143 research outputs found
FAUST Observations in the Fourth Galactic Quadrant
We analyze UV observations with FAUST of four sky fields in the general
direction of the fourth Galactic quadrant, in which we detect 777 UV sources.
This is ~50% more than detected originally by Bowyer et al (1995). We discuss
the source detection process and the identification of UV sources with optical
counterparts. For the first time in this project we use ground-based
objective-prism information for two of the fields, to select the best-matching
optical objects with which to identify the UV sources. Using this, and
correlations with existing catalogs, we present reliable identifications for
\~75% of the sources. Most of the remaining sources have assigned optical
counterparts, but lacking additional information we offer only plausible
identification. We discuss the types of objects found, and compare the observed
population with predictions of our UV Galaxy model.Comment: Dedicated to the memory of Barry Lasker. MNRAS in press. 95 pages, 9
figures. Figures 1-4 are very large; this version contains reduced-format
images. The full images are available at
ftp://wise3.tau.ac.il/ftp/pub/noah/M83_*.p
Routine Million-Particle Simulations of Epoxy Curing with Dissipative Particle Dynamics
Mesoscale simulation techniques have helped to bridge the length scales and time scales needed to predict the microstructures of cured epoxies, but gaps in computational cost and experimental relevance have limited their impact. In this work, we develop an open-source plugin epoxpy for HOOMD-Blue that enables epoxy crosslinking simulations of millions of particles to be routinely performed on a single modern graphics card. We demonstrate the first implementation of custom temperature-time curing profiles with dissipative particle dynamics and show that reaction kinetics depend sensitively on the stochastic bonding rates. We provide guidelines for modeling first-order reaction dynamics in a classic epoxy/hardener/toughener system and show structural sensitivity to the temperature-time profile during cure. We conclude with a discussion of how these efficient large-scale simulations can be used to evaluate ensembles of epoxy processing protocols to quantify the sensitivity of microstructure on processing
Assessment of left atrial volume before and after pulmonary thromboendarterectomy in chronic thromboembolic pulmonary hypertension.
BackgroundImpaired left ventricular diastolic filling is common in chronic thromboembolic pulmonary hypertension (CTEPH), and recent studies support left ventricular underfilling as a cause. To investigate this further, we assessed left atrial volume index (LAVI) in patients with CTEPH before and after pulmonary thromboendarterectomy (PTE).MethodsForty-eight consecutive CTEPH patients had pre- & post-PTE echocardiograms and right heart catheterizations. Parameters included mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), cardiac index, LAVI, & mitral E/A ratio. Echocardiograms were performed 6 ± 3 days pre-PTE and 10 ± 4 days post-PTE. Regression analyses compared pre- and post-PTE LAVI with other parameters.ResultsPre-op LAVI (mean 19.0 ± 7 mL/m2) correlated significantly with pre-op PVR (R = -0.45, p = 0.001), mPAP (R = -0.28, p = 0.05) and cardiac index (R = 0.38, p = 0.006). Post-PTE, LAVI increased by 18% to 22.4 ± 7 mL/m2 (p = 0.003). This change correlated with change in PVR (765 to 311 dyne-s/cm5, p = 0.01), cardiac index (2.6 to 3.2 L/min/m2, p = 0.02), and E/A (.95 to 1.44, p = 0.002).ConclusionIn CTEPH, smaller LAVI is associated with lower cardiac output, higher mPAP, and higher PVR. LAVI increases by ~20% after PTE, and this change correlates with changes in PVR and mitral E/A. The rapid increase in LAVI supports the concept that left ventricular diastolic impairment and low E/A pre-PTE are due to left heart underfilling rather than inherent left ventricular diastolic dysfunction
The Binary White Dwarf LHS 3236
The white dwarf LHS 3236 (WD1639+153) is shown to be a double-degenerate
binary, with each component having a high mass. Astrometry at the U.S. Naval
Observatory gives a parallax and distance of 30.86 +/- 0.25 pc and a tangential
velocity of 98 km/s, and reveals binary orbital motion. The orbital parameters
are determined from astrometry of the photocenter over more than three orbits
of the 4.0-year period. High-resolution imaging at the Keck Observatory
resolves the pair with a separation of 31 and 124 mas at two epochs. Optical
and near-IR photometry give a set of possible binary components. Consistency of
all data indicates that the binary is a pair of DA stars with temperatures near
8000 and 7400 K and with masses of 0.93 and 0.91 M_solar; also possible, is a
DA primary and a helium DC secondary with temperatures near 8800 and 6000 K and
with masses of 0.98 and 0.69 M_solar. In either case, the cooling ages of the
stars are ~3 Gyr and the total ages are <4 Gyr. The combined mass of the binary
(1.66--1.84 M_solar) is well above the Chandrasekhar limit; however, the
timescale for coalescence is long.Comment: Accepted for the Astrophysical Journa
An Adaptive Optics Survey for Close Protostellar Binaries
In order to test the hypothesis that Class I protostellar binary stars are a
product of ejections during the dynamical decay of non-hierarchical multiple
systems, we combined the results of new adaptive optics (AO) observations of
Class I protostars with our previously published AO data to investigate whether
Class I protostars with a widely separated companion (r>200 AU) are more likely
to also have a close companion (r<200 AU). In total, we observed 47 embedded
young stellar objects (YSOs) with either the Subaru natural guide star AO
system or the Keck laser guide star AO system. We found that targets with a
widely separated companion within 5,000 AU are not more likely to have a close
companion. However, targets with another YSO within a projected separation of
