Large-scale morphology and time evolution are investigated for the unified model of bipolar outflows outlined in Shang et al. (2006), where an outflow forms by a radially directed, wide-angle ...magnetized wind interacting with magnetized isothermal toroids in various quasistatic states. The primary wide-angle wind is toroidally magnetized and maintains a cylindrically stratified density profile, mimicking the asymptotic solution of the cold X-wind model. We explore the interplay between the toroidally magnetized primary wind and the surrounding toroids threaded by poloidal magnetic fields and examine how the jet and shell morphology and fine structures within them vary with the physical parameters. The variation in flatness of the density distribution in the ambient isothermal toroids helps shape the varieties of lobe morphology and collimation. The presence of a stronger ambient poloidal field helps shape the outflow, forming a magnetic cocoon and nested multilayered cavities surrounding the wind-filled lobe, which is most evident in the more open configurations of the ambient toroids. The wind-toroid interface is prone to substantial shear and thus unstable to the Kelvin-Helmholtz instability. Magnetic forces in the compressed toroidally magnetized high-velocity wind can generate vorticity, leading to nonlinear patterns within the extended magnetized mixing layers. Magnetic disturbances generated by the interplay could modulate lobe shapes, density, and velocities, giving rise to visual impressions of thicker and rugged shells and apparent episodic distribution of matter. The system maintains a quasi-self-similar evolution in time, which serves as a proxy for understanding the underlying physical mechanisms driving it.
Ages and masses of young stars are often estimated by comparing their luminosities and effective temperatures to pre-main-sequence stellar evolution tracks, but magnetic fields and starspots ...complicate both the observations and evolution. To understand their influence, we study the heavily spotted weak-lined T-Tauri star LkCa 4 by searching for spectral signatures of radiation originating from the starspot or starspot groups. We introduce a new methodology for constraining both the starspot filling factor and the spot temperature by fitting two-temperature stellar atmosphere models constructed from Phoenix synthetic spectra to a high-resolution near-IR IGRINS spectrum. Clearly discernable spectral features arise from both a hot photospheric component ∼ 4100 K and a cool component ∼ 2700-3000 K, which covers ∼80% of the visible surface. This mix of hot and cool emission is supported by analyses of the spectral energy distribution, rotational modulation of colors and of TiO band strengths, and features in low-resolution optical/near-IR spectroscopy. Although the revised effective temperature and luminosity make LkCa 4 appear to be much younger and of much lower mass than previous estimates from unspotted stellar evolution models, appropriate estimates will require the production and adoption of spotted evolutionary models. Biases from starspots likely afflict most fully convective young stars and contribute to uncertainties in ages and age spreads of open clusters. In some spectral regions, starspots act as a featureless "veiling" continuum owing to high rotational broadening and heavy line blanketing in cool star spectra. Some evidence is also found for an anticorrelation between the velocities of the warm and cool components.
Abstract
Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected ...with the high-density tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS-315:
T
bol
∼ 180 K, spectral index ∼0.417), with a moderately high mass-loss rate (∼0.59 × 10
−6
M
⊙
yr
−1
) estimated from CO emission. Together, these features suggest that G205S3 is still in a high-accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS-399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼40°) for G205S3 from CO emission, which may expose the infrared emission from the central core and mislead the spectral classification. However, the compact 1.3 mm continuum, C
18
O emission, location in the bolometric luminosity to submillimeter fluxes diagram, outflow force (∼3.26 × 10
−5
M
⊙
km s
−1
yr
−1
) are also analogous to that of Class I systems. We thus consider G205S3 to be at the very early phase of Class I, and in the late phase of
high accretion
. The episodic ejection could be due to the presence of an unknown binary, a planetary companion, or dense clumps, where the required mass for such high accretion could be supplied by a massive circumbinary disk.
