3,031 research outputs found
Massive stars and globular cluster formation
We first present chemodynamical simulations to investigate how stellar winds
of massive stars influence early dynamical and chemical evolution of forming
globular clusters (GCs). In our numerical models, GCs form in
turbulent,high-density giant molecular clouds (GMCs), which are embedded in a
massive dark matter halo at high redshifts. We show how high-density, compact
stellar systems are formed from GMCs influenced both by physical processes
associated with star formation and by tidal fields of their host halos. We also
show that chemical pollution of GC-forming GMCs by stellar winds from massive
stars can result in star-to-star abundance inhomogeneities among light elements
(e.g., C, N, and O) of stars in GCs. The present model with a canonical initial
mass function (IMF) also shows a C-N anticorrelation that stars with smaller
[C/Fe] have larger [N/Fe] in a GC. Although these results imply that
``self-pollution'' of GC-forming GMCs by stellar winds from massive stars can
cause abundance inhomogeneities of GCs, the present models with different
parameters and canonical IMFs can not show N-rich stars with [N/Fe] ~ 0.8
observed in some GCs (e.g., NGC 6752). We discuss this apparent failure in the
context of massive star formation preceding low-mass one within GC-forming GMCs
(``bimodal star formation scenario''). We also show that although almost all
stars (~97%) show normal He abundances (Y) of ~0.24 some stars later formed in
GMCs can have Y as high as ~0.3 in some models. The number fraction of He-rich
stars with Y >0.26 is however found to be small (~10^-3) for most models.Comment: 10 pages, 8 figures, accepted by Ap
Análise do ponto de equilíbrio do mix em empresa prestadora de serviço de guincho e munck, no município de Cacoal (RO)
Trabalho de Conclusão de Curso apresentado ao Departamento Acadêmico de Ciências Contábeis da Fundação Universidade Federal de Rondônia, campus Professor Francisco Gonçalves Quiles, para obtenção do título de Bacharel em Ciências Contábeis. Orientadora: Prof.ª M.ª Liliane Nery AndradeO presente artigo apresenta os resultados de uma pesquisa realizada em maio de 2017, em uma empresa prestadora de serviços de guincho e munck, localizada no município Cacoal (RO). Esta pesquisa caracteriza-se como um estudo de caso, porque a intenção foi avaliar uma situação concreta realizando um estudo dos custos em profundidade na prestação de serviços de guincho e munck, pois teve como objetivo demonstrar como a análise os custos dos serviços prestados para contribuir para tomada de decisão em empresa de pequeno porte, e conhecer quais os serviços prestados que oferecem maior lucratividade para a empresa. Foi necessário conhecer o mix de produtos, classificarem os gastos com cada prestação de serviço ofertado, calcular o ponto de equilíbrio do mix. O cálculo do PE mix evidenciou que a empresa está trabalhando acima do seu ponto de equilíbrio, que foi obtido para os respectivos serviços. Sendo prestados 03 (três) serviços para o mecanismo operacional munck. 08 (oito) serviços para o mecanismo operacional reboque/guincho,veículo leve perímetro urbano; 03 (três) serviços para o mecanismo operacional reboque/guincho de máquinas pesadas no perímetro urbano; 01 (um) serviço para o mecanismo operacional reboque máquinas pesadas, fora do perímetro urbano com de média de 20km conforme exemplo 1: Riozinho; 05 (cinco) serviços para o mecanismo operacional reboque máquinas pesadas,fora do perímetro urbano com média de 50km conforme exemplo 2: LH Mato Grosso e de 02 (dois) serviços para o mecanismo operacional reboque máquinas pesadas,fora do perímetro urbano com média 120km conforme exemplo 3: Rolim de Moura. O resultado da pesquisa conforme simulação do cálculo do PE mix em unidade revelou que caso a empresa em estudo decida trabalhar apenas com veículos leves será necessário que preste 40 serviços já que o PE obtido foi de aproximadamente 67(sessenta e sete),serviços. Dessa maneira, a margem de contribuição seria menor que o total dos gastos fixos, aumentando o PE e diminuindo muito a margem de contribuição total para a empresa, esta simulação demonstra não ser vantajosa para a empresa
Comparative study of the Martian suprathermal electron depletions based on Mars Global Surveyor, Mars Express and Mars Atmosphere and Volatile EvolutioN missions observations
Nightside suprathermal electron depletions have been observed at Mars by three spacecraft to date: Mars Global Surveyor, Mars Express, and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. This spatial and temporal diversity of measurements allows us to propose here a comprehensive view of the Martian electron depletions through the first multispacecraft study of the phenomenon. We have analyzed data recorded by the three spacecraft from 1999 to 2015 in order to better understand the distribution of the electron depletions and their creation mechanisms. Three simple criteria adapted to each mission have been implemented to identify more than 134,500 electron depletions observed between 125 and 900 km altitude. The geographical distribution maps of the electron depletions detected by the three spacecraft confirm the strong link existing between electron depletions and crustal magnetic field at altitudes greater than ~170 km. At these altitudes, the distribution of electron depletions is strongly different in the two hemispheres, with a far greater chance to observe an electron depletion in the Southern Hemisphere, where the strongest crustal magnetic sources are located. However, the unique MAVEN observations reveal that below a transition region near 160–170 km altitude the distribution of electron depletions is the same in both hemispheres, with no particular dependence on crustal magnetic fields. This result supports the suggestion made by previous studies that these low-altitudes events are produced through electron absorption by atmospheric CO2
