4,270 research outputs found
Massive stellar systems: observational challenges and perspectives in the E-ELT era
We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields
Spontaneous left main coronary artery dissection, possibly due to cystic medial necrosis found in the internal mammary arteries.
A 55-year-old male without previous medical history developed chest pain. Coronary catheterization showed left main coronary dissection. Coronary artery bypass grafting was performed using bilateral internal mammary arteries, which were very fragile. The specimens of the internal mammary arteries sent for pathology showed cystic medial necrosis
Variable stars in Terzan 5: additional evidence of multi-age and multi-iron stellar populations
Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar
populations with very different iron content ({\Delta}[Fe/H] ~1 dex) and with
ages differing by several Gyrs. Here we present an investigation of its
variable stars. We report on the discovery and characterization of three RR
Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known
periods we provide radial velocity and chemical abundances from spectra
acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the
three short period Miras (P<300 d) have radial velocity consistent with being
Terzan 5 members. They have sub-solar iron abundances and enhanced
[{\alpha}/Fe], well matching the age and abundance patterns of the 12 Gyr
metal-poor stellar populations of Terzan 5. Only one, out of the three long
period (P>300 d) Miras analyzed in this study, has a radial velocity consistent
with being Terzan 5 member. Its super-solar iron abundance and solar-scaled
[{\alpha}/Fe] nicely match the chemical properties of the metal rich stellar
population of Terzan 5 and its derived mass nicely agrees with being several
Gyrs younger than the short period Miras. This young variable is an additional
proof of the surprising young sub-population discovered in Terzan 5.Comment: 20 pages, 4 figures, in press on the Ap
On the distance of the Magellanic Clouds using Cepheid NIR and optical-NIR Period Wesenheit Relations
We present the largest near-infrared (NIR) data sets, , ever collected
for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental
(FU) and first overtone (FO) pulsators, and found 4150 (2571 FU, 1579 FO)
Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large
Magellanic Cloud (LMC). Current sample is 2--3 times larger than any sample
used in previous investigations with NIR photometry. We also discuss optical
photometry from OGLE-III. NIR and optical--NIR Period-Wesenheit (PW)
relations are linear over the entire period range () and their slopes are, within the intrinsic dispersions, common between the
MCs. These are consistent with recent results from pulsation models and
observations suggesting that the PW relations are minimally affected by the
metal content. The new FU and FO PW relations were calibrated using a sample of
Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid
pulsation models. By using FU Cepheids we found a true distance moduli of
mag (LMC) and
mag (SMC). These estimates
are the weighted mean over ten PW relations and the systematic errors account
for uncertainties in the zero-point and in the reddening law. We found similar
distances using FO Cepheids
( mag [LMC] and
mag [SMC]). These new MC
distances lead to the relative distance, mag (FU, ) and mag (FO, ),which agrees quite
well with previous estimates based on robust distance indicators.Comment: 17 pages, 7 figure
AKARI Near- to Mid-Infrared Imaging and Spectroscopic Observations of the Small Magellanic Cloud. I. Bright Point Source List
We carried out a near- to mid-infrared imaging and spectroscopic observations
of the patchy areas in the Small Magellanic Cloud using the Infrared Camera on
board AKARI. Two 100 arcmin2 areas were imaged in 3.2, 4.1, 7, 11, 15, and 24
um and also spectroscopically observed in the wavelength range continuously
from 2.5 to 13.4 um. The spectral resolving power (lambda/Delta lambda) is
about 20, 50, and 50 at 3.5, 6.6 and 10.6 um, respectively. Other than the two
100 arcmin2 areas, some patchy areas were imaged and/or spectroscopically
observed as well. In this paper, we overview the observations and present a
list of near- to mid-infrared photometric results, which lists ~ 12,000
near-infrared and ~ 1,800 mid-infrared bright point sources detected in the
