1,239 research outputs found
A Candidate Protoplanet in the Taurus Star Forming Region
HST/NICMOS images of the class I protostar TMR-1 (IRAS04361+2547) reveal a
faint companion with 10.0" = 1400 AU projected separation. The central
protostar is itself resolved as a close binary with 0.31" = 42 AU separation,
surrounded by circumstellar reflection nebulosity. A long narrow filament seems
to connect the protobinary to the faint companion TMR-1C, suggesting a physical
association. If the sources are physically related then we hypothesize that
TMR-1C has been ejected by the protobinary. If TMR-1C has the same age and
distance as the protobinary then current models indicate its flux is consistent
with a young giant planet of several Jovian masses.Comment: 16 pages, 1 figure, Accepted by Astrophysical Journal Letters,
Related information is available at http://www.extrasolar.co
An IR Search for Extinguished Supernovae in Starburst Galaxies
IR and Radio band observations of heavily extinguished regions in starburst
galaxies suggest a very high SN rate associated with such regions. Optically
measured supernova (SN) rates may therefore underestimate the total SN rate by
factors of up to 10, due to the high extinction to SNe in starburst regions.
The IR/radio SN rates come from a variety of indirect means, however, which
suffer from model dependence and other problems.
We describe a direct measurement of the SN rate from a regular patrol of
starburst galaxies done with K' band imaging to minimize the effects of
extinction. A collection of K' measurements of core-collapse SNe near maximum
light is presented. Results of a preliminary SN search using the MIRC camera at
the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics
are described. A monthly patrol of starburst galaxies within 25 Mpc should
yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels)
failed to find extinguished SNe, limiting the SN rate outside the nucleus (at >
15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10
L(solar); 90% confidence). The MIRC camera had insufficient resolution to
search nuclear starburst regions, where SN activity is concentrated, explaining
why we found no heavily obscured SNe. We conclude that high-resolution, small
field SN searches in starburst nuclei are more productive than low resolution,
large-field searches, even for our large galaxies. With our ORCA
high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90%
confidence in 3 years of observations, lower than the most pessimistic
estimate.Comment: AJ Submitted 1998 Dec. 13. View figures and download all as one file
at http://panisse.lbl.gov/public/bruce/irs
Optical Observations of the Binary Pulsar System PSR B1718-19: Implications for Tidal Circularization
We report on Keck and Hubble Space Telescope optical observations of the
eclipsing binary pulsar system PSR B1718-19, in the direction of the globular
cluster NGC 6342. These reveal a faint star (; Vega
system) within the pulsar's 0\farcs5 radius positional error circle. This may
be the companion. If it is a main-sequence star in the cluster, it has radius
\rcomp\simeq0.3 \rsun, temperature \teff\simeq3600 K, and mass
\mcomp\simeq0.3 \msun. In many formation models, however, the pulsar (spun up
by accretion or newly formed) and its companion are initially in an eccentric
orbit. If so, for tidal circularization to have produced the present-day highly
circular orbit, a large stellar radius is required, i.e., the star must be
bloated. Using constraints on the radius and temperature from the Roche and
Hayashi limits, we infer from our observations that \rcomp\simlt0.44 \rsun
and \teff\simgt3300 K. Even for the largest radii, the required efficiency of
tidal dissipation is larger than expected for some prescriptions.Comment: 10 pages, 2 figures, aas4pp2.sty. Accepted for publication in Ap
TWO-SIGMA: A novel two-component single cell model-based association method for single-cell RNA-seq data
