scholarly journals VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate

2021 ◽  
Vol 923 (2) ◽  
pp. 231
Author(s):  
Stephanie Spear ◽  
María José Maureira ◽  
Héctor G. Arce ◽  
Jaime E. Pineda ◽  
Michael Dunham ◽  
...  
Keyword(s):  
Column Density ◽  
Large Scale ◽  
Signal To Noise Ratio ◽  
Major Axis ◽  
Ammonia Emission ◽  
Evolutionary Stage ◽  
Density Peak ◽  
Very Large Array ◽  
The Core ◽  
Radial Profiles

Abstract We use 3 mm continuum NOrthern Extended Millimeter Array and NH3 Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH3 exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 105 cm−3. Virial and density structure analysis reveals the core is marginally bound (α vir = 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions with the nearby outflow, which appears to deflect due to the dense gas near the NH3 column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation.

scholarly journals CHANG-ES

2019 ◽  
Vol 632 ◽  
pp. A11 ◽  
Author(s):  
Silvia Carolina Mora-Partiarroyo ◽  
Marita Krause ◽  
Aritra Basu ◽  
Rainer Beck ◽  
Theresa Wiegert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Major Axis ◽  
Radio Continuum ◽  
Periodic Pattern ◽  
Very Large Array ◽  
The Galaxy ◽  
Continuum Data ◽  
First Time ◽  
The Magnetic Field

Aims. NGC 4631 is an interacting galaxy which exhibits one of the largest gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and polarization properties of its disk and halo emission with new radio continuum data. Methods. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99 GHz) in the C and D array configurations, and at L-band (1.57 GHz) in the B, C, and D array configurations. The Rotation Measure Synthesis algorithm was utilized to derive the polarization properties. Results. We detected linearly polarized emission at C-band and L-band. The magnetic field in the halo is characterized by strong vertical components above and below the central region of the galaxy. The magnetic field in the disk is only clearly seen in the eastern side of NGC 4631, where it is parallel to the plane of the major axis of the galaxy. We detected for the first time a large-scale, smooth Faraday depth pattern in a halo of an external spiral galaxy, which implies the existence of a regular (coherent) magnetic field. A quasi-periodic pattern in Faraday depth with field reversals was found in the northern halo of the galaxy. Conclusions. The field reversals in the northern halo of NGC 4631, together with the observed polarization angles, indicate giant magnetic ropes with alternating directions. To our knowledge, this is the first time such reversals are observed in an external galaxy.

scholarly journals Distribution of methanol and cyclopropenylidene around starless cores

2020 ◽  
Vol 643 ◽  
pp. A60
Author(s):  
S. Spezzano ◽  
P. Caselli ◽  
J. E. Pineda ◽  
L. Bizzocchi ◽  
D. Prudenzano ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Gas Phase ◽  
Column Density ◽  
Large Scale ◽  
Scale Effects ◽  
Carbon Chain ◽  
Observational Constraints ◽  
Chain Molecules ◽  
The Core ◽  
Chemical Segregation

Context. The spatial distribution of molecules around starless cores is a powerful tool for studying the physics and chemistry governing the earliest stages of star formation. Aims. Our aim is to study the chemical differentiation in starless cores to determine the influence of large-scale effects on the spatial distribution of molecules within the cores. Furthermore, we want to put observational constraints on the mechanisms responsible in starless cores for the desorption of methanol from the surface of dust grains where it is efficiently produced. Methods. We mapped methanol, CH3OH, and cyclopropenylidene, c-C3H2, with the IRAM 30 m telescope in the 3 mm band towards six starless cores embedded in different environments, and in different evolutionary stages. Furthermore, we searched for correlations among physical properties of the cores and the methanol distribution. Results. From our maps we can infer that the chemical segregation between CH3OH and c-C3H2 is driven by uneven illumination from the interstellar radiation field (ISRF). The side of the core that is more illuminated has more C atoms in the gas-phase and the formation of carbon-chain molecules like c-C3H2 is enhanced. Instead, on the side that is less exposed to the ISRF the C atoms are mostly locked in carbon monoxide, CO, the precursor of methanol. Conclusions. We conclude that large-scale effects have a direct impact on the chemical segregation that we can observe at core scale. However, the non-thermal mechanisms responsible for the desorption of methanol in starless cores do not show any dependency on the H2 column density at the methanol peak.

scholarly journals Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)

