5,084 research outputs found
A Megacam Survey of Outer Halo Satellites. IV. Two foreground populations possibly associated with the Monoceros substructure in the direction of NGC2419 and Koposov2
The origin of the Galactic halo stellar structure known as the Monoceros ring
is still under debate. In this work, we study that halo substructure using deep
CFHT wide-field photometry obtained for the globular clusters NGC2419 and
Koposov2, where the presence of Monoceros becomes significant because of their
coincident projected position. Using Sloan Digital Sky Survey photometry and
spectroscopy in the area surrounding these globulars and beyond, where the same
Monoceros population is detected, we conclude that a second feature, not likely
to be associated with Milky Way disk stars along the line-of-sight, is present
as foreground population. Our analysis suggests that the Monoceros ring might
be composed of an old stellar population of age t ~ 9Gyr and a new component ~
4Gyr younger at the same heliocentric distance. Alternatively, this detection
might be associated with a second wrap of Monoceros in that direction of the
sky and also indicate a metallicity spread in the ring. The detection of such a
low-density feature in other sections of this halo substructure will shed light
on its nature.Comment: 10 pages, 10 figures, accepted for publication in Ap
Correlations of Globular Cluster Properties: Their Interpretations and Uses
Correlations among the independently measured physical properties of globular
clusters (GCs) can provide powerful tests for theoretical models and new
insights into their dynamics, formation, and evolution. We review briefly some
of the previous work, and present preliminary results from a comparative study
of GC correlations in the Local Group galaxies. The results so far indicate
that these diverse GC systems follow the same fundamental correlations,
suggesting a commonality of formative and evolutionary processes which produce
them.Comment: An invited review, to appear in "New Horizons in Globular Cluster
Astronomy", eds. G. Piotto, G. Meylan, S.G. Djorgovski, and M. Riello, ASPCS,
in press (2003). Latex file, 8 pages, 5 eps figures, style files include
Management of incidentally detected heart murmurs in dogs and cats
A dog or a cat has an incidentally detected heart murmur if the murmur is an unexpected discovery during a veterinary consultation that was not initially focused on the cardiovascular system. This document presents approaches for managing dogs and cats that have incidentally-detected heart murmurs, with an emphasis on murmur characteristics, signalment profiling, and multifactorial decision-making to choose an optimal course for a given patient
The Environment of M85 optical transient 2006-1: constraints on the progenitor age and mass
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of
the small family of V838 Mon-like objects, whose nature is still a mystery.
This event took place in the Virgo cluster of galaxies and peaked at an
absolute magnitude of I~-13. Here we present Hubble Space Telescope images of
M85 OT 2006-1 and its environment, taken before and after the eruption, along
with a spectrum of the host galaxy at the transient location. We find that the
progenitor of M85 OT 2006-1 was not associated with any star forming region.
The g and z-band absolute magnitudes of the progenitor were fainter than about
-4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on
the age of the youngest stars at the location of the progenitor that
corresponds to a mass of <7 solar mass. Previously published line indices
suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is
representative of the progenitor of M85 OT 2006-1, then we can further
constrain its mass to be less than 2 solar mass. We compare the energetics and
mass limit derived for the M85 OT 2006-1 progenitor with those expected from a
simple model of violent stellar mergers. Combined with further modeling, these
new clues may ultimately reveal the true nature of these puzzling events.Comment: 4 pages, accepted to Ap
The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
We describe a program to measure surface brightness fluctuation (SBF)
distances to galaxies observed in the Next Generation Virgo Cluster Survey
(NGVS), a photometric imaging survey covering of the Virgo cluster
in the bandpasses with the Canada-France Hawaii Telescope. We
describe the selection of the sample galaxies, the procedures for measuring the
apparent -band SBF magnitude , and the calibration of the absolute
as a function of observed stellar population properties. The
multi-band NGVS data set provides multiple options for calibrating the SBF
distances, and we explore various calibrations involving individual color
indices as well as combinations of two different colors. Within the color range
of the present sample, the two-color calibrations do not significantly improve
the scatter with respect to wide-baseline, single-color calibrations involving
. We adopt the calibration as reference for the present
galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack
good photometry, we use an alternative relation based on a combination
of and colors, with only a slightly larger observed scatter of
0.12 mag. The agreement of our measurements with the best existing distance
estimates provides confidence that our measurements are accurate. We present a
preliminary catalog of distances for 89 galaxies brighter than
mag within the survey footprint, including members of the background M and W
Clouds at roughly twice the distance of the main body of the Virgo cluster. The
extension of the present work to fainter and bluer galaxies is in progress.Comment: ApJ accepte
The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
Low surface brightness galaxies (LSBGs) represent a significant percentage of
local galaxies but their formation and evolution remain elusive. They may hold
crucial information for our understanding of many key issues (i.e., census of
baryonic and dark matter, star formation in the low density regime, mass
function). The most massive examples - the so called giant LSBGs - can be as
massive as the Milky Way, but with this mass being distributed in a much larger
disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known.
