153 research outputs found
The Fundamental Plane of Open Clusters
We utilize the data from the Apache Point Observatory Galactic Evolution
Experiment-2 (APOGEE-2) in the fourteenth data release of the Sloan Digital Sky
Survey (SDSS) to calculate the line-of-sight velocity dispersion
of a sample of old open clusters (age larger than 100\,Myr) selected from the
Milky Way open cluster catalog of Kharchenko et al. (2013). Together with their
band luminosity , and the half-light radius of the most
probable members, we find that these three parameters show significant pairwise
correlations among each other. Moreover, a fundamental plane-{\it like}
relation among these parameters is found for the oldest open clusters (age
older than 1\,Gyr), with \,mag in the band absolute
magnitude. The existence of this relation, which deviates significantly from
the virial theorem prediction, implies that the dynamical structures of the old
open clusters are quite similar, when survived from complex dynamical evolution
to age older than 1 Gyr.Comment: accepted publication for ApJ lette
A comprehensive study of the young star cluster HD 97950 in NGC 3603
I study the young massive star cluster HD,97950 located in the Galactic giant H,{sc ii} region NGC,3603. My goals are (1) to estimate the survival probability of the cluster, (2) to investigate the origin of its mass segregation, and (3) to investigate the interplay between the cluster and the surrounding interstellar medium (ISM). All the studies are done with data of the Hubble Space Telescope. I determine the cluster velocity dispersion from the stars' relative proper motions, and calculate the virial mass of the cluster. The cluster star formation efficiency is estimated to be about 50%, which suggests that the HD,97950 cluster will most likely survive as a bound cluster to gas expulsion. I apply the minimum spanning tree technique to measure the mass segregation down to 30,M. The high-mass stars are more segregated than low-mass stars, implying that the mass segregation in HD,97950 is mostly of dynamical origin. To improve the age determination for the cluster stars that are severely reddened by the surrounding dusty ISM, I compute a pixel-to-pixel distribution of the gas reddening, , associated with the cluster. The radial profiles of show significant spatial variations around HD,97950. Using photometry, I estimate the stellar reddening of cluster stars. After correcting for foreground reddening, the total to selective extinction ratio in the cluster is . The extinction curve in the filters in the cluster is greyer than the average Galactic extinction laws, but close to the extinction law for starburst galaxies. This indicates that stellar feedback from massive stars changes the dust properties in the HD,97950 cluster in a similar way as in starburst galaxies
Influence of planets on debris disks in star clusters I: the 50 AU Jupiter
Although debris disks may be common in exoplanet systems, only a few systems
are known in which debris disks and planets coexist. Planets and the
surrounding stellar population can have a significant impact on debris disk
evolution. Here we study the dynamical evolution of debris structures around
stars embedded in star clusters, aiming to determine how the presence of a
planet affects the evolution of such structures. We combine NBODY6++GPU and
REBOUND to carry out N-body simulations of planetary systems in star clusters
(N=8000; Rh=0.78 pc) for a period of 100 Myr, in which 100 solar-type stars are
assigned 200 test particles. Simulations are carried out with and without a
Jupiter-mass planet at 50 au. We find that the planet destabilizes test
particles and speeds up their evolution. The planet expels most particles in
nearby and resonant orbits. Remaining test particles tend to retain small
inclinations when the planet is present, and fewer test particles obtain
retrograde orbits. Most escaping test particles with speeds smaller than the
star cluster's escape speed originate from cold regions of the planetary system
or from regions near the planet. We identify three regions within planetary
systems in star clusters: (i) the private region of the planet, where few
debris particles remain (40 - 60 au), (ii) the reach of the planet, in which
particles are affected by the planet (0 - 400 au), and (iii) the territory of
the planetary system, most particles outside which will eventually escape (0 -
700 au).Comment: 17 pages, 20 figures, and 3 tables. Accepted for publication in MNRA
Wealth Inequality and Mental Disability Among the Chinese Population: A Population Based Study
In the study described herein, we investigated and explored the association between wealth inequality and the risk of mental disability in the Chinese population. We used nationally represented, population-based data from the second China National Sample Survey on Disability, conducted in 2006. A total of 1,724,398 study subjects between the ages of 15 and 64, including 10,095 subjects with mental disability only, were used for the analysis. Wealth status was estimated by a wealth index that was derived from a principal component analysis of 10 household assets and four other variables related to wealth. Logistic regression analysis was used to estimate the odds ratio (OR) and 95% confidence interval (CI) for mental disability for each category, with the lowest quintile category as the referent. Confounding variables under consideration were age, gender, residence area, marital status, ethnicity, education, current employment status, household size, house type, homeownership and living arrangement. The distribution of various types and severities of mental disability differed significantly by wealth index category in the present population. Wealth index category had a positive association with mild mental disability (p for trend <0.01), but had a negative association with extremely severe mental disability (p for trend <0.01). Moreover, wealth index category had a significant, inverse association with mental disability when all severities of mental disability were taken into consideration. This study’s results suggest that wealth is a significant factor in the distribution of mental disability and it might have different influences on various types and severities of mental disability
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