958 research outputs found
CNO abundances in the Galactic bulge
The carbon, nitrogen, and oxygen abundances and trends in the bulge are
discussed in the context of our recent analysis of these elements in an
on-going project based on near-IR spectra (Ryde et al. 2009). We obtained these
using the CRIRES spectrometer on the VLT. The formation and evolution of the
Milky Way bulge can be constrained by studying elemental abundances of bulge
stars. Due to the large and variable visual extinction in the line-of-sight
towards the bulge, an analysis in the near-IR is preferred.Comment: Contributed talk at Chemical Abundances in the Universe, Connecting
First Stars to Planets, Proceedings of the International Astronomical Union,
IAU Symposium, Volume 265, K. Cunha, M. Spite and B. Barbuy, eds, Cambridge
University Press, in pres
NTT infrared imaging of star cluster candidates towards the central parts of the Galaxy
We address the issue whether the central parts of the Galaxy harbour young
clusters other than Arches, Quintuplet and the Nuclear Young Cluster. A large
sample of centrally projected cluster candidates has been recently identified
from the 2MASS J, H and Ks Atlas. We provide a catalogue of higher angular
resolution and deeper images for 57 2MASS cluster candidates, obtained with the
near-IR camera SOFI at the ESO NTT telescope. We classify 10 objects as star
clusters, some of them deeply embedded in gas and/or dust clouds. Three other
objects are probably star clusters, although the presence of dust in the field
does not exclude the possibility of their being field stars seen through
low-absorption regions. Eleven objects are concentrations of stars in areas of
little or no gas, and are classified as dissolving cluster candidates. Finally,
31 objects turned out to be the blend of a few bright stars, not resolved as
such in the low resolution 2MASS images. By combining the above results with
other known objects we provide an updated sample of 42 embedded clusters and
candidates projected within 7 degrees. As a first step we study Object 11 of
Dutra & Bica (2000) projected at approximately 1 degree from the nucleus. We
present H and Ks photometry and study the colour-magnitude diagram and
luminosity function. Object 11 appears to be a less massive cluster than Arches
or Quintuplet, and it is located at a distance from the Sun d=8 kpc, with a
visual absorption Av=15.Comment: accepted to A&A, 9 pages, 10 figure
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS III. The first global photometric metallicity map of the Galactic bulge
We investigate the large scale metallicity distribution in the Galactic
bulge, using a large spatial coverage, in order to constrain the bulge
formation scenario. We use the VISTA variables in the Via Lactea (VVV) survey
data and 2MASS photometry, covering 320 sqdeg of the Galactic bulge, to derive
photometric metallicities by interpolating of the (J-Ks)0 colors of individual
Red Giant Branch stars based on a set of globular cluster ridge lines. We then
use this information to construct the first global metallicity map of the bulge
with a resolution of 30'x45'. The metallicity map of the bulge revealed a clear
vertical metallicity gradient of ~0.04 dex/deg (~0.28 dex/kpc), with metal-rich
stars ([Fe/H]~0) dominating the inner bulge in regions closer to the galactic
plane (|b|<5). At larger scale heights, the mean metallicity of the bulge
population becomes significantly more metal-poor. This fits in the scenario of
a boxy-bulge originated from the vertical inestability of the Galactic bar,
formed early via secular evolution of a two component stellar disk. Older,
metal-poor stars dominate at higher scale heights due to the non-mixed orbits
from the originally hotter thick disk stars.Comment: Accepted for publication in A&
DISCOVERY OF RR LYRAE STARS IN THE NUCLEAR BULGE OF THE MILKY WAY
Indexación: Web of ScienceGalactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.http://iopscience.iop.org/article/10.3847/2041-8205/830/1/L14/meta;jsessionid=2531FBFFF06C9ECBA4852FB9D1F89851.c1.iopscience.cld.iop.or
HST NICMOS Photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4
We present results from NICMOS Hubble Space Telescope observations of the
reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan
4, obtained through the filters F110W and F160W (nearly equivalent to J and H).
For the first time the turnoff region of Liller 1 and the main sequence of
Terzan 5 and Terzan 4 are reached, as well as the horizontal branch of UKS 1.
The magnitude difference between the turnoff and the red horizontal branch
is used as an age indicator. From
comparisons with new isochrones in the NICMOS photometric system, we conclude
that the two metal-rich clusters NGC 6528 and Terzan 5 are coeval within
uncertainties () with 47 Tucanae. Liller 1 and UKS 1 are confirmed as
metal-rich globular clusters. Terzan 4 is confirmed as an interesting case of a
metal-poor cluster in the bulge with a blue horizontal branch.Comment: 7 pages, 6 figures, accepted for publication in A&
Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way
The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios
Mass accretion rates from multi-band photometry in the Carina Nebula: the case of Trumpler 14
We present a study of the mass accretion rates of pre-Main Sequence (PMS)
stars in the cluster Trumpler 14 (Tr14) in the Carina Nebula. Using optical
multi-band photometry we were able to identify 356 PMS stars showing H-alpha
excess emission with equivalent width EW(H-alpha)>20\AA. We interpret this
observational feature as indication that these objects are still actively
accreting gas from their circumstellar medium. From a comparison of the HR
diagram with PMS evolutionary models we derive ages and masses of the PMS
stars. We find that most of the PMS objects are younger than 10 Myr with a
median age of ~3 Myr. Surprisingly, we also find that ~20% of the mass
accreting objects are older than 10 Myr. For each PMS star in Trumpler 14 we
determine the mass accretion rate () and discuss its dependence
on mass and age. We finally combine the optical photometry with near-IR
observations to build the spectral energy distribution (SED) for each PMS star
in Tr14. The analysis of the SEDs suggests the presence of transitional discs
in which a large amount of gas is still present and sustains accretion onto the
PMS object at ages older than 10 Myr. Our results, discussed in light of recent
recent discoveries with Herschel of transitional discs containing a massive gas
component around the relatively old PSM stars TW Hydrae, 49 Ceti, and HD 95086,
support a new scenario in which old and evolved debris discs still host a
significant amount of gas.Comment: 12 pages, 13 figures, accepted for publication on A&
The Red Giant Branch in Near-Infrared Colour-Magnitude Diagrams. II: The luminosity of the Bump and the Tip
We present new empirical calibrations of the Red Giant Branch (RGB) Bump and
Tip based on a homogeneous near-Infrared database of 24 Galactic Globular
Clusters. The luminosities of the RGB Bump and Tip in the J, H and K bands and
their dependence on the cluster metallicity have been studied, yielding
empirical relationships. By using recent transformations between the
observational and theoretical planes, we also derived similar calibrations in
terms of bolometric luminosity. Direct comparison between updated theoretical
models and observations show an excellent agreement. The empirical calibration
of the RGB Tip luminosity in the near-Infrared passbands presented here is a
fundamental tool to derive distances to far galaxies beyond the Local Group, in
view of using the new ground-based adaptive optics facilities and, in the next
future, the James Webb Space Telescope.Comment: 7 pages, 7 figures, accepted for publication in MNRA
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