (MCs) is present in nearby open clusters. Nearly all the clusters younger than $sim$2.5 Gyr of both MCs exhibit extended main-sequence turnoffs (eMSTOs) and all the cluster younger than $sim$700 Myr show broadened/split main sequences (MSs). High-resolution spectroscopy has revealed that these clusters host stars with a large spread in the observed projected rotations. In addition to rotation, internal age variation is indicated as a possible responsible for the eMSTOs, making these systems the possible young counterparts of globular clusters with multiple populations. Recent work has shown that the eMSTO+broadened MSs are not a peculiarity of MCs clusters. Similar photometric features have been discovered in a few Galactic open clusters, challenging the idea that the color-magnitude diagrams (CMDs) of these systems are similar to single isochrones and opening new windows to explore the eMSTO phenomenon. We exploit photometry+proper motions from Gaia DR2 to investigate the CMDs of open clusters younger than $sim$1.5 Gyr. Our analysis suggests that: (i) twelve open clusters show eMSTOs and/or broadened MSs, that cannot be due neither to field contamination, nor binaries; (ii) split/broadened MSs are observed in clusters younger than $sim$700 Myr, while older objects display only an eMSTO, similarly to MCs clusters; (iii) the eMSTO, if interpreted as a pure age spread, increases with age, following the relation observed in MCs clusters and demonstrating that rotation is the responsible for this phenomenon.
The chemical homogeneity of surviving stellar clusters contains important clues about interstellar medium (ISM) mixing efficiency, star formation, and the enrichment history of the Galaxy. Existing measurements in a handful of open clusters suggest homogeneity in several elements at the 0.03 dex level. Here we present (i) a new cluster member catalog based only on APOGEE radial velocities and Gaia-DR2 proper motions, (ii) improved abundance uncertainties for APOGEE cluster members, and (iii) the dependence of cluster homogeneity on Galactic and cluster properties, using abundances of eight elements from the APOGEE survey for ten high-quality clusters. We find that cluster homogeneity is uncorrelated with Galactocentric distance, |Z|, age, and metallicity. However, velocity dispersion, which is a proxy for cluster mass, is positively correlated with intrinsic scatter at relatively high levels of significance for [Ca/Fe] and [Mg/Fe]. We also see a possible positive correlation at a low level of significance for [Ni/Fe], [Si/Fe], [Al/Fe], and [Fe/H], while [Cr/Fe] and [Mn/Fe] are uncorrelated. The elements that show a correlation with velocity dispersion are those that are predominantly produced by core-collapse supernovae (CCSNe). However, the small sample size and relatively low correlation significance highlight the need for follow-up studies. If borne out by future studies, these findings would suggest a quantitative difference between the correlation lengths of elements produced predominantly by Type~Ia SNe versus CCSNe, which would have implications for Galactic chemical evolution models and the feasibility of chemical tagging.
Spectroscopic observations are reported for the 2.75 day, double-lined, detached eclipsing binary EPIC 219552514 located at the turnoff of the old nearby open cluster Ruprecht 147. A joint analysis of our radial velocity measurements and the K2 light curve leads to masses of M1 = 1.509 (+0.063 / -0.056) MSun and M2 = 0.649 (+0.015 / -0.014) MSun for the primary and secondary, along with radii of R1 = 2.505 (+0.026 / -0.031) RSun and R2 = 0.652 (+0.013 / -0.012) RSun, respectively. The effective temperatures are 6180 +/- 100 K for the F7 primary and 4010 +/- 170 K for the late K secondary. The orbit is circular, and the stars rotation appears to be synchronized with the orbital motion. This is the third eclipsing system analyzed in the same cluster, following our earlier studies of EPIC 219394517 and EPIC 219568666. By comparison with stellar evolution models from the PARSEC series, we infer an age of 2.67 (+0.39 / -0.55) Gyr that is consistent with the estimates for the other two systems. EPIC 219552514 is a hierarchical triple system, with the period of the slightly eccentric outer orbit being 463 days. The unseen tertiary is either a low-mass M dwarf or a white dwarf.
Intermediate-age star clusters in the LMC present extended main sequence turnoffs (MSTO) that have been attributed to either multiple stellar populations or an effect of stellar rotation. Recently it has been proposed that these extended main sequences can also be produced by ill-characterized stellar variability. Here we present Gemini-S/GMOS time series observations of the intermediate-age cluster NGC 1846. Using differential image analysis, we identified 73 new variable stars, with 55 of those being of the Delta Scuti type, that is, pulsating variables close the MSTO for the cluster age. Considering completeness and background contamination effects we estimate the number of Delta Scuti belonging to the cluster between 40 and 60 members, although this number is based on the detection of a single Delta Scuti within the cluster half-light radius. This amount of variable stars at the MSTO level will not produce significant broadening of the MSTO, albeit higher resolution imaging will be needed to rule out variable stars as a major contributor to the extended MSTO phenomenon. Though modest, this amount of Delta Scuti makes NGC 1846 the star cluster with the highest number of these variables ever discovered. Lastly, our results are a cautionary tale about the adequacy of shallow variability surveys in the LMC (like OGLE) to derive properties of its Delta Scuti population.
The Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) dataset consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope-measured proper motions of Milky Way halo main sequence turnoff stars in the CANDELS fields. In this paper, we present the spectroscopic component of this dataset, and discuss target selection, observing strategy, and survey properties. We present a new method of measuring line-of-sight (LOS) velocities by combining multiple spectroscopic observations of a given star, utilizing Bayesian hierarchical modeling. We present the LOS velocity distributions of the four HALO7D fields, and estimate their means and dispersions. All of the LOS distributions are dominated by the hot halo: none of our fields are dominated by substructure that is kinematically cold in the LOS velocity component. Our estimates of the LOS velocity dispersions are consistent across the different fields, and these estimates are consistent with studies using other types of tracers. To complement our observations, we perform mock HALO7D surveys using the synthetic survey software Galaxia to observe the Bullock & Johnston (2005) accreted stellar halos. Based on these simulated datasets, the consistent LOS velocity distributions across the four HALO7D fields indicates that the HALO7D sample is dominated by stars from the same massive (or few relatively massive) accretion event(s).
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
