466 research outputs found
Stellar Photometry of the Globular Cluster NGC 6229. I. Data Reduction and Morphology of the Brighter Part of the CMD
BV CCD photometry of the central (1.5 arcmin x 2.0 arcmin) part of the mildly
concentrated outer-halo globular cluster NGC 6229 is presented. The data
reduction in such a crowded field was based on a wavelet transform analysis.
Our larger dataset extends the previous results by Carney et al. (1991, AJ,
101, 1699) for the outer and less crowded fields of the cluster, and confirms
that NGC 6229 has a peculiar color-magnitude diagram for its position in the
Galaxy. In particular, NGC 6229's horizontal branch (HB) presents several
interesting features, among which stand out: a well populated and very extended
blue tail; a rather blue overall morphology, with (B-R)/(B+V+R) = 0.24+/-0.02;
a bimodal color distribution, resembling those found for NGC 1851 and NGC 2808;
and gaps on the blue HB. NGC 6229 is the first bimodal-HB cluster to be
identified in the Galactic outer halo. A low value of the R parameter is
confirmed, suggestive of a low helium abundance or of the presence of a quite
substantial population of extreme HB stars fainter than our photometric limit
(~ 2.5 mag below the RR Lyrae level in V). Twelve new possible variable stars
were found in the central part of the cluster. The morphology of the red giant
branch (RGB) also seems to be peculiar. In particular, the RGB luminosity
function ``bump'' is not a prominent feature and has only been tentatively
identified, on the basis of a comparison with a previously reported detection
for M3 (NGC 5272). Finally, we compare the properties of NGC 6229 with those
for other outer-halo globular clusters, and call attention to what appears to
be a bimodal HB distribution for the outer-halo cluster population, where
objects with very red or very blue HB types are much more frequently found than
clusters with intermediate HB types.Comment: 31 pages, LaTeX, uses AASTeX v4.0, 11 postscript figures and 7
postscript tables pasted into text. To appear in The Astronomical Journal
(Feb. 1997 issue
The catalogue of OB associations in IC 1613
We present a catalogue of OB associations in IC 1613. Using an automatic and
objective method (Battinelli's 1991 technique) 60 objects were found. The size
distribution reveals a significant peak at about 60 parsecs if a distance
modulus of 24.27 mag is assumed. Spatial distributions of the detected
associations and H II regions are strongly correlated.Comment: 5 pages, 3 figures, A&A accepte
The VVV Survey reveals classical Cepheids tracing a young and thin stellar disk across the Galaxy's bulge
Solid insight into the physics of the inner Milky Way is key to understanding
our Galaxy's evolution, but extreme dust obscuration has historically hindered
efforts to map the area along the Galactic mid-plane. New comprehensive
near-infrared time-series photometry from the VVV Survey has revealed 35
classical Cepheids, tracing a previously unobserved component of the inner
Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic
mid-plane, traversing across the bulge. The discovered period (age) spread of
these classical Cepheids implies a continuous supply of newly formed stars in
the central region of the Galaxy over the last 100 million years.Comment: Accepted for publication in The Astrophysical Journal Letters.
Near-IR finding charts of the Cepheids are available at the following URL:
http://www.astro.puc.cl/~idekany/pub/inner_disk_ceph_fc.pn
Properties of RR Lyrae stars in the inner regions of the Large Magellanic Cloud. II. The extended sample
All galaxies that have been adequately examined so far have shown an extended
stellar halo. To search for such a halo in the LMC we have obtained
low-resolution spectra for 100 LMC RR Lyrae stars, of which 87 are in the field
and 13 in the clusters NGC1835 and NGC2019. We measured radial velocities for
87 LMC RR Lyrae stars, and metallicities for 78 RR Lyrae stars, nearly tripling
the previous sample. These targets are located in 10 fields covering a wide
range of distances, out to 2.5 degrees from the center of the LMC. Our main
result is that the mean velocity dispersion for the LMC RR Lyrae stars is
50+-2km/s. This quantity does not appear to vary with distance from the LMC
center. The metallicity shows a Gaussian distribution, with mean
[Fe/H]=-1.53+-0.02dex, and dispersion 0.20 dex in the Harris metallicity scale,
confirming that they represent a very homogeneous metal-poor population. There
is no dependence between the kinematics and metallicity of the field RR Lyrae
star population. Using good quality low-resolution spectra from FORS1, FORS2
and GEMINI-GMOS we have found that field RR Lyrae stars in the LMC show a large
velocity dispersion and that this indicate the presence of old and metal-poor
stellar halo. All the evidence so far for the halo, however, is from the
spectroscopy of the inner LMC regions, similar to the inner flattened halo in
our Galaxy. Further study is necessary to confirm this important result.Comment: 12 pages, 4 figure
Long-term Stellar Variability in the Galactic Centre Region
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.We report the detection of variable stars within a 11.5' x 11.5' region near the Galactic centre (GC) that includes the Arches and Quintuplet clusters, as revealed by the VISTA Variables in the Via Lactea (VVV) survey. There are 353 sources that show Ks-band variability, of which the large majority (81%) correspond to red giant stars, mostly in the asymptotic giant branch (AGB) phase. We analyze a population of 52 red giants with long-term trends that cannot be classified into the typical pulsating star categories. Distances and extinctions are calculated for 9 Mira variables, and we discuss the impact of the chosen extinction law on the derived distances. We also report the presence of 48 new identified young stellar object (YSO) candidates in the region.Peer reviewe
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