1,481 research outputs found
Globular Cluster Abundances from High-Resolution Integrated Light Spectra, I: 47 Tuc
We describe the detailed chemical abundance analysis of a high-resolution
(R~35,000), integrated-light (IL), spectrum of the core of the Galactic
globular cluster 47 Tuc, obtained using the du Pont echelle at Las Campanas. We
develop an abundance analysis strategy that can be applied to spatial
unresolved extra- galactic clusters. We have computed abundances for Na, Mg,
Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Ba, La, Nd and Eu. For an
analysis with the known color-magnitude diagram (cmd) for 47 Tuc we obtain a
mean [Fe/H] value of -0.75 +/-0.026+/-0.045 dex (random and systematic error),
in good agreement with the mean of 5 recent high resolution abundance studies,
at -0.70 dex. Typical random errors on our mean [X/Fe] ratios are 0.07-0.10
dex, similar to studies of individual stars in 47 Tuc, although Na and Al
appear enhanced, perhaps due to proton burning in the most luminous cluster
stars. Our IL abundance analysis with an unknown cmd employed theoretical
Teramo isochrones; however, we apply zero-point abundance corrections to
account for the factor of 3 underprediction of stars at the AGB bump
luminosity. While line diagnostics alone provide only mild constraints on the
cluster age (ruling-out ages younger than ~2 Gyr), when theoretical IL B-V
colors are combined with metallicity derived from the Fe I lines, the age is
constrained to 10--15 Gyr and we obtain [Fe/H]=-0.70 +/-0.021 +/-0.052 dex. We
find that Fe I line diagnostics may also be used to constrain the horizontal
branch morphology of an unresolved cluster. Lastly, our spectrum synthesis of
5.4 million TiO lines indicates that the 7300-7600A TiO window should be useful
for estimating the effect of M giants on the IL abundances, and important for
clusters more metal-rich than 47 Tuc.Comment: 40 pages text & references, 4 tables, 19 figures (72 pages total).
Changes include addition of B-V color to help constrain GC age. To appear in
Ap
WIYN Open Cluster Study 1: Deep Photometry of NGC 188
We have employed precise V and I photometry of NGC 188 at WIYN to explore the
cluster luminosity function (LF) and study the cluster white dwarfs (WDs). Our
photometry is offset by V = 0.052 (fainter) from Sandage (1962) and Eggen &
Sandage (1969). All published photometry for the past three decades have been
based on these two calibrations, which are in error by 0.05 +- 0.01. We employ
the Pinsonneault etal (1998) fiducial main sequence to derive a cluster
distance modulus of 11.43 +- 0.08. We report observations that are >= 50%
complete to V = 24.6 and find that the cluster central-field LF peaks at M_I ~
3 to 4. This is unlike the solar neighborhood LF and unlike the LFs of
dynamically unevolved portions of open and globular clusters, which rise
continuously until M_I ~ 9.5. Although we find that >= 50% of the unresolved
cluster objects are multiple systems, their presence cannot account for the
shape of the NGC 188 LF. For theoretical reasons (Terlevich 1987; Vesperini &
Heggie 1997) having to do with the survivability of NGC 188 we believe the
cluster is highly dynamically evolved and that the missing low luminosity stars
are either in the cluster outskirts or have left the cluster altogether. We
identify nine candidate WDs, of which we expect three to six are bona fide
cluster WDs. The luminosities of the faintest likely WD indicates an age
(Bergeron, Wesemael, & Beauchamp 1995) of 1.14 +- 0.09 Gyrs. This is a lower
limit to the cluster age and observations probing to V = 27 or 28 will be
necessary to find the faintest cluster WDs and independently determine the
cluster age. While our age limit is not surprising for this ~6 Gyr old cluster,
our result demonstrates the value of the WD age technique with its very low
internal errors. (abridged)Comment: 26 pages, uuencoded gunzip'ed latex + 16 postscrip figures, to be
published in A
The intermediate-age globular cluster NGC 1783 in the Large Magellanic Cloud
We present Hubble Space Telescope ACS deep photometry of the intermediate-age
globular cluster NGC 1783 in the Large Magellanic Cloud. By using this
photometric dataset, we have determined the degree of ellipticity of the
cluster (=0.140.03) and the radial density profile. This profile
is well reproduced by a standard King model with an extended core (r_c=24.5'')
and a low concentration (c=1.16), indicating that the cluster has not
experienced the collapse of the core.