In this paper, we develop TWO-SIGMA, a TWO-component SInGle cell Model-based Association method for differential expression (DE) analyses in single-cell RNA-seq (scRNA-seq) data. The first component models the probability of âdrop-outâ with a mixed-effects logistic regression model and the second component models the (conditional) mean expression with a mixed-effects negative binomial regression model. TWO-SIGMA is extremely flexible in that it: (i) does not require a log-transformation of the outcome, (ii) allows for overdispersed and zero-inflated counts, (iii) accommodates a correlation structure between cells from the same individual via random effect terms, (iv) can analyze unbalanced designs (in which the number of cells does not need to be identical for all samples), (v) can control for additional sample-level and cell-level covariates including batch effects, (vi) provides interpretable effect size estimates, and (vii) enables general tests of DE beyond two-group comparisons. To our knowledge, TWO-SIGMA is the only method for analyzing scRNA-seq data that can simultaneously accomplish each of these features. Simulations studies show that TWO-SIGMA outperforms alternative regression-based approaches in both type-I error control and power enhancement when the data contains even moderate within-sample correlation. A real data analysis using pancreas islet single-cells exhibits the flexibility of TWO-SIGMA and demonstrates that incorrectly failing to include random effect terms can have dramatic impacts on scientific conclusions. TWO-SIGMA is implemented in the R package twosigma available at https://github.com/edvanburen/twosigma
An Interstellar Conduction Front Within a Wolf-Rayet Ring Nebula Observed with the GHRS
With the High Resolution Spectrograph aboard the Hubble Space Telescope we
obtained high signal-to-noise (S/N > 200 - 600 per 17 km/s resolution element)
spectra of narrow absorption lines toward the Wolf-Rayet star HD 50896. The
ring nebula S308 that surrounds this star is thought to be caused by a
pressure-driven bubble bounded by circumstellar gas (most likely from a red
supergiant or luminous blue variable progenitor) pushed aside by a strong
stellar wind. Our observation has shown for the first time that blueshifted
(approximately 70 km/s relative to the star) absorption components of C IV and
N V arise in a conduction front between the hot interior of the bubble and the
cold shell of swept-up material. These lines set limits on models of the
conduction front. Nitrogen in the shell appears to be overabundant by a factor
~10. The P Cygni profiles of N V and C IV are variable, possibly due to a
suspected binary companion to HD 50896.Comment: 32 pages, Latex, to appear in the Astrophysical Journal, April, 199
Effect of Oral Iron Repletion on Exercise Capacity in Patients With Heart Failure With Reduced Ejection Fraction and Iron Deficiency: The IRONOUT HF Randomized Clinical Trial.
Importance: Iron deficiency is present in approximately 50% of patients with heart failure with reduced left ventricular ejection fraction (HFrEF) and is an independent predictor of reduced functional capacity and mortality. However, the efficacy of inexpensive readily available oral iron supplementation in heart failure is unknown.
Objective: To test whether therapy with oral iron improves peak exercise capacity in patients with HFrEF and iron deficiency.
Design, Setting, and Participants: Phase 2, double-blind, placebo-controlled randomized clinical trial of patients with HFrEF (
Interventions: Oral iron polysaccharide (nâ=â111) or placebo (nâ=â114), 150 mg twice daily for 16 weeks.
Main Outcomes and Measures: The primary end point was a change in peak oxygen uptake (VÌo2) from baseline to 16 weeks. Secondary end points were change in 6-minute walk distance, plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, and health status as assessed by Kansas City Cardiomyopathy Questionnaire (KCCQ, range 0-100, higher scores reflect better quality of life).
Results: Among 225 randomized participants (median age, 63 years; 36% women) 203 completed the study. The median baseline peak VÌo2 was 1196 mL/min (interquartile range [IQR], 887-1448 mL/min) in the oral iron group and 1167 mL/min (IQR, 887-1449 mL/min) in the placebo group. The primary end point, change in peak VÌo2 at 16 weeks, did not significantly differ between the oral iron and placebo groups (+23 mL/min vs -2 mL/min; difference, 21 mL/min [95% CI, -34 to +76 mL/min]; Pâ=â.46). Similarly, at 16 weeks, there were no significant differences between treatment groups in changes in 6-minute walk distance (-13 m; 95% CI, -32 to 6 m), NT-proBNP levels (159; 95% CI, -280 to 599 pg/mL), or KCCQ score (1; 95% CI, -2.4 to 4.4), all Pâ\u3eâ.05.