Abstract
Forbidden neon emission lines from small-scale microjets can probe high-energy processes in low-mass young stellar systems. We obtained spatially resolved Ne
iii
spectra in the microjets ...from the classical T Tauri Star Sz 102 using the Hubble Space Telescope Imaging Spectrograph at a spatial resolution of ∼0.″1. The blueshifted and redshifted Ne
iii
emission both peak in intensity within ∼0.″1 of the star and gradually decay along the flow outward to ∼0.″24. The spatial distribution and extent of the Ne
iii
microjet is consistent with a jet that is ionized close to the base and subsequently recombines on a longer timescale than the flow time. Ca
ii
H and K lines are also detected from the redshifted microjet with a line full-width at half-maximum of ∼170 km s
−1
, consistent with those of other forbidden emission lines, atop a 300 km s
−1
wide stellar component. The launching radius of the Sz 102 jet, inferred from the observed line centroids and the range of inclination angles and stellar masses from the literature, is on the order of ∼0.03 au. The possible proximity of the launching region to the star allows immediate ionization without distance dilution from the circumstellar ionization sources, most likely keV X-ray flares generated by magnetic reconnection events in the star--disk system, to sustain the observed Ne
iii
flux.
Abstract
Hot corinos are of great interest due to their richness in interstellar complex organic molecules (COMs) and the consequent potential prebiotic connection to solar-like planetary systems. ...Recent surveys have reported an increasing number of detected hot corinos in Class 0/I protostars; however, the relationships between their physical properties and the hot-corino signatures remain elusive. In this study, our objective is to establish a general picture of the detectability of hot corinos by identifying the origins of the hot-corino signatures in the sample of young stellar objects (YSOs) obtained from the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps project. We apply spectral energy distribution modeling to our sample and identify the physical parameters of the modeled YSOs directly, linking the detection of hot-corino signatures to the envelope properties of the YSOs. Imaging simulations of the methanol emission further support this scenario. We therefore posit that the observed COM emission originates from the warm inner envelopes of the sample YSOs, based on both the warm region size and the envelope density profile. The former is governed by the source luminosity and is additionally affected by the disk and cavity properties, while the latter is related to the evolutionary stages. This scenario provides a framework for detecting hot-corino signatures toward luminous Class 0 YSOs, with fewer detections being observed toward similarly luminous Class I sources.
A new hypervalent‐iodine(III)‐mediated tandem reaction involving oxidative dearomatization and in situ aziridination of phenolic amines is described, providing a mild and effective method for the ...assembly of structurally interesting and synthetically useful aziridines. Importantly, the densely functionalized aziridines resulting from this unprecedented tandem reaction offer a platform for expeditious access to architecturally diverse aza‐heterocycles through transformations initiated by selective ring‐opening of aziridines.
An unprecedented tandem reaction (oxidative dearomatization/aziridination) of phenolic amines in the presence of hypervalent‐iodine(III) reagent is described. This cascade reaction shows a chemical unification of the oxidative reactivity of phenol and aliphatic primary amine in the chemistry of dearomatization and aziridination, thus providing a new method for the synthesis of unactivated aziridines with dense functionalization.
Multiferroics refer to materials with two or more ferroic orders in one phase within a specific temperature range, including ferroelectricity, ferroelasticity, and ferromagnetism which have been ...widely used in sensors, actuators, and memory devices. Among them, hybrid perovskites exhibiting multiferroicity are generally limited to low dimensions (0D–2D). Designing 3D lead‐free perovskite multiferroics remains a challenge due to Goldschmidt's tolerance factor limitation. Here, a multiferroic perovskite (R‐3AP)RbBr3 (1; 3AP = 3‐ammoniopyrrolidinium) is successfully synthesized by introducing homochirality to the 3D ferroelectric (Rac‐3AP)RbBr3, achieving both ferroelasticity and ferroelectricity. Compound 1 undergoes a structure phase transition at 401 K belonging to Aizu notation 432F2(s), which has 12 ferroelectric equivalent polarization directions and 6 polar axes. Furthermore, 1 exhibits reversible second harmonic generation switching effects. Moreover, while the temperature varies, the reversible and rapid changes of ferroelastic domains in 1 are observed using a polarizing microscope, indicating that it is a ferroelastic material. This work provides a practical method for designing and synthesizing molecule‐based multiferroics.
The work reports a 3D perovskite multiferroics (R‐3AP)RbBr3 (1) based on the 3D rubidium‐based ferroelectric (Rac‐3AP)RbBr3 by using the homochirality strategy. Compound 1 exhibits 432F2(s) ferroelectric–ferroelastic phase transition at 401 K. In addition, 1 exhibits a second harmonic generation (SHG) switch and multi‐axis ferroelectricity with a saturation polarization (Ps) value of 1.21 µC·cm−2.
