58 research outputs found

    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

    A search for the OH 6035 MHz line in high-mass star-forming regions

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    Context. The excited states of OH masers detected in the environment of high-mass young stellar objects (HMYSOs) are important for improving our understanding of the physical conditions of these objects and also provide information about their magnetic fields. Aims. We aim to search for excited-state OH 6035 MHz maser emission in HMYSOs which might have escaped detection in previous surveys or were never searched for. Methods. A sample of HMYSOs derived from untargeted surveys of the 6668 MHz methanol maser line was observed at 6035 MHz OH transition with the Torun 32 m radio telescope. The 6035 MHz detections were observed in the OH 6031 MHz line. Two-thirds of the detections were observed at least three times over a two-year period. Results. Out of 445 targets, 37 were detected at 6035 MHz, including seven new discoveries. The 6031 MHz line was detected towards ten 6035 MHz sources, one of which was not previously reported. All the newly detected sources are faint with the peak flux density lower than 4 Jy and show significant or high variability on timescales of 4 to 20 months. Zeeman pair candidates identified in three new sources imply a magnetic field intensity of 2-11 mG. Comparison of our spectra with those obtained ~10 yr ago indicates different degrees of variability but there is a general increase in the variability index on an ~25 yr timescale, usually accompanied by significant changes in the profile shape

    PoS(10th EVN Symposium)002 The magic of disc-worlds: non-rotating methanol masers PoS(10th EVN Symposium)002

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    In recent studies of methanol masers, a substantial fraction of the objects show maser components aligned in large-scale elliptical configurations. These can be readily interpreted as rings centred on a high mass star in formation, seen in projection. Remarkably, most of these rings do not show signs of rotation, but rather the radial motions dominate. This must mean that their dynamics are governed by other than gravitational forces. In particular, we have studied the methanol masers around Cep A in detail, where it can be argued that the methanol masers show signs of infall. In this paper we discuss the dynamics of the Cep A methanol maser and sources from the Torun blind survey to argue that at least in a fraction of sources methanol masers could be associated with the shock interface between the large scale accretion, regulated by the magnetic field, and a 1000-AU scale circumstellar disk. We discuss the validity of such a model for the overall population of methanol maser sources. 10th European VLBI Network Symposium and EVN Users Meeting: VLBI and the new generation of radio array

    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

    The nature of the methanol maser ring G23.657–00.127 II. Expansion of the maser structure

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    To protect the copyright in your article, the following copyright notice should be included in the credit: “Reproduced with permission from Astronomy & Astrophysics, © ESO”. https://www.aanda.org/for-authors/author-information/copyrightContext. Ring-like distributions of the 6.7 GHz methanol maser spots at milliarcsecond scales represent a family of molecular structures of unknown origin associated with high-mass young stellar objects. Aims: We aim to study G23.657-00.127, which has a nearly circular ring of the 6.7 GHz methanol masers, and is the most suitable target to test hypotheses on the origin of the maser rings. Methods: The European Very Long Baseline Interferometry Network was used at three epochs spanning 10.3 yr to derive the spatio-kinematical structure of the 6.7 GHz methanol maser emission in the target. Results: The maser cloudlets, lying in a nearly symmetric ring, expand mainly in the radial direction with a mean velocity of 3.2 km s-1. There is an indication that the radial component of the velocity increases with cloudlet's distance from the ring centre. The tangential component does not show any clear evidence for rotation of the cloudlets or any relationship with distance from the ring centre. The blue-shifted masers may hint at an anticlockwise rotation of cloudlets in the southern part of the ring. The nearly circular structure of the ring clearly persisted for more than 10 yr. Interferometric data demonstrated that about one quarter of cloudlets show significant variability in their brightness, although the overall spectrum was non-variable in single-dish studies. Conclusions: Taking into account the three-dimensional motion of the maser cloudlets and their spatial distribution along a small ring, we speculate about two possible scenarios where the methanol masers trace either a spherical outflow arising from an (almost) edge-on disc, or a wide angle wind at the base of a protostellar jet. The latter is associated with near- and mid-infrared emission detected towards the ring. High angular resolution images of complementary (thermal) tracers are needed to interpret the environment of methanol masers

    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

    Uraemic symptom burden and clinical condition in women and men of ≥65 years of age with advanced chronic kidney disease: Results from the EQUAL study

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    Background. The epidemiology and prognosis of chronic kidney disease (CKD) differ by sex. We aimed to compare symptom prevalence and the clinical state in women and men of ≥65 years of age with advanced CKD receiving routine nephrology care. Methods. The European QUALity study on treatment in advanced chronic kidney disease (EQUAL) study follows patients from six European countries of ≥65 years of age years whose estimated glomerular filtration rate (eGFR) dropped to ≤20 mL/min/ 1.73 m2 for the first time during the last 6 months. The Dialysis Symptom Index was used to assess the prevalence and severity of 33 uraemic symptoms. Data on the clinical state at baseline were collected from medical records. Prevalence was standardized using the age distribution of women as the reference. Results. The results in women (n = 512) and men (n = 967) did not differ with age (77.0 versus 75.7 years) or eGFR (19.0 versus 18.5). The median number of symptoms was 14 [interquartile range (IQR) 9–19] in women, and 11 (IQR 7–16) in men. Women most frequently reported fatigue {39% [95% confidence interval (CI) 34–45]} and bone/joint pain [37% (95% CI 32–42)] as severe symptoms, whereas more men reported difficulty in becoming sexually aroused [32% (95% CI 28–35)] and a decreased interest in sex [31% (95% CI 28–35)]. Anaemia [73% (95% CI 69–77) versus 85% (95% CI 82–87)] was less common in women than in men, as were smoking history and cardiovascular comorbidity. However, a diagnosis of liver disease other than cirrhosis, psychiatric disease and mild malnutrition were more common among women. Conclusions. Women in secondary care with an incident eGFR ≤20 mL/min/1.73 m2 reported a higher symptom burden, while their clinical state was considered similar or even more favourable as compared with men

    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

    Comparative analysis of passive and hybrid EMI filters to reduce conducted noise

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    W niniejszym artykule została przedstawiona analiza możliwości zastosowania hybrydowych filtrów EMI do tłumienia zaburzeń przewodzonych wspólnych CM. Badana była skuteczność filtrów przy tłumieniu wysokiego poziomu zaburzeń generowanych przez falownik. Przedstawiono również sposób powstawania i propagacji zaburzeń przewodzonych w przykładowym falowniku. Badany był wpływ zastosowania w konstrukcji filtru hybrydowego różnych rdzeni magnetycznych oraz porównano uzyskane tłumienności wtrąceniowe z filtrami pasywnymi. Na koniec wskazano zalety i wady obu technik filtracji.This article presents an analysis of the applicability of hybrid EMI filters to reduce common mode noise. The effectiveness of filters was tested when attenuating the high level of EMI noise generated by the frequency inverter. The method of formation and propagation of conductive EMI noise in an exemplary frequency inverter is also presented. The influence of the use of various magnetic cores in the hybrid EMI filter construction was investigated and the obtained insertion losses with passive filters were compared. The article concludes with the advantages and disadvantages of both filtration techniques
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