The Massive Stellar Population in the Young Association LH 95 in the LMC
We present a spectroscopic study of the most massive stars in the young (4
Myr old) stellar cluster LH 95 in the Large Magellanic Cloud. This analysis
allows us to complete the census of the stellar population of the system,
previously investigated by us down to 0.4 solar masses with deep HST Advanced
Camera for Surveys photometry. We perform spectral classification of the five
stars in our sample, based on high resolution optical spectroscopy obtained
with 2.2m MPG/ESO FEROS. We use complementary ground-based photometry,
previously performed by us, to place these stars in the Hertzsprung-Russel
diagram. We derive their masses and ages by interpolation from evolutionary
models. The average ages and age spread of the most massive stars are found to
be in general comparable with those previously derived for the cluster from its
low mass PMS stars. We use the masses of the 5 sample stars to extend to the
high-mass end the stellar initial mass function of LH 95 previously established
by us. We find that the initial mass function follows a Salpeter relation down
to the intermediate-mass regime at 2 Msun. The second most massive star in LH
95 shows broad Balmer line emission and infrared excess, which are compatible
with a classical Be star. The existence of such a star in the system adds a
constrain to the age of the cluster, which is well covered by our age and age
spread determinations. The most massive star, a 60-70 Msun O2 giant is found to
be younger (<1 Myr) than the rest of the population. Its mass in relation to
the total mass of the system does not follow the empirical relation of the
maximum stellar mass versus the hosting cluster mass, making LH 95 an exception
to the average trend.Comment: 15 pages, 9 figures, MNRAS accepte
Star Cluster collisions - a formation scenario for the Extended Globular Cluster Scl-dE1 GC1
Recent observations of the dwarf elliptical galaxy Scl-dE1 (Sc22) in the
Sculptor group of galaxies revealed an extended globular cluster (Scl-dE1 GC1),
which exhibits an extremely large core radius of about 21.2 pc. The authors of
the discovery paper speculated on whether this object could reside in its own
dark matter halo and/or if it might have formed through the merging of two or
more star clusters. In this paper, we present N-body simulations to explore
thoroughly this particular formation scenario. We follow the merger of two star
clusters within dark matter haloes of a range of masses (as well as in the
absence of a dark matter halo). In order to obtain a remnant which resembles
the observed extended star cluster, we find that the star formation efficiency
has to be quite high (around 33 per cent) and the dark matter halo, if present
at all, has to be of very low mass, i.e. raising the mass to light ratio of the
object within the body of the stellar distribution by at most a factor of a
few. We also find that expansion of a single star cluster following mass loss
provides another viable formation path. Finally, we show that future
measurements of the velocity dispersion of this system may be able to
distinguish between the various scenarios we have explored.Comment: accepted by MNRAS, 9 pages, 2 figures, 9 table
Power-law rheology in the bulk and at the interface: quasi-properties and fractional constitutive equations
Consumer products, such as foods, contain numerous polymeric and particulate additives that play critical roles in maintaining their stability, quality and function. The resulting materials exhibit complex bulk and interfacial rheological responses, and often display a distinctive power-law response under standard rheometric deformations. These power laws are not conveniently described using conventional rheological models, without the introduction of a large number of relaxation modes. We present a constitutive framework using fractional derivatives to model the power-law responses often observed experimentally. We first revisit the concept of quasi-properties and their connection to the fractional Maxwell model (FMM). Using Scott-Blair's original data, we demonstrate the ability of the FMM to capture the power-law response of ‘highly anomalous’ materials. We extend the FMM to describe the viscoelastic interfaces formed by bovine serum albumin and solutions of a common food stabilizer, Acacia gum. Fractional calculus allows us to model and compactly describe the measured frequency response of these interfaces in terms of their quasi-properties. Finally, we demonstrate the predictive ability of the FMM to quantitatively capture the behaviour of complex viscoelastic interfaces by combining the measured quasi-properties with the equation of motion for a complex fluid interface to describe the damped inertio-elastic oscillations that are observed experimentally.United States. National Aeronautics and Space Administration (Microgravity Fluid Sciences (Code UG) for support of this research under grant no. NNX09AV99G
Chemical composition of the Taurus-Auriga association
The Taurus-Auriga association is perhaps the most famous prototype of a
low-mass star forming region, surveyed at almost all wavelengths.
