2,581 research outputs found
Time-Series Photometry of Stars in and around the Lagoon Nebula. I. Rotation Periods of 290 Low-Mass Pre-Main-Sequence Stars in NGC 6530
We have conducted a long-term, wide-field, high-cadence photometric
monitoring survey of ~50,000 stars in the Lagoon Nebula \ion{H}{2} region. This
first paper presents rotation periods for 290 low-mass stars in NGC 6530, the
young cluster illuminating the nebula, and for which we assemble a catalog of
infrared and spectroscopic disk indicators, estimated masses and ages, and
X-ray luminosities. The distribution of rotation periods we measure is broadly
uniform for 0.5 < P < 10 d; the short-period cutoff corresponds to breakup. We
observe no obvious bimodality in the period distribution, but we do find that
stars with disk signatures rotate more slowly on average. The stars' X-ray
luminosities are roughly flat with rotation period, at the saturation level
(). However, we find a significant
positive correlation between and co-rotation radius,
suggesting that the observed X-ray luminosities are regulated by centrifugal
stripping of the stellar coronae. The period-mass relationship in NGC 6530 is
broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the
relationship among the slowest rotators differs from that in the ONC and other
young clusters. We show that the slope of the period-mass relationship for the
slowest rotators can be used as a proxy for the age of a young cluster, and we
argue that NGC 6530 may be slightly younger than the ONC, making it a
particularly important touchstone for models of angular momentum evolution in
young, low-mass stars.Comment: 28 pages, 18 figures, Accepted for publication in ApJ. For a brief
video explaining the key results of this paper, see
http://www.youtube.com/user/OSUAstronomy#p/u/1/WarGh6GiWu
The 2008 outburst in the young stellar system ZCMa: I. Evidence of an enhanced bipolar wind on the AU-scale
Accretion is a fundamental process in star formation. Although the time
evolution of accretion remains a matter of debate, observations and modelling
studies suggest that episodic outbursts of strong accretion may dominate the
formation of the protostar. Observing young stellar objects during these
elevated accretion states is crucial to understanding the origin of unsteady
accretion. ZCMa is a pre-main-sequence binary system composed of an embedded
Herbig Be star, undergoing photometric outbursts, and a FU Orionis star. The
Herbig Be component recently underwent its largest optical photometric outburst
detected so far. We aim to constrain the origin of this outburst by studying
the emission region of the HI Brackett gamma line, a powerful tracer of
accretion/ejection processes on the AU-scale in young stars. Using the
AMBER/VLTI instrument at spectral resolutions of 1500 and 12 000, we performed
spatially and spectrally resolved interferometric observations of the hot gas
emitting across the Brackett gamma emission line, during and after the
outburst. From the visibilities and differential phases, we derive
characteristic sizes for the Brackett gamma emission and spectro-astrometric
measurements across the line, with respect to the continuum. We find that the
line profile, the astrometric signal, and the visibilities are inconsistent
with the signature of either a Keplerian disk or infall of matter. They are,
instead, evidence of a bipolar wind, maybe partly seen through a disk hole
inside the dust sublimation radius. The disappearance of the Brackett gamma
emission line after the outburst suggests that the outburst is related to a
period of strong mass loss rather than a change of the extinction along the
line of sight. Based on these conclusions, we speculate that the origin of the
outburst is an event of enhanced mass accretion, similar to those occuring in
EX Ors and FU Ors.Comment: Accepted for publication in Astronomy and Astrophysics Letter
Do drugs interact together in cardiovascular prevention? A meta-analysis of powerful or factorial randomized controlled trials.
To explore whether preventive cardiovascular drugs (antihypertensive, antiplatelet, lipid lowering and hypoglycemic agents) interact together in cardiovascular prevention.
We searched PubMed®, Web of science™, Embase and Cochrane library for powerful randomized placebo-controlled trials (>1000 patients). We explored whether drug effect on major vascular events changed according to cross-exposure to other drug classes or to cardiovascular risk factors (hypertension or type 2 diabetes), through a meta-analysis of relative odds ratio computed by trial subgroups. A significant interaction was suggested from confidence intervals of the ratio of odds ratios, when they excluded neutral value of 1.
In total, 14 trials with 178,398 patients were included. No significant interaction was observed between co-prescribed drugs or between these medications and type 2 diabetes/hypertension status.
Our meta-analysis is the first one to evaluate drug-drug and drug-hypertension/type 2 diabetes status interactions in terms of cardiovascular risks: we did not observe any significant interaction. This indirectly reinforces the rationale of using several contrasted mechanisms to address cardiovascular prevention; and allows the combination effect prediction by a simple multiplication of their odds ratios. The limited availability of data reported or obtained from authors is a strong argument in favor of data sharing
The STAR Silicon Strip Detector (SSD)
The STAR Silicon Strip Detector (SSD) completes the three layers of the
Silicon Vertex Tracker (SVT) to make an inner tracking system located inside
the Time Projection Chamber (TPC). This additional fourth layer provides two
dimensional hit position and energy loss measurements for charged particles,
improving the extrapolation of TPC tracks through SVT hits. To match the high
multiplicity of central Au+Au collisions at RHIC the double sided silicon strip
technology was chosen which makes the SSD a half million channels detector.