We attempt to bring new insights on its structure and evolution on the basis of
new images covering a wide range in wavelength. We have computed surface
brightness profiles (and average surface brightnesses in 16 regions of
interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these
data to various models, testing a variety of assumptions concerning the
formation and evolution of Malin 1. We find that the surface brightness and
color profiles can be reproduced by a long and quiet star-formation history due
to the low surface density; no significant event, such as a collision, is
necessary. Such quiet star formation across the giant disk is obtained in a
disk model calibrated for the Milky Way, but with an angular momentum
approximately 20 times larger. Signs of small variations of the star-formation
history are indicated by the diversity of ages found when different regions
within the galaxy are intercompared.For the first time, panchromatic images of
Malin 1 are used to constrain the stellar populations and the history of this
iconic example among giant LSBGs. Based on our model, the extreme disk of Malin
1 is found to have a long history of relatively low star formation (about 2
Msun/yr). Our model allows us to make predictions on its stellar mass and
metallicity.Comment: Accepted in Astronomy and Astrophysic
The Next Generation Virgo Cluster Survey. VII. The intrinsic shapes of low-luminosity galaxies in the core of the Virgo cluster, and a comparison with the Local Group
(Abridged) We investigate the intrinsic shapes of low-luminosity galaxies in
the central 300 kpc of the Virgo cluster using deep imaging obtained as part of
the NGVS. We build a sample of nearly 300 red-sequence cluster members in the
yet unexplored magnitude range. The observed distribution of
apparent axis ratios is then fit by families of triaxial models with
normally-distributed intrinsic ellipticities and triaxialities. We develop a
Bayesian framework to explore the posterior distribution of the model
parameters, which allows us to work directly on discrete data, and to account
for individual, surface brightness-dependent axis ratio uncertainties. For this
population we infer a mean intrinsic ellipticity E=0.43, and a mean triaxiality
T=0.16. This implies that faint Virgo galaxies are best described as a family
of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57.
We additionally attempt a study of the intrinsic shapes of Local Group
satellites of similar luminosities. For the LG population we infer a slightly
larger mean intrinsic ellipticity E=0.51, and the paucity of objects with round
apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. We
finally compare the intrinsic shapes of NGVS low-mass galaxies with samples of
more massive quiescent systems, and with field, star-forming galaxies of
similar luminosities. We find that the intrinsic flattening in this
low-luminosity regime is almost independent of the environment in which the
galaxy resides--but there is a hint that objects may be slightly rounder in
denser environments. The comparable flattening distributions of low-luminosity
galaxies that have experienced very different degrees of environmental effects
suggests that internal processes are the main drivers of galaxy structure at
low masses--with external mechanisms playing a secondary role.Comment: Accepted to ApJ. 18 pages, 12 figure
Mise en place de l'extraction liquide-liquide en microsystèmes établir des écoulements segmentés à façon pour optimiser le transfert de masse
National audienceLiquid-liquid extraction is commonly used for radiochemical analysis. When miniaturized, it can benefitfrom the advantages of microfluidic tools i.e. possible coupling, precise control of the interfacial areabetween the aqueous and organic phases, and contact time. A first study, dedicated to liquid-liquidextraction with parallel flows of europium diluted in nitric acid by the N,N′-dimethyl-N,N′-dibutyltetradecylmalonic diamide [1, 2], allowed us to highlight the limitations of parallel flows for aslow chemical system. One way to optimize yields of extraction of the kinetically slow systems is toincrease the specific interfacial area. For this reason, segmented flows formation and characteristicswere investigated, as a function of the physicochemical properties of a biphasic system, flow rates andthe dimensions of a focalized flux junction. In the following, two multiphase models of the droplets sizecorresponding to the transition and dripping regimes were validated and will be used for theoptimization of the specific interfacial area.L’extraction liquide-liquide est couramment utilisée pour les analyses radiochimiques. Miniaturisée,elle peut bénéficier des avantages des outils microfluidiques qui sont la possibilité de réaliser descouplages, le contrôle précis de l’aire interfaciale entre les phases aqueuse et organique en présence,et des temps de contact. Une première étude, dédiée à l’extraction liquide-liquide en flux parallèlesd’europium en milieu nitrique par le N,N’-dimethyl N,N’-dibutyl tetradecylmalonamide [1, 2], a permisde mettre en évidence les limitations des flux parallèles pour un système chimique lent. Une façond’optimiser les rendements d’extraction des systèmes cinétiquement lents est de mettre en œuvre desécoulements permettant d’augmenter l’aire interfaciale spécifique. C’est pourquoi nous étudions laformation d’écoulements segmentés à façon en fonction des propriétés physico-chimiques d’un systèmechimique biphasique, des débits et des dimensions d’une jonction en flux focalisé. L’utilisation de deuxmodèles de calcul des tailles de gouttes en régimes d’écoulements transitoire
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