999 research outputs found
Energy Efficient Engine combustor test hardware detailed design report
The Energy Efficient Engine (E3) Combustor Development effort was conducted as part of the overall NASA/GE E3 Program. This effort included the selection of an advanced double-annular combustion system design. The primary intent was to evolve a design which meets the stringent emissions and life goals of the E3 as well as all of the usual performance requirements of combustion systems for modern turbofan engines. Numerous detailed design studies were conducted to define the features of the combustion system design. Development test hardware was fabricated, and an extensive testing effort was undertaken to evaluate the combustion system subcomponents in order to verify and refine the design. Technology derived from this development effort will be incorporated into the engine combustion system hardware design. This advanced engine combustion system will then be evaluated in component testing to verify the design intent. What is evolving from this development effort is an advanced combustion system capable of satisfying all of the combustion system design objectives and requirements of the E3. Fuel nozzle, diffuser, starting, and emissions design studies are discussed
Red and Blue Shifted Broad Lines in Luminous Quasars
We have observed a sample of 22 luminous quasars, in the range 2.0<z<2.5, at
1.6 microns with the near-infrared (NIR) spectrograph FSPEC on the Multiple
Mirror Telescope. Our sample contains 13 radio-loud and 9 radio-quiet objects.
We have measured the systemic redshifts z_(sys) directly from the strong [O
III]5007 line emitted from the narrow-line-region. From the same spectra, we
have found that the non-resonance broad H lines have a systematic mean
redward shift of 520+/-80 km/s with respect to systemic. Such a shift was not
found in our identical analysis of the low-redshift sample of Boroson & Green.
The amplitude of this redshift is comparable to half the expected gravitational
redshift and transverse Doppler effects, and is consistent with a correlation
between redshift differences and quasar luminosity. From data in the
literature, we confirm that the high-ionization rest-frame ultraviolet broad
lines are blueshifted ~550-1050 km/s from systemic, and that these velocity
shifts systematically increase with ionization potential. Our results allow us
to quantify the known bias in estimating the ionizing flux from the
inter-galactic-medium J_(IGM) via the Proximity Effect. Using redshift
measurements commonly determined from strong broad line species, like Ly\alpha
or CIV1549, results in an over-estimation of J_(IGM) by factors of ~1.9-2.3.
Similarly, corresponding lower limits on the density of baryon Omega_b will be
over-estimated by factors of ~1.4-1.5. However, the low-ionization MgII2798
broad line is within ~50 km/s of systemic, and thus would be the line of choice
for determining the true redshift of 1.0<z<2.2 quasars without NIR
spectroscopy, and z>3.1 objects using NIR spectroscopy.Comment: 12 pages, Latex, 2 figures, 2 tables, Accepted for publication in ApJ
Letter
Energy Efficient Engine (E3) combustion system component technology performance report
The Energy Efficient Engine (E3) combustor effort was conducted as part of the overall NASA/GE E3 Program. This effort included the selection of an advanced double-annular combustion system design. The primary intent of this effort was to evolve a design that meets the stringent emissions and life goals of the E3, as well as all of the usual performance requirements of combustion systems for modern turbofan engines. Numerous detailed design studies were conducted to define the features of the combustion system design. Development test hardware was fabricated, and an extensive testing effort was undertaken to evaluate the combustion system subcomponents in order to verify and refine the design. Technology derived from this effort was incorporated into the engine combustion hardware design. The advanced engine combustion system was then evaluated in component testing to verify the design intent. What evolved from this effort was an advanced combustion system capable of satisfying all of the combustion system design objectives and requirements of the E3
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
Broad P V Absorption in the BALQSO, PG 1254+047: Column Densities, Ionizations and Metal Abundances in BAL Winds
This paper discusses the detection of P V 1118,1128 and other broad
absorption lines (BALs) in archival HST spectra of the low-redshift BALQSO, PG
1254+047. The P V identification is secured by excellent redshift and profile
coincidences with the other BALs, such as C IV 1548,1550 and Si IV 1393,1403,
and by photoionization calculations showing that other lines near this