observed areas. The 10 sigma limits are 16.50, 16.12, 13.28, 11.26, 9.62, and
8.76 in Vega magnitudes at 3.2, 4.1, 7, 11, 15, and 24 um bands, respectively.Comment: 16 pages, 7 figures, accepted for publication in PASJ. Full
resolution version is available at
http://www-irc.mtk.nao.ac.jp/%7Eyita/smc20100112.pd
Interstellar Extinction Law in the J, H, and Ks Bands toward the Galactic Center
We have determined the ratios of total to selective extinction in the
near-infrared bands (J, H, Ks) toward the Galactic center from the observations
of the region |l| < 2.0deg and 0.5deg < |b| < 1.0deg with the IRSF telescope
and the SIRIUS camera. Using the positions of red clump stars in
color-magnitude diagrams as a tracer of the extinction and reddening, we
determine the average of the ratios of total to selective extinction to be
A(Ks)/E(H-Ks) = 1.44+-0.01, A(Ks)/E(J-Ks) = 0.494+-0.006, and A(H)/E(J-H) =
1.42+-0.02, which are significantly smaller than those obtained in previous
studies. From these ratios, we estimate that A(J) : A(H) : A(Ks) = 1 :
0.573+-0.009 : 0.331+-0.004 and E(J-H)/E(H-Ks) = 1.72+-0.04, and we find that
the power law A(lambda) \propto lambda^{-1.99+-0.02} is a good approximation
over these wavelengths. Moreover, we find a small variation in A(Ks)/E(H-Ks)
across our survey. This suggests that the infrared extinction law changes from
one line of sight to another, and the so-called ``universality'' does not
necessarily hold in the infrared wavelengths.Comment: 18 pages, 9 figures, Accepted for publication in the Ap
Lossy data compression with random gates
We introduce a new protocol for a lossy data compression algorithm which is
based on constraint satisfaction gates. We show that the theoretical capacity
of algorithms built from standard parity-check gates converges exponentially
fast to the Shannon's bound when the number of variables seen by each gate
increases. We then generalize this approach by introducing random gates. They
have theoretical performances nearly as good as parity checks, but they offer
the great advantage that the encoding can be done in linear time using the
Survey Inspired Decimation algorithm, a powerful algorithm for constraint
satisfaction problems derived from statistical physics
On the metallicity distribution of classical Cepheids in the Galactic inner disk
We present homogeneous and accurate iron abundances for almost four dozen
(47) of Galactic Cepheids using high-spectral resolution (R40,000) high
signal-to-noise ratio (S/N 100) optical spectra collected with UVES at
VLT. A significant fraction of the sample (32) is located in the inner disk (RG
6.9 kpc) and for half of them we provide new iron abundances. Current
findings indicate a steady increase in iron abundance when approaching the
innermost regions of the thin disk. The metallicity is super-solar and ranges
from 0.2 dex for RG 6.5 kpc to 0.4 dex for RG 5.5 kpc. Moreover,
we do not find evidence of correlation between iron abundance and distance from
the Galactic plane. We collected similar data available in the literature and
ended up with a sample of 420 Cepheids. Current data suggest that the mean
metallicity and the metallicity dispersion in the four quadrants of the
Galactic disk attain similar values. The first-second quadrants show a more
extended metal-poor tail, while the third-fourth quadrants show a more extended
metal-rich tail, but the bulk of the sample is at solar iron abundance.
Finally, we found a significant difference between the iron abundance of
Cepheids located close to the edge of the inner disk ([Fe/H]0.4) and
young stars located either along the Galactic bar or in the nuclear bulge
([Fe/H]0). Thus suggesting that the above regions have had different
chemical enrichment histories. The same outcome applies to the metallicity
gradient of the Galactic bulge, since mounting empirical evidence indicates
that the mean metallicity increases when moving from the outer to the inner
bulge regions.Comment: 10 pages, 5 figures; Corrected typos, corrected Table
Left Ventricular Pseudoaneurysm Found by CT Scan
A 62-year-old male with a previous coronary artery bypass grafting underwent CT scan for evaluation of left epigastric pain. Findings showed a large left ventricular pseudoaneurysm, which was subsequently confirmed by left ventriculogram. The pseudoaneurysm was successfully repaired surgically
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