136 research outputs found
Millimeter Dust Emission in the GQ Lup System
We present Submillimeter Array observations of the GQ Lup system at 1.3
millimeters wavelength with 0\farcs4 (60 AU) resolution. Emission is
detected from the position of the primary star, GQ Lup A, and is marginally
resolved. No emission is detected from the substellar companion, GQ Lup B,
0\farcs7 away. These data, together with models of the spectral energy
distribution, suggest a compact disk around GQ Lup A with mass
M, perhaps truncated by tidal forces. There is no evidence for a gap or
hole in the disk that might be the signature of an additional inner companion
body capable of scattering GQ Lup B out to AU separation from GQ Lup
A. For GQ Lup B to have formed {\it in situ}, the disk would have to have been
much more massive and extended.Comment: 16 pages, 2 figures, accepted to A
A New Probe of the Planet-Forming Region in T Tauri Disks
We present new observations of the FUV (1100-2200 Angstrom) radiation field
and the near- to mid-IR (3--13.5 micron) spectral energy distribution (SED) of
a sample of T Tauri stars selected on the basis of bright molecular disks (GM
Aur, DM Tau, LkCa15). In each source we find evidence for Ly alpha induced H2
fluorescence and an additional source of FUV continuum emission below 1700
Angstroms. Comparison of the FUV spectra to a model of H2 excitation suggests
that the strong continuum emission is due to electron impact excitation of H2.
The ultimate source of this excitation is likely X-ray irradiation which
creates hot photo-electrons mixed in the molecular layer. Analysis of the SED
of each object finds the presence of inner disk gaps with sizes of a few AU in
each of these young (~1 Myr) stellar systems. We propose that the presence of
strong H2 continuum emission and inner disk clearing are related by the
increased penetration power of high energy photons in gas rich regions with low
grain opacity.Comment: 5 pages, 3 figures, accepted by ApJ Letter
Confirmation of a recent bipolar ejection in the very young hierarchical multiple system IRAS 16293-2422
We present and analyze two new high-resolution (approx 0.3 arcsec),
high-sensitivity (approx 50 uJy beam-1) Very Large Array 3.6 cm observations of
IRAS 16293-2422 obtained in 2007 August and 2008 December. The components
A2alpha and A2beta recently detected in this system are still present, and have
moved roughly symmetrically away from source A2 at a projected velocity of
30-80 km s-1. This confirms that A2alpha and A2beta were formed as a
consequence of a very recent bipolar ejection from A2. Powerful bipolar
ejections have long been known to occur in low-mass young stars, but this is
-to our knowledge-- the first time that such a dramatic one is observed from
its very beginning. Under the reasonable assumption that the flux detected at
radio wavelengths is optically thin free-free emission, one can estimate the
mass of each ejecta to be of the order of 10^-8 Msun. If the ejecta were
created as a consequence of an episode of enhanced mass loss accompanied by an
increase in accretion onto the protostar, then the total luminosity of IRAS
16293-2422 ought to have increased by 10-60% over the course of at least
several months. Between A2alpha and A2beta, component A2 has reappeared, and
the relative position angle between A2 and A1 is found to have increased
significantly since 2003-2005. This strongly suggests that A1 is a protostar
rather than a shock feature, and that the A1/A2 pair is a tight binary system.
