Detection of complex organic molecules in young starless core L1521E

Determining the level of chemical complexity within dense starless and gravitationally bound pre-stellar cores is crucial for constructing chemical models, which subsequently constrain the initial chemical conditions of star formation. We have searched for complex organic molecules (COMs) in the young starless core L1521E, and report the first clear detection of dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), and vinyl cyanide (CH2CHCN). Eight transitions of acetaldehyde (CH3CHO) were also detected, five of which (A states) were used to determine an excitation temperature to then calculate column densities for the other oxygen-bearing COMs. If source size was not taken into account (i.e. if filling fraction was assumed to be one), column density was underestimated, and thus we stress the need for higher resolution mapping data. We calculated L1521E COM abundances and compared them to other stages of low-mass star formation, also finding similarities to other starless/pre-stellar cores, suggesting related chemical evolution. The scenario that assumes formation of COMs in gas-phase reactions between precursors formed on grains and then ejected to the cold gas via reactive desorption was tested and was unable to reproduce observed COM abundances, with the exception of CH3CHO. These results suggest that COMs observed in cold gas are formed not by gas-phase reactions alone, but also through surface reactions on interstellar grains. Our observations present a new, unique challenge for existing theoretical astrochemical models. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.The 12-m telescope is operated by the Arizona RadioObservatory (ARO), StewardObservatory,University of Arizona, with funding from the State of Arizona, NSF MRI Grant AST-1531366 (PI Ziurys), NSF MSIP grant SV5-85009/AST- 1440254 (PI Marrone), NSF CAREER grant AST-1653228 (PI Marrone), and a PIRE grant OISE-1743747 (PI Psaltis). Yancy Shirley and Samantha Scibelli were partially supported by NSF Grant AST-1410190 (PI Shirley). Samantha Scibelli is supported by National Science Foundation Graduate Research Fellowship (NSF GRF) Grant DGE-1143953. Anton Vasyunin is supported by the Russian Ministry of Science and Higher Education via the State Assignment Project FEUZ-2020-0038

Droplets I: Pressure-Dominated Sub-0.1 pc Coherent Structures in L1688 and B18

We present the observation and analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using data from the Green Bank Ammonia Survey (GAS), we identify regions of high density and near-constant, almost-thermal, velocity dispersion. Eighteen coherent structures are revealed, twelve in L1688 and six in B18, each of which shows a sharp "transition to coherence" in velocity dispersion around its periphery. The identification of these structures provides a chance to study the coherent structures in molecular clouds statistically. The identified coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4 Msun, generally smaller than previously known coherent cores identified by Goodman et al. (1998), Caselli et al. (2002), and Pineda et al. (2010). We call these structures "droplets." We find that unlike previously known coherent cores, these structures are not virially bound by self-gravity and are instead predominantly confined by ambient pressure. The droplets have density profiles shallower than a critical Bonnor-Ebert sphere, and they have a velocity (VLSR) distribution consistent with the dense gas motions traced by NH3 emission. These results point to a potential formation mechanism through pressure compression and turbulent processes in the dense gas. We present a comparison with a magnetohydrodynamic simulation of a star-forming region, and we speculate on the relationship of droplets with larger, gravitationally bound coherent cores, as well as on the role that droplets and other coherent structures play in the star formation process.Comment: Accepted by ApJ in April, 201

Alignment of dense molecular core morphology and velocity gradients with ambient magnetic fields

Studies of dense core morphologies and their orientations with respect to gas flows and the local magnetic field have been limited to only a small sample of cores with spectroscopic data. Leveraging the Green Bank Ammonia Survey alongside existing sub-millimeter continuum observations and Planck dust polarization, we produce a cross-matched catalogue of 399 dense cores with estimates of core morphology, size, mass, specific angular momentum, and magnetic field orientation. Of the 399 cores, 329 exhibit 2D $\mathrm{v}_\mathrm{LSR}$ maps that are well fit with a linear gradient, consistent with rotation projected on the sky. We find a best-fit specific angular momentum and core size relationship of $J/M \propto R^{1.82 \pm 0.10}$, suggesting that core velocity gradients originate from a combination of solid body rotation and turbulent motions. Most cores have no preferred orientation between the axis of core elongation, velocity gradient direction, and the ambient magnetic field orientation, favouring a triaxial and weakly magnetized origin. We find, however, strong evidence for a preferred anti-alignment between the core elongation axis and magnetic field for protostellar cores, revealing a change in orientation from starless and prestellar populations that may result from gravitational contraction in a magnetically-regulated (but not dominant) environment. We also find marginal evidence for anti-alignment between the core velocity gradient and magnetic field orientation in the L1228 and L1251 regions of Cepheus, suggesting a preferred orientation with respect to magnetic fields may be more prevalent in regions with locally ordered fields.Comment: 33 pages, 28 figures, accepted to MNRA