2020 ◽  
Vol 643 ◽  
pp. A45 ◽  
Author(s):  
J. V. Seidel ◽  
M. Lendl ◽  
V. Bourrier ◽  
D. Ehrenreich ◽  
R. Allart ◽  
...  
Keyword(s):  
Large Scale ◽  
Signal To Noise Ratio ◽  
High Sensitivity ◽  
High Accuracy ◽  
Scale Height ◽  
Light Curves ◽  
Signal To Noise ◽  
System Parameters ◽  
The Core

WASP-127b is one of the puffiest exoplanets found to date, with a mass of only 3.4 Neptune masses, but a radius larger than that of Jupiter. It is located at the border of the Neptune desert, which describes the lack of highly irradiated Neptune-sized planets, and which remains poorly understood. Its large scale height and bright host star make the transiting WASP-127b a valuable target to characterise in transmission spectroscopy. We used combined EulerCam and TESS light curves to recalculate the system parameters. Additionally, we present an in-depth search for sodium in four transit observations of WASP-127b, obtained as part of the Hot Exoplanet Atmosphere Resolved with Transit Spectroscopy (HEARTS) survey with the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. Two nights from this dataset were analysed independently by another team. The team claimed a detection of sodium that is incompatible with previous studies of data from both ground and space. We show that this strong sodium detection is due to contamination from telluric sodium emissions and the low signal-to-noise ratio in the core of the deep stellar sodium lines. When these effects are properly accounted for, the previous sodium signal is reduced to an absorption of 0.46 ± 0.20% (2.3σ), which is compatible with analyses of WASP-127b transits carried out with other instruments. We can fit a Gaussian to the D2 line, but the D1 line was not detected. This indicates an unusual line ratio if sodium exists in the atmosphere. Follow-up of WASP-127 at high resolution and with high sensitivity is required to firmly establish the presence of sodium and analyse its line shape.

scholarly journals Evidence of large-scale energy cascade in the spiral galaxy NGC 5236

2020 ◽  
Vol 496 (2) ◽  
pp. 1803-1810 ◽  
Author(s):  
Meera Nandakumar ◽  
Prasun Dutta
Keyword(s):  
Spiral Galaxy ◽  
Energy Input ◽  
Column Density ◽  
Large Scale ◽  
Power Spectra ◽  
Line Of Sight ◽  
Very Large Array ◽  
The Galaxy ◽  
Scale Turbulence ◽  
Self Gravity

ABSTRACT Turbulence plays an important role in the structure and dynamics of the galaxy and influences various processes therein including star formation. In this work, we investigate the large-scale turbulence properties of the external spiral galaxy NGC 5236. We combine the Very Large Array (VLA) multiconfiguration archival data with the new GMRT observation to estimate the column density and line-of-sight velocity fluctuation power spectra for this galaxy over almost two decades of length scales. The energy input scale to the interstellar medium turbulence is found to be around 6 kpc. Power spectra of the two-dimensional turbulence in the galaxy’s disc follow a power law with a slope −1.23 ± 0.06 for the column density and −1.91 ± 0.08 for the line-of-sight velocity. The measured power spectra slopes strongly suggest in favour of a compressive forcing with a steady energy input of ∼7 × 10−11   erg cm −2 s−1. We conclude that much of these originate from the gravitational instabilities and self-gravity in the disc. This is the first and most comprehensive study of turbulence statistics for any external spiral galaxy.

scholarly journals GASTON: Galactic Star Formation with NIKA2. Evidence for the mass growth of star-forming clumps

2021 ◽  
Author(s):  
A J Rigby ◽  
N Peretto ◽  
R Adam ◽  
P Ade ◽  
M Anderson ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Galactic Plane ◽  
High Sensitivity ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Mass Growth ◽  
Star Forming ◽  
Compact Source

Abstract Determining the mechanism by which high-mass stars are formed is essential for our understanding of the energy budget and chemical evolution of galaxies. By using the New IRAM KIDs Array 2 (NIKA2) camera on the Institut de Radio Astronomie Millimétrique (IRAM) 30-m telescope, we have conducted high-sensitivity and large-scale mapping of a fraction of the Galactic plane in order to search for signatures of the transition between the high- and low-mass star-forming modes. Here, we present the first results from the Galactic Star Formation with NIKA2 (GASTON) project, a Large Programme at the IRAM 30-m telescope which is mapping ≈2 deg2 of the inner Galactic plane (GP), centred on ℓ = 23${_{.}^{\circ}}$9, b = 0${_{.}^{\circ}}$05, as well as targets in Taurus and Ophiuchus in 1.15 and 2.00 mm continuum wavebands. In this paper we present the first of the GASTON GP data taken, and present initial science results. We conduct an extraction of structures from the 1.15 mm maps using a dendrogram analysis and, by comparison to the compact source catalogues from Herschel survey data, we identify a population of 321 previously-undetected clumps. Approximately 80 per cent of these new clumps are 70 μm-quiet, and may be considered as starless candidates. We find that this new population of clumps are less massive and cooler, on average, than clumps that have already been identified. Further, by classifying the full sample of clumps based upon their infrared-bright fraction – an indicator of evolutionary stage – we find evidence for clump mass growth, supporting models of clump-fed high-mass star formation.

