17 research outputs found

    Planetary nebulae with LOFAR 120-168MHz obs.

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    VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'Evidence for cold plasma in planetary nebulae from radio observations with the LOw Frequency ARray (LOFAR).' (bibcode: 2021ApJ...919..121H

    De Novo ACTG1 Variant Expands the Phenotype and Genotype of Partial Deafness and Baraitser–Winter Syndrome

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    Actin molecules are fundamental for embryonic structural and functional differentiation; γ-actin is specifically required for the maintenance and function of cytoskeletal structures in the ear, resulting in hearing. Baraitser–Winter Syndrome (B-WS, OMIM #243310, #614583) is a rare, multiple-anomaly genetic disorder caused by mutations in either cytoplasmically expressed actin gene, ACTB (β-actin) or ACTG1 (γ-actin). The resulting actinopathies cause characteristic cerebrofrontofacial and developmental traits, including progressive sensorineural deafness. Both ACTG1-related non-syndromic A20/A26 deafness and B-WS diagnoses are characterized by hypervariable penetrance in phenotype. Here, we identify a 28th patient worldwide carrying a mutated γ-actin ACTG1 allele, with mildly manifested cerebrofrontofacial B-WS traits, hypervariable penetrance of developmental traits and sensorineural hearing loss. This patient also displays brachycephaly and a complete absence of speech faculty, previously unreported for ACTG1-related B-WS or DFNA20/26 deafness, representing phenotypic expansion. The patient’s exome sequence analyses (ES) confirms a de novo ACTG1 variant previously unlinked to the pathology. Additional microarray analysis uncover no further mutational basis for dual molecular diagnosis in our patient. We conclude that γ-actin c.542C > T, p.Ala181Val is a dominant pathogenic variant, associated with mildly manifested facial and cerebral traits typical of B-WS, hypervariable penetrance of developmental traits and sensorineural deafness. We further posit and present argument and evidence suggesting ACTG1-related non-syndromic DFNA20/A26 deafness is a manifestation of undiagnosed ACTG1-related B-WS

    Recent updates on the Maser Monitoring Organisation

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    The Maser Monitoring Organisation (M2O) is a research community of telescope operators, astronomy researchers and maser theoreticians pursuing a joint goal of reaching a deeper understanding of maser emission and exploring its variety of uses as tracers of astrophysical events. These proceedings detail the origin, motivations and current status of the M2O, as was introduced at the 2021 EVN symposium

    Millimeter methanol emission in the high-mass young stellar object G24.33+0.14

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    <jats:title>Abstract</jats:title> <jats:p>In 2019 September, a sudden flare of the 6.7???GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR??NIRS3, NGC??6334I-MM1, and G358.93???0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8???yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle??3) and the mid-flare phase in 2019 September (ALMA Cycle??6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7???GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle??6//Cycle??3) of 1.16 ?? 0.01, considering an additional absolute flux calibration uncertainty of 10%10\%. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ?? 0.15. In contrast, eight methanol lines observed in Cycle??6 are brighter than those in Cycle??3 with an average flux ratio of 1.23 ?? 0.13, and the higher excitation lines tend to show a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759???GHz (8???1???70??E) line known as a class??I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR??NIRS3 and NGC??6334I-MM1 but is comparable with that in G358.93???0.03-MM1, suggesting different amounts of accreted mass in these events.</jats:p&gt

    Evidence for Cold Plasma in Planetary Nebulae From Radio Observations With the LOw Frequency ARray (LOFAR)

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    We present observations of planetary nebulae with the LOw Frequency ARray (LOFAR) between 120 and 168 MHz. The images show thermal free–free emission from the nebular shells. We have determined the electron temperatures for spatially resolved, optically thick nebulae. These temperatures are 20%–60% lower than those estimated from collisionally excited optical emission lines. This strongly supports the existence of a cold plasma component, which co-exists with hot plasma in planetary nebulae. This cold plasma does not contribute to the collisionally excited lines, but does contribute to recombination lines and radio flux. Neither of the plasma components are spatially resolved in our images, although we infer that the cold plasma extends to the outer radii of planetary nebulae. However, more cold plasma appears to exist at smaller radii. The presence of cold plasma should be taken into account in modeling of radio emission of planetary nebulae. Modelling of radio emission usually uses electron temperatures calculated from collisionally excited optical and/or infrared lines. This may lead to an underestimate of the ionized mass and an overestimate of the extinction correction from planetary nebulae when derived from the radio flux alone. The correction improves the consistency of extinction derived from the radio fluxes when compared to estimates from the Balmer decrement flux ratios

    Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

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    Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort

    Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

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    Context: Periodic flares of maser emission are thought to be induced either by variations of the seed photon flux in young binary systems or the pump rate regulated by stellar and accretion luminosities. Aims: We seek to study the variability of four maser transitions of three different species in G107.298+5.639 to constrain the dominant mechanism of periodic flares. Methods: Light curves of the 6.7 GHz methanol and 22.2 GHz water vapour maser were obtained with the Torun 32 m radio telescope over 39 and 34 cycles, respectively. The target was also monitored at the 1.6 GHz hydroxyl transitions with the Nançay radio telescope over 13 cycles. All these maser lines were imaged using VLBI arrays. Results: The study confirms alternating flares of the methanol and water masers with a period of 34.4 d and reveals the synchronised behaviour of the methanol and hydroxyl masers in this source. The observed spatial distribution of the methanol maser cloudlets and the measured time delays of the flares of individual features imply a ring-like structure of radius 240 au and thickness 30 au. Internal proper motions indicate that the velocity of methanol cloudlets is dominated by a disc-wind component of about 5 km s −1 . The methanol emission detected during only one VLBI observation is located in a region about 550 au from a central star, which also exhibits OH maser flares. The erratic appearance of methanol features can be related to a powering object of relatively low luminosity which, during some variability cycles, can excite molecules only in the nearest part of the disc. A careful analysis of the maser and infrared light curves reveal a strong correlation between the 6.7 GHz line and the infrared flux densities supporting a radiative pumping of the maser. Conclusions: The synchronised behaviour of the hydroxyl 1665/1667 MHz and 6.7 GHz methanol transitions indicates a common pumping mechanism for the periodic flares of G107.298+5.639

    New evidence for Dicke's superradiance in the 6.7 GHz methanol spectral line in the interstellar medium

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    We present new evidence for superradiance (SR) in the methanol 6.7 GHz spectral line for three different star-forming regions: S255IR-NIRS3, G24.329+0.144, and Cepheus A. Our analysis shows that some of the flux–density flares exhibiting fast rise times and asymmetric light curves reported in these sources can naturally be explained within the context of SR. When a threshold for the inverted population column density is exceeded in a maser-hosting region, the radiation mode switches from one regulated by stimulated emission (maser) to SR. Superradiance, as a more efficient energy release mechanism, manifests itself through strong bursts of radiation emanating from spatially compact regions. Elevated inverted population densities and the initiation of SR can be due to a change in radiative pumping. Here, we show that an increase in the pump rate and the inverted population density of only a factor of a few results in a significant increase in radiation. While the changes in the pump rate can take place over a few hundred days, the rise in radiation flux density when SR is initiated is drastic and happens over a much shorter time-scale

    6.7 GHz variability characteristics of new periodic methanol maser sources

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    Discovery of periodic maser emission was an unexpected result from monitoring observations of methanol transitions in high-mass young stellar objects. We report on the detection of five new periodic sources from a monitoring program with the Torun 32 m telescope. Variability with a period of 149 to 540 d and different patterns from sinusoidal-like to intermittent was displayed. Three-dimensional structure of G59.633−0.192 determined from the time delays of burst peaks of the spectral features and high angular resolution map implies that the emission traces a disc. For this source the 6.7 GHz light curve followed the infrared variability supporting a radiative scheme of pumping. An unusual time delay of ∼80 d occurred in G30.400−0.296 could not be explained by the light travel time and may suggest a strong differentiation of physical conditions and excitation in this deeply embedded source. Our observations suggest the intermittent variability may present a simple response of maser medium to the underlying variability induced by the accretion luminosity while other variability patterns may reflect more complex changes in the physical conditions

    A Giant Water Maser Flare in the Galactic Source IRAS 18316-0602

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    The results of long-term monitoring of the Galactic maser source IRAS 18316-0602 (G25.65+1.05) in the water-vapor line at frequency f = 22.235 GHz (6_16-5_23 transitioin) carried out on the 22-m Simeiz, 26-m HartRAO, and 26-m Torun radio telescopes are reported. The source has been episodically observed on the Simeiz telescope since 2000, with more regular observations beginning in 2017. A double flare was observed beginning in September 2017 and continuing to February 2018, which was the most powerful flare registered over the entire history of observations of this object. Most of the monitoring of the flare was carried out in a daily regime. Detailed analysis of the variations of the flux density, which reached a maximum value P ≈ 1.3 × 10^5 Jy, have led to important scientific conclusions about possible mechanisms for the emission in this water line. The exponential growth in the flux density in this double flare testifies that it was associated with a maser that was unsaturated right up to the maximum flux densities observed. An additional argument suggesting the maser was unsaturated is the relatively moderate degree of linear polarization (≈30%), nearly half the value displayed by the Galactic kilomasers in Orion KL. The accurate distance estimate for IRAS 18316-0602 (12.5 kpc) and the flux density at the flare maximum (≈1.3 × 10^5 Jy) makes this the most powerful Galactic kilomaser known. The double form of the flare with exponential rises in flux density rules out the possibility that the flare is the effect of directivity of a radiation beam relative to the observer. The physical nature of the flare is most likely related to internal parameters of the medium in which the maser clumps radiating in the water line are located. A rapid, exponential growth in the flux density of a kilomaser and associated exponential decays requires the presence of an explosive increase in the density of the medium and the photon flux, leading to an increase in the temperature by 10-40 K above the initial base level. A mechanism for the primary energy release in IRAS 18316-0602 is proposed, which is associated with a multiple massive star system located in a stage of evolution preceding its entry onto the main sequence. A flare in this object could initiate gravitational interaction between the central star and a massive companion at its periastron. The resulting powerful gravitational perturbation could lead to the ejection of the envelope of the central supermassive star, which gives rise to an explosive increase in the density and temperature of the associate gas-dust medium when it reaches the disk, where the maser clumps are located
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