5,752 research outputs found
Photometric Metallicities in Bootes I
We present new Stromgren and Washington data sets for the Bootes I dwarf
galaxy, and combine them with the available SDSS photometry. The goal of this
project is to refine a ground-based, practical, accurate method to determine
age and metallicity for individual stars in Bootes I that can be selected in an
unbiased imaging survey, without having to take spectra. We produce photometric
metallicities from Stromgren and Washington photometry, for stellar systems
with a range of . To avoid the decrease in sensitivity of the
Stromgren metallicity index on the lower red-giant branch, we replace the
Stromgren v-filter with the broader Washington C-filter; we find that
is the most successful filter combination, for individual stars with
, to maintain ~0.2 dex -resolution over the whole
red-giant branch. We demonstrate that we can break the isochrones'
age-metallicity degeneracy with these filters, using stars with log g=2.5-3.0,
which have less than a 2% change in their -colour due to age, over a
range of 11-14 Gyr.Comment: 24 pages, 18 figures, accepted by MNRA
Uncovering Multiple Populations with Washington Photometry: I. The Globular Cluster NGC 1851
The analysis of multiple populations (MPs) in globular clusters (GCs) has
become a forefront area of research in astronomy. Multiple red giant branches
(RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been
observed photometrically in many GCs. UV photometry has been crucial in
discovering and analyzing these MPs, but the Johnson U and the Stromgren and
Sloan u filters that have generally been used are relatively inefficient and
very sensitive to reddening and atmospheric extinction. In contrast, the
Washington C filter is much broader and redder than these competing UV filters.
Here we investigate the use of the Washington system to uncover MPs using only
a 1-meter telescope. Our analysis of the well-studied GC NGC 1851 finds that
the C filter is both very efficient and effective at detecting its previously
discovered MPs in the RGB and SGB. Remarkably, we have also detected an
intrinsically broad MS best characterized by two distinct but heavily
overlapping populations that cannot be explained by binaries, field stars, or
photometric errors. The MS distribution is in very good agreement with that
seen on the RGB, with ~30% of the stars belonging to the second population.
There is also evidence for two sequences in the red horizontal branch, but this
appears to be unrelated to the MPs in this cluster. Neither of these latter
phenomena have been observed previously in this cluster. The redder MS stars
are also more centrally concentrated than the blue MS. This is the first time
MPs in a MS have been discovered from the ground, and using only a 1-meter
telescope. The Washington system thus proves to be a very powerful tool for
investigating MPs, and holds particular promise for extragalactic objects where
photons are limited.Comment: 25 pages, 10 figure
Paysages sonores, calme et bien-être dans les quartiers durables. Retours d’expériences de quartiers durables étrangers
A hot horizontal branch star with a close K-type main-sequence companion
Dynamical interactions in binary systems are thought to play a major role in
the formation of extreme horizontal branch stars (EHBs) in the Galactic field.
However, it is still unclear if the same mechanisms are at work in globular
clusters, where EHBs are predominantly single stars. Here we report on the
discovery of a unique close binary system (period ~1.61 days) in the globular
cluster NGC6752, comprising an EHB and a main-sequence companion of 0.63+-0.05
Msun. Such a system has no counterpart among nearly two hundred known EHB
binaries in the Galactic field. Its discovery suggests that either field
studies are incomplete, missing this type of systems possibly because of
selection effects, or that a particular EHB formation mechanism is active in
clusters but not in the field
Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality
We present new deep photometry of the rich globular cluster (GC) systems
around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143
(Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we
also present new reductions of similar HST/ACS data for the Coma supergiants
NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to
the radial limits of our data, comprising from 12000 to 23000 clusters per
galaxy). The metallicity distribution functions (MDFs) of the GCs can still be
matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes
are separated by ~0.8 dex, but the internal dispersions of each mode are so
