272 research outputs found
Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram
We present a V-I color-magnitude diagram for a region 1'-2' from the center
of M32 based on Hubble Space Telescope WFPC2 images. The broad color-luminosity
distribution of red giants shows that the stellar population comprises stars
with a wide range in metallicity. This distribution cannot be explained by a
spread in age. The blue side of the giant branch rises to M_I ~ -4.0 and can be
fitted with isochrones having [Fe/H] ~ -1.5. The red side consists of a heavily
populated and dominant sequence that tops out at M_I ~ -3.2, and extends beyond
V-I=4. This sequence can be fitted with isochrones with -0.2 < [Fe/H] < +0.1,
for ages running from 15 Gyr to 5 Gyr respectively. We do not find the
optically bright asymptotic giant branch stars seen in previous ground-based
work and argue that the majority of them were artifacts of crowding. Our
results are consistent with the presence of the infrared-luminous giants found
in ground-based studies, though their existence cannot be directly confirmed by
our data. There is little evidence for an extended or even a red horizontal
branch, but we find a strong clump on the giant branch itself. If the age
spread is not extreme, the distribution of metallicities in M32 is considerably
narrower than that of the closed-box model of chemical evolution, and also
appears somewhat narrower than that of the solar neighborhood. Overall, the M32
HST color-magnitude diagram is consistent with the average luminosity-weighted
age of 8.5 Gyr and [Fe/H] = -0.25 inferred from integrated spectral indices.Comment: 22 pages, AASTeX, aaspp4 and flushrt style files included, 11
postscript figures, figures 1,2,5,7, and 8 available at
ftp://bb3.jpl.nasa.gov/pub/m32 . Submitted to the Astronomical Journa
The Stellar Content of M31's Bulge
In this paper we analyze the stellar populations present in M31 using nine
sets of adjacent HST-NICMOS Camera 1 and 2 fields with galactocentric distances
ranging from 2' to 20'. These infrared observations provide some of the highest
spatial resolution measurements of M31 to date; our data place tight
constraints on the maximum luminosities of stars in the bulge of M31. The tip
of the red giant branch is clearly visible at Mbol ~ -3.8, and the tip of the
asymptotic giant branch (AGB) extends to Mbol ~ -5. This AGB peak luminosity is
significantly fainter than previously claimed; through direct comparisons and
simulations we show that previous measurements were affected by image blending.
We do observe field-to-field variations in the luminosity functions, but
simulations show that these differences can be produced by blending in the
higher surface brightness fields. We conclude that the red giant branch of the
bulge of M31 is not measurably different from that of the Milky Way's bulge. We
also find an unusually high number of bright blueish stars (7.3/arcmin^2) which
appear to be Galactic foreground stars.Comment: 28 pages, 20 figures (posted here with significantly reduced
resolution), accepted to the A
A sub-horizon framework for probing the relationship between the cosmological matter distribution and metric perturbations
The relationship between the metric and nonrelativistic matter distribution
depends on the theory of gravity and additional fields, providing a possible
way of distinguishing competing theories. With the assumption that the geometry
and kinematics of the homogeneous universe have been measured to sufficient
accuracy, we present a procedure for understanding and testing the relationship
between the cosmological matter distribution and metric perturbations (along
with their respective evolution) using the ratio of the physical size of the
perturbation to the size of the horizon as our small expansion parameter. We
expand around Newtonian gravity on linear, subhorizon scales with coefficient
functions in front of the expansion parameter. Our framework relies on an
ansatz which ensures that (i) the Poisson equation is recovered on small scales
(ii) the metric variables (and any additional fields) are generated and
supported by the nonrelativistic matter overdensity. The scales for which our
framework is intended are small enough so that cosmic variance does not
significantly limit the accuracy of the measurements and large enough to avoid
complications from nonlinear effects and baryon cooling. The coefficient
functions provide a general framework for contrasting the consequences of
Lambda CDM and its alternatives. We calculate the coefficient functions for
general relativity with a cosmological constant and dark matter, GR with dark
matter and quintessence, scalar-tensor theories, f(R) gravity and braneworld
models. We identify a possibly unique signature of braneworld models.
Constraining the coefficient functions provides a streamlined approach for
testing gravity in a scale dependent manner. We briefly discuss the
observations best suited for an application of our framework.Comment: Updated references and minor changes to match the published version
in MNRA
ILEEM-survey on the Heart Team approach and team training for lead extraction procedures
Background: The Heart Team approach has become an integral part of modern cardiovascular medicine. To evaluate current opinions and real-world practice among lead extraction practitioners, an online survey was created and distributed among a pool of lead extraction specialists participating in the International Lead Extraction Expert Meeting (ILEEM) 2018.
Methods: The online survey consisted of 10 questions and was performed using an online survey tool (www.surveymonkey.com). The collector link was sent to 48 lead extraction experts via email.
