276 research outputs found
The metal-rich globular clusters of the Milky Way
We present new (V,V-I)-photometry of the metal-rich globular clusters NGC
5927, 6316, 6342, 6441 and 6760. The clusters show differential reddening up to
dE(V-I)=0.32 mag, for which the CMDs are corrected via extinction maps. There
are hints of a variation in the extinction law. Two different ways to determine
the parameters metallicity, reddening and distance lead to consistent results.
The metallicities of the clusters range between -0.7 <= [M/H] <= 0.0 dex and
the absolute reddening between 0.43 <= E(V-I) <= 0.76 mag. Taking the
differential reddening into account leads to slightly increased distances. From
the resulting parameters we conclude that the usual halo-disk-distinction in
the system of globular clusters seems questionable.Comment: 21 pages, 34 ps-figures; Astronomy and Astrophysics accepte
Deconstructing the Antlia cluster core
The present literature does not give a satisfactory answer to the question
about the nature of the "Antlia galaxy cluster". The radial velocities of
galaxies found in the region around the giant ellipticals NGC 3258/3268 range
from about 1000 km/s to 4000 km/s. We characterise this region and its possible
kinematical and population substructure. We have obtained VLT--VIMOS
multi-object spectra of the galaxy population in the inner part of the Antlia
cluster and measure radial velocities for 45 potential members. We supplement
our galaxy sample with literature data, ending up with 105 galaxy velocities.
We find a large radial velocity dispersion for the entire sample as reported in
previous papers. However, we find three groups at about 1900 km/s, 2800 km/s,
and 3700 km/s, which we interpret as differences in the recession velocities
rather than peculiar velocities. The high radial velocity dispersion of
galaxies in the Antlia region reflects a considerable extension along the line
of sight.Comment: 11 pages, 7 figures, accepted in A&
Planetary Nebula Candidates in Extragalactic Young Star Clusters
During an analysis of optical spectra of 80 young star clusters in several
nearby spiral galaxies, [O III] and [N II] emission lines were noted in some
cases. Three of these emission line sources are identified as likely planetary
nebula (PN) candidates and may represent a rare opportunity to study PNe whose
progenitor stars are known to be of intermediate masses. This paper presents
and discusses basic properties of the PN candidates and their host clusters.
Based on the observed emission line fluxes, the excitation parameters and
luminosities of the nebulae are derived. This allows a crude placement of the
central stars in two of the objects on the H-R diagram, and their temperatures
and luminosities are found to be consistent with post-AGB model tracks for a
central star mass of about 0.60 Msun. Host cluster ages and masses are
estimated from broad-band colours and by comparison with model SSP spectra. One
of the host clusters has an age of 32-65 Myrs, corresponding to a main sequence
turn-off mass of M(TO) = 6.6-9.0 Msun. For the other cluster the age is 282-407
Myrs, corresponding to M(TO) = 3.2-3.6 Msun. By estimating the number of stars
evolving off the main sequence per year, a total of 6 PNe are expected in our
full sample of 80 clusters for aPN lifetime of 10000 years. The factor of two
disagreement with the actual observed number may be due, among other things, to
uncertainties in PN lifetimes. It is interesting to note that all three PN
candidates are associated with clusters which are more diffuse than average.
While PNe have previously been found in some old globular clusters, the
candidates identified here are among the first identified in young star
clusters.Comment: 10 pages, 9 figures. Accepted for publication in A&
Intra Cluster Globular Clusters around NGC 1399 in Fornax?
We investigate whether the globular clusters (GCs) in the recently published
sample of GCs in the Fornax cluster by Bergond and coworkers are indeed
intra-cluster objects. We combine the catalogue of radial velocity measurements
by Bergond et al. with our CTIO MOSAIC photometry in the Washington system and
analyse the relation of metal-poor and metal-rich GCs with their host galaxies.
The metal-rich GCs appear to be kinematically associated with their respective
host galaxies. The vast majority of the metal-poor GCs found in between the
galaxies of the Fornax cluster have velocities which are consistent with them
being members of the very extended NGC 1399 GC system. We find that when the
sample is restricted to the most accurate velocity measurements, the GC
velocity dispersion profile can be described with a mass model derived for the
NGC 1399 GC system within 80 kpc. We identify one ``vagrant'' GC whose radial
velocity suggests that it is not bound to any galaxy unless its orbit has a
very large apogalactic distance.Comment: 4 pages, 4 figures, accepted for publication as a Letter in A&
A study of the old galactic star cluster Berkeley 32
We present new CCD photometry of the distant old open star cluster Berkeley 32 in Johnson V and Cousins I passbands. A total of about 3200 stars have been observed in a field of 13X13 arcmin**2. The colour-magnitude diagram in V, (V-I) has been generated down to V = 22 mag. A broad but well defined main sequence is clearly visible. Some blue stragglers, a well developed subgiant branch and a Red Clump are also seen. By fitting isochrones to this CMD as well as to other CMDs available in the literature, and using the Red Clump location, the reddening, distance and age of the star cluster have been determined. The cluster has a distance of 3.3 kpc, its radius is about 2.4 pc; the reddening E(B-V) is 0.08 mag and the age is 6.3 Gyr. By comparison with theoretical isochrones, a metallicity of [Fe/H]= -0.2 dex has been estimated. We find a much flatter mass function than what has been found for young clusters. If the mass function is a power law dN/dm = const.*m**alpha, then we get alpha = -0.5+-0.3 in the mass range 0.6-1.1 solar masses. This may be seen as a signature of the highly evolved dynamical state of the cluster
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