24 research outputs found
The Radio Light Curve of the Gamma-Ray Nova in V407 Cyg: Thermal Emission from the Ionized Symbiotic Envelope, Devoured from Within by the Nova Blast
We present multi-frequency radio observations of the 2010 nova event in the
symbiotic binary V407 Cygni, obtained with the Karl G. Jansky Very Large Array
and spanning 1-45 GHz and 17-770 days following discovery. This nova---the
first ever detected in gamma rays---shows a radio light curve dominated by the
wind of the Mira giant companion, rather than the nova ejecta themselves. The
radio luminosity grew as the wind became increasingly ionized by the nova
outburst, and faded as the wind was violently heated from within by the nova
shock. This study marks the first time that this physical mechanism has been
shown to dominate the radio light curve of an astrophysical transient. We do
not observe a thermal signature from the nova ejecta or synchrotron emission
from the shock, due to the fact that these components were hidden behind the
absorbing screen of the Mira wind.
We estimate a mass loss rate for the Mira wind of Mdot_w ~ 10^-6 M_sun/yr. We
also present the only radio detection of V407 Cyg before the 2010 nova, gleaned
from unpublished 1993 archival VLA data, which shows that the radio luminosity
of the Mira wind varies by a factor of >~20 even in quiescence. Although V407
Cyg likely hosts a massive accreting white dwarf, making it a candidate
progenitor system for a Type Ia supernova, the dense and radially continuous
circumbinary material surrounding V407 Cyg is inconsistent with observational
constraints on the environments of most Type Ia supernovae.Comment: Resubmitted to ApJ after incorporating referee's comment
Radio studies of novae: a current status report and highlights of new results
Novae, which are the sudden visual brightening triggered by runaway
thermonuclear burning on the surface of an accreting white dwarf, are fairly
common and bright events. Despite their astronomical significance as nearby
laboratories for the study of nuclear burning and accretion phenomena, many
aspects of these common stellar explosions are observationally not
well-constrained and remain poorly understood. Radio observations, modeling and
interpretation can potentially play a crucial role in addressing some of these
puzzling issues. In this review on radio studies of novae, we focus on the
possibility of testing and improving the nova models with radio observations,
and present a current status report on the progress in both the observational
front and theoretical developments. We specifically address the issues of
accurate estimation of ejecta mass, multi-phase and complex ejection phenomena,
and the effect of a dense environment around novae. With highlights of new
observational results, we illustrate how radio observations can shed light on
some of these long-standing puzzles.Comment: 19 pages, 4 figures. Review article published in the Bulletin of the
Astronomical Society of India (BASI) special issue on nova
Binary orbits as the driver of Îł-ray emission and mass ejection in classical novae
Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems. Novae typically expel ïżœ10,000 solar masses of material at velocities exceeding 1,000 km/s. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of the thermonuclear runaway, prolonged optically thick winds, or binary interaction with the nova envelope. Classical novae are now routinely detected in GeV gamma-rays, suggesting that relativistic particles are accelerated by strong shocks in nova ejecta. Here we present high-resolution imaging of the gamma-ray-emitting nova V959 Mon at radio wavelengths, showing that its ejecta were shaped by binary motion: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion. At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of gamma-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae, explaining why many novae are gamma-ray emitters
The infrared view of dust and molecules around V4334 Sgr (Sakuraiâs Object): a 20-year retrospective
Abstract We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakuraiâs Object) over a âŒ20-year period, drawing on ground-, airborne- and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from âŒ1, 200 K in 1998 August to ⌠180 K in 2016 July. The dust mass, assuming amorphous carbon, was âŒ5 Ă 10â10 Mâ in 1998 August, and we estimate that the total dust mass was âŒ2 Ă 10â5 Mâ by âŒ2016. The appearance of a near-infrared excess in 2008 suggests a new episode of (or renewed) mass loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to âŒ16, 000 Lâ before declining to âŒ3, 000 Lâ. There is evidence for weak 6â7m absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakuraiâs Object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C2H2). We use the former to determine the 12C/13C ratio to be 6.4 ± 0.7, 14 times smaller than the Solar System value
