No evidence for mass segregation in massive young clusters

Aims. We investigate the validity of the mass segregation indicators commonly used in analysing young stellar clusters. Methods. We simulate observations by constructing synthetic seeing-limited images of a 1000 massive clusters (10^4 Msun) with a standard IMF and a King-density distribution function. Results. We find that commonly used indicators are highly sensitive to sample incompleteness in observational data and that radial completeness determinations do not provide satisfactory corrections, rendering the studies of radial properties highly uncertain. On the other hand, we find that, under certain conditions, the global completeness can be estimated accurately, allowing for the correction of the global luminosity and mass functions of the cluster. Conclusions. We argue that there is currently no observational evidence of mass segregation in young compact clusters since there is no robust way to differentiate between true mass segregation and sample incompleteness effects. Caution should then be exercised when interpreting results from observations as evidence of mass segregation.Comment: 10 pages, 12 figures, typos corrected. Download a high-resolution version at http://www.astro.up.pt/~jascenso/mseg_v2.pdf (1 MB

Relationship Between Health Literacy and End-Stage Renal Disease among Type II Diabetics

The progression of End Stage Renal Disease (ESRD) among type II diabetics is preventable, yet complications continue to plague many. Reports show that 29.1 million people (9.3%) in the United States have diabetes, and 40% of those individuals develop ESRD. Four research questions explored the relationship between ESRD, health literacy, and healthcare. Data from 2010-2015 from the National Institute of Health (NIH) was quantitatively analyzed. The conceptual framework was the revised health service utilization theory. The target population included 3939 diverse males and females between the ages of 20-75 diagnosed with type II Diabetes. Results from Chi-square, cross-tabulation, binary, and multinomial logistic regression revealed that there is a statistically significant relationship between inadequate health literacy and ESRD (p= \u3c0.05), inadequate health literacy and healthcare services (p= \u3c0.05), and healthcare services and development of ESRD (p=\u3c.001). Findings exposed significant demographic co-factor differences. Males developed ESRD more than females, and African American and Hispanic populations were almost 2 times more likely than Caucasians to develop ESRD. As participants age, odds for developing ESRD increase about 2-3 times. Both race and education were significant predictors of inadequate health literacy. African Americans and Hispanics were 3 times more likely to have inadequate health literacy than Caucasian participants. Lower education increased the odds of having inadequate health literacy approximately 7.6 times. Results show that Caucasian participants had higher education levels and private health insurance, whereas African Americans and Hispanics had lower education and no insurance or Medicaid. Implications from this research show that social determinants among vulnerable populations are impacting an individual\u27s health literacy and ability to adequately manage their health. Evidence from this study generates social change through recognition that health literacy is fundamental when attempting to prevent chronic disease complications and promote positive health

MASSCLEAN - MASSive CLuster Evolution and ANalysis Package - Description and Tests

We present MASSCLEAN, a new, sophisticated and robust stellar cluster image and photometry simulation package. This visualization tool is able to create color-magnitude diagrams and standard FITS images in any of the traditional optical and near-infrared bands based on cluster characteristics input by the user, including but not limited to distance, age, mass, radius and extinction. At the limit of very distant, unresolved clusters, we have checked the integrated colors created in MASSCLEAN against those from other simple stellar population models with consistent results. We have also tested models which provide a reasonable estimate of the field star contamination in images and color-magnitude diagrams. We demonstrate the package by simulating images and color-magnitude diagrams of well known massive Milky Way clusters and compare their appearance to real data. Because the algorithm populates the cluster with a discrete number of tenable stars, it can be used as part of a Monte Carlo Method to derive the pr obabilistic range of characteristics (integrated colors, for example) consistent with a given cluster mass and age. Our simulation package is available for download and will run on any standard desktop running UNIX/Linux. Full documentation on installation and its use is also available. Finally, a web-based version of MASSCLEAN which can be immediately used and is sufficiently adaptable for most applications is available through a web interface.Comment: Revised, 23 pages, 21 figures, submitted to Astronomical Journa

