By matching infrared-selected, massive young stellar objects (MYSOs) and compact H ii regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large ...Area Survey of the Galaxy) survey, we have identified ∼1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1
$_{.}^{\circ}$
5. Combined with an existing sample of radio-selected methanol masers and compact H ii regions, the result is a catalogue of ∼1700 massive stars embedded within ∼1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H ii-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H ii-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.
The Red MSX Source (RMS) survey has identified a sample of ∼1200 massive young stellar objects (MYSOs), compact and ultra-compact H ii regions from a sample of ∼2000 MSX and Two Micron All Sky Survey ...(2MASS) colour-selected sources. We have used the 100-m Green Bank Telescope to search for 22-24 GHz water maser and ammonia (1,1), (2,2) and (3,3) emission towards ∼600 RMS sources located within the northern Galactic plane. We have identified 308 H2O masers which corresponds to an overall detection rate of ∼50 per cent. We find no significant difference in the detection rate for H ii regions and MYSOs which would suggest that the conditions required to produce maser emission are equally likely in both phases. Comparing the detection rates as a function of luminosity, we find the H2O detection rate has a positive dependence on the source luminosity, with the detection rate increasing with increasing luminosity.
We detect ammonia emission towards 479 of these massive young stars, which corresponds to ∼80 per cent. Ammonia is an excellent probe of high-density gas allowing us to measure key parameters such as gas temperatures, opacities and column densities, as well as providing an insight into the gas kinematics. The average kinetic temperature, full width at half-maximum linewidth and total NH3 column density for the sample are approximately 22 K, 2 km s−1 and 2 × 1015 cm−2, respectively. We find that the NH3 (1,1) linewidth and kinetic temperature are correlated with luminosity, and finding no underlying dependence of these parameters on the evolutionary phase of the embedded sources, we conclude that the observed trends in the derived parameters are more likely to be due to the energy output of the central source and/or the linewidth-clump mass relationship.
The velocities of the peak H2O masers and the NH3 emission are in excellent agreement with each other, which would strongly suggest an association between the dense gas and the maser emission. Moreover, we find the bolometric luminosity of the embedded source and the isotropic luminosity of the H2O maser are also correlated. We conclude from the correlations of the cloud and water maser velocities and the bolometric and maser luminosity that there is a strong dynamical relationship between the embedded young massive star and the H2O maser.
A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during its first nine polar orbits about the planet. ...Observations acquired during eight of these orbits provide the first truly global coverage of Jupiter's magnetic field with a coarse longitudinal separation of ~45 deg between perijoves. The magnetic field is represented with a degree 20 spherical harmonic model for the planetary ("internal") field, combined with a simple model of the magnetodisc for the field ("external") due to distributed magnetospheric currents. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("Juno Reference Model through Perijove 9") of the planetary magnetic field with spherical harmonic coefficients well determined through degree and order 10, providing the first detailed view of a planetary dynamo beyond Earth.
Oceanic harmful algal blooms of
diatoms produce the potent mammalian neurotoxin domoic acid (DA). Despite decades of research, the molecular basis for its biosynthesis is not known. By using growth ...conditions known to induce DA production in
, we implemented transcriptome sequencing in order to identify DA biosynthesis genes that colocalize in a genomic four-gene cluster. We biochemically investigated the recombinant DA biosynthetic enzymes and linked their mechanisms to the construction of DA's diagnostic pyrrolidine skeleton, establishing a model for DA biosynthesis. Knowledge of the genetic basis for toxin production provides an orthogonal approach to bloom monitoring and enables study of environmental factors that drive oceanic DA production.
A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only ...two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images.
Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the ‘dominant’ nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption).
ABSTRACT
ATLASGAL is an 870-µm dust survey of 420 deg2 the inner Galactic plane and has been used to identify ∼10 000 dense molecular clumps. Dedicated follow-up observations and complementary ...surveys are used to characterize the physical properties of these clumps, map their Galactic distribution, and investigate the evolutionary sequence for high-mass star formation. The analysis of the ATLASGAL data is ongoing: We present an up-to-date version of the catalogue. We have classified 5007 clumps into four evolutionary stages (quiescent, protostellar, young stellar objects and H ii regions) and find similar numbers of clumps in each stage, suggesting a similar lifetime. The luminosity-to-mass (Lbol/Mfwhm) ratio curve shows a smooth distribution with no significant kinks or discontinuities when compared to the mean values for evolutionary stages indicating that the star formation process is continuous and that the observational stages do not represent fundamentally different stages or changes in the physical mechanisms involved. We compare the evolutionary sample with other star formation tracers (methanol and water masers, extended green objects and molecular outflows) and find that the association rates with these increases as a function of evolutionary stage, confirming that our classification is reliable. This also reveals a high association rate between quiescent sources and molecular outflows, revealing that outflows are the earliest indication that star formation has begun and that star formation is already ongoing in many of the clumps that are dark even at 70 µm.