scholarly journals Star formation thresholds derived From THINGS

2006 ◽  
Vol 2 (S237) ◽  
pp. 397-397
Author(s):  
F. Bigiel ◽  
F. Walter ◽  
E. de Blok ◽  
E. Brinks ◽  
B. Madore
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Gravitational Instability ◽  
Critical Density ◽  
Nearby Galaxy ◽  
Uv Emission ◽  
Radial Profiles ◽  
Wide Range ◽  
First Results ◽  
Type Mass

AbstractWe present first results from THINGS (The HI Nearby Galaxy Survey), which consists of high quality HI maps obtained with the VLA of 34 galaxies across a wide range of galaxy parameters (Hubble type, mass/luminosity). We compare the distribution of HI to the UV emission in our sample galaxies. In particular we present radial profiles of the HI (tracing the neutral interstellar medium) and UV (mainly tracing regions of recent star formation) in our sample galaxies. The azimuthally averaged HI profiles are compared to the predicted critical density above which organized large-scale star formation is believed to start (this threshold is based on the Toomre-Q parameter, which in turn is a measure for local gravitational instability).

scholarly journals A High-Speed, Light-Weight Scalar Magnetometer Bird for km Scale UAV Magnetic Surveying: On Sensor Choice, Bird Design, and Quality of Output Data

2021 ◽  
Vol 13 (4) ◽  
pp. 649
Author(s):  
Arne Døssing ◽  
Eduardo Lima Simoes da Silva ◽  
Guillaume Martelet ◽  
Thorkild Maack Rasmussen ◽  
Eric Gloaguen ◽  
...  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Signal To Noise Ratio ◽  
Regional Scale ◽  
Weather Conditions ◽  
Light Weight ◽  
Output Data ◽  
Efficient Manner ◽  
Flexible System ◽  
Scalar Data

Magnetic surveying is a widely used and cost-efficient remote sensing method for the detection of subsurface structures at all scales. Traditionally, magnetic surveying has been conducted as ground or airborne surveys, which are cheap and provide large-scale consistent data coverage, respectively. However, ground surveys are often incomplete and slow, whereas airborne surveys suffer from being inflexible, expensive and characterized by a reduced signal-to-noise ratio, due to increased sensor-to-source distance. With the rise of reliable and affordable survey-grade Unmanned Aerial Vehicles (UAVs), and the developments of light-weight magnetometers, the shortcomings of traditional magnetic surveying systems may be bypassed by a carefully designed UAV-borne magnetometer system. Here, we present a study on the development and testing of a light-weight scalar field UAV-integrated magnetometer bird system (the CMAGTRES-S100). The idea behind the CMAGTRES-S100 is the need for a high-speed and flexible system that is easily transported in the field without a car, deployable in most terrain and weather conditions, and provides high-quality scalar data in an operationally efficient manner and at ranges comparable to sub-regional scale helicopter-borne magnetic surveys. We discuss various steps in the development, including (i) choice of sensor based on sensor specifications and sensor stability tests, (ii) design considerations of the bird, (iii) operational efficiency and flexibility and (iv) output data quality. The current CMAGTRES-S100 system weighs ∼5.9 kg (including the UAV) and has an optimal surveying speed of 50 km/h. The system was tested along a complex coastal setting in Brittany, France, targeting mafic dykes and fault contacts with magnetite infill and magnetite nuggets (skarns). A 2.0 × 0.3 km area was mapped with a 10 m line-spacing by four sub-surveys (due to regulatory restrictions). The sub-surveys were completed in 3.5 h, including >2 h for remobilisation and the safety clearance of the area. A noise-level of ±0.02 nT was obtained and several of the key geological structures were mapped by the system.