Disks in the Arches cluster -- survival in a starburst environment

Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic center reveal a significant population of near-infrared excess sources. We combine the L'-band excess observations with K'-band proper motions, to confirm cluster membership of excess sources in a starburst cluster for the first time. The robust removal of field contamination provides a reliable disk fraction down to our completeness limit of H=19 mag, or about 5 Msun at the distance of the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable proper motion measurements, all of which are proper motion members of the Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources reveals strong CO bandhead emission, which we interpret as the signature of dense circumstellar disks. The detection of strong disk emission from the Arches stars is surprising in view of the high mass of the B-type main sequence host stars of the disks and the intense starburst environment. We find a disk fraction of 6 +/- 2% among B-type stars in the Arches cluster. A radial increase in the disk fraction from 3 to 10% suggests rapid disk destruction in the immediate vicinity of numerous O-type stars in the cluster core. A comparison between the Arches and other high- and low-mass star-forming regions provides strong indication that disk depletion is significantly more rapid in compact starburst clusters than in moderate star-forming environments.Comment: 51 pages preprint2 style, 22 figures, accepted by Ap

The orbital motion of the Arches cluster — clues on cluster formation near the galactic center

The Arches cluster is one of the most massive, young clusters in the Milky Way. Located inside the central molecular zone in the inner 200 pc of the Galactic center, it formed in one of the most extreme star-forming environments in the present-day Galaxy. Its young age of only 2.5 Myr allows us to observe the cluster despite the strong tidal shear forces in the inner Galaxy. The orbit of the cluster determines its dynamical evolution, tidal stripping, and hence its fate. We have measured the proper motion of the Arches cluster relative to the ambient field from Keck/NIRC2 LGS-AO and VLT/NAOS-CONICA NGS-AO observations taken 4.3 years earlier. When combined with the radial velocity, we derive a 3D space motion of 232 ± 30 km/s for the Arches. This motion is exceptionally large when compared to molecular cloud orbits in the GC, and places stringent constraints on the formation scenarios for starburst clusters in dense, nuclear environments

K-shell x-ray spectroscopy of atomic nitrogen

Absolute {\it K}-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Due to the difficulty of creating a target of neutral atomic nitrogen, no high-resolution {\it K}-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong $1s$ $\rightarrow$ $np$ resonance features throughout the threshold region. An experimental value of 409.64 $\pm$ 0.02 eV was determined for the {\it K}-shell binding energy.Comment: 4 pages, 2 graphs, 1 tabl

The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics

We present the first measurement of the proper motion of the young, compact Arches cluster near the Galactic center from near-infrared adaptive optics (AO) data taken with the recently commissioned laser-guide star (LGS) at the Keck 10-m telescope. The excellent astrometric accuracy achieved with LGS-AO provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken 4.3 years earlier. Over the 4.3 year baseline, a spatial displacement of the Arches cluster with respect to the field population is measured to be 24.0 +/- 2.2 mas, corresponding to a proper motion of 5.6 +/- 0.5 mas/yr or 212 +/- 29 km/s at a distance of 8 kpc. In combination with the known line-of-sight velocity of the cluster, we derive a 3D space motion of 232 +/- 30 km/s of the Arches relative to the field. The large proper motion of the Arches cannot be explained with any of the closed orbital families observed in gas clouds in the bar potential of the inner Galaxy, but would be consistent with the Arches being on a transitional trajectory from x1 to x2 orbits. We investigate a cloud-cloud collision as the possible origin for the Arches cluster. The integration of the cluster orbit in the potential of the inner Galaxy suggests that the cluster passes within 10 pc of the supermassive black hole only if its true GC distance is very close to its projected distance. A contribution of young stars from the Arches cluster to the young stellar population in the inner few parsecs of the GC thus appears increasingly unlikely. The measurement of the 3D velocity and orbital analysis provides the first observational evidence that Arches-like clusters do not spiral into the GC. This confirms that no progenitor clusters to the nuclear cluster are observed at the present epoch.Comment: 22 pdflatex pages including 12 figures, reviewed version accepted by Ap