Rise and fall of the dust shell of the classical nova V339 Delphini
We present infrared spectroscopy of the classical nova V339 Del, obtained over a ⌠2 year period. The in- frared emission lines were initially symmetrical, with HWHM velocities of 525 km sâ1. In later (t >⌠77days, where t is the time from outburst) spectra however, the lines displayed a distinct asymmetry, with a much stronger blue wing, possibly due to obscuration of the receding component by dust. Dust formation com- menced at ⌠day 34.75 at a condensation temperature of 1480 ± 20 K, consistent with graphitic carbon. Thereafter the dust temperature declined with time as Td â tâ0.346, also consistent with graphitic carbon. The mass of dust initally rose, as a result of an increase in grain size and/or number, peaked at ⌠day 100, and then declined precipitously. This decline was most likely caused by grain shattering due to electrostatic stress after the dust was exposed to X-radiation. An Appendix summarises Planck Means for carbon, and the determination of grain mass and radius for a carbon dust shell
Cross-National Differences in Victimization : Disentangling the Impact of Composition and Context
Varying rates of criminal victimization across countries are assumed to be the outcome of countrylevel structural constraints that determine the supply ofmotivated oÂĄenders, as well as the differential composition within countries of suitable targets and capable guardianship. However, previous empirical tests of these âcompositionalâ and âcontextualâ explanations of cross-national diÂĄerences
have been performed upon macro-level crime data due to the unavailability of comparable individual-level data across countries. This limitation has had two important consequences for cross-national crime research. First, micro-/meso-level mechanisms underlying cross-national differences cannot be truly inferred from macro-level data. Secondly, the eÂĄects of contextual measures (e.g. income inequality) on crime are uncontrolled for compositional heterogeneity. In this
paper, these limitations are overcome by analysing individual-level victimization data across 18 countries from the International CrimeVictims Survey. Results from multi-level analyses on theft and violent victimization indicate that the national level of income inequality is positively related to risk, independent of compositional (i.e. micro- and meso-level) diÂĄerences. Furthermore, crossnational variation in victimization rates is not only shaped by diÂĄerences in national context, but
also by varying composition. More speciÂącally, countries had higher crime rates the more they consisted of urban residents and regions with lowaverage social cohesion.
Crop Updates 2007 - Farming Systems
This session covers forty papers from different authors:
1. Quality Assurance and industry stewardship, David Jeffries, Better Farm IQ Manager, Cooperative Bulk Handling
2. Sothis: Trifolium dasyurum (Eastern Star clover), A. Loi, B.J. Nutt and C.K. Revell, Department of Agriculture and Food
3. Poor performing patches of the paddock â to ameliorate or live with low yield? Yvette Oliver1, Michael Robertson1, Bill Bowden2, Kit Leake3and Ashley Bonser3, CSIRO Sustainable Ecosystems1, Department of Food and Agriculture2, Kellerberrin Farmer3
4. What evidence is there that PA can pay? Michael Robertson, CSIRO Floreat, Ian Maling, SilverFox Solutions and Bindi Isbister, Department of Agriculture and Food
5.The journey is great, but does PA pay? Garren Knell, ConsultAg; Alison Slade, Department of Agriculture and Food, CFIG
6. 2007 Seasonal outlook, David Stephens and Michael Meuleners, Department of Agriculture and Food
7. Towards building farmer capacity to better manage climate risk, David Beard and Nicolyn Short, Department of Agriculture and Food
8. A NAR farmers view of his farming system in 2015, Rob Grima, Department of Agriculture and Food
9. Biofuels opportunities in Australia, Ingrid Richardson, Food and Agribusiness Research, Rabobank
