ORCID Profile
0000-0003-4468-761X
Current Organisations
PepsiCo International Ltd
,
University of the West of England
,
Max-Plank-Institut für Radioastronomie
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Publisher: EDP Sciences
Date: 10-2022
DOI: 10.1051/0004-6361/202245024
Abstract: We report the discovery of widespread maser emission in non-metastable inversion transitions of NH 3 toward various parts of the Sagittarius B2 molecular cloud and star-forming region complex. We detect masers in the J , K = (6, 3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH 3 (6,3) maser in Sgr B2(NS), and NH 3 (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in the A-configuration, we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single-dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are 3000 K and reach up to several 10 5 K, manifesting the lines’ maser nature. In view of the masers’ velocity differences with respect to adjacent hot molecular cores and/or UCH II regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH II regions. Overall, Sgr B2 is unique in that it allows us to measure many NH 3 masers simultaneously, which may be essential in order to elucidate their thus far poorly understood origin and excitation.
Publisher: American Astronomical Society
Date: 08-01-2015
Publisher: EDP Sciences
Date: 10-2022
DOI: 10.1051/0004-6361/202244115
Abstract: Class II methanol (CH 3 OH) masers are amongst the clearest signposts of recent high-mass star formation (HMSF). A complete catalogue outlines the distribution of star formation in the Galaxy, the number of young star-forming cores, and the physical conditions of their environment, made possible by the Global View on Star Formation (GLOSTAR) survey. This blind survey of the radio regime of 4–8 GHz maps the Galactic mid-plane in the radio continuum, 6.7 GHz methanol line, the 4.8 GHz formaldehyde line, and several radio recombination lines. We present an analysis of the observations of the 6.7 GHz CH 3 OH maser transition using data from the D-configuration of the Very Large Array (VLA). We analysed data covering Galactic longitudes from –2° l 60° and Galactic latitudes of | b | 1°. We detected a total of 554 methanol masers, out of which 84 are new, and we catalogued their positions, velocity components, and integrated fluxes. With a typical noise level of ~18 mJy beam −1 , this is the most sensitive unbiased methanol survey for methanol masers to date. We also searched for dust continuum and radio continuum associations, finding that 97% of the sources are associated with dust and 12% are associated with radio continuum emission.
Publisher: EDP Sciences
Date: 27-01-2023
DOI: 10.1051/0004-6361/202143019
Abstract: As part of the Global View on Star Formation (GLOSTAR) survey we have used the Karl G. Jansky Very Large Array (VLA) in its B-configuration to observe the part of the Galactic plane between longitudes of 28° and 36° and latitudes from −1° to +1° at the C -band (4–8 GHz). To reduce the contamination of extended sources that are not well recovered by our coverage of the ( u , υ )-plane, we discarded short baselines that are sensitive to emission on angular scales ″ . The resulting radio continuum images have an angular resolution of 1. ″ 0 and a sensitivity of ~60 µJy beam −1 , making it the most sensitive radio survey covering a large area of the Galactic plane with this angular resolution. An automatic source extraction algorithm was used in combination with visual inspection to identify a total of 3325 radio sources. A total of 1457 radio sources are ≥7 σ and comprise our highly reliable catalog 72 of these are grouped as 22 fragmented sources, for ex le, multiple components of an extended and resolved source To explore the nature of the cataloged radio sources, we searched for counterparts at millimeter and infrared wavelengths. Our classification attempts resulted in 93 H II region candidates, 104 radio stars, and 64 planetary nebulae, while it is suggested that most of the remaining radio sources are extragalactic sources. We investigated the spectral indices ( α , S v ∝ v α ) of radio sources classified as H II region candidates and found that many have negative values. This may imply that these radio sources represent young stellar objects that are members of the star clusters around the high-mass stars that excite the H II regions, but not these H II regions themselves. By comparing the peak flux densities from the GLOSTAR and CORNISH surveys, we have identified 49 variable radio sources, most of them with an unknown nature. Additionally, we provide a list of 1866 radio sources detected within 5 to 7 σ levels.
