90 research outputs found
Planetary nebula or symbiotic Mira? Near infrared colours mark the difference
Nebulae around symbiotic Miras look very much like genuine planetary nebulae, although they are formed in a slightly different way. We present near infrared photometry of known and suspected symbiotic nebulae obtained with the Deep Near Infrared Southern Sky Survey (DENIS). We demonstrate that the near infrared colours are an excellent tool to distinguish symbiotic from genuine planetary nebulae. In particular we find that the bipolar planetary nebulae M 2-9 and Mz 3 are in fact symbiotic Miras. Further observations on prototype symbiotic Miras prove that the proposed classification scheme works generally
Structure and mass segregation in Galactic stellar clusters
We quantify the structure of a very large number of Galactic open clusters and look for evidence
of mass segregation for the most massive stars in the clusters. We characterize the structure and
mass segregation ratios of 1276 clusters in the Milky Way Stellar Cluster (MWSC) catalogue
containing each at least 40 stars and that are located at a distance of up to â2 kpc from the Sun.
We use an approach based on the calculation of the minimum spanning tree of the clusters, and
for each one of them, we calculate the structure parameter Q and the mass segregation ratio
MSR. Our findings indicate that most clusters possess a Q parameter that falls in the range
0.7â0.8 and are thus neither strongly concentrated nor do they show significant substructure.
Only 27 per cent can be considered centrally concentrated with Q values >0.8. Of the 1276
clusters, only 14 per cent show indication of significant mass segregation (MSR > 1.5).
Furthermore, no correlation is found between the structure of the clusters or the degree of
mass segregation with their position in the Galaxy. A comparison of the measured Q values
for the young open clusters in the MWSC to N-body numerical simulations that follow the
evolution of the Q parameter over the first 10 Myr of the clusters life suggests that the young
clusters found in the MWSC catalogue initially possessed local mean volume densities of Ïâ
â 10â100 Mïżœ pcâ3
The spatial distribution of substellar objects in IC348 and the Orion Trapezium Cluster
Aims: Some theoretical scenarios suggest the formation of brown dwarfs as
ejected stellar embryos in star-forming clusters. Such a formation mechanism
can result in different spatial distributions of stars and substellar objects.
We aim to investigate the spatial structure of stellar and substellar objects
in two well sampled and nearby embedded clusters, namely IC348 and the Orion
Trapezium Cluster (OTC) to test this hypothesis. Methods:Deep near-infrared
K-band data complete enough to sample the substellar population in IC348 and
OTC are obtained from the literature. The spatial distribution of the K-band
point sources is analysed using the Minimum Spanning Tree (MST) method. The Q
parameter and the spanning trees are evaluated for stellar and substellar
objects as a function of cluster core radius R. Results: The stellar
population in both IC348 and OTC display a clustered distribution whereas the
substellar population is distributed homogeneously in space within twice the
cluster core radius. Although the substellar objects do not appear to be bound
by the cluster potential well, they are still within the limits of the cluster
and not significantly displaced from their birth sites. Conclusions: The
spatially homogeneous distribution of substellar objects is best explained by
assuming higher initial velocities, distributed in a random manner and going
through multiple interactions. The overall spatial coincidence of these objects
with the cluster locations can be understood if these objects are nevertheless
travelling slowly enough so as to feel the gravitational effect of the cluster.
The observations support the formation of substellar objects as ``ejected
stellar embryos''. Higher ejection velocities are necessary but net spatial
displacements may not be necessary to explain the observational data.Comment: 4 pages. Accepted by A&A Letter
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