10. The groundwater depth on the hydrological benefits of lucerne and the subsequent recharge values, Ruhi Ferdowsian1and Geoff Bee2; 1Department of Agriculture and Food, 2Landholder, Laurinya, Jerramungup
11. Subsoil constraints to crop production in the high rainfall zone of Western Australia, Daniel Evans1, Bob Gilkes1, Senthold Asseng2and Jim Dixon3; 1University of Western Australia, 2CSIRO Plant Industry, 3Department of Agriculture and Food
12. Prospects for lucerne in the WA wheatbelt, Michael Robertson, CSIRO Floreat, Felicity Byrne and Mike Ewing, CRC for Plant-Based Management of Dryland Salinity, Dennis van Gool, Department of Agriculture and Food
13. Nitrous oxide emissions from a cropped soil in the Western Australian grainbelt, Louise Barton1, Ralf Kiese2, David Gatter3, Klaus Butterbach-Bahl2, Renee Buck1, Christoph Hinz1and Daniel Murphy1,1School of Earth and Geographical Sciences, The University of Western Australia, 2Institute for Meteorology and Climate Research, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany, 3The Department of Agriculture and Food
14. Managing seasonal risk is an important part of farm management but is highly complex and therefore needs a âhorses for coursesâ approach, Cameron Weeks, Planfarm / Mingenew-Irwin Group, Dr Michael Robertson, Dr Yvette Oliver, CSIRO Sustainable Ecosystems and Dr Meredith Fairbanks, Department of Agriculture and Food
15. Novel use application of clopyralid in lupins, John Peirce, and Brad Rayner Department of Agriculture and Food
16. Long season wheat on the South Coast â Feed and grain in a dry year â a 2006 case study, Sandy White, Department of Agriculture and Food
17. Wheat yield response to potassium and the residual value of PKS fertiliser drilled at different depths, Paul Damon1, Bill Bowden2, Qifu Ma1 and Zed Rengel1; Faculty of Natural and Agricultural Sciences, The University of Western Australia1, Department of Agriculture and Food2
18. Saltbush as a sponge for summer rain, Ed Barrett-Lennard and Meir Altman, Department of Agriculture and Food and CRC for Plant-based Management of Dryland Salinity
19. Building strong working relationships between grower groups and their industry partners, Tracey M. Gianatti, Grower Group Alliance
20. To graze or not to graze â the question of tactical grazing of cereal crops, Lindsay Bell and Michael Robertson, CSIRO Sustainable Ecosystems
21. Can legume pastures and sheep replace lupins? Ben Webb and Caroline Peek, Department of Agriculture and Food
22. EverGraze â livestock and perennial pasture performance during a drought year, Paul Sanford, Department of Agriculture and Food, and CRC for Plant-based Management of Dryland Salinity
23. Crop survival in challenging times, Paul Blackwell1, Glen Riethmuller1, Darshan Sharma1and Mike Collins21Department of Agriculture and Food, 2Okura Plantations, Kirikiri New Zealand
24. Soil health constraints to production potential â a precision guided project, Frank DâEmden, and David Hall, Department of Agriculture and Food
25. A review of pest and disease occurrence in 2006, Mangano, G.P. and Severtson, D.L., Department of Agriculture and Food
26. e-weed â an information resource on seasonal weed management issues, Vanessa Stewart and Julie Roche, Department of Agriculture and Food
27. Review of Pesticide Legislation and Policies in Western Australia, Peter Rutherford, BSc (Agric.), Pesticide Legislation Review, Office of the Chief Medical Adviser, WA Department of Health
28. Future wheat yields in the West Australian wheatbelt, Imma Farré and Ian Foster, Department of Agriculture and Food, Stephen Charles, CSIRO Land and Water
29. Organic matter in WA arable soils: Whatâs active and whatâs not, Frances Hoyle, Department of Agriculture and Food, Australia and Daniel Murphy, UWA
30. Soil quality indicators in Western Australian farming systems, D.V. Murphy1, N. Milton1, M. Osman1, F.C. Hoyle2, L.K Abbott1, W.R. Cookson1and S. Darmawanto1; 1UWA, 2Department of Agriculture and Food
31. Impact of stubble on input efficiencies, Geoff Anderson, formerly employed by Department of Agriculture and Food
32. Mixed farming vs All crop â true profit, not just gross margins, Rob Sands and David McCarthy, FARMANCO Management Consultants, Western Australia
33. Evaluation of Local Farmer Group Network â group leadersâ surveys 2005 and 2006, Paul Carmody, Local Farmer Group Network, Network Coordinator, UWA
34. Seeding rate and nitrogen application and timing effects in wheat, J. Russell, Department of Agriculture and Food, J. Eyres, G. Fosbery and A. Roe, ConsultAg, Northam
