1,585 research outputs found
Morphological transformation of NGC 205?
NGC 205 is a dwarf elliptical galaxy which shows many features that are more
typical of disk galaxies, and our recent study of the central stellar
population has added another peculiarity. In the central regions, star
formation has been on-going continuously for a few hundred Myr, until ca. 20
Myr ago, perhaps fed by gas funneled to the center in the course of
morphological transformation. In this contribution we use a deep, wide-field
image obtained at a scale of 2"/px to show that subtle structures can be
detected in and near the body of the dwarf galaxy. The southern tidal tail can
be mapped out to unprecedented distances from the center, and we suggest that
the northern tail is partially hidden behind a very extended dust lane, or
ring, belonging to M31. A spiral pattern emerges across the body of the galaxy,
but it might be explained by another M31 dust filament.Comment: 2 pages, 1 figure, poster contributed to IAU Symposium 262, Stellar
Populations -- Planning for the Next Decade, G. Bruzual & S. Charlot, ed
Abundance analysis of red clump stars in the old, inner disc, open cluster NGC 4337: a twin of NGC 752?
Open star clusters older than ~ 1 Gyr are rare in the inner Galactic disc.
Still, they are objects that hold crucial information for probing the chemical
evolution of these regions of the Milky Way. We aim at increasing the number of
old open clusters in the inner disc for which high-resolution metal abundances
are available. Here we report on NGC 4337, which was recently discovered to be
an old, inner disc open cluster. We present the very first high-resolution
spectroscopy of seven clump stars that are all cluster members. We performed a
detailed abundance analysis for them. We find that NGC 4337 is marginally more
metal-rich than the Sun, with [Fe/H]=+0.120.05. The abundance ratios of
-elements are generally solar. At odds with recent studies on
intermediate-age and old open clusters in the Galactic disc, Ba is
under-abundant in NGC 4337 compared with the Sun. Our analysis of the iron-peak
elements (Cr and Ni) does not reveal anything anomalous. Based on these
results, we estimate the cluster age to be 1.6 Gyr, and derive
a reddening E(B-V)=0.230.05, and an apparent distance modulus
. Its distance to the Galactic centre is 7.6 kpc. With
this distance and metallicity, NGC 4337 fits the metallicity gradient for the
inner Galactic disc fairly well. The age and metallicity we measured make NGC
4337 a twin of the well-known old open cluster NGC 752. The red clumps of these
two clusters bear an amazing resemblance. But the main sequence of NGC 752 is
significantly more depleted in stars than that of NGC 4337. This would mean
that NGC 752 is in a much more advanced dynamical stage, being on the verge of
dissolving into the general Galactic field. Our results make NGC 4337 an
extremely interesting object for further studies of stellar evolution in the
critical turn-off mass range 1.1-1.4 solar masses.Comment: 7 pages, 8 eps figures, in press in Astronomy and Astrophysics. arXiv
admin note: text overlap with arXiv:1401.156
Naturalness and GUT Scale Yukawa Coupling Ratios in the CMSSM
We analyse the fine-tuning in the Constrained Minimal Supersymmetric Standard
Model (CMSSM) in the light of the present and expected ATLAS and CMS SUSY
searches. Even with 10/fb of data and no discovery of SUSY valid regions might
remain with fine-tuning less than 20. Moreover we investigate the fine-tuning
price of GUT scale Yukawa coupling relations. Considering a 2
constraint for and fine-tuning less than 30 yields an allowed range
of , which points towards the alternative GUT
prediction . Relaxing the constraint to 5
extends the possible region to [1.02,1.70], allowing for approximate
Yukawa coupling unification.Comment: 13 pages, 3 figures; version published in PR
The Earth transiting the Sun as seen from Jupiter's moons: detection of an inverse Rossiter-McLaughlin effect produced by the Opposition Surge of the icy Europa
We report on a multi-wavelength observational campaign which followed the
Earth's transit on the Sun as seen from Jupiter on 5 Jan the 2014. Simultaneous
observations of Jupiter's moons Europa and Ganymede obtained with HARPS from La
Silla, Chile, and HARPS-N from La Palma, Canary Islands, were performed to
measure the Rossiter-McLaughlin effect due to the Earth's passage using the
same technique successfully adopted for the 2012 Venus Transit (Molaro et al
2013). The expected modulation in radial velocities was of about 20 cm/s but an
anomalous drift as large as 38 m/s, i.e. more than two orders of magnitude
higher and opposite in sign, was detected instead. The consistent behaviour of
the two spectrographs rules out instrumental origin of the radial velocity
drift and BiSON observations rule out the possible dependence on the Sun's
magnetic activity. We suggest that this anomaly is produced by the Opposition
Surge on Europa's icy surface, which amplifies the intensity of the solar
radiation from a portion of the solar surface centered around the crossing
Earth which can then be observed as a a sort of inverse Rossiter-McLaughling
effect. in fact, a simplified model of this effect can explain in detail most
features of the observed radial velocity anomalies, namely the extensions
before and after the transit, the small differences between the two
observatories and the presence of a secondary peak closer to Earth passage.