Dedicated electronics have been designed for both readout and control. Also a
novel technique of bonding, the Tape Automated Bonding (TAB), was used to
fullfill the large number of bounds to be done. All aspects of the SSD are
shortly described here and test performances of produced detection modules as
well as simulated results on hit reconstruction are given.Comment: 11 pages, 8 figures, 1 tabl
Online Monitoring of the Osiris Reactor with the Nucifer Neutrino Detector
Originally designed as a new nuclear reactor monitoring device, the Nucifer
detector has successfully detected its first neutrinos. We provide the second
shortest baseline measurement of the reactor neutrino flux. The detection of
electron antineutrinos emitted in the decay chains of the fission products,
combined with reactor core simulations, provides an new tool to assess both the
thermal power and the fissile content of the whole nuclear core and could be
used by the Inter- national Agency for Atomic Energy (IAEA) to enhance the
Safeguards of civil nuclear reactors. Deployed at only 7.2m away from the
compact Osiris research reactor core (70MW) operating at the Saclay research
centre of the French Alternative Energies and Atomic Energy Commission (CEA),
the experiment also exhibits a well-suited configuration to search for a new
short baseline oscillation. We report the first results of the Nucifer
experiment, describing the performances of the 0.85m3 detector remotely
operating at a shallow depth equivalent to 12m of water and under intense
background radiation conditions. Based on 145 (106) days of data with reactor
ON (OFF), leading to the detection of an estimated 40760 electron
antineutrinos, the mean number of detected antineutrinos is 281 +- 7(stat) +-
18(syst) electron antineutrinos/day, in agreement with the prediction 277(23)
electron antineutrinos/day. Due the the large background no conclusive results
on the existence of light sterile neutrinos could be derived, however. As a
first societal application we quantify how antineutrinos could be used for the
Plutonium Management and Disposition Agreement.Comment: 22 pages, 16 figures - Version
High pressure phases in highly piezoelectric Pb(Zr0.52Ti0.48)O3
Two novel room-temperature phase transitions are observed, via synchrotron
x-ray diffraction and Raman spectroscopy, in the Pb(Zr0.52Ti0.48)O3 alloy under
hydrostatic pressures up to 16 GPa. A monoclinic (M)-to-rhombohedral (R1) phase
transition takes place around 2-3 GPa, while this R1 phase transforms into
another rhombohedral phase, R2, at about 6-7 GPa. First-principles calculations
assign the R3m and R3c symmetry to R1 and R2, respectively, and reveal that R2
acts as a pressure-induced structural bridge between the polar R3m and a
predicted antiferrodistortive R-3c phase.Comment: REVTeX, 4 pages with 3 figures embedded. Figs 1 and 3 in colo
Anomalous electronic susceptibility in Bi2Sr2CuO6+d and comparison with other overdoped cuprates
We report magnetic susceptibility performed on overdoped Bi2Sr2CuO6+d powders
as a function of oxygen doping d and temperature T. The decrease of the spin
susceptibility with increasing T is confirmed. At sufficient high temperature,
the spin susceptibility Chi_s presents an unusual linear temperature dependence
Chi_s ~ Chi_s0 -Chi_1 T. Moreover, a linear correlation between Chi_1 and
Chi_s0 for increasing hole concentration is displayed. A temperature Tchi,
independent of hole doping characterizes this scaling. Comparison with other
cuprates of the literature(LSCO, Tl-2201 and Bi-2212), over the same overdoped
range, shows similarities with above results. These non conventional metal
features will be discussed in terms of a singular narrow-band structure.Comment: 16 pages, 4 figure
Vasopressin and oxytocin receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database
Vasopressin (AVP) and oxytocin (OT) receptors (nomenclature as recommended by NC-IUPHAR [92]) are activated by the endogenous cyclic nonapeptides vasopressin and oxytocin. These peptides are derived from precursors which also produce neurophysins (neurophysin I for oxytocin; neurophysin II for vasopressin). Vasopressin and oxytocin differ at only 2 amino acids (positions 3 and 8). There are metabolites of these neuropeptides that may be biologically active [67]
Vasopressin and oxytocin receptors in GtoPdb v.2023.1
Vasopressin (AVP) and oxytocin (OT) receptors (nomenclature as recommended by NC-IUPHAR [94]) are activated by the endogenous cyclic nonapeptides vasopressin and oxytocin. These peptides are derived from precursors which also produce neurophysins (neurophysin I for oxytocin; neurophysin II for vasopressin). Vasopressin and oxytocin differ at only 2 amino acids (positions 3 and 8). There are metabolites of these neuropeptides that may be biologically active [69]
IACT observations of gamma-ray bursts: prospects for the Cherenkov Telescope Array
Gamma rays at rest frame energies as high as 90 GeV have been reported from
gamma-ray bursts (GRBs) by the Fermi Large Area Telescope (LAT). There is
considerable hope that a confirmed GRB detection will be possible with the
upcoming Cherenkov Telescope Array (CTA), which will have a larger effective
area and better low-energy sensitivity than current-generation imaging
atmospheric Cherenkov telescopes (IACTs). To estimate the likelihood of such a
detection, we have developed a phenomenological model for GRB emission between
1 GeV and 1 TeV that is motivated by the high-energy GRB detections of
Fermi-LAT, and allows us to extrapolate the statistics of GRBs seen by lower
energy instruments such as the Swift-BAT and BATSE on the Compton Gamma-ray
Observatory. We show a number of statistics for detected GRBs, and describe how
the detectability of GRBs with CTA could vary based on a number of parameters,
such as the typical observation delay between the burst onset and the start of
ground observations. We also consider the possibility of using GBM on Fermi as
a finder of GRBs for rapid ground follow-up. While the uncertainty of GBM
localization is problematic, the small field-of-view for IACTs can potentially
be overcome by scanning over the GBM error region. Overall, our results
indicate that CTA should be able to detect one GRB every 20 to 30 months with
our baseline instrument model, assuming consistently rapid pursuit of GRB
alerts, and provided that spectral breaks below 100 GeV are not a common
feature of the bright GRB population. With a more optimistic instrument model,
the detection rate can be as high as 1 to 2 GRBs per year.Comment: 28 pages, 24 figures, 4 tables, submitted to Experimental Astronom
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