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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Very Large Array and Jansky Very Large Array observations of the compact radio sources in M8

We analyze high-resolution Very Large Array continuum observations of the M8 region carried out at several epochs that span a period of 30 yr. Our maps reveal two compact sources. One is associated with Her 36 SE, a possible companion of the O7 luminous massive star Her 36, and the other is associated with G5.97–1.17, whose proplyd nature was previously established. Using the analyzed data, we do not find significant time variability in any of these sources. The derived spectral index of ≥0.1 for Her 36 SE, the marginal offset of the radio emission with the previous infrared detection, and the associated X-ray emission previously reported suggest the presence of an unresolved interaction region between the strong winds of Her 36 and Her 36 SE. This region would contribute non-thermal contamination to the global wind emission of Her 36, flattening its spectral index. On the other hand, the emission of G5.97–1.17 can also be explained by a mixture of thermal and non-thermal emission components, with different relative contributions of both emission mechanisms along the proplyd. We argue that the shock created by the photo-evaporation flow of the proplyd with the collimated stellar wind of Her 36 accelerates charged particles in G5.97–1.17, producing considerable synchrotron emission. On the contrary, an electron density enhancement at the southwest of G5.97–1.17 makes the thermal emission dominant over this region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Submillimeter array and very large array observations in the hypercompact H II region G35.58-0.03

The formation of hypercompact (HC) H II regions is an important stage in massive star formation. Spectral line and continuum observations can explore its dynamic conditions. We present high angular resolution observations carried out with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward the HC H II region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected a total of about 25 transitions of 8 different species and their isotopologues (CO, CH{sub 3}CN, SO{sub 2}, CH{sub 3}CCH, OCS, CS, H, and NH{sub 3}). G35.58-0.03 consists of an HC H II core with electron temperature T{sub e}{sup ∗}≧5500 K, emission measure EM ≈1.9 × 10{sup 9} pc cm{sup –6}, local volume electron density n{sub e} = 3.3 × 10{sup 5} cm{sup –3}, and a same width of radio recombination line FWHM ≈ 43.2 km s{sup –1} for both H30α and H38β at its intrinsic core size ∼3714 AU. The H30α line shows evidence of an ionized outflow driving a molecular outflow. Based on the derived Lyman continuum flux, there should be an early-type star equivalent to O6.5 located inside the H II region. From the continuum spectral energy distribution from 3.6 cm, 2.0 cm, 1.3 cm, 1.3 mm and 0.85 mm to 0.45 mm, we distinguished the free-free emission (25% ∼ 55%) from the warm dust component (75% ∼ 45%) at 1.3 mm. The molecular envelope shows evidence of infall and outflow with an infall rate of 0.05 M {sub ☉} yr{sup –1} and a mass loss rate of 5.2 × 10{sup –3} M {sub ☉} yr{sup –1}. The derived momentum (∼0.05 M {sub ☉} km s{sup –1}) is consistent between the infalling and outflowing gas per year. It is suggested that the infall is predominant and the envelope mass of dense core is increasing rapidly, but the accretion in the inner part might already be halted.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DISTANCE AND KINEMATICS OF THE RED HYPERGIANT VY CMa: VERY LONG BASELINE ARRAY AND VERY LARGE ARRAY ASTROMETRY