Publisher: MDPI AG
Date: 23-02-2022
DOI: 10.3390/APP12052339
Abstract: Beam-column joints (BCJs) constructed until the 1970s carry a low shear capability due to the absence of shear reinforcement. Fiber-reinforced polymers (FRP) are more reliable than other materials to strengthen a weak BCJ. To date, plenty of analytical models have been developed to analyze the actual contribution of the FRP to the shear strength of RC BCJs. However, the models developed are either too complex in computational efforts or based on empirical coefficients that result in compromised results. The models that formulate the contribution of FRP to the shear strength of the FRP-strengthened deficient interior BCJ are very limited, and such models are too complex. An adequate BCJs’ FRP strain equation must still be developed to address these issues. Therefore, the FRP effective strain equation and contribution of FRP to RC BCJs are derived in this research work using an updated database of the appropriate BCJs. The initial analytical model of Bousselham, which Del Vecchio later improved, is further extended to FRP-strengthened deficient interior BCJs. For this purpose, an updated database of the 32 tests around the world of FRP-strengthened interior BCJs deficient in seismic reinforcement is prepared. Firstly, the experimental effective FRP strain is derived using the experimental database. Then, a power-type equation is derived for the effective FRP strain by considering the crucial parameters of the FRP-strengthened interior BCJs. Finally, the experimental shear strengths and those determined with the proposed equation of the FRP-strengthened joints are compared. The average ratio between the experimental and analytical (proposed model) joint shear strengths of the considered specimens ensured the accuracy of the suggested model. The suggested approach makes computing the FRP enhancements required to avoid shear failure in interior joints easy and reliable for researchers and field engineers interested in seismically reinforcing existing structures.
Publisher: Oxford University Press (OUP)
Date: 30-11-2016
Publisher: EDP Sciences
Date: 24-01-2019
DOI: 10.1051/0004-6361/201834068
Abstract: We present images of radio recombination lines (RRLs) at wavelengths around 17 cm from the star-forming region W49A to determine the kinematics of ionized gas in the THOR survey (The H I /OH/Recombination line survey of the inner Milky Way) at an angular resolution of 16.′′8 × 13.′′8. The distribution of ionized gas appears to be affected by feedback processes from the star clusters in W49A. The velocity structure of the RRLs shows a complex behavior with respect to the molecular gas. We find a shell-like distribution of ionized gas as traced by RRL emission surrounding the central cluster of OB stars in W49A. We describe the evolution of the shell with the recent feedback model code WARPFIELD that includes the important physical processes and has previously been applied to the 30 Doradus region in the Large Magellanic Cloud. The cloud structure and dynamics of W49A are in agreement with a feedback-driven shell that is re-collapsing. The shell may have triggered star formation in other parts of W49A. We suggest that W49A is a potential candidate for star formation regulated by feedback-driven and re-collapsing shells.
Publisher: American Astronomical Society
Date: 22-04-2016
Publisher: American Astronomical Society
Date: 14-12-2017
Publisher: EDP Sciences
Date: 07-2019
DOI: 10.1051/0004-6361/201935249
Abstract: Context . Radio continuum surveys of the Galactic plane are an excellent way to identify different source populations such as planetary nebulae, H II regions, and radio stars and characterize their statistical properties. The Global View of Star Formation in the Milky Way (GLOSTAR) survey will study the star formation in the Galactic plane between −2° ℓ 85° and | b | 1° with unprecedented sensitivity in both flux density (∼40 μ Jy beam −1 ) and range ofangular scales (∼1".5 to the largest radio structures in the Galaxy). Aims . In this paper we present the first results obtained from a radio continuum map of a 16-square-degree-sized region of the Galactic plane centered on ℓ = 32° and b = 0° (28° ℓ 36° and | b | 1°). This map has a resolution of 18″ and a sensitivity of ∼60−150 μ Jy beam −1 . Methods . We present data acquired in 40 h of observations with the VLA in D-configuration. Two 1 GHz wide sub-bands were observed simultaneously and they were centered at 4.7 and 6.9 GHz. These data were calibrated and imaged using the Obit software package. The source extraction was performed using the BLOBCAT software package and verified through a combination of visual inspection and cross-matching with other radio and mid-infrared surveys. Results . The final catalog consists of 1575 discrete radio sources and 27 large scale structures (including W43 and W44). By cross-matching with other catalogs and calculating the spectral indices ( S ( ν ) ∝ ν α ), we have classified 231 continuum sources as H II regions, 37 as ionization fronts, and 46 as planetary nebulae. The longitude and latitude distribution and negative spectral indices are all consistent with the vast majority of the unclassified sources being extragalactic background sources. Conclusions . We present a catalog of 1575 radio continuum sources and discuss their physical properties, emission nature, and relation to previously reported data. These first GLOSTAR results have increased the number of reliable H II regions in this part of the Galaxy by a factor of four.
Publisher: American Astronomical Society
Date: 07-2006
DOI: 10.1086/502962
Publisher: American Astronomical Society
Date: 28-07-2023
Abstract: We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey: 10 μ as accurate parallaxes and proper motions for two Southern Hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured trigonometric parallaxes and proper motions for the masers associated with the star formation region G232.62+00.99 of π = 0.610 ± 0.011 mas, μ x = −2.266 ± 0.021 mas yr −1 , and μ y = 2.249 ± 0.049 mas yr −1 , which implies its distance to be d = 1.637 ± 0.029 kpc. These measurements represent an improvement in accuracy by more than a factor of 3 over the previous measurements obtained through Very Long Baseline Array observations of the 12 GHz methanol masers associated with this region. We also measure the trigonometric parallax and proper motion for G323.74–00.26 as π = 0.364 ± 0.009 mas, μ x = −3.239 ± 0.025 mas yr −1 , and μ y = − 3.976 ± 0.039 mas yr −1 , which implies a distance of d = 2.747 ± 0.068 kpc. These are the most accurate measurements of trigonometric parallax obtained for 6.7 GHz class II methanol masers to date. We confirm that G232.62+00.99 is in the Local Arm and find that G323.74–00.26 is in the Scutum–Centaurus arm. We also investigate the structure and internal dynamics of both masers.
