513 research outputs found
Tracing the Mass during Low-Mass Star Formation. III. Models of the Submillimeter Dust Continuum Emission from Class 0 Protostars
Seven Class 0 sources mapped with SCUBA at 850 and 450 micron are modeled
using a one dimensional radiative transfer code. The modeling takes into
account heating from an internal protostar, heating from the ISRF, realistic
beam effects, and chopping to model the normalized intensity profile and
spectral energy distribution. Power law density models, n(r) ~ r^{-p}, fit all
of the sources; best fit values are mostly p = 1.8 +/- 0.1, but two sources
with aspherical emission contours have lower values (p ~ 1.1). Including all
sources, = 1.63 +/- 0.33. Based on studies of the sensitivity of the
best-fit p to variations in other input parameters, uncertainties in p for an
envelope model are \Delta p = +/- 0.2. If an unresolved source (e.g., a disk)
contributes 70% of the flux at the peak, p is lowered in this extreme case and
\Delta p = ^{+0.2}_{-0.6}. The models allow a determination of the internal
luminosity ( = 4.0 \lsun) of the central protostar as well as a
characteristic dust temperature for mass determination ( = 13.8 +/-
2.4 K). We find that heating from the ISRF strongly affects the shape of the
dust temperature profile and the normalized intensity profile, but does not
contribute strongly to the overall bolometric luminosity of Class 0 sources.
There is little evidence for variation in the dust opacity as a function of
distance from the central source. The data are well-fitted by dust opacities
for coagulated dust grains with ice mantles (Ossenkopf & Henning 1994). The
density profile from an inside-out collapse model (Shu 1977) does not fit the
data well, unless the infall radius is set so small as to make the density
nearly a power-law.Comment: Accepted to ApJ. 28 pages, 13 figures, uses emulateapj5.st
Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
We have modeled the emission from dust in pre-protostellar cores, including a
self-consistent calculation of the temperature distribution for each input
density distribution. Model density distributions include Bonnor-Ebert spheres
and power laws. The Bonnor-Ebert spheres fit the data well for all three cores
we have modeled. The dust temperatures decline to very low values (\Td \sim 7
K) in the centers of these cores, strongly affecting the dust emission.
Compared to earlier models that assume constant dust temperatures, our models
indicate higher central densities and smaller regions of relatively constant
density. Indeed, for L1544, a power-law density distribution, similar to that
of a singular, isothermal sphere, cannot be ruled out. For the three sources
modeled herein, there seems to be a sequence of increasing central
condensation, from L1512 to L1689B to L1544. The two denser cores, L1689B and
L1544, have spectroscopic evidence for contraction, suggesting an evolutionary
sequence for pre-protostellar cores.Comment: 22 pages, 9 figures, Ap. J. accepted, uses emulateapj5.st
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Incremental Reduction in Risk of Death Associated with Use of Guideline-Recommended Therapies in Patients with Heart Failure: A Nested Case-Control Analysis of IMPROVE HF
Background: Several therapies are guideline-recommended to reduce mortality in patients with heart failure (HF) and reduced left ventricular ejection fraction, but the incremental clinical effectiveness of these therapies has not been well studied. We aimed to evaluate the individual and incremental benefits of guideline-recommended HF therapies associated with 24-month survival. Methods and results: We performed a nested case-control study of HF patients enrolled in IMPROVE HF. Cases were patients who died within 24 months and controls were patients who survived to 24 months, propensity-matched 1:2 for multiple prognostic variables. Logistic regression was performed, and the attributable mortality risk from incomplete application of each evidence-based therapy among eligible patients was calculated. A total of 1376 cases and 2752 matched controls were identified. β-Blocker and cardiac resynchronization therapy were associated with the greatest 24-month survival benefit (adjusted odds ratio for death 0.42, 95% confidence interval (CI), 0.34â0.52; and 0.44, 95% CI, 0.29â0.67, respectively). Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, implantable cardioverter-defibrillators, anticoagulation for atrial fibrillation, and HF education were also associated with benefit, whereas aldosterone antagonist use was not. Incremental benefits were observed with each successive therapy, plateauing once any 4 to 5 therapies were provided (adjusted odds ratio 0.31, 95% CI, 0.23â0.42 for 5 or more versus 0/1, P<0.0001). Conclusions: Individual, with a single exception, and incremental use of guideline-recommended therapies was associated with survival benefit, with a potential plateau at 4 to 5 therapies. These data provide further rationale to implement guideline-recommended HF therapies in the absence of contraindications to patients with HF and reduced left ventricular ejection fraction
The Detection and Characterization of cm Radio Continuum Emission from the Low-mass Protostar L1014-IRS
Observations by the Cores to Disk Legacy Team with the Spitzer Space
Telescope have identified a low luminosity, mid-infrared source within the
dense core, Lynds 1014, which was previously thought to harbor no internal
source. Followup near-infrared and submillimeter interferometric observations
have confirmed the protostellar nature of this source by detecting scattered
light from an outflow cavity and a weak molecular outflow. In this paper, we
report the detection of cm continuum emission with the VLA. The emission is
characterized by a quiescent, unresolved 90 uJy 6 cm source within 0.2" of the
Spitzer source. The spectral index of the quiescent component is between 6 cm and 3.6 cm. A factor of two increase in 6 cm
emission was detected during one epoch and circular polarization was marginally
detected at the level with Stokes {V/I} % . We have
searched for 22 GHz H2O maser emission toward L1014-IRS, but no masers were
detected during 7 epochs of observations between June 2004 and December 2006.
