Recent flow visualization studies in the 0.3-m TCT

Light beams are altered by refractive index changes; flow induced refractive index changes provide the impetus for conventional visualization techniques such as schlieren and shadowgraph. Unfortunately effects related to the flow can be masked by refractive index inhomogeneities external to the test section. A simple shadowgraph scheme was used to assess the flow quality of the Langley 0.3 meter Transonic Cryogenic Tunnel. When the penetration tubes were evacuated the quality of the shadowgraph improved dramatically

Photogrammetric technique for in-flight ranging of trailing vortices using entrained balloons

A method for experimentally determining the radial distance of a probe aircraft from a trailing vortex is described. The method relies on photogrammetric triangulation of targets entrained in the vortex core. The theory and preliminary testing were described using laboratory mock-ups. Solid state video cameras were to provide data at 300 Hz rates. Practical methods for seeding the vortex are under separate investigation and are not addressed

Feasibility of Rayleigh Scattering Flow Diagnostics in the National Transonic Facility

Laser-based Rayleigh light scattering (RLS) was performed in the National Transonic Facility (NTF) at NASA Langley Research Center. The goal was to determine if the free-stream flow undergoes clustering (early stage of condensation from gas to liquid) or remains in a pure diatomic molecular phase. Data indicate that clusters are not observable down to levels of 10% of the total light scatter for a variety of total pressures at one N2 cryogenic-mode total temperature (Tt = -50 F = 227 K) and one air-mode temperature (Tt = +130 F = 327 K). Thus RLS appears viable as a qualitative or quantitative diagnostic for flow density in NTF in the future. Particles are distinguished from optically unresolvable clusters because they are much larger and individually resolvable in the laser beam image with Mie scattering. The same RLS apparatus was also used, without modification, to visualize naturally occurring particles entrained in the flow for both cryogenic and air-modes. Estimates of the free-stream particle flux are presented, which may be important for interpretation of laminar-to-turbulent boundary-layer transition studies.

Implementation of a Pulsed-Laser Measurement System in the National Transonic Facility

A remotely-adjustable laser transmission and imaging system has been developed for use in a high-pressure, cryogenic wind tunnel. Implementation in the National Transonic Facility has proven the system suitable for velocity and signal lifetime measurements over a range of operating conditions. The measurement system allows for the delivery of high-powered laser pulses through the outer pressure shell and into the test section interior from a mezzanine where the laser is free from environmental disturbances (such as vibrations and excessive condensation) associated with operation of the wind tunnel. Femtosecond laser electronic excitation tagging (FLEET) was utilized to provide freestream velocity measurements, and first results show typical data that may be obtained using the system herein described

A Study of the Public School System of Monroe County

The specific aims of the study are: To survey the schools in Monroe County - the one-room rural schools, the two-teacher schools and the consolidated schools. To show the percentage of attendance and percentage of failure in different schools and the cost per pupil attending. To show the relation between teachers qualifications and teachers pay. To study the transportation system; figuring the cost per pupil per mile. To make general recommendations based on data obtained

Development of Background-Oriented Schlieren for NASA Langley Research Center Ground Test Facilities

This paper provides an overview of recent wind tunnel tests performed at the NASA Langley Research Center where the Background-Oriented Schlieren (BOS) technique was used to provide information pertaining to flow-field density disturbances. The facilities in which the BOS technique was applied included the National Transonic Facility (NTF), Transonic Dynamics Tunnel (TDT), 31-Inch Mach 10 Air Tunnel, 15-Inch Mach 6 High-Temperature Air Tunnel, Rotor Test Cell at the 14 by 22 Subsonic Tunnel, and a 13-Inch Low-Speed Tunnel

Advanced optical instruments technology

The science objectives for proposed NASA missions for the next decades push the state of the art in sensitivity and spatial resolution over a wide range of wavelengths, including the x-ray to the submillimeter. While some of the proposed missions are larger and more sensitive versions of familiar concepts, such as the next generation space telescope, others use concepts, common on the Earth, but new to space, such as optical interferometry, in order to provide spatial resolutions impossible with other concepts. However, despite their architecture, the performance of all of the proposed missions depends critically on the back-end instruments that process the collected energy to produce scientifically interesting outputs. The Advanced Optical Instruments Technology panel was chartered with defining technology development plans that would best improve optical instrument performance for future astrophysics missions. At this workshop the optical instrument was defined as the set of optical components that reimage the light from the telescope onto the detectors to provide information about the spatial, spectral, and polarization properties of the light. This definition was used to distinguish the optical instrument technology issues from those associated with the telescope, which were covered by a separate panel. The panel identified several areas for optical component technology development: diffraction gratings; tunable filters; interferometric beam combiners; optical materials; and fiber optics. The panel also determined that stray light suppression instruments, such as coronagraphs and nulling interferometers, were in need of general development to support future astrophysics needs

The Paschen jump as a diagnostic of the diffuse nebular continuum emission in active galactic nuclei

Research at UCI has been supported in part by the NSF grant No. AST-1907290. Support at UCI for HST programs 14744 and 15124 was provided by NASA through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. E.C. acknowledges funding support from HST program number 15413 (for Mrk 110) and NSF grant No. AST-1909199. L.C.H. is supported by the National Science Foundation of China (grant Nos. 11721303, 11991052) and the National Key R&D Program of China (2016YFA0400702). M.C.B. gratefully acknowledges support from the NSF through grant AST-2009230. V.U. acknowledges funding support from the NASA Astrophysics Data Analysis Program grant # 80NSSC20K0450. M.V. gratefully acknowledges support from the Independent Research Fund Denmark via grant No. DFF 8021-00130. G.J.F. acknowledges support by the NSF (grant Nos. 1816537, 1910687), NASA (grant Nos. ATP 17-ATP17-0141, 19-ATP19-0188), and STScI (grant Nos. HST-AR-15018 and HST-GO-16196.003-A). J.M.G. gratefully acknowledges support from NASA under the awards 80NSSC17K0126 and 80NSSC19K1638. W.N.B. acknowledges support from NSF grant No. AST-2106990.Photoionization modeling of active galactic nuclei (AGN) predicts that diffuse continuum (DC) emission from the broad-line region makes a substantial contribution to the total continuum emission from ultraviolet through near-infrared wavelengths. Evidence for this DC component is present in the strong Balmer jump feature in AGN spectra, and possibly from reverberation measurements that find longer lags than expected from disk emission alone. However, the Balmer jump region contains numerous blended emission features, making it difficult to isolate the DC emission strength. In contrast, the Paschen jump region near 8200 Å is relatively uncontaminated by other strong emission features. Here, we examine whether the Paschen jump can aid in constraining the DC contribution, using Hubble Space Telescope Space Telescope Imaging Spectrograph spectra of six nearby Seyfert 1 nuclei. The spectra appear smooth across the Paschen edge, and we find no evidence of a Paschen spectral break or jump in total flux. We fit multicomponent spectral models over the range 6800–9700 Å and find that the spectra can still be compatible with a significant DC contribution if the DC Paschen jump is offset by an opposite spectral break resulting from blended high-order Paschen emission lines. The fits imply DC contributions ranging from ∼10% to 50% at 8000 Å, but the fitting results are highly dependent on assumptions made about other model components. These degeneracies can potentially be alleviated by carrying out fits over a broader wavelength range, provided that models can accurately represent the disk continuum shape, Fe ii emission, high-order Balmer line emission, and other components.Publisher PDFPeer reviewe

A systematic search for changing-look quasars in SDSS

CLM acknowledges support from the STFC Consolidated Grant (Ref. St/M001229/1). NPR acknowledges support from the STFC and the Ernest Rutherford Fellowship scheme. KH acknowledges support from STFC grant ST/M001296/1. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.We present a systematic search for changing-look quasars based on repeat photometry from Sloan Digital Sky Survey (SDSS) and Pan-STARRS1, along with repeat spectra from SDSS and SDSS-III Baryon Oscillation Spectroscopic Survey. Objects with large, |Δg| > 1 mag photometric variations in their light curves are selected as candidates to look for changes in broad emission line (BEL) features. Out of a sample of 1011 objects that satisfy our selection criteria and have more than one epoch of spectroscopy, we find 10 examples of quasars that have variable and/or ‘changing-look’ BEL features. Four of our objects have emerging BELs, five have disappearing BELs, and one object shows tentative evidence for having both emerging and disappearing BELs. With redshifts in the range 0.20 15 per cent of strongly variable luminous quasars display changing-look BEL features on rest-frame time-scales of 8 to 10 yr. Plausible time-scales for variable dust extinction are factors of 2–10 too long to explain the dimming and brightening in these sources, and simple dust reddening models cannot reproduce the BEL changes. On the other hand, an advancement such as disc reprocessing is needed if the observed variations are due to accretion rate changes.Publisher PDFPeer reviewe