Conclusions and Relevance: Among participants with HFrEF with iron deficiency, high-dose oral iron did not improve exercise capacity over 16 weeks. These results do not support use of oral iron supplementation in patients with HFrEF.
Trial Registration: clinicaltrials.gov Identifier: NCT02188784
A comparison of statistical hadronization models
We investigate the sensitivity of fits of hadron spectra produced in heavy
ion collisions to the choice of statistical hadronization model. We start by
giving an overview of statistical model ambiguities, and what they tell us
about freeze-out dynamics. We then use Montecarlo generated data to determine
sensitivity to model choice. We fit the statistical hadronization models under
consideration to RHIC data, and find that a comparison fits can shed
light on some presently contentious questions.Comment: Proceedings for SQM2003 [7th Int. Conf. on Strangeness in Quark
Matter (Atlantic Beach, NC, USA, Mar 12-17, 2003)], to be published in
Journal of Physics G (Typos corrected, reference added
A photoionization model of the compact HII region G29.96-0.02
We present a detailed photoionization model of G29.96-0.02 (hereafter
G29.96), one of the brightest Galactic Ultra Compact HII (UCHII) regions in the
Galaxy. This source has been observed extensively at radio and infrared
wavelengths. The most recent data include a complete ISO (SWS and LWS)
spectrum, which displays a remarkable richness in atomic fine-structure lines.
The number of observables is twice as much as the number available in previous
studies. In addition, most atomic species are now observed in two ionization
stages. The radio and infrared data on G29.96 are best reproduced using a
nebular model with two density components: a diffuse (n_e~680cm-3) extended (~1
pc) component surrounding a compact (~0.1 pc) dense (n_e~57000cm-3) core. The
properties of the ionizing star were derived using state-of-the-art stellar
atmosphere models. CoStar models yield an effective temperature of
\~30^{+2}_{-1} kK whereas more recent non-LTE line blanketed atmospheres with
stellar winds indicate somewhat higher values, Teff~32--38 kK. This range in
Teff is compatible with all observational constraints, including near-infrared
photometry and bolometric luminosity. The range 33-36 kK is also compatible
with the spectral type O5-O8 determined by Watson and Hanson (97) when recent
downward revisions of the effective temperature scale of O stars are taken into
account. The age of the ionizing star of G29.96 is found to be a few 10^6 yr,
much older than the expected lifetime of UCHII regions. Accurate gas phase
abundances are derived with the most robust results being Ne/S=7.5 and N/O=0.43
(1.3 and 3.5 times the solar values, respectively).Comment: Accepted in Astronomy and Astrophysic
The ISO-IRAS Faint Galaxy Survey: Early results
We present preliminary results for AGNs and starburst galaxies the ISO-IRAS Faint Galaxy Survey (IIFGS). The goal of the survey is to produce a database of infrared-luminous galaxies at redshifts of about 0.1â1 to help explore the AGN-starburst relationship, study the cosmological evolution of luminous infrared galaxies, and identify possible protogalaxy candidates. The candidate list of âŒ3700 sources has been extracted from the IRAS Faint Source Survey using criteria selecting for faint, infrared-bright galaxies. The ISO observations will confirm the IRAS detections, yield sensitive 12 & 90 ÎŒm fluxes, and provide positions to âŒ6" accuracy which will allow unambiguous optical identifications. Confirmed sources are being followed up with ground-based observations to determine optical magnitudes and accurate redshifts. In this preliminary phase we have in hand âŒ100 observed fields and are developing techniques to maximize the sensitivity of the observations. Early results for the ISOCAM 12 ÎŒm images indicate we can reliably detect sources as faint as âŒ0.5âmJy; âŒ80% of the fields contain at least one source
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