We also derived the cluster age, by using the Pisa Evolutionary Library (PEL)
isochrones, with three different amount of overshooting (namely,
=0.0, 0.10 and 0.25). From the comparison of the observed
Color-Magnitude Diagram (CMD) and Main Sequence (MS) Luminosity Function (LF)
with the theoretical isochrones and LFs, we find that only models with the
inclusion of some overshooting (=0.10-0.25) are able to reproduce
the observables. By using the magnitude difference between the mean level of the He-clump and the flat
region of the SGB, we derive an age =1.40.2 Gyr.Comment: Accepted to publication by A
The Star Formation History of the Local Group dwarf galaxy Leo I
We present a quantitative analysis of the star formation history (SFH) of the
Local Group dSph galaxy Leo I, from the information in its HST [(V-I),I]
color-magnitude diagram (CMD). The method we use is based in comparing, via
synthetic CMDs, the expected distribution of stars in the CMD for different
evolutionary scenarios, with the observed distribution. We consider the SFH to
be composed by the SFR(t), the Z(t), the IMF, and a function ,
controlling the fraction and mass ratio distribution of binary stars.
The comparison between the observed CMD and the model CMDs is done through
chi-square minimization of the differences in the number of stars in a set of
regions of the CMD.
Our solution for the SFH of Leo I defines a minimum of chi-square in a well
defined position of the parameter space, and the derived SFR(t) is robust, in
the sense that its main characteristics are unchanged for different
combinations of the remaining parameters. However, only a narrow range of
assumptions for Z(t), IMF and result in a good agreement between
the data and the models, namely: Z=0.0004, a Kroupa et al. (1993) IMF or
slightly steeper, and a relatively large fraction of binary stars. Most star
formation activity (70% to 80%) occurred between 7 and 1 Gyr ago. At 1 Gyr ago,
it abruptly dropped to a negligible value, but seems to have been active until
at least ~ 300 Myr ago. Our results don't unambiguously answer the question of
whether Leo I began forming stars around 15 Gyr ago, but it appears that the
amount of this star formation, if existing at all, would be small.Comment: 25 pages + 14 figures. Accepted by The Astronomical Journa
Quantum chemical topological analysis of hydrogen bonding in HX…HX and CH3X…HX dimers (X = Br, Cl, F)
We present a systematic investigation of the nature and strength of the hydrogen bonding in HX···HX and CH3X…HX (X = Br, Cl and F) dimers using ab initio MP2/aug-cc-pVTZ calculations in the framework of the quantum theory of atoms in molecules (QTAIM) and electron localisation functions (ELFs) methods. The electron density of the complexes has been characterised, and the hydrogen bonding energy, as well as the QTAIM and ELF parameters, is consistent, providing deep insight into the origin of the hydrogen bonding in these complexes. It was found that in both linear and angular HX…HX and CH3X…HX dimers, F atoms form stronger HB than Br and Cl, but they need short (∼2 Å) X…HX contacts.The authors are grateful to FAPESP and FAPEMIG for financially supporting this research and for a scholarship (to R.A.C.), to CAPES for the scholarships (to F.A.L. and R.T.S.) and to CNPq for the fellowships (to T.C.R., M.P.F., E.F.F.C. and R.R.). J.A. also thanks Universitat Jaume I-Fundacio´n Bancaixa (Project P1.1B2010-10), Generalitat Valenciana for Prometeo/2009/053 project, Ministerio de Ciencia e Innovacio´n for project CTQ2009-14541-C02 and Programa de Cooperacio´n Cientı´fica con Iberoamerica (Brazil), Ministerio de Educacio´n (PHB2009-0065-PC)
Orbifold projection in supersymmetric QCD at N_f\leq N_c
Supersymmetric orbifold projection of N=1 SQCD with relatively small number
of flavors (not larger than the number of colors) is considered. The purpose is
to check whether orbifolding commutes with the infrared limit. On the one hand,
one considers the orbifold projection of SQCD and obtains the low-energy
description of the resulting theory. On the other hand, one starts with the
low-energy effective theory of the original SQCD, and only then perfoms
orbifolding. It is shown that at finite N_c the two low-energy theories
obtained in these ways are different. However, in the case of stabilized
run-away vacuum these two theories are shown to coincide in the large N_c
limit. In the case of quantum modified moduli space, topological solitons
carrying baryonic charges are present in the orbifolded low-energy theory.