Results: A total of 43 answers were collected (89% return rate) from lead extraction experts in 16 different countries. A great majority (83.7%) of the respondents performed more than 30 lead extraction procedures per year. The most common procedural environment in this survey was the hybrid operating room (67.4%). Most procedures were performed by electrophysiologists and cardiologists (80.9%). Important additional members of the current lead extraction teams were cardiac surgeons (79.1%), anesthesiologists (95.3%) and operating room scrub nurses (76.7%). An extended Heart Team is regarded beneficial for patient care by 86.0%, with potential further members being infectious diseases specialists, intensivists and radiologists. Team training activities are performed in 48.8% of participating centers.
Conclusions: This survey supports the importance of establishing lead extraction Heart Teams in specialized lead extraction centers to potentially improve patient outcomes. The concept of a core and an extended heart team approach in lead extraction procedures is introduced
The Discovery of Y Dwarfs Using Data from the Wide-field Infrared Survey Explorer (WISE)
We present the discovery of seven ultracool brown dwarfs identified with the
Wide-field Infrared Survey Explorer (WISE). Near-infrared spectroscopy reveals
deep absorption bands of H_2O and CH_4 that indicate all seven of the brown
dwarfs have spectral types later than UGPS J072227.51-054031.2, the latest type
T dwarf currently known. The spectrum of WISEP J182831.08+265037.8 is distinct
in that the heights of the J- and H-band peaks are approximately equal in units
of f_lambda, so we identify it as the archetypal member of the Y spectral
class. The spectra of at least two of the other brown dwarfs exhibit absorption
on the blue wing of the H-band peak that we tentatively ascribe to NH_3. These
spectral morphological changes provide a clear transition between the T dwarfs
and the Y dwarfs. In order to produce a smooth near-infrared spectral sequence
across the T/Y dwarf transition, we have reclassified UGPS J0722-0540 as the T9
spectral standard and tentatively assign WISEP J173835.52+273258.9 as the Y0
spectral standard. In total, six of the seven new brown dwarfs are classified
as Y dwarfs: four are classified as Y0, one is classified as Y0 (pec?), and
WISEP J1828+2650 is classified as >Y0. We have also compared the spectra to the
model atmospheres of Marley and Saumon and infer that the brown dwarfs have
effective temperatures ranging from 300 K to 500 K, making them the coldest
spectroscopically confirmed brown dwarfs known to date.Comment: Submitted June 11 and accepted August 2 for publication in the
Astrophysical Journa
Ventricular pacing or dual-chamber pacing for sinus-node dysfunction
BACKGROUND
Dual-chamber (atrioventricular) and single-chamber (ventricular) pacing are alternative treatment approaches for sinus-node dysfunction that causes clinically significant bradycardia. However, it is unknown which type of pacing results in the better outcome. METHODS
We randomly assigned a total of 2010 patients with sinus-node dysfunction to dual-chamber pacing (1014 patients) or ventricular pacing (996 patients) and followed them for a median of 33.1 months. The primary end point was death from any cause or nonfatal stroke. Secondary end points included the composite of death, stroke, or hospitalization for heart failure; atrial fibrillation; heart-failure score; the pacemaker syndrome; and the quality of life. RESULTS
The incidence of the primary end point did not differ significantly between the dual-chamber group (21.5 percent) and the ventricular-paced group (23.0 percent, P=0.48). In patients assigned to dual-chamber pacing, the risk of atrial fibrillation was lower (hazard ratio, 0.79; 95 percent confidence interval, 0.66 to 0.94; P=0.008), and heart-failure scores were better (P CONCLUSIONS
In sinus-node dysfunction, dual-chamber pacing does not improve stroke-free survival, as compared with ventricular pacing. However, dual-chamber pacing reduces the risk of atrial fibrillation, reduces signs and symptoms of heart failure, and slightly improves the quality of life. Overall, dual-chamber pacing offers significant improvement as compared with ventricular pacing
HST-NICMOS Observations of M31's Metal Rich Globular Clusters and Their Surrounding Fields: II. Results
We have obtained HST-NICMOS observations of five of M31's most metal rich
globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest
from the nucleus we statistically subtract the field population and estimate
metallicities using K-(J-K) color-magnitude diagrams (CMDs). Based on the
slopes of their infrared giant branches we estimate [Fe/H]=-1.22+/-0.43 for G1
and -0.15+/-0.37 for G280. We combine our infrared observations of G1 with two
epochs of optical HST-WFPC2 V-band data and identify at least one LPV based on
color and variability. The location of G1's giant branch in the K-(V-K) CMD is
very similar to that of M107, indicating a higher metallicity than our purely
infrared CMD: [Fe/H]=-0.9+/-0.2.
For the field surrounding G280, we estimate the metallicity to be -1.3 with a
spread of 0.5 from the slope and width of the giant branch. Based on the
numbers and luminosities of the brightest giants, we conclude that only a small
fraction of the stars in this field could be as young as 2 Gyr, while the
majority have ages closer to 10 Gyr.
The K-band luminosity functions (LFs) of the upper few magnitudes of G1 and
G280, as well as for the fields surrounding all clusters, are indistinguishable
from the LF measured in the bulge of our Galaxy. This indicates that these
clusters are very similar to Galactic clusters, and at least in the surrounding
fields observed, there are no significant populations of young luminous stars.Comment: AAS LaTeX v5.0, 17 pages. Submitted to the A
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