Velocity-coherent substructure in TMC-1: inflow and fragmentation

Filamentary structures have been found nearly ubiquitously in molecular clouds and yet their formation and evolution is still poorly understood. We examine a segment of Taurus Molecular Cloud 1 (TMC-1) that appears as a single, narrow filament in continuum emission from dust. We use the Regularized Optimization for Hyper-Spectral Analysis (ROHSA), a Gaussian decomposition algorithm that enforces spatial coherence when fitting multiple velocity components simultaneously over a data cube. We analyse HC5N (9-8) line emission as part of the Green Bank Ammonia Survey and identify three velocity-coherent components with ROHSA. The two brightest components extend the length of the filament, while the third component is fainter and clumpier. The brightest component has a prominent transverse velocity gradient of 2.7 ± 0.1 km s-1 pc-1 that we show to be indicative of gravitationally induced inflow. In the second component, we identify regularly spaced emission peaks along its length. We show that the local minima between pairs of adjacent HC5N peaks line up closely with submillimetre continuum emission peaks, which we argue is evidence for fragmentation along the spine of TMC-1. While coherent velocity components have been described as separate physical structures in other star-forming filaments, we argue that the two bright components identified in HC5N emission in TMC-1 are tracing two layers in one filament: a lower density outer layer whose material is flowing under gravity towards the higher density inner layer of the filament. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society

Velocity-coherent Filaments in NGC 1333: Evidence for Accretion Flow?

Recent observations of global velocity gradients across and along molecular filaments have been interpreted as signs of gas accreting onto and along these filaments, potentially feeding star-forming cores and protoclusters. The behavior of velocity gradients in filaments, however, has not been studied in detail, particularly on small scales (<0.1 pc). In this paper, we present MUFASA, an efficient, robust, and automatic method to fit ammonia lines with multiple velocity components, generalizable to other molecular species. We also present CRISPy, a Python package to identify filament spines in 3D images (e.g., position-position-velocity cubes), along with a complementary technique to sort fitted velocity components into velocity-coherent filaments. In NGC 1333, we find a wealth of velocity gradient structures on a beam-resolved scale of ∼0.05 pc. Interestingly, these local velocity gradients are not randomly oriented with respect to filament spines and their perpendicular, i.e., radial, component decreases in magnitude toward the spine for many filaments. Together with remarkably constant velocity gradients on larger scales along many filaments, these results suggest a scenario in which gas falling onto filaments is progressively damped and redirected to flow along these filaments. © 2020. The American Astronomical Society. All rights reserved

Enhancing Oral Vaccine Potency by Targeting Intestinal M Cells

The immune system in the gastrointestinal tract plays a crucial role in the control of infection, as it constitutes the first line of defense against mucosal pathogens. The attractive features of oral immunization have led to the exploration of a variety of oral delivery systems. However, none of these oral delivery systems have been applied to existing commercial vaccines. To overcome this, a new generation of oral vaccine delivery systems that target antigens to gut-associated lymphoid tissue is required. One promising approach is to exploit the potential of microfold (M) cells by mimicking the entry of pathogens into these cells. Targeting specific receptors on the apical surface of M cells might enhance the entry of antigens, initiating the immune response and consequently leading to protection against mucosal pathogens. In this article, we briefly review the challenges associated with current oral vaccine delivery systems and discuss strategies that might potentially target mouse and human intestinal M cells

Relative alignment between dense molecular cores and ambient magnetic field: The synergy of numerical models and observations

The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in (i) a 3D magnetohydrodynamic simulation, (ii) synthetic observations generated from the simulation at different viewing angles, and (iii) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc to core scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flows along the magnetic field towards dense cores. When comparing the observed cores identified from the Green Bank Ammonia Survey and Planck polarizationinferredmagnetic field orientations,we find that the relative core-field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field.We argue that this feature of relative core-field orientation could be used to probe the relative significance of the magnetic field within the cloud. © 2020 Oxford University Press. All rights reserved.The authors would like to thank Juan Soler, who originally provided the smoothed Planck polarization maps, and Mark Heyer for encouraging critiques that improved the paper. C-YC, LMF, and Z-YL acknowledge support from National Science Foundation (of United States) (NSF) grant AST-1815784. EAB was supported by a REU summer research fellowship at the National Radio Astronomy Observatory (NRAO), and LMF acknowledges support as a Jansky Fellow of NRAO. NRAO is a facility of the NSF (operated under cooperative agreement by Associated Universities, Inc.). LMF and Z-YL acknowledge support from National Aeronautics and Space Administration (of the United States) (NASA) 80NSSC18K0481. Z-YL was supported in part by NASA 80NSSC18K1095 and NSF AST-1716259. AP acknowledges the financial support of the Russian Science Foundation project 19-72-00064. SSRO and HH-HC acknowledge support from a Cottrell Scholar Award from Research Corporation. AC-T acknowledges support from Ministry of Economy and Competitiveness (of Spain) (MINECO) project AYA2016-79006-P. This research made use of ASTROPY (Astropy Collaboration 2013; Price-Whelan et al. 2018) and ASTRODENDRO, a PYTHON package to compute dendrograms of astronomical data. The authors thank the staff at the Green Bank Telescope for their help facilitating the Green Bank Ammonia Survey. The Green Bank Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc

Sensore stellare per controllo assetto di piccoli satelliti

Lo scopo è quello di proporre un sistema di controllo, caratterizzato da accuratezza della misura nell’ordine del decimo di grado, e utilizzabile in quei satelliti che, per dimensioni e budget di missione, devono farne generalmente a meno, che può aggiungere informazioni importanti per l’interpretazione delle misure a cui è destinata la missione satellitar