| 1. |
- D'Orazi, V., et al.
(författare)
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Mapping of shadows cast on a protoplanetary disk by a close binary system
- 2019
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 3:2, s. 167-172
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Tidskriftsartikel (refereegranskat)abstract
- For a comprehensive understanding of planetary formation and evolution, we need to investigate the environment in which planets form: circumstellar disks. Here we present high-contrast imaging observations of V4046 Sagittarii, a 20-Myr-old close binary known to host a circumbinary disk. We have discovered the presence of rotating shadows in the disk, caused by mutual occultations of the central binary. Shadow-like features are often observed in disks(1,2), but those found thus far have not been due to eclipsing phenomena. We have used the phase difference due to light travel time to measure the flaring of the disk and the geometrical distance of the system. We calculate a distance that is in very good agreement with the value obtained from the Gaia mission's Data Release 2 (DR2), and flaring angles of alpha = (6.2 +/- 0.6)degrees and alpha = (8.5 +/- 1.0)degrees for the inner and outer disk rings, respectively. Our technique opens up a path to explore other binary systems, providing an independent estimate of distance and the flaring angle, a crucial parameter for disk modelling.
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| 2. |
- Claudi, R., et al.
(författare)
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SPHERE dynamical and spectroscopic characterization of HD142527B
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
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Tidskriftsartikel (refereegranskat)abstract
- Aims. HD142527 is one of the most frequently studied Herbig Ae/Be stars with a transitional disk that hosts a large cavity that is up to about 100 au in radius. For this reason, it has been included in the guaranteed time observation (GTO) SpHere INfrared survey for Exoplanets (SHINE) as part of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT) in order to search for low-mass companions that might explain the presence of the gap. SHINE is a large survey within about 600 young nearby stars are observed with SPHERE with the aim to constrain the occurrence and orbital properties of the giant planet population at large (>5 au) orbital separation around young stars. Methods. We used the IRDIFS observing mode of SPHERE (IRDIS short for infrared dual imaging and spectrograph plus IFS or integral field spectrograph) without any coronagraph in order to search for and characterize companions as close as 30 mas of the star. Furthermore, we present the first observations that ever used the sparse aperture mask (SAM) for SPHERE both in IRDIFS and IRDIFS_EXT modes. All the data were reduced using the dedicated SPHERE pipeline and dedicated algorithms that make use of the principal component analysis (PCA) and reference differential imaging (RDI) techniques. Results. We detect the accreting low-mass companion HD142527B at a separation of 73 mas (11.4 au) from the star. No other companions with mass greater than 10 M-J are visible in the field of view of IFS (similar to 100 au centered on the star) or in the IRDIS field of view (similar to 400 au centered on the star). Measurements from IFS, SAM IFS, and IRDIS suggest an M6 spectral type for HD142527B, with an uncertainty of one spectral subtype, compatible with an object of M = 0.11 +/- 0.06 M-circle dot and R = 0.15 +/- 0.07 R-circle dot. The determination of the mass remains a challenge using contemporary evolutionary models, as they do not account for the energy input due to accretion from infalling material. We consider that the spectral type of the secondary may also be earlier than the type we derived from IFS spectra. From dynamical considerations, we further constrain the mass to 0.26(-0.14)(+0.16) , which is consistent with both our spectroscopic analysis and the values reported in the literature. Following previous methods, the lower and upper dynamical mass values correspond to a spectral type between M2.5 and M5.5 for the companion. By fitting the astrometric points, we find the following orbital parameters: a period of P = 35 137 yr; an inclination of i = 121 130 degrees, a value of Omega = 124 135 degrees for the longitude of node, and an 68% confidence interval of similar to 18-57 au for the separation at periapsis. Eccentricity and time at periapsis passage exhibit two groups of values: similar to 0.2-0.45 and similar to 0.45-0.7 for e, and similar to 2015-2020 and similar to 2020-2022 for T-0. While these orbital parameters might at first suggest that HD142527B is not the companion responsible for the outer disk truncation, a previous hydrodynamical analysis of this system showed that they are compatible with a companion that is able to produce the large cavity and other observed features.
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| 3. |
- Alam, Syed Bahauddin, et al.
(författare)
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Small modular reactor core design for civil marine propulsion using micro-heterogeneous duplex fuel. Part I: Assembly-level analysis
- 2019
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 346, s. 157-175
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Tidskriftsartikel (refereegranskat)abstract
- In an effort to de-carbonise commercial freight shipping, there is growing interest in the possibility of using nuclear propulsion systems. In this reactor physics study, we seek to design a soluble-boron-free (SBF) and low-enriched uranium (LEU) (<20% U-235 enrichment) civil nuclear marine propulsion small modular reactor (SMR) core that provides at least 15 effective full-power-years (EFPY) life at 333 MWth using 18% U-235 enriched micro-heterogeneous ThO2-UO2 duplex fuel and 15% U-235 enriched homogeneously mixed all-UO2 fuel. We use WIMS to develop subassembly designs and PANTHER to examine whole-core arrangements.The assembly-level behaviours of candidate burnable poison (BP) materials and control rods are investigated. We examine gadolinia (Gd2O3), erbia (Er2O3) and ZrB2 integral fuel burnable absorber (IFBA) as BPs. We arrive at a design with the candidate fuels loaded into 13 x 13 assemblies using IFBA pins for reactivity control. Taking advantage of self-shielding effects, this design maintains low and stable assembly reactivity with relatively little burnup penalty. Thorium-based duplex fuel offers better performance than all-UO2 fuel with all BP options considered. Duplex fuel has similar to 20% lower reactivity swing and, in consequence, lower initial reactivity than all-UO2 fuel. The lower initial reactivity and smaller reactivity swing make the task of reactivity control through BP design easier in the thorium-rich duplex core. For control rod design, we examine boron carbide (B4C), hafnium, and Ag-In-Cd alloy. All the candidate materials exhibit greater rod worth for the duplex design. For both fuels, B4C has the highest rod worth. In particular, one of the major objectives of this study is to offer/explore a thorium-based candidate alternative fuel platform for the proposed marine core. It is proven by literature reviews that the ability of the duplex fuel was never explored in the context of a single-batch, LEU, SBF, long-life SMR core. In this regard, the motivation of this paper is to observe the neutronic performance of the proposed duplex fuel with respect to the UO2 fuel and 'open the option' of designing the functional cores with both the duplex and UO2 fuel cores.
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| 4. |
- Bhattacharya, S., et al.
(författare)
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Evolution of collectivity and evidence of octupole correlations in Br 73
- 2019
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Ingår i: Physical Review C. - 2469-9985. ; 100:1
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states in the Br73 nucleus have been populated via the Cr50(Si28,αp)Br73 fusion evaporation reaction with a beam energy of 90 MeV. The deexciting gamma rays were detected using the Indian National Gamma Array (INGA). Using the γ-γ coincidence technique, two new bands and eight new interconnecting transitions have been added. The strong interconnecting E1 transitions, between positive and negative parity bands, ensure the existence of octupole correlations at low spin. Line shapes have been observed for 17 transitions, which were analyzed by the Doppler-shift attenuation method to determine the lifetime of excited states of the yrast negative parity band and its signature partner band along with the positive parity band. The deduced transitional quadrupole moments Qt for the ground state band decrease with increasing spin, with their values ranging from 2.88 to 1.00 eb. A similar trend in the quadrupole moment has also been observed for the signature partner as well as for the positive parity band. This decrease in Qt with increasing spin for these bands is interpreted in terms of the cranked Nilsson-Strutinsky model and total Routhian surface calculations, which indicate possible band termination at higher spin.
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