25,000 AU are much more likely to have a close companion. Most importantly,
every target with a close companion has another YSO within a projected
separation of 25,000 AU. We came to the same conclusions after considering a
restricted sample of targets within 500 pc and close companions wider than 50
AU to minimize incompleteness effects. The Orion star forming region was found
to have an excess of both close binaries and YSOs within 25,000 AU compared to
other star forming regions. We interpret these observations as strong evidence
that many close Class I binary stars form via ejections and that many of the
ejected stars become unbound during the Class I phase.Comment: 22 pages, 3 figures, 2 table
IRAS03063+5735: A Bowshock Nebula Powered by an Early B Star
Mid-infrared images from the Spitzer Space Telescope Galactic Legacy Infrared
MidPlane Survey Extraordinaire program reveal that the infrared source IRAS
03063+5735 is a bowshock nebula produced by an early B star, 2MASS
03101044+5747035. We present new optical spectra of this star, classify it as a
B1.5 V, and determine a probable association with a molecular cloud complex at
V_LSR=-38 -- -42 km/s in the outer Galaxy near l=140.59 degr, b=-0.250 degr. On
the basis of spectroscopic parallax, we estimate a distance of 4.0 +/-1 kpc to
both the bowshock nebula and the molecular complex. One plausible scenario is
that this a high-velocity runaway star impinging upon a molecular cloud. We
identify the HII region and stellar cluster associated with IRAS 03064+5638 at
a projected distance of 64 pc as one plausible birth site. The
spectrophotometric distance and linkage to a molecular feature provides another
piece of data helping to secure the ill-determined rotation curve in the outer
Galaxy. As a by-product of spectral typing this star, we present empirical
spectral diagnostic diagrams suitable for approximate spectral classification
of O and B stars using He lines in the little-used yellow-red portion of the
optical spectrum.Comment: Accepted for publication in the Astronomical Journa
A Search for Distant Solar System Bodies in the Region of Sedna
We present the results of a wide-field survey for distant Sedna-like bodies
in the outer solar system using the 1.2-m Samuel Oschin Telescope at Palomar
Observatory. We searched ~12,000 square degrees down to a mean limiting
magnitude of 21.3 in R. A total number of 53 Kuiper belt objects and Centaurs
have been detected; 25 of which were discovered in this survey. No additional
Sedna-like bodies with perihelia beyond 70 AU were found despite a sensitivity
to motions out to ~1000 AU. We place constraints on the size and distribution
of objects on Sedna orbits.Comment: 10 pages, 3 figures, accepted by ApJ Letter
Parallax and Distance Estimates for Twelve Cataclysmic Variable Stars
We report parallax and distance estimates for twelve more cataclysmic
binaries and related objects observed with the 2.4m Hiltner telescope at MDM
Observatory. The final parallax accuracy is typically about 1 mas. For only one
of the twelve objects, IR Gem, do we fail to detect a significant parallax.
Notable results include distances for V396 Hya (CE 315), a helium double
degenerate with a relatively long orbital period, and for MQ Dra
(SDSSJ155331+551615), a magnetic system with a very low accretion rate. We find
that the Z Cam star KT Persei is physically paired with a K main-sequence star
lying 15 arcsec away. Several of the targets have distance estimates in the
literature that are based on the white dwarf's effective temperature and flux;
our measurements broadly corroborate these estimates, but tend to put the stars
a bit closer, indicating that the white dwarfs may have rather larger masses
than assumed. As a side note, we briefly describe radial velocity spectroscopy
that refines the orbital period of V396 Hya to 65.07 +- 0.08 min.Comment: Accepted for Astronomical Journal. 19 pages, no figure
Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B
We report the discovery of a widely separated (258\farcs3\pm0\farcs4) T
dwarf companion to the Gl 570ABC system. This new component, Gl 570D, was
initially identified from the Two Micron All Sky Survey (2MASS). Its
near-infrared spectrum shows the 1.6 and 2.2 \micron CH absorption bands
characteristic of T dwarfs, while its common proper motion with the Gl 570ABC
system confirms companionship. Gl 570D (M = 16.470.07) is nearly a
full magnitude dimmer than the only other known T dwarf companion, Gl 229B, and
estimates of L = (2.80.3)x10 L_{\sun} and T = 75050
K make it significantly cooler and less luminous than any other known brown
dwarf companion. Using evolutionary models by Burrows et al. and an adopted age
of 2-10 Gyr, we derive a mass estimate of 5020 M for this object.Comment: 13 pages, 2 figures, 2 tables, accepted by ApJ
Properties of the Distant Kuiper Belt: Results from the Palomar Distant Solar System Survey
We present the results of a wide-field survey using the 1.2-m Samuel Oschin
Telescope at Palomar Observatory. This survey was designed to find the most
distant members of the Kuiper belt and beyond. We searched ~12,000 deg2 down to
a mean limiting magnitude of 21.3 in R. A total number of 52 KBOs and Centaurs
have been detected, 25 of which were discovered in this survey. Except for the
re-detection of Sedna, no additional Sedna-like bodies with perihelia greater
than 45 AU were detected despite sensitivity out to distances of 1000 AU. We
discuss the implications for a distant Sedna- like population beyond the Kuiper
belt, focusing on the constraints we can place on the embedded stellar cluster
environment the early Sun may be have been born in, where the location and
distribution of Sedna-like orbits sculpted by multiple stellar encounters is
indicative of the birth cluster size. We also report our observed latitude
distribution and implications for the size of the plutino population.Comment: 40 pages, 12 figures, 3 tables Accepted by Ap
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