Progressive Evolution of the Core of the Fast Breeder Test Reactor

2010 ◽  
Author(s):  
S. Varatharajan ◽  
K. V. Sureshkumar ◽  
K. V. Kasiviswanathan ◽  
G. Srinivasan
Keyword(s):  
Fast Reactor ◽  
Large Scale ◽  
Power Reactor ◽  
Test Bed ◽  
Fast Breeder Test Reactor ◽  
The Core ◽  
Linear Heat ◽  
Mox Fuel ◽  
Test Reactor ◽  
Carbide Fuel

The second stage of Indian nuclear programme envisages the deployment of fast reactors on a large scale for the effective use of India’s limited uranium reserves. The Fast Breeder Test Reactor (FBTR) at Kalpakkam is a loop type, sodium cooled fast reactor, meant as a test bed for the fuels and structural materials for the Indian fast reactor programme. The reactor was made critical with a unique high plutonium MK-I carbide fuel (70% PuC+30%UC). Being a unique untested fuel of its kind, it was decided to test it as a driver fuel, with conservative limits on Linear Heat Rating and burn-up, based on out-of-pile studies. FBTR went critical in Oct 1985 with a small core of 23 MK-I fuel subassemblies. The Linear Heat Rating and burn-up limits for the fuel were conservatively set at 250 W/cm & 25 GWd/t respectively. Based on out-of-pile simulation in 1994, it was possible to raise the LHR to 320 W/cm. It was decided that when the fuel reaches the target burn-up of 25 GWd/t, the MK-I core would be progressively replaced with a larger core of MK-II carbide fuel (55% PuC+45%UC). Induction of MK-II subassemblies was started in 1996. However, based on the Post-Irradiation Examination (PIE) of the MK-I fuel at 25, 50 & 100 GWd/t, it became possible to enhance the burn-up of the MK-I fuel to 155 GWd/t. More than 900 fuel pins of MK-I composition have reached 155 GWd/t without even a single failure and have been discharged. One subassembly (61 pins) was taken to 165 GWd/t on trial basis, without any clad failure. The core has been progressively enlarged, adding MK-I subassemblies to compensate for the burn-up loss of reactivity and replacement of discharged subassemblies. The induction of MK-II fuel was stopped in 2003. One test subassembly simulating the composition of the MOX fuel (29% PuO2) to be used in the 500 MWe Prototype Fast Breeder Reactor was loaded in 2003. It is undergoing irradiation at 450 W/cm, and has successfully seen a burn-up of 92.5 GWd/t. In 2006, it was proposed to test high Pu MOX fuel (44% PuO2), in order to validate the fabrication and fuel cycle processes developed for the power reactor MOX fuel. Eight MOX subassemblies were loaded in FBTR core in 2007. The current core has 27 MK-I, 13 MK-II, eight high Pu MOX and one power reactor MOX fuel subassemblies. The reactor power has been progressively increased from 10.5 MWt to 18.6 MWt, due to the progressive enlargement of the core. This paper presents the evolution of the core based on the progressive enhancement of the burn-up limit of the unique high Pu carbide fuel.

Performance of Core Exit Thermocouple for PWR Accident Management Action in Vessel Top Break LOCA Simulation Experiment at OECD/NEA ROSA Project

2008 ◽  
Author(s):  
Mitsuhiro Suzuki ◽  
Takeshi Takeda ◽  
Hideo Nakamura
Keyword(s):  
Time Delay ◽  
Large Scale ◽  
Simulation Experiment ◽  
Three Dimensional ◽  
Test Facility ◽  
Large Temperature ◽  
Energy Agency ◽  
Pressurized Water ◽  
The Core ◽  
Accident Management

Presented are experiment results of the Large Scale Test Facility (LSTF) conducted at the Japan Atomic Energy Agency (JAEA) with a focus on core exit thermocouple (CET) performance to detect core overheat during a vessel top break loss-of-coolant accident (LOCA) simulation experiment. The CET temperatures are used to start accident management (AM) action to quickly depressurize steam generator (SG) secondary sides in case of core temperature excursion. Test 6-1 is the first test of the OECD/NEA ROSA Project started in 2005, simulating withdraw of a control rod drive mechanism penetration nozzle at the vessel top head. The break size is equivalent to 1.9% cold leg break. The AM action was initiated when CET temperature rose up to 623K. There was no reflux water fallback onto the CETs during the core heat-up period. The core overheat, however, was detected with a time delay of about 230s. In addition, a large temperature discrepancy was observed between the CETs and the hottest core region. This paper clarifies the reasons of time delay and temperature discrepancy between the CETs and heated core during boil-off including three-dimensional steam flows in the core and core exit. The paper discusses applicability of the LSTF CET performance to pressurized water reactor (PWR) conditions and a possibility of alternative indicators for earlier AM action than in Test 6-1 is studied by using symptom-based plant parameters such as a reactor vessel water level detection.

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