35. Foliar fungicide application and disease control in barley, J. Russell, Department of Agriculture and Food, J. Eyres, G. Fosbery and A. Roe, ConsultAg, Northam
36. Brown manuring effects on a following wheat crop in the central wheatbelt, , J. Russell, Department of Agriculture and Food, J. Eyres, G. Fosbery and A. Roe, ConsultAg, Northam
37. Management of annual pastures in mixed farming systems â transition from a dry season, Dr Clinton Revell and Dr Phil Nichols; Department of Agriculture and Food
38. The value of new annual pastures in mixed farm businesses of the wheatbelt, Dr Clinton Revell1, Mr Andrew Bathgate2and Dr Phil Nichols1; 1Department of Agriculture and Food, 2Farming Systems Analysis Service, Albany
39. The influence of winter SOI and Indian Ocean SST on WA winter rainfall, Meredith Fairbanks and Ian Foster, Department of Agriculture and Food
40. Market outlook â Grains, Anne Wilkins, Market Analyst, Grains, Department of Agriculture and Foo
Magnetic Fields toward Ophiuchus-B Derived from SCUBA-2 Polarization Measurements
We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope in Hawaii. This work is part of the B-fields in Star-forming Region Observations survey initiated to understand the role of magnetic fields in star formation for nearby star-forming molecular clouds. We present a first look at the geometry and strength of magnetic fields in Oph-B. The field geometry is traced over ~0.2 pc, with clear detection of both of the sub-clumps of Oph-B. The field pattern appears significantly disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered, with a tendency to be along the major axis of the clump, parallel to the filamentary structure within which it lies. The degree of polarization decreases systematically toward the dense core material in the two sub-clumps. The field lines in the lower density material along the periphery are smoothly joined to the large-scale magnetic fields probed by NIR polarization observations. We estimated a magnetic field strength of 630 ± 410 ÎŒG in the Oph-B2 sub-clump using a DavisâChandrasekharâFermi analysis. With this magnetic field strength, we find a mass-to-flux ratio λ = 1.6 ± 1.1, which suggests that the Oph-B2 clump is slightly magnetically supercritical
JCMT BISTRO Survey: Magnetic Fields within the Hub-filament Structure in IC 5146
We present the 850 ÎŒm polarization observations toward the IC 5146 filamentary cloud taken using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) and its associated polarimeter (POL-2), mounted on the James Clerk Maxwell Telescope, as part of the B-fields In STar forming Regions Observations. This work is aimed at revealing the magnetic field morphology within a core-scale (lesssim1.0 pc) hub-filament structure (HFS) located at the end of a parsec-scale filament. To investigate whether the observed polarization traces the magnetic field in the HFS, we analyze the dependence between the observed polarization fraction and total intensity using a Bayesian approach with the polarization fraction described by the Rice likelihood function, which can correctly describe the probability density function of the observed polarization fraction for low signal-to-noise ratio data. We find a power-law dependence between the polarization fraction and total intensity with an index of 0.56 in A V ~ 20â300 mag regions, suggesting that the dust grains in these dense regions can still be aligned with magnetic fields in the IC 5146 regions. Our polarization maps reveal a curved magnetic field, possibly dragged by the contraction along the parsec-scale filament. We further obtain a magnetic field strength of 0.5 ± 0.2 mG toward the central hub using the DavisâChandrasekharâFermi method, corresponding to a mass-to-flux criticality of ~1.3 ± 0.4 and an AlfvĂ©nic Mach number of <0.6. These results suggest that gravity and magnetic field are currently of comparable importance in the HFS and that turbulence is less important
The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2
We present and analyze observations of polarized dust emission at 850 ÎŒm toward the central 1 Ă 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the DavisâChandrasekharâFermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 â 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 ± 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 ± 0.02. Additionally, the mean AlfvĂ©n Mach number is 0.35 ± 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical