20,215 research outputs found
Herschel-PACS Measurements of Nitrogen Enrichment in Nebulae around Wolf-Rayet Stars
For three nebulae that have early-WN Wolf-Rayet exciting stars, NGC 6888, WR
8 and Abell 48, we have obtained Herschel-PACS line scans of the [N III] 57 um
and [O III] 88 micron lines, along with the 122 and 205 micron lines of [N II].
From the former two lines we have derived N/O abundance ratios,
equal to the overall N/O ratio under a wide range of nebular conditions. We
find that all of the nebulae observed possess significant nitrogen enrichment,
with derived N/O ratios greater than solar. The two nebulae with massive
Wolf-Rayet exciting stars, NGC 6888 and WR8 are found to have N/O ratios that
are enhanced by factors of 7 - 10 relative to the solar N/O ratio, consistent
with an origin as material ejected just before the onset of the Wolf-Rayet
phase. The other nebula, Abell 48, has recently been reclassified as a member
of the rare class of three planetary nebulae that have early-WN central stars
and are not of Peimbert Type I. We derive a nebular N/O ratio for it that is a
factor of 4 enhanced relative to solar and slightly above the range of N/O
values that have been measured for the other three members of its [WN]
planetary nebula class.Comment: 11 pages, 5 figures, MNRAS accepte
OH emission from cometary knots in planetary nebulae
We model the molecular emission from cometary knots in planetary nebulae
(PNe) using a combination of photoionization and photodissociation region (PDR)
codes, for a range of central star properties and gas densities. Without the
inclusion of ionizing extreme ultraviolet (EUV) radiation, our models require
central star temperatures to be near the upper limit of the range
investigated in order to match observed H and OH surface brightnesses
consistent with observations - with the addition of EUV flux, our models
reproduce observed OH surface brightnesses for .
For , the predicted OH surface brightness is much
lower, consistent with the non-detection of this molecule in PNe with such
central star temperatures. Our predicted level of H emission is somewhat
weaker than commonly observed in PNe, which may be resolved by the inclusion of
shock heating or fluorescence due to UV photons. Some of our models also
predict ArH and HeH rotational line emission above detection
thresholds, despite neither molecule having been detected in PNe, although the
inclusion of photodissociation by EUV photons, which is neglected by our
models, would be expected to reduce their detectability.Comment: Accepted by MNRAS, 11 pages, 15 figures. Author accepted manuscript.
Accepted on 24/04/18. Deposited on 27/04/1
Modelling the ArH emission from the Crab Nebula
We have performed combined photoionization and photodissociation region (PDR)
modelling of a Crab Nebula filament subjected to the synchrotron radiation from
the central pulsar wind nebula, and to a high flux of charged particles; a
greatly enhanced cosmic ray ionization rate over the standard interstellar
value, , is required to account for the lack of detected [C I]
emission in published Herschel SPIRE FTS observations of the Crab Nebula. The
observed line surface brightness ratios of the OH and ArH transitions
seen in the SPIRE FTS frequency range can only be explained with both a high
cosmic ray ionization rate and a reduced ArH dissociative recombination
rate compared to that used by previous authors, although consistent with
experimental upper limits. We find that the ArH/OH line strengths and
the observed H vibration-rotation emission can be reproduced by model
filaments with cm,
and visual extinctions within the range found for dusty globules in the Crab
Nebula, although far-infrared emission from [O I] and [C II] is higher than the
observational constraints. Models with cm
underpredict the H surface brightness, but agree with the ArH and
OH surface brightnesses and predict [O I] and [C II] line ratios consistent
with observations. These models predict HeH rotational emission above
detection thresholds, but consideration of the formation timescale suggests
that the abundance of this molecule in the Crab Nebula should be lower than the
equilibrium values obtained in our analysis.Comment: Accepted by MNRAS. Author accepted manuscript. Accepted on
05/09/2017. Deposited on 05/09/1
PLTTER user's guide
The PLTTER graphics system, which is part of CDDMS is discussed. CDDMS is a comprehensive system for data basing and subsequent plotting of data acquired during wind tunnel tests or from computational flow analyses. The PLTTER is a system which creates report-quality plots of data which is stored on a CDDMS data base. The Requests file system allows plot-controlling information to be arranged in the way which is most appropriate for any application. The PLTTER system features many capabilities which are especially useful when plotting wind tunnel data. The PLTTER offers a variety of page formats, different grid options and parametric curve fitting algorithms, and a powerful legend capability to identify relevant information about individual curves. One or more plots on a page can be suppressed if desired so that an established page format can be maintained. Final plot output may be standard Versatec plots, QMS Laser printer plots, or microfiche
Structured total least norm and approximate GCDs of inexact polynomials
The determination of an approximate greatest common divisor (GCD) of two inexact polynomials f=f(y) and g=g(y) arises in several applications, including signal processing and control. This approximate GCD can be obtained by computing a structured low rank approximation S*(f,g) of the Sylvester resultant matrix S(f,g). In this paper, the method of structured total least norm (STLN) is used to compute a low rank approximation of S(f,g), and it is shown that important issues that have a considerable effect on the approximate GCD have not been considered. For example, the established works only yield one matrix S*(f,g), and therefore one approximate GCD, but it is shown in this paper that a family of structured low rank approximations can be computed, each member of which yields a different approximate GCD. Examples that illustrate the importance of these and other issues are presented
A study of the drooped leading edge airfoil
Wind tunnel tests were conducted to examine various aspects of the drooped-leading edge airfoil which reduces the tendency for an airplane to enter a spin after stall occurs. Three baseline models were used for tests of two dimensional models: NACA 0015, 0014.6, and 0014.2. The 14.6% and 14.2% models were derived from NACA 0015 sections by increasing the chord and matching the profiles aft section. Force, balance data (lift, drag, pitching moment) were obtained for each model at a free-steam Reynold's number of 2.66 x 10 to the 6th power/m. In addition, oil flow visualization tests were performed at various angles of attack. An existing NACA 64 sub 1 A211 airfoil was used in a second series of tests. The leading edge flap was segmented in three parts which allowed various baseline/drooped leading edge configurations to be tested. Force balance and flow visualization tests were completer at chord Renolds numbers of 0.44 x 10 to the 6th power, 1.4 x 10 to the 6th power, and 2.11 x 10 to the 6th power. Test results are included
Views of Coaching Practice Expressed by School-Based Coaches
This study reports on the views of coaching expressed by school-based coaches and coaching experts in response to observing the practice of a novice coach featured in a video. Researchers hypothesized that a coach participant\u27s observations about another coach\u27s practice would be a useful tool for examining participants\u27 beliefs about coaching. Researchers compared responses from school-based coaches to the responses of coaching experts and views expressed in leading coaching literature in order to examine the variation in school-based coaches\u27 views. Analysis of responses from both practicing coaches and coaching experts revealed eight themes that describe components of the videotaped coaching cycle: 1) coaching relationships; 2) the use of praise by the coach; 3) discussions of student learning; 4) how coaches respond to teachers\u27 questions; 5) how coaches prompt reflection; 6) how coaches address teacher knowledge and learning; 7) discussions of mathematics content; and, 8) facilitation of the coaching session. The analysis also revealed that these themes correspond to accepted domains of coaching knowledge reported in the coaching literature
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