We present a complete sample of molecular clumps containing compact and ultracompact H ii (UC H ii) regions between = 10° and 60° and |b| < 1°, identified by combining the APEX Telescope Large Area ...Survey of the Galaxy submm and CORNISH radio continuum surveys with visual examination of archival infrared data. Our sample is complete to optically thin, compact and UC H ii regions driven by a zero-age main-sequence star of spectral type B0 or earlier embedded within a 1000 M clump. In total we identify 213 compact and UC H ii regions, associated with 170 clumps. Unambiguous kinematic distances are derived for these clumps and used to estimate their masses and physical sizes, as well as the Lyman continuum fluxes and sizes of their embedded H ii regions. We find a clear lower envelope for the surface density of molecular clumps hosting massive star formation of 0.05 g cm−2, which is consistent with a similar sample of clumps associated with 6.7 GHz masers. The mass of the most massive embedded stars is closely correlated with the mass of their natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by current stellar atmosphere models. The properties of clumps associated with compact and UC H ii regions are very similar to those associated with 6.7 GHz methanol masers and we speculate that there is little evolution in the structure of the molecular clumps between these two phases. Finally, we identify a significant peak in the surface density of compact and UC H ii-regions associated with the W49A star-forming complex, noting that this complex is truly one of the most massive and intense regions of star formation in the Galaxy.
Kainic acid, the flagship member of the kainoid family of natural neurochemicals, is a widely used neuropharmacological agent that helped unravel the key role of ionotropic glutamate receptors, ...including the kainate receptor, in the central nervous system. Worldwide shortages of this seaweed natural product in the year 2000 prompted numerous chemical syntheses, including scalable preparations with as few as six‐steps. Herein we report the discovery and characterization of the concise two‐enzyme biosynthetic pathway to kainic acid from l‐glutamic acid and dimethylallyl pyrophosphate in red macroalgae and show that the biosynthetic genes are co‐clustered in genomes of Digenea simplex and Palmaria palmata. Moreover, we applied a key biosynthetic α‐ketoglutarate‐dependent dioxygenase enzyme in a biotransformation methodology to efficiently construct kainic acid on the gram scale. This study establishes both the feasibility of mining seaweed genomes for their biotechnological prowess.
Kainic acid is a marine natural product that has been used as an anthelmintic agent for centuries and, more recently, a neurological tool. Using a genomic sequencing approach, the genes responsible for the biosynthesis of kainic acid were discovered in two different seaweeds. In vitro characterization validated enzymatic activity and enabled gram‐scale production of kainic acid using a biotransformation approach.
Abstract
We present HST spectroscopy for 45 cataclysmic variables (CVs), observed with HST/COS and HST/STIS. For 36 CVs, the white dwarf is recognisable through its broad Ly α absorption profile and ...we measure the white dwarf effective temperatures (T
eff) by fitting the HST data assuming log g = 8.35, which corresponds to the average mass for CV white dwarfs (≃0.8 M⊙). Our results nearly double the number of CV white dwarfs with an accurate temperature measurement. We find that CVs above the period gap have, on average, higher temperatures (〈T
eff〉 ≃ 23 000 K) and exhibit much more scatter compared to those below the gap (〈T
eff〉 ≃ 15 000 K). While this behaviour broadly agrees with theoretical predictions, some discrepancies are present: (i) all our new measurements above the gap are characterized by lower temperatures (T
eff ≃ 16 000–26 000 K) than predicted by the present-day CV population models (T
eff ≃ 38 000–43 000 K); (ii) our results below the gap are not clustered in the predicted narrow track and exhibit in particular a relatively large spread near the period minimum, which may point to some shortcomings in the CV evolutionary models. Finally, in the standard model of CV evolution, reaching the minimum period, CVs are expected to evolve back towards longer periods with mean accretion rates
$\dot{M}\lesssim 2 \times 10^{-11}\,\mathrm{M}_{\odot }\,\mathrm{yr}^{-1}$
, corresponding to T
eff ≲ 11 500 K. We do not unambiguously identify any such system in our survey, suggesting that this major component of the predicted CV population still remains elusive to observations.
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