3,842 research outputs found
Elemental Abundance Ratios in Stars of the Outer Galactic Disk. II. Field Red Giants
We summarize a selection process to identify red giants in the direction of
the southern warp of the Galactic disk, employing VI_C photometry and
multi-object spectroscopy. We also present results from follow-up
high-resolution, high-S/N echelle spectroscopy of three field red giants,
finding [Fe/H] values of about -0.5. The field stars, with Galactocentric
distances estimated at 10 to 15 kpc, support the conclusion of Yong, Carney, &
de Almeida (2005) that the Galactic metallicity gradient disappears beyond R_GC
values of 10 to 12 kpc for the older stars and clusters of the outer disk. The
field and cluster stars at such large distances show very similar abundance
patterns, and, in particular, all show enhancements of the "alpha" elements O,
Mg, Si, Ca, and Ti and the r-process element Eu. These results suggest that
Type II supernovae have been significant contributors to star formation in the
outer disk relative to Type Ia supernovae within the past few Gyrs. We also
compare our results with those available for much younger objects. The limited
results for the H II regions and B stars in the outer disk also suggest that
the radial metallicity gradient in the outer disk is shallow or absent. The
much more extensive results for Cepheids confirm these trends, and that the
change in slope of the metallicity gradient may occur at a larger
Galactocentric distance than for the older stars and clusters. However, the
younger stars also show rising alpha element enhancements with increasing R_GC,
at least beyond 12 kpc. These trends are consistent with the idea of a
progressive growth in the size of the Galactic disk with time, and episodic
enrichment by Type II supernovae as part of the disk's growth. [Abridged]Comment: Accepted for publication in A
Observable Signatures of Planet Accretion in Red Giant Stars I: Rapid Rotation and Light Element Replenishment
The orbital angular momentum of a close-orbiting giant planet can be
sufficiently large that, if transferred to the envelope of the host star during
the red giant branch (RGB) evolution, it can spin-up the star's rotation to
unusually large speeds. This spin-up mechanism is one possible explanation for
the rapid rotators detected among the population of generally slow-rotating red
giant stars. These rapid rotators thus comprise a unique stellar sample
suitable for searching for signatures of planet accretion in the form of
unusual stellar abundances due to the dissemination of the accreted planet in
the stellar envelope. In this study, we look for signatures of replenishment in
the Li abundances and (to a lesser extent) 12C/13C, which are both normally
lowered during RGB evolution. Accurate abundances were measured from high
signal-to-noise echelle spectra for samples of both slow and rapid rotator red
giant stars. We find that the rapid rotators are on average enriched in lithium
compared to the slow rotators, but both groups of stars have identical
distributions of 12C/13C within our measurement precision. Both of these
abundance results are consistent with the accretion of planets of only a few
Jupiter masses. We also explore alternative scenarios for understanding the
most Li-rich stars in our sample---particularly Li regeneration during various
stages of stellar evolution. Finally, we find that our stellar samples show
non-standard abundances even at early RGB stages, suggesting that initial
protostellar Li abundances and 12C/13C may be more variable than originally
thought.Comment: Accepted for publication in the Astrophysical Journal. 29 pages in
emulateapj format, including 16 figures and 12 tables. Tables 4 and 8 are
provided in their entirety as plain text ancillary files (and will also be
available in the electronic edition of ApJ
A Study of the B-V Colour Temperature Relation
We attempt to construct a B-V colour temperature relation for stars in the
least model dependent way employing the best modern data. The fit we obtained
with the form Teff = Teff((B-V)0,[Fe/H],log g) is well constrained and a number
of tests show the consistency of the procedures for the fit. Our relation
covers from F0 to K5 stars with metallicity [Fe/H] = -1.5 to +0.3 for both
dwarfs and giants. The residual of the fit is 66 K, which is consistent with
what are expected from the quality of the present data. Metallicity and surface
gravity effects are well separated from the colour dependence. Dwarfs and
giants match well in a single family of fit, differing only in log g. The fit
also detects the Galactic extinction correction for nearby stars with the
amount E(B-V) = 0.26 +/-0.03 mag/kpc. Taking the newly obtained relation as a
reference we examine a number of B-V colour temperature relations and
atmosphere models available in the literature. We show the presence of a
systematic error in the colour temperature relation from synthetic calculations
of model atmospheres; the systematic error across K0 to K5 dwarfs is 0.04-0.05