Hybrid metal halides (HMHs) based phase transition materials have received widespread attention due to their excellent performance and potential applications in energy harvesting, optoelectronics, ...ferroics, and actuators. Nevertheless, effectively regulating the properties of phase transitions is still a thorny problem. In this work, two chiral lead‐free HMHs (R‐3FP)2SbCl5 (1; 3FP=3‐fluoropyrrolidinium) and (R‐3FP)2SbBr5 (2) were synthesized. By replacing the halide ions in the inorganic skeleton, the phase transition temperature of 2 changes with an increase of about 20 K, compared with 1. Meanwhile, both compounds display reversible dielectric switching properties. Through crystal structure analysis and Hirshfeld surface analysis, their phase transitions are ascribed to the disorder of the cations and deformation of the inorganic chains.
This article reports a pair of 1D lead‐free hybrid metal halides: (R‐3FP)2SbCl5 (1; 3FP=3‐fluoropyrrolidinium) and (R‐3FP)2SbBr5 (2) exhibit high temperature triggered structural phase transition and dielectric switching properties. By halogen substitution in the inorganic framework, the dielectric switch temperature of 2 increased about 20 K, compared with 1.
Abstract
For the active T-Taur star RW Aur A we have performed long-term (∼10 yr) monitoring observations of (1) jet imaging in the Fe II 1.644
μ
m emission line using Gemini-NIFS and VLT-SINFONI; ...(2) optical high-resolution spectroscopy using CFHT-ESPaDOnS; and (3)
V
-band photometry using the CrAO 1.25-m telescope and AAVSO. The latter two observations confirm the correlation of time variabilities between (A) the Ca II 8542 Å and O I 7772 Å line profiles associated with magnetospheric accretion, and (B) optical continuum fluxes. The jet images and their proper motions show that four knot ejections occurred at the star over the past ∼15 yr with an irregular interval of 2–6 yr. The timescale and irregularity of these intervals are similar to those of the dimming events seen in the optical photometry data. Our observations show a possible link between remarkable (Δ
V
< −1) photometric rises and jet knot ejections. Observations over another few years may confirm or reject this trend. If confirmed, this would imply that the location of the jet launching region is very close to the star (
r
≲ 0.1 au) as predicted by some jet launching models. Such a conclusion would be crucial for understanding disk evolution within a few astronomical units of the star, and therefore possible ongoing planet formation at these radii.
The last case of infection with wild-type poliovirus indigenous to China was reported in 1994, and China was certified as a poliomyelitis-free region in 2000. In 2011, an outbreak of infection with ...imported wild-type poliovirus occurred in the province of Xinjiang.
We conducted an investigation to guide the response to the outbreak, performed sequence analysis of the poliovirus type 1 capsid protein VP1 to determine the source, and carried out serologic and coverage surveys to assess the risk of viral propagation. Surveillance for acute flaccid paralysis was intensified to enhance case ascertainment.
Between July 3 and October 9, 2011, investigators identified 21 cases of infection with wild-type poliovirus and 23 clinically compatible cases in southern Xinjiang. Wild-type poliovirus type 1 was isolated from 14 of 673 contacts of patients with acute flaccid paralysis (2.1%) and from 13 of 491 healthy persons who were not in contact with affected persons (2.6%). Sequence analysis implicated an imported wild-type poliovirus that originated in Pakistan as the cause of the outbreak. A public health emergency was declared in Xinjiang after the outbreak was confirmed. Surveillance for acute flaccid paralysis was enhanced, with daily reporting from all public and private hospitals. Five rounds of vaccination with live, attenuated oral poliovirus vaccine (OPV) were conducted among children and adults, and 43 million doses of OPV were administered. Trivalent OPV was used in three rounds, and monovalent OPV type 1 was used in two rounds. The outbreak was stopped 1.5 months after laboratory confirmation of the index case.
The 2011 outbreak in China showed that poliomyelitis-free countries remain at risk for outbreaks while the poliovirus circulates anywhere in the world. Global eradication of poliomyelitis will benefit all countries, even those that are currently free of poliomyelitis.
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