Unfortunately, like several other young clusters/associations, this T
association lacks an extensive abundance analysis determination. We present a
high-resolution spectroscopic study of seven low-mass members of Taurus-Auriga,
including both weak-lined and classical T Tauri stars designed to help robustly
determine their metallicity. After correcting for spectral veiling, we
performed equivalent width and spectral synthesis analyses using the GAIA set
of model atmospheres and the 2002 version of the code MOOG. We find a solar
metallicity, obtaining a mean value of [Fe/H]=0.05. The
-element Si and the Fe-peak one Ni confirm a solar composition. Our
work shows that the dispersion among members is well within the observational
errors at variance with previous claims. As in other star forming regions, no
metal-rich members are found, reinforcing the idea that old planet-host stars
form in the inner part of the Galactic disc and subsequently migrate.Comment: In press on A\&
Cluster vs. Field Elliptical Galaxies and Clues on their Formation
Using new observations for a sample of 931 early-type galaxies we investigate
whether the \mg2--\so relation shows any dependence on the local environment.
The galaxies have been assigned to three different environments depending on
the local overdensity: clusters, groups, and field, having used our
completeredshift database to guide the assignment of galaxies. It is found that
cluster, group and field early-type galaxies follow almost identical \mg2--\so\
relations, with the largest \mg2 zero-point difference (clusters minus field)
being only mag. No correlation of the residuals is found with
the morphological type or the bulge to disk ratio. Using stellar population
models in a differential fashion, this small zero-point difference implies a
luminosity-weighted age difference of only Gyr between the
corresponding stellar populations, with field galaxies being younger. The
mass-weighted age difference could be significantly smaller, if minor events of
late star formation took place preferentially in field galaxies. We combine
these results with the existing evidence for the bulk of stars in cluster
early-type galaxies having formed at very high redshift, and conclude that the
bulk of stars in galactic spheroids had to form at high redshifts (z\gsim 3),
no matter whether such spheroids now reside in low or high density regions. The
cosmological implications of these findings are briefly discussed.Comment: 16 pages, 2 figures, accepted for publication in the ApJ.
Line strengths of early-type galaxies
In this paper we present measurements of velocity dispersions and Lick
indices for 509 galaxies in the local Universe, based on high signal-to-noise,
long slit spectra obtained with the 1.52 m ESO telescope at La Silla. The
conversion of our measurements into the Lick/IDS system was carried out
following the general prescription of Worthey and Ottaviani 1997. Comparisons
of our measurements with those of other authors show, in general, good
agreement. We also examine the dependence between these indices (e.g., Hbeta,
Mg_2, Fe5270 and NaD) and the central velocity dispersion (sigma), and we find
that they are consistent with those previously reported in the literature.
Benefiting from the relatively large size of the sample, we are able to
investigate the dependence of these relations on morphology and environment,
here represented by the local galaxy density. We find that for metallic lines
these relations show no significant dependence on environment or morphology,
except in the case of NaD, which shows distinct behavior for E and S0. On the
other hand, the Hbeta-logsigma shows a significant difference as a function of
the local density of galaxies, which we interpret as being caused by the
truncation of star formation in high density environments. Comparing our
results with those obtained by other authors we find a few discrepancies,
adding to the ongoing debate about the nature of these relations. Finally, we
report that the scatter of the Mg indices versus sigma relations correlate with
Hbeta, suggesting that age may contribute to the scatter. Furthermore, this
scatter shows no significant dependence on morphology or environment. Our
results are consistent with the current downsizing model, where low mass
galaxies have an extended star formation history (abridged).Comment: 88 pages, 24 figures, to be published in AJ, for further information
see http://staff.on.br/ogand
Diffuse light and building history of the galaxy cluster Abell 2667
We have searched for diffuse intracluster light in the galaxy cluster Abell
2667 (z=0.233) from HST images in three filters. We have applied to these
images an iterative multi-scale wavelet analysis and reconstruction technique,
which allows to subtract stars and galaxies from the original images. We detect
a zone of diffuse emission south west of the cluster center (DS1), and a second
faint object (ComDif), within DS1. Another diffuse source (DS2) may be
detected, at lower confidence level, north east of the center. These sources of
diffuse light contribute to 10-15% of the total visible light in the cluster.
Whether they are independent entities or are part of the very elliptical
external envelope of the central galaxy remains unclear. VLT VIMOS integral
field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif
but do not allow to compute a redshift. A hierarchical substructure detection
method reveals the presence of several galaxy pairs and groups defining a
similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The
analysis of archive XMM-Newton and Chandra observations shows X-ray emission
elongated in the same direction. The X-ray temperature map shows the presence
of a cool core, a broad cool zone stretching from north to south and hotter
regions towards the north east, south west and north west. This possibly
suggests shock fronts along these directions produced by infalling material.
These various data are consistent with a picture in which diffuse sources are
concentrations of tidal debris and harassed matter expelled from infalling
galaxies by tidal stripping and undergoing an accretion process onto the
central cluster galaxy; as such, they are expected to be found along the main
infall directions.Comment: Accepted for publication in Astronomy and Astrophysic
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