mag in B-V, which means 0.25-0.3 mag in Mv for the K star range. We also argue
for the error in the temperature scale used in currently popular stellar
population synthesis models; synthetic colours from these models are somewhat
too blue for aged elliptical galaxies. We derive the colour index of the sun
(B-V)sun = 0.627 +/-0.018, and discuss that redder colours (e.g., 0.66-0.67)
often quoted in the literature are incompatible with the colour-temperature
relation.Comment: AASLaTeX (aaspp4.sty),36 pages (13 figures included), submitted to
Astronomical Journal, replaced (typo in author name
High resolution elemental abundance analysis of the Hyades Supercluster
The existence of a kinematically defined moving group of stars centred at U =
-40, V = -17 km/s referred to as the Hyades Supercluster, has been suggested as
the debris of an originally large star forming event, with its core being the
present day Hyades open cluster. Using high-resolution UVES spectra, we present
elemental abundances for a range of alpha, Fe-peak and neutron-capture elements
for 26 proposed supercluster stars. Our results show that the sample stars
display a heterogeneous abundance distribution, with a clump around [Fe/H] =
+0.15. We also calculate stellar radial velocities and U,V,W space velocities.
Enforcing a strict chemical and kinematical membership criteria, we find 4
supercluster stars share the Hyades open cluster abundances and kinematics,
while many of the remaining stars fit the disc field kinematics and abundance
range. We discuss our findings in the context of the Hyades supercluster being
a dispersed star-forming remnant, a stellar stream of purely dynamical origin
or a result of several processes.Comment: accepted by MNRA
Brazilian National Defence Policy: foreign policy, national security, economic growth, and technological innovation
With the worldâs ninth largest economy and comprising nearly 60% of South Americaâs GDP, 47% of its territory, and 49% of its population, Brazil has become a regional power and an important actor in world affairs over recent decades. This scenario has led the government to re-evaluate its role in the world order, resulting in the enactment of the National Defence Policy, whose objective was to consolidate the country as a regional power while at the same time addressing national security issues, promoting economic development through a series of defence programmes, restructuring the defence industrial base, fostering innovation through technology and knowledge transfer to Brazil, and indigenous research and development. However, the policyâs implementation suffers from several challenges discussed in this article, which may test the capability and competence of Brazilian policymakers, military, industrialists, and other individuals and organisations involved in its implementation
Stellar abundances and ages for metal-rich Milky Way globular clusters - Stellar parameters and elemental abundances for 9 HB stars in NGC6352
[ABRIDGED] Metal-rich globular clusters provide important tracers of the
formation of our Galaxy. Moreover, and not less important, they are very
important calibrators for the derivation of properties of extra-galactic
metal-rich stellar populations. Nonetheless, only a few of the metal-rich
globular clusters in the Milky Way have been studied using high-resolution
stellar spectra to derive elemental abundances. In this paper we present
elemental abundances for nine HB stars in the metal-rich globular cluster
NGC6352. The elemental abundances are based on high-resolution, high
signal-to-noise spectra obtained with VLT/UVES. The elemental abundances have
been derived using standard LTE calculations. We find that NGC6352 has [Fe/H]=
-0.55, is enhanced in the alpha-elements to about +0.2 dex for Ca, Si, and Ti
relative to Fe. For the iron-peak elements we find solar values. Based on the
spectroscopically derived stellar parameters we find that an E(B-V)=0.24 and
(m-M) roughly equal to 14.05 better fits the data than the nominal values. An
investigation of log(gf)-values for suitable FeI lines lead us to the
conclusion that the commonly used correction to the May et al.(1974) data
should not be employed. Note: only the postscript reproduces the finding chart
correctly.Comment: 24 pages (including on-line only table with all equivalent width
measurements), 12 figures, Accepted for publication in A&A. Note: only the
postscript reproduces the finding chart correctl
Comparing Perceptual and Computational Complexity for Short Rhythmic Patterns