L1014-IRS appears to be a low-mass, accreting protostar which exhibits cm
emission from a thermal jet or a wind, with a variable non-thermal emission
component. The quiescent cm radio emission is noticeably above the correlation
of 3.6 cm and 6 cm luminosity versus bolometric luminosity, indicating more
radio emission than expected. We characterize the cm continuum emission in
terms of observations of other low-mass protostars, including updated
correlations of centimeter continuum emission with bolometric luminosity and
outflow force, and discuss the implications of recent larger distance estimates
on the physical attributes of the protostar and dense molecular core.Comment: 14 pages. Accepted for publication in Ap
Chemistry and Dynamics in Pre-Protostellar Cores
We have compared molecular line emission to dust continuum emission and
modeled molecular lines using Monte Carlo simulations in order to study the
depletion of molecules and the ionization fraction in three preprotostellar
cores, L1512, L1544, and L1689B. L1512 is much less dense than L1544 and
L1689B, which have similar density structures. L1689B has a different
environment from those of L1512 and L1544. We used density and temperature
profiles, calculated by modeling dust continuum emission in the submillimeter,
for modeling molecular line profiles. In addition, we have used molecular line
profiles and maps observed in several different molecules toward the three
cores. We find a considerable diversity in chemical state among the three
cores. The molecules include those sensitive to different timescales of
chemical evolution such as CCS, the isotopes of CO and HCO+, DCO+, and N2H+.
The CO molecule is significantly depleted in L1512 and L1544, but not in
L1689B. CCS may be in the second enhancement of its abundance in L1512 and
L1544 because of the significant depletion of CO molecules. N2H+ might already
start to be depleted in L1512, but it traces very well the distribution of dust
emission in L1544. On the other hand, L1689B may be so young that N2H+ has not
reached its maximum yet. The ionization fraction has been calculated using
H13CO+ and DCO+. This study suggests that chemical evolution depends on the
absolute timescale during which a core stays in a given environment as well as
its density structure.Comment: 33 pages, 12 figures, accepted to Ap
Tracing the Mass during Low-Mass Star Formation, IV: Observations and Modeling of the Submillimeter Continuum Emission from Class I Protostars
We present results from the observations and modeling of seventeen Class I
cores with the Submillimetre Common Users Bolometer Array (SCUBA) on the James
Clerk Maxwell Telescope (JCMT). By modeling the transfer of radiation through
the envelope for nine cores, we find, for a power law distribution
n(r)=n_f(r/r_f)^-p, the average and standard deviation p=1.6 +/- 0.4 and a
median of p=1.8. However, the inclusion of a disk or other point-like component
can cause the derived p to be shallower by as much as 0.5. In addition, we test
the Shu collapse model for our sources and discuss the application of simpler
analyses that derive a density power law distribution directly from the slope
of the intensity radial profile. The total mass of the envelope in our sample
has a range from 0.04 to 5.0 M_sun, but these masses disagree with the virial
masses derived from molecular line observations. Finally, we discuss the nature
of these sources in light of various evolutionary indicators and find that
T_bol and L_obs/L_smm are often inconsistent in distinguishing Class 0 from
Class I cores.Comment: Accepted to ApJS. 50 pages with 27 figures and 12 tables.
High-resolution figures at http://peggysue.as.utexas.edu/cyoung
A Very Low-Carbohydrate Diet Improves Symptoms and Quality of Life in Diarrhea-Predominant Irritable Bowel Syndrome
Patients with diarrhea-predominant IBS (IBS-D) anecdotally report symptom improvement after initiating a very low-carbohydrate diet (VLCD). This is the first study to prospectively evaluate a VLCD in IBS-D
Spitzer observations of a 24 micron shadow: Bok Globule CB190
We present Spitzer observations of the dark globule CB190 (L771). We observe
a roughly circular 24 micron shadow with a 70 arcsec radius. The extinction
profile of this shadow matches the profile derived from 2MASS photometry at the
outer edges of the globule and reaches a maximum of ~32 visual magnitudes at
the center. The corresponding mass of CB190 is ~10 Msun. Our 12CO and 13CO J =
2-1 data over a 10 arcmin X 10 arcmin region centered on the shadow show a
temperature ~10 K. The thermal continuum indicates a similar temperature for
the dust. The molecular data also show evidence of freezeout onto dust grains.