These solitons may restore the correspondence between the two theories provided
that the soliton mass tends to zero in the large N_c limit.Comment: 10 pages; misprint corrected, reference adde
Indocyanine green fluorescence image processing techniques for breast cancer macroscopic demarcation
Re-operation due to disease being inadvertently close to the resection margin is a major challenge in breast conserving surgery (BCS). Indocyanine green (ICG) fluorescence imaging could be used to visualize the tumor boundaries and help surgeons resect disease more efficiently. In this work, ICG fluorescence and color images were acquired with a custom-built camera system from 40 patients treated with BCS. Images were acquired from the tumor in-situ, surgical cavity post-excision, freshly excised tumor and histopathology tumour grossing. Fluorescence image intensity and texture were used as individual or combined predictors in both logistic regression (LR) and support vector machine models to predict the tumor extent. ICG fluorescence spectra in formalin-fixed histopathology grossing tumor were acquired and analyzed. Our results showed that ICG remains in the tissue after formalin fixation. Therefore, tissue imaging could be validated in freshly excised and in formalin-fixed grossing tumor. The trained LR model with combined fluorescence intensity (pixel values) and texture (slope of power spectral density curve) identified the tumor’s extent in the grossing images with pixel-level resolution and sensitivity, specificity of 0.75 ± 0.3, 0.89 ± 0.2.This model was applied on tumor in-situ and surgical cavity (post-excision) images to predict tumor presence
Autonomous Bursting in a Homoclinic System
A continuous train of irregularly spaced spikes, peculiar of homoclinic
chaos, transforms into clusters of regularly spaced spikes, with quiescent
periods in between (bursting regime), by feeding back a low frequency portion
of the dynamical output. Such autonomous bursting results to be extremely
robust against noise; we provide experimental evidence of it in a CO2 laser
with feedback. The phenomen here presented display qualitative analogies with
bursting phenomena in neurons.Comment: Submitted to Phys. Rev. Lett., 14 pages, 5 figure
Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud
We present Washington system C,T_1 CMDs of 13 star clusters and their
surrounding fields which lie in the outer parts of the LMC disk. Ages are
determined by means of the magnitude difference between the giant branch clump
and the turnoff, while metallicities are derived from the location of the giant
and subgiant branches as compared to fiducial star clusters. We find that in
most cases the stellar population of each star cluster is quite similar to that
of the field where it is embedded. Three particular fields present remarkable
properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a
surrounding field which shares the same properties. (ii) The field surrounding
the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that
we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509
present CMDs with a secondary clump ~0.45 mag fainter than the dominant
intermediate age clump, suggesting a stellar population component located
behind the LMC disk at a distance comparable to that of the SMC. The mean
metallicity derived for the intermediate age outer disk clusters is
=-0.7 and for their surrounding fields =-0.6. These values are
significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a
sample of clusters of similar age, but are in good agreement with several
recent studies. A few clusters stand out in the age--metallicity relation in
the sense that they are intermediate age clusters at relatively low metallicity
([Fe/H]~-1).Comment: LaTeX, to be published in July, 1998 Astronomical Journa
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