Publisher: Informa UK Limited
Date: 10-04-2023
Publisher: Springer Science and Business Media LLC
Date: 14-08-2013
DOI: 10.1038/NATURE12499
Abstract: Earth's nearest candidate supermassive black hole lies at the centre of the Milky Way. Its electromagnetic emission is thought to be powered by radiatively inefficient accretion of gas from its environment, which is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which the black hole can be fed. The magnetization of the gas, however, which is a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of accretion, remove angular momentum from the infalling gas, expel matter through relativistic jets and lead to synchrotron emission such as that previously observed. Here we report multi-frequency radio measurements of a newly discovered pulsar close to the Galactic Centre and show that the pulsar's unusually large Faraday rotation (the rotation of the plane of polarization of the emission in the presence of an external magnetic field) indicates that there is a dynamically important magnetic field near the black hole. If this field is accreted down to the event horizon it provides enough magnetic flux to explain the observed emission--from radio to X-ray wavelengths--from the black hole.
Publisher: Oxford University Press (OUP)
Date: 05-2010
Publisher: American Astronomical Society
Date: 23-04-2015
Publisher: EDP Sciences
Date: 22-04-2011
Publisher: EDP Sciences
Date: 10-2018
DOI: 10.1051/0004-6361/201731872
Abstract: Context. The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. Aims. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. Methods. This OH study is part of the H I /OH/Recombination line survey of the inner Milky Way (THOR). THOR is a Karl G. Jansky Very Large Array (VLA) large program of atomic, molecular and ionized gas in the range 15° ≤ l ≤ 67° and | b |≤ 1°. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the optical depths derived from these observations with literature 13 CO(1–0) and H I observations to determine the OH abundance. Results. We detect absorption in the 1665 and 1667 MHz transitions, that is, the “main” hyperfine structure lines, for continuum sources stronger than F cont ≥ 0.1 Jy beam−1. OH absorption is found against approximately 15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption occurs in molecular clouds that are associated with Galactic H II regions. We find OH and 13 CO gas to have similar kinematic properties. The data indicate that the OH abundance decreases with increasing hydrogen column density. The derived OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for A V 10−20. Towards the lowest column densities, we find sources that exhibit OH absorption but no 13 CO emission, indicating that OH is a well suited tracer of the low column density molecular gas. We also present spatially resolved OH absorption towards the prominent extended H II -region W43. Conclusions. The unbiased nature of the THOR survey opens a new window onto the gas properties of the interstellar medium. The characterization of the OH abundance over a large range of hydrogen gas column densities contributes to the understanding of OH as a molecular gas tracer and provides a starting point for future investigations.
Publisher: American Astronomical Society
Date: 27-06-2013
Publisher: MDPI AG
Date: 22-10-2022
DOI: 10.3390/MA15217420
Abstract: Accumulating vast amounts of pollutants drives modern civilization toward sustainable development. Construction waste is one of the prominent issues impeding progress toward net-zero. Pollutants must be utilized in constructing civil engineering structures for a green ecosystem. On the other hand, large-scale production of industrial steel fibers (ISFs) causes significant damage to the goal of a sustainable environment. Recycled steel fibers (RSFs) from waste tires have been suggested to replace ISFs. This research critically examines RSF’s application in the mechanical properties’ improvement of concrete and mortar. A statistical analysis of dimensional parameters of RSFs, their properties, and their use in manufacturing various cement-based composites are given. Furthermore, comparative assessments are carried out among the improvements in compressive, split tensile, and flexural strengths of plain and RSF-incorporated concrete and mortar. In addition, the optimum contents of RSF for each strength property are also discussed. The influence of RSFs parameters on various strength properties of concrete and mortars is discussed. The possible applications of RSF for various civil engineering structures are reviewed. The limitations and errors noticed in previous review papers are also outlined. It is found that the maximum enhancement in compressive strength (CS), split tensile strength (STS), and flexure strength (FS) are 78%, 149%, and 157%, respectively, with the addition of RSF into concrete. RSF increased cement mortars’ CS, STS, and FS by 46%, 50.6%, and 69%, respectively. The current study encourages the building sector to use RSFs for sustainable concrete.
