The Performance Analysis of Two Relatively Small Capacity Urban Retrofit Stormwater Controls

This paper details field investigations that were conducted on the performance of small capacity urban retrofit stormwater control measures. The objective of the two year study (2013–2015) was to provide performance data on stormwater retrofits that could not be fully sized according to conventional standards due to space constraints. In many states performance credits are not granted to stormwater management controls that are not designed to manage regionally derived water quality volumes. In retrofit applications there may exist numerous limitations to conventionally sized systems such as limited rights of way, setback distances or existing utilities. The larger scale objective of green infrastructure implementation is to improve receiving water quality and therefore even undersized systems, to some extent, meet this objective. This study introduces data on two systems: an innovative bioretention design with a water treatment residual amended filter media and an internal storage reservoir; and an undersized linear subsurface gravel wetland sized to optimize both phosphorus and nitrogen removal. The systems were retrofitted into existing developed areas and were sized at less than the water quality volume due to limited space at each location. The bioretention system (IBSC) was constructed in a commercial area in the town of Durham, NH in summer 2011 and the subsurface gravel wetland system (SGWSC) was constructed in a narrow drainage right of way in a residential neighbourhood of Durham, NH in the fall of 2013. Sediment and metal removals for both undersized systems were high with median removal efficiencies in the SGW of 75% for both total suspended solids (TSS) and total zinc (TZn). The Durham IBSC recorded median removal efficiency (RE) of 86% for TSS and TZn. Total phosphorus (TP) REs were higher than conventional bioretention systems with the subsurface gravel wetland system achieving a median RE of 53% and the Durham IBSC achieving a median RE of 40% for TP. Both systems reduced total nitrogen (TN) by approximately 20% (23% for SGWSC and 21% for Durham IBSC) with median effluent concentrations of 1.4 mg/L. This project was funded by the U.S. Environmental Protection Agency Region 1, Regional Applied Research Effort (RARE) Program. Additional information can be found in the full project report Performance Analysis of Two Relatively Small Capacity Urban Retrofit Stormwater Controls (Houle et al. 2015)

X-ray spectral diagnostics of activity in massive stars

X-rays give direct evidence of instabilities, time-variable structure, and shock heating in the winds of O stars. The observed broad X-ray emission lines provide information about the kinematics of shock-heated wind plasma, enabling us to test wind-shock models. And their shapes provide information about wind absorption, and thus about the wind mass-loss rates. Mass-loss rates determined from X-ray line profiles are not sensitive to density-squared clumping effects, and indicate mass-loss rate reductions of factors of 3 to 6 over traditional diagnostics that suffer from density-squared effects. Broad-band X-ray spectral energy distributions also provide mass-loss rate information via soft X-ray absorption signatures. In some cases, the degree of wind absorption is so high that the hardening of the X-ray SED can be quite significant. We discuss these results as applied to the early O stars zeta Pup (O4 If), 9 Sgr (O4 V((f))), and HD 93129A (O2 If*).Comment: To appear in the proceedings of IAU 272: Active OB Star

Mass loss from inhomogeneous hot star winds II. Constraints from a combined optical/UV study

Mass-loss rates currently in use for hot, massive stars have recently been seriously questioned, mainly because of the effects of wind clumping. We investigate the impact of clumping on diagnostic ultraviolet resonance and optical recombination lines. Optically thick clumps, a non-void interclump medium, and a non-monotonic velocity field are all accounted for in a single model. We used 2D and 3D stochastic and radiation-hydrodynamic (RH) wind models, constructed by assembling 1D snapshots in radially independent slices. To compute synthetic spectra, we developed and used detailed radiative transfer codes for both recombination lines (solving the "formal integral") and resonance lines (using a Monte-Carlo approach). In addition, we propose an analytic method to model these lines in clumpy winds, which does not rely on optically thin clumping. Results: Synthetic spectra calculated directly from current RH wind models of the line-driven instability are unable to in parallel reproduce strategic optical and ultraviolet lines for the Galactic O-supergiant LCep. Using our stochastic wind models, we obtain consistent fits essentially by increasing the clumping in the inner wind. A mass-loss rate is derived that is approximately two times lower than predicted by the line-driven wind theory, but much higher than the corresponding rate derived from spectra when assuming optically thin clumps. Our analytic formulation for line formation is used to demonstrate the potential impact of optically thick clumping in weak-winded stars and to confirm recent results that resonance doublets may be used as tracers of wind structure and optically thick clumping. (Abridged)Comment: 14 pages+1 Appendix, 8 figures, 3 tables. Accepted for publication in Astronomy and Astrophysics. One reference updated, minor typo in Appendix correcte

Atmospheres and Winds of PN Central Stars

The progress over the last years in modelling the atmospheres and winds of PN central stars is reviewed. We discuss the effect of the inclusion of the blanketing by millions of metal lines in NLTE on the diagnostics of photospheric and stellar wind lines, which can be used to determine stellar parameters such as effective temperature, gravity, radius, mass loss rate and distance. We also refer to recent work on the winds of massive O-type stars, which indicates that their winds are possibly inhomogeneous and clumped. We investigate implications from this work on the spectral diagnostics of PN central stars and introduce a method to determine wind clumping factors from the relative strengths of Halpha and HeII 4686. Based on new results we discuss the wind properties of CSPN.Comment: 8 pages, 12 figures; Proceedings, IAU Symposium No. 234, 2006, "Planetary Nebulae in our Galaxy and Beyond", M.J. Barlow and R.H. Mendez, ed