We estimate a distance to CB190 of 400 pc using the spectroscopic parallax of a
star associated with the globule. Bonnor-Ebert fits to the density profile, in
conjunction with this distance, yield xi_max = 7.2, indicating that CB190 may
be unstable. The high temperature (56 K) of the best fit Bonnor-Ebert model is
in contradiction with the CO and thermal continuum data, leading to the
conclusion that the thermal pressure is not enough to prevent free-fall
collapse. We also find that the turbulence in the cloud is inadequate to
support it. However, the cloud may be supported by the magnetic field, if this
field is at the average level for dark globules. Since the magnetic field will
eventually leak out through ambipolar diffusion, it is likely that CB190 is
collapsing or in a late pre-collapse stage.Comment: 16 pages, 13 figures, accepted for publication in Ap
An ammonia spectral map of the L1495-B218 filaments in the Taurus molecular cloud. I. Physical properties of filaments and dense cores
We present deep NH3 observations of the L1495-B218 filaments in the Taurus molecular cloud covering over a 3° angular range using the K-band focal plane array on the 100 m Green Bank Telescope. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed NH3 (1, 1) and (2, 2) with a spectral resolution of 0.038 km sâ1 and a spatial resolution of 31''. Most of the ammonia peaks coincide with intensity peaks in dust continuum maps at 350 and 500 Îźm. We deduced physical properties by fitting a model to the observed spectra. We find gas kinetic temperatures of 8â15 K, velocity dispersions of 0.05â0.25 km sâ1, and NH3 column densities of 5 Ă 1012 to 1 Ă 1014 cmâ2. The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithms, identifies a total of 55 NH3 structures, including 39 leaves and 16 branches. The masses of the NH3 sources range from 0.05 to 9.5 . The masses of NH3 leaves are mostly smaller than their corresponding virial mass estimated from their internal and gravitational energies, which suggests that these leaves are gravitationally unbound structures. Nine out of 39 NH3 leaves are gravitationally bound, and seven out of nine gravitationally bound NH3 leaves are associated with star formation. We also found that 12 out of 30 gravitationally unbound leaves are pressure confined. Our data suggest that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and undergo collapse to form a protostar
Effect of a Hospital and Postdischarge Quality Improvement Intervention on Clinical Outcomes and Quality of Care for Patients With Heart Failure With Reduced Ejection Fraction: The CONNECT-HF Randomized Clinical Trial
Importance: Adoption of guideline-directed medical therapy for patients with heart failure is variable. Interventions to improve guideline-directed medical therapy have failed to consistently achieve target metrics, and limited data exist to inform efforts to improve heart failure quality of care.
Objective: To evaluate the effect of a hospital and postdischarge quality improvement intervention compared with usual care on heart failure outcomes and care.
Design, Setting, and Participants: This cluster randomized clinical trial was conducted at 161 US hospitals and included 5647 patients (2675 intervention vs 2972 usual care) followed up after a hospital discharge for acute heart failure with reduced ejection fraction (HFrEF). The trial was performed from 2017 to 2020, and the date of final follow-up was August 31, 2020.
Interventions: Hospitals (nâ=â82) randomized to a hospital and postdischarge quality improvement intervention received regular education of clinicians by a trained group of heart failure and quality improvement experts and audit and feedback on heart failure process measures (eg, use of guideline-directed medical therapy for HFrEF) and outcomes. Hospitals (nâ=â79) randomized to usual care received access to a generalized heart failure education website.
Main Outcomes and Measures: The coprimary outcomes were a composite of first heart failure rehospitalization or all-cause mortality and change in an opportunity-based composite score for heart failure quality (percentage of recommendations followed).
Results: Among 5647 patients (mean age, 63 years; 33% women; 38% Black; 87% chronic heart failure; 49% recent heart failure hospitalization), vital status was known for 5636 (99.8%). Heart failure rehospitalization or all-cause mortality occurred in 38.6% in the intervention group vs 39.2% in usual care (adjusted hazard ratio, 0.92 [95% CI, 0.81 to 1.05). The baseline quality-of-care score was 42.1% vs 45.5%, respectively, and the change from baseline to follow-up was 2.3% vs -1.0% (difference, 3.3% [95% CI, -0.8% to 7.3%]), with no significant difference between the 2 groups in the odds of achieving a higher composite quality score at last follow-up (adjusted odds ratio, 1.06 [95% CI, 0.93 to 1.21]).
Conclusions and Relevance: Among patients with HFrEF in hospitals randomized to a hospital and postdischarge quality improvement intervention vs usual care, there was no significant difference in time to first heart failure rehospitalization or death, or in change in a composite heart failure quality-of-care score.
Trial Registration: ClinicalTrials.gov Identifier: NCT03035474
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