Publisher: American Astronomical Society
Date: 10-12-2013
Publisher: EDP Sciences
Date: 25-02-2022
DOI: 10.1051/0004-6361/202142891
Abstract: Context. Molecular maser lines are signposts of high-mass star formation, probing the excitation and kinematics of very compact regions in the close environment of young stellar objects and providing useful targets for trigonometric parallax measurements. Aims. Only a few NH 3 (9,6) masers are known so far, and their origin is still poorly understood. Here we aim to find new NH 3 (9,6) masers to provide a better observational basis for studying their role in high-mass star-forming regions. Methods. We carried out NH 3 (9,6) observations toward Cepheus A and G34.26+0.15 with the Effelsberg 100-meter telescope (beam size 49′′) and the Karl G. Jansky Very Large Array (JVLA beam size about 1′′.2). Results. We discovered new NH 3 (9,6) masers in Cep A and G34.26+0.25, which increases the number of known high-mass star-forming regions hosting NH 3 (9,6) masers from five to seven. Long-term monitoring (20 months) at Effelsberg shows that the intensity of the (9,6) maser in G34.26+0.25 is decreasing, while the Cep A maser remains stable. Compared to the Effelsberg data and assuming linear variations between the epochs of observation, the JVLA data indicate no missing flux. This suggests that the NH 3 (9,6) emission arises from single compact emission regions that are not resolved by the interferometric measurements. As JVLA imaging shows, the NH 3 (9,6) emission in Cep A originates from a sub-arcsecond-sized region, slightly to the west (0′′.28 ± 0′′.10) of the peak position of the 1.36 cm continuum object, HW2. In G34.26+0.25, three NH 3 (9,6) maser spots are observed: one is close to the head of the cometary ultracompact H II region C, and the other two are emitted from a compact region to the west of the hypercompact H II region A. Conclusions. The newly found (9,6) masers appear to be related to outflows. The higher angular resolution of JVLA and very long baseline interferometry observations are needed to provide more accurate positions and constraints for pumping scenarios.
Publisher: EDP Sciences
Date: 11-2018
DOI: 10.1051/0004-6361/201833642
Abstract: Context Radio continuum surveys of the Galactic plane can find and characterize H II regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (≤25 ″ ) at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21 cm. Aims . Our goal is to investigate the 21 cm radio continuum emission in the northern Galactic plane at 25″ resolution. Methods We observed a large percentage of the Galactic plane in the first quadrant of the Milky Way ( l = 14.0−67.4° and | b | ≤ 1.25°) with the Karl G. Jansky Very Large Array (VLA) in the C-configuration covering six continuum spectral windows (SPW). These data provide a detailed view on the compact as well as extended radio emission of our Galaxy and thousands of extragalactic background sources. Results We used the BLOBCAT software and extracted 10 916 sources. After removing spurious source detections caused by the side lobes of the synthesized beam, we classified 10 387 sources as reliable detections. We smoothed the images to a common resolution of 25 ″ and extracted the peak flux density of each source in each SPW to determine the spectral indices α (assuming I ( ν ) ∝ ν α ). By cross-matching with catalogs of H II regions, SNRs, PNe, and pulsars, we found radio counterparts for 840 H II regions, 52 SNRs, 164 PNe, and 38 pulsars. We found 79 continuum sources that are associated with X-ray sources. We identified 699 ultra-steep spectral sources ( α −1.3) that could be high-redshift galaxies. About 9000 of the sources we extracted are not classified specifically, but based on their spatial and spectral distribution, a large percentage of these are likely to be extragalactic background sources. More than 7750 sources do not have counterparts in the SIMBAD database and more than 3760 sources do not have counterparts in the NED database. Conclusions Studying the long wavelengths centimeter continuum emission and the associated spectral indices allows us to characaterize a large percentage of Galactic and extragalactic radio sources in the area of the northern inner Milky Way. This database will be extremely useful for future studies of a erse set of astrophysical objects.
Publisher: American Astronomical Society
Date: 10-2022
Abstract: We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span ∼40–2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion’s forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity ∼0.06 c that carries an energy of ≈10 49 erg. Our modeling further reveals a flat CSM density profile ρ CSM ∝ R −0.03±0.22 up to a break radius R br ≈ (1.96 ± 0.10) × 10 16 cm, with a steep density gradient following ρ CSM ∝ R −2.3±0.5 at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass ∼0.021 M ☉ , and that the progenitor’s effective mass-loss rate varied with time over the range (50–500) × 10 −5 M ☉ yr −1 for an adopted wind velocity v w = 1000 km s −1 and shock microphysical parameters ϵ e = 0.1, ϵ B = 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass loss powered by gravity waves and/or interaction with a binary companion.
Publisher: EDP Sciences
Date: 09-2020
Publisher: American Astronomical Society
Date: 28-05-2015
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: Pakistan
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Andreas Brunthaler.