We report astrometric results of phase-referencing very long baseline interferometry observations of 43 GHz SiO maser emission toward the red hypergiant VY Canis Majoris (VY CMa) using the Very Long Baseline Array (VLBA). We measured a trigonometric parallax of 0.83 {+-} 0.08 mas, corresponding to a distance of 1.20{sup +0.13}{sub -0.10} kpc. Compared to previous studies, the spatial distribution of SiO masers has changed dramatically, while its total extent remains similar. The internal motions of the maser spots are up to 1.4 mas yr{sup -1}, corresponding to 8 km s{sup -1}, and show a tendency for expansion. After modeling the expansion of maser spots, we derived an absolute proper motion for the central star of {mu}{sub x} = -2.8 {+-} 0.2 and {mu}{sub y} = 2.6 {+-} 0.2 mas yr{sup -1} eastward and northward, respectively. Based on the maser distribution from the VLBA observations, and the relative position between the radio photosphere and the SiO maser emission at 43 GHz from the complementary Very Large Array observations, we estimate the absolute position of VY CMa at mean epoch 2006.53 to be {alpha}{sub J2000} = 07{sup h}22{sup m}58.{sup s}3259 {+-} 0.{sup s}0007, {delta}{sub J2000} = -25 Degree-Sign 46'03.''063 {+-} 0.''010. The position and proper motion of VY CMa from the VLBA observations differ significantly with values measured by the Hipparcos satellite. These discrepancies are most likely associated with inhomogeneities and dust scattering the optical light in the circumstellar envelope. The absolute proper motion measured with VLBA suggests that VY CMa may be drifting out of the giant molecular cloud to the east of it.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Fabrication and characterization of large arrays of mesoscopic gold rings on large-aspect-ratio cantilevers

We have fabricated large arrays of mesoscopic metal rings on ultrasensitive cantilevers. The arrays are defined by electron beam lithography and contain up to 10{sup 5} rings. The rings have a circumference of 1 μm, and are made of ultrapure (6N) Au that is deposited onto a silicon-on-insulator wafer without an adhesion layer. Subsequent processing of the SOI wafer results in each array being supported at the end of a free-standing cantilever. To accommodate the large arrays while maintaining a low spring constant, the cantilevers are nearly 1 mm in both lateral dimensions and 100 nm thick. The extreme aspect ratio of the cantilevers, the large array size, and the absence of a sticking layer are intended to enable measurements of the rings' average persistent current in the presence of relatively small magnetic fields. We describe the motivation for these measurements, the fabrication of the devices, and the characterization of the cantilevers' mechanical properties. We also discuss the devices' expected performance in measurements of .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

AN EXPANDED VERY LARGE ARRAY AND CARMA STUDY OF DUSTY DISKS AND TORII WITH LARGE GRAINS IN DYING STARS

We report the results of a pilot multiwavelength survey in the radio continuum (X, Ka, and Q bands, i.e., from 3.6 cm to 7 mm) carried out with the Expanded Very Large Array (EVLA) in order to confirm the presence of very large dust grains in dusty disks and torii around the central stars in a small sample of post-asymptotic giant branch (pAGB) objects, as inferred from millimeter (mm) and submillimeter (submm) observations. Supporting mm-wave observations were also obtained with the Combined Array for Research in Millimeter-wave Astronomy toward three of our sources. Our EVLA survey has resulted in a robust detection of our most prominent submm emission source, the pre-planetary nebula (PPN) IRAS 22036+5306, in all three bands, and the disk-prominent pAGB object, RV Tau, in one band. The observed fluxes are consistent with optically thin free-free emission, and since they are insignificant compared to their submm/mm fluxes, we conclude that the latter must come from substantial masses of cool, large (mm-sized) grains. We find that the power-law emissivity in the cm-to-submm range for the large grains in IRAS22036 is {nu}{sup {beta}}, with {beta} = 1-1.3. Furthermore, the value of {beta} in the 3-0.85 mm range for the three disk-prominent pAGB sources ({beta} {<=} 0.4) is significantly lower than that of IRAS22036, suggesting that the grains in pAGB objects with circumbinary disks are likely larger than those in the dusty waists of pre-planetary nebulae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Almost perfect in-phase and anti-phase chaotic and periodic phase synchronization in large arrays of diode lasers