large that the total MDF becomes very broad and nearly continuous from [Fe/H] =
-2.4 to Solar. There are, however, significant differences between galaxies in
the relative numbers of \emph{metal-rich} clusters, suggesting that they
underwent significantly different histories of mergers with massive, gas-rich
halos. Lastly, the proportion of metal-poor GCs rises especially rapidly
outside projected radii R > 4 R_eff, suggesting the importance of accreted
dwarf satellites in the outer halo. Comprehensive models for the formation of
GCs as part of the hierarchical formation of their parent galaxies will be
needed to trace the systematic change in structure of the MDF with galaxy mass,
from the distinctly bimodal form in smaller galaxies up to the broad continuum
that we see in the very largest systems.Comment: In press for Astrophysical Journa
Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure
Layer-by-layer oxide molecular beam epitaxy has been used to synthesize
cuprate-nickelate multilayer structures of composition
(LaCuO)/LaO/(LaNiO). In a combined experimental and
theoretical study, we show that these structures allow a clean separation of
dopant and doped layers. Specifically, the LaO layer separating cuprate and
nickelate blocks provides an additional charge that, according to density
functional theory calculations, is predominantly accommodated in the
interfacial nickelate layers. This is reflected in an elongation of bond
distances and changes in valence state, as observed by scanning transmission
electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted
charge disproportionation in the nickelate interface layers leads to a
thickness-dependent metal-to-insulator transition for , as observed in
electrical transport measurements. The results exemplify the perspectives of
charge transfer in metal-oxide multilayers to induce doping without introducing
chemical and structural disorder
Untersuchungen zur Selektion dürreresistenter Reben-Sämlinge und Beziehungen zwischen der Dürreresistenz der Unterlage und den Leistungen des Edelreises
Die Beziehungen zwischen der Dürreresistenz von Vitis-Arten, -Sorten und Sämlingen interspezifischer Kreuzungen und dem Transpirationsverhalten sowie der Wurzelstruktur, die für die Wasseraufnahme von erheblicher Bedeutung ist, wurden untersucht.An Hand eines Feldversuches, bei dem Sämlinge unterschiedlicher Dürreresistenz als Unterlagen Verwendung fanden, wurde auch die Leistungsbeeinflussung in Abhängigkeit von der Dürreresistenz der Unterlagen überprüft. Es wurde nachgewiesen, daß Sämlinge mit starker Wurzelentwicklung, insbesondere beim Vorliegen eines extensiven Wurzeltypes, überwiegend gute Dürreresistenz aufweisen. Entscheidend dafür ist insbesondere auch die Relation zwischen der Wurzel- und Triebentwicklung. Die Triebentwicklung ist eng korreliert mit den Eigenschaften des Wurzelsystems, so daß unter Berücksichtigung der Triebentwicklung selektioniert werden kann, wobei für die Vorselektion Sorten mit langen Trieben und geringer Geiztriebbildung zu berücksichtigen sind, da diese Eigenschaften mit starker Wurzelentwicklung und extensiver Wurzelstruktur korreliert sind.An Hand eines Pfropfversuches, der unter Verwendung von Kreuzungssämlingen verschiedener Dürreresistenz erstellt wurde, ließ sich nachweisen, daß Sämlinge mittlerer Dürreresistenz in den meisten Jahren besonders günstige Ertragsbeeinflussungen des Edelreises bewirken. Sämlinge mit extrem hoher Dürreresistenz erhalten nur Bedeutung für besonders trockene Lagen.Die Leistungsbeeinflussung von Edelreissorten in Abhängigkeit von der Dürreresistenz der Unterlagssorte läßt sowohl einen Einfluß der Transpirationsverhältnisse der Unterlagssorte als auch des Wasseraufnahmevermögens, also der Leistungen des Wurzelsystems, vermuten
Detailed abundances in stars belonging to ultra-faint dwarf spheroidal galaxies
We report preliminary results concerning the detailed chemical composition of
metal poor stars belonging to close ultra-faint dwarf galaxies (hereafter
UfDSphs). The abundances have been determined thanks to spectra obtained with
X-Shooter, a high efficiency spectrograph installed on one of the ESO VLT
units. The sample of ultra-faint dwarf spheroidal stars have abundance ratios
slightly lower to what is measured in field halo star of the same
metallicity.We did not find extreme abundances in our Hercules stars as the one
found by Koch for his 2 Hercules stars. The synthesis of the neutron capture
elements Ba and Sr seems to originate from the same nucleosynthetic process in
operation during the early stages of the galactic evolution.Comment: 3 pages, 1 figure; OMEG11 conference (Tokyo, Nov 2011
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