Planet Hunters IX. KIC 8462852 – where's the flux? Boyajian, T. S; LaCourse, D. M; Rappaport, S. A ...
Monthly notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
4
Journal Article
Recenzirano
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Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to ∼20 per cent. The dipping activity can last for between 5 and 80 d. We ...characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC 8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artefact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that are needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds 10−6 M⊕, corresponding to an original rocky body of >100 km in diameter. We discuss the necessity of future observations to help interpret the system.
Planet Hunters IX. KIC 8462852 – where's the flux? Boyajian, T. S.; LaCourse, D. M.; Rappaport, S. A. ...
Monthly Notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
4
Journal Article
Planet Hunters IX. KIC 8462852 - where's the flux? Boyajian, T S; LaCourse, D M; Rappaport, S A ...
Monthly notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
4
Journal Article
Recenzirano
Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to ~20 per cent. The dipping activity can last for between 5 and 80 d. We ...characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC 8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artefact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that are needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds 10 super( -6) M..., corresponding to an original rocky body of >100 km in diameter. We discuss the necessity of future observations to help interpret the system. (ProQuest: ... denotes formulae/symbols omitted.)
Over the duration of the Kepler mission, KIC8462852 was observed to undergo irregularly shaped, aperiodic dips in flux of up to \(\sim 20\)\%. The dipping activity can last for between 5 and 80 days. ...We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve. We determine that KIC8462852 is a typical main-sequence F3 V star that exhibits no significant IR excess, and has no very close interacting companions. In this paper, we describe various scenarios to explain the dipping events observed in the Kepler light curve. We confirm that the dipping signals in the data are not caused by any instrumental or data processing artifact, and thus are astrophysical in origin. We construct scenario-independent constraints on the size and location of a body in the system that is needed to reproduce the observations. We deliberate over several assorted stellar and circumstellar astrophysical scenarios, most of which have problems explaining the data in hand. By considering the observational constraints on dust clumps in orbit around a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet or planetesimal fragments, all of which are associated with a single previous break-up event, possibly caused by tidal disruption or thermal processing. The minimum total mass associated with these fragments likely exceeds \(10^{-6}\)~\mearth, corresponding to an original rocky body of \(>100\)~km in diameter. We discuss the necessity of future observations to help interpret the system.
Phosphogypsum (PG) samples from four distinct sources in the Southeastern US were analyzed to explore the variation in total metal content between newly generated (fresh) PG and PG disposed of in ...phosphogypsum stacks for different lengths of time (stack). Fresh PG exhibited greater total metal concentrations relative to stack PG, including those identified in the literature as important from a risk assessment perspective (As, Cd, Co, Cr, Cu, Pb, and Zn). The pH varied between fresh and stack PG, with some stack samples exhibiting lower pH than fresh samples, however the relationship between pH and age of sample was not linear. Stack samples with pH values similar to fresh samples possessed lower concentrations of total inorganic metals than fresh samples suggesting that process water drainage and stack location play an important role in the reusability of PG as they can affect the pH of stack PG and total inorganic metal concentrations. Overall observations show that stacking PG for three or more years prior to beneficial reuse provides a construction material with lower total metal concentrations than fresh PG.
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•Critical analysis of trace metal concentrations in PG at various stages.•Four sources of PG from various stages of life are evaluated.•Total element concentrations are consistently lower in stack than in fresh PG.•Direct exposure risk associated with stack PG is lower than fresh PG.
Concentrations of 25 inorganic elements were measured in both bulk ash and individual ash components from residuals at three municipal solid waste incineration (MSWI) facilities in the US (two ...combined ash (CA) and one bottom ash (BA)). Concentrations were assessed based on particle size and component to understand the contribution from each fraction. The results found that among facilities, the finer size fractions contained elevated concentrations of trace elements of concern (As, Pb, Sb) when compared to the coarse fraction, but concentrations varied among facilities depending on the type of ash and differences in advanced metals recovery processes. This study focused on several constituents of potential concern, As, Ba, Cu, Pb, and Sb, and found that the main components of MSWI ash (glass, ceramic, concrete, and slag) are sources of these elements in the ash streams. For many elements, concentrations were significantly higher in CA bulk and component fractions opposed to BA streams. An acid treatment procedure and scanning electron microscopy/energy-dispersive x-ray spectroscopy analysis revealed that some elements, such as As in concrete, are result of the inherent properties of the component, but other elements, such as Sb, form on the surface during or after incineration and can be removed. Some Pb and Cu concentrations were attributed to inclusions in the glass or slag introduced into the material during the incineration process. Understanding the contributions of each ash component provides critical information for developing strategies to reduce trace element concentrations in ash streams to promote reuse opportunities.