In this paper we study phase synchronization in large arrays of weakly coupled single mode semiconductor laser diodes. We show that if the coupling topology is chosen appropriately, the laser array exhibits robust phase synchrony (including chaotic and non-chaotic phase synchrony). Furthermore, one can define coupling topologies that lead to chaotic anti-phase synchronization. To the best of our knowledge, chaotic anti-phase synchronization has not been observed in large arrays of coupled nonlinear oscillators. Additionally, when diodes are coupled via a decayed non-local coupling scheme, the leading spatial mode can be stable. This leads to an almost-perfect phase synchronous state where the phases are synchronized, but the system is not set exactly on the synchronization manifold. This almost-perfect phase synchronous state is robust to noise and frequency disorder and can be realized under periodic (fixed-intensity limit cycle) continuous-wave and chaotic behavior. The presented result is an example of the broader phenomenon of linear transverse mode selection taking place in a coupled oscillator system with nonlinear dynamics.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Multiplexed charge-locking device for large arrays of quantum devices

We present a method of forming and controlling large arrays of gate-defined quantum devices. The method uses an on-chip, multiplexed charge-locking system and helps to overcome the restraints imposed by the number of wires available in cryostat measurement systems. The device architecture that we describe here utilises a multiplexer-type scheme to lock charge onto gate electrodes. The design allows access to and control of gates whose total number exceeds that of the available electrical contacts and enables the formation, modulation and measurement of large arrays of quantum devices. We fabricate such devices on n-type GaAs/AlGaAs substrates and investigate the stability of the charge locked on to the gates. Proof-of-concept is shown by measurement of the Coulomb blockade peaks of a single quantum dot formed by a floating gate in the device. The floating gate is seen to drift by approximately one Coulomb oscillation per hour.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

THE GOULD's BELT VERY LARGE ARRAY SURVEY. I. THE OPHIUCHUS COMPLEX

We present large-scale (∼2000 arcmin{sup 2}), deep (∼20 μJy), high-resolution (∼1'') radio observations of the Ophiuchus star-forming complex obtained with the Karl G. Jansky Very Large Array at λ = 4 and 6 cm. In total, 189 sources were detected, 56 of them associated with known young stellar sources, and 4 with known extragalactic objects; the other 129 remain unclassified, but most of them are most probably background quasars. The vast majority of the young stars detected at radio wavelengths have spectral types K or M, although we also detect four objects of A/F/B types and two brown dwarf candidates. At least half of these young stars are non-thermal (gyrosynchrotron) sources, with active coronas characterized by high levels of variability, negative spectral indices, and (in some cases) significant circular polarization. As expected, there is a clear tendency for the fraction of non-thermal sources to increase from the younger (Class 0/I or flat spectrum) to the more evolved (Class III or weak line T Tauri) stars. The young stars detected both in X-rays and at radio wavelengths broadly follow a Güdel-Benz relation, but with a different normalization than the most radioactive types of stars. Finally, we detect a ∼70 mJy compact extragalactic source near the center of the Ophiuchus core, which should be used as gain calibrator for any future radio observations of this region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Large arrays of dual-polarized multichroic TES detectors for CMB measurements with the SPT-3G receiver

Now, detectors for cosmic microwave background (CMB) experiments are background limited, so a straightforward alternative to improve sensitivity is to increase the number of detectors. Large arrays of multichroic pixels constitute an economical approach to increasing the number of detectors within a given focal plane area. We present the fabrication of large arrays of dual-polarized multichroic transition-edge-sensor (TES) bolometers for the South Pole Telescope third-generation CMB receiver (SPT-3G). The complete SPT-3G receiver will have 2690 pixels, each with six detectors, allowing for individual measurement of three spectral bands (centered at 95 GHz, 150 GHz and 220 GHz) in two orthogonal polarizations. In total, the SPT-3G focal plane will have 16140 detectors. Each pixel is comprised of a broad-band sinuous antenna coupled to a niobium microstrip transmission line. In-line filters are used to define the different band-passes before the millimeter-wavelength signal is fed to the respective Ti/Au TES sensors. Detectors are read out using a 64x frequency domain multiplexing (fMux) scheme. The microfabrication of the SPT-3G detector arrays involves a total of 18 processes, including 13 lithography steps. Together with the fabrication process, the effect of processing on the Ti/Au TES's T-c is discussed. In addition, detectors fabricated with Ti/Au TES films with Tc between 400 mK 560 mK are presented and their thermal characteristics are evaluated. Optical characterization of the arrays is presented as well, indicating that the response of the detectors is in good agreement with the design values for all three spectral bands (95 GHz, 150 GHz, and 220 GHz). The measured optical efficiency of the detectors is between 0.3 and 0.8. Our results discussed here are extracted from a batch of research of development wafers used to develop the baseline process for the fabrication of the arrays of detectors to be deployed with the SPT-3G receiver. Results from these research and development wafers have been incorporated into the fabrication process to get the baseline fabrication process presented here. SPT-3G is scheduled to deploy to the South Pole Telescope in late 2016.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

