624 research outputs found
Out-of-hospital cardiac arrest and survival in a patient with Noonan syndrome and multiple lentigines: a case report
BACKGROUND: A 9-year-old Arabic boy attending middle school presented with an out-of-hospital cardiac arrest due to ventricular fibrillation recorded by Holter electrocardiographic monitoring. He had a background history of Noonan syndrome with multiple lentigines (also known as LEOPARD syndrome), a rare condition of autosomal dominant inheritance with approximately 200 cases reported worldwide. CASE PRESENTATION: Apart from characteristic features, the boy was known to have asymmetric septal hypertrophy with a maximum wall thickness of 24âmm measured by cardiovascular magnetic resonance imaging. A day prior to the event, he attended cardiology follow-up at our institution, and Holter monitoring was commenced. Following cardiopulmonary resuscitation by bystanders and paramedics, he reverted back into sinus rhythm after a total downtime of 24âmin. He was initially treated in the intensive care unit and underwent implantable cardioverter defibrillator implantation. He has made a full recovery and remains at the top of his class. CONCLUSION: This case demonstrates that sudden cardiac arrest in patients with secondary forms of hypertrophic cardiomyopathy is not necessarily protected by apparently favorable phenotypes and that events may be preceded by non-sustained ventricular tachycardia observed by Holter monitoring. Implantable cardioverter defibrillator implantation plays a critical role in both primary and secondary prevention in patients at high risk of out-of-hospital cardiac arrest
On the Correlation between the Magnetic Activity Levels, the Metallicities and the Radii of Low-Mass Stars
The recent burst in the number of radii measurements of very low-mass stars
from eclipsing binaries and interferometry of single stars has opened more
questions about what can be causing the discrepancy between the observed radii
and the ones predicted by the models. The two main explanations being proposed
are a correlation between the radius of the stars and their activity levels or
their metallicities. This paper presents a study of such correlations using all
the data published to date. The study also investigates correlations between
the radii deviation from the models and the masses of the stars. There is no
clear correlation between activity level and radii for the single stars in the
sample. Those single stars are slow rotators with typical velocities v_rot sini
< 3.0 km s^-1. A clear correlation however exists in the case of the faster
rotating members of binaries. This result is based on the of X-ray emission
levels of the stars. There also appears to be an increase in the deviation of
the radii of single stars from the models as a function of metallicity, as
previously indicated by Berger et al. (2006). The stars in binaries do not seem
to follow the same trend. Finally, the Baraffe et al. (1998) models reproduce
well the radius observations below 0.30-0.35Msun, where the stars become fully
convective, although this result is preliminary since almost all the sample
stars in that mass range are slow rotators and metallicities have not been
measured for most of them. The results in this paper indicate that stellar
activity and metallicity play an important role on the determination of the
radius of very low-mass stars, at least above 0.35Msun.Comment: 22 pages, 4 figures. Accepted for publication on Ap
Cluster Evolution in the ROSAT North Ecliptic Pole Survey
The deepest region of the ROSAT All-Sky Survey, at the North Ecliptic Pole,
has been studied to produce a complete and unbiased X-ray selected sample of
clusters of galaxies. This sample is used to investigate the nature of cluster
evolution and explore potential implications for large-scale structure models.
The survey is 99.6% optically identified. Spectroscopic redshifts have been
measured for all the extragalactic identifications. In this Letter, first
results on cluster evolution are presented based on a comparison between the
number of the observed clusters in the North Ecliptic Pole survey and the
number of expected clusters assuming no-evolution models. At z>0.3 there is a
deficit of clusters with respect to the local universe which is significant at
> 4.7sigma. The evolution appears to commence at L_{0.5-2.0} > 1.8x10^{44} erg
s^{-1} in our data. The negative evolution goes in the same direction as the
original EMSS result, the results from the 160 deg^{2} survey by Vikhlinin et
al. (1998) and the recent results from the RDCS (Rosati et al. 2000). At lower
redshifts there is no evidence for evolution, a result in agreement with these
and other cluster surveys.Comment: 17 pages, 3 figures. Accepted for publication in ApJ Letter
The ROSAT North Ecliptic Pole Survey: The Optical Identifications
The X-ray data around the North Ecliptic Pole (NEP) of the ROSAT All Sky
Survey have been used to construct a contiguous area survey consisting of a
sample of 445 individual X-ray sources above a flux of ~2x10^-14 erg cm^-2 s^-1
in the 0.5-2.0 keV energy band. The NEP survey is centered at RA (2000) = 18h
00m, DEC(2000) = +66deg 33arcmin and covers a region of 80.7 sq. deg at a
moderate Galactic latitude of b = 29.8deg. Hence, the NEP survey is as deep and
covers a comparable solid angle to the ROSAT serendipitous surveys, but is also
contiguous. We have identified 99.6% of the sources and determined redshifts
for the extragalactic objects. In this paper we present the optical
identifications of the NEP catalog of X-ray sources including basic X-ray data
and properties of the sources. We also describe with some detail the optical
identification procedure. The classification of the optical counterparts to the
NEP sources is very similar to that of previous surveys, in particular the
Einstein Extended Medium Sensitivity Survey (EMSS). The main constituents of
the catalog are active galactic nuclei (~49%), either type 1 or type 2
according to the broadness of their permitted emission lines. Stellar
counterparts are the second most common identification class (~34%). Clusters
and groups of galaxies comprise 14%, and BL Lacertae objects 2%. One non-AGN
galaxy, and one planetary nebula have also been found. The NEP catalog of X-ray
sources is a homogeneous sample of astronomical objects featuring complete
optical identification.Comment: Accepted for publication in the ApJS; 33 pages including 12
postscript figures and 3 tables; uses emulateapj.sty. On-line source catalog
at http://www.eso.org/~cmullis/research/nep-catalog.htm
Discovery of 9 New Companions to Nearby Young M Stars with the Altair AO System
We present results of a high-resolution, near-infrared survey of 41 nearby,
young (<~300 Myr) M0-M5.0 dwarfs using the Altair natural guide star adaptive
optics system at the Gemini North telescope. Twelve of the objects appear to be
binaries, 7 of which are reported here for the first time. One triple system
was discovered. Statistical properties are studied and compared with earlier (F
to K) and later (>= M6 very low-mass, VLM) populations. We find that the
separation distribution of the binaries in this sample peaks at 13+14-9 AU,
which is consistent with previous measurements of early-M binaries. Hence,
early-M binaries seem to occur in--on average--tighter systems than G binaries.
At the same time they are significantly wider than field VLM binary stars. The
distribution of mass ratios q of primary and secondary stars was found to show
an intermediate distribution between the strongly q-->1 peaked distribution of
field VLM systems and the almost flat distribution of earlier-type stars.
Consequently, we show evidence for relatively young, early-M binaries
representing a transition between the well known earlier star distributions and
the recently examined field VLM population characteristics. Despite the fact
that this survey was dedicated to the search for faint brown dwarf and
planetary mass companions, all planetary mass candidates were background
objects. We exclude the existence of physical companions with masses greater
than 10 Jupiter masses (M_Jup) at separations of >~40 AU and masses greater
than 24 M_Jup for separations >~10 AU around 37 of the 41 observed objects.Comment: To appear in the January 1, 2007 issue of the Astrophysical Journal,
12 pages, 13 figures. Minor typographical and grammatical changes. Wrong
round off in binary fraction correcte
The North Ecliptic Pole Supercluster
We have used the ROSAT All-Sky Survey to detect a known supercluster at
z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our
understanding of this supercluster's characteristics, approximately doubling
our knowledge of the structure's spatial extent and tripling the cluster/group
membership compared to the optical discovery data. The supercluster is a rich
structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS
galaxies, and various other objects. A majority of these components were
discovered with the X-ray data, but the supercluster is also robustly detected
in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the
North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on
to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the
deep exposure over a large solid angle, we have detected for the first time a
significant population of X-ray emitting galaxy groups in a supercluster. These
results demonstrate the effectiveness of X-ray observations with contiguous
coverage for studying structure in the Universe.Comment: Accepted for publication in The Astrophysical Journal; 5 pages with 2
embedded figures; uses emulateapj.sty; For associated animations, see
http://www.ifa.hawaii.edu/~mullis/nep3d.html; A high-resolution color
postscript version of the full paper is available at
http://www.ifa.hawaii.edu/~mullis/papers/nepsc.ps.g
1ES 1927+654: Persistent and rapid X-ray variability in an AGN with low intrinsic neutral X-ray absorption and narrow optical emission lines
We present X-ray and optical observations of the X-ray bright AGN 1ES
1927+654. The X-ray observations obtained with ROSAT and Chandra reveal
persistent, rapid and large scale variations, as well as steep 0.1-2.4 keV
(Gamma = 2.6 +/- 0.3) and 0.3-7.0 keV (Gamma = 2.7 +/- 0.2) spectra. The
measured intrinsic neutral X-ray column density is approximately 7e20cm^-2. The
X-ray timing properties indicate that the strong variations originate from a
region, a few hundred light seconds from the central black hole, typical for
type 1 AGN. High quality optical spectroscopy reveals a typical Seyfert 2
spectrum with some host galaxy contamination and no evidence of Fe II
multiplets or broad hydrogen Balmer wings. The intrinsic optical extinction
derived from the BLR and NLR are A_V >= 3.7 and A_V=1.7, respectively. The
X-ray observations give an A_V value of less than 0.58, in contrast to the
optical extinction values. We discuss several ideas to explain this apparent
difference in classification including partial covering, an underluminous BLR
or a high dust to gas ratio.Comment: 8 pages including 10 figures. Accepted for publication in Astronomy
and Astrophysic
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