According to Leibniz âMusic is the hidden arithmetical exercise of a mind unconscious that it is calculating.â The perception or experience of time is an essential aspect of listenersâ engagement with music. As such listenersâ experience of rhythmic patterns and their aesthetic response can enhance our understanding of the perception of time. Studies by Berlyne suggest that aesthetic evaluations are low for stimuli that are too simple or too complex with a preference for intermediate level of complexity. In musical terms we would expect listeners to respond negatively to music that is purely repetitive or to music that seems incomprehensibly random and to prefer music that manages to balance familiarity with variation. We present a study that aims to match listenersâ evaluation of rhythmic complexity with computational measures of complexity. We selected five measures derived from information theory - Shannon's entropy, entropy rate, excess entropy, transient information, and Kolmogorov complexity. Rhythmic sequences, covering a wide spectrum of complexity levels according to these measures, were generated algorithmically as binary sequences. These sequences were synthesized as drum patterns with 1s as hits and 0s as rests. 32 participants were asked to guess whether the last beat of each sequence was supposed to be a drum hit or a rest. We averaged the participantsâ scores in order to assign an implicit rating of rhythm complexity to each sequence. We also obtained an explicit rating of complexity by asking the participants to rate the perceived difficulty of guessing the last beat for each sequence. Finally, the participants completed the Gold-MSI questionnaire and a shortened version of the Raven's matrices, in order to investigate the effects of musicality and visual pattern identification on the perception of rhythm complexity. The Kolmogorov complexity of the sequences was correlated with the scores on the explicit task (r=.973, p<.001), and the entropy rate of the sequences was correlated with the scores on both implicit (r=.670, p=.012) and explicit tasks (r=.909, p<.001). There was also a Kolmogorov complexity-by-musicality interaction (F=5.498, p=.026), confirming the influence of musical expertise in the perception of rhythm complexity. There was no effect of the scores on the Raven's matrices, showing that auditory sequence perception and visual pattern identification seem to be different abilities. These results show that information-theoretical concepts capture some salient features of rhythm perception, and provide the framework for further studies on the aesthetic perception of rhythm
Main competencies to manage complex defence projects
This research adds a comprehensive way of assessing competencies, contrasting with the usual reductionist approach that uses off-the-shelf instruments. The study reveals 27 competencies to manage complex projects based upon a comprehensive analysis of 22 interviews with senior practitioners associated with the most strategic projects from the Brazilian Army. These competencies were divided into 10 groups, namely influencing, communication, team working, cognitive, management, contextual skills, professionalism, project management knowledge, and personal skills and attributes. Surprisingly, both emotional skills and social competencies were not prominent. The results contribute to advance our knowledge by revealing that practitioners involved in complex defence projects value more technical and individual competencies. This study analyses competencies across several complex projects in the defence sector, providing insights to practitioners and expanding the academic debate focused on other industries and single cases. Organisations might use the competencies to recruit, select, and develop human resources involved in complex defence initiatives
Bolometric correction and spectral energy distribution of cool stars in Galactic clusters
We have investigated the relevant trend of the bolometric correction (BC) at
the cool-temperature regime of red giant stars and its possible dependence on
stellar metallicity. Our analysis relies on a wide sample of optical-infrared
spectroscopic observations, along the 3500A-2.5micron wavelength range, for a
grid of 92 red giant stars in five (3 globular + 2 open) Galactic clusters,
along the -2.2<[Fe/H]<+0.4 metallicity range. Bolometric magnitudes have been
found within an internal accuracy of a few percent. Making use of our new
database, we provide a set of fitting functions for the V and K BC vs. Teff and
broad-band colors, valid over the interval 3300K<Teff<5000K, especially suited
for Red Giants. No evident drift of both BC(V) and BC(K) with [Fe/H] is found.
Things may be different, however, for the B-band correction, given a clear
(B-V) vs. [Fe/H] correlation in place for our data, with metal-poor stars
displaying a "bluer" (B-V) with respect to the metal-rich sample, for fixed
Teff. Our empirical bolometric scale supports the conclusion that (a) BC(K)
from the most recent studies are reliable within <0.1 mag over the whole
color/temperature range considered in this paper, and (b) the same conclusion
apply to BC(V) only for stars warmer than ~3800K. At cooler temperatures the
agreement is less general, and MARCS models are the only ones providing a
satisfactory match to observations.Comment: 18 pages with 12 color figures and 12 tables. To appear in the MNRAS.
Full spectral catalog of stars available at
http://www.bo.astro.it/~eps/home.htm
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