HIGH-RESOLUTION VERY LARGE ARRAY IMAGING OF SLOAN DIGITAL SKY SURVEY STRIPE 82 AT 1.4 GHz

We present a high-resolution radio survey of the Sloan Digital Sky Survey (SDSS) Southern Equatorial Stripe, a.k.a. Stripe 82. This 1.4 GHz survey was conducted with the Very Large Array primarily in the A-configuration, with supplemental B-configuration data to increase sensitivity to extended structure. The survey has an angular resolution of 1.''8 and achieves a median rms noise of 52 {mu}Jy beam{sup -1} over 92 deg{sup 2}. This is the deepest 1.4 GHz survey to achieve this large of an area, filling a gap in the phase space between small, deep and large, shallow surveys. It also serves as a pilot project for a larger high-resolution survey with the Expanded Very Large Array. We discuss the technical design of the survey and details of the observations, and we outline our method for data reduction. We present a catalog of 17,969 isolated radio components, for an overall source density of {approx}195 sources deg{sup -2}. The astrometric accuracy of the data is excellent, with an internal check utilizing multiply observed sources yielding an rms scatter of 0.''19 in both right ascension and declination. A comparison to the SDSS DR7 Quasar Catalog further confirms that the astrometry is well tied to the optical reference frame, with mean offsets of 0.''02 {+-} 0.''01 in right ascension, and 0.''01 {+-} 0.''02 in declination. A check of our photometry reveals a small, negative CLEAN-like bias on the level of 35 {mu}Jy. We report on the catalog completeness, finding that 97% of FIRST-detected quasars are recovered in the new Stripe 82 radio catalog, while faint, extended sources are more likely to be resolved out by the resolution bias. We conclude with a discussion of the optical counterparts to the catalog sources, including 76 newly detected radio quasars. The full catalog as well as a search page and cutout server are available online at http://third.ucllnl.org/cgi-bin/stripe82cutout.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Limiting Surface Density Method Application to Large Arrays of Highly Heterogeneous Shipping Packages

This work represents the initial phase of an overall effort to reduce the analytical burdens and increase flexibility of the K-Area Complex which provides stewardship of special nuclear materials. A hand calculation method is being extended to apply to large arrays of highly heterogeneous shipping packages. This method has the potential to quickly determine the impact of perturbations on the array. The objective of the particular work reported herein is twofold. First, the analytical results upon which the Limiting Surface Density (LSD) method was originally based were reproduced using the modern computational code KENO-VI in SCALE 6.1. The second objective was to test the classic LSD method on storage of large arrays of highly heterogeneous shipping packages. Specifically, the objective is to determine if the method is adequate for existing arrays of 9975 shipping packages with fissile metal content. The classic LSD method was derived for simple packages of bare spheres of fissile material centered in an air filled cubic unit cell and placed in a cubic-pitch water-reflected array, the properties of which could then be translated to more practical array and package geometries. The classic method did not address highly heterogeneous packages which are close to neutronically decoupled from other identical packages. Therefore, the material based array constant (called c{sub 2}) as defined by the classic method is determined specifically for the packages in question. (authors)

42 ENGINEERING↗
DOE OSTI2011

UNVEILING EXTRAGALACTIC STAR FORMATION USING RADIO RECOMBINATION LINES: AN EXPANDED VERY LARGE ARRAY PILOT STUDY WITH NGC 253

Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of Expanded Very Large Array (EVLA) observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nuclear starburst galaxy. We detect the previously unobserved H58{alpha} and H59{alpha} RRLs and make simultaneous sensitive measurements of the continuum. We measure integrated line fluxes of 44.3 {+-} 0.7 W m{sup -2} and 39.9 {+-} 0.8 W m{sup -2} for the H58{alpha} and H59{alpha} lines, respectively. The thermal gas in NGC 253 is kinematically complex with multiple velocity components. We constrain the density of the thermal gas to (1.4-4) x 10{sup 4} cm{sup -3} and estimate an ionizing photon flux of 1 x 10{sup 53} s{sup -1}. We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound, which is consistent with the outflow of gas inferred from the X-ray and H{alpha} measurements. The line profiles, fluxes, and kinematics of the H58{alpha} and H59{alpha} lines agree with those of RRLs at different frequencies confirming the accuracy of the previous, more difficult, high-frequency observations. We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the Very Large Array. These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE GOULD’S BELT VERY LARGE ARRAY SURVEY. V. THE PERSEUS REGION

We present multiepoch, large-scale (∼2000 arcmin{sup 2}), fairly deep (∼16 μJy), high-resolution (∼1″) radio observations of the Perseus star-forming complex obtained with the Karl G. Jansky Very Large Array at frequencies of 4.5 and 7.5 GHz. These observations were mainly focused on the clouds NGC 1333 and IC 348, although we also observed several fields in other parts of the Perseus complex. We detect a total of 206 sources, 42 of which are associated with young stellar objects (YSOs). The radio properties of about 60% of the YSOs are compatible with a nonthermal radio emission origin. Based on our sample, we find a fairly clear relation between the prevalence of nonthermal radio emission and evolutionary status of the YSOs. By comparing our results with previously reported X-ray observations, we show that YSOs in Perseus follow a Güdel–Benz relation with κ = 0.03, consistent with other regions of star formation. We argue that most of the sources detected in our observations but not associated with known YSOs are extragalactic, but provide a list of 20 unidentified radio sources whose radio properties are consistent with being YSO candidates. Finally, we also detect five sources with extended emission features that can clearly be associated with radio galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Wafer-scale growth of large arrays of perovskite microplate crystals for functional electronics and optoelectronics

Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercalated with methylammonium iodide to produce perovskite crystals. Structural and optical characterizations demonstrate that the resulting materials display excellent crystalline quality and optical properties. We further show that perovskite crystals can be selectively grown on prepatterned electrode arrays to create independently addressable photodetector arrays and functional field effect transistors. Furthermore, the ability to grow perovskite microplates and to precisely place them at specific locations offers a new material platform for the fundamental investigation of the electronic and optical properties of perovskite materials and opens a pathway for integrated electronic and optoelectronic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

We present the results of Very Large Array NH{sub 3} (J,K)=(1,1) and (2,2) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig–Haro objects. We report the detection of a new source, NH{sub 3}–S, in the vicinity of HH 111/HH 121 (∼0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH{sub 3}–S. We also use HCO{sup +} and HCN (J=4−3) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array {sup 13}CO, {sup 12}CO, and C{sup 18}O (J=2−1), N{sub 2}D{sup +} (J=3−2), and {sup 13}CS (J=5−4) data to gain insight into the nature of NH{sub 3}–S. The chemical structure of NH{sub 3}–S shows evidence for “selective freeze-out,” an inherent characteristic of dense cold cores. The inner part of NH{sub 3}–S shows subsonic nonthermal velocity dispersions indicating a “coherent core,” while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH{sub 3}–S. The properties of NH{sub 3}–S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig–Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH{sub 3}–S and if/how its evolution is affected by nearby jets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

