51,974 research outputs found
Null type instrument for simplifying two dimensional field plotting
Vacuum tube bridge operates in two modes, tracing and fixed potential. It reduces plotting time by fifty percent and improves measurement precision
Hubble Space Telescope Constraints on the Winds and Astrospheres of Red Giant Stars
We report on an ultraviolet spectroscopic survey of red giants observed by
the Hubble Space Telescope, focusing on spectra of the Mg II h & k lines near
2800 A in order to study stellar chromospheric emission, winds, and
astrospheric absorption. We focus on spectral types between K2 III and M5 III,
a spectral type range with stars that are noncoronal, but possessing strong,
chromospheric winds. We find a very tight relation between Mg II surface flux
and photospheric temperature, supporting the notion that all K2-M5 III stars
are emitting at a basal flux level. Wind velocities (V_w) are generally found
to decrease with spectral type, with V_w decreasing from ~40 km/s at K2 III to
~20 km/s at M5 III. We find two new detections of astrospheric absorption, for
Sigma Pup (K5 III) and Gamma Eri (M1 III). This absorption signature had
previously only been detected for Alpha Tau (K5 III). For the three
astrospheric detections the temperature of the wind after the termination shock
correlates with V_w, but is lower than predicted by the Rankine-Hugoniot shock
jump conditions, consistent with the idea that red giant termination shocks are
radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic
simulation of the Gamma Eri astrosphere is provided to explore this further.Comment: 16 pages, 8 figures, to appear in The Astrophysical Journa
Photoionisation and Heating of a Supernova Driven, Turbulent, Interstellar Medium
The Diffuse Ionised Gas (DIG) in galaxies traces photoionisation feedback
from massive stars. Through three dimensional photoionisation simulations, we
study the propagation of ionising photons, photoionisation heating and the
resulting distribution of ionised and neutral gas within snapshots of
magnetohydrodynamic simulations of a supernova driven turbulent interstellar
medium. We also investigate the impact of non-photoionisation heating on
observed optical emission line ratios. Inclusion of a heating term which scales
less steeply with electron density than photoionisation is required to produce
diagnostic emission line ratios similar to those observed with the Wisconsin
H{\alpha} Mapper. Once such heating terms have been included, we are also able
to produce temperatures similar to those inferred from observations of the DIG,
with temperatures increasing to above 15000 K at heights |z| > 1 kpc. We find
that ionising photons travel through low density regions close to the midplane
of the simulations, while travelling through diffuse low density regions at
large heights. The majority of photons travel small distances (< 100pc);
however some travel kiloparsecs and ionise the DIG.Comment: 10 pages, 13 figures, accepted to MNRA
Design, fabrication and evaluation of chalcogenide glass Luneburg lenses for LiNbO3 integrated optical devices
Optical waveguide Luneburg lenses of arsenic trisulfide glass are described. The lenses are formed by thermal evaporation of As2S3 through suitably placed masks onto the surface of LiNbO3:Ti indiffused waveguides. The lenses are designed for input apertures up to 1 cm and for speeds of f/5 or better. They are designed to focus the TM sub 0 guided mode of a beam of wavelength, external to the guide, of 633 nm. The refractive index of the As2S3 films and the changes induced in the refractive index by exposure to short wavelength light were measured. Some correlation between film thickness and optical properties was noted. The short wavelength photosensitivity was used to shorten the lens focal length from the as deposited value. Lenses of rectangular shape, as viewed from above the guide, as well as conventional circular Luneburg lenses, were made. Measurements made on the lenses include thickness profile, general optical quality, focal length, quality of focal spot, and effect of ultraviolet irradiation on optical properties
Influence of airfoil geometry on delta wing leading-edge vortices and vortex-induced aerodynamics at supersonic speeds
An assessment of the influence of airfoil geometry on delta wing leading edge vortex flow and vortex induced aerodynamics at supersonic speeds is discussed. A series of delta wing wind tunnel models were tested over a Mach number range from 1.7 to 2.0. The model geometric variables included leading edge sweep and airfoil shape. Surface pressure data, vapor screen, and oil flow photograph data were taken to evaluate the complex structure of the vortices and shocks on the family of wings tested. The data show that airfoil shape has a significant impact on the wing upper surface flow structure and pressure distribution, but has a minimal impact on the integrated upper surface pressure increments
Improved V II log() Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
New experimental absolute atomic transition probabilities are reported for
203 lines of V II. Branching fractions are measured from spectra recorded using
a Fourier transform spectrometer and an echelle spectrometer. The branching
fractions are normalized with radiative lifetime measurements to determine the
new transition probabilities. Generally good agreement is found between this
work and previously reported V II transition probabilities. Use of two
spectrometers, independent radiometric calibration methods, and independent
data analysis routines enables a reduction in systematic uncertainties, in
particular those due to optical depth errors. In addition, new hyperfine
structure constants are measured for selected levels by least squares fitting
line profiles in the FTS spectra. The new V II data are applied to high
resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to
determine new, more accurate V abundances. Lines covering a range of wavelength
and excitation potential are used to search for non-LTE effects. Very good
agreement is found between our new solar photospheric V abundance, log
{\epsilon}(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value.
In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of
[V/Fe] = 0.24.Comment: 32 pages, 7 tables (3 machine-readable), 8 figures; accepted for
publication in ApJ
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