wavelength, e.g. Fe III 1123, should be much weaker than P V. The observed BAL
strengths imply that either 1) there are extreme abundance ratios such as [C/H]
>~ +1.0, [Si/H] >~ +1.8 and [P/C] >~ +2.2, or 2) at least some of the lines are
much more optically thick than they appear. I argue that the significant
presence of P V absorption indicates severe line saturation, which is disguised
in the observed (moderate-strength) BALs because the absorber does not fully
cover the continuum source(s) along our line(s) of sight. Computed optical
depths for all UV resonance lines show that the observed BALs are consistent
with solar abundances if 1) the ionization parameter is at least moderately
high, log U >~ -0.6, 2) the total hydrogen column density is log N_H(cm-2) >~
22.0, and 3) the optical depths in strong lines like C IV and O VI 1032,1038
are >~25 and >~80, respectively. These optical depths and column densities are
at least an order of magnitude larger than expected from the residual
intensities in the BAL troughs, but they are consistent with the large
absorbing columns derived from X-ray observations of BALQSOs. The outflowing
BALR, at velocities from -15,000 to -27,000 km/s in PG 1254+047, is therefore a
strong candidate for the X-ray absorber in BALQSOs.Comment: 16 pages (LaTeX) plus 8 pages of figures in one file
(pg1254_figs.ps.gz), in press with Ap
Observations of Lyman-alpha Absorption in a Triple Quasar System
We have obtained follow-up observations of the quasar pair LBQS 0107-025A,B
and new observations of the nearby quasar LBQS 0107-0232 with the Hubble Space
Telescope Faint Object Spectrograph. Extended wavelength coverage of LBQS
0107-025A and B using the G270H grating was also obtained. This triple system
is unique in providing sensitivity to coherent Ly-alpha absorption on
transverse scales of approximately 1 Mpc at z < 1. Monte Carlo simulations were
used to establish the confidence level for matches between absorption features
in different lines of sight as a function of velocity separation. Pairwise,
there are 8, 9, and 12 lines that match between spectra. Three instances of
matches between all three lines of sight were found with velocity separations
of less than 550 kms^-1. Two of the pairings have coincident lines within
|Delta v| < 200 kms^-1 that would occur with less than 10% probability by
chance. Taking into account the equivalent widths of the lines, one of these
triple coincidences is significant at the 99.99% confidence level, based on
Monte Carlo simulations with random line placements. Matches with strong lines
preferentially have small velocity separations. These same simulations are used
to demonstrate that the distribution of matches for a population of absorbers
randomly distributed in velocity space is peaked toward |Delta v| = 0, which
has implications for the statistical significance of matches. One of the triple
coincidences appears to be a strong absorber with a sheet-like, but
inhomogeneous, geometry and a coherence length approaching or exceeding 1 Mpc.Comment: 23 pages, 9 figures, accepted for publication in the Astrophysical
Journa
Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
We present X-ray and optical analysis of 188 AGN identified from 497 hard
X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra
fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These
medium depth X-ray observations enable us to detect a representative subset of
those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background.
Brighter than our optical spectroscopic limit, we achieve a reasonable degree
of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been
classified): broad emission line AGN (62%), narrow emission line galaxies
(24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that
most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties
characterized by broad emission lines and blue colors, similiar to
optically-selected quasars from the Sloan Digital Sky Survey but with a slighly
broader color distribution. However, we also find a significant population of
redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray
absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line
galaxies, with red optical colors characteristically dominated by luminous,
early type galaxy hosts rather than from dust reddening of an AGN. We also find
a number of atypical AGN; for instance, several luminous AGN show both strong
X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find
that 81% of X-ray selected AGN can be easily interpreted in the context of
current AGN unification models. Most of the deviations seem to be due to an
optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the
Astrophysical Journa
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