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•Trace element concentrations determined for individual components of incineration ash.•Glass, ceramic, concrete, and slag are sources of trace element concentrations.•As, Ba, and Sb attributed to surface products formed pre- and post-incineration.•Pb and Cu embed in glass or slag due to phase changes during incineration process.•Pre- or post-processing of MSWI ash could decrease trace element concentration.
•Recycled MSWI bottom ash as partial replacement of natural aggregates in concrete.•Incorporating Portland limestone cement presents another avenue for sustainability.•Both ash streams investigated ...met performance metrics for reuse.•Advanced metal recovery has little impact on MSWI-ash amended concrete performance.
The optimization of alternative materials in concrete production continues to garner considerable attention in order to meet sustainability goals and supplement natural materials. Portland limestone cement (PLC) and municipal solid waste incineration (MSWI) bottom ash (BA) have been proposed separately as green cement and coarse aggregate supplement in low-strength concrete production, creating sustainable products and alternative disposal scenario for a waste material. This study discusses the impact of advanced ash processing techniques on aggregates and presents the performance of concrete incorporating both of these products with PLC for the first time. Two sources of MSWI BA were investigated, one as-produced (TMR) and one processed with novel advanced metals recovery (AMR). The AMR process reduced total Al content in ash compared to TMR (20,500 vs 17,000 mg/kg), though not aluminum oxide content, as the AMR process targets metallic aluminum. A composition study on both aggregates supports a reduction in ferrous and non-ferrous metals following the AMR process. All control and test mixes met 28-day compressive strength requirements (17 Mpa). Both AMR and TMR MSWI BA-amended concretes yielded compressive strengths below control specimens (no ash) ranging from 17 to 23 MPa, with little to no difference observed dependent on MSWI BA processing. The life-cycle discussion supports benefits deriving from supplementing naturally mined materials and recovering ferrous and nonferrous metals with the AMR process.
•Phosphogypsum (PG) has been investigated as a road base supplement.•Chemical performance of PG varies based on source, wet process, and aging conditions.•Behavior of chemical constituents should be ...monitored for specific PG reuse opportunities.•Blending or stabilizing PG with alkaline materials for base affects element mobility.•Laboratory and pilot-scale chemical analysis of PG amended road base is limited.
The use of phosphogypsum as an amendment to graded aggregate road base serves as an alternative to traditional and recycled aggregate sources. This provides a solution to issues currently faced by the phosphoric acid industry due to limited recycling opportunities, aggravated by a lack of understanding of variability in phosphogypsum due to source, location, and process worldwide. This manuscript provides a comprehensive overview of the chemical differences in phosphogypsum from around the globe and discusses the opportunities and challenges associated with phosphogypsum-amended road bases. The literature reveals that although mineralogical composition between sources remains similar (calcium sulfate), the total and leachable constituent concentrations vary significantly between facilities worldwide, impacting applicability and behavior as a road base material. Different approaches include using phosphogypsum as a base material alone, blended with aggregate, or stabilized and several studies report physical and environmental success, although thorough environmental monitoring of pilot-scale risk is lacking.
The use of phosphogypsum (PG) as a construction material continues to gain considerable attention worldwide. In the United States(US), the specific use of PG as a road base material has received ...renewed interest on a federal level. Previous work investigated the use of road base, either PG alone or stabilized with cementitious materials. This study investigated the physical characteristics of compacted PG sources and novel blends with traditional base aggregates compared to industry and state requirements. Specimens were created by blending up to 50% PG from five gypstacks in Florida, US with limerock (LR) and recycled concrete aggregate (RCA). The LBR for PG-LR and PG-RCA blends surpassed bearing strength (LBR) requirements and ranged from 102 to 130% and 155–210% at 50:50 ratios, and increased by 2–60% with decreasing PG content from 50 to 30%. The data suggest success of PG-amended granular base reported here relies largely on the strength of the original aggregate.
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