This phenomenon, observed here for the first time, should be observed every
time similar Earth alignments occur with rocky bodies without atmospheres. We
predict it should be observed again during the next conjunction of Earth and
Jupiter in 2026.Comment: 9 pages, 7 figure
Updated properties of the old open cluster Melotte 66: Searching for multiple stellar populations
Multiple generations of stars are routinely encountered in globular clusters
but no convincing evidence has been found in Galactic open clusters to date. In
this paper we use new photometric and spectroscopic data to search for multiple
stellar population signatures in the old, massive open cluster, Melotte~66. The
cluster is known to have a red giant branch wide in color, which could be an
indication of metallicity spread. Also the main sequence is wider than what is
expected from photometric errors only. This evidence might be associated with
either differential reddening or binaries. Both hypothesis have, however, to be
evaluated in detail before recurring to the presence of multiple stellar
populations. New, high-quality, CCD UBVI photometry have been acquired to this
aim with high-resolution spectroscopy of seven clump stars, that are
complemented with literature data. Our photometric study confirms that the
width of the main sequence close to the turn off point is entirely accounted
for by binary stars and differential reddening, with no need to advocate more
sofisticated scenarios, such as metallicity spread or multiple main sequences.
By constructing synthetic color-magnitude diagrams, we infer that the binary
fraction has to be as large as 30 and their mass ratio in the range 0.6-1.0.
As a by-product of our simulations, we provide new estimates of the cluster
fundamental parameters. We measure a reddening E(B-V)=0.150.02, and
confirm the presence of a marginal differential reddening. The distance to the
cluster is kpc and the age is 3.40.3 Gyr, which is
somewhat younger and better constrained than previous estimates. Our detailed
abundance analysis reveals that, overall, Melotte~66 looks like a typical
object of the old thin disk population.Comment: 14 pages, 18 eps figure, in press in Astronomy and Astrophysics.
Abstract shortened to fit arXiv constraint
Chemical abundance analysis of the old, rich open cluster Trumpler 20
Trumpler 20 is an open cluster located at low Galactic longitude, just beyond
the great Carina spiral arm, and whose metallicity and fundamental parameters
were very poorly known until now. As it is most likely a rare example of an
old, rich open cluster -- possibly a twin of NGC 7789 -- it is useful to
characterize it. To this end, we determine here the abundance of several
elements and their ratios in a sample of stars in the clump of Trumpler 20. The
primary goal is to measure Trumpler 20 metallicity, so far very poorly
constrained, and revise the cluster's fundamental parameters. We present
high-resolution spectroscopy of eight clump stars. Based on their radial
velocities, we identify six bona fide cluster members, and for five of them
(the sixth being a fast rotator) we perform a detailed abundance analysis.
We find that Trumpler 20 is slightly more metal-rich than the Sun, having
[Fe/H]=+0.090.10. The abundance ratios of alpha-elements are generally
solar. In line with recent studies of clusters as old as Trumpler 20, Ba is
overabundant compared to the Sun. Our analysis of the iron-peak elements (Cr
and Ni) does not reveal anything anomalous. Based on these results, we
re-estimate the cluster age to be 1.5 Gyr. Its distance to the
Galactic centre turns out to be 7.3 kpc. With this distance and metallicity,
Trumpler 20 fits fairly well in the metallicity gradient for the galactic inner
disc. With this new study, the characterization of Trumpler~20 is now on much
more solid ground. Further studies should focus on the estimate of the binary
fraction and on its main sequence membership.Comment: 13 pages, 6 eps figures, in press in Astronomy and Astrophysic
The photospheric solar oxygen project: II. Non-concordance of the oxygen abundance derived from two forbidden lines
In the Sun, the two forbidden [OI] lines at 630 and 636 nm were previously
found to provide discrepant oxygen abundances. aims: We investigate whether
this discrepancy is peculiar to the Sun or whether it is also observed in other
stars. method: We make use of high-resolution, high signal-to-noise ratio
spectra of four dwarf to turn-off stars, five giant stars, and one sub-giant
star observed with THEMIS, HARPS, and UVES to investigate the coherence of the
two lines. results: The two lines provide oxygen abundances that are
consistent, within observational errors, in all the giant stars examined by us.
On the other hand, for the two dwarf stars for which a measurement was
possible, for Procyon, and for the sub-giant star Capella, the 636 nm line
provides systematically higher oxygen abundances, as already seen for the Sun.
conclusions: The only two possible reasons for the discrepancy are a serious
error in the oscillator strength of the NiI line blending the 630 nm line or
the presence of an unknown blend in the 636 nm line, which makes the feature
stronger. The CN lines blending the 636 nm line cannot be responsible for the
discrepancy. The CaI autoionisation line, on the red wing of which the 636 nm
line is formed, is not well modelled by our synthetic spectra. However, a
better reproduction of this line would result in even higher abundances from
the 636 nm, thus increasing the discrepancy.Comment: A&A accepte
Multi-agent quality of experience control
In the framework of the Future Internet, the aim of the Quality of Experience (QoE) Control functionalities is to track the personalized desired QoE level of the applications. The paper proposes to perform such a task by dynamically selecting the most appropriate Classes of Service (among the ones supported by the network), this selection being driven by a novel heuristic Multi-Agent Reinforcement Learning (MARL) algorithm. The paper shows that such an approach offers the opportunity to cope with some practical implementation problems: in particular, it allows to face the so-called âcurse of dimensionalityâ of MARL algorithms, thus achieving satisfactory performance results even in the presence of several hundreds of Agents
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