EXPANDED VERY LARGE ARRAY CONTINUUM OBSERVATIONS TOWARD HOT MOLECULAR CORE CANDIDATES

We have used the Expanded Very Large Array (EVLA) with two 1 GHz wide bands to obtain K-band (1.3 cm) continuum observations toward the following five hot molecular core candidates: IRAS 18151 - 1208, IRAS 18182 - 1433, IRAS 18345 - 0641, IRAS 18470 - 0044, and IRAS 19012 + 0536. The sources were selected from the 2002 list of Sridharan et al. and are characterized by high FIR luminosity, dense molecular and dust condensations, massive large-scale CO flows, and the absence of strong cm continuum emission. These properties are indicative of massive star-forming regions in an evolutionary phase prior to ultra- or hypercompact H II regions. We detect a total of 10 individual 1.3 cm continuum sources toward this sample, and derive in-band spectral indices between 19.3 and 25.5 GHz consistent with thermal free-free emission, for all sources except component A in IRAS 18182 - 1433, which has a negative spectral index indicative of synchrotron emission. We suggest that in most cases the 1.3 cm sources are due to shock-induced ionization, rather than direct photoionization by massive objects. The momentum rate present in these ionized flows is sufficient to drive the large-scale molecular flows. We discuss a number of morphological features supporting this hypothesis. The present observations demonstrate that the EVLA has sufficient sensitivity to study the regions near very young massive stars in the cm continuum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE EXPANDED VERY LARGE ARRAY: A NEW TELESCOPE FOR NEW SCIENCE

Since its commissioning in 1980, the Very Large Array (VLA) has consistently demonstrated its scientific productivity. However, its fundamental capabilities have changed little since 1980, particularly in the key areas of sensitivity, frequency coverage, and velocity resolution. These limitations have been addressed by a major upgrade of the array, which began in 2001 and will be completed at the end of 2012. When completed, the Expanded VLA-the EVLA-will provide complete frequency coverage from 1 to 50 GHz, a continuum sensitivity of typically 1 {mu}Jy beam{sup -1} (in 9 hr with full bandwidth), and a modern correlator with vastly greater capabilities and flexibility than the VLA's. In this Letter, we describe the goals of the EVLA project, its current status, and the anticipated expansion of capabilities over the next few years. User access to the array through the Open Shared Risk Observing and Resident Shared Risk Observing programs is described. The following papers in this special issue, derived from observations in its early science period, demonstrate the astonishing breadth of this most flexible and powerful general-purpose telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EXPANDED VERY LARGE ARRAY OBSERVATIONS OF THE RADIO EVOLUTION OF SN 2011dh

We report on Expanded Very Large Array observations of the Type IIb supernova 2011dh, performed over the first 100 days of its evolution and spanning 1-40 GHz in frequency. The radio emission is well described by the self-similar propagation of a spherical shockwave, generated as the supernova ejecta interact with the local circumstellar environment. Modeling this emission with a standard synchrotron self-absorption (SSA) model gives an average expansion velocity of v Almost-Equal-To 0.1c, supporting the classification of the progenitor as a compact star (R{sub *} Almost-Equal-To 10{sup 11} cm). We find that the circumstellar density is consistent with a {rho}{proportional_to}r{sup -2} profile. We determine that the progenitor shed mass at a constant rate of Almost-Equal-To 3 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, assuming a wind velocity of 1000 km s{sup -1} (values appropriate for a Wolf-Rayet star), or Almost-Equal-To 7 Multiplication-Sign 10{sup -7} M{sub Sun} yr{sup -1} assuming 20 km s{sup -1} (appropriate for a yellow supergiant [YSG] star). Both values of the mass-loss rate assume a converted fraction of kinetic to magnetic energy density of {epsilon}{sub B} = 0.1. Although optical imaging shows the presence of a YSG, the rapid optical evolution and fast expansion argue that the progenitor is a more compact star-perhaps a companion to the YSG. Furthermore, the excellent agreement of the radio properties of SN 2011dh with the SSA model implies that any YSG companion is likely in a wide, non-interacting orbit.

79 ASTRONOMY AND ASTROPHYSICS↗