Including component B, IRAS 16293-2422 therefore appears to be a very young
hierarchical multiple system.Comment: Accepted for publication in The Astrophysical Journa
Resolving the CO Snow Line in the Disk around HD 163296
We report Submillimeter Array (SMA) observations of CO (J=2--1, 3--2 and
6--5) and its isotopologues (13CO J=2--1, C18O J=2--1 and C17O J=3--2) in the
disk around the Herbig Ae star HD 163296 at ~2" (250 AU) resolution, and
interpret these data in the framework of a model that constrains the radial and
vertical location of the line emission regions. First, we develop a physically
self-consistent accretion disk model with an exponentially tapered edge that
matches the spectral energy distribution and spatially resolved millimeter dust
continuum emission. Then, we refine the vertical structure of the model using
wide range of excitation conditions sampled by the CO lines, in particular the
rarely observed J=6--5 transition. By fitting 13CO data in this structure, we
further constrain the vertical distribution of CO to lie between a lower
boundary below which CO freezes out onto dust grains (T ~ 19 K) and an upper
boundary above which CO can be photodissociated (the hydrogen column density
from the disk surface is ~ 10^{21} cm-2). The freeze-out at 19 K leads to a
significant drop in the gas-phase CO column density beyond a radius of ~155 AU,
a "CO snow line" that we directly resolve. By fitting the abundances of all CO
isotopologues, we derive isotopic ratios of 12C/13C, 16O/18O and 18O/17O that
are consistent with quiescent interstellar gas-phase values. This detailed
model of the HD 163296 disk demonstrates the potential of a staged, parametric
technique for constructing unified gas and dust structure models and
constraining the distribution of molecular abundances using resolved
multi-transition, multi-isotope observations.Comment: 40 pages, 13 figures, accepted for publication in Ap
Reduction of prevalence of patients meeting the criteria for metabolic syndrome with tirzepatide: a post hoc analysis from the SURPASS Clinical Trial Program
Background: Metabolic syndrome is characterized as the co-occurrence of interrelated cardiovascular risk factors, including insulin resistance, hyperinsulinemia, abdominal obesity, dyslipidemia and hypertension. Once weekly tirzepatide is approved in the US and EU for the treatment of type 2 diabetes (T2D) and obesity. In the SURPASS clinical trial program for T2D, tirzepatide demonstrated greater improvements in glycemic control, body weight reduction and other cardiometabolic risk factors versus placebo, subcutaneous semaglutide 1 mg, insulin degludec, and insulin glargine. This post hoc analysis assessed the effect of tirzepatide use on the prevalence of patients meeting the criteria for metabolic syndrome across SURPASS 1â5. Methods: Metabolic syndrome was defined as having â„ 3 of 5 criteria according to the US National Cholesterol Education Program: Adult Treatment Panel III. Analyses were based on on-treatment data at the primary endpoint from patients adherent to treatment (taking â„ 75% study drug). A logistic regression model with metabolic syndrome status as the response variable, metabolic syndrome status at the baseline visit as an adjustment, and randomized treatment as fixed explanatory effect was used. The effect of tirzepatide use on the prevalence of patients meeting the criteria for metabolic syndrome by categorical weight loss, background medication and gender were assessed. Results: In SURPASS, the prevalence of patients meeting the criteria for metabolic syndrome at baseline was 67â88% across treatment groups with reductions at the primary endpoint to 38â64% with tirzepatide versus 64â82% with comparators. Reductions in the prevalence of patients meeting the criteria for metabolic syndrome was significantly greater with all tirzepatide doses versus placebo, semaglutide 1 mg, insulin glargine, and insulin degludec (p < 0.001). Individual components of metabolic syndrome were also reduced to a greater extent with tirzepatide vs comparators. Greater reductions in body weight were associated with greater reductions in the prevalence of patients meeting the criteria for metabolic syndrome and its individual components. Background SGLT2i or sulfonylurea use or gender did not impact the change in prevalence of patients meeting the criteria for metabolic syndrome. Conclusions: In this post hoc analysis, tirzepatide at all doses studied was associated with a greater reduction in the prevalence of patients meeting the criteria for metabolic syndrome compared to placebo, semaglutide 1 mg, insulin degludec, and insulin glargine. Although more evidence is needed, these data would support greater potential improvement in cardiovascular risk factor profile with tirzepatide treatment in people across the continuum of T2D
Chemical Imaging of the CO Snow Line in the HD 163296 Disk
The condensation fronts (snow lines) of H2O, CO, and other abundant volatiles in the midplane of a protoplanetary disk affect several aspects of planet formation. Locating the CO snow line, where the CO gas column density is expected to drop substantially, based solely on CO emission profiles, is challenging. This has prompted an exploration of chemical signatures of CO freeze-out. We present ALMA Cycle 1 observations of the N2H+ J = 3â2 and DCO+ J = 4â3 emission lines toward the disk around the Herbig Ae star HD 163296 at ~0farcs5 (60 AU) resolution, and evaluate their utility as tracers of the CO snow line location. The N2H+ emission is distributed in a ring with an inner radius at 90 AU, corresponding to a midplane temperature of 25 K. This result is consistent with a new analysis of optically thin C18O data, which implies a sharp drop in CO abundance at 90 AU. Thus N2H+ appears to be a robust tracer of the midplane CO snow line. The DCO+ emission also has a ring morphology, but neither the inner nor the outer radius coincide with the CO snow line location of 90 AU, indicative of a complex relationship between DCO+ emission and CO freeze-out in the disk midplane. Compared to TW Hya, CO freezes out at a higher temperature in the disk around HD 163296 (25 versus 17 K in the TW Hya disk), perhaps due to different ice compositions. This highlights the importance of actually measuring the CO snow line location, rather than assuming a constant CO freeze-out temperature for all disks.Astronom
The TW Hya Disk at 870 microns: Comparison of CO and Dust Radial Structures
We present high resolution (0.3" = 16 AU), high signal-to-noise ratio
Submillimeter Array observations of the 870 microns (345 GHz) continuum and CO
J=3--2 line emission from the protoplanetary disk around TW Hya. Using
continuum and line radiative transfer calculations, those data and the
multiwavelength spectral energy distribution are analyzed together in the
context of simple two-dimensional parametric disk structure models. Under the
assumptions of a radially invariant dust population and (vertically integrated)
gas-to-dust mass ratio, we are unable to simultaneously reproduce the CO and
dust observations with model structures that employ either a single, distinct
outer boundary or a smooth (exponential) taper at large radii. Instead, we find
that the distribution of millimeter-sized dust grains in the TW Hya disk has a
relatively sharp edge near 60 AU, contrary to the CO emission (and
optical/infrared scattered light) that extends to a much larger radius of at
least 215 AU. We discuss some possible explanations for the observed radial
distribution of millimeter-sized dust grains and the apparent CO-dust size
discrepancy, and suggest that they may be hallmarks of substructure in the dust
disk or natural signatures of the growth and radial drift of solids that might
be expected for disks around older pre-main sequence stars like TW Hya.Comment: ApJ, in press (fixed typo in Equation 4
A 4-wk high-fructose diet alters lipid metabolism without affecting insulin sensitivity or ectopic lipids in healthy humans
BACKGROUND: High fructose consumption is suspected to be causally linked to the epidemics of obesity and metabolic disorders. In rodents, fructose leads to insulin resistance and ectopic lipid deposition. In humans, the effects of fructose on insulin sensitivity remain debated, whereas its effect on ectopic lipids has never been investigated. OBJECTIVE: We assessed the effect of moderate fructose supplementation on insulin sensitivity (IS) and ectopic lipids in healthy male volunteers (n = 7). DESIGN: IS, intrahepatocellular lipids (IHCL), and intramyocellular lipids (IMCL) were measured before and after 1 and 4 wk of a high-fructose diet containing 1.5 g fructose . kg body wt(-1) . d(-1). Adipose tissue IS was evaluated from nonesterified fatty acid suppression, hepatic IS from suppression of hepatic glucose output (6,6-2H2-glucose), and muscle IS from the whole-body glucose disposal rate during a 2-step hyperinsulinemic euglycemic clamp. IHCL and IMCL were measured by 1H magnetic resonance spectroscopy. RESULTS: Fructose caused significant (P < 0.05) increases in fasting plasma concentrations of triacylglycerol (36%), VLDL-triacylglycerol (72%), lactate (49%), glucose (5.5%), and leptin (48%) without any significant changes in body weight, IHCL, IMCL, or IS. IHCL were negatively correlated with triacylglycerol after 4 wk of the high-fructose diet (r = -0.78, P < 0.05). CONCLUSION: Moderate fructose supplementation over 4 wk increases plasma triacylglycerol and glucose concentrations without causing ectopic lipid deposition or insulin resistance in healthy humans
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